Adhesive composition, adhesive sheet, and display device

Abstract

The present invention provides an adhesive composition suitable for forming a highly durable adhesive layer while possessing sufficient elastic modulus. [Solution] An adhesive composition containing a (meth)acrylic copolymer (A) and an amine-based silane coupling agent (B). The (meth)acrylic copolymer (A) comprises, as constituent units, an alkyl (meth)acrylate (a1), a (meth)acrylate (a2) having an epoxy group, and a (meth)acrylate (a3) ​​having a hydroxyl group.

Description

Technical Field

[0001] The present invention relates to an adhesive composition, an adhesive sheet, and a display device, and particularly to an adhesive composition for an optical film.

Background Art

[0002] Adhesive compositions are used for fixing various components. Such adhesive compositions may be required to have a high elastic modulus. For example, when an adhesive composition is used to adhere a film in an environment where temperature changes exist, it is desirable to prevent dimensional changes of the film. As an example, liquid crystal displays and organic EL displays are used as display devices for electronic devices. Various optical members constituting such display devices are generally fixed by an adhesive. For example, an optical film such as a surface protection film or a polarizing film may be attached and fixed to a display by an adhesive. In such applications, dimensional changes of the optical film accompanying temperature changes cause color unevenness in the display device. Patent Document 1 discloses increasing the storage elastic modulus of an adhesive in order to suppress dimensional changes of a film. Specifically, Patent Document 1 discloses combining a plurality of curing agents contained in an adhesive composition at a specific ratio and allowing sufficient curing to proceed.

[0003] In particular, in display devices for mobile and vehicle-mounted applications, strict durability, particularly heat resistance, is required. In such applications, it is desirable that the adhesive layer has durability so that foaming or peeling does not occur at the film edge portion in a high-temperature environment or a high-temperature and high-humidity environment. Patent Document 2 describes controlling the amount of use of an isocyanate-based crosslinking agent in order to achieve both reworkability and durability of the adhesive layer. On the other hand, with the recent trend of weight reduction and thinning of electronic devices, thinning of the adhesive layer has been required. For this reason, it has become more difficult to obtain sufficient durability.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-128439 [Patent Document 2] Japanese Patent Publication No. 2019-32508 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The inventors of this application investigated increasing the elastic modulus of the adhesive layer and incorporating a large amount of crosslinking agent into the adhesive composition as methods to prevent dimensional changes in the film. However, it was found that incorporating a large amount of crosslinking agent reduces the durability of the adhesive layer.

[0006] Thus, there was a challenge in providing an adhesive composition suitable for forming a highly durable adhesive layer while possessing sufficient elastic modulus. [Means for solving the problem]

[0007] The adhesive composition according to one embodiment of the present invention is An adhesive composition containing a (meth)acrylic copolymer (A) and an amine-based silane coupling agent (B), The (meth)acrylic copolymer (A) comprises, as constituent units, an alkyl (meth)acrylate (a1), an epoxy group-containing (meth)acrylate (a2), and a hydroxyl group-containing (meth)acrylate (a3). [Effects of the Invention]

[0008] This provides an adhesive composition suitable for forming a highly durable adhesive layer while possessing sufficient elastic modulus. [Modes for carrying out the invention]

[0009] 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.

[0010] An adhesive composition according to one embodiment of the present invention contains an acrylic copolymer (A) and an amine-based silane coupling agent (B). Here, the acrylic copolymer (A) includes, as constituent units, an alkyl (meth)acrylate (a1), an epoxy group-containing (meth)acrylate (a2), and a hydroxyl group-containing (meth)acrylate (a3).

[0011] 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.

[0012] <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.

[0013] 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"). In this specification, (meth)acrylic acid refers to acrylic acid and methacrylic acid. Also, (meth)acrylate refers to acrylate and methacrylate.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] From the viewpoint of increasing the storage modulus, the number of carbon atoms in the alkyl(meth)acrylate (a1) alkyl group is preferably 1 to 20, more preferably 1 to 14, and even more preferably 1 to 10.

