Adhesive composition, adhesive, adhesive sheet, and adhesive sheet for image display device

Abstract

In order to obtain an adhesive composition having exceptional adhesive properties and moist heat resistance as well as low permittivity and a low dielectric loss tangent, provided is an adhesive composition containing an acrylic resin (A) and a hydrophilicity-imparting agent (B), wherein: the acrylic resin (A) is a copolymer of a copolymer component (a) that contains a methacrylic acid alkyl ester monomer (a1) having a C10-36 alkyl chain, and a polar-group-containing ethylenic unsaturated monomer (a2); the polar-group-containing ethylenic unsaturated monomer (a2) content is less than 3 wt% relative to the copolymer component (a); and the hydrophilicity-imparting agent (B) is a compound (B1) that has a –(CnH2nO)m- (where n is 2-6, and m is 2-25) structure and that contains at least one ethylenic unsaturated group.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition, an adhesive made from such an adhesive composition, an adhesive sheet, and an adhesive sheet for an image display device. More specifically, it relates to an adhesive composition that exhibits excellent adhesive properties and resistance to moisture and heat, as well as low dielectric constant and low dielectric loss tangent, an adhesive, an adhesive sheet, and an adhesive sheet for an image display device using the same. [Background technology]

[0002] In recent years, touch panels, which combine a display and a position input device, have become widely used in televisions, computer monitors, laptops, mobile phones, smartphones, tablet devices, and other mobile devices, with capacitive touch panels being particularly popular. A touch panel typically consists of a display made of organic EL or liquid crystal, a transparent conductive film substrate (ITO substrate), and a protective film (glass), with a transparent adhesive sheet used to bond these components together.

[0003] Adhesives for such transparent adhesive sheets require not only adhesive properties such as adhesive strength, but also shock absorption to prevent damage to the display from external impacts, excellent optical properties (transparency), and a low dielectric constant to suppress malfunctions of the touch panel caused by noise generated from the display components and other peripheral components.

[0004] As adhesives with low dielectric constant, for example, adhesives using (meth)acrylic polymers obtained by polymerizing monomer components mainly containing alkyl (meth)acrylates having branched alkyl chains with 10 to 18 carbon atoms at the ester group terminus (see, for example, Patent Document 1), adhesives using copolymers of monomer mixtures containing monomers each containing a specific amount of an alkyl methacrylate monomer having a long-chain alkyl chain with 10 or more carbon atoms in the alkyl ester moiety and an alkyl methacrylate monomer having an alkyl chain with 1 to 9 carbon atoms in the alkyl ester moiety (see, for example, Patent Document 2), and adhesive compositions containing methacrylic polymers obtained by polymerizing monomer components containing 40 to 99.5% by weight of alkyl methacrylate having C10 to C18 alkyl chains in the side chains, and having a glass transition temperature (Tg) of 0°C or lower (see, for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-246477 [Patent Document 2] Japanese Patent Publication No. 2015-40237 [Patent Document 3] Japanese Patent Publication No. 2013-1761 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in recent years, with the increasing frequency of transmitted signals, adhesives are required to have lower dielectric properties, particularly low dielectric loss tangent, in the high-frequency band (millimeter wave band). In this context, although the technologies disclosed in the above-mentioned Patent Documents 1 and 2 have obtained adhesives with low dielectric constants, they are still not sufficient in terms of low dielectric loss tangent, and further improvements are needed. Furthermore, while the technology disclosed in Patent Document 3 exhibits good low dielectric properties, it is unsatisfactory in terms of adhesive properties and moisture and heat resistance as an adhesive, making it difficult to achieve a good balance between low dielectric properties, adhesive properties, and moisture and heat resistance.

[0007] Therefore, against this background, the present invention provides an adhesive composition that exhibits excellent tackiness and heat resistance, as well as low dielectric constant and low dielectric loss tangent. [Means for solving the problem]

[0008] However, in view of these circumstances, the inventors have conducted extensive research and have found that an acrylic adhesive composition can be obtained in which an acrylic resin is copolymerized with an alkyl methacrylate monomer having an alkyl chain with a large number of carbon atoms and a copolymer component containing a specific amount of polar group-containing (meth)acrylic acid ester monomer as the copolymer component constituting the acrylic resin, and a specific hydrophilicity imparting agent is used to obtain an adhesive that exhibits excellent tackiness and heat resistance, as well as low dielectric constant and low dielectric loss tangent.

[0009] In other words, the gist of the present invention is as follows: [1] to

[11] . [1] An adhesive composition containing an acrylic resin (A) and a hydrophilic agent (B), The acrylic resin (A) is a copolymer of a copolymer component (a) containing an alkyl methacrylate monomer (a1) having an alkyl chain with 10 to 36 carbon atoms, and a polar group-containing ethylenically unsaturated monomer (a2). The content of the polar group-containing ethylenically unsaturated monomer (a2) is less than 3% by weight relative to the copolymer component (a), The hydrophilic agent (B) is -(C n H 2n An adhesive composition containing a compound (B1) having an O)m-(n is 2-6, m is 2-25) structure and containing at least one ethylenically unsaturated group. [2] The adhesive composition according to [1], wherein in the copolymer component (a), the content of the alkyl methacrylate monomer (a1) having an alkyl chain with 10 to 36 carbon atoms is 50 to 95% by weight based on the copolymer component (a). [3] The adhesive composition according to [1] or [2], wherein the alkyl methacrylate monomer (a1) having an alkyl chain with 10 to 36 carbon atoms contains an alkyl methacrylate monomer (a1-1) having an alkyl chain with 10 to 15 carbon atoms and an alkyl methacrylate monomer (a1-2) having an alkyl chain with 16 to 36 carbon atoms. [4] The adhesive composition according to any one of [1] to [3], wherein the content of the alkyl methacrylate monomer in the copolymer component (a) is 80 to 99% by weight based on the copolymer component (a), and the average number of carbon atoms of the alkyl chain of the alkyl methacrylate monomer is 10 to 15. [5] The adhesive composition according to any one of [1] to [4], wherein the acrylic resin (A) has an active energy ray crosslinkable structural site. [6] The adhesive composition according to [5], wherein the active energy ray crosslinkable structural site is a benzophenone-based crosslinkable structural site. [7] The adhesive composition according to any one of [1] to [6], wherein the weight average molecular weight of the acrylic resin (A) is 150,000 to 1,500,000. [8] An adhesive obtained by crosslinking the adhesive composition according to any one of [1] to [7]. [9] An adhesive obtained by crosslinking the adhesive composition according to any one of [1] to [7] with active energy rays.

