Adhesive Sheet, Laminate, Optical Device, Image Display Device, and Method for Manufacturing the Same

Abstract

To provide an adhesive sheet which is excellent in reworkability and has high transparency, a laminate having the adhesive sheet, and an optical device and an image display device.SOLUTION: An adhesive sheet contains a cured product of an adhesive composition, wherein the adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), an oligomer (C) which has a specific glass transition point and is composed of a (meth)acrylic resin, and a crosslinking agent (D). The crosslinkable (meth)acrylic copolymer (A) is a polymer containing a (meth)acrylate unit (a) having an alkyl group having 4 to 10 carbon atoms, and a monomer unit (b) having a carboxy group and / or a hydroxyl group. The adhesive sheet has a predetermined adhesive force to glass, and has a haze of 0-2%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, a laminate including the adhesive sheet, an optical device, and an image display device. Furthermore, the present invention relates to a method for manufacturing an optical device and an image display device.

Background Art

[0002] Conventionally, display devices such as liquid crystal displays (LCDs) or input devices used in combination with display devices such as touch panels have been widely used. When bonding optical members in the manufacture of these display devices and input devices, a transparent adhesive sheet is used. Also, a transparent adhesive sheet is used when bonding a display device and an input device.

[0003] After bonding optical members with an adhesive sheet, there is a demand to rework the adhesive sheet, that is, to re-peel the adhesive sheet, in order to adjust the position of the optical members or to remove foreign matters such as air bubbles between the members. For this reason, the development of an adhesive sheet with improved reworkability has also been promoted. For example, Patent Documents 1 to 3 disclose techniques for imparting reworkability to an adhesive sheet by containing particles in an adhesive layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technologies disclosed in Patent Documents 1 to 3, although the reworkability can be imparted to the pressure-sensitive adhesive sheet, the haze increases due to the inclusion of particles, resulting in impaired transparency, so there is a problem that its use for optical applications is restricted. In the pressure-sensitive adhesive sheet, it is strongly desired to achieve both the reworkability and transparency. However, since the two are in a trade-off relationship, it has not been easy to obtain a pressure-sensitive adhesive sheet having excellent reworkability and high transparency.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a pressure-sensitive adhesive sheet having excellent reworkability and high transparency, a laminate including the pressure-sensitive adhesive sheet, an optical device, and an image display device.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by forming a pressure-sensitive adhesive sheet with a specific component, and have completed the present invention.

[0008] That is, the present invention includes, for example, the subject matters described in the following items. Item 1 In a pressure-sensitive adhesive sheet formed of 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), an oligomer (C) composed of a (meth)acrylic resin having a glass transition temperature in the range of 45°C to 70°C, and a crosslinking agent (D), the crosslinkable (meth)acrylic copolymer (A) has an alkyl group having 4 to 10 carbon atoms and is a polymer containing a (meth)acrylic ester unit (a) and a monomer unit (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). An adhesive sheet satisfying the following physical properties (1), (2), and (3). Physical property (1): The adhesion to glass 30 minutes after lamination, measured according to the method for measuring adhesion described in JIS Z 0237, is 0.01 to 5 N / 25 mm. Physical property (2): The adhesion to glass, measured according to the method for measuring adhesion described in JIS Z 0237, after laminating the adhesive sheet to a glass plate and heat-treating it at 100°C and 0.5 MPa for 30 minutes, is 10 N / 25 mm or more. Physical property (3): The haze measured according to JIS K 7136 is 0 to 2%. Item 2 The 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 The adhesive sheet according to Item 1 or 2, wherein the weight average molecular weight of the oligomer (C) composed of the (meth)acrylic resin is 5,000 to 20,000. Item 4 The 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 oligomer (C) composed of the (meth)acrylic resin is 0 to 0.05. Item 5 The adhesive sheet according to any one of Items 1 to 4, wherein the crosslinking agent (D) contains one selected from the group consisting of isocyanate compounds, epoxy compounds, and metal chelates. Item 6 A laminate comprising the adhesive sheet according to any one of Items 1 to 5 and an adherend. Item 7 An optical device comprising the laminate according to Item 6. Item 8 An image display device comprising the laminate according to Item 6. Item 9 A method for manufacturing an optical device comprising a laminate, the method including a heating step of laminating the adhesive sheet according to any one of Items 1 to 5 and an adherend and heating the laminate. Item 10 A method for manufacturing an image display device including a laminate, the method including a heating step of laminating an adhesive sheet according to any one of Items 1 to 5 and an adherend and heating the laminate.

Advantages of the Invention

[0009] The adhesive sheet of the present invention is excellent in reworkability and has high transparency.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. In this specification, expressions such as "containing" and "including" include the concepts of "containing", "including", "substantially consisting of", and "consisting only of". In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as a lower limit value and an upper limit value.

[0012] 1. Adhesive Sheet The adhesive sheet according to one embodiment of the present invention is formed of a cured product of an adhesive composition. That is, the adhesive sheet of this embodiment is obtained by curing an adhesive composition.

[0013] The adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), an oligomer (C) composed of a (meth)acrylic resin having a glass transition temperature (Tg) in the range of 45°C to 70°C, and a crosslinking agent (D). Further, the adhesive sheet of this embodiment has the following physical properties (1), (2), and (3).

[0014] According to the pressure-sensitive adhesive sheet of this embodiment, it has excellent reworkability (i.e., position adjustment ability), and moreover, it has high transparency. In addition to having an initial adhesive force suitable for reworkability, the pressure-sensitive adhesive sheet of this embodiment has the property of being able to increase the adhesive force by heating after bonding adherends to each other (so-called heat-bonding property). Thereby, the pressure-sensitive adhesive sheet of this embodiment can also firmly bond adherends to each other.

[0015] <Crosslinkable (meth)acrylic copolymer (A)> The crosslinkable (meth)acrylic copolymer (A) is a polymer containing a (meth)acrylic ester unit (a) having an alkyl group with 4 to 10 carbon atoms and a monomer unit (b) having a carboxy group and / or a hydroxyl group. Note that the "unit" in the (meth)acrylic ester unit (a) and the "monomer unit" mean repeating units constituting the polymer. Hereinafter, the (meth)acrylic ester unit (a) having an alkyl group with 4 to 10 carbon atoms is simply referred to as "(meth)acrylic ester unit (a)", and the monomer unit (b) having a carboxy group and / or a hydroxyl group is simply referred to as "monomer unit (b)".

[0016] Also, in this specification, "(meth)acrylic" means "acrylic" or "methacrylic", "(meth)acrylate" means "acrylate" or "methacrylate", and "(meth)allyl" means "allyl" or "methallyl".

