TWI848114B - Adhesive sheet - Google Patents

Abstract

The present invention provides an adhesive sheet including an adhesive layer. The adhesive layer includes a polymerized reaction product of the following composition, the composition including: (A) at least one of a monomer having an aromatic ring and an oligomer containing a repeating unit having an aromatic ring, and (B) a monomer having a hydroxyl group or a carboxyl group. The glass transition temperature Tg _A based on the composition of the monomer components constituting the adhesive layer is higher than -3°C and is below 40°C.

Description

Adhesive sheet

The present invention relates to an adhesive sheet.

Adhesive sheets are used to adhere to adherends by being firmly attached to them for purposes such as bonding adherends to each other, fixing an object to an adherend, and reinforcing an adherend. In the past, adhesive sheets that exert a high adhesive force from the initial stage of attachment were used for such purposes.

Moreover, recently, an adhesive sheet has been proposed that exhibits low adhesive force at the initial stage of being attached to an adherend and then greatly increases the adhesive force (Japanese Patent No. 6223836, Japanese Patent No. 5890596, Japanese Patent No. 5951153). According to the adhesive sheet having such characteristics, before the adhesive force increases, the re-attachment property (secondary processing property) useful for suppressing the reduction of yield due to wrong attachment or attachment failure of the female adhesive sheet can be exerted, and after the adhesive force increases, the strong adhesiveness suitable for the original purpose of the adhesive sheet can be exerted.

[The problem the invention is trying to solve]

In order to provide an adhesive sheet that can show low adhesion at the initial stage of attachment and then greatly increase adhesion as described above, the inventors and others conducted further research. As a result, it was found that in order to solve the above-mentioned problem, it is effective to use monomers and/or oligomers with specific structures, thereby completing the present invention. [Technical means for solving the problem]

According to the present specification, an adhesive sheet including an adhesive layer is provided. The adhesive layer includes a polymerized reaction product of the following composition, the composition including: (A) at least one of a monomer having an aromatic ring and an oligomer containing a repeating unit having an aromatic ring, and (B) a monomer having a hydroxyl group or a carboxyl group. The adhesive layer preferably has a glass transition temperature Tg _A higher than -3°C and below 40°C based on the composition of the monomer components constituting the adhesive layer. According to the adhesive layer, an adhesive sheet that can show a low adhesive force at the initial stage of attachment and then significantly increase the adhesive force can be well realized.

In the following, a monomer having an aromatic ring may be referred to as an "aromatic ring-containing monomer", and similarly, a monomer having a hydroxyl group may be referred to as a "hydroxyl-containing monomer", and a monomer having a carboxyl group may be referred to as a "carboxyl-containing monomer", etc. In the following, a repeating unit having an aromatic ring may be referred to as an "aromatic ring-containing repeating unit", and an oligomer containing an aromatic ring-containing repeating unit may be referred to as an "oligomer AR".

In some embodiments, the composition at least comprises the aromatic ring-containing monomer as the (A). The composition comprising the aromatic ring-containing monomer and the (B) forms a polymer containing an aromatic ring-containing repeating unit and at least one of a hydroxyl-containing repeating unit and a carboxyl-containing repeating unit by polymerization. The adhesive layer containing such a polymer can well realize an adhesive sheet that can show a low adhesive force at the initial stage of attachment and then greatly increase the adhesive force.

As the aromatic ring-containing monomer of (A), for example, at least one selected from the group consisting of benzyl acrylate, ethoxylated phenylphenol acrylate, diphenylmethyl acrylate, and phenoxybenzyl acrylate can be preferably used. The use of the aromatic ring-containing monomer is advantageous from the viewpoint of adjusting the adhesive properties and/or optical properties of the adhesive sheet.

In some embodiments, 55% by weight or more of the monomer components constituting the adhesive layer may be monomers having an aromatic ring. According to the adhesive layer comprising a large number of repeating units derived from monomers containing an aromatic ring as described above, an adhesive sheet that exhibits low adhesion at the initial stage of attachment and then increases adhesion significantly can be well realized.

In some aspects, the composition preferably contains more than 50 wt % of the monomers as acrylic monomers. This may be advantageous from the perspective of ease of adjustment of the polymerization reactivity or adhesive properties of the composition.

In some embodiments, the composition at least comprises the oligomer containing repeating units having an aromatic ring (oligomer AR) as the above (A). This can achieve at least one effect of suppressing the initial adhesion and improving the subsequent adhesion rise. As the above oligomer AR, for example, styrene oligomers can be used well.

In some embodiments, the composition further comprises (C) at least one alkyl (meth)acrylate having a homopolymer glass transition temperature of -40°C or less. By means of (C), the glass transition temperature Tg _A or the adhesive properties can be well adjusted.

The adhesive force N1 (hereinafter, also referred to as "initial adhesive force") of some preferred adhesive sheets after being attached to a stainless steel plate and 30 minutes at 23°C is less than 5 N/20 mm, and the adhesive force N2 (hereinafter, also referred to as "adhesion after heating") after being attached to a stainless steel plate and heated at 80°C for 5 minutes and 30 minutes at 23°C is more than twice the above-mentioned adhesive force N1. According to the technology disclosed herein, an adhesive sheet having a low adhesive force at the initial stage of attachment and a greatly increased adhesive force by heating for a short time can be provided.

Furthermore, appropriate combinations of the above-mentioned elements may also be included in the scope of the invention claimed by this Japanese patent application.

The following describes the preferred implementation of the present invention. With regard to matters other than those specifically mentioned in this specification and required for the implementation of the present invention, the industry can understand them based on the instructions on the implementation of the invention recorded in this specification and the technical common sense at the time of application. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, in the following figures, the components and parts that play the same role are sometimes described with the same symbols, and sometimes repeated descriptions are omitted or simplified. In addition, the implementation forms recorded in the figures are modeled for the purpose of clearly explaining the present invention, and may not accurately represent the size or scale of the actual product provided.

In this specification, "acrylic monomer" refers to a monomer having at least one (meth)acrylic group in one molecule. Here, "(meth)acrylic group" includes both acryl and methacrylic groups. Therefore, the concept of acrylic monomers here can include both monomers having acryl groups (acrylic monomers) and monomers having methacrylic groups (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" includes both acrylic acid and methacrylic acid, and "(meth)acrylate" includes both acrylate and methacrylate.

Furthermore, in this specification, the so-called "monomer components constituting the adhesive layer", whether used as a starting material in the form of a monomer or in the form of a pre-formed polymer (which may be an oligomer), means the monomer corresponding to the monomer unit contained in all polymers contained in the adhesive layer.

<Structure example of adhesive sheet> The adhesive sheet disclosed herein is composed of an adhesive layer. The adhesive sheet disclosed herein may be in the form of an adhesive sheet with a substrate having the adhesive layer laminated on one or both sides of a supporting substrate, or in the form of an adhesive sheet without a supporting substrate. Hereinafter, the supporting substrate may also be referred to as a "substrate".

The structure of an adhesive sheet of an embodiment is schematically shown in FIG1. The adhesive sheet 1 is a single-sided adhesive sheet with a substrate having a sheet-shaped supporting substrate 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A side. The adhesive layer 21 is fixed to the first surface 10A side of the supporting substrate 10. The adhesive sheet 1 is used by attaching the adhesive layer 21 to an adherend. As shown in FIG. 1 , the adhesive sheet 1 before use (i.e. before being attached to an adherend) may be a constituent element of an adhesive sheet 100 with a peeling liner in which a surface (adhesive surface) 21A of an adhesive layer 21 abuts against a peeling liner 31 whose side opposite to the adhesive layer 21 becomes a peeling surface (peeling surface). As the peeling liner 31, for example, a peeling liner formed by providing a peeling layer formed by a peeling treatment agent on one side of a sheet-like substrate (liner substrate) so that the single side becomes a peeling surface can be preferably used. Alternatively, the peeling pad 31 may be omitted, and the second surface 10B of the supporting substrate 10 may be used as the peeling surface. The adhesive sheet 1 may be rolled up so that the adhesive surface 21A contacts the second surface 10B of the supporting substrate 10 (rolled form). When the adhesive sheet 1 is attached to an adherend, the peeling pad 31 or the second surface 10B of the supporting substrate 10 is peeled off from the adhesive surface 21A, and the exposed adhesive surface 21A is pressed against the adherend.

The structure of an adhesive sheet of another embodiment is schematically shown in FIG2. The adhesive sheet 2 is a double-sided adhesive sheet with a substrate, which includes a sheet-shaped supporting substrate 10 having a first surface 10A and a second surface 10B, an adhesive layer 21 disposed on the first surface 10A side, and an adhesive layer 22 disposed on the second surface 10B side. The adhesive layer (first adhesive layer) 21 is fixed to the first surface 10A of the supporting substrate 10, and the adhesive layer (second adhesive layer) 22 is fixed to the second surface 10B of the supporting substrate 10. The adhesive sheet 2 is used by attaching the adhesive layers 21 and 22 to different parts of an adherend. The locations where the adhesive layers 21 and 22 are attached may be locations of different components or different locations within a single component. As shown in FIG2 , the adhesive sheet 2 before use may be a component of an adhesive sheet 200 with a peeling liner attached in which the surface (first adhesive surface) 21A of the adhesive layer 21 and the surface (second adhesive surface) 22A of the adhesive layer 22 are in contact with the peeling liner 31 and 32 that are at least opposite to the adhesive layers 21 and 22 and serve as peeling surfaces. As the peeling pads 31 and 32, for example, a peeling layer formed by a peeling agent is provided on one side of a sheet-like substrate (pad substrate) so that the single side becomes a peeling surface. Alternatively, the peeling pad 32 may be omitted, and a peeling pad 31 having both sides as peeling surfaces may be used, and an adhesive sheet with a peeling pad attached may be formed in a form (roll form) in which the second adhesive surface 22A abuts against the back side of the peeling pad 31 by overlapping the peeling pad 32 and rolling the peeling pad 31 into a spiral shape.