[10] An adhesive sheet having an adhesive layer composed of the adhesive according to [8] or [9].

[11] An adhesive sheet for an image display device having an adhesive layer composed of the adhesive according to [8] or [9].

Advantages of the Invention

[0010] The adhesive obtained from the adhesive composition of the present invention exhibits excellent adhesive properties and resistance to moisture and heat, as well as low dielectric constant and low dielectric loss tangent, making it particularly useful as an adhesive for bonding optical components that constitute touch panels, image display devices, and the like.

[0011] Generally, in order to impart low dielectric properties (low dielectric constant and low dielectric loss tangent) to adhesive compositions using acrylic resins, it is known that a larger amount of alkyl(meth)acrylic acid ester monomers with 10 or more carbon atoms in the alkyl chain are copolymerized in order to lower the dipole moment of the molecule. However, acrylic resins copolymerized with copolymer components having a large number of carbon atoms in the alkyl chain tend to have poor adhesive properties such as tackiness and holding power, especially at high temperatures. To solve this, functional groups such as acids are generally introduced, but introducing highly polar functional groups tends to make it difficult to obtain a low dielectric loss tangent at high frequencies. The present invention has found that by using an acrylic resin obtained using an alkyl methacrylate monomer having an alkyl chain of a predetermined length and a polar group-containing (meth)acrylic acid ester monomer in combination with a specific hydrophilicity imparting agent, it is possible to obtain a resin that exhibits excellent adhesive properties, resistance to humid and heat, and low dielectric properties, particularly a low dielectric loss tangent. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below, but these are merely examples of preferred embodiments. In this invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate. "Acrylic resin" is a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer. Furthermore, "sheet" conceptually encompasses sheets, films, and tapes.

[0013] The adhesive composition of the present invention contains an acrylic resin (A) and a hydrophilicity imparting agent (B), wherein the acrylic resin (A) is a copolymer of a copolymer component (a) containing an alkyl methacrylate monomer (a1) having an alkyl chain having 10 to 36 carbon atoms (hereinafter sometimes simply referred to as "alkyl methacrylate monomer (a1)") and a specific amount of polar group-containing ethylenically unsaturated monomer (a2), and the hydrophilicity imparting agent (B) is -(C n H 2n The present invention includes a compound (B1) having an O)m-(n is 2-6, m is 2-25) structure and containing at least one ethylenically unsaturated group. The components used in the present invention will be described below.

[0014] The acrylic resin (A) used in the present invention is a copolymer of copolymer component (a) containing an alkyl methacrylate monomer (a1) and a specific amount of polar group-containing ethylenically unsaturated monomer (a2), as described above. The monomers contained in copolymer component (a) will be described below.

[0015] [Alkyl methacrylate monomer having an alkyl chain with 10 to 36 carbon atoms (a1)] Examples of alkyl methacrylate monomers (a1) having an alkyl chain with 10 to 36 carbon atoms used in the present invention include linear aliphatic methacrylates such as decyl methacrylate, lauryl methacrylate, tridecyl methacrylate, cetyl methacrylate, stearyl methacrylate, and myristyl methacrylate, and branched aliphatic methacrylates such as isodecyl methacrylate, isotridecyl methacrylate, isomiristyl methacrylate, isostearyl methacrylate, and isotetracosyl methacrylate. These may be used individually or in combination of two or more. Among these, lauryl methacrylate, tridecyl methacrylate, and stearyl methacrylate are preferred from the viewpoint of achieving both low dielectric properties and adhesive properties.

[0016] The content of the alkyl methacrylate monomer (a1) is typically 50 to 95% by weight, preferably 55 to 90% by weight, and particularly preferably 60 to 85% by weight, relative to copolymer component (a), due to its low dielectric constant and excellent adhesive properties. If the content is too low, the dielectric constant tends to increase and the thermal stability of the acrylic resin (A) tends to decrease, while if the content is too high, the adhesive strength tends to decrease.

[0017] Furthermore, from the viewpoint of low dielectric properties, it is preferable that the alkyl methacrylate monomer (a1) contains an alkyl methacrylate monomer (a1-1) having an alkyl chain with 10 to 15 carbon atoms (hereinafter sometimes simply referred to as "alkyl methacrylate monomer (a1-1)") and an alkyl methacrylate monomer (a1-2) having an alkyl chain with 16 to 36 carbon atoms (hereinafter sometimes simply referred to as "alkyl methacrylate monomer (a1-2)").