[0017] (Meth)acrylic ester unit (a) is a repeating unit derived from a (meth)acrylic ester compound having an alkyl group with 4 to 10 carbon atoms. (Meth)acrylic ester compounds having an alkyl group with 4 to 10 carbon atoms can include, for example, well-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, etc. can be mentioned. The (meth)acrylic ester compound having an alkyl group with 4 to 10 carbon atoms preferably does not have a hydroxyl group and / or a carboxyl group.

[0018] In (meth)acrylic ester unit (a), the number of carbon atoms of the alkyl group is preferably 4 to 8, and more preferably 4 to 6.

[0019] The (meth)acrylic ester unit (a) contained in the crosslinkable (meth)acrylic copolymer (A) may be only one type or may include two or more types.

[0020] In the crosslinkable (meth)acrylic copolymer (A), the content ratio 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 desired reworkability and transparency and can satisfy physical properties (1) to (3). When the content ratio of the (meth)acrylic ester unit (a) is less than 50% by mass, the initial adhesion performance (adhesion 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 likely to be improved, the content ratio 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, still more preferably 65% by mass or more, and particularly preferably 70% by mass or more. Also, in terms of the reworkability and transparency of the pressure-sensitive adhesive sheet being more likely to be improved, the content ratio of the (meth)acrylic ester unit (a) in the crosslinkable (meth)acrylic copolymer (A) is preferably 94% by mass or less, more preferably 93% by mass or less, still more preferably 92% by mass or less, and particularly preferably 90% by mass or less.

[0021] In the present invention, the content of each structural unit in the crosslinkable (meth)acrylic copolymer (A) can be regarded as corresponding to the amount of the polymerizable monomer derived from the structural unit used when producing the crosslinkable (meth)acrylic copolymer (A).

[0022] The monomer unit (b) is a repeating unit derived from a monomer having a carboxy group and / or a hydroxyl group.

[0023] Examples of the monomer having a carboxy group can widely include known carboxy group-containing polymerizable monomers, and specifically include acrylic acid, methacrylic acid, and the like.

[0024] Examples of the monomer having a hydroxyl group can widely include known hydroxyl group-containing polymerizable monomers, and specifically include 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, and the like.

[0025] The crosslinkable (meth)acrylic copolymer (A) can contain both a monomer unit (b) having a carboxy group and a monomer unit having a hydroxyl group, or can 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, their content ratios are not particularly limited, and a desired pressure-sensitive adhesive sheet can be obtained with any content ratio.

[0026] In the crosslinkable (meth)acrylic copolymer (A), the content ratio of the monomer unit (b) is 1% by mass or more and 50% by mass or less. When the content ratio of the monomer unit (b) is less than 1% by mass, the initial adhesion performance (adhesion performance before heat treatment) of the pressure-sensitive adhesive sheet deteriorates, and when it exceeds 50% by mass, the initial adhesive force of the pressure-sensitive adhesive sheet becomes too large to obtain a desired reworkability. In terms of the pressure-sensitive adhesive sheet being likely to have excellent reworkability and transparency, the content ratio 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, still more preferably 2.5% by mass or more. Also, in terms of the pressure-sensitive adhesive sheet being likely to have excellent reworkability and transparency, the content ratio 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, still more preferably 25% by mass or less, particularly preferably 20% by mass or less.

[0027] The crosslinkable (meth)acrylic copolymer (A) can contain other constitutional units other than the (meth)acrylic ester unit (a) and the monomer unit (b) as long as the effects of the present invention are not inhibited. The other constitutional units are, for example, copolymerizable with the (meth)acrylic ester compound Constituent units derived from compounds can be broadly cited. Such compounds specifically include (meth)acrylic ester compounds having 3 or fewer carbon atoms (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, etc.), (meth)acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinyl pyrrolidone, vinyl pyridine, etc. In addition, amino group-containing (meth)acrylic esters, glycidyl group-containing (meth)acrylic esters, alkoxyalkyl group-containing (meth)acrylic esters, etc. can also be cited.

[0028] When the crosslinkable (meth)acrylic copolymer (A) contains the above other constituent units, the content ratio is 15% by mass or less, preferably 10% by mass or less, 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 only of (meth)acrylic ester units (a) and monomer units (b) (that is, the content ratio of other constituent units in the crosslinkable (meth)acrylic copolymer (A) may be 0% by mass).

[0029] In the crosslinkable (meth)acrylic copolymer (A), the sequence order of each constituent unit is not particularly limited, and for example, a random copolymer, a block copolymer, a graft copolymer, etc. can be formed. In terms of easy production, it is preferably a random copolymer.

[0030] The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. For example, in terms of easily suppressing the initial adhesive strength of the adhesive sheet while easily increasing the adhesive strength after heating, the weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer means the value before crosslinking with the crosslinking agent described later. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is measured by gel permeation chromatography (GPC) and is a value determined based on polystyrene standards.

[0031] The crosslinkable (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition can be only one kind, or can be two or more kinds.

[0032] The production method of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. For example, the crosslinkable (meth)acrylic copolymer (A) can be obtained by a production method using a known polymerization method. The crosslinkable (meth)acrylic copolymer (A) can also be obtained from commercially available products or the like.

[0033] The refractive index of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. In terms of enhancing 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, more preferably 1.46 to 1.49. Here, the refractive index of the crosslinkable (meth)acrylic copolymer (A) refers to the value measured by Method A described in JIS K 7142 (2014) "Plastics - Method for Determining Refractive Index".

[0034] <Poly(methyl methacrylate) (B)> The poly(methyl methacrylate) (B) is a polymer obtained by polymerizing a polymerizable monomer M mainly composed of methyl methacrylate (MMA). Such a polymerizable monomer M preferably contains 50% by mass or more of MMA, more preferably 70% by mass or more, still 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 thereof is not particularly limited. The polymerizable monomer M may be only MMA. In this case, the inclusion of monomers inevitably contained in MMA is allowed.

[0035] The weight average molecular weight of the methyl methacrylate polymer (B) is not particularly limited. For example, in terms of the ease of improving the reworkability of the pressure-sensitive adhesive sheet and being able to suppress the haze to a lower level, the weight average molecular weight of the methyl methacrylate polymer (B) is preferably from 1,000 to 10,000. The weight average molecular weight of the methyl methacrylate polymer (B) is a value measured by gel permeation chromatography (GPC) and determined based on polystyrene standards.

[0036] The methyl methacrylate polymer (B) may have either a non-crosslinked structure or a crosslinked structure.

[0037] The methyl methacrylate polymer (B) contained in the pressure-sensitive adhesive composition can be only one kind, or two or more kinds.

