Adhesive composition and adhesive sheet

Abstract

To provide an adhesive composition that exhibits appropriate adhesive strength while possessing rheological properties suitable for flexible components. [Solution] An adhesive composition containing an acrylic copolymer (A) and an amine-based silane coupling agent (B). The acrylic copolymer (A) comprises an alkyl (meth)acrylate (a1) and an epoxy group-containing (meth)acrylate (a2) as constituent units.

Description

Technical Field

[0001] The present invention relates to an adhesive composition and an adhesive sheet, and particularly to an adhesive composition for flexible members.

Background Art

[0002] An adhesive layer used for a flexible member such as a flexible display requires certain rheological properties. For example, such an adhesive layer is required to have resilience. The resilience of the adhesive layer can be improved by enhancing the cohesiveness of the adhesive. For example, Patent Document 1 discloses enhancing the cohesive force by increasing the amount of a crosslinking agent in an adhesive for a flexible image display device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the cohesiveness of the adhesive is enhanced, the adhesive force of the adhesive tends to decrease.

[0005] Thus, there has been a problem of providing an adhesive composition that can exhibit appropriate adhesive force while having rheological properties suitable for flexible members.

Means for Solving the Problems

[0006] An adhesive composition according to an embodiment of the present invention is an adhesive composition containing an acrylic copolymer (A) and an amine-based silane coupling agent (B), The acrylic copolymer (A) comprises an alkyl (meth)acrylate (a1) and an epoxy group-containing (meth)acrylate (a2) as constituent units. [Effects of the Invention]

[0007] This invention provides an adhesive composition that exhibits appropriate adhesive strength while possessing rheological properties suitable for flexible components. [Modes for carrying out the invention]

[0008] The embodiments will be described in detail below. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way.

[0009] relating to one embodiment of the present invention For bonding flexible components The adhesive composition contains an acrylic copolymer (A) and an amine-based silane coupling agent (B) in an amount of 0.05 parts by mass or more and less than 8.0 parts by mass per 100 parts by mass of the acrylic copolymer (A). It does not contain a hardening agent (C). Here, the acrylic copolymer (A) comprises, as constituent units, 60% by mass or more and 99.9% by mass or less of alkyl (meth)acrylate (a1) and 0.1% by mass or more and 20% by mass or less of epoxy group-containing (meth)acrylate (a2), and the Tg of the acrylic copolymer (A) is -100°C or more and -30°C or less.

[0010] The adhesive composition may be in the form of a mixture of an acrylic copolymer (A), an amine-based silane coupling agent (B), and optionally a solvent. On the other hand, the adhesive composition may be a combination of multiple unmixed compositions. For example, the adhesive composition may be a combination of a separate first composition and a second composition. An adhesive composition kit according to one embodiment of the present invention may comprise multiple compositions such as a first composition and a second composition. In one embodiment, the first composition may be, for example, a composition comprising an acrylic copolymer (A) and optionally a solvent. The second composition may be a composition comprising an amine-based silane coupling agent (B), optionally a curing agent (C), and optionally a solvent. These multiple compositions can be mixed and used before forming the adhesive layer.

[0011] <Acrylic copolymer (A)> Acrylic copolymer (A) is a copolymer of unsaturated carboxylic acids. In this specification, unsaturated carboxylic acids include unsaturated carboxylic acids and dehydration condensates of unsaturated carboxylic acids with other components. For example, unsaturated carboxylic acids include unsaturated carboxylic acid esters and unsaturated carboxylic acid amides. Furthermore, acrylic copolymer (A) is a polymer of two or more monomers.

[0012] In one embodiment, the acrylic copolymer (A) is a homopolymer or copolymer of (meth)acrylic acids. That is, the acrylic copolymer (A) may have one or more repeating units derived from (meth)acrylic acids (hereinafter referred to as "(meth)acrylic acid repeating units"). (Meth)acrylic acids include (meth)acrylic acid and (meth)acrylate. In this specification, (meth)acrylic acid refers to acrylic acid and methacrylic acid. Also, (meth)acrylate refers to acrylate and methacrylate.

[0013] As described above, the acrylic copolymer (A) contains alkyl (meth)acrylate (a1) as a constituent unit. The acrylic copolymer (A) may contain one or more alkyl (meth)acrylate (a1) as a constituent unit.

[0014] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and 1-methylheptyl (meth)acrylate. Examples include alkyl(meth)acrylates having linear or branched alkyl groups such as n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-undecyl(meth)acrylate, lauryl(meth)acrylate, n-tridecyl(meth)acrylate, and n-tetradecyl(meth)acrylate; and alkyl(meth)acrylates having alicyclic alkyl groups such as cyclohexyl(meth)acrylate, 4-tert-butylcyclohexyl(meth)acrylate, isobornyl(meth)acrylate, and dicyclopentanyl(meth)acrylate.