[0018] Examples of the alkyl methacrylate monomer (a1-1) mentioned above include linear aliphatic methacrylates such as decyl methacrylate, lauryl methacrylate, and tridecyl methacrylate, and branched aliphatic methacrylates such as isodecyl methacrylate and isotridecyl methacrylate. These may be used individually or in combination of two or more. Among these, linear aliphatic methacrylates are preferred from the viewpoint of achieving both low dielectric properties and adhesive properties, and lauryl methacrylate and tridecyl methacrylate are more preferred.

[0019] The content of the alkyl methacrylate monomer (a1-1) is preferably 30 to 85% by weight, more preferably 40 to 80% by weight, and particularly preferably 50 to 75% by weight, relative to copolymer component (a), in order to achieve both low dielectric properties and adhesive properties. If the content is too low, the dielectric constant tends to increase and the thermal stability of the acrylic resin (A) tends to decrease, while if the content is too high, the adhesive properties tend to decrease.

[0020] Examples of the alkyl methacrylate monomers (a1-2) mentioned above include linear aliphatic methacrylates such as cetyl methacrylate, stearyl methacrylate, and myristyl methacrylate, and branched aliphatic methacrylates such as isomiristyl methacrylate, isostearyl methacrylate, and isotetracosyl methacrylate. These may be used individually or in combination of two or more. Among these, methacrylates having alkyl chains with 18 to 24 carbon atoms are preferred, and stearyl methacrylate is more preferred, due to their ease of increasing monomer conversion during copolymerization and their ability to achieve both low dielectric properties and adhesive properties.

[0021] The content of the alkyl methacrylate monomer (a1-2) is typically 1 to 50% by weight, preferably 5 to 40% by weight, and particularly preferably 10 to 30% by weight, relative to copolymer component (a), in terms of dielectric constant and tackiness. If the content is too low, the dielectric constant tends to increase, and if the content is too high, the adhesive properties tend to decrease.

[0022] Furthermore, in copolymer component (a), the content ratio (a1-1 / a1-2) of the alkyl methacrylate monomer (a1-1) and the alkyl methacrylate monomer (a1-2) is usually 1 / 99 to 99 / 1, preferably 30 / 70 to 95 / 5, and more preferably 55 / 45 to 90 / 10. When the content ratio of alkyl methacrylate monomer (a1-1) and alkyl methacrylate monomer (a1-2) is within the above range, the material tends to exhibit excellent low dielectric properties.

[0023] [Polar group-containing ethylenically unsaturated monomer (a2)] Examples of the polar group-containing ethylenically unsaturated monomer (a2) mentioned above include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and cyano group-containing monomers. These may be used individually or in combination of two or more. Among these, hydroxyl group-containing monomers are preferred due to their excellent adhesive properties and reactivity with the thermal crosslinking agent (D) described later.

[0024] Examples of the hydroxyl group-containing monomers mentioned above include hydroxyalkyl ester monomers of (meth)acrylate such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and other primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, N-methylol (meth)acrylamide, and hydroxyethylacrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate. Among these, hydroxyalkyl ester monomers of (meth)acrylate are preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are more preferred, with 4-hydroxybutyl acrylate being particularly preferred, due to their low levels of impurities such as di(meth)acrylate and ease of production.

[0025] Examples of the above-mentioned carboxyl group-containing monomers include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid.

[0026] Examples of the above-mentioned amino group-containing monomers include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and their quaternary derivatives.

[0027] Examples of the above-mentioned amide group-containing monomers include (meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, vinylpyrrolidone, and acryloylmorpholin.

[0028] Examples of the above-mentioned cyano group-containing monomers include acrylonitrile and methacrylonitrile.

[0029] The content of the polar group-containing ethylenically unsaturated monomer (a2) is less than 3% by weight relative to copolymer component (a) from the viewpoint of achieving both low dielectric properties and adhesive properties, preferably 0.01% by weight or more and less than 3% by weight, more preferably 0.05% by weight or more and 2.5% by weight or less, even more preferably 0.1% by weight or more and 2% by weight or less, and particularly preferably 0.2% by weight or more and 1% by weight or less. If the content is too high, the relative permittivity and dielectric loss tangent tend to increase. Conversely, if the content is too low, the compatibility with the hydrophilicity-imparting agent (B) described later tends to decrease, as do the tackiness and durability tend to decrease.

[0030] In addition to the alkyl methacrylate monomer (a1) and polar group-containing ethylenically unsaturated monomer (a2) used in the present invention, it is preferable from the viewpoint of adhesiveness that the copolymer component (a) used contains an alkyl methacrylate monomer (a3) ​​having an alkyl chain with 1 to 9 carbon atoms [hereinafter sometimes simply referred to as "alkyl methacrylate monomer (a3)"].

[0031] [Alkyl methacrylate monomer having an alkyl chain with 1 to 9 carbon atoms (a3)] Examples of the alkyl methacrylate monomer (a3) ​​mentioned above include linear aliphatic methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, and n-hexyl methacrylate; branched aliphatic methacrylates such as iso-butyl methacrylate, tert-butyl methacrylate, and 2-ethylhexyl methacrylate; and cyclic aliphatic methacrylates such as cyclohexyl methacrylate. These may be used alone or in combination of two or more. Among these, ethyl methacrylate is preferred in terms of compatibility with the hydrophilicity imparting agent (B) described later and its resistance to humid and heat, while 2-ethylhexyl methacrylate is preferred in terms of cohesive force and low dielectric properties.

[0032] The content of the alkyl methacrylate monomer (a3) ​​is usually 1 to 50% by weight, preferably 5 to 40% by weight, and particularly preferably 10 to 35% by weight, relative to the copolymer component (a). If the content is too low, the adhesive strength tends to be insufficient, and if the content is too high, the adhesive properties and handling properties at high temperatures tend to decrease.