[0018] As described above, the acrylic copolymer (A) further comprises (meth)acrylate (a2) having epoxy groups as constituent units. A crosslinked structure can be introduced into the acrylic copolymer (A) by reaction between the (meth)acrylate (a2) having epoxy groups and an amine-based silane coupling agent (B). The inventors of this application believe that this crosslinked structure contributes to improving the adhesion of the adhesive layer. The acrylic copolymer (A) may contain one or more types of (meth)acrylate (a2) having epoxy groups as constituent units.

[0019] (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.

[0020] Examples of (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 glycidyl ether of 4-hydroxybutyl (meth)acrylate.

[0021] Preferred examples of (meth)acrylate (a2) having an epoxy group include (meth)acrylate having a glycidyl group. For example, (meth)acrylate (a2) having an epoxy group can be glycidyl acrylate or glycidyl methacrylate. Also, (meth)acrylate (a2) having an epoxy group may have a glycidyl group bonded via an ether bond. For example, (meth)acrylate (a2) having an epoxy group can be glycidyloxyalkyl (meth)acrylate such as glycidyl ether of 4-hydroxybutyl (meth)acrylate.

[0022] As described above, the acrylic copolymer (A) further contains (meth)acrylate (a3) having a hydroxy group as a constituent unit. (Meth)acrylate (a3) having a hydroxy group can bind to the amine-based silane coupling agent (B). The inventors of the present application believe that this binding contributes to the improvement of the durability of the adhesive layer. The acrylic copolymer (A) can contain one or more (meth)acrylates (a3) having a hydroxy group as a constituent unit.

[0023] (Meth)acrylate (a3) having a hydroxy group can be an ester of (meth)acrylic acid and a diol. This diol can be a hydrocarbon group having two or more hydroxy groups. Here, one or more of the carbon atoms constituting the hydrocarbon group may be substituted with an oxygen atom and / or a nitrogen atom. The number of carbon atoms of the hydrocarbon group having two hydroxy groups is preferably 2 or more and 12 or less, more preferably 2 or more and 6 or less.

[0024] Examples of (meth)acrylate (a3) having a hydroxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate.

[0025] The acrylic copolymer (A) may contain a structural unit other than alkyl (meth)acrylate (a1), (meth)acrylate (a2) having an epoxy group, and (meth)acrylate (a3) having a hydroxy group. The types of structural units contained in the acrylic copolymer (A) are not particularly limited. For example, the acrylic copolymer (A) can contain other (meth)acrylates as structural units. Further, the acrylic copolymer (A) can contain a vinyl monomer or an amide group-containing monomer as a structural unit.

[0026] Examples of vinyl monomers include compounds having a vinyl group other than (meth)acrylate, such as styrene monomers like styrene, α-methylstyrene, vinyltoluene, vinylpyridine, and divinylbenzene; compounds in which a nitrogen atom is bonded to a vinyl group, such as vinylpyrrolidone and vinylcarbazole; compounds in which a carbonyloxy group is bonded to a vinyl group, such as vinyl acetate; acrylonitrile; conjugated diene monomers like butadiene, isoprene, and chloroprene; vinyl halides such as vinyl chloride and vinyl bromide; and vinylidenes such as vinylidene chloride.

[0027] Examples of monomers containing an amide group include acrylamide and methacrylamide; and N-substituted (meth)acrylamides such as N-vinylpyrrolidone, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N'-methylenebisacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, and diacetoneacrylamide.

[0028] 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 80% by mass or more, and even more preferably 90% by mass or more, while being 100% by mass or less.

[0029] 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 70% by mass or more, more preferably 75% by mass or more, and may also be 80% by mass or more, while on the other hand, it is, for example, 95% by mass or less. Furthermore, from the viewpoint of increasing the storage modulus, the proportion of alkyl (meth)acrylate (a1) having an alkyl group with 1 to 4 carbon atoms contained in the acrylic copolymer (A) as a constituent unit is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, while on the other hand, it is, for example, 95% by mass or less.

[0030] The proportion of epoxy group-containing (meth)acrylate (a2) in the acrylic copolymer (A) as a constituent unit is, from the viewpoint of improving initial adhesion and / or heat resistance, for example, 0.05% by mass or more and 30% by mass or less, preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less.

[0031] The proportion of (meth)acrylate (a3) ​​having a hydroxyl group contained as a constituent unit in the acrylic copolymer (A) is, for example, 0.1% by mass or more and 30% by mass or less, preferably 0.5% by mass or more and 20% by mass or less, and more preferably 3.0% by mass or more and 15% by mass or less, from the viewpoint of improving initial adhesion and / or heat resistance.

