JP7543945B2 - Adhesive sheet, laminate, optical device, and image display device - Google Patents

Description

The present invention relates to an adhesive sheet, a laminate including the adhesive sheet, an optical device, and an image display device.

Traditionally, input devices that are used in combination with display devices such as liquid crystal displays (LCDs) or display devices such as touch panels have been widely used. In the manufacture of these display devices and input devices, a transparent adhesive sheet is used when bonding optical members. A transparent adhesive sheet is also used when bonding the display device and the input device.

After optical components are bonded together with an adhesive sheet, there is a demand to re-attach the adhesive sheet, i.e., to rework (re-peel off) the adhesive sheet in order to adjust the position of the optical components or to remove foreign matter such as air bubbles between the components. For this reason, development of adhesive sheets with improved reworkability is also underway. For example, Patent Documents 1 to 3 disclose technologies that can impart reworkability to adhesive sheets by incorporating particles into the adhesive layer.

International Publication No. 2019/239616 JP 2015-3943 A JP 2015-3944 A

However, while the techniques disclosed in Patent Documents 1 to 3 can impart reworkability to pressure-sensitive adhesive sheets, the inclusion of particles increases haze and impairs transparency, limiting their use in optical applications. There is a strong demand for pressure-sensitive adhesive sheets that have both reworkability and transparency, but because there is a trade-off between the two, it has not been easy to obtain a pressure-sensitive adhesive sheet that is both highly transparent and has excellent reworkability.

The present invention has been made in view of the above, and aims to provide an adhesive sheet that is excellent in reworkability and has high transparency, a laminate that includes the adhesive sheet, and an optical device and an image display device.

As a result of extensive research into achieving the above objective, the inventors discovered that the above objective could be achieved by forming an adhesive sheet from specific components, leading to the completion of the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
In a pressure-sensitive adhesive sheet formed from a cured product of a pressure-sensitive adhesive composition,
The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D),
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group having 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group,
The crosslinkable (meth)acrylic copolymer (A) contains 50 to 95% by mass of the (meth)acrylic ester unit (a) and 1 to 50% by mass of the monomer unit (b),
The methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
A pressure-sensitive adhesive sheet that satisfies the following physical properties (1), (2), and (3).
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.
Physical property (2): The adhesive sheet is attached to a glass plate and heat-treated at 100° C. and 0.5 MPa for 30 minutes. The adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more.
Physical property (3): Haze measured in accordance with JIS K 7136 is 0 to 2%.
Item 2
Item 2. The pressure-sensitive adhesive sheet according to item 1, wherein the weight average molecular weight of the methyl methacrylate polymer (B) is 1,000 to 10,000.
Item 3
Item 3. The pressure-sensitive adhesive sheet according to item 1 or 2, wherein the (meth)acrylic resin particles (C) have an average particle size of 0.1 to 5 μm.
Item 4
Item 4. The pressure-sensitive adhesive sheet according to any one of items 1 to 3, wherein the refractive index difference between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) is 0 to 0.05.
Item 5
Item 5. The pressure-sensitive adhesive sheet according to any one of items 1 to 4, wherein the crosslinking agent (D) comprises one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate.
Item 6
Item 6. A laminate comprising the pressure-sensitive adhesive sheet according to any one of items 1 to 5 and an adherend.
Item 7
Item 7. An optical device comprising the laminate according to item 6.
Item 8
Item 7. An image display device comprising the laminate according to item 6.

The adhesive sheet of the present invention has excellent reworkability and high transparency.

1 is a schematic diagram showing an example of an embodiment of a pressure-sensitive adhesive sheet with a release sheet.

The embodiments of the present invention will be described in detail below. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "consist essentially of" and "consist only of". In addition, in this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

1. Pressure-sensitive adhesive sheet The pressure-sensitive adhesive sheet of the present invention is formed from a cured product of a pressure-sensitive adhesive composition. In other words, the pressure-sensitive adhesive sheet of the present invention is obtained by curing the pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D). The pressure-sensitive adhesive sheet of the present invention also has the physical properties (1), (2), and (3) described below.

The adhesive sheet of the present invention has excellent reworkability (i.e., position adjustment ability) and also has high transparency. Furthermore, the adhesive sheet of the present invention has an initial adhesive strength suitable for reworkability, and also has a property that allows the adhesive strength to be increased by heating after bonding adherends together (so-called heat adhesion). This makes it possible for the adhesive sheet of the present invention to firmly bond adherends together.

<Crosslinkable (meth)acrylic copolymer (A)>
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group with 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group. The terms "unit" and "monomer unit" in the (meth)acrylic ester units (a) refer to repeating units constituting a polymer. Hereinafter, the (meth)acrylic ester units (a) having an alkyl group with 4 to 10 carbon atoms will be referred to simply as "(meth)acrylic ester units (a)" and the monomer units (b) having a carboxy group and/or a hydroxyl group will be referred to simply as "monomer units (b)."

In addition, in this specification, "(meth)acrylic" means "acrylic" or "methacrylic", "(meth)acrylate" means "acrylate" or "methacrylate", and "(meth)allyl" means "allyl" or "methallyl".

The (meth)acrylic ester unit (a) is a repeating unit derived from a (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms. Examples of the (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms include a wide variety of known (meth)acrylic ester compounds, specifically, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, and the like. It is preferable that the (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms does not have a hydroxyl group or a carboxy group.

In the (meth)acrylic ester unit (a), the alkyl group preferably has 4 to 8 carbon atoms, and more preferably has 4 to 6 carbon atoms.

The (meth)acrylic ester unit (a) contained in the crosslinkable (meth)acrylic copolymer (A) may be of only one type, or may contain two or more types.

In the crosslinkable (meth)acrylic copolymer (A), the content of the (meth)acrylic ester unit (a) is 50% by mass or more and 95% by mass or less. In this case, the pressure-sensitive adhesive sheet can have the desired reworkability and transparency and satisfies the physical properties (1) to (3). If the content of the (meth)acrylic ester unit (a) is less than 50% by mass, the initial adhesive performance (adhesive performance before heat treatment) of the pressure-sensitive adhesive sheet may deteriorate. In terms of the reworkability and transparency of the pressure-sensitive adhesive sheet being more easily improved, the content of the (meth)acrylic ester unit (a) in the crosslinkable (meth)acrylic copolymer (A) is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% by mass or more, and particularly preferably 70% by mass or more. In addition, in order to more easily improve the reworkability and transparency of the pressure-sensitive adhesive sheet, the content of (meth)acrylic ester units (a) in the crosslinkable (meth)acrylic copolymer (A) is preferably 94% by mass or less, more preferably 93% by mass or less, even more preferably 92% by mass or less, and particularly preferably 90% by mass or less.