[0033] Furthermore, in the copolymer component (a) used in the present invention, the content ratio (a1 / a3) of alkyl methacrylate monomer (a1) and alkyl methacrylate monomer (a3) ​​is preferably 50 / 50 to 95 / 5 by weight. More preferably it is 55 / 45 to 93 / 7, and particularly preferably 60 / 40 to 90 / 10. When the content ratio (a1 / a3) is within the above range, it tends to have excellent adhesive properties and low dielectric properties.

[0034] [(meth)acrylic acid ester monomer containing an active energy ray crosslinkable structural site (a4)] In the present invention, it is preferable to use an active energy ray crosslinkable structural moiety-containing (meth)acrylic acid ester monomer (a4) as the copolymer component (a) of the acrylic resin (A), in that it can efficiently cure (crosslink) the acrylic resin (A) and enhance its cohesive strength. The above-mentioned active energy ray crosslinkable structure-containing (meth)acrylic acid ester monomer (a4) is preferably one that contains a (meth)acrylic acid ester monomer having a benzophenone-based crosslinkable structure, as this allows for efficient crosslinking by active energy rays such as ultraviolet rays and electron beams. Examples of the above-mentioned (meth)acrylic acid ester monomer having a benzophenone-based crosslinkable structure include 4-(meth)acryloyloxybenzophenone.

[0035] An acrylic resin (A) obtained by copolymerizing an active energy ray crosslinkable structural moiety-containing (meth)acrylic acid ester monomer (a4) has an active energy ray crosslinkable structural moiety, and such an active energy ray crosslinkable structural moiety can react with a portion of the acrylic resin (A) or with other curing components contained in the adhesive composition upon irradiation with active energy rays to form a crosslinked structure.

[0036] The content of the active energy ray crosslinkable structure-containing (meth)acrylic acid ester monomer (a4) is preferably 0.01 to 5% by weight relative to copolymer component (a), in terms of retention force when forming the crosslinked structure with active energy rays, efficient manufacturing, and adhesive strength. In particular, the content of the (meth)acrylic acid ester monomer having a benzophenone structure is preferably 0.01 to 5% by weight relative to copolymer component (a), especially preferably 0.1 to 2% by weight, and even more preferably 0.2 to 1% by weight. If the content is too low, the retention force when forming the crosslinked structure with active energy rays tends to decrease. Furthermore, in order to create a processable adhesive sheet, a large amount of active energy ray is required when forming the crosslinked structure, requiring a large amount of energy during adhesive sheet production, making efficient manufacturing difficult. Also, if the content is too high, the cohesive force of the entire system increases too much, and the adhesive strength tends to decrease.

[0037] Furthermore, when introducing an active energy ray crosslinkable structural site into an acrylic resin (A), hydroxyl groups can be included in the acrylic resin (A), and these hydroxyl groups can be reacted with an ethylenically unsaturated group-containing isocyanate compound to introduce an ethylenically unsaturated group as the active energy ray crosslinkable structural site.

[0038] Furthermore, in the present invention, if necessary, the copolymerization component (a) may also contain other copolymerizable ethylenically unsaturated monomers (a5).

[0039] [Other copolymerizable ethylenically unsaturated monomers (a5)] Other copolymerizable ethylenically unsaturated monomers (a5) include, for example, alkyl acrylate monomers having an alkyl chain of 1 to 9 carbon atoms such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate; aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; cyclohexyl acrylate, cyclohexyl Alicyclic monomers such as oxyalkyl (meth)acrylate, tert-butylcyclohexyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; ether chain-containing monomers such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene glycol mono(meth)acrylate;Other examples include styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyltoluene, vinylpyridine, dialkyl itaconate, dialkyl fumarate, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. These can be used individually or in combination of two or more types.

[0040] Furthermore, when the aim is to increase the molecular weight of the acrylic resin (A), other copolymerizable ethylenically unsaturated monomers (a5) such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and compounds having two or more ethylenically unsaturated groups such as divinylbenzene can also be used in combination.

[0041] The content of other copolymerizable ethylenically unsaturated monomers (a5) is usually 20% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less, relative to copolymer component (a). If the content is too high, the dielectric properties tend to decrease, and the adhesive strength tends to decrease.

[0042] The acrylic resin (A) used in the present invention can be produced by copolymerizing a copolymer component (a) which includes the above-mentioned alkyl methacrylate monomer (a1) and polar group-containing ethylenically unsaturated monomer (a2) as essential components, and further appropriately includes alkyl methacrylate monomer (a3), active energy ray crosslinkable structural moiety-containing (meth)acrylic acid ester monomer (a4), and other copolymerizable ethylenically unsaturated monomers (a5).

[0043] Furthermore, in the copolymer component (a), from the viewpoint of low dielectric properties, particularly low dielectric loss tangent, it is preferable that the content of alkyl methacrylate monomer in copolymer component (a) is 80 to 99% by weight relative to copolymer component (a), more preferably 90 to 99% by weight, and particularly preferably 95 to 99% by weight. In particular, it is preferable that the total content of alkyl methacrylate monomer (a1) and alkyl methacrylate monomer (a3) ​​is within the above range relative to copolymer component (a).

[0044] Furthermore, the average number of carbon atoms in the alkyl chain of the alkyl methacrylate monomer contained in the copolymer component (a) is preferably 10 to 15, and more preferably 11 to 14, from the viewpoint of low dielectric properties, particularly low dielectric loss tangent. In particular, it is preferable that the average number of carbon atoms in the alkyl chains of alkyl methacrylate monomer (a1) and alkyl methacrylate monomer (a3) ​​is within the above range.

