WO2025023120A1 - Method for separating member, and pressure-sensitive adhesive sheet - Google Patents

Abstract

Provided is a method in which from a structure comprising a first member, a second member, and an adhesive part interposed between the first member and the second member and adherent to both the first member and the second member, the first member and/or the second member is separated after a heat treatment. The adhesive part includes a curable pressure-sensitive adhesive layer. The separation method includes a step (fluid supply step) in which a fluid is supplied to the adhesive part from the first-member side or the second-member side.

Description

Method for separating components and adhesive sheet

The present invention relates to a member separating method and an adhesive sheet.
This application claims priority based on Japanese Patent Application No. 2023-122024, filed on July 26, 2023, the entire contents of which are incorporated herein by reference.

Generally, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state at temperatures near room temperature, and have the property of easily adhering to an adherend when pressure is applied. Adhesives are widely used in a variety of fields in the form of a supported adhesive sheet having an adhesive layer on a support, or in the form of a support-less adhesive sheet without a support, due to the ease of application to an adherend. Some such adhesives are used by adhering to an adherend, and are removed from the adherend after their adhesive purpose has been fulfilled. Patent documents 1 to 4 are prior art documents that disclose this type of conventional technology. Patent documents 1 to 4 disclose thermosetting adhesives.

Incidentally, a method is known in which a substrate is held by suction on a holding table having multiple flow holes connected to a vacuum device and a gas supply device by operating a vacuum device, and then gas is supplied after circulation by the gas supply device to eliminate the reduced pressure state between the substrate and the holding table, and the substrate is detached from the holding table (for example, Patent Document 5).

Japanese Patent Application Publication No. 2015-29105 Japanese Patent Application Publication No. 2016-204617 Japanese Patent Application Publication No. 2019-56101 Japanese Patent Application Publication No. 10-209087 Japanese Patent No. 6990038

　Adhesives used in applications where the adhesive is peeled off from an adherend are required to have good adhesion while attached to the adherend, and to have the ability to be easily peeled off from the adherend after the adhesive has completed its purpose. For example, it is desirable for an adhesive applied to an adherend that is to be heat-treated to have easy peelability, so that it can be easily peeled off from the adherend after being heated while attached to the adherend. As an adhesive with such performance, an adhesive that has a certain adhesive strength when fixed and can reduce its peel strength at an appropriate time can be used. As an adhesive that can reduce the peel strength, for example, an ultraviolet-irradiation peelable adhesive that reduces its peel strength by irradiating ultraviolet light is known. In addition, the present inventors have been conducting research and development of thermosetting adhesives based on a design concept different from conventional ones, and have succeeded in obtaining an adhesive that has easy peelability (heat-induced peelability) and reduces its peel strength when attached to an adherend and heated at a high temperature.

However, for example, when the adherend is a brittle material such as a semiconductor wafer or thin glass, even after the peeling strength of the adhesive has been reduced, the force of the peeling operation may be biased toward one part of the adherend, causing the adherend to be damaged. In addition, when joining rigid bodies together, even after the adhesive strength to the adherend has been reduced, it is not possible to deform the rigid adherend and use it to peel off the adhesive, so a considerable amount of force is required to release the adhesion of the entire adhesive surface, and it may be difficult to manually release the bonded adherends.

On the other hand, if the peeling strength of the adhesive is excessively reduced by UV irradiation or heat treatment, the adherend may separate from the adhesive at an unintended time due to minor external forces such as vibration, or even without any external force, and may be damaged by being dropped, etc. For example, a technology is known in which adhesives that become easily peelable when heated contain a foaming agent or heat-expandable microspheres, and the adhesive is foamed or expanded by heating to a specified temperature, causing it to peel off. However, such heat-peelable adhesives can naturally peel off from the adherend when heated, making it difficult to separate the adhesive from the adherend at the desired time after heat treatment.

It would be useful if a method could be realized that would enable adherends that have limitations or are difficult to peel, such as the brittle materials and rigid bodies mentioned above, to be separated from an adhesive sheet at a desired time without damaging the adherend, or to easily release the adhesion between rigid bodies.

The present invention was created in consideration of the above circumstances, and aims to provide a method for separating components using a curable adhesive and utilizing a fluid. Another related aim of the present invention is to provide an adhesive sheet that can be used in the above separation method.

According to this specification, a method is provided for separating at least one of a first member and a second member from a structure including a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhering to the first member and the second member after a heat treatment. The adhesive portion has a curable adhesive layer. The separation method also includes a step of supplying a fluid to the adhesive portion from the first member side or the second member side (fluid supply step).

In the above method, the adhesive portion having the curable adhesive layer is cured by the heat treatment or by applying an appropriate adhesive curing treatment such as irradiation with active energy rays after the heat treatment, and the adhesive strength to the first member and the second member can be reduced while holding the first member and the second member without separating them. By supplying a fluid from one of the members, the fluid acts on the adhesive points of the members, and at least one of the first member and the second member is separated from the adhesive portion. In this way, the members are separated by the hardening of the adhesive and the action of the fluid, so that even if the members are made of a brittle material, the members are unlikely to be damaged during separation. Furthermore, even if the first and second members are rigid bodies, they can be easily separated from each other by only a force in a direction perpendicular to the adhesive surface, for example.

In some preferred embodiments, the adhesive layer is in contact with the first member. The adhesive portion has a hole that connects the first member and the second member. The separation method includes, as the fluid supplying step, a step of supplying the fluid from the second member side to the hole in the adhesive portion. According to this configuration and method, the fluid is supplied from the second member side and acts to separate the first member from the adhesive layer through the hole in the adhesive portion. Based on this action, the first member is separated from the adhesive layer.

In some preferred embodiments, the adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator. The adhesive layer containing an ethylenically unsaturated group and a radical polymerization initiator can be effectively cured by heat treatment, irradiation with active energy rays, etc.

In some preferred embodiments, the adhesive layer is a thermosetting adhesive layer. A thermosetting adhesive layer can be cured by utilizing a heat treatment.

In some preferred embodiments, the radical polymerization initiator is a thermal polymerization initiator. By using an adhesive layer containing a thermal polymerization initiator as a radical polymerization initiator, the adhesive strength to a member can be reduced by utilizing a heat treatment.

In some embodiments, the first member and the second member are non-transparent to light. The technology disclosed herein uses a thermosetting adhesive that can be cured by heat treatment and lose its adhesive strength, and is therefore applicable to the separation of non-transparent members as described above.

In some embodiments, the adhesive portion is made of the pressure-sensitive adhesive layer. Alternatively, in some other embodiments, the adhesive portion has a laminated structure including a first pressure-sensitive adhesive layer as the pressure-sensitive adhesive layer, a base layer, and a second pressure-sensitive adhesive layer, in that order. The technology disclosed herein can be preferably implemented in an embodiment having an adhesive portion having any of the above configurations.

In some embodiments, the adhesive layer has a gel fraction increase of 10% or more after heat treatment at 180°C for 30 minutes. With an adhesive layer (thermosetting adhesive) that has a large gel fraction after heating, the adhesive strength to the member can be reduced by utilizing heat treatment.

In some embodiments, the adhesive layer preferably has a Young's modulus Y1 [MPa] after heat treatment at 180°C for 30 minutes that is 100 times or more the Young's modulus Y0 [MPa] before heating, i.e., a Young's modulus change ratio after heating (Y1/Y0) of 100 or more. The higher the Young's modulus change ratio after heating, the higher the degree of hardening of the adhesive layer when heated, and the easier it tends to be to obtain easy peelability by heating. With an adhesive layer that satisfies the above characteristics, the adhesive strength to a member can be effectively reduced by utilizing heat treatment.

Also, according to this specification, there is provided an adhesive sheet used as a joint in any of the separation methods disclosed herein. This adhesive sheet has a curable adhesive layer. By using an adhesive sheet having a curable adhesive layer as an adhesive part, the separation method disclosed herein is preferably carried out.

Also, according to this specification, there is provided an adhesive sheet having an adhesive layer. This adhesive sheet has holes. The adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator. According to the adhesive sheet having the above configuration, the adherend can be easily peeled off with little load by supplying a fluid to the holes after heat treatment. The adhesive sheet having the above configuration can be preferably applied to the separation method disclosed herein.

FIG. 1 is a cross-sectional view showing a schematic example of a structure used in a separation method. FIG. 11 is a cross-sectional view showing a schematic diagram of another embodiment of a structure used in the separation method.

Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.
In the following drawings, the same reference numerals may be used to denote components or parts having the same function, and duplicated descriptions may be omitted or simplified. In addition, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the product actually provided.

In this specification, the "base polymer" of an adhesive refers to the main component of the rubber-like polymer contained in the adhesive. The rubber-like polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In addition, in this specification, the "main component" refers to a component that is contained in an amount of more than 50% by weight, unless otherwise specified.

In this specification, "acrylic polymer" refers to a polymer that contains, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. In this specification, an acrylic polymer is defined as a polymer that contains a monomer unit derived from an acrylic monomer.

In addition, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" refers collectively to acryloyl groups and methacryloyl groups. Therefore, the concept of acrylic monomer here can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" refers collectively to acrylic acid and methacrylic acid, and "(meth)acrylate" refers collectively to acrylate and methacrylate. The same applies to other similar terms.

Furthermore, in this specification, "weight" may be read as "mass." For example, "% by weight" may be read as "% by mass," and "parts by weight" may be read as "parts by mass."

<Method of separating components>
The member separation method disclosed herein is a method for separating at least one of a first member and a second member from a structure having the first member and the second member after a heat treatment.

(Structure)
The structure used in the above separation method has a cross-sectional structure, for example, as shown in FIG. 1. The structure 100 shown in FIG. 1 has a first member 10, an adhesive portion 30, and a second member 20 in this order. The adhesive portion 30 is disposed between the first member 10 and the second member 20 and adheres to the first member 10 and the second member 20. In the embodiment of FIG. 1, the first member 10 and the second member 20 are sheet-shaped or plate-shaped, and the adhesive portion 30 is a layered body. The adhesive portion 30 is composed of a curable adhesive layer 31 and bonds the first member 10 and the second member 20. In other words, the first member 10 and the second member 20 are bonded via the adhesive portion 30 including the curable adhesive layer 31. In this embodiment, the first member 10 is a semiconductor wafer, and the second member 20 is a metal member. Further, a substrate-less adhesive sheet 30 made of a curable adhesive layer 31 is used as the adhesive part 30. More specifically, a first adhesive surface (first adhesive surface) which is one surface 30A of the adhesive part (adhesive sheet) 30 is adhered to a first member 10 as an adherend, and a second adhesive surface (second adhesive surface) which is the other surface 30B (the surface opposite to the one surface) of the adhesive part (adhesive sheet) 30 is adhered to a second member 20 as an adherend.

Furthermore, the second member 20 has a flow hole 25, and the adhesive portion 30 also has a hole (through hole) 35, which connects the first member 10 and the second member 20. In the structure 100, the second member 20 and the adhesive portion 30 are arranged so that the openings of the flow holes 25 and the holes 35 match, and the first member 10 is arranged on the holes 35 and contacts the curable adhesive layer 31.

(Heat Treatment)
In the member separation method disclosed herein, first, a heat treatment is performed on the structure 100. The heat treatment may be a heat treatment on at least one of the first member 10 and the second member 20. In this embodiment, heating for processing the semiconductor wafer as the first member 10 corresponds to the above-mentioned heat treatment. Alternatively, the heat treatment may be a heat treatment on the adhesive portion 30. When the curable adhesive layer 31 is a thermosetting adhesive, the heat treatment on the adhesive portion 30 may correspond to a heat curing treatment or an adhesive strength reducing treatment step.

The temperature of the heat treatment is appropriately set depending on the purpose of the heat treatment. The heat resistance of the member is also taken into consideration when setting the heat treatment temperature. Although not particularly limited, the heat treatment temperature may be, for example, over 100°C, 120°C or more, 150°C or more (e.g., over 150°C), 160°C or more, or 170°C or more. The upper limit of the heat treatment temperature is generally about 250°C or less, and may be 230°C or less or 200°C or less. The heat treatment time is not particularly limited, but may be, for example, 3 minutes or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 60 minutes or more, more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. There is no particular upper limit to the heat treatment time, but it may be, for example, within 10 hours, within 5 hours, or within 3 hours. From the viewpoint of the efficiency of the heating process, it may be, for example, within 1 hour or within 30 minutes. There are no particular limitations on the heating means, and means such as placing the material in a high-temperature chamber such as an oven or blowing hot air can be used.

In an embodiment in which the curable adhesive layer 31 of the adhesive portion 30 is a thermosetting adhesive, the curable adhesive layer 31 may be cured by the above-mentioned heat treatment, and the adhesive strength of the adhesive portion 30 may be reduced. In an embodiment in which the curable adhesive layer 31 is a curable adhesive other than a thermosetting adhesive, for example, in an embodiment in which the curable adhesive layer 31 is an active energy ray curable adhesive such as an ultraviolet ray curable adhesive, the curable adhesive layer 31 may be irradiated with active energy rays such as ultraviolet rays before or after the above-mentioned heat treatment to cure the curable adhesive layer 31 and reduce the adhesive strength.

After the heat treatment or adhesive curing treatment, the adhesive strength of the adhesive portion 30 that had firmly bonded the first member 10 and the second member 20 is reduced, but the first member 10 and the second member 20 are held together without being separated. Specifically, the curable adhesive layer 31 can hold the first member 10 and the second member 20 to such an extent that they do not peel off from each other. This reduction in adhesive strength and holding state is preferably achieved, for example, by using an adhesive containing an ethylenically unsaturated group and a radical polymerization initiator, which will be described later, although there are no particular limitations thereon. This prevents the members 10 and 20 from being separated from the adhesive portion 30 at an unintended timing.

(Fluid supplying process)
Next, a fluid is supplied to the adhesive portion 30 from the side of the second member 20. Specifically, air A is supplied to the through hole 25 of the second member 20. The supplied air A passes through the through hole 25 and further passes through the hole 35 of the adhesive portion 20 to reach the first member 10. The air A presses the surface 10A of the first member 10 (the surface in contact with the adhesive portion 30) so as to separate the first member 10 from the adhesive portion 30. This action creates a gap on the adhesive surface between the first member 10 and the adhesive portion 30, centered on the opening of the hole 35, and the air A moves along the surface direction between the surface 10A of the first member 10 and the first adhesive surface 30A of the adhesive portion 30 so as to expand the gap, and the first member 10 and the adhesive portion 30 are separated. According to this separation method, since the load during separation is substantially only the air supply, the semiconductor wafer, which is the first member 10, is less likely to be damaged during separation. Moreover, the first member 10 can be easily separated only by a force (air pressure) in a direction perpendicular to the adhesive surface between the first member 10 and the adhesive portion 30 .

The fluid is not limited to air, and various gases such as nitrogen gas can be used. The fluid is also not limited to gas, and liquids such as water, ethanol, and other organic solvents can be used. The fluid supply means is not particularly limited, and any publicly known or commonly used gas or liquid supply device can be used. The amount of fluid supplied (supply rate) is appropriately set according to the purpose, the type of material, the adhesive sheet, the size, etc.