[0032] The molecular weight of the acrylic copolymer (A) is not particularly limited. From the viewpoint of heat resistance, it is preferable that the acrylic copolymer (A) has a high mass-average molecular weight. The mass-average molecular weight of the acrylic copolymer (A) is, for example, 1 million to 10 million, preferably 2 million to 6 million, and more preferably 2.5 million to 4 million. In this specification, the mass-average molecular weight is the polystyrene-equivalent molecular weight measured by gel permeation chromatography.

[0033] From the viewpoint of initial adhesion and / or heat resistance, the Tg of the acrylic copolymer (A) is preferably -50°C to 0°C, more preferably -50°C to -40°C, and even more preferably -50°C to -30°C. The Tg of the acrylic copolymer (A) is calculated from FOX based on the glass transition temperature of the monomer homopolymer.

[0034] In one embodiment, the adhesive composition may contain resins other than the acrylic copolymer (A). From the viewpoint of obtaining appropriate tackiness, 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.

[0035] <Amine-based silane coupling agent (B)> Silane coupling agents are generally silicon compounds that possess functional groups that bond with both organic and inorganic materials within their molecules. Amine-based silane coupling agents (B) are silane coupling agents that have an amino group. Acrylic copolymers (A) can contain one or more amine-based silane coupling agents (B). According to the inventors' research, amine-based silane coupling agents (B) have a strong effect in improving adhesion even in small amounts.

[0036] 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.

[0037] 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. The amino group may be a primary amino group or a secondary amino group. It is preferable that the organic group having an amino group has a primary amino group in that it improves reactivity with (meth)acrylate (a2) having an epoxy group. The number of amino groups in the organic group having an amino group is not particularly limited.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] From the viewpoint of improving initial adhesion, heat resistance, and / or heat and moisture resistance, the amount of amine-based silane coupling agent (B) per 100 parts by mass of acrylic copolymer (A) in the adhesive composition is preferably 0.01 parts by mass or more and 5.5 parts by mass or less, more preferably 0.01 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.1 parts by mass or more and 4.0 parts by mass or less, more preferably 0.2 parts by mass or more and 3.0 parts by mass or less, and even more preferably 0.5 parts by mass or more and 3.0 parts by mass or less.

[0043] The adhesive composition may further contain one or more other silane coupling agents. Examples of other silane coupling agents include epoxy group-containing silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and epoxy group-containing alkoxysilane oligomers; γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, and mercapto group-containing alkoxysilane oligomers; and γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, and mercapto group-containing alkoxysilane oligomers. Examples include silane coupling agents containing mercapto groups such as siliane oligomers; amino group-containing silane coupling agents such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; and isocyanate group-containing silane coupling agents such as γ-isocyanatetopropyltrimethoxysilane and γ-isocyanatetopropyltriethoxysilane.

[0044] <Hardening agent (C)> The curing agent (C) has the effect of curing the adhesive composition by crosslinking the acrylic copolymer (A).

[0045] 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.

[0046] Other examples of curing agents (C) include isocyanate compounds, metal chelate compounds, aziridine compounds, and melamine compounds. The curing agent (C) can be selected depending on the type of acrylic copolymer (A).

[0047] 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).

[0048] <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.

[0049] <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.

[0050] 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.

[0051] 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.

[0052] Examples of polymerization initiators include oil-soluble organic peroxides such as 2,4-dichlorobenzoyl peroxide, t-butyl peroxypivalate, benzoyl peroxide, o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, t-butyl peroxy-2-ethylhexanoate, cyclohexanone peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, lauroyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, and t-butyl peroxide; as well as oil-soluble azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-(2,4-dimethyl-4-methoxyvaleronitrile). The polymerization initiator is preferably an oil-soluble azo compound. One or more compounds can be used as polymerization initiators.

[0053] <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 optical films.

[0054] For example, an adhesive optical film according to one embodiment comprises an optical film and an adhesive layer containing the adhesive composition according to this embodiment, laminated on at least one surface of the optical film. Such an adhesive optical film can be laminated onto a display device, for example. The type of optical film is not particularly limited. Examples of optical films include surface protection films, polarizing films, phase difference films, brightness enhancement films, anti-reflective films, privacy films, blue light cut films, and transparent conductive films.