The structure of another embodiment of the adhesive sheet is schematically shown in FIG3. The adhesive sheet 3 is constructed as a double-sided adhesive sheet without a substrate including an adhesive layer 21. The adhesive sheet 3 is used by attaching a first adhesive surface 21A including one surface (first surface) of the adhesive layer 21 and a second adhesive surface 21B including the other surface (second surface) of the adhesive layer 21 to different parts of the adherend. As shown in FIG3, the adhesive sheet 3 before use can be a constituent element of an adhesive sheet 300 with a peel-off liner in the form of a first adhesive surface 21A and a second adhesive surface 21B abutting against peel-off liner 31, 32 which respectively serve as peel-off surfaces on at least the sides opposite to the adhesive layer 21. Alternatively, the peeling pad 32 may be omitted and a peeling pad 31 having two peeling surfaces may be used, and the peeling pad 31 may be overlapped with the adhesive sheet 3 and rolled into a spiral shape to form an adhesive sheet with a peeling pad attached in a form in which the second adhesive surface 21B abuts against the back surface of the peeling pad 31 (roll shape).

Furthermore, the concept of adhesive sheet herein may include adhesive tape, adhesive film, adhesive label, etc. The adhesive sheet may be in the form of a roll, a single sheet, or may be cut into appropriate shapes or punched according to the purpose or usage. The adhesive layer in the technology disclosed herein is typically formed continuously, but is not limited thereto, and may be formed into regular or irregular patterns such as dots or strips.

The adhesive layer constituting the adhesive sheet disclosed herein comprises a polymerized reactant of the following composition, the composition comprising: (A) at least one of a monomer containing an aromatic ring and an oligomer containing a repeating unit containing an aromatic ring (hereinafter, also referred to as "component (A)"), and (B) a monomer having a hydroxyl group or a carboxyl group (hereinafter, also referred to as "component (B)"). The adhesive layer comprising such a polymerized reactant is suitable for realizing an adhesive sheet that can show a relatively low adhesive force at the initial stage of attachment and then greatly increase the adhesive force.

<Component (A)> (Aromatic ring-containing monomer) The aromatic ring-containing monomer as component (A) is a compound containing an aromatic ring in its structure and containing an ethylenically unsaturated group such as a (meth)acryl group, a vinyl group, an allyl group, etc. The aromatic ring-containing monomer can be used alone or in combination of two or more. The number of aromatic rings contained in one molecule of the aromatic ring-containing monomer can be one or more (typically 2 to 5, for example 2 to 4). The number of ethylenically unsaturated groups contained in one molecule of the aromatic ring-containing monomer is typically one.

The aromatic ring in the aromatic ring-containing monomer may be a carbon ring such as a condensed ring of a benzene ring, a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring, or may be a heterocyclic ring such as a pyridine ring, a pyrimidine ring, a pyrrolidine ring, an imidazole ring, a pyrazole ring, a thiazole ring, etc. When the aromatic ring-containing monomer contains two or more benzene rings, the benzene rings may form a biphenyl skeleton or a fluorene skeleton.

The above aromatic ring may have one or more substituents on the ring-forming atoms, or may not have a substituent. In the case of having a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, and a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.). In a substituent containing a carbon atom, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In some embodiments, the above aromatic ring may be an aromatic ring having no substituent on the ring-forming atoms, or having one or more substituents selected from the group consisting of an alkyl group and an alkoxy group.

The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. The linking group may be, for example, a group including one or more structures selected from an alkylene group, an alkylene oxide group, a poly(alkylene oxide) group, a phenyl group, an alkylphenyl group, an alkoxyphenyl group, a group in which one or more hydrogen atoms in the group are replaced by a hydroxyl group (e.g., a hydroxyalkylene oxide group), an oxy group (-O-), etc. In several aspects, an aromatic ring-containing monomer having a structure in which the aromatic ring and the ethylenically unsaturated group are bonded directly or via a linking group selected from the group consisting of an alkylene oxide group, an alkylene oxide group, and a poly(alkylene oxide) group may be well used. The number of carbon atoms in the alkylene oxide group and the alkylene oxide group is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. The number of repetitions of the oxyalkylene unit in the poly(oxyalkylene) group may be, for example, 2 to 3.

Examples of aromatic ring-containing monomers that can be used preferably include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. Aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can be used alone or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds can also be used in combination.

Specific examples of (meth)acrylates containing a benzene ring include: benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, chlorobenzyl (meth)acrylate, etc. These are examples of (meth)acrylates containing a benzene ring that do not contain a biphenyl skeleton or a fluorene skeleton. Furthermore, in the above-mentioned ethoxylated phenol (meth)acrylate, "ethoxylation" means that an oxyethyl chain is interposed between the phenoxy group and the (meth)acryloyl group. The repetition number of the oxyethylene units in the oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. The same is true for the ethoxylation of other aromatic ring-containing (meth)acrylates disclosed herein.

On the other hand, as specific examples of (meth)acrylates containing a biphenyl skeleton among (meth)acrylates containing a benzene ring, there can be cited: phenylphenol (meth)acrylates or ethoxylated phenylphenol (meth)acrylates, such as phenylphenol (meth)acrylate; diphenylmethyl (meth)acrylate, etc. The concept of the ethoxylated phenylphenol (meth)acrylate includes: phenylphenol ethyl (meth)acrylate (i.e., ethoxylated phenylphenol (meth)acrylate having 1 oxyethyl unit), and ethoxylated phenylphenol (meth)acrylate having more than 1 oxyethyl unit (e.g., 2 to 3).

The (meth)acrylate containing a fluorene skeleton among the (meth)acrylate containing a benzene ring is preferably a compound having a structure in which a (meth)acryloyl group is bonded to a fluorene skeleton (which may also constitute a bisphenol fluorene skeleton) directly or via a linking group containing an oxyalkylene chain (monooxyalkylene chain or polyoxyalkylene chain). Specific examples of the (meth)acrylate containing a fluorene skeleton include: 9,9-bis(4-hydroxyphenyl)fluorene (meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (meth)acrylate, etc. In some aspects of the technology disclosed herein, the above-mentioned (meth)acrylate containing a fluorene skeleton may not be used from the viewpoint of improving the adhesion and the like.

Specific examples of the (meth)acrylate having a naphthyl ring include hydroxyethylated β-naphthol acrylate, 2-naphthylethyl (meth)acrylate, 2-naphthyloxyethyl acrylate, and 2-(4-methoxy-1-naphthyloxy)ethyl (meth)acrylate.

When an aromatic ring-containing (meth)acrylate is used as component (A), the aromatic ring-containing acrylate can be preferably used in several aspects from the viewpoint of polymerization reactivity, etc. The proportion of the aromatic ring-containing acrylate in the aromatic ring-containing (meth)acrylate used may be, for example, more than 50% by weight, 75% by weight or more, 90% by weight or more, or substantially 100% by weight (typically 99.5 to 100% by weight).

Examples of vinyl compounds containing aromatic rings include vinyl compounds containing a carbon ring (typically a benzene ring) or a heterocyclic ring as the aromatic ring. Specific examples of vinyl compounds containing aromatic rings include: vinyl compounds containing aromatic rings having a vinyl substituent on a carbon ring (typically a benzene ring) such as styrene, α-methylstyrene, vinyltoluene, tert-butylstyrene, vinylnaphthalene, etc.; and vinyl compounds containing aromatic rings having a vinyl substituent on a heterocyclic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrrol, N-vinylimidazole, N-vinyloxazole, etc. Preferred vinyl compounds containing aromatic rings include styrene, α-methylstyrene, and vinyltoluene. Among them, styrene is preferred.

As the aromatic ring-containing monomer of component (A), a homopolymer having a glass transition temperature in the range of -30°C to 65°C can be preferably used. In some aspects, the glass transition temperature of the homopolymer of the aromatic ring-containing monomer can be, for example, -20°C to -10°C or 0°C, and 60°C to 60°C, 50°C to 40°C or 35°C. An aromatic ring-containing monomer having a homopolymer glass transition temperature between any of the upper temperature limits and any of the lower temperature limits can achieve an adhesive sheet having both low initial adhesion and increased adhesion thereafter.

Preferred examples of monomers containing aromatic rings that can be used as component (A) include: benzyl (meth)acrylate, ethoxylated phenylphenol (meth)acrylates such as o-phenylphenol ethyl (meth)acrylate, diphenyl methyl (meth)acrylates such as p-diphenyl methyl (meth)acrylate, phenoxybenzyl (meth)acrylate such as m-phenoxybenzyl (meth)acrylate, and benzene ring-containing (meth)acrylates such as (meth) phenoxybenzyl (meth)acrylate; and aromatic ring-containing vinyl compounds such as styrene.

In some aspects where the aromatic ring-containing (meth)acrylate is used as component (A), the ratio of the benzene ring-containing (meth)acrylate in the aromatic ring-containing (meth)acrylate may be, for example, more than 50% by weight, more than 75% by weight, more than 90% by weight, or substantially 100% by weight (typically 99.5 to 100% by weight).

(Oligomer AR) In the technology disclosed herein, as the above-mentioned component (A), an oligomer (oligomer AR) containing a repeating unit containing an aromatic ring can be used instead of the above-mentioned aromatic ring-containing monomer or in combination with the aromatic ring-containing monomer. The above-mentioned oligomer AR is a polymer containing a monomer unit derived from an aromatic ring-containing monomer. As the above-mentioned aromatic ring-containing monomer, a monomer selected from the monomers exemplified as aromatic ring-containing monomers that can be used as component (A) can be used alone or in combination of two or more. By using the oligomer AR, at least one effect of suppressing the initial adhesion and improving the subsequent adhesion rise can be achieved.

The weight ratio of the monomer containing an aromatic ring in the monomer components constituting the oligomer AR (hereinafter, also referred to as the "aromatic ring-containing monomer ratio of the oligomer AR") can be, for example, 30% by weight or more. The above ratio is usually preferably more than 50% by weight, more preferably more than 70% by weight, and further preferably more than 90% by weight. According to the use of an oligomer AR containing a relatively large amount of monomer containing an aromatic ring as described above, there is a tendency to better exert the above effect. In some embodiments, the above ratio can be more than 95% by weight, can be more than 98% by weight, and can also be substantially 100% by weight (typically 99.5 to 100% by weight).

As the monomer component constituting the oligomer AR, an aromatic ring-containing vinyl compound can be used well. Particularly preferred is an aromatic ring-containing vinyl compound having a vinyl substituent on a carbon ring (typically a benzene ring), and styrene is preferred. In some aspects, an oligomer AR in which the ratio of styrene in the monomer component constituting the oligomer AR exceeds 50% by weight can be used well. The above-mentioned ratio of styrene is more preferably 70% by weight or more, further preferably 90% by weight or more, can be 95% by weight or more, can be 98% by weight or more, and can also be substantially 100% by weight (typically 99.5 to 100% by weight).