[0015] The alkyl group of alkyl(meth)acrylate(a1) may have further substituents such as aromatic hydrocarbon groups, alkoxy groups, aryloxy groups, or polyoxyalkylene groups. Examples of such alkyl(meth)acrylate(a1) include benzyl(meth)acrylate, 2-phenylethyl(meth)acrylate, and naphthylmethyl(meth)acrylate; 2-methoxyethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate, and 2-butoxyethyl(meth)acrylate; 2-phenoxyethyl(meth)acrylate, and 3-phenoxypropyl(meth)acrylate; 2-(2-ethoxyethoxy)ethyl(meth)acrylate, methoxypolyethylene glycol(meth)acrylate, phenoxydiethylene glycol(meth)acrylate, phenoxytriethylene glycol(meth)acrylate, and nonylphenoxypolyethylene glycol(meth)acrylate; and the like.

[0016] From the viewpoint of keeping the storage modulus low at low temperatures, the number of carbon atoms in the alkyl(meth)acrylate (a1) alkyl group is preferably 1 to 20, more preferably 1 to 12, even more preferably 4 to 12, and particularly preferably 8 to 12.

[0017] From the viewpoint of lowering the Tg of the acrylic copolymer (A), it is preferable that the Tg of the alkyl (meth)acrylate (a1) when used as a homopolymer is -50°C or lower. Specific examples of such alkyl (meth)acrylate (a1) include 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), and butyl acrylate (Tg: -52°C).

[0018] From the viewpoints of adhesive force and rheological properties, as the alkyl (meth)acrylate (a1), alkyl (meth)acrylates having an alkyl group with 6 to 9 carbon atoms, such as 2-ethylhexyl acrylate and isononyl acrylate, are preferred.

[0019] As described above, the acrylic copolymer (A) further contains a (meth)acrylate (a2) having an epoxy group as a constituent unit. By the reaction of the (meth)acrylate (a2) having an epoxy group and the amine-based silane coupling agent (B), a crosslinked structure can be introduced into the acrylic copolymer (A). The inventors of the present application consider that this crosslinked structure contributes to the improvement of the cohesive force and adhesiveness of the adhesive layer. The acrylic copolymer (A) can contain one or more (meth)acrylates (a2) having an epoxy group as a constituent unit.

[0020] The (meth)acrylate (a2) having an epoxy group can be an ester of (meth)acrylic acid and epoxy alcohol. The epoxy alcohol can be a hydrocarbon group having an epoxy group and a hydroxy group. Here, the hydrocarbon group may have an internal ether bond. The number of carbon atoms of the epoxy alcohol is preferably 2 or more and 12 or less, more preferably 3 or more and 8 or less.

[0021] Examples of the (meth)acrylate having an epoxy group include epoxyalkyl (meth)acrylates such as glycidyl (meth)acrylate, 2-methylglycidyl (meth)acrylate, and 3,4-epoxycyclohexylmethyl (meth)acrylate, and epoxyalkoxyalkyl (meth)acrylates such as 4-hydroxybutyl (meth)acrylate glycidyl ether.

[0022] Preferable examples of the (meth)acrylate (a2) having an epoxy group include (meth)acrylates having a glycidyl group. For example, the (meth)acrylate (a2) having an epoxy group can be glycidyl acrylate or glycidyl methacrylate. Further, the (meth)acrylate (a2) having an epoxy group may have a glycidyl group bonded via an ether bond. For example, the (meth)acrylate (a2) having an epoxy group can be a glycidyloxyalkyl (meth)acrylate such as 4-hydroxybutyl (meth)acrylate glycidyl ether.

[0023] The acrylic copolymer (A) may contain a structural unit other than the alkyl (meth)acrylate (a1) and the (meth)acrylate (a2) having an epoxy group. The type of the structural unit contained in the acrylic copolymer (A) is not particularly limited. For example, the acrylic copolymer (A) may contain, as a structural unit, a (meth)acrylate (a3) having a hydroxy group and / or a (meth)acrylate (a4) having a carboxy group. Since the (meth)acrylate (a3) having a hydroxy group and the (meth)acrylate (a4) having a carboxy group have high polarity, it is expected that the adhesiveness of the adhesive layer formed using such an adhesive composition is improved. The acrylic copolymer (A) can contain one or more kinds of (meth)acrylates (a3) having a hydroxy group and / or (meth)acrylates (a4) having a carboxy group as a structural unit.

[0024] Examples of hydroxyl group-containing (meth)acrylates (a3) ​​include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and polyoxyalkylene (meth)acrylates such as polypropylene glycol monoacrylate. From the viewpoint of lowering the Tg of the acrylic copolymer (A), it is preferable that the Tg of the homopolymer of the hydroxyl group-containing (meth)acrylate (a3) ​​be -20°C or lower.