[0045] While conventional polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used to polymerize the acrylic resin (A) described above, in the present invention, it is preferable to produce it by solution polymerization because it allows for the safe, stable production of the acrylic resin (A) with any monomer composition. The following is an example of a preferred method for producing the acrylic resin (A) used in the present invention.

[0046] First, the copolymer and polymerization initiator are mixed or added dropwise to an organic solvent, and solution polymerization is carried out.

[0047] Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as n-hexane, esters such as methyl acetate, ethyl acetate, and butyl acetate, aliphatic alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, aliphatic ethers such as dimethyl ether and diethyl ether, aliphatic halogenated hydrocarbons such as methylene chloride and ethylene chloride, and cyclic ethers such as tetrahydrofuran. These may be used individually or in combination of two or more. Among these solvents, esters and ketones are preferred, and ethyl acetate and acetone are particularly preferred.

[0048] As polymerization initiators used in the above polymerization reaction, ordinary radical polymerization initiators such as azo polymerization initiators and peroxide polymerization initiators can be used. Examples of azo polymerization initiators include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobi Examples of peroxide polymerization initiators include 4-methoxy-2,4-dimethylvaleronitrile, and peroxide polymerization initiators include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. These may be used individually or in combination of two or more. Among these, azo polymerization initiators are preferred, and more preferably 2,2'-azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0049] The amount of polymerization initiator used is typically 0.001 to 10 parts by weight per 100 parts by weight of copolymer component (a), preferably 0.1 to 8 parts by weight, particularly preferably 0.5 to 6 parts by weight, even more preferably 1 to 4 parts by weight, especially preferably 1.5 to 3 parts by weight, and most preferably 2 to 2.5 parts by weight. If the amount of polymerization initiator used is too small, the polymerization rate of the acrylic resin (A) decreases, the residual monomers increase, and the weight-average molecular weight of the acrylic resin (A) tends to increase. If the amount used is too large, the acrylic resin (A) tends to gel.

[0050] For solution polymerization, polymerization can be carried out according to conventionally known polymerization conditions. For example, a copolymer component (a) containing a (meth)acrylic monomer and a polymerization initiator can be mixed or added dropwise to a solvent and polymerized under predetermined polymerization conditions.

[0051] The polymerization temperature in the above polymerization reaction is usually 40 to 120°C, but in the present invention, 50 to 90°C is preferred for stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily, and if it is too low, the activity of the polymerization initiator decreases, which tends to reduce the polymerization rate and increase the amount of residual monomer.

[0052] Furthermore, while there are no particular restrictions on the polymerization time in the polymerization reaction, it is preferably 0.5 hours or more, more preferably 1 hour or more, more preferably 2 hours or more, and especially preferably 5 hours or more, from the addition of the last polymerization initiator. Furthermore, polymerization reactions are preferably carried out under reflux of the solvent, as this facilitates heat removal. Thus, the acrylic resin (A) used in the present invention can be manufactured.

[0053] <Acrylic resin (A)> The weight-average molecular weight of the above acrylic resin (A) is preferably 150,000 to 1,500,000, more preferably 200,000 to 1,000,000, particularly preferably 250,000 to 800,000, and especially preferably 300,000 to 600,000. If the weight-average molecular weight is too high, the viscosity tends to become too high, reducing coating properties and handling capabilities, while if it is too low, the cohesive force tends to decrease, reducing adhesive properties. The weight-average molecular weight of the acrylic resin (A) mentioned above is the weight-average molecular weight at the time of completion of manufacturing, and is the weight-average molecular weight of the acrylic resin (A) that has not been heated or otherwise subjected to post-manufacturing processes.

[0054] Furthermore, the degree of dispersion (weight-average molecular weight / number-average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, particularly 7 or less, and especially preferably 5 or less. If the degree of dispersion is too high, the durability of the adhesive layer tends to decrease and foaming tends to occur, while if it is too low, handling tends to decrease. The lower limit of the degree of dispersion is usually 1.1 from the standpoint of manufacturing limitations.

[0055] Note that the above weight-average molecular weight is the weight-average molecular weight converted to standard polystyrene molecular weight, and was obtained using a high-performance liquid chromatograph (Waters 2695 (main unit) and Waters 2414 (detector) manufactured by Waters Japan) with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10⁶). 7 Separation range: 100~2×10 7 The measurement is performed by using three tubes in series (theoretical plate count: 10,000 stages / tube, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm), and the number-average molecular weight can be measured using the same method. Furthermore, the degree of dispersion can be determined from the weight-average molecular weight and the number-average molecular weight.

[0056] The acrylic resin (A) used in the present invention preferably has a glass transition temperature (Tg) of -100 to 50°C, more preferably -50 to 20°C, and even more preferably -15 to 10°C. If the glass transition temperature is too high, the adhesive strength tends to decrease due to a decrease in step-following ability and adhesion. If the glass transition temperature is too low, the low dielectric properties at high frequencies tend to deteriorate, and the adhesive properties at high temperatures tend to decrease.

[0057] The glass transition temperature (Tg) is determined by the following measurement method. The release sheet is peeled off the adhesive sheet before irradiation with the activated energy ray described later, and multiple adhesive sheets are laminated to create an adhesive sheet with a thickness of approximately 650 μm in an uncrosslinked state. The dynamic viscoelasticity of the created sheet is measured under the following conditions, and the temperature at which the loss tangent (loss modulus G'' / storage modulus G'=tanδ) is maximized is read and taken as the glass transition temperature (Tg) of the acrylic resin (A).