In the present invention, the content of each constituent unit in the crosslinkable (meth)acrylic copolymer (A) can be considered to be equal to the amount of polymerizable monomer derived from the corresponding constituent unit used when producing the crosslinkable (meth)acrylic copolymer (A).

Monomer unit (b) is a repeating unit derived from a monomer having a carboxy group and/or a hydroxyl group.

The monomer having a carboxy group can be, for example, a wide variety of known polymerizable monomers containing a carboxy group, specifically acrylic acid, methacrylic acid, etc.

Examples of monomers having a hydroxyl group include a wide variety of known hydroxyl group-containing polymerizable monomers, specifically 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, polyalkylene glycol mono(meth)acrylate, etc.

The crosslinkable (meth)acrylic copolymer (A) may contain, as the monomer unit (b), both a monomer unit having a carboxy group and a monomer unit having a hydroxyl group, or may contain only one of them. When the monomer unit (b) contains both a monomer unit having a carboxy group and a monomer unit having a hydroxyl group, the content ratio of these is not particularly limited, and the desired adhesive sheet can be obtained at any content ratio.

In the crosslinkable (meth)acrylic copolymer (A), the content of the monomer unit (b) is 1% by mass or more and 50% by mass or less. If the content of the monomer unit (b) is less than 1% by mass, the initial adhesive performance (adhesive performance before heat treatment) of the adhesive sheet deteriorates, and if it exceeds 50% by mass, the initial adhesive strength of the adhesive sheet becomes too large, making it impossible to obtain the desired reworkability. In order that the adhesive sheet is likely to have excellent reworkability and transparency, the content of the monomer unit (b) in the crosslinkable (meth)acrylic copolymer (A) is preferably 1.5% by mass or more, more preferably 2% by mass or more, and even more preferably 2.5% by mass or more. In addition, in order that the adhesive sheet is likely to have excellent reworkability and transparency, the content of the monomer unit (b) in the crosslinkable (meth)acrylic copolymer (A) is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

The crosslinkable (meth)acrylic copolymer (A) may contain other structural units other than the (meth)acrylic ester unit (a) and the monomer unit (b) as long as the effect of the present invention is not impaired. Examples of other structural units include a wide range of structural units derived from compounds that are copolymerizable with the (meth)acrylic ester compound. Specific examples of such compounds include (meth)acrylic ester compounds having 3 or less carbon atoms (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, etc.), (meth)acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinylpyrrolidone, vinylpyridine, etc., and also include amino group-containing (meth)acrylic esters, glycidyl group-containing (meth)acrylic esters, alkoxyalkyl group-containing (meth)acrylic esters, etc.

When the crosslinkable (meth)acrylic copolymer (A) contains the other structural units, the content is 15% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total mass of the crosslinkable (meth)acrylic copolymer (A). The crosslinkable (meth)acrylic copolymer (A) may be composed of only (meth)acrylic ester units (a) and monomer units (b) (i.e., the content of the other structural units in the crosslinkable (meth)acrylic copolymer (A) may be 0% by mass).

In the crosslinkable (meth)acrylic copolymer (A), the order of arrangement of each constituent unit is not particularly limited, and it is possible to form, for example, a random copolymer, a block copolymer, a graft copolymer, etc., and a random copolymer is preferable in terms of ease of production.

The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. For example, the weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is preferably 100,000 to 2,000,000, and more preferably 200,000 to 1,500,000, in order to keep the initial adhesive strength of the adhesive sheet low while making it easy to increase the adhesive strength after heating. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer means the value before crosslinking with a crosslinking agent described later. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is a value measured by gel permeation chromatography (GPC) and calculated based on polystyrene standards.

The pressure-sensitive adhesive composition may contain only one type of crosslinkable (meth)acrylic copolymer (A), or may contain two or more types.

The method for producing the crosslinkable (meth)acrylic copolymer (A) is not particularly limited, and the crosslinkable (meth)acrylic copolymer (A) can be obtained, for example, by a production method using a known polymerization method. The crosslinkable (meth)acrylic copolymer (A) can also be obtained from commercial products, etc.

The refractive index of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. In terms of increasing the transparency of the pressure-sensitive adhesive sheet, the refractive index of the crosslinkable (meth)acrylic copolymer (A) is preferably 1.45 to 1.50, and more preferably 1.46 to 1.49. The refractive index of the crosslinkable (meth)acrylic copolymer (A) referred to here indicates the value measured by Method A described in JIS K 7142 (2014) "Plastics - Determination of refractive index".

<Methyl methacrylate polymer (B)>
The methyl methacrylate polymer (B) is a polymer obtained by polymerizing a polymerizable monomer M mainly composed of methyl methacrylate (MMA). The polymerizable monomer M preferably contains 50% by mass or more of MMA, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the polymerizable monomer M contains a polymerizable monomer other than MMA, the type is not particularly limited. The polymerizable monomer M may be only MMA. In this case, the inclusion of a monomer inevitably contained in MMA is permitted.

The weight average molecular weight of the methyl methacrylate polymer (B) is not particularly limited. For example, the weight average molecular weight of the methyl methacrylate polymer (B) is preferably 1,000 to 10,000, in that the reworkability of the pressure-sensitive adhesive sheet is easily improved and haze can be further reduced. The weight average molecular weight of the methyl methacrylate polymer (B) is a value measured by gel permeation chromatography (GPC) and calculated based on polystyrene standards.

The methyl methacrylate polymer (B) may have either a non-crosslinked structure or a crosslinked structure.

The adhesive composition may contain only one type of methyl methacrylate polymer (B), or may contain two or more types.

The method for producing the methyl methacrylate polymer (B) is not particularly limited, and for example, the methyl methacrylate polymer (B) can be obtained by a production method using a known polymerization method. The methyl methacrylate polymer (B) can also be obtained from commercial products, etc.

<(Meth)acrylic resin particles (C)>
The (meth)acrylic resin particles (C) are a fine particle material containing a (meth)acrylic resin as a main component.