[0038] The production method of the methyl methacrylate polymer (B) is not particularly limited. 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 commercially available products or the like.

[0039] <Oligomer (C) composed of (meth)acrylic resin> The oligomer (hereinafter also referred to as (meth)acrylic oligomer) (C) composed of (meth)acrylic resin is an oligomer containing (meth)acrylic resin as the main component.

[0040] In the (meth)acrylic oligomer (C), the type of the (meth)acrylic resin is not particularly limited, and known (meth)acrylic resins can be widely exemplified. Examples of the (meth)acrylic resin include polymers of (meth)acrylic acid esters. Such (meth)acrylic acid esters specifically include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and in addition, (meth)acrylic ester compounds having an alkyl group with 4 to 10 carbon atoms as described above, hydroxyl group-containing (meth)acrylic acid ester compounds such as (meth)acrylic acid hydroxyalkyl (alkyl carbon number is, for example, 2 to 10), epoxy group-containing (meth)acrylic acid ester compounds such as glycidyl (meth)acrylate, carboxyl group-containing (meth)acrylic acid ester compounds, and the like.

[0041] The (meth)acrylic resin in the (meth)acrylic oligomer (C) may be a homopolymer or a copolymer, but in terms of being easily able to lower haze, it is preferably a homopolymer. When the (meth)acrylic resin is a copolymer, examples include polymers containing two or more of the above-mentioned (meth)acrylic ester units, and it can also be a copolymer of a (meth)acrylic ester and a polymerizable monomer other than the (meth)acrylic ester. Examples of the polymerizable monomer other than the (meth)acrylic ester include styrene, α-methylstyrene, maleic anhydride, (meth)acrylonitrile, vinyl acetate, vinyl chloride, vinyl pyrrolidone, vinyl pyridine, etc. However, in terms of being easily able to lower haze, a copolymer consisting only of (meth)acrylic ester units or a copolymer consisting of (meth)acrylic ester units and (meth)acrylic acid units is preferred.

[0042] The (meth)acrylic resin in the (meth)acrylic oligomer (C) can have a crosslinked structure or can also have 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.

[0043] (Meta)acrylic oligomer (C) has a glass transition temperature (Tg) of 45°C to 70°C, preferably 50°C to 65°C. By setting the glass transition temperature (Tg) of (meta)acrylic oligomer (C) within the above range, the reworkability of the pressure-sensitive adhesive sheet is likely to be improved. Yes.

[0044] The weight average molecular weight of (meta)acrylic oligomer (C) is not particularly limited. In terms of the ease of improving the reworkability of the pressure-sensitive adhesive sheet and the tendency to lower haze, the weight average molecular weight of (meta)acrylic oligomer (C) is preferably 500 to 20,000, more preferably 8,000 to 18,000.

[0045] In this specification, the weight average molecular weight of (meta)acrylic oligomer (C) is a value measured by gel permeation chromatography (GPC) and determined based on polystyrene standards. However, when using a commercially available (meta)acrylic oligomer, if the manufacturer's guaranteed value or measured value of the weight average molecular weight is known, that value shall be taken as the weight average molecular weight of the (meta)acrylic oligomer.

[0046] The refractive index of (meta)acrylic oligomer (C) is not particularly limited. In terms of enhancing the transparency of the pressure-sensitive adhesive sheet, the refractive index of (meta)acrylic oligomer (C) is preferably 1.45 to 1.50, more preferably 1.46 to 1.49.

[0047] More specifically regarding the refractive index of (meta)acrylic oligomer (C), it is even more preferable that the difference (absolute value) in refractive index between the crosslinkable (meta)acrylic copolymer (A) and (meta)acrylic oligomer (C) contained in the pressure-sensitive adhesive composition is 0 to 0.05. In this case, the pressure-sensitive adhesive sheet can have more excellent transparency.

[0048] The refractive index of the (meth)acrylic oligomer (C) referred to herein indicates the value measured by Method B described in JIS K 7142 (2014) "Plastics - Methods for Measuring Refractive Index". The refractive index of the crosslinkable (meth)acrylic copolymer (A) referred to herein indicates the value measured by Method A described in JIS K 7142 (2014) "Plastics - Methods for Measuring Refractive Index".

[0049] The (meth)acrylic oligomer (C) contained in the pressure-sensitive adhesive composition can be only one kind, or can be two or more kinds.

[0050] The production method of the (meth)acrylic oligomer (C) is not particularly limited. For example, the (meth)acrylic oligomer (C) can be produced by a method similar to a known method. Also, the (meth)acrylic oligomer (C) can be obtained from commercially available products.

[0051] <Crosslinking agent (D)> The crosslinking agent (D) can broadly include components for allowing the crosslinking reaction of the crosslinkable (meth)acrylic copolymer (A) to proceed. In particular, the crosslinking agent can broadly include components capable of reacting with a carboxy group or a hydroxyl group.

[0052] Such a crosslinking agent (D) can be selected, for example, from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds.

[0053] Among them, the crosslinking agent (D) preferably 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 later in combination.

[0054] Examples of the isocyanate compound include tolylene diisocyanate, isophorone di Polyisocyanates such as sociate, chlorophenylene diisocyanate, diphenylmethane diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, etc.; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, etc., and aromatic isocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, etc. The isocyanate compound can be used alone or as a mixture of two or more different types. Examples of commercially available products include tolylene diisocyanate compounds (manufactured by Nippon Polyurethane Industry Co., Ltd., Coronate L), xylylene diisocyanate compounds (manufactured by Mitsui Chemicals, Inc., Takenate D-110N), etc.

[0055] 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-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexanone, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, etc. Examples of commercially available epoxy compounds include TETRAD-C (manufactured by Mitsubishi Gas Chemical Company, Inc.), TETRAD-X (manufactured by Mitsubishi Gas Chemical Company, Inc.), etc.

[0056] Examples of metal chelate compounds include known metal chelate compounds used in crosslinking reactions. Examples of commercially available products include aluminum chelate A (manufactured by Kawaken Fine Chemicals Co., Ltd.), etc.

[0057] <Adhesive Composition> As described above, the pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), a (meth)acrylic oligomer (C), and a crosslinking agent (D).

[0058] In the pressure-sensitive adhesive composition, 1 to 15 parts by mass of the methyl methacrylate polymer (B) is contained per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A). When the content of the methyl methacrylate polymer (B) per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A) is less than 1 part by mass, the initial adhesive strength of the pressure-sensitive adhesive sheet becomes too high and the desired reworkability cannot be obtained. When it exceeds 15 parts by mass, the haze increases and the transparency of the pressure-sensitive adhesive sheet deteriorates. It is preferable that 2 parts by mass or more of the methyl methacrylate polymer (B) is contained 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. Also, it is preferable that 14 parts by mass or less of the methyl methacrylate polymer (B) is contained 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.