Another example of the structure used in the separation method is shown in FIG. 2. The structure 200 shown in FIG. 2 differs from the structure 100 shown in FIG. 1 in that the adhesive portion 30 has a laminated structure including a first adhesive layer 31, a base layer 34, and a second adhesive layer 32 in this order. The adhesive sheet 30 used as the adhesive portion 30 is configured as a double-sided adhesive sheet with a base material in which the first adhesive layer 31 and the second adhesive layer 32 are provided on the first surface 34A and the second surface 34B of the base material layer 34 (e.g., a resin film), respectively. In this embodiment, both the first adhesive layer 31 and the second adhesive layer 32 are curable adhesive layers. Other points regarding the structure 200 are basically the same as those of the structure shown in FIG. 1, so the description will not be repeated. According to the adhesive portion 30 shown in FIG. 2, for example, by making the composition or characteristics of the first adhesive layer 31 and the second adhesive layer 32 different, the separability of the first member 10 and the second member 20 can be made different, and only the members to be separated can be reliably separated, or the timing of separation of the members can be made different. It is also possible to separate only one of the first member 10 and the second member 20 at a desired timing, and not separate the other from the adhesive portion 30, or to separate it by a different method or at a different timing. For example, after separating the first member 10 and the second member 20 from the structure 200, the adhesive portion (adhesive sheet) 30 remaining on the separated member can be easily peeled off from the member.

In the structure 200, both the first adhesive layer 31 and the second adhesive layer may be curable as described above, or only one of the adhesive layers may be curable.

In the above separation method, the first member does not have a through hole, but the first member may have a through hole and the second member may be separated by supplying a fluid to the adhesive portion from the first member side. In this case, the second member may have a through hole or may not have a through hole. The number of through holes provided in the first member and the second member is not limited to 1, and may be an appropriate number from, for example, about 1 to 50. Depending on the size of the members, the number of through holes may be 2 or more, 5 or more, or 10 or more so that separation is performed with less load. When a porous material is used as the first member and the second member, the porous structure may be used as a fluid passage. In that case, it is not necessary to provide a through hole in the first member and the second member. The size of the through hole is not particularly limited, and may be appropriately set according to the purpose and the material and size of the members, for example, to have an opening with a diameter in the range of about 10 microns to several centimeters (more specifically, for example, about 10 μm to 5 cm).

In addition, the number of holes in the adhesive portion (adhesive sheet) is one, but is not limited to this, and can be an appropriate number, for example, from about 1 to 50, depending on the number of flow holes in the first member and the second member. Depending on the size of the members, the number of holes may be two or more, five or more, or ten or more, so that separation is performed with less load. When multiple holes are provided in the adhesive portion (adhesive sheet), it is preferable to arrange the holes at a predetermined interval, such as equal intervals, so that the load of the fluid is not concentrated on one part of the member. Alternatively, the adhesive portion (adhesive sheet) may not have holes. In that case, the second member can be separated from the adhesive portion by the fluid supplied from the flow hole of the second member. When flow holes are provided in the first member and fluid is supplied, the first member can be separated from the adhesive portion. In other words, by adjusting the hole settings and the fluid supply method, it is possible to separate only one of the first member and the second member from the adhesive joint, or to separate both the first member and the second member from the adhesive joint at the same time or at different times. The size of the hole is not particularly limited, and can be set appropriately depending on the purpose, the size of the opening of the flow hole, and the material and size of the member, for example, with an opening having a diameter ranging from about 10 microns to several centimeters (more specifically, for example, about 10 μm to 5 cm). The size of the hole opening may be the same as or different from the size of the opening of the flow hole of the member.

In addition, in the above separation method, the first member, second member, and adhesive portion that constitute the structure are all configured in a layered, sheet-like, or plate-like shape, and the structure has the form of a laminated structure (laminate), but the shapes of the first member, second member, and adhesive portion do not have to be layered, sheet-like, or plate-like, and can have various shapes. For example, the first member and second member only need to have a surface that contacts the adhesive portion, and may have various three-dimensional member shapes, such as complex shapes and curved shapes, based on the application and purpose of use. The adhesive portion can also have various shapes to match the surface shapes of the first member and second member.

In addition, in this specification, the word "member" in the terms "first member" and "second member" is used to mean a component of a structure, and is not limited to any other meaning. For example, the first member and the second member may each be an independent item or part, or each may be a member that constitutes a different item.

The structure may also include other members and components in addition to the first and second members. For example, if the first and second members are part of a product, the structure may be composed of multiple members and elements.

In addition, the adhesive sheet disclosed herein (more specifically, the adhesive sheet described below) can be one in which, for example, high-temperature heat treatment as described above hardens the adhesive, reducing the peel strength or suppressing the increase in peel strength, and even if the heated state continues for a long period of time, an increase in peel strength (heavy peeling) does not occur or is suppressed. Therefore, it is possible to maintain easy peelability by heat even after a long period of heat treatment.

Below, the adhesive sheet that can be used as the adhesive portion in the separation method disclosed herein will be described in detail, followed by a detailed description of the first member and the second member. Note that the adhesive sheets and structures provided below in this specification are suitable for the separation method described above, but can be used in aspects that are not limited to the separation method described above. Thus, the adhesive sheets and structures disclosed herein are not limited to being used in the separation method described above.

<Adhesive sheet>
The adhesive sheet disclosed herein is configured to include an adhesive layer. The adhesive sheet may be a substrate-attached adhesive sheet having the above-mentioned adhesive layer on both sides of a non-releasable substrate (support substrate), or may be a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-releasable substrate. Typically, the adhesive sheet is made of an adhesive layer) having the above-mentioned adhesive layer held by a release liner. The concept of adhesive sheet here may include those called adhesive tape, adhesive film, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet before use. Alternatively, it may be an adhesive sheet in the form of a processed form into various shapes.

<Adhesive Layer>
As the adhesive layer, various curable adhesive layers can be used. As a result, the adhesive layer is cured by heating, irradiation with active energy rays, etc., and the adhesive strength to the adherend can be reduced. The adhesive constituting such an adhesive layer may be a thermosetting adhesive that is cured by heating, or an active energy ray curable adhesive (typically an ultraviolet ray curable adhesive) that is cured by irradiation with active energy rays such as ultraviolet rays.

In this specification, a curable adhesive (layer) refers to an adhesive (layer) that satisfies at least one of the following conditions: the gel fraction is increased by 5% or more compared to the initial state (before the curing treatment) and the Young's modulus is increased by 2.0 times or more when subjected to a predetermined curing treatment (for example, a heating treatment or an active energy ray irradiation treatment under predetermined conditions). For example, in this specification, a thermosetting adhesive (layer) refers to an adhesive (layer) that satisfies at least one of the following conditions: the gel fraction is increased by 5% or more (preferably 10% or more) compared to the initial state (before heating) when subjected to a heating treatment at 180°C for 30 minutes and the Young's modulus is increased by 2.0 times or more (preferably 5.0 times or more or 10 times or more). The above gel fraction and Young's modulus are measured by the method described in the Examples below.

Although not particularly limited, in some embodiments, it is preferable to use a thermosetting adhesive layer as the adhesive layer. With a thermosetting adhesive layer, the adhesive layer can be cured efficiently and effectively by utilizing a heat treatment. As such an adhesive layer, although not particularly limited, various adhesive layers containing an ethylenically unsaturated group and a radical polymerization initiator can be preferably used. As a result, the adhesive layer is preferably cured by heating or irradiation with active energy rays, etc., and the adhesive force to the adherend can be better reduced. The adhesive constituting such an adhesive layer may be a thermosetting adhesive that is cured by heating, or may be an active energy ray curable adhesive (typically an ultraviolet ray curable adhesive) that is cured by irradiation with active energy rays such as ultraviolet rays. Although not particularly limited, the above ethylenically unsaturated group can be included in the adhesive layer by using a polymer or monomer (hereinafter, sometimes referred to as a "combined monomer" for the purpose of distinguishing it from the monomer component used in the synthesis of the above polymer) that has an ethylenically unsaturated group as the polymer or monomer that can be included in the adhesive layer.

The following mainly describes an adhesive layer containing an ethylenically unsaturated group and a radical polymerization initiator, but it is not intended to limit the adhesive layer disclosed herein to the adhesive layer having the above configuration. For example, as the adhesive layer (curable adhesive layer) disclosed herein, it is also possible to use other curable adhesive layers, such as a curable adhesive layer (typically a thermosetting adhesive layer) that utilizes a curing reaction of an epoxy-acid (e.g., an acid anhydride).

(polymer)
In the technology disclosed herein, the type of adhesive is not particularly limited. The adhesive layer may contain one or more of various rubber-like polymers such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers that can be used in the field of adhesives. The above polymers may be used as base polymers in adhesives and function as structural polymers that form the adhesive. From the viewpoint of adhesive performance, cost, etc., an adhesive containing an acrylic polymer or a rubber polymer as a base polymer may be preferably adopted. Among them, an adhesive (acrylic adhesive) having an acrylic polymer with excellent heat resistance as a base polymer is preferable.

　The following mainly describes acrylic adhesives and adhesive layers made of such adhesives, i.e., adhesive sheets having acrylic adhesive layers, but it is not intended to limit the adhesive layers disclosed herein to acrylic adhesive layers.

(Acrylic polymer)
In some embodiments, the acrylic polymer is an acrylic polymer in which more than 50% by weight of the monomer components constituting the polymer is an acrylic monomer. The proportion of the acrylic monomer in the monomer components is suitably 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, and may be, for example, 90% by weight or more. The upper limit of the proportion of the acrylic monomer in the monomer components constituting the acrylic polymer is 100% by weight, and the proportion of the acrylic monomer may be, for example, 98% by weight or less, 95% by weight or less, or 92% by weight or less, from the viewpoint of obtaining the effect of using a non-acrylic monomer. The acrylic monomer may be used alone or in combination of two or more kinds.

In some preferred embodiments, the monomer component includes an alkoxy group-containing (meth)acrylate. Acrylic polymers that include an alkoxy group-containing (meth)acrylate as a monomer component tend to provide good adhesion and are compatible with, for example, the monomer contained in the adhesive layer described below (hereinafter, sometimes referred to as "combined monomer" to distinguish it from the monomer component used in the synthesis of the polymer). The alkoxy group-containing (meth)acrylate can be used alone or in combination of two or more.

Examples of alkoxy group-containing (meth)acrylates include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; alkoxy(poly)alkylene glycol (meth)acrylates such as methoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate; and the like. Of these, alkoxyalkyl (meth)acrylates are preferred, and among these, alkoxyalkyl (meth)acrylates having an alkoxy group with 1 to 4 carbon atoms (e.g., 1, 2 or 3 carbon atoms) are more preferred, with methoxyethyl (meth)acrylate being particularly preferred.

The content of the alkoxy group-containing (meth)acrylate in the monomer component constituting the acrylic polymer is not particularly limited. From the viewpoint of effectively obtaining the effect of using the alkoxy group-containing (meth)acrylate, the content of the alkoxy group-containing (meth)acrylate in the monomer component is usually about 1% by weight or more, for example, 10% by weight or more, or 30% by weight or more. In some embodiments, the content of the alkoxy group-containing (meth)acrylate in the monomer component is, for example, more than 30% by weight, preferably 40% by weight or more, more preferably 50% by weight or more (for example, more than 50% by weight), and even more preferably 55% by weight or more, from the viewpoint of adhesive properties such as adhesive strength and compatibility with the blended monomer. The upper limit of the content of the alkoxy group-containing (meth)acrylate in the above monomer component is approximately 99% by weight or less in some embodiments, from the viewpoint of introducing an ethylenically unsaturated group into the polymer and obtaining the effects of other copolymerizable monomers such as functional group-containing monomers, and may be 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight or less, and even more preferably 65% by weight or less, and may be 60% by weight or less.

In some other embodiments, the monomer component constituting the acrylic polymer may contain a chain alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms at the ester end. Hereinafter, a chain alkyl (meth)acrylate having an alkyl group having X to Y carbon atoms at the ester end may be referred to as a "C _X-Y alkyl (meth)acrylate". In this specification, "chain" is used to mean both linear and branched. The chain alkyl (meth)acrylates may be used alone or in combination of two or more.

Non-limiting specific examples of C _1-20 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl. (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

In an embodiment in which a C _1-20 alkyl (meth)acrylate is used as a monomer component constituting an acrylic polymer, it is preferable to use at least a C _4-20 alkyl (meth)acrylate as the C _1-20 alkyl (meth)acrylate, and it is more preferable to use at least a C _4-18 alkyl (meth)acrylate. In some embodiments, it is preferable to use a C 4-8 alkyl (meth)acrylate as the C _1-20 alkyl (meth)acrylate. Of these, it is more preferable to use a C _4-8 alkyl acrylate. The C _4-8 alkyl (meth)acrylate may be used alone or in combination of two or more. The use of a _{C 4-8 alkyl} (meth)acrylate tends to make it easier to obtain good adhesive properties (adhesive strength, etc.). For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as the monomer component is preferable, and an acrylic polymer containing at least 2EHA is particularly preferable. In some other embodiments in which a C _1-20 alkyl (meth)acrylate is used, a C _7-12 alkyl (meth)acrylate may be preferably used. The C _{7-12 alkyl (meth)acrylate may be used alone or in combination of two or more. As the C 7-12 alkyl} (meth)acrylate, a C _7-10 alkyl acrylate is preferred, a C _7-9 alkyl acrylate is more preferred, and a C ₈ alkyl acrylate is even more preferred.

In an embodiment in which a C _1-20 alkyl (meth)acrylate is used as a monomer component constituting an acrylic polymer, the content of the C _1-20 alkyl (meth)acrylate in the monomer component is not particularly limited. From the viewpoint of effectively obtaining the effect of using the C _1-20 alkyl (meth)acrylate, in some embodiments, the content of the C _1-20 alkyl (meth)acrylate in the monomer component is usually about 1% by weight or more, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more (for example, more than 50% by weight). In some embodiments, from the viewpoint of introducing an ethylenically unsaturated group into the polymer or obtaining the effects of other copolymerizable monomers, the content of the C _1-20 alkyl (meth)acrylate is about 99% by weight or less, may be 90% by weight or less, may be about 70% by weight or less, may be 50% by weight or less (for example, less than 50% by weight), may be 30% by weight or less, may be 10% by weight or less, may be 1% by weight or less, or may be 0.1% by weight or less. The monomer component may be substantially free of C _1-20 alkyl (meth)acrylate.

In some embodiments, the monomer components constituting the acrylic polymer preferably contain other monomers other than the above alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. Such other monomers may be monomers (copolymerizable monomers) that are copolymerizable with the alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. The other monomers may be used, for example, to introduce an ethylenically unsaturated group into the polymer. As the other monomers, monomers having a polar group (e.g., a carboxy group, a hydroxyl group, a nitrogen atom-containing ring, etc.) may be preferably used. The monomers having a polar group may be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the adhesive. The other monomers may be used alone or in combination of two or more.