In the (meth)acrylic resin particles (C), the type of (meth)acrylic resin is not particularly limited, and a wide variety of known (meth)acrylic resins can be exemplified. Examples of (meth)acrylic resins include polymers of (meth)acrylic acid esters. Specific examples of such (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate, as well as the above-mentioned (meth)acrylic ester compounds having an alkyl group with 4 to 10 carbon atoms, hydroxyalkyl (meth)acrylate (having an alkyl carbon number of, for example, 2 to 10), and glycidyl (meth)acrylate. Among these, the (meth)acrylic resin is preferably a methyl (meth)acrylate polymer, in that it is easy to impart reworkability to the pressure-sensitive adhesive sheet and to reduce haze.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) may be a homopolymer or a copolymer. When the (meth)acrylic resin is a copolymer, examples include polymers containing two or more of the above-mentioned (meth)acrylic ester units, and the (meth)acrylic resin may also be a copolymer of a (meth)acrylic ester and a polymerizable monomer other than the (meth)acrylic ester. Examples of polymerizable monomers other than the (meth)acrylic ester include styrene, α-methylstyrene, maleic anhydride, (meth)acrylonitrile, vinyl acetate, vinyl chloride, vinylpyrrolidone, and vinylpyridine.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) is preferably a homopolymer of a (meth)acrylic acid ester, a copolymer of a (meth)acrylic acid ester, or a copolymer of a (meth)acrylic ester and a polymerizable monomer other than the (meth)acrylic ester, and more preferably a homopolymer of a (meth)acrylic acid ester or a copolymer of a (meth)acrylic acid ester. Among these, it is particularly preferable that the (meth)acrylic resin particles (C) are crosslinked or non-crosslinked polymethyl methacrylate particles, in that the refractive index and haze can be easily adjusted.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) can have a crosslinked structure or a non-crosslinked structure. When the (meth)acrylic resin has a crosslinked structure, the crosslinked structure can be formed by a known crosslinking agent such as a polyfunctional polymerizable monomer.

The average particle size of the (meth)acrylic resin particles (C) is not particularly limited. In terms of improving the reworkability of the adhesive sheet and reducing haze, the average particle size of the (meth)acrylic resin particles (C) is preferably 0.1 to 5 μm, and more preferably 0.2 to 3 μm.

In this specification, the average particle size of the (meth)acrylic resin particles (C) means a value measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Specifically, one fine particle observed in a TEM image or SEM image of the pressure-sensitive adhesive sheet is randomly selected, and its maximum length (Dmax) and maximum perpendicular length (DV-max) are measured to calculate the geometric mean value of the fine particle (i.e., the value of (Dmax x DV-max) ^1/2 ). The geometric mean value of each of a total of 100 fine particles is calculated in the same manner, and the average value is determined as the average particle size of the (meth)acrylic resin particles (C) contained in the pressure-sensitive adhesive sheet. That is, the average particle size of the (meth)acrylic resin particles (C) means the number-average particle size. The maximum length (Dmax) is the maximum length at two points on the contour of the particle image, and the maximum perpendicular length (DV-max) is the shortest length between two straight lines parallel to the maximum length when the particle image is sandwiched between these two straight lines.

The refractive index of the (meth)acrylic resin particles (C) is not particularly limited. From the viewpoint of increasing the transparency of the adhesive sheet, the refractive index of the (meth)acrylic resin particles (C) is preferably 1.45 to 1.51, and more preferably 1.46 to 1.50.

More specifically, with regard to the refractive index of the (meth)acrylic resin particles (C), it is further preferable that the difference (absolute value) in the refractive index between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) contained in the pressure-sensitive adhesive composition is 0 to 0.05. In this case, the pressure-sensitive adhesive sheet can have better transparency.

The refractive index of the (meth)acrylic resin particles (C) referred to here is the value measured by method B described in JIS K 7142 (2014) "Plastics - Determination of refractive index." The refractive index of the crosslinkable (meth)acrylic copolymer (A) referred to here is the value measured by method A described in JIS K 7142 (2014) "Plastics - Determination of refractive index."

The adhesive composition may contain only one type of (meth)acrylic resin particles (C), or may contain two or more types.

The method for producing the (meth)acrylic resin particles (C) is not particularly limited, and the (meth)acrylic resin particles (C) can be produced, for example, by a method similar to a known method. The (meth)acrylic resin particles (C) can also be obtained from commercial products.

<Crosslinking Agent (D)>
The crosslinking agent (D) may be a wide variety of components capable of promoting the crosslinking reaction of the crosslinkable (meth)acrylic copolymer (A). In particular, the crosslinking agent may be a wide variety of components capable of reacting with a carboxy group or a hydroxyl group.

Such a crosslinking agent (D) can be selected from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds.

Among them, it is preferable that the crosslinking agent (D) contains one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate. In this case, the resulting pressure-sensitive adhesive sheet can exhibit excellent reworkability and tends to have high transparency. When the crosslinking agent (D) contains a metal chelate, it is preferable to use a crosslinking retarder described below in combination.

Examples of isocyanate compounds include polyisocyanates such as tolylene diisocyanate, isophorone diisocyanate, chlorophenylene diisocyanate, diphenylmethane diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and xylylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate and cyclohexylene diisocyanate; and aromatic isocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4'-diphenylmethane diisocyanate. The isocyanate compounds can be used alone or in combination of two or more different types. Examples of commercially available products include a tolylene diisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and a xylylene diisocyanate compound (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.).

Examples of epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexanone, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and sorbitol polyglycidyl ether. Commercially available epoxy compounds include, for example, TETRAD-C (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and TETRAD-X (manufactured by Mitsubishi Gas Chemical Co., Ltd.).

Examples of metal chelate compounds include known metal chelate compounds used in crosslinking reactions, and examples of commercially available products include Aluminum Chelate A (manufactured by Kawaken Fine Chemicals Co., Ltd.).

<Adhesive Composition>
As described above, the pressure-sensitive adhesive composition contains the crosslinkable (meth)acrylic copolymer (A), the methyl methacrylate polymer (B), the (meth)acrylic resin particles (C), and the crosslinking agent (D).