In some aspects, as the oligomer AR, one without ethylenic unsaturated groups can be preferably used. The oligomer AR is clearly distinguished from the monomer or macromolecular monomer. For example, it is preferably an oligomer AR without ethylenic unsaturated groups and non-reactive to hydroxyl groups and carboxyl groups. Such oligomer AR typically exists in the adhesive layer in a form that is not chemically bonded to the polymer formed by the monomers contained in the above-mentioned composition. According to the adhesive layer containing the oligomer AR in this form, there is a tendency to better exert at least one effect of suppressing the initial adhesion and improving the subsequent adhesion increase by the mobility of the oligomer AR in the adhesive layer. As a preferred example of the oligomer AR having no ethylenically unsaturated group and being non-reactive with respect to a hydroxyl group and a carboxyl group, there can be cited a styrene oligomer substantially composed of styrene.

The weight average molecular weight (Mw) of the oligomer AR is not particularly limited. From the viewpoint of easily exerting the effect produced by using the oligomer AR, the Mw of the oligomer AR is generally preferably about 0.5×10 ³ or more and about less than 10×10 ^3. In some embodiments, the Mw of the oligomer AR may be, for example, 1.0×10 ³ or more, 1.5×10 ³ or more, or 2.0×10 ³ or more. If the Mw becomes higher, the cohesion of the adhesive layer tends to be improved. In addition, in some embodiments, the Mw of the oligomer AR may be, for example, 8.0×10 ³ or less, 6.0×10 ³ or less, or 4.0×10 ³ or less. If the Mw becomes lower, the adhesion tends to be improved.

Furthermore, in this specification, the Mw of polymers and oligomers can be obtained by polystyrene conversion by gel permeation chromatography (GPC). Specifically, it can be obtained by using the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation) as a GPC measuring device and measuring under the following conditions. [GPC measurement conditions] Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate: 0.6 mL/min Column temperature (measurement temperature): 40°C Column: Sample column: 1 TSKguardcolumn SuperHZ-H + 2 TSKgel SuperHZM-H (Tosoh) Reference column: 1 TSKgel SuperH-RC (Tosoh) Detector: Differential refractometer (RI) Standard sample: Polystyrene

(Ratio of aromatic ring-containing monomers in monomer components) The monomer components constituting the above-mentioned adhesive layer contain aromatic ring-containing monomers by using the above-mentioned component (A). The above-mentioned aromatic ring-containing monomer may be an aromatic ring-containing monomer used as component (A) in the form of a monomer (hereinafter, sometimes expressed as "monomer m _AR1 "), or may be an aromatic ring-containing monomer used as component (A) in the form of an aromatic ring-containing repeating unit constituting an oligomer AR (hereinafter, sometimes expressed as "monomer m _AR2 "). The weight ratio of aromatic ring-containing monomers in the monomer components constituting the adhesive layer (i.e., the total weight of monomer m _AR1 and monomer m _AR2 in the weight of the monomer component; hereinafter, sometimes expressed as "ratio of aromatic ring-containing monomers in the monomer component") is not particularly limited. From the perspective of well exerting the effect of using the monomer and/or oligomer AR containing an aromatic ring, the above-mentioned monomer ratio containing an aromatic ring is usually preferably 10% by weight or more, preferably 25% by weight or more, can be 35% by weight or more, and can also be 45% by weight or more. In some preferred embodiments, the above-mentioned monomer ratio containing an aromatic ring can be, for example, 55% by weight or more, can be 60% by weight or more, and can also be 65% by weight or more. In addition, the above-mentioned monomer ratio containing an aromatic ring is typically less than 100% by weight, and is usually preferably 95% by weight or less. From the perspective of the ease of adjusting the glass transition temperature Tg _A or the increase in adhesion, in some embodiments, the above-mentioned monomer ratio containing an aromatic ring is preferably 90% by weight or less, can be 85% by weight or less, can be 80% by weight or less, and can also be 75% by weight or less.

In some preferred embodiments, an aromatic ring-containing monomer and an oligomer AR can be used together as component (A). In this way, an adhesive sheet that exhibits a relatively low adhesive force at the initial stage of attachment and then greatly increases the adhesive force can be well realized. When an aromatic ring-containing monomer and an oligomer AR are used together, the ratio of the amount of the monomer m _AR2 used relative to the amount of the monomer m _AR1 used (based on weight) is not particularly limited. In some embodiments, by setting the above-mentioned usage ratio (m _AR2 /m _AR1 ) to a range of 0.1 to 10, the effect of using the aromatic ring-containing monomer and the oligomer AR together can be better exerted. The above usage ratio may be, for example, 0.3 or more, 0.5 or more, 0.7 or more, 1.0 or more, 1.2 or more, or 1.5 or more. Also, the above usage ratio may be, for example, 7 or less, 5 or less, 3 or less, or 2 or less.

(High refractive index monomer) In some embodiments, a high refractive index monomer can be preferably used as at least a part of the aromatic ring-containing monomer contained in the monomer component constituting the adhesive layer. Here, the "high refractive index monomer" in this specification refers to a monomer whose homopolymer has a refractive index of approximately 1.50 or more (typically 1.51 or more). The refractive index of the homopolymer of the aromatic ring-containing monomer can be measured using a commercially available Abbe refractometer (e.g., model "DR-M2", manufactured by ATAGO Corporation).

Examples of the aromatic ring-containing monomers belonging to the above-mentioned high refractive index monomers include benzyl acrylate, ethoxylated o-phenylphenol acrylate, p-diphenylmethyl acrylate, m-phenoxybenzyl acrylate, styrene, etc. When the monomer components constituting the adhesive layer contain high refractive index monomers, it can be advantageous, for example, in adhesive sheets that can be used for optical purposes. The proportion of the high refractive index monomer in the aromatic ring-containing monomers contained in the above-mentioned monomer components can, for example, exceed 50% by weight, can be 75% by weight or more, can be 90% by weight or more, and can also be substantially 100% by weight (typically 99.5 to 100% by weight).

<Component (B)> As component (B), a monomer having a hydroxyl group or a carboxyl group is used. A monomer having a hydroxyl group (a hydroxyl-containing monomer) is a compound containing a hydroxyl group and an ethylenically unsaturated group in its structure. A monomer having a carboxyl group (a carboxyl-containing monomer) is a compound containing a carboxyl group and an ethylenically unsaturated group in its structure. As component (B), a monomer not containing an aromatic ring is typically used. As the above-mentioned ethylenically unsaturated group, a (meth)acryloyl group is preferred, and an acryl group is more preferred. In the monomer used as component (B), the number of ethylenically unsaturated groups contained in one molecule of the monomer is typically one.

Examples of hydroxyl-containing monomers include hydroxyl alkyl (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, but are not limited thereto. Examples of hydroxyl-containing monomers that can be used well include 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. The hydroxyl-containing monomers can be used alone or in combination of two or more.

Examples of carboxyl-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, butyric acid, isobutylene acid, etc., but are not limited thereto. Examples of hydroxyl-containing monomers that can be used well include acrylic acid and methacrylic acid. Carboxyl-containing monomers can be used alone or in combination of two or more. Hydroxyl-containing monomers and carboxyl-containing monomers can also be used in combination.

The amount of component (B) used is not particularly limited and can be set according to the purpose. In some embodiments, the amount of component (B) used can be, for example, 0.01% by weight or more of the monomer component constituting the adhesive layer, and is usually preferably set to 0.1% by weight or more, and more preferably set to 0.5% by weight or more. In some embodiments, the amount of component (B) used can be, for example, 1% by weight or more of the above-mentioned monomer component, and can also be 1.5% by weight or more. In addition, the amount of component (B) used is usually appropriately set to 40% by weight or less of the monomer component, can be set to 30% by weight or less, can be set to 20% by weight or less, and can also be set to 10% by weight or less or 5% by weight or less.

When a hydroxyl-containing monomer is used as component (B), the amount used is not particularly limited, and is usually preferably set to 0.01% by weight or more (preferably 0.1% by weight or more, for example 0.5% by weight or more) of the monomer component constituting the adhesive layer. In some embodiments, the amount of the hydroxyl-containing monomer used can be set to, for example, 1% by weight or more of the above-mentioned monomer component, or can be set to 1.5% by weight or more. In addition, the amount of the hydroxyl-containing monomer used is usually preferably set to 40% by weight or less of the monomer component, can be set to 30% by weight or less, can be set to 20% by weight or less, can also be set to 10% by weight or less, or can be set to 5% by weight or less.

The amount used when using a carboxyl-containing monomer as component (B) is not particularly limited, and is usually appropriately set to more than 0.01% by weight (preferably more than 0.1% by weight, for example more than 0.5% by weight) of the monomer component constituting the adhesive layer. In several aspects, the amount of the carboxyl-containing monomer used can be set to, for example, more than 1% by weight of the above-mentioned monomer component, or more than 1.5% by weight. In addition, the amount of the carboxyl-containing monomer used is usually appropriately set to less than 40% by weight of the monomer component, can be set to less than 30% by weight, can be set to less than 20% by weight, can also be set to less than 10% by weight or less than 5% by weight. The technology disclosed here can be well implemented, for example, using only a hydroxyl-containing monomer as component (B).

The reason why an adhesive sheet having both initial low adhesion and subsequent increased adhesion is achieved by using an adhesive layer containing a polymerized reaction product of a composition including the above-mentioned component (A) and the above-mentioned component (B) is considered to be as follows, for example, but it is hoped that it will not be subject to theoretical constraints. That is, by using the above-mentioned component (A), the above-mentioned adhesive layer contains a molecular chain containing an aromatic ring. The molecular chain containing an aromatic ring can contribute to the expression of initial low adhesion and subsequent increased adhesion by moving away from the interface with the above-mentioned adherend in the adhesive layer after being attached to the adherend. The above-mentioned component (B) is believed to have the effect of making the above-mentioned molecular chain containing an aromatic ring easy to move in the adhesive layer due to the polarity of the hydroxyl group and/or the carboxyl group. However, the explanation should not be limited to this reason.

<Adhesive layer> (Glass transition temperature Tg _A ) With respect to the adhesive layer, the glass transition temperature Tg _A based on the composition of the monomer components constituting the adhesive layer is preferably 40°C or less. By making the glass transition temperature Tg _A not too high, there is a tendency to exert good adhesion increase properties. From this point of view, the glass transition temperature Tg _A may be, for example, below 35°C, below 30°C, or below 25°C. In some embodiments of the adhesive sheet disclosed herein, the glass transition temperature Tg _A may be, for example, below 20°C, below 15°C, below 10°C, or below 5°C.