Other monomers that can be used include, for example, carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, monomers containing a sulfonic acid group or a phosphoric acid group, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, monomers having a succinimide skeleton, maleimides, itaconimides, aminoalkyl (meth)acrylates, alkoxysilyl group-containing monomers, vinyl esters, vinyl ethers, aromatic vinyl compounds, olefins, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, and other heterocyclic ring-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylates, and (meth)acrylic acid esters obtained from alcohols derived from terpene compounds.

When using other monomers such as those mentioned above, the amount used is not particularly limited, but it is appropriate that it is 1 weight % or more of the total monomer components. From the viewpoint of better exerting the effect of using the other monomers, the amount of the other monomers used may be 10 weight % or more of the total monomer components, 20 weight % or more, or 30 weight % or more. Also, from the viewpoint of making it easier to balance the adhesive properties, it is appropriate that the amount of the other monomers used is 60 weight % or less of the total monomer components, and it is preferably 50 weight % or less (for example, less than 50 weight %), and may be 45 weight % or less.

In some embodiments, the monomer component constituting the acrylic polymer includes a monomer having a nitrogen atom. The use of a monomer having a nitrogen atom can increase the cohesive strength of the adhesive and favorably improve the adhesive strength. As the monomer having a nitrogen atom, for example, an amide group-containing monomer, an amino group-containing monomer, or a monomer having a nitrogen atom-containing ring can be used. The monomer having a nitrogen atom can be used alone or in combination of two or more types.

Non-limiting examples of monomers having a nitrogen atom include the following:
Amide group-containing monomers: for example, (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide; N-monoalkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-hydroxyalkyl(meth)acrylamides such as N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl(meth)acrylamide such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and others such as N,N-dimethylaminopropyl(meth)acrylamide, alkoxydiacetone(meth)acrylamide, vinylformamide, and vinylacetamide.
Amino group-containing monomers: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidone N-vinyl morpholine, N-(meth)acryloylmorpholine, N-vinyl morpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinyl pyrazole, N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, N-vinyl pyridazine, and the like (for example, lactams such as N-vinyl-2-caprolactam).

A suitable example of a monomer having a nitrogen atom is a monomer having a nitrogen atom-containing ring. Among these, N-vinyl-2-pyrrolidone (NVP) and N-acryloylmorpholine (ACMO) are preferred.

The amount of the monomer having a nitrogen atom (preferably a monomer having a nitrogen atom-containing ring) used is not particularly limited. In some embodiments, the amount of the monomer having a nitrogen atom used in the monomer component may be 1% by weight or more, or may be 3% by weight or more. In some preferred embodiments, the amount of the monomer having a nitrogen atom used in the monomer component is 5% by weight or more, more preferably 7% by weight or more, even more preferably 9% by weight or more, or may be 10% by weight or more, or may be 12% by weight or more, or may be 14% by weight or more. The more the amount of the monomer having a nitrogen atom used, the more the cohesive strength of the adhesive tends to improve. In some embodiments, the amount of the monomer having a nitrogen atom used is suitably, for example, 40% by weight or less of the entire monomer component, and may be 35% by weight or less. In some preferred embodiments, the amount of the monomer having a nitrogen atom used in the monomer component is 30% by weight or less, more preferably 25% by weight or less, even more preferably 20% by weight or less, or may be 18% by weight or less.

In some embodiments, the monomer component includes a hydroxyl group-containing monomer. The use of a hydroxyl group-containing monomer can adjust the cohesive strength and crosslink density of the adhesive, improving the adhesive strength. In addition, a hydroxyl group-containing monomer can be preferably used as a means of introducing an ethylenically unsaturated group into a polymer. Examples of hydroxyl group-containing monomers that can be used include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. For example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) can be preferably used. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

When a hydroxyl group-containing monomer is used, the amount used is not particularly limited, and may be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more of the total monomer components. In some embodiments, the amount of the hydroxyl group-containing monomer used is 1% by weight or more of the total monomer components, more preferably 2% by weight or more, or 3% by weight or more. In some preferred embodiments, the amount of the hydroxyl group-containing monomer used is 5% by weight or more of the total monomer components, more preferably 7% by weight or more, even more preferably 10% by weight or more, and particularly preferably 12% by weight or more. Such an amount of the hydroxyl group-containing monomer is suitable when the hydroxyl group-containing monomer is used as a means for introducing an ethylenically unsaturated group into the polymer. In some embodiments, the amount of the hydroxyl group-containing monomer used is, for example, 40% by weight or less of the total monomer components, and is preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 15% by weight or less.

In some preferred embodiments, the monomer component of the acrylic polymer is a monomer having a polar group (polar group-containing monomer) that is a combination of a monomer having a nitrogen atom (e.g., an amide group-containing monomer such as (meth)acrylamide, a monomer having a nitrogen atom-containing ring such as NVP or ACMO) and a hydroxyl group-containing monomer (e.g., HEA, 4HBA). This allows for a good balance between adhesive strength and cohesive strength. In an embodiment in which a monomer having a nitrogen atom and a hydroxyl group-containing monomer are used in combination, the weight ratio (A _N /A _OH ) of the amount of the monomer having a nitrogen atom A _N to the amount of the hydroxyl group-containing monomer A _OH is not particularly limited, and may be, for example, 0.1 or more, 0.5 or more, 1.0 or more, 1.2 or more, 1.5 or more, or 1.8 or more. The weight ratio (A _N /A _OH ) may be, for example, 10 or less, 5 or less, 3 or less, or 2.5 or less.

In some embodiments, the monomer component may include a carboxy group-containing monomer. Non-limiting examples of carboxy group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and the like. Preferred examples include AA and MAA. The carboxy group-containing monomers may be used alone or in combination of two or more. For example, AA and MAA may be used in combination.

The amount of the carboxyl group-containing monomer used may be, for example, 0.01% by weight or more, 0.1% by weight or more, 1% by weight or more, 3% by weight or more, 6% by weight or more, or 8% by weight or more of the total monomer components. The greater the amount of the carboxyl group-containing monomer used, the greater the tendency for the adhesive to have improved cohesive strength. The proportion of the carboxyl group-containing monomer may be, for example, 20% by weight or less, 10% by weight or less, 3% by weight or less, 1% by weight or less (for example, less than 1% by weight), or 0.1% by weight or less. The monomer components may be substantially free of the carboxyl group-containing monomer.

In addition, when an acrylic polymer having an ethylenically unsaturated group, which will be described later, is used as the polymer, it is preferable to use, as the other monomer, a monomer having a functional group (functional group A) that can react with a functional group (functional group B) of a compound having an ethylenically unsaturated group, which will be described later. In this embodiment, the type of the other monomer is determined by the above-mentioned compound type. As the other monomer having functional group A, for example, a carboxy group-containing monomer, an epoxy group-containing monomer, a hydroxyl group-containing monomer, or an isocyanate group-containing monomer is preferable, and a hydroxyl group-containing monomer is particularly preferable. By using a hydroxyl group-containing monomer as the other monomer, the acrylic polymer has a hydroxyl group. On the other hand, by using, for example, an isocyanate group-containing monomer as the compound having an ethylenically unsaturated group, the hydroxyl group of the acrylic polymer reacts with the isocyanate group of the compound, and the ethylenically unsaturated group derived from the compound is introduced into the acrylic polymer.

When using other monomers for the purpose of reacting with a compound having an ethylenically unsaturated group, the amount of the other monomers (preferably hydroxyl group-containing monomers) is appropriately set to about 1% by weight or more of the total monomer components from the viewpoint of adhesive properties such as curability and cohesive strength of the adhesive, and is preferably about 5% by weight or more, more preferably about 10% by weight or more, and may be about 12% by weight or more. Also, from the viewpoint of maintaining good adhesive properties such as adhesive strength, the amount of the other monomers is appropriately set to about 40% by weight or less of the total monomer components, and is preferably about 30% by weight or less, more preferably about 25% by weight or less, and may be about 20% by weight or less (e.g., 15% by weight or less).

The acrylic polymer may contain, as another monomer component, a polyfunctional monomer having at least two ethylenically unsaturated groups, such as a (meth)acryloyl group or a vinyl group. By using a polyfunctional monomer as a monomer component, the cohesive strength of the adhesive can be increased. The polyfunctional monomer can be used as a crosslinking agent. There are no particular limitations on the polyfunctional monomer, and for example, one or more suitable monomers from those exemplified as blended monomers contained in the adhesive layer described below can be used alone or in combination.

The amount of polyfunctional monomer used is not particularly limited, and can be appropriately set so that the purpose of using the polyfunctional monomer is achieved. The amount of polyfunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (e.g., about 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately achieved by setting the amount of polyfunctional monomer used to about 0.001% by weight or more of the monomer component (e.g., about 0.01% by weight or more).

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as methods for synthesizing acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately adopted. For example, solution polymerization can be preferably adopted. As a monomer supply method when performing solution polymerization, a lump-sum charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, and the like can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one of the following solvents or a mixture of two or more solvents can be used: aromatic compounds such as toluene (typically aromatic hydrocarbons); acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, but not limited to, azo-based polymerization initiators, peroxide-based polymerization initiators, redox-based polymerization initiators formed by combining peroxides with reducing agents, substituted ethane-based polymerization initiators, etc. can be used. As the polymerization initiator, for example, one or more of the radical polymerization initiators (e.g., thermal polymerization initiators) exemplified below to be added to the adhesive layer can be selected and used.

The amount of the polymerization initiator used is not particularly limited and may be a normal amount depending on the polymerization method and polymerization mode. For example, about 0.001 to 5 parts by weight (typically about 0.01 to 2 parts by weight, e.g., about 0.01 to 1 part by weight) of the polymerization initiator can be used per 100 parts by weight of the total monomer components to be polymerized.

(Polymer having an ethylenically unsaturated group)
In some embodiments, the adhesive layer comprises a polymer having an ethylenically unsaturated group such as an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group. According to the adhesive containing the polymer having an ethylenically unsaturated group, the ethylenically unsaturated group of the polymer reacts when heated or by irradiation with active energy rays, etc., and the adhesive can be cured to a high degree of curing, and excellent peelability (e.g., heat peelability and heat resistance peelability) can be obtained. In addition, according to the adhesive containing the polymer having an ethylenically unsaturated group, in an embodiment in which the adhesive layer contains a monomer (compounded monomer), sufficient peelability (e.g., heat peelability and heat resistance peelability) can be realized while limiting the amount of the compounded monomer used.

In some embodiments, a polymer having an ethylenically unsaturated group in a side chain is used as the polymer having an ethylenically unsaturated group. As the monomer component of the polymer having an ethylenically unsaturated group, one or more of the monomer components exemplified for the above polymer can be used in the above content range.

The amount of ethylenically unsaturated groups in a polymer having ethylenically unsaturated groups is not particularly limited, and from the viewpoint of curability, etc., it is appropriate to make it 0.01 mmol per 1 g of polymer (hereinafter also referred to as mmol/g) or more, and it may be 0.1 mmol/g or more, or 0.5 mmol/g or more. In addition, the amount of ethylenically unsaturated groups in the above polymer is appropriate to be 10.0 mmol/g or less, and may be 5.0 mmol/g or less, 3.0 mmol/g or less, 2.5 mmol/g or less, or 2.0 mmol/g or less.

The amount of the ethylenically unsaturated group in the polymer is measured by the following method, for example, when the ethylenically unsaturated group is a (meth)acryloyl group.
First, 0.25 mg of the polymer to be measured is dissolved in 50 mL of THF (tetrahydrofuran), and 15 mL of methanol is added to obtain a solution. Next, 10 mL of 4N aqueous sodium hydroxide is added to the above solution to obtain a mixed solution. Next, the above mixed solution is stirred at a liquid temperature of 40° C. for 2 hours. Furthermore, 10.2 mL of 4N methanesulfonic acid solution is added to the above mixed solution and stirred. 5 mL of demineralized water is added to this, followed by 2 mL of methanol to prepare a measurement solution.
The content of (meth)acrylic acid in the measurement solution is measured by HPLC (High Performance Liquid Chromatography) (absolute calibration curve method), and the content of ethylenically unsaturated groups is calculated.
(HPLC measurement conditions)
Column: Phenomenex Synergi 4μ Polar-RP 80A (4.6 mm x 250 mm)
Column temperature: 40°C
Flow rate: 1.0mL/min
Detector wavelength: 210 nm
Eluent: THF (for HPLC) 55/buffer water (containing 0.2% phosphoric acid and 0.2% triethylamine) 45
Aqueous solution injection volume: 5 μL

An example of a method for measuring the content of ethylenically unsaturated groups other than (meth)acryloyl groups is a method for measuring the bromine number in accordance with JIS K2605: 1996. In this measurement method, the content of ethylenically unsaturated groups other than (meth)acryloyl groups is determined by converting the number of grams of bromine ( _Br2 ) added to 100 g of the polymer to be measured into the number of moles of bromine ( _Br2 ) added to 1 g of the polymer.

The method of introducing an ethylenically unsaturated group into a polymer is not particularly limited, and an appropriate method can be selected from among methods known to those skilled in the art. From the viewpoint of molecular design, etc., a method of introducing an ethylenically unsaturated group into a side chain of a polymer is preferable. For example, a method of reacting (typically condensation, addition reaction) a compound having an ethylenically unsaturated group and a functional group (functional group B) that can react with a functional group (functional group A) introduced into an acrylic polymer by copolymerization, so that the ethylenically unsaturated group does not disappear, can be preferably adopted. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among them, a combination of a hydroxyl group and an isocyanate group is preferable from the viewpoint of reaction traceability. From the viewpoint of polymer design, etc., a combination in which the acrylic polymer has a hydroxyl group and the above compound has an isocyanate group is particularly preferable.

The compound having an ethylenically unsaturated group may have a functional group B capable of reacting with functional group A, as described above. Suitable examples of such compounds include isocyanate group-containing monomers (isocyanate group-containing compounds) such as 2-(meth)acryloyloxyethyl isocyanate. Of these, 2-(meth)acryloyloxyethyl isocyanate is more preferred. An acrylic polymer having an ethylenically unsaturated group can be obtained by reacting the isocyanate group of the isocyanate group-containing compound having an ethylenically unsaturated group with the hydroxyl group of the acrylic polymer to form a bond (specifically a urethane bond).

The amount of the compound having an ethylenically unsaturated group (e.g., an isocyanate group-containing monomer) added is not particularly limited, but from the viewpoint of reactivity with the functional group A (e.g., a hydroxyl group) in the polymer, the molar ratio (M _A /M B ) of the moles of the functional group A (M _A ) to the moles of the functional group B ( _isocyanate group) (M _B ) may be set in the range of about 0.5 to 2 (e.g., 1 to 1.5).

In embodiments in which a polymer having an ethylenically unsaturated group is used as the polymer, the content of the polymer having an ethylenically unsaturated group in the adhesive layer is not particularly limited. In some embodiments, the amount of the polymer having an ethylenically unsaturated group used is suitably about 10% by weight or more of the total polymer (specifically, base polymer) contained in the adhesive layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the adhesive layer may consist essentially of a polymer having an ethylenically unsaturated group.