[0025] Examples of (meth)acrylates (a4) having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, 2-carboxyethyl acrylate, mono(2-acryloyloxyethyl) succinate, and mono-2-(methacryloyloxy)ethyl phthalate.

[0026] From the viewpoint of obtaining appropriate adhesion, the proportion of (meth)acrylic acid repeating units contained in the acrylic copolymer (A) as constituent units is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, while being 100% by mass or less.

[0027] From the viewpoint of obtaining appropriate adhesion, the proportion of alkyl (meth)acrylate (a1) contained in the acrylic copolymer (A) as a constituent unit is, for example, 60% by mass or more, preferably 75% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, while on the other hand, it is, for example, 99.9% by mass or less. Furthermore, from the viewpoint of lowering the Tg of the acrylic copolymer (A), the proportion of alkyl (meth)acrylate (a1) having an alkyl group with 8 to 12 carbon atoms contained in the acrylic copolymer (A) as a constituent unit is, for example, 60% by mass or more, preferably 75% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, while on the other hand, it is, for example, 99.9% by mass or less.

[0028] The proportion of epoxy-group-containing (meth)acrylate (a2) as a constituent unit in the acrylic copolymer (A) is preferably, for example, 0.1% to 20% by mass, more preferably 0.5% to 10% by mass, and more preferably 1.0% to 5.0% by mass, from the viewpoint of increasing the crosslinking density and lowering the shear deformation rate. By increasing the proportion of epoxy-group-containing (meth)acrylate (a2), the shear deformation rate can be lowered. Furthermore, by lowering the proportion of epoxy-group-containing (meth)acrylate (a2), the adhesive strength can be improved.

[0029] The proportion of (meth)acrylate (a3) ​​having a hydroxyl group contained as a constituent unit in the acrylic copolymer (A) is preferably 0.1% by mass or more and 20% by mass or less, preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less, from the viewpoint of improving initial adhesion and rheological properties.

[0030] The proportion of (meth)acrylate (a4) having a carboxyl group contained in the acrylic copolymer (A) as a constituent unit is preferably 0.1% by mass or more and 10% by mass or less, preferably 0.5% by mass or more and 5.0% by mass or less, and more preferably 1.0% by mass or more and 3.0% by mass or less, from the viewpoint of improving initial adhesion.

[0031] The molecular weight of the acrylic copolymer (A) is not particularly limited. The acrylic copolymer (A) may be an oligomer having a mass-average molecular weight of, for example, less than 100,000. Alternatively, the acrylic copolymer (A) may be a polymer having a mass-average molecular weight of 100,000 or more. The mass-average molecular weight of the oligomer acrylic copolymer (A) is, for example, 500 or more and less than 100,000, preferably 1,000 or more and less than 100,000, and more preferably 10,000 or more and less than 100,000. The mass-average molecular weight of the polymer acrylic copolymer (A) is, for example, 100,000 or more and 10,000,000 or less, preferably 100,000 or more and 5,000,000 or less, and more preferably 1,000,000 or more and 3,000,000 or less. In this specification, the mass-average molecular weight is the polystyrene-equivalent molecular weight measured by gel permeation chromatography.

[0032] From the viewpoint of the flexibility and tackiness of the adhesive, the Tg of the acrylic copolymer (A) is preferably -100°C to -30°C, more preferably -90°C to -40°C, and even more preferably -80°C to -50°C. Lowering the Tg of the acrylic copolymer (A) can lower the storage modulus of the adhesive. Conversely, increasing the Tg of the acrylic copolymer (A) can improve the tackiness of the adhesive. The Tg of the acrylic copolymer (A) is calculated based on the FOX formula.

[0033] In one embodiment, the adhesive composition may contain resins other than the acrylic copolymer (A). From the viewpoint of obtaining appropriate rheological properties, the proportion of the acrylic copolymer (A) in the total resin contained in the adhesive composition is, for example, 60% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, while being 100% by mass or less.

[0034] <Amine-based silane coupling agent (B)> Silane coupling agents are generally silicon compounds that possess functional groups that bond to both organic and inorganic materials within their molecules. Amine-based silane coupling agents (B) are silane coupling agents that contain an amino group. Acrylic copolymers (A) may contain one or more amine-based silane coupling agents (B).

[0035] Many silane coupling agents have a structure in which an organic group and one or more alkoxy groups are bonded to a silicon atom. In one embodiment, the amine-based silane coupling agent (B) has an organoalkoxysilane structure in which an organic group having an amino group and one or more alkoxy groups are bonded to a silicon atom. Alternatively, the amine-based silane coupling agent (B) may be an oligomer, i.e., an organopolysiloxane, in which the above-mentioned organoalkoxysilanes are bonded via siloxane bonds.