[0058] [Measurement conditions] Measuring instrument: DVA-225 (manufactured by IT Measurement & Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -100~60℃ Measurement frequency: 1Hz

[0059] In the adhesive composition of the present invention, the content of the acrylic resin (A) is preferably 90% by weight or more, more preferably 95 to 99.9% by weight, particularly preferably 98 to 99.8% by weight, and especially preferably 99 to 99.5% by weight, relative to the total adhesive composition.

[0060] <Hydrophilicity-enhancing agent (B)> The adhesive composition of the present invention contains a hydrophilicity imparting agent (B), wherein such hydrophilicity imparting agent (B) is -(C n H 2nThe compound (B1) (hereinafter abbreviated as "hydrophilicity imparting agent (B1)") has an O)m-(n is 2-6, m is 2-25) structure and contains at least one ethylenically unsaturated group. The value of n is usually 2-6, preferably 2-4, and more preferably 2-3, from the viewpoint of compatibility with acrylic resins and heat and humidity resistance when used as an adhesive. The value of m is usually 2-25, preferably 4-14, and more preferably 5-10, from the viewpoint of compatibility with acrylic resin (A) and heat and humidity resistance when used as an adhesive. If n or m is too large, compatibility with acrylic resins tends to decrease, and if it is too small, heat and humidity resistance tends to decrease. The inclusion of the above-mentioned hydrophilicity imparting agent (B1) in the adhesive composition improves its resistance to moisture and heat when used as an adhesive.

[0061] Examples of the hydrophilicity imparting agent (B1) include (poly)ethylene glycol mono(meth)acrylate, (poly)butylene glycol mono(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, (poly)pentamethylene glycol di(meth)acrylate, (poly)hexamethylene glycol di(meth)acrylate, ethylene oxide (EO)-modified trimethylolpropane triacrylate, EO-modified glycerin triacrylate, and the like. The hydrophilicity imparting agent (B1) can be used alone or in combination of two or more. Among these, a hydrophilicity imparting agent containing two ethylenically unsaturated groups is preferred in that it can achieve both adhesive properties and resistance to moisture and heat, and (poly)ethylene glycol di(meth)acrylate is particularly preferred.

[0062] The content of the hydrophilicity imparting agent (B1) described above is preferably 5 parts by weight or less, more preferably 0.01 to 3 parts by weight, and even more preferably 0.1 to 1 part by weight, per 100 parts by weight of the acrylic resin (A), in order to achieve a balance between adhesive strength, low dielectric loss tangent, and moisture and heat resistance. If there is too much of the hydrophilicity imparting agent (B1), the adhesive strength tends to decrease and the dielectric loss tangent tends to increase. If there is too little, the moisture and heat resistance tends to decrease.

[0063] Furthermore, while it is preferable that the hydrophilicity imparting agent (B) is only hydrophilicity imparting agent (B1), it may also contain other hydrophilicity imparting agents (B) other than hydrophilicity imparting agent (B1), and the content of such agents is 10% by weight or less, preferably 5% by weight or less, with a lower limit of 0% by weight.

[0064] In addition to the acrylic resin (A) and hydrophilicity-imparting agent (B) described above, the adhesive composition of the present invention may also contain a crosslinkable monomer (C), a thermal crosslinking agent (D), a silane coupling agent, and a photopolymerization initiator.

[0065] [Crossable monomer (C)] The above-mentioned crosslinkable monomer (C) is excluding the above-mentioned hydrophilicity imparting agent (B), and examples include crosslinking agents such as polyfunctional monomers. By including the crosslinkable monomer (C), it is possible to adjust the cohesive force of the entire adhesive layer and obtain stable adhesive properties.

[0066] The above crosslinkable monomer (C) is preferably a polyfunctional monomer containing two or more ethylenically unsaturated groups in one molecule. Examples include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, isocyanurate ethylene oxide modified tri(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, urethane(meth)acrylate, etc. The above polyfunctional monomers can be used alone or in combination of two or more. Among these, alkyl (meth)acrylates containing two ethylenically unsaturated groups in one molecule are preferred because they can achieve both adhesive properties and a low dielectric loss tangent. In particular, 1,9-nonanediol di(meth)acrylate and 1,10-decanediol di(meth)acrylate are preferred.

[0067] The content of the above-mentioned crosslinkable monomer (C) is usually 20 parts by weight or less per 100 parts by weight of acrylic resin (A), preferably 0.1 to 10 parts by weight, and particularly preferably 1 to 5 parts by weight. If the amount of crosslinkable monomer (C) is too low, the holding power tends to decrease, and if it is too high, the adhesive strength tends to decrease.

[0068] [Thermal crosslinking agent (D)] The thermal crosslinking agent (D) that can be used in the present invention exhibits excellent tackiness by reacting mainly with polar groups derived from polar group-containing (meth)acrylic acid ester monomers (a2), which are constituent monomers of the acrylic resin (A). Examples of the thermal crosslinking agent (D) include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferably used in terms of improving adhesion to the substrate and reactivity with the acrylic resin (A).

[0069] Examples of the above-mentioned isocyanate-based crosslinking agents include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, and adduct compounds of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, as well as burette and isocyanurate compounds of these polyisocyanate compounds. Among these, isocyanate-based crosslinking agents containing an alicyclic structure and an isocyanurate skeleton are preferred.

[0070] Examples of the epoxy crosslinking agents mentioned above include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, and the like.