In some other embodiments, the polymer may be a polymer that is substantially free of ethylenically unsaturated groups such as acryloyl groups, methacryloyl groups, vinyl groups, and allyl groups (the amount of ethylenically unsaturated groups is less than 0.01 mmol/g). The amount of such polymer used is suitably about 10% by weight or more of the entire polymer (specifically, base polymer) contained in the adhesive layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the adhesive layer may be substantially composed of a polymer that is substantially free of ethylenically unsaturated groups.

The molecular weight of the polymer (e.g., acrylic polymer) is not particularly limited and can be set in an appropriate range according to the required performance. The weight average molecular weight (Mw) of the polymer is suitably about 1×10 ⁴ or more, for example, about 10×10 ⁴ or more. By using a polymer having a Mw of a predetermined value or more, the cohesive force and the adhesive force can be well balanced. In some embodiments, the Mw may be 20×10 ⁴ or more, 30×10 ⁴ or more, about 40×10 4 or more, about 50×10 ⁴ or more, for example, about 55×10 ⁴ or more, from the viewpoint of obtaining heat resistance and good adhesiveness. The upper limit of the Mw of the polymer is not particularly limited, and may be, for example, about 1000×10 ⁴ or less, or about 100×10 ⁴ or less. Here, Mw refers to a value calculated in terms of standard polystyrene obtained by gel permeation ^{chromatography} (GPC). As the GPC device, for example, a model named "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) may be used.

(monomer)
In some embodiments, the adhesive layer preferably contains a monomer (a blended monomer) in addition to the polymer. The monomer has an ethylenically unsaturated group. The ethylenically unsaturated group of the monomer functions as a polymerizable functional group (typically a radically polymerizable functional group). By including the monomer in the adhesive layer, the monomer is included in the adhesive layer in a pre-reacted (unreacted) state. As a result, after the adhesive layer is formed, the monomer included in the adhesive layer reacts during heat treatment under predetermined conditions or by irradiation with active energy rays, etc., to reduce the adhesive force and realize easy peelability (e.g., easy peelability by heating). For example, when the adhesive layer is designed as a thermosetting adhesive, the monomer can be included to form a thermosetting adhesive that has heat resistance and easy peelability even after heat treatment. More specifically, usually, when the adhesive is attached to an adherend and heated, for example, at a high temperature, it is adsorbed to the surface of the adherend. Therefore, the adhesive strength to the adherend is strengthened, resulting in heavy peeling. For example, in an embodiment in which the adhesive contains a monomer together with a thermal polymerization initiator (e.g., a peroxide-based polymerization initiator), the reaction (radical polymerization reaction) between the monomer and the thermal polymerization initiator proceeds rapidly upon heating, and the adhesive can be cured prior to the adhesive being adsorbed to the adherend. This can reduce the adhesive strength to the adherend. Furthermore, even if heating is continued thereafter, the adhesive strength to the adherend does not increase and is maintained within a predetermined range, so that the adhesive can exhibit excellent heat peelability. The technology disclosed herein is not limited to the above considerations. The above monomers can be used alone or in combination of two or more.

Examples of ethylenically unsaturated groups contained in the above monomers include, but are not limited to, acryloyl groups, methacryloyl groups, vinyl groups, and allyl groups. Suitable examples of ethylenically unsaturated groups include acryloyl groups and methacryloyl groups. Of these, acryloyl groups are preferred. Hereinafter, compounds having acryloyl groups and/or methacryloyl groups may be referred to as acrylic monomers. Compounds having vinyl groups may be referred to as vinyl monomers.

Although not particularly limited, it is appropriate to use a monomer having a molecular weight of 100 or more as the above monomer. In some preferred embodiments, the molecular weight of the above monomer may be, for example, 150 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more. The molecular weight of the above monomer is usually about 100,000 or less, for example, about 10,000 or less (e.g., less than 10,000) is appropriate, 5,000 or less (e.g., less than 5,000) is preferable, 1,500 or less, 1,000 or less (e.g., less than 1,000), 800 or less, or 600 or less. The use of the above monomer having a molecular weight in the above range can be advantageous, for example, in terms of the preparation and coatability of the adhesive composition. The above molecular weight is a molecular weight calculated from the manufacturer's nominal value or molecular structure. For the above monomers having a molecular weight equal to or greater than a certain value, the weight average molecular weight (Mw) calculated using standard polystyrene standards obtained by GPC may be used.

In some preferred embodiments, the monomer has a weight loss rate of 1% or less (specifically, 1.0% or less) when reaching 180°C in TGA (thermogravimetric analysis) under a temperature rise condition of 10°C/min. By using a monomer having heat resistance with a weight loss rate of 1% or less at 180°C (hereinafter also referred to as "heat-resistant monomer"), the adhesive layer has easy peelability (e.g., easy peelability by heating) based on the inclusion of the monomer, while suppressing outgas generation during heating. By using the heat-resistant monomer, for example, it is possible to achieve both easy peelability by heating and reduced outgassing. From the viewpoint of reducing outgassing, in some preferred embodiments, the weight loss rate of the heat-resistant monomer at 180°C is 0.9% or less, more preferably 0.8% or less, even more preferably 0.7% or less, particularly preferably 0.6% or less, and may be 0.5% or less. The lower limit of the weight loss rate of the heat-resistant monomer when heated to 180°C is theoretically 0%, and may be 0.1% or more in practice, 0.2% or more, or 0.3% or more. As the heat-resistant monomer, trimethylolpropane triacrylate (TMPTA, weight loss rate when reaching 180°C is 1%) and dipentaerythritol hexaacrylate (DPHA, weight loss rate when reaching 180°C is 0.5%) are preferably used. The heat-resistant monomer may be used alone or in combination of two or more kinds.

Specifically, the weight loss rate of the above monomer when heated to 180°C can be measured using a differential thermal analyzer (manufactured by TA Instruments, product name "Discovery TGA") under measurement conditions of a temperature rise of 10°C/min, in an air atmosphere, and at a flow rate of 25 mL/min.

In some preferred embodiments, a polyfunctional monomer is used as the monomer. In this specification, a polyfunctional monomer refers to a polymerizable compound having two or more ethylenically unsaturated groups in one molecule, and includes those called oligomers. Hereinafter, a compound having two or more acryloyl groups and/or methacryloyl groups may be referred to as a polyfunctional acrylic monomer. Also, a compound having two or more vinyl groups may be referred to as a polyfunctional vinyl monomer.

In some preferred embodiments, the number of ethylenically unsaturated groups contained in one molecule of the polyfunctional monomer may be 3 or more, preferably 4 or more, more preferably 5 or more, and may be 6 or more. The more ethylenically unsaturated groups in the polyfunctional monomer, the easier it is to obtain peelability. For example, when the adhesive layer is designed as a thermosetting adhesive, it tends to have good curing properties when heated and to be easily peelable when heated. In addition, a polyfunctional monomer having a larger number of ethylenically unsaturated groups (functional groups) can be used to obtain easy peelability (e.g., easy peelability when heated) with a relatively small amount of use. This is advantageous because it also leads to a reduction in the amount of outgassing derived from the polyfunctional monomer. The upper limit of the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer is not limited to a specific range, and may be, for example, 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer may be, for example, 10 or less, 8 or less, or 6 or less. Multifunctional monomers having the above number of ethylenically unsaturated groups tend to provide both good adhesion and easy peelability (e.g., easy peelability upon heating), and also tend to have excellent storage stability.

As the polyfunctional monomer, various polyfunctional acrylate monomers having two or more ethylenically unsaturated groups or polyfunctional vinyl monomers can be used. Among them, polyfunctional acrylate monomers can be preferably used. Although not particularly limited, polyfunctional acrylate monomers tend to be compatible and easily exhibit desired properties when used in combination with acrylic polymers. The polyfunctional acrylate monomers and polyfunctional vinyl monomers can each be used alone or in combination of two or more.

　Multifunctional monomers include 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, allyl (meth)acrylate, alkylene oxide modified bisphenol A di(meth)acrylate, alkylene oxide modified neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, dimethylol dicyclopentadi(meth)acrylate, vinyl (meth)acrylate, divinylbenzene, etc. difunctional monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxy tri(meth)acrylate, glycerin propoxy triacrylate, tetramethylolmethane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; tetrafunctional monomers such as pentaerythritol alkoxy tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate. pentafunctional monomers such as sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate; hexafunctional monomers such as dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide modified hexa(meth)acrylate, and caprolactone modified dipentaerythritol hexa(meth)acrylate; and di- or higher functional epoxy acrylates, polyester acrylates, and urethane acrylates. Among these, preferred examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Of these, dipentaerythritol hexa(meth)acrylate is particularly preferred.

In the embodiment in which the adhesive layer contains a polyfunctional monomer, the content of the polyfunctional monomer in the adhesive layer is not particularly limited. In some embodiments, the content of the polyfunctional monomer may be approximately 1 part by weight or more, or 3 parts by weight or more, per 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the adhesive layer. The appropriate amount of the polyfunctional monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, the content of the polyfunctional monomer is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 15 parts by weight or more, even more preferably 20 parts by weight or more, and even more preferably 25 parts by weight or more, from the viewpoint of improving peelability (e.g., improving peelability by heating). By including a sufficient amount of polyfunctional monomer in the adhesive layer, for example, when the adhesive layer is designed as a thermosetting adhesive layer, the polyfunctional monomer contained in the adhesive layer reacts quickly upon heating, and the adhesive layer is thermally cured, thereby realizing easy peeling by heating. The upper limit of the content of the polyfunctional monomer in the adhesive layer is not particularly limited, and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of the polyfunctional monomer relative to 100 parts by weight of the polymer is suitably about 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the polyfunctional monomer relative to 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less (e.g., less than 20 parts by weight), 18 parts by weight or less, 15 parts by weight or less, or 12 parts by weight or less. According to the technology disclosed herein, the desired easy peelability (e.g., easy peelability by heating) can be preferably achieved with a composition in which the amount of monomer in the adhesive layer is limited as described above. In addition, by limiting the amount of the polyfunctional monomer used, the generation of low molecular weight components derived from the polyfunctional monomer after the reaction of the polyfunctional monomer is suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

In embodiments in which a polyfunctional monomer is used as the monomer, the amount of the polyfunctional monomer in the total monomer is not particularly limited. In some embodiments, from the viewpoint of effectively exerting the effect of containing the polyfunctional monomer, the amount of the polyfunctional monomer is appropriately about 10% by weight or more of the total monomer, preferably 30% by weight or more, more preferably about 50% by weight or more (e.g., more than 50% by weight), even more preferably 70% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may be 99 to 100% by weight. In some embodiments, the monomer contained in the adhesive composition may essentially consist of the polyfunctional monomer.

Furthermore, one or more types of monofunctional monomers containing one ethylenically unsaturated group in one molecule may be used as the above monomer. As the monofunctional monomer, known monofunctional acrylate monomers or vinyl monomers may be used. For example, one or more types of acrylate monomers (alkoxy group-containing (meth)acrylates, chain alkyl (meth)acrylates, etc.) exemplified as monomer components of the above polymer may be used.

In the embodiment in which the adhesive layer contains the monomer, the content of the monomer in the adhesive layer is not particularly limited. In some embodiments, the content of the monomer may be about 1 part by weight or more, or may be 3 parts by weight or more, per 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the adhesive layer. The appropriate amount of the monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, the content of the monomer is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 15 parts by weight or more, even more preferably 20 parts by weight or more, and even more preferably 25 parts by weight or more, from the viewpoint of improving peelability (e.g., improving peelability by heating). By including a sufficient amount of the monomer in the adhesive layer, for example, when the adhesive layer is designed as a thermosetting adhesive layer, the monomer contained in the adhesive layer reacts quickly upon heating, and the adhesive layer is thermally cured, thereby realizing easy peeling by heating. The upper limit of the content of the monomer in the adhesive layer is not particularly limited, and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of the monomer relative to 100 parts by weight of the polymer is appropriate to be approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the monomer relative to 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less (e.g., less than 20 parts by weight), 18 parts by weight or less, 15 parts by weight or less, or 12 parts by weight or less. According to the technology disclosed herein, the desired improvement in easy peelability (e.g., easy peelability upon heating) can be preferably realized with a composition in which the amount of monomer in the pressure-sensitive adhesive layer is limited as described above. In addition, by limiting the amount of the monomer used, the generation of low molecular weight components derived from the monomer after the reaction of the monomer is suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

(Radical Polymerization Initiator)
In some embodiments, the adhesive layer preferably contains a radical polymerization initiator. In an embodiment in which the adhesive layer contains an ethylenically unsaturated group, the radical polymerization initiator may react with the ethylenically unsaturated group contained in the adhesive layer to cure the adhesive. This can reduce the adhesive strength to the adherend. Suitable examples of the radical polymerization initiator include a thermal polymerization initiator and a photopolymerization initiator. By incorporating a thermal polymerization initiator in the adhesive layer, the adhesive layer can be designed as a thermosetting adhesive layer. In addition, by incorporating a photopolymerization initiator in the adhesive layer, the adhesive layer can be designed as an active energy ray curable adhesive layer. The radical polymerization initiator can be used alone or in combination of two or more types. For example, a thermal polymerization initiator and a photopolymerization initiator may be used in combination. Although not particularly limited, the technology disclosed herein can be preferably implemented by an adhesive layer containing a thermal polymerization initiator suitable for a process including a heat treatment.

(Thermal Polymerization Initiator)
In some embodiments, the adhesive layer contains a thermal polymerization initiator. Here, the thermal polymerization initiator refers to a polymerization initiator that generates radicals by heating. By including a thermal polymerization initiator in the adhesive layer, the thermal polymerization initiator reacts with the ethylenically unsaturated group in the adhesive layer during heat treatment under a predetermined condition, for example, in an embodiment in which the adhesive layer contains an ethylenically unsaturated group, to reduce the adhesive strength and realize easy peeling by heating. By including a thermal polymerization initiator, a thermosetting adhesive having heat resistance and easy peeling property even after heat treatment can be formed.

As the thermal polymerization initiator, one or more suitable types can be selected and used from various thermal polymerization initiators such as peroxide-based polymerization initiators, azo-based polymerization initiators, redox-based polymerization initiators formed by combining peroxides with reducing agents, and substituted ethane-based polymerization initiators.

In some embodiments, the thermal polymerization initiator preferably contains at least a peroxide-based polymerization initiator. By including a peroxide-based polymerization initiator in the adhesive layer as a thermal polymerization initiator, for example in an embodiment in which the adhesive layer contains an ethylenically unsaturated group, the reaction of the ethylenically unsaturated group in the adhesive layer during heating, i.e., the curing reaction of the adhesive layer, proceeds rapidly, and it is possible to reliably exhibit easy peelability by heating for various adherends including materials that easily adhere to the adhesive layer by heating. One of the reasons for this is thought to be the high initiation efficiency of peroxide-based polymerization initiators (particularly organic peroxide-based polymerization initiators). In addition, peroxide-based polymerization initiators generate radicals (-O.) by cleaving -O-O- contained in the compound, but since this cleavage reaction is reversible, it is thought that recombination of -O-O- occurs if the radical does not collide with the ethylenically unsaturated group of the blended monomer or polymer. This recombined initiator can undergo a cleavage reaction again during a specified heating time, collide with the blended monomer, etc., and react. Therefore, with a peroxide-based polymerization initiator, the thermal curing of the adhesive layer proceeds quickly, with a reaction speed that is significantly faster than that of other initiators (e.g., azo-based initiators). And since the thermal curing speed is faster than the speed at which the adhesive layer and the adherend become firmly attached due to heating, it is believed that the peeling force after heating is reliably reduced, and heat-induced easy peelability and heat-resistant easy peelability are obtained. Note that the technology disclosed herein is not limited to the above considerations.