In the adhesive composition, the methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A). If the content of the methyl methacrylate polymer (B) per 100 parts by mass of the (meth)acrylic copolymer (A) is less than 1 part by mass, the initial adhesive strength of the adhesive sheet becomes too large and the desired reworkability cannot be obtained, and if the content exceeds 15 parts by mass, the haze increases and the transparency of the adhesive sheet deteriorates. The methyl methacrylate polymer (B) is preferably contained in an amount of 2 parts by mass or more per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A), more preferably 2.5 parts by mass or more, and even more preferably 3 parts by mass or more. In addition, the methyl methacrylate polymer (B) is preferably contained in an amount of 14 parts by mass or less per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A), more preferably 13 parts by mass or less, and even more preferably 12 parts by mass or less.

In the adhesive composition, the content of the (meth)acrylic resin particles (C) is not particularly limited, and can be, for example, 0.3 to 5 parts by mass, and preferably 0.5 to 3 parts by mass, per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A). In this case, the obtained adhesive sheet can have a small haze value while maintaining excellent reworkability.

In the pressure-sensitive adhesive composition, the content of the crosslinking agent (D) is not particularly limited, and can be, for example, 0.01 to 5 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A). In this case, the processability of the resulting pressure-sensitive adhesive sheet is likely to be improved. The content of the crosslinking agent (D) can be 0.05 to 3 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A).

As described above, the adhesive composition contains the crosslinkable (meth)acrylic copolymer (A), the methyl methacrylate polymer (B), the (meth)acrylic resin particles (C), and the crosslinking agent (D), and may also contain a solvent as necessary. When the adhesive composition contains a solvent, the coatability of the adhesive composition is improved, making it easier to form an adhesive sheet.

Examples of solvents include hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane; alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, and diacetone alcohol; ethers such as diethyl ether, diisopropyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, and ethyl butyrate; and polyols and derivatives thereof such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate.

The content of the solvent in the adhesive composition is not particularly limited, and is preferably 25 to 500 parts by mass, and more preferably 30 to 400 parts by mass, per 100 parts by mass of the crosslinkable (meth)acrylic copolymer. In addition, the content of the solvent relative to the total mass of the adhesive composition is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass.

The adhesive composition may contain one solvent or two or more solvents.

The adhesive composition may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Examples of other components include known components used as additives to adhesive compositions. Other components may be selected as necessary from, for example, crosslinking retarders, plasticizers, antioxidants, metal corrosion inhibitors, tackifiers, silane coupling agents, ultraviolet absorbers, and light stabilizers such as hindered amine compounds. Dyes and pigments may also be added for coloring purposes.

Examples of crosslinking retarders include acetylacetone. In particular, when the crosslinking agent (D) contains a metal chelate, it is preferable to use a crosslinking retarder in combination. Examples of plasticizers include non-functional acrylic polymers. Examples of non-functional acrylic polymers include polymers consisting of only acrylic monomer units that have no functional groups other than acrylate groups, and polymers consisting of acrylic monomer units that have no functional groups other than acrylate groups and non-acrylic monomer units that have no functional groups. Since non-functional acrylic polymers do not crosslink, they can improve step-following ability without affecting adhesion.

Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. These antioxidants may be used alone or in combination of two or more. As a metal corrosion inhibitor, benzoriazole-based resins are preferred because of their compatibility with the adhesive and their high effectiveness. Examples of the tackifier include rosin-based resins, terpene-based resins, terpene-phenol-based resins, coumarone-indene-based resins, styrene-based resins, xylene-based resins, phenol-based resins, and petroleum resins. Examples of the silane coupling agent include mercaptoalkoxysilane compounds (e.g., mercapto-substituted alkoxy oligomers, etc.). Examples of the ultraviolet absorbing agent include benzotriazole-based compounds, benzophenone-based compounds, and triazine-based compounds.

When the pressure-sensitive adhesive composition contains other components, the content ratio thereof is not particularly limited, and can be, for example, 15 parts by mass or less, preferably 10 parts by mass or less, per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A).

The method for preparing the adhesive composition is not particularly limited, and for example, any of the known methods for preparing adhesive compositions can be widely used.

<Constitution and properties of pressure-sensitive adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention (hereinafter, simply referred to as "pressure-sensitive adhesive sheet") is made of the cured product of the pressure-sensitive adhesive composition described above. That is, the pressure-sensitive adhesive sheet of the present invention can be obtained by curing the pressure-sensitive adhesive composition described above. The cured product of the pressure-sensitive adhesive composition can function as a pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet can be composed of, for example, only a pressure-sensitive adhesive layer. That is, the pressure-sensitive adhesive sheet can also be formed of only a cured product of the pressure-sensitive adhesive composition. The pressure-sensitive adhesive layer can have a single-layer structure, or can have a multilayer structure in which a plurality of single-layer pressure-sensitive adhesive layers are laminated. The pressure-sensitive adhesive sheet may be either a single-sided pressure-sensitive adhesive sheet or a double-sided pressure-sensitive adhesive sheet, and is preferably a double-sided pressure-sensitive adhesive sheet.

<Physical properties of adhesive sheet>
(Physical Properties 1)
The pressure-sensitive adhesive sheet satisfies the following physical property (1).
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.

In the physical property (1), when measuring the adhesive strength of the adhesive sheet to glass, the adhesive strength to glass is measured 1 minute after application to glass in accordance with the adhesive strength measurement method described in JIS Z 0237. More specifically, 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300) is applied to one side of the adhesive sheet, and then this is treated in an autoclave for 30 minutes at 100 ° C and 0.5 MPa (meaning gauge pressure). The adhesive sheet having a PET substrate on one side thus treated is applied to soda glass (Hiraoka Special Glass Manufacturing Co., Ltd., the pressure-bonded surface is the opposite side to the tin float). At this time, a measurement sample is prepared in accordance with the 180 ° peel adhesive strength measurement method described in JIS Z 0237, except that soda glass is used as the test plate. Then, the adhesive strength is measured 1 minute after application at a peel speed of 300 mm / min. This adhesive strength is the adhesive strength to glass in physical property (1).

In physical property (1), the adhesive strength to glass is preferably 0.05 N/25 mm or more, since this particularly improves reworkability. In addition, the adhesive strength to glass in physical property (1) is preferably 4.8 N/25 mm or less, more preferably 4.6 N/25 mm or less, and even more preferably 4.5 N/25 mm or less.

The adhesive strength to glass in property (1) can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of methyl methacrylate polymer (B), the average particle size and amount of (meth)acrylic resin particles (C), and the amount of crosslinking agent (D).

(Physical Properties 2)
The pressure-sensitive adhesive sheet satisfies the following physical property (2).
Physical property (2): The adhesive sheet is attached to a glass plate and heat-treated at 100° C. and 0.5 MPa for 30 minutes. The adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more.