[0036] The organic group having an amino group is not particularly limited. The number of carbon atoms in the organic group having an amino group is preferably 1 to 20, and more preferably 2 to 12. In terms of improved reactivity with the (meth)acrylate (a2) having an epoxy group, it is preferable that the organic group having an amino group has a primary amino group. The number of amino groups in the organic group having an amino group is not particularly limited.

[0037] Specific examples of organic groups having an amino group include aminoalkyl groups such as 2-aminoethyl, 3-aminopropyl, 2-aminopropyl, 4-aminobutyl, and 8-aminooctyl. The number of carbon atoms in the aminoalkyl group is preferably 1 to 20. Here, the amino group of the aminoalkyl group may have substituents. Aminoalkyl groups having such substituted amino groups are also included in aminoalkyl groups. Examples of substituents include alkyl groups, aryl groups, aminoalkyl groups, and poly(aminoalkylene) groups. Specific examples of such organic groups having an amino group include N-alkylaminoalkyl groups such as N-ethyl-3-aminopropyl; N-arylaminoalkyl groups such as N-phenyl-3-aminopropyl; N-(aminoalkyl)aminoalkyl groups such as N-2-(aminoethyl)-3-aminopropyl and N-2-(aminoethyl)-8-aminooctyl; and N-[N-aminoalkyl(aminoalkyl)]aminoalkyl groups such as 3-[2-(2-aminoethylamino)ethylamino]propyl.

[0038] As described above, an organic group having an amino group may be a hydrocarbon group in which one or more carbon atoms are substituted with nitrogen atoms. The nitrogen atom may substitute for a terminal carbon atom of the hydrocarbon group, or for a carbon atom inside the hydrocarbon group. Here, the hydrocarbon group may be linear, branched, or cyclic. Furthermore, the hydrocarbon group may be an aliphatic hydrocarbon group. In addition, one or more carbon atoms of this hydrocarbon group may be further substituted with oxygen atoms.

[0039] Other substituents besides the amino group-containing organic group that can bond to the silicon atom include alkoxy groups such as methoxy and ethoxy groups, and alkyl groups such as methyl and ethyl groups. For example, the amine-based silane coupling agent (B) can have a structure in which an alkoxysilyl group such as a trialkoxysilyl group like a trimethoxysilyl group, a triethoxysilyl group, or a tri(2-methoxyethoxy)silyl group; an alkyldialkoxysilyl group such as a methyldimethoxysilyl group; or a dialkylalkoxysilyl group such as a dimethylmethoxysilyl group is bonded to the above-mentioned amino group-containing organic group. That is, in one embodiment, the amine-based silane coupling agent (B) is an alkoxysilane having the above-mentioned aminoalkyl group, for example, a trialkoxysilane having an aminoalkyl group.

[0040] Specific examples of amine-based silane coupling agents (B) include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and N-2-(aminoethyl)-3-aminopropyltriethoxysilane.

[0041] From the viewpoint of the restorability and tackiness of the adhesive, the amount of amine-based silane coupling agent (B) per 100 parts by mass of acrylic copolymer (A) in the adhesive composition is preferably 0.05 parts by mass or more and less than 8.0 parts by mass, more preferably 0.1 parts by mass or more and 7.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 6.5 parts by mass or less, even more preferably 1.0 part by mass or more and 6.0 parts by mass or less, and even more preferably 1.5 parts by mass or more and 5.0 parts by mass or less. Increasing the amount of amine-based silane coupling agent (B) improves the restorability. Also, decreasing the amount of amine-based silane coupling agent (B) improves the tackiness.

[0042] <Hardening agent (C)> The curing agent (C) has the effect of curing the adhesive composition by crosslinking the acrylic copolymer (A).

[0043] Examples of the curing agent (C) include epoxy curing agents. Examples of epoxy curing agents include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, N,N-diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane.

[0044] Other examples of curing agents (C) include metal chelating curing agents and aziridine curing agents. The curing agent (C) can be selected according to the type of acrylic copolymer (A).

[0045] From the viewpoint of obtaining appropriate adhesive strength, the content of the curing agent (C) in the adhesive composition is preferably 0.01 parts by mass or more and 1.0 part by mass or less, more preferably 0.02 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.05 parts by mass or more and 0.1 parts by mass or less, per 100 parts by mass of the acrylic copolymer (A).

[0046] However, since the amine-based silane coupling agent (B) has the effect of curing the adhesive composition, it is not essential that the adhesive composition contains a curing agent (C). For this reason, in one embodiment, from the viewpoint of adhesive strength, the content of the curing agent (C) in the adhesive composition, particularly the content of the epoxy-based curing agent, is preferably 1.0 part by mass or less, more preferably 0.1 part by mass or less, and even more preferably 0.01 part by mass or less, per 100 parts by mass of the acrylic copolymer (A).