As the peroxide-based polymerization initiator, for example, organic peroxides such as diacyl peroxides, peroxy esters, peroxy dicarbonates, monoperoxy carbonates, peroxy ketals, dialkyl peroxides, hydroperoxides, and ketone peroxides are preferably used. Suitable examples of peroxide-based polymerization initiators include benzoyl peroxide compounds (typically dibenzoyl peroxide (BPO)) having a benzoyl group that may have a substituent. The peroxide-based polymerization initiators can be used alone or in combination of two or more.

Specific examples of peroxide polymerization initiators include BPO, 1,1-di(t-hexylperoxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, and 1,3-bis(t-butylperoxy)-m-isopropanol. Examples include diphenylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, diisopropylbenzene hydroperoxide, t-butylcumyl peroxide, didecanoyl peroxide, dilauroyl peroxide, 2,4-dichlorobenzoyl peroxide, di(4-t-butylcyclohexyl)peroxydicarbonate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl hydroperoxide, and di-t-butyl peroxide.

In an embodiment in which the adhesive layer contains a peroxide-based polymerization initiator, the content of the peroxide-based polymerization initiator in the adhesive layer is not particularly limited. In some embodiments, the content of the peroxide-based polymerization initiator in the adhesive layer is suitably 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer, and is preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, particularly preferably 0.5 parts by weight or more, may be 0.6 parts by weight or more, or may be 0.7 parts by weight or more. The higher the content of the peroxide-based polymerization initiator, the higher the frequency of collision between the peroxide-based polymerization initiator and the ethylenically unsaturated group in the adhesive layer containing an ethylenically unsaturated group, for example, and the easier it is for the curing reaction to proceed. In addition, in some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the polymer is suitably 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., 1.1 parts by weight or less), and may be 1.0 parts by weight or less (e.g., less than 1.0 parts by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By setting the content of the peroxide-based polymerization initiator within a predetermined range, it is possible to preferably realize a pressure-sensitive adhesive having efficient thermosetting and easy peeling by heating while obtaining adhesive properties such as adhesive strength and storage stability.

In an embodiment in which the adhesive layer contains a monomer (a blended monomer) and a peroxide-based polymerization initiator, the content of the peroxide-based polymerization initiator in the adhesive layer can also be specified by the relative relationship with the blended monomer in the adhesive layer. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomer is preferably 0.1 parts by weight or more, more preferably 0.8 parts by weight or more, even more preferably 1.0 parts by weight or more, even more preferably 1.2 parts by weight or more, particularly preferably 1.5 parts by weight or more, and may be 2.0 parts by weight or more, or may be 2.5 parts by weight or more. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomer is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and may be 7 parts by weight or more. The amount of the peroxide-based polymerization initiator used can be preferably adopted, for example, in a composition in which the monomer content is limited. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomer may be, for example, about 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, or 10 parts by weight or less. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomer may be, for example, 7 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less.

In some other embodiments, the adhesive layer contains, as a thermal polymerization initiator, a persulfate such as potassium persulfate or ammonium persulfate; an azo compound such as an azonitrile compound, an azoamide compound, an azoester compound, an alkyl azo compound, an azoamidine compound, an azoimidazoline compound, or a polymeric azo compound, more specifically, 2,2'-azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexane-1-carbonitrile), 4,4-azobis(4-cyanovaleric acid), 2,2'-azobis(N -butyl-2-methylpropionamide, 2,2'-azobis(2,4,4-trimethylpentane), etc.; substituted ethane initiators such as phenyl-substituted ethane; redox initiators formed by combining a peroxide with a reducing agent, such as a combination of a persulfate with sodium hydrogen sulfite, or a combination of a peroxide with sodium ascorbate; etc. Thermal polymerization initiators other than these peroxide-based polymerization initiators are also called non-peroxide-based polymerization initiators. Non-peroxide-based polymerization initiators may be used in addition to peroxide-based polymerization initiators.

Although not particularly limited, in order to effectively exert the effects of the peroxide-based polymerization initiator, in some embodiments, the proportion of the peroxide-based polymerization initiator in the total thermal polymerization initiator contained in the adhesive layer is suitably approximately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95 to 100% by weight. The thermal polymerization initiator contained in the adhesive layer may be composed of a peroxide-based polymerization initiator.

In some embodiments, it is preferable to use a thermal polymerization initiator whose self-decomposition acceleration temperature (SADT) [°C] satisfies the formula: SADT+10≧60;. Here, the SADT of the thermal polymerization initiator is defined as the minimum temperature at which heat generation or self-accelerating decomposition of 6°C or more occurs within 7 days in a certain amount of container. SADT indicates the environmental temperature at the boundary of whether the thermal polymerization initiator causes decomposition. Based on the fact that the maximum temperature to which the adhesive can be exposed during storage is 60°C, the inventors have experimentally confirmed that if the thermal polymerization initiator has a SADT that is -10°C of the maximum storage temperature or higher, the self-decomposition of the thermal polymerization initiator in the adhesive is suppressed, and storage stability that can maintain good heat-peelability after storage is obtained. This is thought to be because heat is relatively less transmitted in the adhesive (solid) than in the case of the thermal polymerization initiator alone. Based on this discovery, an adhesive designed with a thermal polymerization initiator having a SADT that satisfies the above formula (hereinafter also referred to as a high SADT initiator) can suppress decomposition of the thermal polymerization initiator in the adhesive, even when the adhesive is exposed to a temperature of approximately 60°C before use, and the adhesive can maintain the desired heat-peelability. An adhesive containing a thermal polymerization initiator made of a high SADT initiator has good storage stability and can maintain good heat-peelability after storage, even when stored for a long period of time or when there is a temperature change during storage. In this specification, the nominal value listed in the manufacturer's catalog, etc., is used as the SADT of the thermal polymerization initiator.

The amount of the thermal polymerization initiator contained in the adhesive layer is not particularly limited. In some embodiments, the content of the thermal polymerization initiator in the adhesive layer is suitably 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer, and is preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, and particularly preferably 0.5 parts by weight or more, and may be 0.6 parts by weight or more, or may be 0.7 parts by weight or more. The higher the content of the thermal polymerization initiator, for example, in the adhesive layer containing an ethylenically unsaturated group, the higher the frequency of collision between the thermal polymerization initiator and the ethylenically unsaturated group, and the easier it is for the curing reaction to proceed. In addition, in some embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer is suitably 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., 1.1 parts by weight or less), and may be 1.0 parts by weight or less (e.g., less than 1.0 parts by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By keeping the total amount of the thermal polymerization initiator within a predetermined range, it is possible to preferably realize a pressure-sensitive adhesive having efficient thermosetting and easy peeling by heating while obtaining adhesive properties such as adhesive strength and storage stability.

Although not particularly limited, in some preferred embodiments, the total proportion of the above-mentioned polymer (specifically, base polymer, for example, acrylic polymer), the above-mentioned monomer (for example, polyfunctional acrylic monomer) and thermal polymerization initiator (peroxide-based polymerization initiator, etc.) in the entire adhesive layer is suitably 50% by weight or more (for example, more than 50% by weight and 100% by weight or less) from the viewpoint of effectively achieving a decrease in peel strength when heated, and is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, and may be 95% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99 to 100% by weight).

(Photopolymerization initiator)
In some embodiments, the adhesive layer contains a photopolymerization initiator. Here, the photopolymerization initiator refers to a polymerization initiator that generates radicals by decomposing itself when irradiated with active energy rays such as ultraviolet rays. By including a photopolymerization initiator in the adhesive layer, when the adhesive layer is irradiated with active energy rays, for example, in an embodiment in which the adhesive layer contains an ethylenically unsaturated group, the photopolymerization initiator reacts with the ethylenically unsaturated group in the adhesive layer to harden, thereby reducing the adhesive strength and realizing easy peeling. As the photopolymerization initiator, for example, one or more suitable types can be selected from ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, oxime ester-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, alkylphenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like, and can be used.

In an embodiment in which the adhesive layer contains a photopolymerization initiator, the amount of photopolymerization initiator contained in the adhesive layer is not particularly limited, and can be, for example, in the same range as the content of the thermal polymerization initiator. In other words, the range of the content of the thermal polymerization initiator relative to 100 parts by weight of the polymer can be applied as the range of the content of the photopolymerization initiator.

(Crosslinking Agent)
The adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary, mainly for the purpose of crosslinking within the adhesive layer or between the adhesive layer and its adjacent surface. The crosslinking agent is typically contained in the adhesive layer in a form after crosslinking reaction. The use of the crosslinking agent allows the cohesive strength of the adhesive layer to be appropriately adjusted.

The type of crosslinking agent is not particularly limited, and can be selected from conventionally known crosslinking agents so that the crosslinking agent exerts an appropriate crosslinking function within the adhesive layer, for example, depending on the composition of the adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. These can be used alone or in combination of two or more. From the viewpoint of achieving a good balance between adhesiveness and cohesive strength, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and carbodiimide-based crosslinking agents are preferred, and isocyanate-based crosslinking agents are particularly preferred.

As an isocyanate-based crosslinking agent, a polyfunctional isocyanate compound having two or more functionalities can be used. Examples include aromatic isocyanates such as tolylene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Examples of commercially available products include isocyanate adducts such as trimethylolpropane/tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, product name "Coronate L"), trimethylolpropane/hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, product name "Coronate HL"), isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, product name "Coronate HX"), and trimethylolpropane/xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-110N"), etc.

As the epoxy crosslinking agent, those having two or more epoxy groups in one molecule can be used without any particular restrictions. Epoxy crosslinking agents having 3 to 5 epoxy groups in one molecule are preferred. Specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's product names "TETRAD-X" and "TETRAD-C", DIC Corporation's product name "Epicron CR-5L", Nagase ChemteX Corporation's product name "Denacol EX-512", Nissan Chemical Industries' product name "TEPIC-G", etc.

As the oxazoline-based crosslinking agent, any agent having one or more oxazoline groups in one molecule can be used without any particular limitation.
Examples of the aziridine crosslinking agent include trimethylolpropane tris[3-(1-aziridinyl)propionate], trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)], and the like.
As the carbodiimide-based crosslinking agent, a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups can be used.

In some embodiments, an isocyanate-based crosslinking agent is used as the crosslinking agent. The isocyanate-based crosslinking agent can easily form an adhesive having good peelability while exhibiting a good balance of adhesive properties such as adhesive strength and cohesive strength. The isocyanate-based crosslinking agent can be used alone or in combination of two or more. Although not particularly limited, the amount of the isocyanate-based crosslinking agent used is preferably less than 3 parts by weight per 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer. By limiting the amount of the isocyanate-based crosslinking agent used, the crosslinking density is appropriately suppressed, and at such a crosslinking density, for example, in an embodiment in which the adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator, the ethylenically unsaturated group in the adhesive layer and the radical polymerization initiator frequently collide with each other during heat treatment or by irradiation with active energy rays, and hardening proceeds, thereby improving the peelability. For example, when the adhesive layer is designed as a thermosetting adhesive, the desired heat peelability and heat resistance peelability can be expressed. The technology disclosed herein is not limited to the above considerations. From this viewpoint, in some preferred embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer is 2 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 parts by weight or less, even more preferably 0.8 parts by weight or less, and particularly preferably 0.6 parts by weight or less. By limiting the amount of the isocyanate-based crosslinking agent used, there is a tendency for sufficient adhesive strength to be easily obtained. In addition, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer may be, for example, 0.01 parts by weight or more, and in some preferred embodiments, it may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of the isocyanate-based crosslinking agent used within the above range, it is possible to preferably obtain an adhesive that exhibits adhesive properties such as adhesive strength and cohesive strength in a well-balanced manner while preferably achieving the effects of the technology disclosed herein.

When a crosslinking agent is used, the amount of crosslinking agent used may be more than 0 parts by weight per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the adhesive layer, from the viewpoint of realizing an adhesive that exhibits a good balance of adhesive properties such as adhesive strength and cohesive strength, and may be, for example, 0.001 parts by weight or more, or may be 0.01 parts by weight or more. In some preferred embodiments, the amount of crosslinking agent used per 100 parts by weight of the polymer may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. Furthermore, the upper limit of the amount of crosslinking agent used may vary depending on the type of crosslinking agent used, and is therefore not limited to a specific range, but it is preferable that it is limited to a predetermined amount or less. By limiting the amount of the crosslinking agent used, the crosslinking density is appropriately suppressed, and at such a crosslinking density, during heat treatment or by irradiation with active energy rays, for example, in an embodiment in which the adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator, the ethylenically unsaturated group in the adhesive layer and the radical polymerization initiator collide frequently to proceed curing, and the peelability can be improved. For example, when the adhesive layer is designed as a thermosetting adhesive, the desired heat peelability and heat resistance peelability can be expressed. Note that the technology disclosed herein is not limited to the above considerations. For example, the amount of the crosslinking agent used is suitably less than 10 parts by weight relative to 100 parts by weight of the polymer, and in some embodiments, it is preferably less than 5 parts by weight, and may be less than 3 parts by weight. In some embodiments, the amount of the crosslinking agent used is suitably less than 1 part by weight relative to 100 parts by weight of the polymer, and is preferably 0.9 parts by weight or less, and may be 0.8 parts by weight or less, 0.7 parts by weight or less, 0.6 parts by weight or less, or 0.5 parts by weight or less. Limiting the amount of crosslinking agent used tends to make it easier to achieve sufficient adhesive strength.

A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used can be, for example, about 0.0001 parts by weight or more, about 0.001 parts by weight or more, or about 0.005 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer, and can be about 1 part by weight or less, about 0.1 parts by weight or less, or about 0.05 parts by weight or less.

The adhesive composition used to form the adhesive layer may contain a compound that generates keto-enol tautomerism as a crosslinking retarder, if desired. For example, a compound that generates keto-enol tautomerism may be preferably used in an adhesive composition that contains an isocyanate-based crosslinking agent or an adhesive composition that can be used by blending an isocyanate-based crosslinking agent. This can provide an effect of extending the pot life of the adhesive composition.
As the compound that causes keto-enol tautomerization, various β-dicarbonyl compounds can be used. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetates such as methyl acetoacetate and ethyl acetoacetate; propionylacetates such as ethyl propionylacetate; isobutyrylacetates such as ethyl isobutyrylacetate; malonic acid esters such as methyl malonate and ethyl malonate; and the like. Among these, preferred compounds include acetylacetone and acetoacetates. The compounds that cause keto-enol tautomerization can be used alone or in combination of two or more.
The amount of the compound that causes keto-enol tautomerization used may be, for example, 0.1 parts by weight or more and 20 parts by weight or less, and appropriately 0.5 parts by weight or more and 15 parts by weight or less, for example, 1 part by weight or more and 10 parts by weight or less, or may be 1 part by weight or more and 5 parts by weight or less, relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer.