[0059] In the pressure-sensitive adhesive composition, the content of the (meth)acrylic oligomer (C) is not particularly limited. For example, it can be 0.8 to 10 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A), and preferably 1 to 6 parts by mass. In this case, the obtained pressure-sensitive adhesive sheet can have a reduced haze value while maintaining excellent reworkability.

[0060] In the pressure-sensitive adhesive composition, the content of the crosslinking agent (D) is not particularly limited. For example, it can be 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 obtained pressure-sensitive adhesive sheet is likely to be enhanced. 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).

[0061] As described above, the pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), a (meth)acrylic oligomer (C), and a crosslinking agent (D), and may further contain a solvent as needed. When the pressure-sensitive adhesive composition contains a solvent, the coatability of the pressure-sensitive adhesive composition is improved, and it becomes easier to form a pressure-sensitive adhesive sheet.

[0062] Examples of the solvent 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 their derivatives 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.

[0063] The content of the solvent in the pressure-sensitive adhesive composition is not particularly limited, and is preferably 25 to 500 parts by mass, more preferably 30 to 400 parts by mass, per 100 parts by mass of the crosslinkable (meth)acrylic copolymer. In addition, the content ratio of the solvent to the total mass of the pressure-sensitive adhesive composition is preferably 10 to 90% by mass, more preferably 20 to 80% by mass.

[0064] The solvent contained in the pressure-sensitive adhesive composition can be a single type or two or more types.

[0065] The pressure-sensitive adhesive composition can contain other components as long as the effects of the present invention are not impaired. Examples of other components include known components used as additives to the pressure-sensitive adhesive composition. As other components, for example, crosslinking retardants, plasticizers, antioxidants, metal corrosion inhibitors, tackifiers, silane coupling agents, ultraviolet absorbers, light stabilizers such as hindered amine compounds, etc. can be selectively chosen as needed. Also, dyes or pigments may be added for coloring purposes.

[0066] Examples of the crosslinking retardant include acetylacetone, etc. Particularly when the crosslinking agent (D) contains a metal chelate, it is preferable to use a crosslinking retardant in combination. Examples of the plasticizer include non-functional group acrylic polymers. Examples of the non-functional group acrylic polymer include a polymer composed only of acrylic monomer units having no functional groups other than acrylate groups, and a polymer composed of acrylic monomer units having no functional groups other than acrylate groups and non-acrylic monomer units having no functional groups. Since the non-functional group acrylic polymer does not crosslink, it can enhance the step-following property without affecting the adhesiveness.

[0067] Examples of the antioxidant include phenolic antioxidants, amine antioxidants, lactone antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. These antioxidants may be used alone or in combination of two or more. As the metal corrosion inhibitor , from the viewpoint of the compatibility and high effect of the pressure-sensitive adhesive, benzotriazole-based resins can be cited as preferred examples. 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, petroleum resins, etc. Examples of the silane coupling agent include mercaptoalkoxysilane compounds (for example, mercapto group-substituted alkoxy oligomers, etc.). Examples of the ultraviolet absorber include benzotriazole-based compounds, benzophenone-based compounds, triazine-based compounds, etc.

[0068] When the adhesive composition contains other components, their content ratios are not particularly limited. For example, it can be 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).

[0069] The method for preparing the adhesive composition is not particularly limited. For example, the known methods for preparing adhesive compositions can be widely adopted.

[0070] <Configuration and Physical Properties of the Adhesive Sheet> The adhesive sheet of this embodiment (hereinafter simply referred to as "adhesive sheet") is composed of a cured product of the aforementioned adhesive composition. That is, the adhesive sheet of this embodiment can be obtained by curing the aforementioned adhesive composition. The cured product of the adhesive composition can function as an adhesive layer in the adhesive sheet. The adhesive sheet can be composed of, for example, only the adhesive layer. That is, the adhesive sheet can also be formed only of the cured product of the adhesive composition. The adhesive layer can have a single-layer structure, or can have a multilayer structure in which a plurality of single-layer adhesive layers are laminated. The adhesive sheet can be either a single-sided adhesive sheet or a double-sided adhesive sheet, and is preferably a double-sided adhesive sheet.

[0071] <Physical Properties of the Adhesive Sheet> (Physical Property 1) The adhesive sheet satisfies the following physical property (1). Physical Property (1); The adhesive force to glass 30 minutes after bonding, measured according to the method for measuring adhesive force described in JIS Z 0237, is 0.01 to 5 N / 25 mm.

[0072] In Physical Property (1), when measuring the glass adhesion of the adhesive sheet, in accordance with the adhesion measurement method described in JIS Z 0237, the glass adhesion after 30 minutes from the time of bonding to the glass is measured. More specifically, after bonding 100 μm PET (manufactured by Toyobo Co., Ltd. / product number: Cosmo Shine A4300) to one surface of the adhesive sheet, this is treated in an autoclave at 100 °C and 0.5 MPa (meaning gauge pressure) for 30 minutes. The adhesive sheet having a PET substrate on one side thus treated is bonded to soda lime glass (the pressure-bonding surface of Hiraoka Special Glass Co., Ltd. is the opposite side of the tin float). At this time, a measurement sample is prepared in accordance with the 180° peel adhesion measurement method described in JIS Z 0237, except that soda lime glass is used for the test plate. Then, the adhesion is measured at a peel rate of 300 mm / min 30 minutes after pressure bonding. This adhesion is defined as the glass adhesion in Physical Property (1).

[0073] In Physical Property (1), the value of the glass adhesion is preferably 0.05 N / 25 mm or more in terms of particularly improving the reworkability. Further, the glass adhesion 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.

[0074] The glass adhesion in Physical Property (1) can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the blending amount of the methyl methacrylate polymer (B), the glass transition temperature, weight average molecular weight and blending amount of the (meth)acrylic oligomer (C), and the blending amount of the crosslinking agent (D). can be adjusted by adjustment.

[0075] (Physical Property 2) The adhesive sheet satisfies the following Physical Property (2). Physical Property (2); The glass adhesion measured in accordance with the adhesion measurement method described in JIS Z 0237 after heat-treating the adhesive sheet bonded to a glass plate at 85 °C and 0.5 MPa (meaning gauge pressure) for 30 minutes is 10 N / 25 mm or more.