[0071] Examples of the above-mentioned aziridine crosslinking agents include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinylcarboxyamide), and N,N'-hexamethylene-1,6-bis(1-aziridinylcarboxyamide).

[0072] Examples of the melamine-based crosslinking agents mentioned above include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexapoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resin.

[0073] Examples of the aldehyde-based crosslinking agents mentioned above include glyoxal, malondialdehyde, succinidaldehyde, maleidaldehyde, glutardialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0074] Examples of the amine-based crosslinking agents mentioned above include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0075] Examples of the above-mentioned metal chelating crosslinking agents include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

[0076] Furthermore, these thermal crosslinking agents (D) may be used individually or in combination of two or more types.

[0077] The content of the above-mentioned thermal crosslinking agent (D) is usually 10 parts by weight or less per 100 parts by weight of acrylic resin (A), preferably 0.01 to 5 parts by weight, and particularly preferably 0.1 to 3 parts by weight. If the amount of thermal crosslinking agent (D) is too small, the cohesive force will be insufficient and sufficient durability will not be obtained, and if it is too large, the adhesive strength will tend to decrease.

[0078] [Silane coupling agent] The adhesive composition of the present invention may contain a silane coupling agent for improved durability under high temperature and high humidity conditions.

[0079] The silane coupling agents mentioned above are not particularly limited and any known agents can be used. Examples include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatetopropyltriethoxysilane. These may be used individually or in combination of two or more. Among these, 3-glycidoxypropyltrimethoxysilane is preferred.

[0080] The content of the silane coupling agent is usually 5 parts by weight or less per 100 parts by weight of acrylic resin (A), preferably 0.01 to 3 parts by weight, and more preferably 0.05 to 2 parts by weight. If the content of such silane coupling agent is too high, bleed-out tends to reduce the adhesive properties and transparency. If the content is too low, durability under high temperature and high humidity conditions tends to decrease.

[0081] [Photopolymerization initiator] The adhesive composition of the present invention can be crosslinked (cured) to form an adhesive, but a photopolymerization initiator may be further added to efficiently perform crosslinking. In particular, if the acrylic resin (A) does not have an active energy ray crosslinkable structural site, it is preferable to add a photopolymerization initiator.

[0082] Such photopolymerization initiators are not particularly limited as long as they generate radicals upon the action of light. Examples include acetophenone-based, benzoin-based, thioxanthone-based, and acylphosphine oxide-based photopolymerization initiators. However, it is preferable to use a hydrogen abstraction type benzophenone-based photopolymerization initiator because it can efficiently crosslink intermolecularly or intramolecularly.

[0083] Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. These may be used individually or in combination of two or more.

[0084] Furthermore, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, 4-dimethylaminobenzoate ethyl, 4-dimethylaminobenzoate (n-butoxy)ethyl, 4-dimethylaminobenzoate isoamyl, 4-dimethylaminobenzoate 2-ethylhexyl, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. may be used in combination with these photopolymerization initiators. These auxiliary agents may be used alone or in combination of two or more.

[0085] The amount of photopolymerization initiator added is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, and even more preferably 0.5 to 2 parts by weight, per 100 parts by weight of acrylic resin (A). If the amount is too small, the curing speed tends to decrease or curing to be insufficient, and if it is too large, the curing performance does not improve and economic efficiency tends to decrease.

[0086] Furthermore, the adhesive composition of the present invention may optionally contain other adhesives, or conventionally known additives such as crosslinking accelerators, antistatic agents, tackifiers, and functional dyes. These may be used individually or in combination of two or more.

[0087] Thus, the adhesive composition of the present invention can be obtained by mixing an acrylic resin (A), a hydrophilicity imparting agent (B), and optionally a crosslinkable monomer (C), a thermal crosslinking agent (D), a silane coupling agent, a photopolymerization initiator, and other optional components. The mixing method is not particularly limited, and various methods can be employed, such as mixing all components at once, or mixing optional components first and then mixing the remaining components all at once or sequentially.

[0088] <Adhesive> As described above, the adhesive composition of the present invention becomes an adhesive when the adhesive composition is crosslinked (cured), or when the acrylic resin (A) has an active energy ray crosslinkable structure, by irradiation with active energy rays, the acrylic resin (A) contained in the adhesive composition forms a crosslinked structure at least on an intramolecular and intermolecular basis. The above adhesive has excellent adhesive properties and heat and moisture resistance, and exhibits low dielectric constant and low dielectric loss tangent, making it suitable for bonding optical components constituting touch panels, image display devices, and the like.

[0089] Furthermore, when bonding the optical components, an adhesive sheet having an adhesive layer made of the above-mentioned adhesive composition is usually used. The above-mentioned adhesive sheet can be obtained by providing an adhesive layer made of adhesive on a base sheet. Moreover, by providing the adhesive layer on a release sheet, a double-sided adhesive sheet can be made.

[0090] <Adhesive sheet> The above adhesive sheet can be manufactured, for example, as follows. First, the adhesive composition of the present invention is applied directly to a base sheet, either as is or with its concentration adjusted using a suitable organic solvent. Then, it is dried by, for example, heat treatment at 80-105°C for 0.5-10 minutes, and this is attached to a base sheet or release sheet. Finally, active energy ray irradiation is performed to crosslink (cure) the adhesive composition, and further aging is performed as necessary to produce an adhesive sheet having an adhesive layer made of the above adhesive. Alternatively, by forming the adhesive layer on a release sheet instead of a base sheet and attaching the release sheet to the adhesive layer on the opposite side, a base-less double-sided adhesive sheet can be produced. The resulting adhesive sheet or double-sided adhesive sheet is used after peeling off the release sheet from the adhesive layer.