[0047] <Other additives> The adhesive composition may contain other resins or additives. Examples of additives include curing retarders, antistatic agents, tackifiers, antioxidants, heat stabilizers, light stabilizers, UV absorbers, leveling agents, defoamers, antibacterial agents, humectants, pigments, dyes, and fragrances. The adhesive composition may contain one or more of these additives.

[0048] <Manufacturing method> The adhesive composition according to this embodiment can be prepared by known methods. For example, the adhesive composition can be prepared by mixing an acrylic copolymer (A) and an amine-based silane coupling agent (B), and optionally a curing agent (C), a solvent, and additives.

[0049] Acrylic copolymer (A) can be prepared by known methods. For example, acrylic copolymer (A) can be prepared by solution polymerization. Specifically, acrylic copolymer (A) can be prepared by polymerizing a mixture of a solvent, monomer, and polymerization initiator in an inert gas atmosphere such as nitrogen gas at a temperature of about 50 to 90°C for 4 to 12 hours.

[0050] As solvents, for example, ester-based solvents such as methyl acetate, ethyl acetate, or butyl acetate; ketone-based solvents such as acetone, methyl ethyl ketone, or methyl isobutyl ketone; or hydrocarbon-based solvents such as toluene, xylene, hexane, or heptane can be used.

[0051] Radical polymerization initiators can be used as polymerization initiators. Specific examples of polymerization initiators include persulfates such as potassium persulfate, sodium persulfate, or ammonium persulfate; oil-soluble azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyric acid)dimethyl, or 1,1'-azobis(cyclohexane-1-carbonitride); and 2,2'-azobis[2-methyl-N- Examples include water-soluble azo compounds such as (2-hydroxyethyl)propionamide, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] or its salts, 2,2'-azobis(2-methylpropionamidine) or its salts, or 4,4'-azobis(4-cyanovaleric acid) or its salts; or organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butylperoxy-2-ethylhexanoate, or t-butylperoxyisobutyrate.

[0052] <How to use> An adhesive layer can be prepared using the adhesive composition according to this embodiment. An adhesive layer according to one embodiment comprises the adhesive composition according to this embodiment. For example, an adhesive layer can be prepared by applying the adhesive composition and drying it. Furthermore, an adhesive sheet according to one embodiment comprises an adhesive layer containing the adhesive composition according to this embodiment. Such an adhesive sheet can be prepared by applying the adhesive composition to a substrate and drying it. The adhesive layer thus obtained can be used to bond optical components such as surface protection films or polarizing films.

[0053] The method of applying the adhesive composition is not particularly limited. For application, for example, a Meyer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, or spin coater can be used. The drying method is also not particularly limited. Examples of drying methods include hot air drying, infrared drying, and reduced pressure drying. Drying conditions can be selected according to the composition of the adhesive composition, film thickness, and type of solvent. In one embodiment, drying is performed at 80°C to 150°C, preferably 100°C to 140°C.

[0054] The thickness of the resulting adhesive layer is not particularly limited. For example, the thickness of the adhesive layer is 1 μm to 200 μm, preferably 3 μm to 100 μm.

[0055] Thus, the method for manufacturing an adhesive sheet according to one embodiment includes a step of forming an adhesive layer from an adhesive composition. For example, by forming an adhesive layer on a base sheet, an adhesive sheet comprising a base sheet and an adhesive layer can be manufactured. Alternatively, by forming an adhesive layer on a release sheet and peeling the adhesive layer from the release sheet, an adhesive sheet consisting only of an adhesive layer can be manufactured.

[0056] As in this embodiment, by using an adhesive composition comprising an acrylic copolymer (A) containing an epoxy group-containing (meth)acrylate (a2) and an amine-based silane coupling agent (B), an adhesive layer with appropriate adhesive strength while possessing rheological properties suitable for flexible members can be formed. Techniques to increase adhesive strength, such as the use of high-Tg monomers, low molecular weight resins, and reduced crosslinking density, can affect rheological properties. On the other hand, the inventors of this application have found that the amine-based silane coupling agent (B) has a strong effect in improving adhesive strength even in small amounts, while having little effect on rheological properties. However, the amine-based silane coupling agent reacts with isocyanate curing agents, which are commonly used for crosslinking acrylic copolymers. The inventors of this application have found that by using an acrylic copolymer (A) containing an epoxy group-containing (meth)acrylate (a2), crosslinking can be promoted without the use of other curing agents.

[0057] An adhesive composition according to one embodiment possesses both resilience and adhesive strength. That is, by using an amine-based silane coupling agent (B), the adhesiveness of the adhesive layer can be improved without significantly impairing the resilience of the adhesive layer. Furthermore, when using an amine-based silane coupling agent (B), increasing the amount added can further improve the resilience without significantly impairing the adhesiveness of the adhesive layer.