[0076] In Physical Property (2), when measuring the adhesion of the adhesive sheet to glass, a measurement sample is prepared in the same manner as in the method of Physical Property (1). Thereafter, this measurement sample is treated in an autoclave at 85°C and 0.5 MPa (gauge pressure) for 30 minutes and then left standing in an environment of 23°C and 50% relative humidity for 2 hours. Next, the adhesion is measured at a peeling rate of 300 mm / min by the same method as in Physical Property (1). This adhesion is defined as the adhesion to glass in Physical Property (2).

[0077] In Physical Property (2), the value of the adhesion to glass is preferably 10 N / 25 mm or more, more preferably 15 N / 25 mm or more, in terms of the adhesion to the adherend after heat treatment being likely to increase. Further, the adhesion to glass in Physical Property (2) is not particularly limited, and for example, it is preferably 50 N / 25 mm or less in terms of easy disposal and disassembly of displays and the like.

[0078] The adhesion to glass in Physical Property (2) can be adjusted by adjusting the types and ratios of the constitutional units of the crosslinkable (meth)acrylic copolymer, the blending amount of the methyl methacrylate polymer (B), the glass transition temperature, weight average molecular weight and blending amount of the (meth)acrylic oligomer (C), and the blending amount of the crosslinking agent (D).

[0079] (Physical Property 3) The adhesive sheet satisfies the following Physical Property (3). Physical Property (3); The haze measured according to JIS K 7136 is 0 to 2%.

[0080] In physical property (3), when measuring the haze of the pressure-sensitive adhesive sheet, the measurement is carried out in accordance with JIS K 7136. Specifically, a pair of transparent glass plates (manufactured by Matsunami Glass Industry Co., Ltd., S9112) with a thickness of 1.2 mm are bonded together with the pressure-sensitive adhesive sheet to prepare a laminated sample so that air or the like does not mix in. Using this laminated sample, the haze is measured in accordance with JIS K7136 (2000). For this measurement, a haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. can be used. The laminated sample can be prepared, for example, as follows. Peel off the release sheet on the light release side of the pressure-sensitive adhesive sheet with a release sheet, bond it to one transparent glass plate, and then bond the other transparent glass plate to the surface from which the release sheet (heavy release separator) on the heavy release side has been peeled off so that air or the like does not mix in. After treating this in an autoclave at 100 °C and 0.5 MPa (meaning gauge pressure) for 30 minutes, it is left standing in an environment of 23 °C and 50% relative humidity for 2 hours to obtain a laminated sample.

[0081] In physical property (3), the haze value is preferably 1.9% or less, more preferably 1.8% or less, in terms of the transparency of the pressure-sensitive adhesive sheet being likely to increase. The haze value may be 0%.

[0082] The haze value can be adjusted by adjusting the types and ratios of the constituent units of the crosslinkable (meth)acrylic copolymer (A), the blending amount of the methyl methacrylate polymer (B), and the glass transition temperature, weight average molecular weight, and blending amount of the (meth)acrylic oligomer (C).

[0083] Since the pressure-sensitive adhesive sheet has the above physical property (1), the initial adhesive force is not too strong, and thus it has excellent position adjustment ability (reworkability). Therefore, when the pressure-sensitive adhesive sheet of this embodiment is used for bonding members such as in the application of bonding optical members, the pressure-sensitive adhesive sheet can be easily peeled off from the optical member, so that the re-bonding operation can be easily performed, and also, glue residue derived from the pressure-sensitive adhesive sheet is less likely to occur.

[0084] Since the pressure-sensitive adhesive sheet has the above physical properties (2), the adhesive force can be increased by heating after bonding the members together. As a result, it becomes possible to firmly bond the adherends to each other. Thus, the pressure-sensitive adhesive sheet of this embodiment has succeeded in keeping the initial adhesive force low while increasing the adhesive force after heating, and has both two contradictory adhesive performances.

[0085] Furthermore, since the pressure-sensitive adhesive sheet has the above physical property (3), it has high transparency. Therefore, the pressure-sensitive adhesive sheet of this embodiment is also suitable for use in optical applications and the like where high transparency is required.

[0086] As described above, by having the physical properties (1) to (3), the pressure-sensitive adhesive sheet of this embodiment can impart reworkability to the pressure-sensitive adhesive sheet while imparting high transparency, and can achieve both the transparency and reworkability of the pressure-sensitive adhesive sheet, which were conventionally in a trade-off relationship. In addition, the pressure-sensitive adhesive sheet of this embodiment does not show peeling even after a lapse of time after bonding, and is excellent in stability over time.

[0087] <Other characteristics of the pressure-sensitive adhesive sheet> The thickness of the pressure-sensitive adhesive sheet is not particularly limited because it can be appropriately set according to the application. For example, it is preferably 5 to 300 μm, more preferably 8 to 200 μm, and particularly preferably 10 to 150 μm.

[0088] The gel fraction of the pressure-sensitive adhesive sheet is not particularly limited either, and can be appropriately set according to the components and types contained in the pressure-sensitive adhesive sheet. For example, the gel fraction of the pressure-sensitive 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 heating the pressure-sensitive adhesive sheet. However, in the pressure-sensitive adhesive sheet of the present invention, since the change in the gel fraction before and after heating is small, it is preferable that the gel fraction of the pressure-sensitive adhesive sheet after heat treatment at 85°C and 0.5 MPa for 30 minutes is also within the above range.

[0089] The gel fraction of the adhesive layer is the value measured by the following method. First, collect about 0.1 g of the adhesive sheet (adhesive layer) into a sample bottle, add 30 ml of ethyl acetate, and shake for 24 hours. Then, filter the contents of this sample bottle through a 150-mesh stainless steel wire mesh, and dry the residue on the wire mesh at 100 °C for 1 hour to measure the dry mass (g). The gel fraction is determined from the obtained dry mass by the following formula 1. Gel fraction (mass %) = (dry mass / mass of the collected adhesive sheet) × 100 ··· Formula 1

[0090] <Method of using the adhesive sheet> The method of using the adhesive sheet of this embodiment is not particularly limited. For example, a method similar to that of a known adhesive sheet can be adopted. When the adhesive sheet of this embodiment is the above-mentioned heat-adhesive sheet, the adhesive sheet can be used by a method of heating the adhesive sheet after bringing it into contact with the surface of the adherend. By performing such heating, the adhesion of the adhesive sheet to the adherend is enhanced. Further, since the adhesive sheet has excellent reworkability, the position adjustment of the adhesive sheet before heating can also be easily performed.

[0091] The heating after bringing the adhesive sheet into contact with the surface of the adherend can be, for example, 50 to 120 °C and the heating time can be appropriately set according to the heating temperature and can be, 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 performing such a heat treatment, the adhesive strength of the adhesive sheet is significantly increased and it adheres more firmly to the adherend.