[0055] Furthermore, a display device according to one embodiment includes an optical film having a display surface and further laminated to the display surface via an adhesive layer containing the adhesive composition according to this embodiment. The type of display device is not particularly limited. The display device may be, for example, a liquid crystal display or an organic EL display. The display device may also be an in-vehicle display device or an organic EL terminal device.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The peel-off adhesive strength of the adhesive layer of the adhesive sheet is preferably 2.0 N / 25 mm or more, more preferably 3.0 N / 25 mm or more, more preferably 5.0 N / 25 mm or more, and particularly preferably 8.0 N / 25 mm or more. On the other hand, for example, it may be 15 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 in accordance with the provisions of JIS Z0237:2009, after the adhesive layer has been bonded to the glass plate and left for 60 minutes at 23°C and 50% RH, under conditions of a peel angle of 180° and a peel speed of 300 mm / min.

[0060] The storage modulus (G') of the adhesive layer at 230°C is preferably 30kPa or higher, more preferably 40kPa or higher, and even more preferably 50kPa or higher. On the other hand, it is, for example, 100kPa or lower. A high storage modulus (G') at 230°C indicates that dimensional changes of the film, especially at high temperatures, can be suppressed. Furthermore, the storage modulus (G') of the adhesive layer at 0°C is preferably 50kPa or higher, more preferably 80kPa or higher, and even more preferably 90kPa or higher. On the other hand, it is, for example, 200kPa or lower. A high storage modulus (G') at 0°C indicates that dimensional changes of the film, near room temperature, can be suppressed. Furthermore, the storage modulus (G') of the adhesive layer in the range of 0 to 230°C is preferably 30kPa or higher, more preferably 40kPa or higher, and even more preferably 50kPa or higher. On the other hand, it is, for example, 100kPa or lower.

[0061] 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. [Examples]

[0062] [Manufacturing Examples A1-A8: Preparation of Acrylic Copolymers (A1-A8)] Acrylic copolymers (A1-A8) related to production examples A1-A8 were prepared using monomers with the composition ratios shown in Table 1.

[0063] Specifically, nitrogen gas was sealed into a reaction apparatus equipped with a stirrer, thermometer, and reflux condenser. Then, 100 parts by mass of the monomer mixture, 140 parts of ethyl acetate, and 0.05 parts by mass of polymerization initiator (azobisisobutyronitrile) in the ratios shown in Table 1 were added. The reaction solution was then stirred and reacted at 55°C for 7 hours in a nitrogen gas stream. After the reaction was complete, the reaction solution was diluted with ethyl acetate to obtain an acrylic copolymer solution with a solid content of 15.0% by mass. The mass-average molecular weight of each acrylic copolymer obtained is shown in Table 1.

[0064] [Examples 1-13 and Comparative Examples 1-6] The adhesive composition was obtained by thoroughly mixing the types and amounts of each component shown in Table 2. Table 2 shows the type of acrylic copolymer (A) used in each example and comparative example, and the solid content in parts by mass of each component.

[0065] Furthermore, the adhesive compositions obtained in each example and comparative example were coated onto a release substrate (a polyethylene terephthalate (PET) film with a silicone-treated surface). The solvent was removed by drying the resulting adhesive composition at 120°C. In this way, an adhesive layer with a thickness of 20 μm was formed. The resulting samples were used as samples for viscoelasticity measurements.

[0066] Similarly, a 20 μm thick adhesive layer was formed on a release substrate, and then a 38 μm thick PET film with an easy-adhesion layer was laminated to the adhesive layer. Afterward, samples for adhesive strength evaluation were prepared by curing in an atmosphere of 23°C and 50% RH for 7 days. The sample size was 25 mm × 70 mm.

[0067] Similarly, a 20 μm thick adhesive layer was formed on a release substrate, and then a 110 μm polarizing film was laminated to the adhesive layer. Afterward, samples for durability evaluation were prepared by curing in an atmosphere of 23°C and 50% RH for 7 days. The sample size was 80 mm × 150 mm.