The glass transition temperature Tg _A is usually preferably higher than -3°C, more preferably higher than 0°C. This can appropriately achieve low initial adhesion. From the perspective of easily controlling the increase in adhesion after attachment, in some embodiments, the glass transition temperature Tg _A can be, for example, higher than 5°C, higher than 10°C, higher than 15°C, or higher than 18°C.

Here, the glass transition temperature Tg _A refers to the glass transition temperature obtained by the Fox equation based on the composition of the monomer corresponding to the above-mentioned monomer component. The Fox equation refers to the relationship between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1/Tg＝Σ(Wi/Tgi) In the above Fox equation, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of the monomer i in the copolymer (copolymerization ratio based on weight), and Tgi represents the glass transition temperature of the homopolymer of the monomer i (unit: K). As the glass transition temperature of the homopolymer used to calculate Tg, the value described in the known materials such as "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) is used. For monomers for which multiple values are recorded in the above polymer manual, the highest value is adopted. When the Tg of the homopolymer is not recorded in the public knowledge, the value obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 is used. In addition, in this specification, the calculation of the above Tg _A is performed only for monofunctional monomers (i.e., monomers having a single ethylenically unsaturated group in one molecule) as the object.

(Alkyl (meth)acrylate) In some aspects of the technology disclosed herein, the composition used to prepare the above-mentioned polymer reactant may further include an alkyl (meth)acrylate. As the alkyl (meth)acrylate, an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms (i.e., _C1-20 ) at the ester end can be preferably used.

Specific examples of _C1-20 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, 1-butyl (meth)acrylate, 2-octyl (meth)acrylate, 1-octyl (meth)acrylate, 1-butyl (meth)acrylate, 1-octyl ... The present invention also includes, but is not limited to, 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.

When using such an alkyl (meth)acrylate, the amount used can be set in a manner that a better effect is achieved. The above-mentioned amount can be, for example, 5% by weight or more of the monomer component constituting the adhesive layer, usually preferably 10% by weight or more, or 15% by weight or more, or 20% by weight or more. In addition, the above-mentioned amount is usually preferably less than 80% by weight of the above-mentioned monomer component, preferably less than 75% by weight, less than 65% by weight, or less than 55% by weight. In some preferred embodiments, the amount of alkyl (meth)acrylate used may be less than 45% by weight of the above-mentioned monomer component, less than 40% by weight, less than 35% by weight, or less than 30% by weight.

In some preferred aspects, the composition may include an alkyl (meth)acrylate having a homopolymer glass transition temperature of -40°C or less (preferably -50°C or less) (hereinafter, also referred to as "component (C)") as the alkyl (meth)acrylate. By using component (C) appropriately, the glass transition temperature Tg _A or the adhesive properties can be effectively adjusted. The glass transition temperature of the homopolymer of the alkyl (meth)acrylate used as component (C) may be, for example, -85°C or more, -75°C or more, -65°C or more, or -60°C or more.

Preferred examples of (meth)acrylic acid alkyl esters that can be used as component (C) include: n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), etc. For example, a composition comprising one or both of BA and 2EHA is preferred, and a composition comprising at least BA is more preferred. When BA and 2EHA are used together, the weight ratio of their usage (BA:2EHA) is not particularly limited. The above weight ratio may be, for example, 5:95 or more, 20:80 or more, or 40:60 or more. In a preferred embodiment, the weight ratio of BA:2EHA may be 50:50 or more. In addition, the above weight ratio may be, for example, less than 95:5, less than 80:20, or less than 60:40.

The amount used when using component (C) can be set in a manner that exerts a better use effect. From the perspective of increasing the adhesion after the adhesion is increased, the above-mentioned amount can be, for example, more than 5% by weight of the monomer components constituting the adhesive layer, usually more than 10% by weight, and can also be more than 15% by weight or more than 20% by weight. In addition, from the perspective of suppressing the initial adhesion, the above-mentioned amount is usually more than 80% by weight of the monomer components constituting the adhesive layer, preferably less than 75% by weight, less than 65% by weight, and less than 55% by weight. In several preferred embodiments, the amount of component (C) used may be less than 45% by weight, less than 40% by weight, less than 35% by weight, or less than 30% by weight of the above-mentioned monomer components.

(Copolymerizable monomer) The composition used to prepare the above-mentioned polymer reactant may further include other monomers (copolymerizable monomers) that can copolymerize with the monomer that can be used as component (B) and the monomer that can be used as component (A). Copolymerizable monomers may be used alone or in combination of two or more.

As non-limiting specific examples of copolymerizable monomers, the following can be cited. Nitrogen-containing monomers: for example (meth)acrylamide; 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, N,N-di(tert-butyl) (meth)acrylamide and other N,N-dialkyl (meth)acrylamide; N-ethyl (meth)acrylamide; N-alkyl (meth) acrylamides such as enamide, N-isopropyl (meth) acrylamide, N-butyl (meth) acrylamide, and N-n-butyl (meth) acrylamide; N-vinyl carboxylic acid amides such as N-vinyl acetylamide; monomers having alkoxy and amide groups, such as N-methoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, and N-butoxymethyl (meth) acrylamide; Alkyl (meth) acrylamide; N,N-dimethylaminopropyl (meth) acrylamide; N-vinyl-2-pyrrolidone, N-methylvinyl pyrrolidone, N-vinyl piperidone, N-vinyl piperidine, N-(meth) acrylyl-2-pyrrolidone, N-(meth) acryl piperidine, N-(meth) acryl pyrrolidine, N-vinyl thiophene, N-(meth) acryl thiophene, N-vinyl- Monomers with a nitrogen-containing ring such as 3-vinyl-2-caprolactam, etc.; (meth)acrylic acid aminoethyl esters such as (meth)acrylic acid N,N-dimethylaminoethyl ester, (meth)acrylic acid N,N-diethylaminoethyl ester, (meth)acrylic acid tert-butylaminoethyl ester; In addition, monomers with a succinimide skeleton, succinimides, and iconimides, etc. Alkoxy-containing monomers: for example, 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate, and other (meth)acrylate alkoxyalkyl esters; (meth)acrylate alkoxyalkylene glycol esters such as methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol (meth)acrylate. Anhydride-containing monomers: for example, maleic anhydride and itaconic anhydride. Epoxy-containing monomers: for example, epoxy-containing acrylates such as (meth)acrylate glycidyl or (meth)acrylate-2-ethyl glycidyl ether, allyl glycidyl ether, (meth)acrylate glycidyl ether, and the like. Cyano-containing monomers: for example, acrylonitrile and methacrylonitrile, and the like. Isocyanate-containing monomers: such as 2-isocyanatoethyl (meth)acrylate, etc. Vinyl esters: such as vinyl acetate, vinyl propionate, etc. Vinyl ethers: such as vinyl alkyl ethers such as methyl vinyl ether or ethyl vinyl ether. Olefins: such as ethylene, butadiene, isoprene, isobutylene, etc. (Meth)acrylates with alicyclic hydrocarbon groups: such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobutylene (meth)acrylate, dicyclopentyl (meth)acrylate, etc. In addition, heterocyclic (meth)acrylates such as tetrahydrofuranyl (meth)acrylate, halogen-containing (meth)acrylates such as vinyl chloride or fluorine-containing (meth)acrylates, silicon-containing (meth)acrylates such as silicone (meth)acrylate, monomers containing sulfonic acid groups or phosphoric acid groups, and (meth)acrylates obtained from terpene compound derivative alcohols may be used.

When such copolymerizable monomers are used, the amount used is not particularly limited, and is usually preferably set to 0.01% by weight or more of the monomer components constituting the adhesive layer. From the perspective of better exerting the effect of the copolymerizable monomer, the amount of the copolymerizable monomer used can be set to 0.1% by weight or more of the monomer components, and can also be set to 1% by weight or more. In addition, from the perspective of easily achieving a balance with other performances, the amount of the copolymerizable monomer used is usually preferably set to 40% by weight or less of the monomer components, preferably 30% by weight or less, can be 20% by weight or less, can be 15% by weight or less, can be 10% by weight or less, and can also be 7.5% by weight or less.

(N-vinyl cyclic amide) In some embodiments, the above composition preferably contains at least one monomer selected from the group consisting of N-vinyl cyclic amides represented by the following general formula (M1).

[Chemistry 1] Here, ^R1 in the above general formula (M1) is a divalent organic group.

By using N-vinyl cyclic amides, the cohesive force or polarity of the adhesive can be adjusted, and the adhesion after the adhesion is increased (for example, the adhesion after heating is N2) can be increased. Specific examples of N-vinyl cyclic amides include: N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-oxo-1-ol, N-vinyl-2-caprolactam, N-vinyl-3,5-oxo-1-ol-dione, etc. N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam are particularly preferred.

When N-vinyl cyclic amide is used, the amount used is not particularly limited, and is usually preferably set to 0.01% by weight or more (preferably 0.1% by weight or more, for example 0.5% by weight or more) of the monomer components constituting the adhesive layer. In some embodiments, the amount of N-vinyl cyclic amide used can be set to 1% by weight or more of the above-mentioned monomer components, can be set to 3% by weight or more, and can also be set to 4% by weight or more. In addition, from the perspective of easily achieving a balance with other properties, the amount of N-vinyl cyclic amide used is usually preferably set to 40% by weight or less of the monomer components, preferably 30% by weight or less, can be 20% by weight or less, can be 15% by weight or less, can be 10% by weight or less, and can also be 7.5% by weight or less.

In some embodiments, the weight ratio of the monomer having a polyorganosiloxane skeleton (hereinafter, also referred to as a monomer containing a polyorganosiloxane structure) in the monomer components constituting the adhesive layer may be, for example, less than 1% by weight. In some embodiments, the weight ratio may be less than 0.5% by weight, less than 0.1% by weight, less than 0.05% by weight, or 0% by weight (i.e., the monomer components not including the monomer containing a polyorganosiloxane structure). According to the technology disclosed herein, even if the amount of the monomer containing a polyorganosiloxane structure is limited as described above, an adhesive sheet with low adhesion in the initial stage of attachment and excellent adhesion increase thereafter can be well achieved. The ability to suppress the amount of monomer containing a polyorganosiloxane structure used can be an advantageous feature in adhesive sheets suitable for applications that avoid the use of siloxane (e.g., electronic equipment applications, etc.).