[0092] <Adhesive sheet with release sheet> As shown in FIG. 1, an adhesive sheet with a release sheet can also be formed from the adhesive sheet of this embodiment. The adhesive sheet with a release sheet 10 can have release sheets 12a and 12b on both surfaces of the adhesive layer 11 (adhesive sheet).

[0093] As the release sheet, for example, known release sheets can be widely applied. For example, a releasable laminated sheet in which a release agent layer is formed on one side of a base material for a release sheet can be mentioned. In addition, low-polarity base materials formed of polyolefin films such as polyethylene films and polypropylene films can be mentioned. As the base material for the release sheet, for example, papers and polymer films are used.

[0094] As the release agent constituting the release agent layer, for example, general-purpose addition-type or condensation-type silicone-based release agents or long-chain alkyl group-containing compounds are used. In particular, addition-type silicone-based release agents with high reactivity are preferably used. Specific examples of silicone-based release agents include BY24-4527, SD-7220, etc. manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3600, KS-774, X62-2600, etc. manufactured by Shin-Etsu Chemical Co., Ltd. Further, 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. Specific examples of the silicone resin include BY24-843, SD-7292, SHR-1404, etc. manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.

[0095] The releasable laminated sheet can also be obtained from commercially available products. For example, a heavy separator film which is a polyethylene terephthalate film subjected to a release treatment manufactured by Teijin DuPont Films Limited, and a light separator film which is a polyethylene terephthalate film subjected to a release treatment manufactured by Teijin DuPont Films Limited can be mentioned.

[0096] The pressure-sensitive adhesive sheet with a release sheet preferably has a pair of release sheets with different release forces on both surfaces of the pressure-sensitive adhesive sheet. That is, for the release sheet, in order to facilitate peeling, it is preferable that the releasability between the release sheet 12a and the release sheet 12b is different. When the releasability from one side is different from that from the other side, it becomes easy to peel only the release sheet with higher releasability (light peeling side) prior to the heavy peeling side.

[0097] <Applications of the pressure-sensitive adhesive sheet> The pressure-sensitive adhesive sheet of this embodiment can be applied to various applications. For example, it can be used to bond optical members used in optical devices and the like.

[0098] Examples of the optical member include components in optical products such as touch panels or image display devices. Examples of the components of a touch panel 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 conductive polymer is coated on a transparent resin film, a hard coat film, and a fingerprint-resistant film.

[0099] Examples of the components of an image display device include an antireflection film used in a liquid crystal display device , an alignment film, a polarizing film, a retardation film, a brightness enhancement film, and the like. Further, the pressure-sensitive adhesive sheet of the present invention may be used for bonding between modules such as a liquid crystal module and a touch panel module.

[0100] Specific materials that can be bonded with the pressure-sensitive adhesive sheet include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, cellulose acylate, and the like.

[0101] 2. Manufacturing method of the pressure-sensitive adhesive sheet The manufacturing method of the pressure-sensitive adhesive sheet of this form is not particularly limited, and known methods can be widely adopted. Among them, it is preferable to form a pressure-sensitive adhesive sheet by a manufacturing method including a step of applying the above-described pressure-sensitive adhesive composition onto a release sheet to form a coating film, and a step of heating this coating film. In such a manufacturing 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).

[0102] The application of the pressure-sensitive adhesive composition can be carried out using a known coating apparatus. Examples of the coating apparatus include an applicator, a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a microgravure coater, a rod blade coater, a lip coater, a die coater, a curtain coater, and the like.

[0103] The base material used when applying the pressure-sensitive adhesive composition is not particularly limited. For example, the pressure-sensitive adhesive composition can be applied to various base materials such as a resin base material and a glass base material. For example, when obtaining a pressure-sensitive adhesive sheet with a release sheet, the release sheet can be selected as the base material. Also, the pressure-sensitive adhesive composition can be directly applied onto the member to be adhered.

[0104] The thickness after applying the pressure-sensitive adhesive composition is not particularly limited either, and can be appropriately set according to the thickness of the target pressure-sensitive adhesive layer.

[0105] In the step of heating the coating film, the heating temperature is not particularly limited, and for example, it is preferably set to 50 to 150°C. The heating time can be appropriately adjusted according to the heating temperature, the thickness of the coating film, and the solvent content of the pressure-sensitive adhesive composition, and for example, it can be set to 1 to 60 minutes. For heating the coating film, known heating apparatuses such as a heating furnace and an infrared lamp can be used. Also, after heating, it is preferable to perform an aging treatment of leaving the pressure-sensitive adhesive sheet standing at a constant temperature for a certain period. The aging treatment can be carried out, for example, by leaving it standing at 23°C for 7 days.

[0106] 3. Laminate Another form of the present invention is a laminate, which includes the above-described adhesive sheet and an adherend. When the adhesive sheet is a double-sided adhesive sheet, the adherend is preferably provided directly on both sides of the adhesive sheet. In this case, the laminate has a structure in which the adherend / adhesive sheet / adherend are laminated in this order. The adherend can be, for example, the above-described optical member.

[0107] The laminate of this form can be applied to various uses, and can be preferably used, for example, in optical devices, image display devices, etc. In particular, since the laminate of the present invention is formed by being adhered with a highly transparent adhesive sheet, when applied to an optical device, an image display device, etc., the design and visibility of the image can be further improved.

[0108] As described above, the heating step of heating after laminating the adhesive sheet and the adherend can be, for example, 50 to 120 °C, and the heating time can be appropriately set according to the heating temperature, for example, it can be 1 to 120 minutes. Pressure may be applied during the heat treatment. For example, it is preferable to apply a pressure of 0.2 to 0.9 MPa.

Examples

[0109] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the aspects of these examples.

[0110] [Synthesis of crosslinkable (meth)acrylic copolymer A-1] A monomer in which butyl acrylate (BA), acrylic acid (AA), and methyl acrylate (MA) were blended so that the mass ratio was 87:3:10 was heated to 60 °C in ethyl acetate, which is a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile) and polymerized. Thereby, a solution of a crosslinkable (meth)acrylic copolymer (A-1) (denoted as "A-1" in Table 1) having a solid content concentration of 30% by mass and a weight average molecular weight of 740,000 was obtained.

[0111] [Synthesis of Crosslinkable (Meth)acrylic Copolymer A-2] A monomer mixture with BA, 2-hydroxyethyl acrylate (2HEA), and MA in a mass ratio of 70:20:10 was heated to 60 °C in ethyl acetate, which was used as a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile) for polymerization. As a result, a solution of crosslinkable (meth)acrylic copolymer (A-2) (designated as "A-2" in Table 1) with a solid content concentration of 35% by mass and a weight average molecular weight of 600,000 was obtained.