In physical property (2), when measuring the adhesive strength of the adhesive sheet to glass, a measurement sample is prepared in the same manner as in physical property (1). This measurement sample is then treated in an autoclave at 100°C and 0.5 MPa (gauge pressure) for 30 minutes, and then allowed to stand in an environment of 23°C and 50% relative humidity for 2 hours. The adhesive strength is then measured at a peeling speed of 300 mm/min in the same manner as in physical property (1). This adhesive strength is regarded as the adhesive strength to glass in physical property (2).

In physical property (2), the adhesive strength to glass is preferably 10 N/25 mm or more, more preferably 15 N/25 mm or more, even more preferably 20 N/25 mm or more, and particularly preferably 25 N/25 mm or more, in order that the adhesive strength to the adherend after heat treatment is likely to increase. In addition, the adhesive strength to glass in physical property (2) is not particularly limited, and is preferably 50 N/25 mm or less, in order that, for example, displays and the like can be easily disposed of or disassembled.

The adhesive strength to glass in physical property (2) can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of methyl methacrylate polymer (B), the average particle size and amount of (meth)acrylic resin particles (C), and the amount of crosslinking agent (D).

(Physical Properties 3)
The pressure-sensitive adhesive sheet satisfies the following physical property (3).
Physical property (3): Haze measured in accordance with JIS K 7136 is 0 to 2%.

In the physical property (3), the haze of the adhesive sheet is measured in accordance with JIS K 7136. Specifically, a pair of transparent glass plates (S9112, manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1.2 mm is laminated with an adhesive sheet to prepare a laminated sample, and the haze is measured using the laminated sample in accordance with JIS K7136 (2000). A haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. can be used for this measurement. The laminated sample is prepared, for example, as follows. The release sheet on the light release side of the adhesive sheet with release sheet is peeled off and laminated to one transparent glass plate, and then the other transparent glass plate is laminated to the surface from which the release sheet (heavy release separator) on the heavy release side has been peeled off, so as to prevent air from being mixed in. This is then treated in an autoclave at 100°C and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23°C and 50% relative humidity to obtain a laminated sample.

In terms of physical property (3), the haze value is preferably 1.9% or less, and more preferably 1.8% or less, in that the transparency of the pressure-sensitive adhesive sheet is easily increased. The haze value may be 0%.

The haze value can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of the methyl methacrylate polymer (B), and the refractive index, average particle size, and amount of the (meth)acrylic resin particles (C).

Since the adhesive sheet has the above physical property (1), the initial adhesive strength is not too strong, and as a result, the adhesive sheet has excellent position adjustment ability (reworkability). Therefore, when the adhesive sheet of the present invention is used for bonding components together, such as for bonding optical components, the adhesive sheet can be easily peeled off from the optical component, making it easy to re-bond the components and less likely to leave adhesive residue from the adhesive sheet.

Since the adhesive sheet has the above physical property (2), the adhesive strength can be increased by bonding the members together and then heating them. This makes it possible to firmly bond the adherends together. In this way, the adhesive sheet of the present invention has succeeded in keeping the initial adhesive strength low while increasing the adhesive strength after heating, and thus combines two opposing adhesive properties.

Furthermore, since the pressure-sensitive adhesive sheet has the above-mentioned physical property (3), it has high transparency. Therefore, the pressure-sensitive adhesive sheet of the present invention is also suitable for use in optical applications and the like that require high transparency.

As described above, the adhesive sheet of the present invention has physical properties (1) to (3), and thus can impart reworkability to the adhesive sheet while also imparting high transparency, thereby achieving both transparency and reworkability of the adhesive sheet, which have traditionally been in a trade-off relationship. Furthermore, the adhesive sheet of the present invention does not peel off even after the passage of time after application, and has excellent stability over time.

<Other properties of the adhesive sheet>
The thickness of the pressure-sensitive adhesive sheet is not particularly limited as it can be appropriately set depending on the application, and is, for example, preferably 5 to 300 μm, more preferably 8 to 200 μm, and particularly preferably 10 to 150 μm.

The gel fraction of the adhesive sheet is not particularly limited and can be set appropriately depending on the components and types contained in the adhesive sheet. For example, the gel fraction of the adhesive sheet is 35 to 100%, preferably 40 to 95%, and more preferably 45 to 90%. Note that the above gel fraction is the gel fraction before the adhesive sheet is heated, but since the change in gel fraction before and after heating is small in the adhesive sheet of the present invention, it is preferable that the gel fraction of the adhesive sheet after heat treatment for 30 minutes under conditions of 100°C and 0.5 MPa is also within the above range.

The gel fraction of the adhesive layer is a value measured by the following method. First, about 0.1 g of the adhesive sheet (adhesive layer) is collected in a sample bottle, 30 ml of ethyl acetate is added, and the mixture is shaken for 24 hours. The contents of the sample bottle are then filtered through a 150 mesh stainless steel wire mesh, and the residue on the wire mesh is dried at 100° C. for 1 hour to measure the dry mass (g). The gel fraction is calculated from the obtained dry mass using the following formula 1.
Gel fraction (mass%)=(dry mass/collected mass of adhesive sheet)×100 Equation 1

<How to use the adhesive sheet>
The method of using the adhesive sheet of the present invention is not particularly limited, and for example, the same method of use as known adhesive sheets can be adopted.When the adhesive sheet of the present invention is the above-mentioned heat-adhesive sheet, the adhesive sheet can be used by contacting the adhesive sheet of the present invention with the surface of the adherend and then heating the adhesive sheet.By heating in this way, the adhesive sheet can be made to adhere to the adherend more closely.In addition, since the adhesive sheet has excellent reworkability, the position of the adhesive sheet before heating can be easily adjusted.

After contacting the adhesive sheet with the surface of the adherend, the adhesive sheet can be heated to, for example, 50 to 120°C, and the heating time can be set appropriately depending on the heating temperature, for example, 1 to 120 minutes. Pressure may be applied during the heat treatment, and it is preferable to apply a pressure of, for example, 0.2 to 0.9 MPa. By carrying out such a heat treatment, the adhesive strength of the adhesive sheet is significantly increased, and it adheres more firmly to the adherend.