(Other ingredients)
The adhesive layer may contain, as necessary, various additives that are common in the field of adhesives, such as tackifiers, silane coupling agents, peel strength regulators (surfactants, etc.), viscosity regulators (e.g. thickeners), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, antiaging agents, etc. As for such various additives, those that are conventionally known can be used in the usual manner, and they do not particularly characterize the present invention, so detailed explanations will be omitted.
The technology disclosed herein can achieve desired adhesive properties such as adhesive strength without using a tackifier. In some embodiments, the content of the tackifier in the adhesive layer can be, for example, less than 10 parts by weight, or even less than 5 parts by weight, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer. The content of the tackifier may be less than 1 part by weight (for example, less than 0.5 parts by weight), or less than 0.1 parts by weight (0 parts by weight or more and less than 0.1 parts by weight). The adhesive layer may be free of a tackifier.

The adhesive layer may exhibit the desired heat-peelability without using heat-expandable microspheres, a foaming agent, or the like. In some embodiments, the content of heat-expandable microspheres in the adhesive layer may be, for example, less than 1 part by weight, or even less than 0.1 part by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the adhesive layer. The content of foaming agent in the adhesive layer may be, for example, less than 1 part by weight, or even less than 0.1 part by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the adhesive layer. The adhesive layer may contain neither heat-expandable microspheres nor a foaming agent.

(Form of Pressure-Sensitive Adhesive Composition)
The adhesive layer disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive in a solvent (aqueous solvent) mainly composed of water, and the concept of the aqueous adhesive composition here may include those called water-dispersed adhesive compositions (compositions in which an adhesive is dispersed in water), water-soluble adhesive compositions (compositions in which an adhesive is dissolved in water), etc. In addition, the solvent-based adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent.

Although not particularly limited, the adhesive layer disclosed herein can be preferably formed using a solvent-based adhesive composition. The above-mentioned solvent-based adhesive composition is an adhesive composition in a form containing adhesive-forming components in an organic solvent. The solvent-based adhesive composition typically contains a solution polymer of a monomer component and, optionally, other additives. The effects of the technology disclosed herein can be effectively exhibited in a form having a solvent-based adhesive (layer). The solvent contained in the solvent-based adhesive composition can be appropriately selected from conventionally known organic solvents. For example, any one solvent selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc., or a mixture of two or more solvents can be used.

(Formation of Pressure-Sensitive Adhesive Layer)
The adhesive layer disclosed herein can be formed by a conventionally known method. The adhesive composition is applied (e.g., coated) to a suitable surface, and then a curing treatment is appropriately performed to form the adhesive in the form of a layer (adhesive layer). The curing means (e.g., drying, crosslinking, polymerization, cooling, etc.) of the adhesive composition may be applied by only one type, or may be applied by two or more types simultaneously or in multiple stages. In the case of a solvent-based adhesive composition, the adhesive can typically be formed by drying (preferably further crosslinking) the composition.

For example, in the case of a substrate-less double-sided adhesive sheet, a method can be adopted in which an adhesive composition is applied to a surface (release surface) having releasability, and then the adhesive composition is cured to form an adhesive layer on the surface. In the case of an adhesive sheet with a substrate, a method (direct method) can be adopted in which an adhesive composition is directly applied (typically coated) to the substrate and cured to form an adhesive layer. Alternatively, a method (transfer method) can be adopted in which an adhesive composition is applied to a surface (release surface) having releasability, cured to form an adhesive layer on the surface, and the adhesive layer is transferred to a substrate. The release surface can be the surface of a release liner, the back surface of a substrate that has been subjected to a release treatment, or the like. The adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as dots or stripes.

The pressure-sensitive adhesive composition can be applied using a known or commonly used coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a die coater, a bar coater, a knife coater, a spray coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation, a curtain coating method, or the like.
From the viewpoint of promoting the crosslinking reaction and improving the production efficiency, the adhesive composition is preferably dried under heating. The drying temperature is not particularly limited, but can be, for example, about 40 to 100 ° C., and is usually preferably about 60 to 80 ° C. For example, drying at the above temperature (for example, drying for about 1 to 10 minutes, more specifically, drying for about 3 to 7 minutes) is performed at a low heating temperature and the solvent volatilization is in progress, so that the reaction of the monomer and the deactivation of the thermal polymerization initiator are negligible in the adhesive composition containing the monomer and the thermal polymerization initiator. In addition, after drying the adhesive composition, aging may be performed for the purpose of adjusting the component migration in the adhesive layer, progressing the crosslinking reaction, and relaxing distortion that may exist in the substrate or the adhesive layer.

(Thickness)
The thickness of the adhesive layer is not particularly limited. The thickness of the adhesive layer is usually 1 μm or more, may be 2 μm or more, or may be 3 μm or more. The larger the thickness of the adhesive layer, the more the adhesive strength to the adherend tends to improve. In some preferred embodiments, the thickness of the adhesive layer is 5 μm or more, may be 10 μm or more, may be 15 μm or more, may be 20 μm or more, may be 25 μm or more. The upper limit of the thickness of the adhesive layer is, for example, appropriately about 200 μm or less, may be 100 μm or less (for example, less than 100 μm), or may be 50 μm or less. By limiting the thickness of the adhesive layer within a predetermined range, it is possible to prevent the occurrence of glue residue due to cohesive failure, and it is easy to obtain peelability. In addition, a thin adhesive layer is advantageous in terms of thinning the adhesive sheet, and tends to be excellent in followability to the adherend. In some preferred embodiments, the thickness of the adhesive layer is 40 μm or less, and may be 30 μm or less.

(Gel Fraction)
The gel fraction of the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, from the viewpoint of obtaining sufficient adhesion to the adherend and good peelability (e.g., easy peelability by heating), the initial (before heating) gel fraction (weight basis) of the pressure-sensitive adhesive layer is, for example, suitably 85% or less, preferably 80% or less, more preferably 75% or less, and may be 70% or less, 65% or less, or 60% or less. The lower the initial gel fraction, the easier it is to obtain high peelability (e.g., easy peelability by heating). In addition, from the viewpoint of obtaining pressure-sensitive adhesive layer formability, appropriate cohesiveness, and holding power, in some embodiments, the initial gel fraction of the pressure-sensitive adhesive layer is suitably 20% or more, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more, and may be 60% or more, or may be 65% or more. Pressure-sensitive adhesives having an appropriate initial gel fraction within the above range tend to have good curing reactivity (e.g., heat curing reactivity).

In some embodiments, the gel fraction of the pressure-sensitive adhesive layer after heating is preferably higher than the gel fraction before heating.
Increase in gel fraction after heating [%] = (G1/G0-1) x 100
(In the above formula, G1 is the gel fraction [%] of the pressure-sensitive adhesive layer after heat treatment at 180° C. for 30 minutes, and G0 is the gel fraction [%] of the pressure-sensitive adhesive layer before heating.)
The gel fraction increase after heating calculated by is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and may be 40% or more, 50% or more, 60% or more, or 70% or more. The pressure-sensitive adhesive having the above gel fraction increase after heating is easily cured by heating, and tends to easily obtain a high peel force reduction rate after heating, and thus excellent heat peelability and heat resistance peelability. In some embodiments, the upper limit of the gel fraction increase after heating is appropriately set according to the desired thermosetting property, and may be, for example, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less.

Although not particularly limited, in some embodiments, the gel fraction after heating (by weight) of the adhesive layer is appropriately 50% or more (e.g., more than 50%) from the viewpoint of exhibiting easy peelability upon heating, and is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more, and may be 95% or more. In some embodiments, the gel fraction after heating of the adhesive layer may be, for example, 99% or less, 95% or less, or 90% or less.

The gel fraction of the adhesive layer can be adjusted mainly by the monomer composition of the polymer, Mw, the presence or absence and amount of blended monomers, the type and amount of crosslinking agent, etc. The gel fraction after heating can be adjusted mainly by the design of the polymer (e.g., the amount of ethylenically unsaturated groups introduced), the blend, type and amount of blended monomers, and the use, type and amount of thermal polymerization initiator. Specifically, each of the above gel fractions is measured by the method described in the Examples below.

(Young's Modulus)
Although not particularly limited, in some embodiments, the Young's modulus Y1 [MPa] of the pressure-sensitive adhesive layer after 30 minutes of heat treatment at 180 ° C. is preferably 100 times or more of the Young's modulus Y0 [MPa] before heating, that is, the Young's modulus change ratio after heating (Y1 / Y0) is preferably 100 or more. The higher the Young's modulus change ratio after heating (Y1 / Y0), the higher the degree of curing of the pressure-sensitive adhesive layer during heating, and the easier it is to obtain excellent heat peelability. In some preferred embodiments, the Young's modulus change ratio after heating (Y1 / Y0) may be 200 or more, 300 or more, 500 or more, 800 or more, 1000 or more, 1200 or more, 1500 or more, 1800 or more, or 2000 or more. In addition, from the viewpoint of providing the pressure-sensitive adhesive layer with an appropriate elastic modulus before heating, in some embodiments, the above-mentioned Young's modulus change ratio after heating (Y1/Y0) is suitably about 10,000 or less, preferably 5,000 or less, more preferably 2,500 or less, may be 1,500 or less, may be 1,000 or less, or may be 500 or less.

Although not particularly limited, in some embodiments, the Young's modulus before heating (initial Young's modulus) Y0 of the adhesive layer is, for example, suitably about 10 MPa or less, preferably 1 MPa or less, more preferably 0.5 MPa or less, even more preferably 0.3 MPa or less, and may be 0.2 MPa or less. An adhesive layer having the above pre-heating Young's modulus Y0 tends to easily obtain sufficient adhesion to the adherend and good peelability (e.g., easy peelability by heating). In addition, from the viewpoint of obtaining adhesive layer formability, appropriate cohesiveness, and holding power, in some embodiments, the Young's modulus before heating Y0 of the adhesive layer is suitably 0.01 MPa or more, preferably 0.03 MPa or more, more preferably 0.05 MPa or more, even more preferably 0.08 MPa or more, and may be 0.10 MPa or more, 0.12 MPa or more, or 0.15 MPa or more.

Although not particularly limited, in some embodiments, the Young's modulus Y1 after heating of the adhesive layer is suitably 10 MPa or more, preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 70 MPa or more. In some preferred embodiments, the Young's modulus Y1 after heating may be 100 MPa or more, 150 MPa or more, or 200 MPa or more. An adhesive layer having a Young's modulus after heating of a predetermined value or more tends to have a high degree of hardening after heating and to easily obtain excellent peelability upon heating. In some embodiments, the Young's modulus Y1 after heating may be, for example, approximately 500 MPa or less, 300 MPa or less, 150 MPa or less, 100 MPa or less, 70 MPa or less, or 50 MPa or less.

The Young's modulus of the adhesive layer can be adjusted mainly by the monomer composition of the polymer, Mw, whether or not and the amount of blended monomers are blended, the type and amount of crosslinking agent, etc. The Young's modulus after heating Y1 can be adjusted mainly by the design of the polymer (for example, the amount of ethylenically unsaturated groups introduced), the blend, type and amount of blended monomers, and the use, type and amount of thermal polymerization initiator. Specifically, each of the above Young's moduli Y0 and Y1 is measured by the method described in the Examples below.

<First Pressure-Sensitive Adhesive Layer and Second Pressure-Sensitive Adhesive Layer>
In an embodiment in which a substrate-attached double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on each side of the substrate is used as the pressure-sensitive adhesive sheet, the matters described above regarding the pressure-sensitive adhesive layer are applied to the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer provided on each side of the substrate. In addition, one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be designed within the scope of the matters described above regarding the pressure-sensitive adhesive layer, and the other pressure-sensitive adhesive layer may be designed to be non-curable. For example, the other pressure-sensitive adhesive layer may be designed to substantially not contain at least one (e.g., both) of an ethylenically unsaturated group and a radical polymerization initiator. In that case, the matters described above regarding the pressure-sensitive adhesive layer are applied except for the matters related to the ethylenically unsaturated group and the radical polymerization initiator. Alternatively, a pressure-sensitive adhesive layer formed from a known or commonly used pressure-sensitive adhesive may be used for the other of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer.

In embodiments in which a double-sided adhesive sheet with a substrate is used as the adhesive sheet, the type, composition, formation method, etc. of the first adhesive layer and the second adhesive layer may be the same or different. In addition, the properties (gel fraction properties, Young's modulus properties, etc.) of the first adhesive layer and the second adhesive layer may be the same or different. Furthermore, the thicknesses of the first adhesive layer and the second adhesive layer may be the same or different. Although not particularly limited, in some embodiments, the first adhesive layer may have a composition including a blended monomer and a radical polymerization initiator, and the second adhesive layer may have a composition not including at least one of the blended monomer and the radical polymerization initiator (e.g., a thermal polymerization initiator such as a peroxide-based polymerization initiator). Also, although not particularly limited, one of the first adhesive layer and the second adhesive layer may be designed so that the Young's modulus change ratio after heating (Y1/Y0) is 100 or more, and the other may be designed so that the Young's modulus change ratio after heating (Y1/Y0) is less than 100 (for example, 50 or less, 30 or less, 10 or less, or 3 or less). In this case, the Young's modulus of the other adhesive layer is as described above for the pre-heat Young's modulus (initial Young's modulus) Y0 before and after the heat treatment at 180° C. for 30 minutes.

<Base layer>
The adhesive sheet disclosed herein may include a substrate layer. Various sheet-like substrates can be used as the substrate (layer) that supports (backs) the adhesive layer. As the substrate, a resin film, paper, cloth (woven fabric, nonwoven fabric, etc.), a rubber sheet, a foam sheet, a metal foil, a composite of these, etc. can be used. Examples of the resin film include polyolefin film; polyester film; vinyl chloride resin film; vinyl acetate resin film; polyamide resin film; fluororesin film; cellophane; and the like. Non-limiting examples of polyester films include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and the like. Other examples of the resin film include resin films formed from one or more engineering plastics (which may be super engineering plastics), such as polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, and polyimide resins. The use of engineering plastics is preferable from the viewpoint of heat resistance.

In some preferred embodiments, a resin film having a predetermined rigidity (strength) and excellent processability and handling properties is used as the substrate (layer). Among them, from the viewpoint of heat resistance, polyester films, polyamide resin films, and engineering plastic films (e.g., polyimide resin films, etc.) are preferred as the resin film substrate. In this specification, the term "resin film" typically refers to a non-porous film, and typically refers to a resin film that does not substantially contain air bubbles (voidless). Therefore, the resin film is a concept that is distinguished from foam films and nonwoven fabrics. The density of the resin film that can be used as the substrate can be about 0.85 to 1.50 g/cm ³ (e.g., 0.90 g/cm ³ to 1.20 g/cm ³ , typically 0.92 g/cm ³ to 1.05 g/cm ³ ). The resin film may be a single-layer structure, or a multi-layer structure of two or more layers (e.g., a three-layer structure).

The base layer (e.g., a resin film) can contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents, as necessary. The amount of additives to be added is not particularly limited, and can be set appropriately depending on the application, etc.