[0068] [Adhesion strength measurement] The release substrate was peeled off from the samples obtained for adhesion evaluation in each example and comparative example, and the adhesive layer was attached to glass. The samples were then pressurized in an autoclave at 0.5 MPa and 50°C for 20 minutes. After that, they were left for 1 hour at 23°C and 50% RH. Subsequently, the peel adhesion force (N / 25 mm) was measured using a tensile testing machine in accordance with JIS Z0237:2009, under conditions of a peeling speed of 300 mm / min and a peeling angle of 180 degrees. The results of the adhesion force measurement are shown in Table 2.

[0069] [Measurement of storage modulus] The release sheets were peeled off from the viscoelasticity evaluation samples obtained in each example and comparative example, and the samples were placed in a solid shearing jig (PP08). The storage modulus (G') was then measured using a rheometer (Anton Paar: MCR302e) under the following conditions. Shear strain: 0.1%, Frequency: 1.0Hz, Normal force: 1N, Measurement temperature: 0~230℃, Heating rate: 5℃ / min The measurement results for the storage modulus are shown in Table 2.

[0070] [Heat resistance and moisture resistance evaluation] The release substrate was peeled off from the durability evaluation samples obtained in each example and comparative example, and the adhesive layer was attached to glass. Then, the samples were left for 500 hours in an atmosphere of either 85°C (DRY), 105°C (DRY), or 85°C 85%RH. Afterward, foaming and peeling were visually inspected. The evaluation results are shown in Table 2. In Table 2, the evaluation results are represented by the following symbols. A: No foaming or peeling was observed on the polarizing plate. B: Slight foaming or peeling was observed on the polarizing plate. F: Foaming or peeling was observed on the polarizing plate.

[0071] [Table 1]

[0072] [Table 2]

[0073] The components shown in Table 1 are as follows: BA: Butyl acrylate MA: Methyl acrylate LA: Lauryl acrylate BZA: Benzyl acrylate PHEA: Phenoxyethyl acrylate P2EA: Phenoxydiethylene glycol acrylate GMA: Glycidyl methacrylate 4HBAGE: 4-Hydroxybutyl acrylate glycidyl ether HEA: 2-hydroxyethyl acrylate 4HBA: 4-Hydroxybutyl acrylate VAC: Vinyl acetate DMAA: Dimethylacrylamide

[0074] The components shown in Table 2 are as follows: 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) TEPA: Tetraethylenepentamine PACM: 4,4'-methylenebis(cyclohexylamine) Takenate D-101E: Manufactured by Mitsui Chemicals, Ltd., tolylene diisocyanate crosslinking agent. Tetrad C: A multifunctional epoxy curing agent manufactured by Mitsubishi Gas Chemical Company.

[0075] As shown in Table 2, the adhesive layers of Examples 1 to 13, prepared using an adhesive composition containing an acrylic copolymer (A) comprising alkyl (meth)acrylate (a1), epoxy-grouped (meth)acrylate (a2), and hydroxyl-grouped (meth)acrylate (a3) ​​as constituent units, and an amine-based silane coupling agent (B), exhibited sufficient storage modulus of 50 kPa or more at 230°C, while adequately suppressing foaming or peeling under high temperature and high temperature / high humidity conditions. Furthermore, the adhesive layers of Examples 1 to 13 exhibited sufficient storage modulus of 90 kPa or more at 25°C. These results indicate that the adhesive layers of Examples 1 to 13 possess dimensional change suppression effects and durability over various temperature ranges. In addition, the adhesive layers of Examples 1 to 13 exhibited sufficient tackiness of 3.4 N / 25 mm or more.

[0076] In particular, in Examples 1 to 3, increasing the amount of amine-based silane coupling agent (B) improved the storage modulus, while also improving heat resistance and heat-sensitive moisture resistance. Furthermore, increasing the amount of amine-based silane coupling agent (B) also improved the adhesive strength.

[0077] Furthermore, according to the inventors' studies, by adding more than 0.005 parts by mass, particularly 0.5 parts by mass or more, of the amine-based silane coupling agent (B) per 100 parts by mass of the acrylic copolymer (A), the storage modulus, heat resistance, and moisture-heat resistance were significantly improved compared to the case where the addition amount was 0.005 parts by mass or less. Also, by adding less than 6.0 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 moisture-heat resistance was significantly improved compared to the case where the addition amount was 6.0 parts by mass or more.