<Adhesive sheet with release sheet>
As shown in Fig. 1, the pressure-sensitive adhesive sheet of the present invention can be formed into a pressure-sensitive adhesive sheet with a release sheet. The pressure-sensitive adhesive sheet with a release sheet 10 can have release sheets 12a and 12b on both surfaces of a pressure-sensitive adhesive layer 11 (pressure-sensitive adhesive sheet).

As the release sheet, for example, a wide variety of known release sheets can be used, including a release laminate sheet in which a release agent layer is formed on one side of a release sheet substrate, and other low-polarity substrates made of polyolefin films such as polyethylene films and polypropylene films. For example, paper and polymer films can be used as the release sheet substrate.

As the release agent constituting the release agent layer, for example, a general-purpose addition type or condensation type silicone-based release agent or a compound containing a long chain alkyl group is used. In particular, an addition type silicone-based release agent having high reactivity is preferably used. Specific examples of the silicone-based release agent include BY24-4527 and SD-7220 manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3600, KS-774, and X62-2600 manufactured by Shin-Etsu Chemical Co., Ltd. In addition, as the silicone-based release agent, it is also preferable to contain a silicone resin, which is an organosilicon compound having SiO ₂ units and (CH ₃ ) ₃ SiO _1/2 units or CH ₂ ═CH(CH ₃ )SiO _1/2 units in the silicone-based release agent. Specific examples of silicone resins include BY24-843, SD-7292, SHR-1404, etc. manufactured by Dow Corning Toray Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.

The peelable laminate sheet can be obtained commercially, for example, a heavy separator film made by Teijin DuPont Films Co., Ltd., which is a release-treated polyethylene terephthalate film, or a light separator film made by Teijin DuPont Films Co., Ltd., which is a release-treated polyethylene terephthalate film.

The adhesive sheet with release sheet preferably has a pair of release sheets with different release strengths on both surfaces of the adhesive sheet. That is, to facilitate peeling, it is preferable that the release sheets 12a and 12b have different releasability. If the releasability from one side is different from the releasability from the other, it becomes easier to peel off only the release sheet with the higher releasability (light release side) before the heavy release side.

<Applications of adhesive sheets>
The pressure-sensitive adhesive sheet of the present invention can be used for various applications, for example, for bonding optical members used in optical devices and the like.

Examples of optical components include components in optical products such as touch panels or image display devices. Examples of components in touch panels include an ITO film in which an ITO film is provided on a transparent resin film, ITO glass in which an ITO film is provided on the surface of a glass plate, a transparent conductive film in which a transparent resin film is coated with a conductive polymer, a hard coat film, and a fingerprint-resistant film.

Constituent members of image display devices include, for example, anti-reflection films, alignment films, polarizing films, retardation films, and brightness enhancement films used in liquid crystal display devices. The pressure-sensitive adhesive sheet of the present invention may also be used to bond modules together, such as a liquid crystal module and a touch panel module.

Specific examples of materials that can be bonded with an adhesive sheet include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, and cellulose acylate.

2. Method for producing the pressure-sensitive adhesive sheet The method for producing the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and a wide variety of known methods can be used.Among them, it is preferable to form the pressure-sensitive adhesive sheet by a production method including a step of forming a coating film by applying the above-mentioned pressure-sensitive adhesive composition on a release sheet, and a step of heating this coating film.In such a production method, when the pressure-sensitive adhesive composition contains a solvent, the solvent is removed in the heating step, and at the same time, the reaction of the crosslinkable (meth)acrylic copolymer and the crosslinking agent proceeds to form a cured product (pressure-sensitive adhesive layer).

The adhesive composition can be applied using a known coating device. Examples of coating devices include an applicator, blade coater, air knife coater, roll coater, bar coater, gravure coater, microgravure coater, rod blade coater, lip coater, die coater, curtain coater, etc.

The substrate used for applying the adhesive composition is not particularly limited. For example, the adhesive composition can be applied to various substrates such as a resin substrate or a glass substrate. For example, when obtaining an adhesive sheet with a release sheet, a release sheet can be selected as the substrate. The adhesive composition can also be applied directly onto the member to be adhered.

The thickness of the adhesive composition after application is not particularly limited and can be set appropriately depending on the desired thickness of the adhesive layer.

In the step of heating the coating film, the heating temperature is not particularly limited, and is preferably, for example, 50 to 150°C. The heating time can be appropriately adjusted depending on the heating temperature, the thickness of the coating film, and the content of the solvent in the adhesive composition, and can be, for example, 1 to 60 minutes. A known heating device such as a heating furnace or an infrared lamp can be used to heat the coating film. After heating, it is preferable to carry out an aging treatment in which the adhesive sheet is left to stand at a constant temperature for a certain period of time. The aging treatment can be carried out, for example, by leaving it to stand at 23°C for 7 days.

3. Laminate The laminate of the present invention comprises the pressure-sensitive adhesive sheet of the present invention described above and an adherend. When the pressure-sensitive adhesive sheet is a double-sided pressure-sensitive adhesive sheet, the adherend is preferably provided directly on both sides of the pressure-sensitive adhesive sheet. In this case, the laminate has a structure in which the adherend/pressure-sensitive adhesive sheet/adherend are laminated in this order. The adherend can be, for example, the optical member described above.

The laminate of the present invention can be used in a variety of applications, and can be suitably used in, for example, optical devices, image display devices, etc. In particular, since the laminate of the present invention is formed by bonding with a highly transparent adhesive sheet, it can further improve the design and visibility of the image when applied to optical devices, image display devices, etc.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[Synthesis of Crosslinkable (Meth)acrylic Copolymer A-1]
Monomers prepared by mixing butyl acrylate (BA), acrylic acid (AA) and methyl acrylate (MA) in a mass ratio of 87:3:10 were polymerized in ethyl acetate, a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile) by heating to 60° C. This resulted in a solution of a crosslinkable (meth)acrylic copolymer (A-1) (represented as “A-1” in Table 1) having a solid content concentration of 30% by mass and a weight average molecular weight of 740,000.

[Synthesis of Crosslinkable (Meth)acrylic Copolymer A-2]
A monomer mixture of BA, 2-hydroxyethyl acrylate (2HEA) and MA in a mass ratio of 70:20:10 was polymerized in ethyl acetate, a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile), by heating to 60° C. As a result, a solution of a crosslinkable (meth)acrylic copolymer (A-2) (shown as “A-2” in Table 1) having a solid content concentration of 35% by mass and a weight average molecular weight of 600,000 was obtained.