The method for producing the resin film is not particularly limited. For example, conventional resin film molding methods such as extrusion molding, inflation molding, T-die casting molding, and calendar roll molding can be appropriately used.

The substrate layer may be substantially composed of a resin film. Alternatively, the substrate layer may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer, an anti-reflection layer), a printing layer or a lamination layer for imparting a desired appearance, an antistatic layer, an undercoat layer, a release layer, and other surface treatment layers.

The thickness of the base layer is not particularly limited and can be appropriately selected depending on the purpose, but can generally be 1 to 500 μm. From the viewpoints of processability, handling, workability, etc., the thickness of the base layer is suitably 2 μm or more (for example, 3 μm or more, typically 5 μm or more), and may be approximately 7 μm or more, or may be 10 μm or more. In addition, the thickness of the base layer is suitably approximately 200 μm or less, and from the viewpoints of weight reduction and thinness, it is preferably approximately 100 μm or less, more preferably approximately 50 μm or less, and may be 30 μm or less, 20 μm or less, or 15 μm or less. When the thickness of the base layer is reduced, the flexibility of the adhesive sheet and its ability to follow the surface shape of the adherend tend to improve.

The surface of the base layer facing the adhesive layer may be subjected to conventional surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, etc., as necessary. Such surface treatments may be treatments for improving the adhesion between the base layer and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the base layer. The composition of the primer is not particularly limited, and may be appropriately selected from known ones. The thickness of the undercoat layer is not particularly limited, but is, for example, about 0.01 μm to 1 μm, and preferably about 0.1 μm to 1 μm. The back surface of the base layer may be subjected to the various surface treatments described above, antistatic treatment, etc.

<Total thickness>
The total thickness of the adhesive sheet disclosed herein (which may include the adhesive layer and the base layer, but does not include the release liner) is not particularly limited, and is suitably in the range of about 5 to 1000 μm. The total thickness of the adhesive sheet may be 10 μm or more, 15 μm or more, or 20 μm or more, from the viewpoints of adhesive properties, handling, and the like. In some embodiments, the total thickness of the adhesive sheet may be 30 μm or more, 40 μm or more, or 50 μm or more. In addition, from the viewpoints of weight reduction and thinning, in some embodiments, the total thickness of the adhesive sheet is 500 μm or less, or may be 300 μm or less. In some preferred embodiments, the total thickness of the adhesive sheet is 100 μm or less (e.g., less than 100 μm), more preferably 80 μm or less, or may be 70 μm or less. Reducing the thickness of the adhesive sheet is advantageous in terms of thinning, miniaturization, weight reduction, resource saving, and the like.

<Release liner>
The release liner used in the adhesive sheet (adhesive sheet before use) disclosed herein is not particularly limited, and may be, for example, a release liner in which the surface of a liner substrate such as a resin film or paper has been subjected to a release treatment, or a release liner made of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.). For the release treatment, for example, a silicone-based or long-chain alkyl-based release treating agent may be used. In some embodiments, a release-treated resin film may be preferably used as the release liner.

<Characteristics of adhesive sheet>
(Post-heat peel force F1)
Although not particularly limited, in some embodiments, the peeling force F1 after heating of the pressure-sensitive adhesive sheet is not particularly limited and can be appropriately set so as to show the desired easy peeling property after heating. In some embodiments, from the viewpoint of the easy peeling property, the peeling force F1 after heating is suitably less than 3.0 N/20 mm, advantageously 2.0 N/20 mm or less, and preferably 1.0 N/20 mm or less. In some embodiments where a higher level of easy peeling property is required after heating, the peeling force F1 after heating may be, for example, less than 1.0 N/20 mm, preferably 0.8 N/20 mm or less, more preferably 0.6 N/20 mm or less, even more preferably 0.5 N/20 mm or less, may be 0.4 N/20 mm or less, may be 0.3 N/20 mm or less, may be 0.2 N/20 mm or less, or may be less than 0.2 N/20 mm. In this way, a pressure-sensitive adhesive sheet with a low peeling force F1 after heating can easily peel off the adherend while suppressing the load applied to the adherend. Therefore, it can be preferably used in an embodiment in which it is attached to an adherend made of a brittle material (typically a hard brittle material) such as a glass material or a semiconductor material. The peeling force F1 after heating is typically more than 0 N/20 mm, and from the viewpoint of the adherend retention after heating, it is appropriate to be 0.01 N/20 mm or more. The peeling force F1 after heating may be, for example, 0.05 N/20 mm or more, 0.1 N/20 mm or more, 0.2 N/20 mm or more, 0.3 N/20 mm or more, or 0.4 N/20 mm or more. In some embodiments, the peeling force F1 after heating may be 0.5 N/20 mm or more, 0.8 N/20 mm or more, 1.0 N/20 mm or more, 1.5 N/20 mm or more, or 2.0 N/20 mm or more. The post-heat peel strength F1 refers to the peel strength (peeling strength) measured in an environment of 23° C. and 50% RH after the tape is attached to a glass plate and heat-treated at 180° C. for 30 minutes.

(Pre-heat peel force F0)
Although not particularly limited, in some embodiments, the initial (pre-heating) peel strength F0 of the PSA sheet is suitably, for example, 0.5 N/20 mm or more, advantageously 0.8 N/20 mm or more, and preferably 1.0 N/20 mm or more or greater than 1.0 N/20 mm. A PSA sheet exhibiting the above pre-heating peel strength F0 can exhibit good adhesion to an adherend, for example, can adequately hold the adherend. From the viewpoint of making it easier to obtain better adhesion (e.g., retention performance of an adherend), in some embodiments, the pre-heating peel force F0 may be, for example, 1.2 N/20 mm or more, 1.5 N/20 mm or more, 1.8 N/20 mm or more, 2.0 N/20 mm or more, 3.0 N/20 mm or more, 4.0 N/20 mm or more, 5.0 N/20 mm or more, 7.0 N/20 mm or more, 8.0 N/20 mm or more, 9.0 N/20 mm or more, or 10 N/20 mm or more. The upper limit of the pre-heating peeling force F0 is appropriately set according to the required adhesiveness, and is not limited to a specific range, and may be, for example, approximately 30 N/20 mm or less, 20 N/20 mm or less, 15 N/20 mm or less, 10 N/20 mm or less, 5.0 N/20 mm or less, or 3.0 N/20 mm or less. Note that the pre-heating peeling force F0 refers to the peel strength (peel force) against a glass plate measured under conditions of a peel angle of 180 degrees and a speed of 300 mm/min in an environment of 23°C.

(Reduced Peel Force after Heating A)
Although not particularly limited thereto, in some embodiments, the PSA sheet can be calculated by the following formula based on the pre-heating peel strength F0 and the post-heating peel strength F1:
Peel force reduction rate after heating A [%] = (1 - F1/F0) x 100;
It is appropriate that the post-heat peel strength reduction rate A obtained by is higher than 20% (for example, higher than 30%), advantageously higher than 40%, and preferably higher than 50%. A pressure-sensitive adhesive sheet satisfying the above characteristics can exhibit good adhesion to an adherend while exhibiting good easy peelability (easy peelability upon heating) at the time of peeling after heat treatment. In some preferred embodiments, the post-heat peel strength reduction rate A may be 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 97% or more. The higher the post-heat peel strength reduction rate A, the better the easy peelability upon heating. In some embodiments, the post-heat peel strength reduction rate A is preferably less than 99.9%. A pressure-sensitive adhesive sheet having a post-heat peel strength reduction rate A of less than 99.9% can maintain the adhesion state with the adherend after heating while having the desired easy peelability from the adherend. This prevents the adherend from naturally peeling off from the PSA sheet due to heating and the resulting defects. From this viewpoint, the peel strength reduction rate A after heating may be 99.0% or less, and may be, for example, less than 95.0%.

The pre-heating peeling force, post-heating peeling force, and the relative relationship between them can be achieved and adjusted based on the contents of this specification by appropriately selecting the type of polymer contained in the adhesive layer (monomer composition, etc.), the presence or absence, type and amount of other components that may be contained in the adhesive layer (for example, a thermal polymerization initiator, described below, and a polyfunctional monomer), and combinations thereof, as well as the presence or absence, type and amount of a crosslinking agent used in each adhesive layer, etc.

In addition, in an embodiment in which a substrate-attached double-sided adhesive sheet having an adhesive layer on each side of the substrate is used as the adhesive sheet, the pre-heat peel strength and post-heat peel strength of the first adhesive layer surface and the second adhesive layer surface may be the same or different.

Specifically, the peel force before heating F0 and the peel force after heating F1 are measured by the following method.
(Pre-heat peel force F0)
The adhesive sheet is cut to a size of 20 mm wide and 100 mm long, and the adhesive surface of the adhesive sheet is pressed and bonded to an alkaline glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35 mm, blue plate edge polished product) as an adherend under an environment of 23 ° C. and 50% RH by rolling a 2 kg roller back and forth once. The adherend to which the adhesive sheet is attached is left for 6 hours under the same environment and used as an evaluation sample. The evaluation sample is set in a tensile tester under an environment of 23 ° C. and 50% RH, and the peel strength (peel force before heating) F0 [N / 20 mm width] is measured when the adhesive sheet is peeled off from the adherend under the conditions of a peel angle of 180 degrees and a speed of 300 mm / min. As the tensile tester, a Shimadzu product name "EZ-S 500N" or an equivalent product can be used. Furthermore, when the pressure-sensitive adhesive sheet used to prepare the evaluation sample is a double-sided pressure-sensitive adhesive sheet, the measurement may be performed with the non-measurement surface backed with a PET film.

(Post-heat peel force F1)
Using the pressure sensitive adhesive sheet, prepare an evaluation sample by the method described in the above-mentioned pre-heat peeling force F0 measurement. The obtained evaluation sample is heated in an oven at 180°C for 30 minutes, and then removed from the oven and left to stand in an environment of 23°C and 50% RH for 30 minutes. Then, the evaluation sample is set in a tensile tester in the same environment, and the peel strength (post-heat peeling force) F1 [N/20mm width] is measured when the pressure sensitive adhesive sheet is peeled off from the adherend under the conditions of a peel angle of 180° and a speed of 300mm/min. The adherend, tensile tester, and other items are the same as those in the measurement of pre-heat peeling force F0.

<First Member and Second Member>
The materials of the first member and the second member are not particularly limited, and various materials exemplified as the adherend material described later can be used. For example, a material containing one or more of glass, semiconductor material (silicon wafer, etc.), metal material, ceramic material, and resin material can be used. In the technology disclosed herein, glass, semiconductor material, metal material, and ceramic material can be used as the first member and the second member. Since these have a predetermined heat resistance, the heating easy peeling technology disclosed herein can be applied. In addition, the above materials are typical examples of rigid materials. When the first member and the second member are both rigid bodies, the deformation of the members cannot be used to separate the members, but by applying the separation method disclosed herein, the bond between the rigid bodies can be easily released. In addition, thin glass and semiconductor materials are typical examples of brittle materials and hard and brittle materials. By applying the separation method disclosed herein to a structure to which members made of such materials are bonded, the members can be separated without damaging the members. The materials of the first member and the second member may be the same or different.

The term "rigid body" refers to an object that has a rigidity and size that is not substantially deformed by human force. Although not particularly limited, the term "rigid body" in this specification refers to an object that satisfies at least one of the following: a tensile modulus of elasticity of 1×10 ¹⁰ Pa or more; and a bending rigidity of 0.01 Pa·m ³ or more.

The tensile modulus refers to the tensile modulus measured in accordance with JIS K7161. More specifically, it is measured by the following method.
[Tensile test]
The measurement object is cut into a strip of 10 mm width to prepare a test piece. The test piece is stretched under the following conditions in accordance with JIS K7161 to obtain a stress-strain curve.
(Stretching conditions)
Measurement temperature: 25°C
Pulling speed: 300 mm/min Chuck distance: 50 mm
As the tensile tester, a universal tensile/compression tester (device name "tensile/compression tester, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent can be used.
The tensile modulus is determined from the linear regression of the stress-strain curve.
The bending stiffness value D [Pa·m ³ ] is expressed by the following formula, where the thickness of the material is h [m], the Poisson's ratio of the material is ν, and the tensile modulus of elasticity is E [Pa]:
D=Eh ³ /12(1-ν ² );
This is the value calculated by:

In some embodiments, the first member and the second member may be non-transparent to light (typically non-transparent to ultraviolet light). Examples of such non-transparent member materials include semiconductor materials such as silicon wafers and metal materials. According to the technology disclosed herein, the adhesive strength of a thermosetting adhesive can be reduced by heat treatment, so that the non-transparent member can be separated in situations where a non-transparent member is used and an ultraviolet-exposure peelable adhesive cannot be applied.

In some embodiments, for example when the first member is a glass plate or a semiconductor wafer, the second member may be a plate (also called a support stand) that supports the first member. For example, a combination of the first member and the second member as described above may be used in processing optical members including glass plates or processing semiconductor wafers. An example of the support stand is one that has one or more flow hole openings on the surface that adheres to the adhesive portion (i.e., the surface on which the adhesive sheet is placed). The support stand is typically made of metal, but may be made of a ceramic material or a resin material.

The thickness of the first member and/or the second member is not particularly limited, and in some embodiments, may be, for example, approximately 0.05 mm or more, approximately 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, or approximately 0.5 mm or more. Glass (e.g., glass plate), semiconductor material (e.g., silicon wafer), metal material (e.g., metal plate), and ceramic material (e.g., ceramic plate) having a predetermined thickness or more may have properties as a rigid body, so there is a great advantage in applying the technology disclosed herein. In some embodiments, the thickness may be approximately 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, or 5 mm or more. The maximum thickness of the first member and/or the second member is not particularly limited, and may be about 30 cm or less, about 10 cm or less, about 1 cm or less, about 5 mm or less, or about 2 mm or less. In some embodiments, the thickness of the first member and/or the second member may be approximately 1 mm or less (e.g., less than 1 mm), 0.7 mm or less, 0.5 mm or less (e.g., less than 0.5 mm), or 0.3 mm or less. Glass (e.g., glass plate) and semiconductor materials (e.g., silicon wafers) having a thickness of a certain amount or less may have the properties of brittle materials (typically hard and brittle materials), so there is a great advantage in applying the technology disclosed herein.

<Applications>
The applications to which the separation method and adhesive sheet disclosed herein are applied are not particularly limited. They can be used in various applications requiring separation of members bonded by an adhesive. Examples of such applications include masking applications requiring heat resistance in the adhesive sheet, temporary fixing applications, and protective applications. In addition, the adhesive sheet can also be preferably used as a process material that is fixed to an adherend and peeled off in the manufacturing process of electronic devices and electronic components. In addition, a suitable application of the separation method and adhesive sheet disclosed herein includes semiconductor element manufacturing applications. For example, the adhesive sheet can be preferably used as a wafer fixing sheet that fixes the wafer to a fixing plate in semiconductor wafer processing (typically silicon wafer processing). In addition, the adhesive sheet disclosed herein can also be preferably used as a protective sheet that protects the wafer in the above-mentioned wafer processing. In particular, during the manufacture of semiconductor elements, the semiconductor elements may be exposed to heat in the processing step, etc., so that an adhesive sheet having heat resistance and easy peelability is preferably used.