[0058] Furthermore, the adhesive composition according to one embodiment possesses both flexibility and adhesive strength. Flexibility is one of the desirable rheological properties of an adhesive layer used for a flexible member. Generally, the flexibility of an adhesive layer can be improved by increasing its flexibility. For example, by using a low-Tg (meth)acrylic copolymer as the material for the adhesive layer, the storage modulus of the adhesive layer can be lowered, thereby increasing the flexibility of the adhesive layer. However, if the storage modulus of the adhesive layer is lowered too much, the adhesiveness of the adhesive layer tends to decrease. In one embodiment, by using an amine-based silane coupling agent (B), the adhesiveness of the adhesive layer can be improved without significantly impairing the flexibility of the adhesive layer. In particular, even when a low-Tg (meth)acrylic copolymer is used as the material for the adhesive layer, the adhesiveness of the adhesive layer can be improved by using an amine-based silane coupling agent (B).

[0059] An adhesive composition according to one embodiment possesses the above-described properties of resilience, flexibility, and tackiness. Such an adhesive composition is particularly suitable for forming an adhesive for use on flexible members.

[0060] The peel-off adhesive strength of the adhesive layer of the adhesive sheet is preferably 2.0 N / 25 mm or more, more preferably 2.5 N / 25 mm or more, and even more preferably 3.0 N / 25 mm or more. On the other hand, it may be, for example, 10 N / 25 mm or less. In this specification, peel-off adhesive strength refers to the peel-off adhesive strength from the glass plate. The peel-off adhesive strength is measured under the conditions of 23°C and 50% RH, peel angle of 180°, and peel speed of 300 mm / min, in accordance with the provisions of JIS Z0237:2009, as described in the examples.

[0061] The storage modulus (G') of the adhesive layer at -20°C is preferably 100 kPa or less, more preferably 90 kPa or less, even more preferably 80 kPa or less, and particularly preferably 70 kPa or less. On the other hand, it is, for example, 10 kPa or more. The storage modulus (G') of the adhesive layer at 25°C is preferably 100 kPa or less, more preferably 50 kPa or less, even more preferably 40 kPa or less, and particularly preferably 35 kPa or less. On the other hand, it is, for example, 10 kPa or more. A low storage modulus means that the adhesive layer has high flexibility, i.e., that the adhesive layer has rheological properties that are more suitable for flexible members. In this specification, the storage modulus is the shear storage modulus. The storage modulus is measured under the conditions of shear strain: 0.1%, frequency: 1.0 Hz, and normal force: 1 N, as described in the examples.

[0062] The shear deformation rate of the adhesive layer is preferably 100% or less, more preferably 80% or less, even more preferably 65% ​​or less, and particularly preferably 45% or less. A low shear deformation rate means that the adhesive layer has high resilience, i.e., that the adhesive layer has rheological properties more suitable for flexible members. In this specification, the shear deformation rate is measured 600 seconds after releasing a shear stress of 2 kPa applied for 600 seconds under normal force: 1 N and measurement temperature: 60°C, as described in the examples. [Examples]

[0063] [Production Examples A1-A10: Preparation of (meth)acrylic copolymers (A1-A10)] (Meth)acrylic copolymers (A1-A10) related to production examples A1-A10 were prepared using monomers with the composition ratios shown in Table 1.

[0064] Specifically, 100 parts by mass of a monomer mixture in the proportions shown in Table 1, 0.04 parts by mass of a polymerization initiator (azobisisobutyronitrile), and 40 parts by mass of ethyl acetate and 30 parts by mass of acetone as reaction solvents were added to a reaction apparatus equipped with a stirrer, thermometer, and reflux condenser. The reaction solution was then stirred and reacted under the reflux temperature of ethyl acetate for 5 hours. After the reaction was complete, the solution was diluted with ethyl acetate and cooled to room temperature to obtain a solution of acrylic copolymer (A).

[0065] Table 1 shows the glass transition temperature (Tg) of each acrylic copolymer (A). Tg is a theoretical value obtained from the following FOX equation. 1 / Tg=W1 / Tg1+W2 / Tg2+...Wn / Tgn In the above formula, Tg represents the glass transition temperature (in K) of the copolymer of n monomer components (monomers 1 to n). W1, W2, ...Wn represent the mass fraction of each monomer (1, 2, ...n) relative to the total amount of n monomer components. Tg1, Tg2, ...Tgn represent the glass transition temperature (in K) of the homopolymer of each monomer (1, 2, ...n).

[0066] [Examples 1-9 and Comparative Examples 1-2] The adhesive composition was obtained by thoroughly mixing the types and amounts of each component shown in Table 1. Table 2 shows the types of acrylic copolymers (A), the types of amine-based silane coupling agents (B), and the solid content parts of each component used in each example and comparative example.