[Synthesis of methyl methacrylate polymer B-1]
A solution of methyl methacrylate (MMA) and a polymerization initiator AIBN dissolved in ethyl acetate was heated to 80° C. to polymerize, thereby obtaining a methyl methacrylate polymer (B-1) (represented as “B-1” in Table 1) having a weight average molecular weight of 5,000.

[Synthesis of methyl methacrylate polymer B-2]
A solution of methyl methacrylate (MMA) and a polymerization initiator AIBN dissolved in ethyl acetate was heated to 80° C. to polymerize, thereby obtaining a methyl methacrylate polymer (B-2) having a weight average molecular weight of 9,000.

Example 1
[Preparation of Pressure-Sensitive Adhesive Composition]
The raw materials containing 3 parts by mass of methyl methacrylate polymer (B-1), 1 part by mass of MX-80H3WT (average particle size 0.8 μm, manufactured by Soken Chemical Industries, Ltd.) as (meth)acrylic resin particles (C), 0.1 parts by mass and 0.5 parts by mass of an epoxy compound (Tetrad X, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and a metal chelate compound (Aluminum Chelate A, manufactured by Kawaken Fine Chemicals Co., Ltd.) as crosslinking agents, 5 parts by mass of acetylacetone (manufactured by Tokyo Chemical Industry Co., Ltd.) as a crosslinking retarder, and 0.5 parts by mass of a silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to ethyl acetate so that the concentration of the raw materials was 25% by mass, and stirred to prepare a pressure-sensitive adhesive composition a-1.

[Preparation of adhesive sheet]
The pressure-sensitive adhesive composition a-1 prepared as described above was uniformly applied with an applicator to the surface of a 50 μm-thick polyethylene terephthalate film (first release sheet, Oji F-Tex Co., Ltd., 50RL-07(2)) equipped with a release agent layer treated with a silicone-based release agent, so as to form a coating film with a coating thickness of 25 μm after drying. The coating film was dried at 100° C. for 3 minutes in an air-circulating constant temperature oven, thereby forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) on the surface of the first release sheet.

Next, a 38 μm-thick second release sheet (Oji F-Tex Co., Ltd., 38RL-07(L)) with a release strength different from that of the first release sheet was attached to the surface of the adhesive layer, and the sheet was left to cure for 14 days under conditions of 23°C and 50% relative humidity. This resulted in an adhesive sheet with release sheet having a first release sheet/adhesive sheet/second release sheet configuration in which the adhesive layer (adhesive sheet) is sandwiched between a pair of release sheets with different release strengths.

Example 2
An adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that the (meth)acrylic resin particles (C) were changed to MX-300 (average particle size 3 μm, manufactured by Soken Chemical & Engineering Co., Ltd.).

Example 3
Raw materials containing 10 parts by mass of methyl methacrylate polymer (B-2), 1.5 parts by mass of XX-5910 (average particle size 0.3 μm, manufactured by Sekisui Chemical Co., Ltd.) as (meth)acrylic resin particles (C), 0.1 part by mass of an isocyanate compound (Coronate L-55, manufactured by Tosoh Corporation) as a crosslinking agent, and 0.5 parts by mass of a silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) per 100 parts by mass of acrylic copolymer (A-2), were added to ethyl acetate so that the concentration of the raw materials was 27% by mass, and stirred to prepare a pressure-sensitive adhesive composition a-2.

Next, an adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that adhesive composition a-1 was replaced with adhesive composition a-2.

Example 4
An adhesive sheet with a release sheet was obtained in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were changed to BMSA-18GN (average particle size 0.8 μm, manufactured by Sekisui Chemical Co., Ltd.) and the amount used was changed to 2 parts by mass.

Example 5
A pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 4, except that the amount of the (meth)acrylic resin particles (C) used was changed to 0.5 parts by mass.

(Comparative Example 1)
An adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that the adhesive composition was prepared without using the (meth)acrylic resin particles (C).

(Comparative Example 2)
An adhesive sheet with a release sheet was obtained in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were replaced with melamine resin particles Eposter M30 (average particle size 3 μm, manufactured by Nippon Shokubai Co., Ltd.).

(Comparative Example 3)
An adhesive sheet with a release sheet was obtained in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were changed to MBX-20 (average particle size 20 μm, manufactured by Sekisui Chemical Co., Ltd.) and the amount used was changed to 1 part by mass.

[Physical Property 1: Adhesion to Glass]
The adhesive strength was measured according to the method for measuring adhesive strength described in JIS Z 0237. First, the release sheet on the light release side of the adhesive sheet with release sheet was peeled off and laminated with 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300), and then treated in an autoclave at 100°C and 0.5 MPa (gauge pressure) for 30 minutes to obtain an adhesive sheet having a PET substrate on one side. The release sheet on the heavy release side of this adhesive sheet having a PET substrate on one side was peeled off and laminated to soda glass (Hiraoka Special Glass Manufacturing Co., Ltd., the pressure-bonded surface was the opposite side to the tin float). At this time, a measurement sample was prepared according to the method for measuring 180° peel adhesive strength described in JIS Z 0237, except that soda glass was used as the test plate. Then, the adhesive strength was measured at a peel speed of 300 mm/min 1 minute after pressure bonding, and this adhesive strength was taken as the adhesive strength to glass in physical property (1).

[Physical Property 2: Adhesion to Glass]
A measurement sample was prepared in the same manner as in the physical property 1, up to the step of bonding to the test plate. After that, the measurement sample was treated for 30 minutes at 100°C and 0.5 MPa (gauge pressure) using an autoclave, and then left to stand for 2 hours in an environment of 23°C and 50% relative humidity. Then, the adhesive strength was measured at a peeling speed of 300 mm/min in the same manner as in the physical property (1), and this adhesive strength was defined as the adhesive strength to glass in the physical property (2).

[Physical property 3: Haze]
The haze of the adhesive sheet was measured in accordance with JIS K 7136. Specifically, a pair of transparent glass plates (S9112, manufactured by Matsunami Glass Industry Co., Ltd.) having a thickness of 1.2 mm was laminated with an adhesive sheet to prepare a laminated sample, and the laminated sample was used to measure the haze in accordance with JIS K7136 (2000). A haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measurement. The laminated sample was prepared as follows. First, the release sheet on the light release side of the adhesive sheet with a release sheet was peeled off and laminated to one transparent glass plate, and then the other transparent glass plate was laminated to the surface from which the release sheet (heavy release separator) on the heavy release side was peeled off so as not to allow air to be mixed in. This was treated in an autoclave under conditions of 100°C and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23°C and relative humidity of 50% to obtain a laminated sample.