[0078] On the other hand, the adhesive layers of Comparative Examples 1 to 5, which were prepared using an adhesive composition containing an acrylic copolymer (A) containing epoxy group-containing (meth)acrylate (a2) and hydroxyl group-containing (meth)acrylate (a3) ​​as constituent units, but without an amine-based silane coupling agent (B), exhibited foaming or peeling under high temperature or high temperature and high humidity conditions. For example, in Comparative Example 4, in which the acrylic copolymer (A) was crosslinked using an isocyanate curing agent, sufficient storage modulus was not obtained at 230°C, and heat resistance at 105°C was also insufficient. In Comparative Example 5, in which the ratio of hydroxyl group-containing monomers in the acrylic copolymer (A) was further increased, the storage modulus improved somewhat, but a decrease in heat resistance at 85°C was observed. Furthermore, in Comparative Example 3, in which a large amount of curing agent was added, although the storage modulus at 25°C improved, the storage modulus at 230°C did not improve much, and adhesive strength, heat resistance, and heat and humidity resistance all decreased.

[0079] Furthermore, as in Comparative Examples 1 and 2, adding other amine compounds instead of the amine-based silane coupling agent (B) was not effective. Also, as in Comparative Examples 3 to 5, adding other silane coupling agents instead of the amine-based silane coupling agent (B) was not effective.

[0080] Furthermore, in the adhesive layer of Comparative Example 6, which was prepared using an adhesive composition containing an acrylic copolymer (A) that does not contain a hydroxyl group-containing (meth)acrylate (a3) ​​as a constituent unit, and an amine-based silane coupling agent (B), a sufficient storage modulus of elasticity at 230°C was not obtained. In addition, the heat resistance of the adhesive layer of Comparative Example 6 at 105°C was also insufficient.

[0081] As can be seen from the comparison between Example 1 and Comparative Example 6, the inclusion of a (meth)acrylate (a3) ​​having a hydroxyl group as a constituent unit in the acrylic copolymer (A) is effective in improving the storage modulus and durability even when the adhesive composition does not contain an isocyanate curing agent.

[0082] These results demonstrate that a combination of a (meth)acrylic copolymer (A) containing epoxy groups (a2) and hydroxyl groups (a3) ​​as constituent units, and an amine-based silane coupling agent (B), can achieve both elastic modulus and durability. On the other hand, as shown in Examples 7, 8, and 11, an amine-based silane coupling agent (B) may be used in combination with other curing agents 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 comprising a (meth)acrylic copolymer (A) and an amine-based silane coupling agent (B) in an amount of 0.2 parts by mass or more and 5.5 parts by mass or less per 100 parts by mass of the acrylic copolymer (A), The (meth)acrylic copolymer (A) comprises, as constituent units, 60% by mass or more and 95% by mass or less of alkyl (meth)acrylate (a1), 0.05% by mass or more and 30% by mass or less of epoxy group (meth)acrylate (a2), and 0.1% by mass or more and 30% by mass or less of hydroxy group (meth)acrylate (a3), in an adhesive composition.

2. The adhesive composition according to claim 1, wherein the alkyl (meth)acrylate (a1) has 1 to 14 carbon atoms in the alkyl group.

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

4. The adhesive composition according to claim 1, wherein the mass-average molecular weight of the (meth)acrylic copolymer (A) is 1 million or more and 4 million or less.

5. The adhesive composition according to claim 1, wherein the glass transition temperature of the (meth)acrylic copolymer (A) is -50°C or higher and 0°C or lower.

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

7. The adhesive sheet according to claim 6, wherein the storage modulus (G') of the adhesive layer at 230°C is 50 kPa or more.

8. The adhesive sheet according to claim 6, wherein the peel-off adhesive force of the adhesive layer from the glass plate is 2.0 N / 25 mm or more, and the peel-off adhesive force is measured after the adhesive layer has been bonded to the glass plate and left for 60 minutes at 23°C and 50% RH, under conditions of a peel angle of 180° and a peel speed of 300 mm / min.

9. A display device having a display surface, the display surface comprising an optical film laminated via an adhesive layer containing the adhesive composition described in any one of claims 1 to 5.

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