(Polymer P) Typically, the adhesive layer in the technology disclosed herein includes a polymer P formed by monomers contained in the above composition (including at least a monomer that can be used as component (B) and a monomer that can be used as component (A), and may further include other monomers), and further includes an oligomer AR in the case where an oligomer AR is used as component (A).

In the embodiment where only aromatic ring-containing monomers are used as component (A) (i.e., the embodiment where oligomer AR is not used), the weight ratio of aromatic ring-containing monomers in the monomers contained in the above-mentioned composition (hereinafter also referred to as "aromatic ring-containing monomer ratio of polymer P") can be, for example, 10 wt % or more. From the viewpoint of easily exerting the initial low adhesion and the subsequent adhesion increase, it is usually preferably 25 wt % or more, can be 35 wt % or more, can be 45 wt % or more, can be 55 wt % or more, can be 60 wt % or more, and can also be 65 wt % or more. Furthermore, in the above aspect, the ratio of the monomer containing an aromatic ring in the polymer P may be, for example, 95 wt % or less. From the perspective of improving the adhesion, it is usually preferably 90 wt % or less, may be 85 wt % or less, may be 80 wt % or less, and may also be 75 wt % or less.

In the embodiment using oligomer AR as component (A), the ratio of monomers containing aromatic rings in polymer P can be, for example, 5% by weight or more, preferably 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the ratio of monomers containing aromatic rings in polymer P can be, for example, 25% by weight or more, 30% by weight or more, 35% by weight or more, or 40% by weight or more, in consideration of the compatibility between polymer P and oligomer AR. In addition, in the above embodiment, the ratio of monomers containing aromatic rings in polymer P can be, for example, 85% by weight or less, and from the viewpoint of easily improving the adhesion after the adhesion is increased, it is preferably 70% by weight or less, 60% by weight or less, or 50% by weight or less.

In some embodiments, the difference between the ratio of the aromatic ring-containing monomer of the oligomer AR ( _RO [wt%]) and the ratio of the aromatic ring-containing monomer of the polymer P ( _RP [wt%]), i.e., | _RO - _RP |, may be, for example, 90 or less. From the viewpoint of improving the compatibility between the oligomer AR and the polymer P, it is usually preferably 80 or less, preferably 70 or less, may be 65 or less, and may also be 60 or less. From the viewpoint of more easily expressing the initial low adhesion, in some embodiments, | _RO - _RP | may be, for example, 10 or more, 25 or more, 40 or more, and may also be 50 or more. From the viewpoint of the adhesion increase property, the relationship between _RO and _RP is preferably _RO ≧ _RP , and more preferably _RO > _RP .

In the embodiment using the oligomer AR as the component (A), the glass transition temperature based on the composition of the monomers contained in the above composition, that is, the glass transition temperature (Tg _P ) of the polymer P is not particularly limited. The above glass transition temperature Tg _P may be, for example, above -70°C, above -60°C, or above -50°C. In some embodiments, from the viewpoint of more easily exhibiting initial low adhesion, the above glass transition temperature Tg _P may be, for example, above -40°C, above -35°C, above -30°C, or above -25°C. Furthermore, the above glass transition temperature Tg _P may be, for example, below 30°C, below 20°C, below 10°C, below 5°C, or below 0°C. From the viewpoint of improving the mobility of the oligomer AR and thus effectively increasing the adhesive force, in some aspects, the glass transition temperature _TgP may be, for example, -5°C or lower, -10°C or lower, or -15°C or lower.

The glass transition temperature (Tg _O ) of the oligomer AR is not particularly limited, and may be, for example, -10°C or higher, or 0°C or higher. From the viewpoint of achieving good initial low adhesion, the glass transition temperature (Tg _O ) is usually preferably 10°C or higher, preferably 20°C or higher, 35°C or higher, 50°C or higher, 65°C or higher, or 75°C or higher. The glass transition temperature (Tg _O ) may be, for example, 180°C or lower, and from the viewpoint of achieving good adhesion increase, it is usually preferably 150°C or lower, 130°C or lower, or 110°C or lower.

From the viewpoint of better exerting the initial low adhesion and the subsequent adhesion increase, the glass transition temperature (Tg _O [°C]) of the oligomer AR is preferably higher than the glass transition temperature (Tg _P [°C]) of the polymer P, and Tg _O -Tg _P is preferably 10 or more. From the viewpoint of more easily exerting the effect produced by using the oligomer AR, in some aspects, Tg _O -Tg _P may be, for example, 30°C or more, 50°C or more, 70°C or more, 85°C or more, 100°C or more, or 105°C or more. From the same viewpoint, in some aspects, Tg _O -Tg _P may be, for example, 200°C or less, and is usually preferably 180°C or less, 160°C or less, 140°C or less, or 130°C or less.

Furthermore, the glass transition temperature (Tg _P ) of the polymer P and the glass transition temperature (Tg _O ) of the oligomer AR are determined by the above-mentioned Fox formula based on the composition of the monomer components constituting the polymer P (i.e., the composition of the monomers contained in the above-mentioned composition) and the composition of the monomer components constituting the oligomer AR, respectively.

In some aspects, the monomers contained in the composition may be acrylic monomers, for example, 30% by weight or more thereof. From the viewpoint of ease of adjustment of polymerization reactivity or adhesive properties, the weight ratio of the acrylic monomers in the monomers contained in the composition may be, for example, preferably more than 50% by weight, more preferably more than 65% by weight, more than 80% by weight, more than 90% by weight, more than 95% by weight, or substantially 100% by weight (for example, more than 99.9% by weight and less than 100% by weight).

(Crosslinking agent) In order to adjust the cohesive force or suppress the initial adhesion, a crosslinking agent may be used in the adhesive layer as needed. As a crosslinking agent, epoxy crosslinking agents, isocyanate crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, silane coupling agents, alkyl etherified melamine crosslinking agents, metal chelate crosslinking agents and other crosslinking agents known in the field of adhesives can be used. As other examples of crosslinking agents, monomers having two or more ethylenically unsaturated groups in one molecule, i.e., multifunctional monomers, can be cited. The crosslinking agent may be used alone or in combination of two or more.

Examples of isocyanate crosslinking agents include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, and adducts of these with polyols such as trihydroxymethylpropane. Alternatively, a compound having at least one isocyanate group and one or more unsaturated bonds in one molecule, specifically 2-isocyanatoethyl (meth)acrylate, etc. can also be used as an isocyanate crosslinking agent. These may be used alone or in combination of two or more.

Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin epoxy resins, ethyl glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trihydroxymethylpropane triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N,N,N',N'-tetraglycidyl meta-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. These can be used alone or in combination of two or more.

Examples of the polyfunctional monomer include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trihydroxymethylpropane tri(meth)acrylate, tetrahydroxymethylmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butanediol (meth)acrylate, hexanediol di(meth)acrylate, and the like. As other examples, polyfunctional monomers containing a fluorene skeleton such as 9,9-bis(4-hydroxyphenyl)fluorene di(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene di(meth)acrylate can be cited. Commercially available products of the polyfunctional monomers include products such as "OGSOL EA-0200", "OGSOL EA-0300", "OGSOL EA-0500", and "OGSOL EA-1000" manufactured by Osaka Gas Chemicals. For example, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and trihydroxymethylpropane tri(meth)acrylate can be preferably used. The polyfunctional monomers can be used alone or in combination of two or more.

When a crosslinking agent (which may be a multifunctional monomer) is used, the amount used is not particularly limited. For example, it can be set in the range of about 0.01 to 5.0 parts by weight relative to 100 parts by weight of the monomer component constituting the adhesive layer. In some embodiments, the amount of the crosslinking agent used can be, for example, 0.01 parts by weight or more, or 0.03 parts by weight or more relative to 100 parts by weight of the monomer contained in the above composition. By increasing the amount of the crosslinking agent used, there is a tendency to suppress the initial adhesion and improve the secondary processing properties. On the other hand, from the viewpoint of improving the adhesion, the amount of the crosslinking agent used is usually appropriately set to 5.0 parts by weight or less, preferably 3.0 parts by weight or less, and can be 2.0 parts by weight or less, 1.0 parts by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, or 0.1 parts by weight or less or 0.08 parts by weight or less, relative to 100 parts by weight of the monomer contained in the above-mentioned composition.

(Other additives) The adhesive layer may contain an adhesive-imparting resin as needed. Examples of adhesive-imparting resins include rosin-based adhesive-imparting resins, terpene-based adhesive-imparting resins, phenol-based adhesive-imparting resins, hydrocarbon-based adhesive-imparting resins, ketone-based adhesive-imparting resins, polyamide-based adhesive-imparting resins, epoxy-based adhesive-imparting resins, and elastic-based adhesive-imparting resins. These adhesive-imparting resins may be used alone or in combination of two or more. As the adhesive imparting resin, a resin having a softening point (softening temperature) of about 80°C or more (preferably about 100°C or more, for example, about 120°C or more) can be preferably used. There is no particular upper limit on the softening point, for example, it can be about 200°C or less (typically 180°C or less). The softening point of the adhesive imparting resin can be measured based on the softening point test method (global method) specified in JIS K2207. In the case of using the adhesive imparting resin, its usage is not particularly limited, and can be set in a manner to exert appropriate adhesive properties according to the purpose or use. For example, the content of the tackifier resin relative to 100 parts by weight of the monomer contained in the above composition (the total amount of the tackifier resins when two or more tackifier resins are included) can be approximately 0.5 to 200 parts by weight, 5 to 100 parts by weight, or 10 to 50 parts by weight. The technology disclosed herein can also be well implemented in a state where the adhesive layer does not substantially contain the tackifier resin.

In addition, the adhesive layer in the technology disclosed herein may also contain leveling agents, plasticizers, softeners, coloring agents (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, etc., which are known additives that can be used in adhesives, within the scope that does not significantly hinder the effects of the present invention.

<Method for forming adhesive layer> The adhesive layer of the adhesive sheet disclosed herein contains a polymerized product of a composition comprising at least component (A) and component (B). The method for polymerizing the monomers contained in the above composition is not particularly limited, and various polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, photopolymerization, etc. can be used alone or in appropriate combination.