[Weight average molecular weight]
The weight average molecular weights of the crosslinkable (meth)acrylic copolymer (A) and the methyl methacrylate polymer (B) were measured by gel permeation chromatography (GPC) under the following conditions.
Solvent: Tetrahydrofuran Column: Shodex KF801, KF803L, KF800L, KF800D (four columns manufactured by Showa Denko K.K. were used in combination)
Column temperature: 40°C
・Sample concentration: 0.5% by mass
Detector: RI-2031plus (JASCO)
Pump: RI-2080plus (JASCO)
・Flow rate (flow rate): 0.8ml/min
Injection volume: 10 μl
Calibration curve: Standard polystyrene Shodex standard polystyrene (manufactured by Showa Denko KK) A calibration curve using 10 samples with Mw=1,320 to 2,500,000 was used.

[Measurement of refractive index]
The refractive index of the crosslinkable (meth)acrylic copolymer (A) was measured in accordance with Method A described in JIS K 7142 (2014) "Plastics - Determination of refractive index". The refractive index of the (meth)acrylic resin particles (C) was measured in accordance with Method B described in JIS K 7142 (2014) "Plastics - Determination of refractive index".

(Evaluation of Adhesive Sheets)
The pressure-sensitive adhesive sheets obtained in each of the Examples and Comparative Examples were evaluated according to the following procedures.

[Position adjustment ability (reworkability)]
A test piece was obtained by cutting a pressure-sensitive adhesive sheet having a PET substrate on one side, obtained in the process of preparing a sample for measuring physical property (1), into a size of 50 mm x 60 mm. A laminate was prepared by pressing the pressure-sensitive adhesive sheet onto a float glass sheet (manufactured by Nippon Sheet Glass Co., Ltd.) measuring 30 mm x 40 mm (thickness 10 mm) so that the center of the float glass sheet and the center of the adhesive sheet overlapped each other. In an environment of 23°C and 50% relative humidity, the adhesive sheet was placed on a horizontal table so that the adhesive sheet side faced the table and pressure-bonded. Within one minute of bonding, the adhesive sheet protruding from the glass plate was removed. While lightly holding the glass plate with one hand, the glass plate was picked up with the other hand and peeled upward from the adhesive sheet. The peelability at this time was evaluated according to the following criteria.
◯: Easy to peel off and excellent reworkability.
×: Not peelable or difficult to peelable (for example, it can only be peeled off by placing the adhesive sheet side up and pulling up the adhesive sheet from the edge), and poor reworkability.

[Whether or not peeling occurs over time]
The laminate prepared in the process of evaluating the position adjustability (reworkability) was treated for 240 hours using a thermohygrostat at 65° C. (relative humidity 95%), and then left to stand for 60 minutes in an environment of 23° C. and 50% relative humidity. Thereafter, it was visually evaluated according to the following criteria.
○: No peeling or lifting occurs ×: Peeling or lifting occurs at the edges, etc.

[Image design and visibility]
The release sheet on the light release side of the adhesive sheet with release sheet was peeled off, and the adhesive sheet was laminated with 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300), and the adhesive sheet was cut into a size of 150 mm x 70 mm to obtain a test piece. Next, the release sheet on the heavy release side of this test piece was peeled off, and the entire surface of the exposed surface and the surface opposite to the black printed surface of a 150 mm x 70 mm (thickness 6 mm) float plate glass (manufactured by Nippon Sheet Glass Co., Ltd.) having a black printed surface were laminated using a hand roller to obtain a laminated sample. The obtained laminate was treated in an autoclave under conditions of 100 ° C. and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23 ° C. and relative humidity 50% to prepare an evaluation sample. Apart from this evaluation sample, a float plate glass similar to the float plate glass used to prepare the evaluation sample was prepared as a blank. The PET surface of the evaluation sample was visually compared with the glass surface opposite the black printed surface of the blank product, and the design and visibility of the image were evaluated based on the following criteria.
◯: Blackness and glossiness similar to that of the blank product.
△: Slightly less black and glossy than the blank product.
×: Inferior blackness and glossiness compared to the blank product.

Table 1 shows the preparation conditions for the adhesive sheets of each of the above-mentioned Examples and Comparative Examples, as well as the physical properties and evaluation results of each adhesive sheet. In Table 1, "(A)-(C) refractive index difference" refers to the refractive index difference (absolute value) between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C).

From Table 1, it can be seen that the adhesive sheets obtained in the examples have excellent reworkability and low haze, i.e., excellent transparency. Moreover, the adhesive sheets obtained in the examples did not peel off even after time had passed after lamination, and had excellent stability over time. Furthermore, the laminates produced using the adhesive sheets obtained in the examples were found to have excellent image design and visibility, making them suitable for use in image display devices, etc.

10: Adhesive sheet with release sheet 11: Adhesive layer 12a: Release sheet 12b: Release sheet

Claims (8)

In a pressure-sensitive adhesive sheet formed from a cured product of a pressure-sensitive adhesive composition,
The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D),
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group having 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group,
The crosslinkable (meth)acrylic copolymer (A) contains 50 to 95% by mass of the (meth)acrylic ester unit (a) and 1 to 50% by mass of the monomer unit (b),
The methyl methacrylate polymer (B) is not particulate,
The (meth)acrylic resin particles (C) are mainly composed of a methyl methacrylate polymer,
The methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
A pressure-sensitive adhesive sheet that satisfies the following physical properties (1), (2), and (3).
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.
Physical property (2): The adhesive sheet is attached to a glass plate and heat-treated at 100° C. and 0.5 MPa for 30 minutes. The adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more.
Physical property (3): Haze measured in accordance with JIS K 7136 is 0 to 2%. The adhesive sheet according to claim 1, wherein the weight average molecular weight of the methyl methacrylate polymer (B) is 1,000 to 10,000. The adhesive sheet according to claim 1 or 2, wherein the average particle size of the (meth)acrylic resin particles (C) is 0.1 to 5 μm. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the refractive index difference between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) is 0 to 0.05. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the crosslinking agent (D) comprises one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate. A laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 5 and an adherend. An optical device comprising the laminate according to claim 6. An image display device comprising the laminate according to claim 6.

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