[0067] Furthermore, the adhesive compositions obtained in each example and comparative example were coated onto a release film (a 38 μm thick polyethylene terephthalate (PET) film with a silicone-treated surface). The resulting adhesive composition was dried in a 120°C dryer for 120 seconds. The thickness of the resulting adhesive layer was 50 μm (dry). Subsequently, another 50 μm thick PET film was laminated onto the adhesive layer, and cured in a 60°C atmosphere for 4 days to prepare an adhesive sheet for adhesion evaluation.

[0068] Furthermore, as described above, ten layers of 50 μm thick adhesive layer were laminated onto the release film. Then, another 50 μm thick PET film was bonded to the adhesive layer, and cured for four days in a 60°C atmosphere to produce an adhesive sheet for viscoelasticity evaluation. This adhesive sheet had an adhesive layer with a thickness of 500 μm.

[0069] [Adhesion strength measurement] For each example and comparative example, the adhesive sheets obtained for adhesion evaluation were measured in accordance with JIS Z0237:2009, under conditions of 23°C and 50%RH, to measure the 180° peel adhesion to a test plate. Specifically, a test specimen was prepared by cutting the adhesive sheet to a width of 25 mm, peeling off the release film, attaching it to a glass plate, and pressing it back and forth once with a 2 kg load using a pressure roll. After leaving the test specimen at 23°C for 24 hours, the adhesion to the glass plate was measured by peeling off the adhesive sheet at a peeling speed of 300 mm / min.

[0070] The results of the adhesive strength measurement are shown in Table 1. If the adhesive strength is 2N or higher, it can be evaluated as having no practical problems. Adhesive sheets with such adhesive strength can be suitably used as adhesive sheets for foldable devices.

[0071] [Measurement of storage modulus] The adhesive sheets obtained for viscoelastic evaluation in each example and comparative example were punched out into 8 mm diameter discs. The storage modulus of the obtained samples was measured using a rheometer (Anton Paar: MCR302e, jig: PP08) under the following conditions. Shear strain: 0.1%, Frequency: 1.0Hz, Normal force: 1N, Measurement temperature: -30~100℃, Heating rate: 5℃ / min

[0072] Table 1 shows the measured storage modulus at -20°C and 25°C. If the storage modulus at -20°C is 0.1 MPa or less, it can be considered to have no practical problems.

[0073] [Shear deformation ratio measurement] The adhesive sheets obtained for viscoelasticity evaluation in each example and comparative example were punched out into 8 mm diameter discs. The shear deformation rate of the obtained samples was measured using a rheometer (Anton Paar: MCR302e, jig: PP08) under the following conditions. Condition 1 (0-600 seconds): Shear stress: 2kPa, Normal force: 1N, Measurement temperature: 60℃, Time: 600s Condition 2 (600-1200 seconds): Shear stress: 0 kPa, Normal force: 1 N, Measurement temperature: 60°C, Time: 600 s

[0074] Table 1 shows the measurement results of the shear deformation rate 600 seconds after the start of measurement under Condition 2. This shear deformation rate represents the recovery of the adhesive after load removal. If the shear deformation rate is 100% or less, it can be evaluated that there are no practical problems.

[0075] [Table 1]

[0076] The components shown in Table 1 are as follows: BA: Butyl acrylate (Tg / -52℃) 2EHA: 2-Ethylhexyl acrylate (Tg / -70℃) NOAA: Normal Octyl Acrylate (Tg / -65℃) AIN: Isononyl acrylate (Tg / -58℃) LA: Lauryl acrylate (Tg / -23℃) GMA: Glycidyl methacrylate (Tg / 46℃) 4HBAGE: 4-Hydroxybutyl acrylate glycidyl ether (Tg / -59℃) 4HBA: 4-Hydroxybutyl acrylate (Tg / -32℃) AAc: Acrylic acid (Tg / 106℃) KBM-903: Silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., 3-aminopropyltrimethoxysilane) KBM-603: Silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) KBM-6803: Silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-8-aminooctyltrimethoxysilane) Epoxy curing agent: Multifunctional epoxy curing agent (manufactured by Mitsubishi Gas Chemical Company, product name: Tetrad X) Isocyanate curing agent: Isocyanurate of tolylene diisocyanate (manufactured by Mitsui Chemicals Polyurethane Co., Ltd., product name: Takenate D-262)

[0077] As shown in Table 1, the adhesive layers of Examples 1 to 9, prepared using an adhesive composition containing an acrylic copolymer (A) comprising alkyl (meth)acrylate (a1) and (meth)acrylate (a2) having a glycidyl group as constituent units, and an amine-based silane coupling agent (B), exhibit appropriate adhesive strength while possessing rheological properties suitable for flexible members. That is, these adhesive layers have sufficient adhesive strength of 2N or more, while having a shear deformation rate of 100% or less, and exhibiting sufficient resilience.