The initiator used for the polymerization can be appropriately selected from previously known thermal initiators or photoinitiators according to the polymerization method. Non-limiting examples of thermal initiators include: azo initiators such as 2,2'-azobisisobutyronitrile (AIBN), persulfates such as potassium persulfate, peroxide initiators, redox initiators, etc. Non-limiting examples of photoinitiators include: benzoin ether photoinitiators, acetophenone photoinitiators, α-ketol photoinitiators, aromatic sulfonyl chloride photoinitiators, photoactive oxime photoinitiators, benzoin photoinitiators, benzoyl photoinitiators, benzophenone photoinitiators, ketal photoinitiators, 9-oxysulfuron photoinitiators. The initiator may be a photoinitiator, an acylphosphine oxide-based photoinitiator, etc. The initiator may be used alone or in combination of two or more.

In some aspects, photopolymerization can be used as a method for obtaining a polymerized reactant from the above composition. For example, a method of irradiating a composition comprising component (A) and component (B) as essential components, other components used as needed, and a photoinitiator with ultraviolet light (UV) can be well adopted. The above UV irradiation can be performed all at once or in stages. As an example of an aspect of performing UV irradiation in stages, the following aspect can be cited: after irradiating the above composition with UV in a suitable reaction container, partially polymerizing the monomers contained in the composition, applying the composition to a suitable surface, and completely polymerizing the monomers on the surface. In an aspect of performing photopolymerization of the composition in stages, a part of the components (monomers, oligomers, etc.) can also be added in the middle of the above-mentioned staged photopolymerization. For example, a mixture containing a portion of the monomers used in the above composition may be irradiated with UV, the monomers in the mixture may be partially or completely polymerized, and then the remaining monomers may be added and mixed, and then irradiated with UV to form a polymerized product. In addition, in the case of using oligomers, for example, after partially polymerizing the monomers used in the above composition, the oligomer and other materials used as needed may be added, and further polymerized to form a polymerized product.

In other aspects, solution polymerization can be preferably used. As a polymerization solvent, for example, ethyl acetate, toluene, etc. can be used. The solution concentration is usually about 20 to 80% by weight. As an initiator, various well-known ones such as azo series and peroxide series can be used. In order to adjust the molecular weight, a chain transfer agent can also be used. The reaction temperature can be about 50 to 80°C. The reaction time can be about 1 to 8 hours.

The adhesive layer of the adhesive sheet disclosed herein may be a hardened layer of an adhesive composition containing a composition comprising the above-mentioned component (A) and the above-mentioned component (B) or a partial polymer thereof. That is, the adhesive layer can be formed by applying (e.g., coating) the above-mentioned adhesive composition to an appropriate surface and then appropriately performing a hardening treatment. When two or more hardening treatments (drying, crosslinking, polymerization, cooling, etc.) are performed, they may be performed simultaneously or in multiple stages. In an adhesive composition using a partial polymer of the above-mentioned composition, typically, a final copolymerization reaction is performed as the above-mentioned hardening treatment. That is, a complete polymer is formed from a partial polymer. For example, if it is a photocurable adhesive composition, light irradiation is performed. Hardening treatments such as crosslinking and drying may also be performed as needed. For example, when a photocurable adhesive composition must be dried, photocuring can be performed after drying. In the case of an adhesive composition using a complete polymer, typically, as the above-mentioned curing treatment, drying (heat drying), crosslinking, etc. are performed as necessary.

The adhesive composition can be applied by using a commonly used coating machine such as a gravure roll coater, a reverse roll coater, a contact roll coater, a dip roll coater, a rod coater, a doctor blade coater, or a spray coater.

The thickness of the adhesive layer is not particularly limited, and can be set to 1 μm or more, for example. In some embodiments, the thickness of the adhesive layer can be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. By increasing the thickness of the adhesive layer, the adhesive force tends to increase after heating. In addition, in some embodiments, the thickness of the adhesive layer can be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. If the thickness of the adhesive layer is not too large, it can be advantageous from the perspective of thinning the adhesive sheet. Furthermore, in the case of an adhesive sheet having a first adhesive layer and a second adhesive layer on the first and second surfaces of a substrate, the thickness of the adhesive layer can at least be applied to the thickness of the first adhesive layer. The thickness of the second adhesive layer can also be selected from the same range. In addition, in the case of an adhesive sheet without a substrate, the thickness of the adhesive sheet is consistent with the thickness of the adhesive layer.

<Supporting substrate> Some types of adhesive sheets may be in the form of an adhesive sheet with a substrate having an adhesive layer on one or both sides of the supporting substrate. The material of the supporting substrate is not particularly limited and can be appropriately selected according to the purpose of use or the usage of the adhesive sheet. Non-limiting examples of the substrate that can be used include: polyolefin films with polyolefins such as polypropylene (PP) or ethylene-propylene copolymer as the main component, polyester films with polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) as the main component, and plastic films such as polyvinyl chloride films with polyvinyl chloride as the main component; including Foam sheets of polyurethane foam, polyethylene (PE) foam, polychloroprene foam, etc.; woven fabrics and non-woven fabrics formed by various fibrous materials (which may be natural fibers such as linen and cotton, synthetic fibers such as polyester and vinyl, semi-synthetic fibers such as acetate, etc.) alone or by blending; Japanese paper, woodfree paper, kraft paper, wrinkled paper, etc.; metal foils such as aluminum foil and copper foil, etc. It can also be a substrate composed of these composite structures. As examples of such composite substrates, for example, there can be listed: a substrate composed of a structure formed by laminating metal foil and the above-mentioned plastic film, a plastic substrate reinforced with inorganic fibers such as glass cloth, etc.

In some aspects, various film substrates can be used well. The above-mentioned film substrate can be a porous substrate such as a foam film or a non-woven fabric sheet, a non-porous substrate, or a substrate having a structure formed by laminating a porous layer and a non-porous layer. In some aspects, as the above-mentioned film substrate, a resin film that can independently maintain its shape (self-supporting or non-dependent) as a base film can be used well. The "resin film" here refers to a non-porous structure, and typically refers to a resin film that does not substantially contain bubbles (pores). Therefore, the concept of the above-mentioned resin film is different from that of a foam film or a non-woven fabric. As the above-mentioned resin film, a (self-supporting or non-dependent) resin film that can independently maintain its shape can be used well. The resin film may be a single-layer structure or a multi-layer structure of two or more layers (eg, a three-layer structure).

Examples of the resin material constituting the resin film include polyester, polyolefin, nylon 6, nylon 66, partially aromatic polyamides such as polyamide (PA), polyimide (PI), polyamide imide (PAI), polyetheretherketone (PEEK), polyethersulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polytetrafluoroethylene (PTFE) and other fluororesins, acrylic resins, polyacrylates, polystyrene, polyvinyl chloride, polyvinylidene chloride and other resins.

The resin film may be formed using a resin material containing only one type of such resin, or may be formed using a resin material blended with two or more types of resin. The resin film may be unstretched or stretched (e.g., uniaxially stretched or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially stretched polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP/PE blended film, etc. may be used well. As examples of resin films that are preferred from the viewpoint of strength or dimensional stability, PET film, PEN film, PPS film, and PEEK film may be cited. From the viewpoint of ease of acquisition, PET film and PPS film are particularly preferred, and PET film is preferred.

In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, lubricants, and anti-adhesive agents may be added as needed within the range that does not significantly hinder the effects of the present invention. The amount of additives added is not particularly limited and can be appropriately set according to the purpose of the adhesive sheet.

The method for producing the resin film is not particularly limited. For example, a conventionally known general resin film forming method such as extrusion forming, inflation forming, T-die die casting, calender roll forming, etc. may be appropriately adopted.

The substrate may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include: an optical property adjustment layer (e.g., a coloring layer, an anti-reflection layer), a printing layer or a lamination layer for giving the substrate a desired appearance, an antistatic layer, a primer layer, a peeling layer, and other surface treatment layers.

The thickness of the substrate is not particularly limited and can be selected according to the purpose or usage of the adhesive sheet. The thickness of the substrate can be, for example, 1000 μm or less. In some embodiments, from the perspective of operability or processability of the adhesive sheet, the thickness of the substrate can be, for example, 500 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less. From the perspective of miniaturization or lightweight of products using the adhesive sheet, in some embodiments, the thickness of the substrate can be, for example, 160 μm or less, 130 μm or less, 100 μm or less, 90 μm or less, 70 μm or less, 50 μm or less, 25 μm or less, 10 μm or less, or 5 μm or less. If the thickness of the substrate becomes smaller, the softness of the adhesive sheet or the ability to follow the surface shape of the adherend tends to be improved. In addition, from the perspective of operability or processability, the thickness of the substrate can be, for example, 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, or 25 μm or more. In several embodiments, the thickness of the substrate can be, for example, 30 μm or more, 35 μm or more, 55 μm or more, 75 μm or more, or 120 μm or more. For example, in an adhesive sheet that can be used for the purpose of reinforcing, supporting, and impact mitigating the adherend, a substrate with a thickness of 30 μm or more can be well used.

If necessary, the surface of one side of the substrate on which the adhesive layer is laminated may be subjected to a previously known surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkaline treatment, or a primer coating to form a primer layer. Such a surface treatment may be a treatment for improving the grip of the adhesive layer on the substrate. The composition of the primer used to form the primer layer is not particularly limited and may be appropriately selected from the known ones. The thickness of the primer layer is not particularly limited and is generally preferably about 0.01 μm to 1 μm, preferably about 0.1 μm to 1 μm. As other treatments that may be applied to the substrate as necessary, there can be cited antistatic layer formation treatment, coloring layer formation treatment, printing treatment, etc. These treatments may be applied alone or in combination.

<Adhesive sheet> (Characteristics of adhesive sheet, etc.) In some embodiments of the adhesive sheet disclosed herein, the adhesive force N1 (initial adhesive force) after the adhesive sheet is attached to a stainless steel plate and left at 23°C for 30 minutes may be, for example, 7 N/20 mm or less. From the perspective of improving secondary processability, the above initial adhesive force is preferably less than 5 N/20 mm, more preferably less than 4 N/20 mm, less than 3 N/20 mm, less than 2 N/20 mm, or less than 1 N/20 mm. There is no particular restriction on the lower limit of the initial adhesive force, and for example, it may be greater than 0.01 N/20 mm. From the perspective of workability when attached to an adherend or preventing positional displacement before the adhesive force increases, the adhesive force N1 is usually preferably greater than 0.1 N/20 mm, and may be greater than 0.2 N/20 mm. From the perspective of easily obtaining higher adhesion after heating, in some aspects, the initial adhesion may be, for example, 0.5 N/20 mm or more, 0.7 N/20 mm or more, 1.2 N/20 mm or more, or 1.5 N/20 mm or more.