The separation method and adhesive sheet disclosed herein can also be applied to optical applications. More specifically, the adhesive sheet disclosed herein can be used as an optical adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members. The optical member refers to a member having optical properties (for example, polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical member is not particularly limited as long as it has optical properties, but examples of the optical member include members constituting devices (optical devices) such as display devices (image display devices) and input devices, or members used in these devices. Examples of the display devices include liquid crystal display devices, organic EL (electroluminescence) display devices, PDPs (plasma display panels), electronic paper, etc. Examples of the input devices include touch panels, etc.

The separation method and adhesive sheet disclosed herein are also suitable for applications in which brittle materials (typically hard and brittle materials) such as glass or semiconductor materials are bonded together and then separated. For example, the separation method and adhesive sheet disclosed herein can be preferably used in applications in which two adherends are fixed together, at least one of which is made of a brittle material such as glass or semiconductor material.

The type of material to be attached (adherend material) disclosed herein is not particularly limited. The adhesive sheet disclosed herein can be used for fixing and protecting various members and materials. Examples of the adherend material include glass such as alkali glass and non-alkali glass; semiconductor materials such as silicon wafers; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; resin materials such as polyester resins such as PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, and transparent polyimide resins; and the like. Suitable examples of the adherend material include glass materials such as alkali glass and semiconductor wafers. The above glass material can be, for example, a glass plate having a surface partially provided with a transparent conductive film (e.g., an ITO (indium tin oxide) film) or an FPC (flexible printed circuit board), as used in tablet computers, mobile phones, organic LEDs (light-emitting diodes), and the like.

The matters disclosed in this specification include the following.
[1] A method for separating at least one of a first member and a second member from a structure including a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhesively bonded to the first member and the second member after a heat treatment, the method comprising:
The adhesive portion has a curable adhesive layer,
A separation method comprising a step of supplying a fluid to the adhesive portion from the first member side or the second member side (fluid supplying step).
[2] The pressure-sensitive adhesive layer is in contact with the first member,
the adhesive portion is provided with a hole communicating with the first member and the second member,
The separation method according to the above-mentioned [1], wherein the fluid supplying step is a step of supplying the fluid to the hole of the adhesive portion from the second member side.
[3] The method for separating according to the above [1] or [2], wherein the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator.
[4] The separation method according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive layer is a thermosetting pressure-sensitive adhesive layer.
[5] The method for separating according to any one of the above [1] to [4], wherein the radical polymerization initiator is a thermal polymerization initiator.
[6] The separation method according to any one of [1] to [5] above, wherein the first member and the second member are non-transmissive to light.
[7] The separation method according to any one of the above-mentioned [1] to [6], wherein the pressure-sensitive adhesive layer has an increase in gel fraction of 10% or more after heat treatment at 180° C. for 30 minutes.
[8] The method for separating the pressure-sensitive adhesive layer according to any one of [1] to [7] above, wherein the Young's modulus Y1 [MPa] after heat treatment at 180° C. for 30 minutes is 100 times or more the Young's modulus Y0 [MPa] before heating.
[9] The adhesive portion is
The pressure-sensitive adhesive layer may be formed of the adhesive layer.
The separation method according to any one of [1] to [8] above, wherein the pressure-sensitive adhesive layer has a laminated structure including a first pressure-sensitive adhesive layer, a base layer, and a second pressure-sensitive adhesive layer in this order.
[10] A pressure-sensitive adhesive sheet used as an adhesive part in the separation method according to any one of [1] to [9] above,
An adhesive sheet having a curable adhesive layer.
[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
A hole is provided,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator.

Below, several examples of the present invention are described, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Evaluation method>
(Gel Fraction)
The gel fraction (weight ratio of the matter insoluble in ethyl acetate) of the pressure-sensitive adhesive layer is measured by the following method.
About 0.1 g of the adhesive sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene film (weight Wg2) with an average pore size of 0.2 μm in a purse shape, and the opening is tied with string (weight Wg3). As the porous polytetrafluoroethylene (PTFE) film, the product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or an equivalent product is used.
The package is immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23° C.) for 7 days to elute only the sol component in the adhesive layer outside the film, and then the package is taken out and the ethyl acetate adhering to the outer surface is wiped off, and the package is dried at 130° C. for 2 hours, and the weight (Wg4) of the package is measured. The gel fraction of the adhesive layer can be calculated by substituting each value into the following formula.
Gel fraction [%] = [(Wg4 - Wg2 - Wg3) / Wg1] x 100
The gel fraction of the pressure-sensitive adhesive layer is measured initially (gel fraction before heating) and after the pressure-sensitive adhesive layer is heat-treated in an oven at 180° C. for 30 minutes, removed from the oven and allowed to stand in an environment of 23° C. and 50% RH for 30 minutes (gel fraction after heating).

(Young's Modulus)
The adhesive layer is prepared in a state where both sides are covered with release liners, and cut together with the release liners to a size of 80 mm in width (when the adhesive layer is 30 μm thick) and 30 mm in length, and one release liner is removed from the adhesive layer, and the adhesive layer is wound up on the other release liner in the length direction so as not to trap air bubbles, to prepare a rod-shaped sample of 30 mm in length. The rod-shaped sample is set in a tensile tester (manufactured by ORIENTEC, product name "RTC-1150A") and pulled under conditions of a measurement temperature of 23°C, a chuck distance of 10 mm, and a pulling speed of 50 mm/min, and the initial elastic modulus is determined from the rise of the obtained stress-strain curve (S-S curve), and this is the Young's modulus [MPa] of the adhesive layer. The reason why the cut width of the adhesive layer is set to 80 mm is so that the cross-sectional area of the adhesive layer in the cross section along the width direction is within the range of 2 to 2.5 ^mm2 . For example, when the adhesive layer thickness is not 30 μm as in Comparative Example 1 (adhesive layer thickness 10 μm), it is desirable to adjust the cut width according to the thickness of the adhesive layer so that the cross-sectional area is approximately the same.
The Young's modulus of the pressure-sensitive adhesive layer is measured initially (Young's modulus before heating) and after the pressure-sensitive adhesive layer is heat-treated in an oven at 180° C. for 30 minutes, removed from the oven and allowed to stand in an environment of 23° C. and 50% RH for 30 minutes (Young's modulus after heating).

Example 1
(Preparation of Pressure-Sensitive Adhesive Composition)
A reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer and a stirrer was charged with 100 parts of a monomer component containing methoxyethyl acrylate (MEA), acryloylmorpholine (ACMO) and hydroxyethyl acrylate (HEA) in a molar ratio of 80:20:20, and 65 parts of toluene as a polymerization solvent, and 0.2 parts of benzoyl peroxide was added as a thermal polymerization initiator, and a polymerization reaction (solution polymerization) was carried out for 6 hours at 61 ° C. under a nitrogen atmosphere to obtain a solution containing an acrylic polymer a. To this solution of the acrylic polymer a, methacryloyloxyethyl isocyanate (MOI) in an amount equivalent to 16 moles relative to 20 moles of HEA used as a raw material for the acrylic polymer a was added, and an addition reaction treatment was carried out in an air stream at 50 ° C. for 48 hours to obtain a solution of an acrylic polymer A having a methacryloyl group at the side chain end.
To 100 parts of acrylic polymer A, 10 parts of dipentaerythritol hexaacrylate (DPHA) as a polyfunctional monomer, 0.3 parts of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-101E"), and 0.8 parts of benzoyl peroxide (manufactured by NOF Corporation, product name "Niper BW", SADT: 75°C) as a thermal polymerization initiator were added and mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The adhesive composition obtained above was applied to the release surface of a commercially available PET release liner and dried at 80° C. for 5 minutes to form an adhesive layer having a thickness of 30 μm. The release surface of another commercially available PET release liner was attached to this adhesive layer. Then, aging was performed at 50° C. for 3 days. In this way, a substrateless double-sided adhesive sheet having a thickness of 30 μm and both sides protected by the two PET release liners was obtained.

(Fabrication of Structure)
The double-sided pressure-sensitive adhesive sheet with release liner was cut to a size of 16 cm square, and the second adhesive surface exposed by peeling off one release liner from the double-sided pressure-sensitive adhesive sheet was attached to a stainless steel (SUS) plate (thickness 5 mm, about 20 cm square) as a second member. This SUS plate was provided with a circulation hole (opening diameter about 1 cm) near the center. Then, using a drill, a through hole having a diameter similar to that of the opening of the SUS plate was formed in the double-sided pressure-sensitive adhesive sheet to match the opening of the circulation hole of the SUS plate. Next, the first adhesive surface exposed by peeling off the other release liner from the double-sided pressure-sensitive adhesive sheet was attached to a silicon wafer (thickness 300 μm, 6-inch mirror wafer manufactured by Shin-Etsu Chemical Co., Ltd.) as a first member. In this way, a structure having a cross section as shown in FIG. 1 was obtained. This structure has a silicon wafer (first member), a pressure-sensitive adhesive sheet (adhesive portion), and a SUS plate (second member) in this order.

Example 2
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and the pressure-sensitive adhesive composition was applied to the release surface of a commercially available PET release liner and dried at 80°C for 5 minutes to form a 30 μm thick pressure-sensitive adhesive layer. Two of these pressure-sensitive adhesive layers were prepared and attached to each surface of a 12.5 μm thick polyimide (PI) film (product name "Kapton 50H", manufactured by Toray DuPont Co., Ltd.). Then, aging was performed at 50°C for 3 days. In this manner, a substrate-attached double-sided pressure-sensitive adhesive sheet having a 30 μm thick pressure-sensitive adhesive layer was obtained. This pressure-sensitive adhesive sheet has a first pressure-sensitive adhesive layer, a PI film (substrate layer), and a second pressure-sensitive adhesive layer in this order, and the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer have the same composition. Each adhesive surface of the pressure-sensitive adhesive sheet is protected by a PET release liner.
Except for using the above-mentioned double-sided pressure-sensitive adhesive sheet with substrate, a structure having a silicon wafer (first member), a pressure-sensitive adhesive sheet (adhesive portion), and a SUS plate (second member) in this order was obtained in the same manner as in Example 1. This structure has a cross section as shown in FIG.

Example 3
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the polyfunctional monomer and the thermal polymerization initiator were not added. A substrate-attached double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer, a PI film (substrate layer), and a second pressure-sensitive adhesive layer in this order was obtained in the same manner as in Example 2, except that the pressure-sensitive adhesive layer formed using the obtained pressure-sensitive adhesive composition was used as the second pressure-sensitive adhesive layer. The first pressure-sensitive adhesive layer of this pressure-sensitive adhesive sheet is the same as the first pressure-sensitive adhesive layer of Example 2.
Except for using the double-sided pressure-sensitive adhesive sheet with the substrate, a structure having a silicon wafer (first member), a pressure-sensitive adhesive sheet (adhesive portion), and a SUS plate (second member) in this order was obtained in the same manner as in Example 2. This structure has a cross section as shown in FIG.

<Examples 4 to 5>
A structure having a cross section as diagrammatically shown in FIG. 1 was obtained in the same manner as in Example 1, except that the first member was changed to a stainless steel plate having a thickness of 5 mm (Example 4) or a glass plate having a thickness of 300 μm (Example 5).

<Comparative Example 1>
A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer was charged with 97 parts of n-butyl acrylate (BA), 3 parts of acrylic acid (AA), and 43 parts of ethyl acetate as a polymerization solvent, and 0.2 parts of 2,2′-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator. A polymerization reaction (solution polymerization) was carried out at 61° C. for 6 hours under a nitrogen atmosphere to obtain a solution containing an acrylic polymer B.
To the solution of acrylic polymer B, 0.5 parts of an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., product name "Tetrad C") was added per 100 parts of acrylic polymer B, and the mixture was mixed uniformly to prepare a pressure-sensitive adhesive composition.
An adhesive sheet was obtained in the same manner as in Example 1, except that an adhesive layer having a thickness of 10 μm was formed using the adhesive composition obtained above, and a structure was obtained using the adhesive sheet.

<Separation test>
The structures according to each example were heat-treated in an oven at 180° C. for 30 minutes, removed from the oven and left to stand in an environment of 23° C. and 50% RH for 30 minutes, and then air was supplied at a predetermined pressure to the flow holes of the second member to attempt separation of the first member. If the members could be separated without being damaged, it was judged as "○" (passed). If the members could not be separated, it was recorded as "unseparable".

　An overview of each example and the evaluation results are shown in Table 1.

As shown in Table 1, the structures according to Examples 1 to 5, in which the adhesive sheet, which is the adhesive portion, has a curable adhesive layer, passed the separation test. In Examples 1 to 3, it was possible to separate a thin silicon wafer without damaging it, and in Example 5, it was possible to separate a thin glass plate without damaging it. In Example 4, it was possible to easily separate the bond between 5 mm thick SUS plates in the vertical direction. On the other hand, in Comparative Example 1, in which a non-curable adhesive was used, it was not possible to separate the members in the separation test. In the above separation test, the structures according to Examples 1 to 5 had the first and second members that were not peeled off from the adhesive portion and were held in place before air was supplied after the heat treatment.

　Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

10 First member 10A Surface (surface in contact with adhesive portion)
20 Second member 25 Flow hole 30 Adhesive portion (adhesive sheet)
30A First adhesive surface 30B Second adhesive surface 31 Curable adhesive layer (first adhesive layer)
32 Second adhesive layer 34 Base layer 35 Hole 100, 200 Structure A Air

Claims (11)

A method for separating at least one of a first member and a second member from a structure including a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhesively bonded to the first member and the second member after a heat treatment, the method comprising:
The adhesive portion has a curable adhesive layer,
A separation method comprising a step of supplying a fluid to the adhesive portion from the first member side or the second member side (fluid supplying step). the pressure-sensitive adhesive layer is in contact with the first member,
the adhesive portion is provided with a hole communicating with the first member and the second member,
The separation method according to claim 1 , wherein the fluid supplying step is a step of supplying the fluid to the hole in the adhesive portion from a side of the second member. The separation method according to claim 1 or 2, wherein the adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator. The separation method according to claim 1 or 2, wherein the adhesive layer is a thermosetting adhesive layer. The separation method according to claim 3, wherein the radical polymerization initiator is a thermal polymerization initiator. The separation method according to claim 1 or 2, wherein the first member and the second member are non-transparent to light. The separation method according to claim 1 or 2, wherein the adhesive layer has a gel fraction increase of 10% or more after heat treatment at 180°C for 30 minutes. The separation method according to claim 1 or 2, wherein the Young's modulus Y1 [MPa] of the adhesive layer after heat treatment at 180°C for 30 minutes is 100 times or more the Young's modulus Y0 [MPa] before heating. The adhesive portion is
The pressure-sensitive adhesive layer may be formed of the adhesive layer.
The separation method according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a laminate structure including a first pressure-sensitive adhesive layer, a base layer, and a second pressure-sensitive adhesive layer in this order. A pressure-sensitive adhesive sheet used as an adhesive part in the separation method according to claim 1 or 2,
An adhesive sheet having a curable adhesive layer. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
A hole is provided,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator.

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