[0112] [Synthesis of Methyl Methacrylate Polymer B-1] A solution prepared by dissolving methyl methacrylate (MMA) and polymerization initiator AIBN in ethyl acetate was heated to 80 °C for polymerization, thereby obtaining a methyl methacrylate polymer (B-1) (designated as "B-1" in Table 1) with a weight average molecular weight of 5000.

[0113] [Synthesis of Methyl Methacrylate Polymer B-2] A solution prepared by dissolving methyl methacrylate (MMA) and polymerization initiator AIBN in ethyl acetate was heated to 80 °C for polymerization, thereby obtaining a methyl methacrylate polymer (B-2) with a weight average molecular weight of 9000.

[0114] (Example 1) [Preparation of Adhesive Composition] To 100 parts by mass of acrylic copolymer (A-1), 3 parts by mass of methyl methacrylate polymer (B-1), 1 part by mass of (meth)acrylic oligomer (C) UG-4035 (Tg: 52 °C, molecular weight: 11000, manufactured by Toagosei Co., Ltd.), 0.05 part by mass of an epoxy compound (Tetrad X, manufactured by Mitsubishi Gas Chemical Company, Inc.) as a crosslinking agent, and 0.5 part 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 became 25% by mass, and the adhesive composition a-1 was prepared by stirring.

[0115] [Production of Adhesive Sheet] The 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)) having a release agent layer treated with a silicone-based release agent, so that the coating thickness after drying was 25 μm, forming a coating film. The coating film was dried at 100° C. for 3 minutes in an air-circulating thermostatic oven, forming an adhesive layer (adhesive sheet) on the surface of the first release sheet.

[0116] Next, a second release sheet (Oji F-Tex Co., Ltd., 38RL-07(L)) having a thickness of 38 μm and a release strength different from that of the first release sheet was attached to the surface of the pressure-sensitive adhesive layer. This was aged for 14 days under a humidity condition of 50%. As a result, an adhesive sheet with release sheet was obtained having a first release sheet / adhesive sheet / second release sheet configuration in which the adhesive layer (adhesive sheet) was sandwiched between a pair of release sheets with different release strengths.

[0117] Example 2 An adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that the (meth)acrylic oligomer (C) was changed to UG-4070 (Tg: 58° C., molecular weight: 9700, manufactured by Toagosei Co., Ltd.).

[0118] Example 3 The raw materials containing 10 parts by mass of methyl methacrylate polymer (B-2), 1 part by mass of UH-2170 (Tg: 60°C, molecular weight: 14,000, manufactured by Toa Gosei Co., Ltd.) as the (meth)acrylic oligomer (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.) were added to ethyl acetate so that the concentration of the raw materials was 27% by mass, and stirred to prepare adhesive composition a-2.

[0119] Next, a pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition a-1 was changed to the pressure-sensitive adhesive composition a-2.

[0120] (Example 4) An adhesive sheet with a release sheet was obtained in the same procedure as in Example 3, except that the (meth)acrylic oligomer (C) was changed to UC-3000 (Tg: 65°C, molecular weight: 10,000, manufactured by Toagosei Co., Ltd.) and the amount used was changed to 2 parts by mass.

[0121] (Example 5) An adhesive sheet with a release sheet was obtained in the same procedure as in Example 4, except that the amount of the (meth)acrylic oligomer (C) used was changed to 5 parts by mass.

[0122] (Comparative Example 1) An adhesive sheet with a release sheet was obtained in the same procedure as in Example 1, except that the adhesive composition was prepared without using the (meth)acrylic oligomer (C).

[0123] (Comparative Example 2) An adhesive sheet with a release sheet was obtained in the same procedure as in Example 5, except that the (meth)acrylic oligomer (C) was changed to UF-5080 (Tg: 75°C, molecular weight: 17,000, manufactured by Toagosei Co., Ltd.).

[0124] [Physical Property 1; Adhesion to Glass] It was in accordance with the method for measuring adhesion described in JIS Z 0237. First, the release sheet on the light peeling side of the adhesive sheet with a release sheet was peeled off and laminated with 100 μm PET (manufactured by Toyobo Co., Ltd. / product number: Cosmo Shine A4300). Then, it was 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 peeling side of this adhesive sheet having a PET substrate on one side was peeled off and laminated with soda lime glass (the pressure-bonding surface of Hiraoka Special Glass Co., Ltd. is the opposite side of the tin float). At this time, a measurement sample was prepared in accordance with the method for measuring 180° peel adhesion described in JIS Z 0237, except that soda lime glass was used for the test plate. Then, the adhesion was measured at a peeling rate of 300 mm / minute 1 minute after pressure bonding, and this adhesion was taken as the adhesion to glass in Physical Property (1).

[0125] [Physical property 2; Adhesion to glass] Up to the pressure bonding to the test plate, a measurement sample was prepared in the same manner as the method for Physical property 1. Thereafter, this measurement sample was treated in an autoclave at 85 °C and 0.5 MPa (gauge pressure) for 30 minutes, and then left standing in an environment of 23 °C and 50% relative humidity for 2 hours. Then, the adhesion was measured at a peeling rate of 300 mm / min by the same method as in Physical property (1), and this adhesion was taken as the adhesion to glass in Physical property (2).

[0126] [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 (manufactured by Matsunami Glass Industry Co., Ltd., S9112) with a thickness of 1.2 mm were bonded together with the adhesive sheet so that air and the like did not mix in, to prepare a laminated sample. Using this laminated sample, the haze was measured 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, bonded to one transparent glass plate, and then the other transparent glass plate was bonded to the surface from which the release sheet (heavy release separator) on the heavy release side was peeled off so that air and the like did not mix in. This was treated in an autoclave at 100 °C and 0.5 MPa (gauge pressure) for 30 minutes, and then left standing in an environment of 23 °C and 50% relative humidity for 2 hours to obtain a laminated sample.

[0127] [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 using gel permeation chromatography (GPC) by the following method. The measurement conditions of GPC are as follows. · Solvent: Tetrahydrofuran · Column: Shodex KF801, KF803L, KF800L, KF800D (manufactured by Showa Denko K.K., four columns connected and used) · Column temperature: 40 °C · Sample concentration: 0.5 mass%​ ·Detector: RI-2031plus (manufactured by JASCO) ·Pump: RI-2080plus (manufactured by JASCO) ·Flow rate: 0.8 ml / min ·Injection volume: 10 μl ·Calibration curve: A calibration curve using 10 samples of standard polystyrene Shodex standard polystyrene (manufactured by Showa Denko K.K.) with Mw ranging from 1320 to 2,500,000 was used.