The adhesive sheet disclosed herein is bonded to a stainless steel plate and heated at 80°C for 5 minutes, and then at 23°C for 30 minutes. The ratio of the adhesive force N2 (adhesion after heating) to the adhesive force N1 (initial adhesion), that is, N2/N1 (adhesion increase ratio), is preferably 2 N/20 mm or more. Thereby, good secondary processability can be exhibited at the initial stage of bonding, and the adhesive force can be greatly increased by subsequent heating, etc. From the perspective of taking into account both secondary processability and strong adhesion during use at a higher level, N2/N1 is preferably 3 or more, more preferably 4 or more, and further preferably 6 or more. In several aspects, the N2/N1 of the adhesive sheet can be 8 or more, 10 or more, 15 or more, 20 or more, 25 or more, or 30 or more. There is no particular upper limit on N2/N1. From the perspective of ease of manufacturing or economy of the adhesive sheet, in some embodiments, N2/N1 may be, for example, 80 or less, 60 or less, or 45 or less.

Here, the adhesion force N1 [N/20 mm] is obtained by measuring the 180° peeling adhesion at a peeling angle of 180 degrees and a tensile speed of 300 mm/min after being pressed onto a stainless steel (SUS) plate as an adherend and placed in an environment of 23°C and 50% RH for 30 minutes. The adhesion force N2 [N/20 mm] is obtained by measuring the 180° peeling adhesion at a peeling angle of 180 degrees and a tensile speed of 300 mm/min after being pressed onto a SUS plate as an adherend and heated at 80°C for 5 minutes and then placed in an environment of 23°C and 50% RH for 30 minutes. As the adherend, a SUS304BA plate is used in the measurement of either the adhesion force N1 or N2. During the measurement, a suitable backing material (e.g., a PET film with a thickness of about 25 μm) can be attached to the adhesive sheet of the measurement object as needed for reinforcement. More specifically, the adhesion forces N1 and N2 can be measured according to the method described in the following embodiments.

The adhesion force N2 (adhesion force after heating) is usually preferably 3 N/20 mm or more, preferably 5 N/20 mm or more, and more preferably 7.5 N/20 mm or more. In some embodiments, the adhesion force N2 may be 10 N/20 mm or more, 12 N/20 mm or more, or 15 N/20 mm or more. There is no particular upper limit on the adhesion force after heating. From the perspective of easily taking into account good secondary processability at the initial stage of attachment, in some embodiments, the adhesion force after heating may be, for example, 70 N/20 mm or less, 60 N/20 mm or less, or 50 N/20 mm or less.

Furthermore, in this specification, the adhesion of the adhesive sheet after heating represents a characteristic of the adhesive sheet, and does not limit the usage of the adhesive sheet. In other words, the usage of the adhesive sheet disclosed here is not limited to the usage of 80°C for 5 minutes. For example, it can also be used in the usage without special heating to the room temperature area (usually 20°C to 30°C, typically 23°C to 25°C) or above. In this usage, the adhesion can also be increased for a long time to achieve a strong connection. In addition, the adhesive sheet disclosed here can promote the increase of adhesion by performing a heat treatment at any time after attachment. The heating temperature in the heat treatment is not particularly limited and can be set in consideration of workability, economy, heat resistance of the substrate of the adhesive sheet or the adherend, etc. The above-mentioned heating temperature may be, for example, less than 150°C, may be below 120°C, may be below 100°C, may be below 80°C, or may be below 70°C. Furthermore, the above-mentioned heating temperature may be, for example, above 35°C, may be above 50°C, may be above 60°C, may be above 80°C, or may be above 100°C. By using a higher heating temperature, the adhesion can be increased by a shorter treatment time. The heating time is not particularly limited, for example, it may be less than 1 hour, may be less than 30 minutes, may be less than 10 minutes, or may be less than 5 minutes. Alternatively, a longer heating treatment may be performed within the limit that no significant thermal degradation occurs to the adhesive sheet or the adherend. Furthermore, the heating treatment may be performed once or in multiple times.

(Adhesive sheet attached to substrate) When the adhesive sheet disclosed here is in the form of an adhesive sheet attached to substrate, the thickness of the adhesive sheet may be, for example, less than 1000 μm, less than 600 μm, less than 350 μm, or less than 250 μm. From the perspective of miniaturization, lightness, and thinness of products to which the adhesive sheet is applied, in some embodiments, the thickness of the adhesive sheet may be, for example, less than 200 μm, less than 175 μm, less than 140 μm, less than 120 μm, or less than 110 μm. In addition, from the perspective of operability, the thickness of the adhesive sheet may be, for example, more than 10 μm, more than 25 μm, more than 50 μm, more than 80 μm, more than 100 μm, or more than 130 μm. There is no particular upper limit on the thickness of the adhesive sheet. Furthermore, the thickness of the adhesive sheet refers to the thickness of the portion attached to the adherend. For example, in the adhesive sheet 1 of the structure shown in FIG. 1 , it refers to the thickness from the adhesive surface 21A of the adhesive sheet 1 to the second surface 10B of the substrate 10 , excluding the thickness of the peeling pad 31 .

<Adhesive sheet with peel-off liner> The adhesive sheet disclosed herein can be in the form of an adhesive product in which the surface (adhesive surface) of the adhesive layer abuts against the peel-off surface of the peel-off liner. Therefore, this specification can provide an adhesive sheet with peel-off liner (adhesive product) comprising any adhesive sheet disclosed herein and a peel-off liner having a peel-off surface abutting against the adhesive surface of the adhesive sheet.

The peeling pad is not particularly limited, and can be used, for example, a peeling pad having a peeling layer on the surface of a pad base material such as a resin film or paper (which may be a paper laminated with a resin such as polyethylene), or a peeling pad including a resin film formed using a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.). In terms of excellent surface smoothness, it can be well used as a peeling pad having a peeling layer on the surface of a resin film as a pad base material, or a peeling pad including a resin film formed using a low-adhesion material. The resin film is not particularly limited as long as it can protect the adhesive layer, and examples thereof include polyethylene (PE) film, polypropylene (PP) film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, etc. The release layer can be formed by using, for example, a known release agent such as a polysilicone release agent, a long-chain alkyl release agent, an olefin release agent, a fluorine release agent, a fatty amide release agent, molybdenum sulfide, and silica powder.

<Application> The adhesive sheet provided by this specification can suppress the adhesive force to a lower level within a short time at room temperature after being attached to an adherend, for example. The above-mentioned adhesive sheet can exert good secondary processing properties during the period of suppressing the above-mentioned adhesive force to a lower level, so it can help suppress the yield or improve the quality of the product containing the adhesive sheet. In addition, the above-mentioned adhesive sheet can significantly increase the adhesive force by aging (which can be heating, time, a combination of the above, etc.). For example, after being attached to an adherend, by heating at the desired time, the adhesive sheet can be firmly attached to the adherend. According to this usage pattern, for example, in the manufacture of electronic devices such as portable electronic devices, or the manufacture of automobiles or home appliances, which includes the step of attaching the adhesive sheet to the adherend, the degree of freedom of operation of the adhesive sheet is increased. Therefore, the above-mentioned adhesive sheet can be well used as a bonding material in, for example, electronic devices, automobiles, home appliances, etc. In addition, it can also be well used for optical purposes such as bonding optical films used in image display devices such as liquid crystal displays, plasma displays, organic EL displays, etc. The adhesive sheet disclosed here can also be a structure using the above-mentioned optical film as a substrate (support substrate).

As can be understood from the above description and the following examples, the matters disclosed in this specification include the following contents. [1] An adhesive sheet comprising an adhesive layer, wherein the adhesive layer comprises a polymerized reaction product of the following composition, the composition comprising: (A) at least one of a monomer having an aromatic ring and an oligomer containing a repeating unit having an aromatic ring, and (B) a monomer having a hydroxyl group or a carboxyl group, and the glass transition temperature Tg _A based on the composition of the monomer components constituting the adhesive layer is higher than -3°C and is lower than 40°C. [2] An adhesive sheet as described in [1] above, wherein the composition at least comprises the monomer having an aromatic ring as the above (A). [3] The adhesive sheet as described in [2] above, wherein the composition comprises at least one selected from the group consisting of benzyl acrylate, ethoxylated phenylphenol acrylate, diphenylmethyl acrylate and phenoxybenzyl acrylate as the monomer having an aromatic ring. [4] The adhesive sheet as described in any one of [1] to [3] above, wherein 55% by weight or more of the monomer components constituting the adhesive layer are monomers having an aromatic ring. [5] The adhesive sheet as described in any one of [1] to [4] above, wherein more than 50% by weight of the monomers contained in the composition are acrylic monomers. [6] The adhesive sheet as described in any one of [1] to [5] above, wherein the composition comprises at least the oligomer containing repeating units having an aromatic ring as the above (A). [7] The adhesive sheet as described in [6] above, wherein the composition comprises a styrene oligomer as the oligomer containing a repeating unit having an aromatic ring. [8] The adhesive sheet as described in any one of [1] to [7] above, wherein the monomer having a hydroxyl group or a carboxyl group in (B) is an acrylic monomer. [9] The adhesive sheet as described in any one of [1] to [8] above, wherein the composition further comprises an alkyl (meth)acrylate having a homopolymer glass transition temperature of -40°C or less. [10] The adhesive sheet as described in any one of [1] to [9] above, wherein the composition further comprises N-vinyl cyclic amide. [11] An adhesive sheet as described in any one of the above [1] to [10], wherein the adhesive force N1 after being attached to a stainless steel plate and being kept at 23°C for 30 minutes is less than 5 N/20 mm. [12] An adhesive sheet as described in any one of the above [1] to [11], wherein the adhesive force N2 after being attached to a stainless steel plate and being heated at 80°C for 5 minutes and being kept at 23°C for 30 minutes is at least twice the adhesive force N1. [13] An adhesive composition for preparing an adhesive layer of an adhesive sheet as described in any one of the above [1] to [12]. [14] An adhesive composition comprising a polymerized product of a composition comprising: (A) at least one of a monomer having an aromatic ring and an oligomer containing a repeating unit having an aromatic ring, and (B) a monomer having a hydroxyl group or a carboxyl group, wherein the glass transition temperature Tg _C of the monomer components constituting the adhesive composition is higher than -3°C and is lower than 40°C. [Example]

Hereinafter, several embodiments of the present invention will be described, but it is not intended to limit the present invention to the specific embodiments. Furthermore, "parts" and "%" in the following description are by weight unless otherwise specified.