[0078] In particular, as shown in Examples 5 and 6, increasing the amount of amine-based silane coupling agent (B) tends to improve resilience. On the other hand, even when the amount of amine-based silane coupling agent (B) is increased to 5 parts by mass, no significant decrease in adhesive strength is observed. Also, as shown in Examples 2 and 3, increasing the amount of epoxy-group-containing (meth)acrylate (a2) included as a constituent unit in the acrylic copolymer (A) tends to improve resilience. On the other hand, even when the ratio of epoxy-group-containing (meth)acrylate (a2) is increased to 20% by mass, no significant decrease in adhesive strength is observed.

[0079] Furthermore, according to the inventors' studies, by adding more than 0.01 parts by mass, particularly 0.1 parts by mass or more, of the amine-based silane coupling agent (B) per 100 parts by mass of the acrylic copolymer (A), the shear deformation rate could be significantly reduced compared to the case where the amount added was 0.01 parts by mass or less. Also, by adding less than 8.0 parts by mass, particularly 5.0 parts by mass or less, of the amine-based silane coupling agent (B) per 100 parts by mass of the acrylic copolymer (A), the adhesive strength could be significantly increased compared to the case where the amount added was 8.0 parts by mass or more. Moreover, by including less than 30% by mass, particularly 20% by mass or less, of epoxy groups (meth)acrylate (a2) as a constituent unit in the acrylic copolymer (A), the adhesive strength could be significantly increased compared to the case where 30% by mass or more of epoxy groups (meth)acrylate (a2) were included.

[0080] Furthermore, the adhesive layers of Examples 1 to 9 have a storage modulus of 0.1 MPa or less at -20°C. That is, these adhesive layers have sufficient flexibility at low temperatures. Also, the adhesive layers of Examples 1 to 9 have a storage modulus of 0.1 MPa or less at 25°C. That is, these adhesive layers have sufficient flexibility at room temperature.

[0081] Furthermore, according to the inventors' studies, by including (meth)acrylate (a2) having less than 30% by mass, particularly 20% by mass or less, of epoxy groups as a constituent unit in the acrylic copolymer (A), it was possible to significantly lower the storage modulus at -20°C compared to the case where (meth)acrylate (a2) having 30% by mass or more of epoxy groups.

[0082] On the other hand, in Comparative Example 1, where the acrylic copolymer (A) did not contain (meth)acrylate (a2) having epoxy groups as a constituent unit, the shear deformation ratio was greater than 100%. Furthermore, in Comparative Example 2, where the adhesive composition was crosslinked using an isocyanate curing agent (C) without using an amine-based silane coupling agent (B), the adhesive strength was lower than 2N. This result indicates that the combination of (meth)acrylate (a2) having epoxy groups and the isocyanate curing agent (C) can achieve both adhesiveness and rheological properties. On the other hand, as shown in Example 9, an amine-based silane coupling agent (B) and other curing agents may be used in combination for crosslinking the adhesive composition.

[0083] Furthermore, according to one embodiment of the present invention, by improving the durability of the adhesive, it is possible to reduce the disposal of adherends such as optical components, thereby contributing to Goal 12 of the United Nations Sustainable Development Goals (SDGs), "Responsible Consumption and Production."

[0084] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. An adhesive composition for bonding flexible members, comprising an acrylic copolymer (A), and an amine-based silane coupling agent (B) in an amount of 0.05 parts by mass or more and less than 8.0 parts by mass per 100 parts by mass of the acrylic copolymer (A), and not containing a curing agent (C), The acrylic copolymer (A) comprises, as constituent units, 60% by mass or more and 99.9% by mass or less of alkyl (meth)acrylate (a1), and 0.1% by mass or more and 20% by mass or less of epoxy group-containing (meth)acrylate (a2). The Tg of the acrylic copolymer (A) is -100°C or higher and -30°C or lower. Adhesive composition for bonding flexible components.

2. The adhesive composition according to claim 1, wherein the alkyl (meth)acrylate (a1) has 1 to 12 carbon atoms in the alkyl group.

3. The adhesive composition according to claim 1, wherein the (meth)acrylate (a2) having the epoxy group is an ester of (meth)acrylic acid and an epoxy alcohol having 1 to 12 carbon atoms.

4. The adhesive composition according to claim 1, wherein the amine-based silane coupling agent (B) has a primary amino group.

5. An adhesive sheet comprising an adhesive layer containing the adhesive composition according to any one of claims 1 to 4.

6. The adhesive sheet according to claim 5, wherein the peeling adhesive strength of the adhesive layer from the glass plate is 2.0 N / 25 mm or more under the conditions of 23°C, 50% RH, peeling angle of 180°, and peeling speed of 300 mm / min.

7. The adhesive sheet according to claim 5, wherein the storage modulus (G') of the adhesive layer at -20°C is 100 kPa or less.

8. An optical member comprising a base sheet and an adhesive layer containing the adhesive composition described in any one of claims 1 to 4.

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