[0128] [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 - Method for determining refractive index". Also, the refractive index of the (meth)acrylic oligomer (C) was measured in accordance with Method B described in JIS K 7142 (2014) "Plastics - Method for determining refractive index".

[0129] [Evaluation of adhesive sheet] Each evaluation of the adhesive sheets obtained in each example and comparative example was carried out according to the following procedure.

[0130] [Position adjustment ability (reworkability)] During the process of preparing the measurement sample of physical property (1), an adhesive sheet having a PET substrate on one side was cut into a size of 50 mm × 60 mm to obtain a test piece. This test piece was pressed onto a float plate glass (manufactured by Nippon Sheet Glass Co., Ltd.) with a size of 30 mm × 40 mm (thickness 10 mm) using a hand roller so that the center point of the float plate glass and the center point of the adhesive sheet overlapped each other to form a laminate. This laminate was placed on a horizontal table in an environment of 23°C and 50% relative humidity with the adhesive sheet side facing the table and was pressure-bonded. Within 1 minute after pressure-bonding, while gently holding down the part of the adhesive sheet that protruded from the glass plate with one hand, the glass plate was lifted with the other hand to peel the glass plate upward from the adhesive sheet. The peelability at this time was evaluated according to the following criteria. ○: Easily peeled off, excellent in reworkability. ○: Easily peeled off, excellent in reworkability. ×: It does not peel off or is difficult to peel off (for example, it does not peel off unless peeled off by pulling up the adhesive sheet from the end with the adhesive sheet side facing up), and has poor reworkability.

[0131] [Presence or absence of peeling over time] The laminate produced in the process of evaluating the position adjustment ability (reworkability) was treated in an autoclave at 85 °C and 0.5 MPa (gauge pressure) for 30 minutes, then treated for 240 hours using a constant temperature and humidity layer at 65 °C (relative humidity 95%), and then left standing in an environment of 23 °C and 50% relative humidity for 60 minutes. Then, it was visually evaluated according to the following criteria. ○: No peeling or lifting occurred. ×: Peeling or lifting occurred at the edge or other parts.

[0132] [Design and visibility of the image] The release sheet on the easy-peeling side of the adhesive sheet with a release sheet was peeled off, and an adhesive sheet bonded to 100 μm PET (manufactured by Toyobo Co., Ltd. / product number: Cosmo Shine A4300) was cut into a size of 150 mm × 70 mm to obtain a test piece. Next, the release sheet on the heavy-peeling side of this test piece was peeled off, and the entire exposed surface and the surface on the opposite side of the black printed surface of a 150 mm × 70 mm (thickness 6 mm) float plate glass (manufactured by Nippon Sheet Glass Co., Ltd.) having a black printed surface were bonded using a hand roller to obtain a laminated sample. The obtained laminate was treated in an autoclave at 85 °C and 0.5 MPa (gauge pressure) for 30 minutes, and then left standing in an environment of 23 °C and 50% relative humidity for 2 hours to produce an evaluation sample. Separately from this evaluation sample, a float plate glass similar to the float plate glass used for producing the evaluation sample was prepared as a blank. Then, the PET surface side of the evaluation sample was visually compared with the glass surface on the opposite side of the black printed surface of the blank, and the design and visibility of the image were evaluated based on the following criteria. ○: It has the same blackness and gloss as the blank. △: It is slightly lacking in blackness and gloss compared to the blank. ×: It is inferior in blackness and gloss compared to the blank.

[0133]

Table 1

[0134] Table 1 shows the physical properties and evaluation results of each pressure-sensitive adhesive sheet in addition to the production conditions of the pressure-sensitive adhesive sheets of the above-described respective examples and comparative examples. In Table 1, “(A)-(C) refractive index difference” means the refractive index difference (absolute value) between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic oligomer (C).

[0135] It was found from Table 1 that the pressure-sensitive adhesive sheets obtained in the examples have excellent reworkability and low haze, that is, excellent transparency. Moreover, the pressure-sensitive adhesive sheets obtained in the examples did not show peeling even after the passage of time after bonding and were also excellent in stability over time. Furthermore, it was found that the laminate produced using the pressure-sensitive adhesive sheets obtained in the examples is also suitable for applications such as image display devices because of its excellent design and visibility of images.

Explanation of Signs

[0136] 10 Pressure-sensitive adhesive sheet with release sheet 11 Adhesive layer 12a Release sheet 12b Release sheet

Claims

1. In an adhesive sheet formed of a cured product of an adhesive composition, the adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), an oligomer (C) composed of a (meth)acrylic resin having a glass transition point in the range of 45°C to 70°C, and a crosslinking agent (D), the crosslinkable (meth)acrylic copolymer (A) is a polymer containing a (meth)acrylic ester unit (a) having an alkyl group with 4 to 10 carbon atoms and a monomer unit (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), the content of the oligomer (C) composed of the (meth)acrylic resin is 0.8 to 10 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A), the weight average molecular weight of the oligomer (C) composed of the (meth)acrylic resin is 5000 to 14000, an adhesive sheet satisfying the following physical properties (1), (2), and (3). Physical property (1); The adhesive force to glass after 30 minutes of bonding is 0.01 to 5 N / 25 mm, measured according to the method for measuring adhesive force described in JIS Z 0237. Physical property (2); The adhesive force to glass measured according to the method for measuring adhesive force described in JIS Z 0237 after heat treatment at 100°C and 0.5 MPa for 30 minutes with the adhesive sheet bonded to a glass plate is 10 N / 25 mm or more. Physical property (3); The haze measured according to JIS K 7136 is 0 to 2%.

2. The adhesive sheet according to claim 1, wherein the weight average molecular weight of the methyl methacrylate polymer (B) is 1000 to 10000.

3. The refractive index difference between the crosslinkable (meth)acrylic copolymer (A) and the oligomer (C) composed of the (meth)acrylic resin is 0 to 0.05, The adhesive sheet according to claim 1 or 2.

4. The adhesive sheet according to any one of claims 1 to 3, wherein the crosslinking agent (D) contains one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate.

5. A laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 4 and an adherend.

6. An optical device comprising the laminate according to claim 5.

7. An image display device comprising the laminate according to claim 5.

8. A method for manufacturing an optical device comprising a laminate, the method including a heating step of laminating the pressure-sensitive adhesive sheet according to any one of claims 1 to 4 and an adherend and heating the laminate.

9. A method for manufacturing an image display device comprising a laminate, the method including a heating step of laminating the pressure-sensitive adhesive sheet according to any one of claims 1 to 4 and an adherend and heating the laminate.

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