<Preparation of Adhesive Compositions C1 to C6> Under a nitrogen atmosphere, a mixture of monomers and photoinitiators of the types and amounts shown in Table 1 was irradiated with ultraviolet light to partially polymerize the monomers contained in the mixture, and then a mixed styrene oligomer was further added to the amounts of crosslinking agents (multifunctional monomers) and adhesive compositions C1 and C5 shown in Table 1 to prepare adhesive compositions C1 to C6. In addition, the values in parentheses in Table 1 and Examples 1 and 5 represent the weight fraction [%] of each monomer and styrene oligomer relative to the total amount of the monomers and oligomers used.

<Preparation of Adhesive Sheet> (Example 1) Prepare two types of peeling pads R1 and R2 in which one side of a polyester film is formed into a peeling surface using a silicone-based peeling treatment agent. As peeling pad R1, "DIAFOIL MRF" (thickness 38 μm) manufactured by Mitsubishi Resin Co., Ltd. is used. As peeling pad R2, "DIAFOIL MRE" (thickness 38 μm) manufactured by Mitsubishi Resin Co., Ltd. is used. Adhesive composition C1 is applied to the peeling surface of the peeling pad R1 to form a coating layer with a thickness of 100 μm. Next, the peelable liner R2 is covered on the surface of the coating layer in such a manner that the peelable surface thereof becomes the side of the coating layer to block the air, and the coating layer is hardened to form an adhesive layer by irradiating ultraviolet rays with an illumination of 3 mW/cm ² for 360 seconds using a chemical light lamp manufactured by Toshiba. In this way, an adhesive sheet of Example 1 including the adhesive layer is prepared. Furthermore, the above-mentioned illumination value is a measured value measured using an industrial UV tester with a peak sensitivity wavelength of about 350 nm (manufactured by TOPCON, trade name "UVR-T1", light receiving part model UD-T36).

(Examples 2 to 6) Examples 2 to 6 were prepared in the same manner as the adhesive sheet of Example 1 except that adhesive compositions C2 to C6 were used instead of adhesive composition C1.

<Adhesion to SUS> The adhesive sheets of each example were cut together with the peeling pad into pieces with a width of 20 mm as test pieces, and the SUS plate (SUS304BA plate) cleaned with toluene was used as the adherend. The initial adhesion and the adhesion after heating were measured according to the following procedure. (Measurement of initial adhesion (N1)) Under a standard environment of 23°C and 50%RH, the peeling pad covering the adhesive surface of each test piece was peeled off, and a 2 kg roller was moved back and forth once to press the exposed adhesive surface against the adherend. After the test piece pressed against the adherend is placed in the above standard environment for 30 minutes, a universal tensile compression tester (device name "tensile compression tester, TCM-1kNB" manufactured by Minebea) is used to measure the 180° peeling adhesion (relative to the above stretching resistance) under the conditions of a peeling angle of 180 degrees and a stretching speed of 300 mm/min in accordance with JIS Z0237. The measurement is performed 3 times, and the average value is taken as the initial adhesion (N1) [N/20 mm]. (Measurement of adhesion after heating (N2)) The test piece pressed against the adherend in the same manner as the initial adhesion was heated at 80°C for 5 minutes, and then placed in the above standard environment for 30 minutes, and the 180° peel adhesion was measured in the same manner. The measurement was performed 3 times, and the average value was taken as the adhesion after heating (N2) [N/20 mm].

<Adhesion increase ratio (N2/N1)> Based on the initial adhesion (N1) and the adhesion after heating (N2) obtained by the above measurement, the adhesion increase ratio (N2/N1) is calculated.

The obtained results are shown in Table 1.

[Table 1] Table 1 example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Single [unit] n-Butyl acrylate 44 (24.4) twenty two twenty four 44 (36.7) 44 2-Ethylhexyl acrylate twenty three 4-Hydroxybutyl acrylate 2 (1.1) 1 1 1 2 (1.7) 2 acrylic acid 1 N-vinyl-2-pyrrolidone 10 (5.6) 5 5 2 10 (8.3) 10 BZ 44 (24.4) twenty two twenty four twenty three 44 (36.7) 44 A-LEN-10 50 46 50 Oligomers[parts] Styrene oligomers 80 (44.4) 20 (16.7) Tg _A [℃] twenty one 2 0 -5.2 -7.6 -twenty two Ratio of monomer containing aromatic ring in monomer component [wt%] 69 72 70 73 53 44 Crosslinking agent [parts] DPHA 0.05 0.05 0.05 0.05 0.05 0.05 Photoinitiator [unit] Omnirad 184 0.05 0.05 0.05 0.05 0.05 0.05 Omnirad 651 0.05 0.05 0.05 0.05 0.05 0.05 Initial adhesion (N1) [N/20 mm] 0.4 2.9 0.9 14.5 18.6 9.9 Adhesion after heating (N2) [N/20 mm] 14.6 twenty one 8.5 15.6 26.8 13.5 Adhesion force increase ratio (N2/N1) 36.5 7.2 9.4 1.1 1.4 1.4 •BZA: Benzyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "viscose #160", Tg 11°C •A-LEN-10: o-Ethoxylated phenylphenol acrylate, manufactured by Shin-Nakamura Industry Co., Ltd., Tg 33°C •Styrene oligomer: manufactured by Yasuhara Chemical Co., Ltd., trade name "YS resin SX-100", Mw about 2500, Tg 100°C •DPHA: Dipentaerythritol hexaacrylate, manufactured by Nippon Kayaku Co., Ltd., trade name "KAYARAD DPHA" •Omnirad 184: 1-Hydroxycyclohexyl-phenyl-ketone, manufactured by IGM Regins Co., Ltd. •Omnirad 651: 2,2-Dimethoxy-1,2-diphenylethane-1-one, manufactured by IGM Regins Co., Ltd.

In addition, when calculating the above Tg _A , the values listed in the columns of Table 1 are used as the glass transition temperatures of the homopolymers of the aromatic ring-containing monomers. The styrene oligomers used in Examples 1 and 5 are homopolymers of styrene, and their Tg is 100°C. As the glass transition temperatures of the homopolymers of other monomers, the following values are used. n-Butyl acrylate: -55°C, 2-ethylhexyl acrylate: -70°C, 4-hydroxybutyl acrylate: -32°C, acrylic acid: 105°C, N-vinyl-2-pyrrolidone: 54°C.

As shown in Table 1, it was confirmed that the adhesive sheets of Examples 1 to 3 showed good low adhesion at the initial stage and the adhesive force increased significantly by heating, compared with the adhesive sheets of Examples 4 to 6 whose glass transition temperature Tg _A based on the composition of the monomer components constituting the adhesive layer was -3°C or less. The adhesive sheet of Example 1 obtained particularly good results.

The specific examples of the present invention have been described in detail above, but these are only examples and do not limit the scope of the patent application. The technology described in the scope of the patent application includes various changes and modifications of the specific examples described above.

1: Adhesive sheet 2: Adhesive sheet 3: Adhesive sheet 10: Support substrate 10A: First side 10B: Second side 21: Adhesive layer (first adhesive layer) 21A: Adhesive surface (first adhesive surface) 21B: Adhesive surface (second adhesive surface) 22: Adhesive layer (second adhesive layer) 22A: Adhesive surface (second adhesive surface) 31: Peel-off pad 32: Peel-off pad 100: Adhesive sheet with peel-off pad (adhesive product) 200: Adhesive sheet with peel-off pad (adhesive product) 300: Adhesive sheet with peel-off pad (adhesive product)

FIG. 1 is a cross-sectional view schematically showing the structure of an adhesive sheet in one embodiment. FIG. 2 is a cross-sectional view schematically showing the structure of an adhesive sheet in another embodiment. FIG. 3 is a cross-sectional view schematically showing the structure of an adhesive sheet in another embodiment.

1: Adhesive sheet

10: Support substrate

10A: First side

10B: Second side

21: Adhesive layer (first adhesive layer)

21A: Adhesive surface (first adhesive surface)

31: Peel off the liner

100: Adhesive sheet with peel-off liner (adhesive product)

Claims (9)

An adhesive sheet includes an adhesive layer, wherein the adhesive layer includes a polymerized reaction product of the following composition, wherein the composition includes: (A) at least one of a monomer having an aromatic ring and an oligomer containing a repeating unit having an aromatic ring, and (B) a monomer having a hydroxyl group or a carboxyl group, wherein the glass transition temperature Tg _A of the monomer components constituting the adhesive layer is higher than -3°C and lower than 40°C, and 35% by weight to 90% by weight of the monomer components constituting the adhesive layer are monomers having an aromatic ring, and the adhesive sheet has an adhesion force N2 of 3N/20mm or more after being attached to a stainless steel plate and heated at 80°C for 5 minutes and then at 23°C for 30 minutes. As in the adhesive sheet of claim 1, the composition at least comprises the monomer having an aromatic ring as the above-mentioned (A). As in claim 2, the adhesive sheet, wherein the composition comprises at least one selected from the group consisting of benzyl acrylate, ethoxylated phenylphenol acrylate, diphenyl methyl acrylate and phenoxybenzyl acrylate as the monomer having an aromatic ring. An adhesive sheet as claimed in any one of claims 1 to 3, wherein 55% by weight or more and 90% by weight of the monomer components constituting the adhesive layer are monomers having an aromatic ring. As in any one of claims 1 to 3, the adhesive sheet, wherein more than 50% by weight of the monomers contained in the above composition are acrylic monomers. As in any one of claims 1 to 3, the adhesive sheet, wherein the composition at least comprises the oligomer containing repeating units having an aromatic ring as the above (A). As in claim 6, the adhesive sheet, wherein the composition comprises styrene oligomer as the oligomer containing repeating units having an aromatic ring. An adhesive sheet as claimed in any one of claims 1 to 3, wherein the composition further comprises an alkyl (meth)acrylate having a homopolymer glass transition temperature of below -40°C. If the adhesive sheet of any of claim items 1 to 3 has an adhesive force N1 of less than 5N/20mm after being attached to a stainless steel plate and at 23°C for 30 minutes, and the adhesive force N2 after being attached to a stainless steel plate and heated at 80°C for 5 minutes and then at 23°C for 30 minutes is more than twice the above adhesive force N1.