[0091] Examples of the above-mentioned base sheets include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyfluoroethylene; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; synthetic resin sheets such as polystyrene, polycarbonate, polyarylate, and polyimide; metal foils of aluminum, copper, and iron; paper such as fine paper and glassine paper; and textiles and nonwoven fabrics made of glass fibers, natural fibers, and synthetic fibers. These base sheets can be used as single layers or as multi-layered structures made by laminating two or more types. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and other factors.

[0092] Furthermore, as the release sheet, for example, various synthetic resin sheets, paper, textiles, nonwoven fabrics, etc., as exemplified in the base sheet, can be used, which have been treated with a release agent. It is preferable to use a silicone-based release sheet.

[0093] Furthermore, the coating method for the above-mentioned adhesive composition is not particularly limited as long as it is a general coating method, and examples include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

[0094] As active energy rays for crosslinking (curing) the adhesive composition on the above-mentioned release sheet, various types of light rays can be used, including far-ultraviolet rays, ultraviolet rays, near-ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and gamma rays, as well as electron beams, proton beams, and neutron beams. However, curing by ultraviolet rays is preferred due to the curing speed, ease of obtaining irradiation equipment, and cost.

[0095] The gel fraction of the adhesive layer of the above adhesive sheet is preferably 10 to 100% by weight, more preferably 30 to 90% by weight, and especially preferably 50 to 80% by weight, from the viewpoint of durability and adhesive strength. If the gel fraction is too low, the cohesive force decreases, which tends to reduce durability. If the gel fraction is too high, the cohesive force increases, which tends to reduce adhesive strength.

[0096] Adjusting the gel fraction to the above range can be achieved, for example, by adjusting the amount of active energy ray irradiation or the content of active energy ray crosslinkable structural sites in the acrylic resin (A), or by adjusting the type and amount of crosslinking agent or photopolymerization initiator.

[0097] The gel fraction mentioned above serves as an indicator of the degree of crosslinking (degree of hardening) and can be calculated, for example, by the following method: An adhesive sheet (without a release sheet) consisting of a polymer sheet (e.g., polyethylene terephthalate (PET) film) as the base material is wrapped in a 200-mesh stainless steel wire mesh and immersed in toluene maintained at 23°C for 24 hours. The weight percentage of the insoluble adhesive component remaining in the wire mesh is taken as the gel fraction. However, the weight of the base material is subtracted.

[0098] The thickness of the adhesive layer of the above adhesive sheet is usually preferably 25 to 3000 μm, more preferably 50 to 1000 μm, and particularly preferably 75 to 300 μm. If the thickness of the adhesive layer is too thin, the shock absorption performance tends to decrease, and if it is too thick, the overall thickness of the optical component increases, which tends to reduce its practicality.

[0099] In this invention, the thickness of the adhesive layer is determined by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire laminate containing the adhesive layer, using the "ID-C112B" manufactured by Mitutoyo Corporation.

[0100] The adhesive layer described above preferably has a relative permittivity of 3.0 or less at 1 MHz, more preferably 2.7 or less, and even more preferably 2.5 or less. The lower limit of the relative permittivity is usually 1.0. If the relative permittivity at 1 MHz is too high, the capacitance between the electrodes on the touch panel becomes large, which tends to cause malfunctions. Conversely, if it is too low, the capacitance becomes small, which tends to reduce detection sensitivity.

[0101] The adhesive layer described above preferably has a relative permittivity of 3.0 or less at 10 GHz, and more preferably 2.8 or less. The lower limit of the relative permittivity is usually 1.0. If the dielectric constant at 10 GHz is too high, there is a tendency for transmission loss to increase in antennas, sensors, wiring, etc. that come into contact with the adhesive layer.

[0102] Furthermore, the adhesive layer preferably has a dielectric loss tangent of 0.005 or less at 10 GHz, particularly 0.004 or less, and more preferably 0.003 or less. If the dielectric loss tangent at 10 GHz is too high, transmission loss tends to increase in antennas, sensors, wiring, etc. that are in contact with the adhesive layer.

[0103] The adhesive layer of the adhesive sheet of the present invention preferably has a haze value of 2% or less when the thickness of the adhesive layer is 150 μm, and is particularly preferably 0 to 1.5%, and more preferably 0 to 1%. If the haze value exceeds 2%, the adhesive layer tends to whiten and its transparency decreases.

[0104] Furthermore, in the present invention, an optical member with an adhesive layer can be obtained by laminating the above-mentioned adhesive layer onto an optical member. In addition, optical members can be bonded together using the above-mentioned double-sided adhesive sheet.

[0105] Examples of the optical components mentioned above include displays (organic EL, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (film), and transparent wiring, which constitute touch panels and image display devices. [Examples]

[0106] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to weight basis. The weight-average molecular weight and glass transition temperature of the acrylic resin were measured according to the method described above.

[0107] [Manufacturing Example 1: Manufacturing of Acrylic Resin [A-1]] In a 2L flask with a condenser, add 27 parts ethyl acetate (boiling point 77°C) and 3 parts acetone (boiling point 56°C) as polymerization solvents, 0.02 parts 2,2'-azobisisobutyronitrile (AIBN, half-life 65°C) as polymerization initiator, 20 parts pre-mixed monomer solution (stearyl methacrylate (SMA:a1-2), 53.55 parts mixture of lauryl methacrylate and tridecyl methacrylate (SLMA:a1-1), and 4-hydroxybutyl acrylate (4HBA:a2 100 parts of a mixed solution containing 1 part of 2-ethylhexyl methacrylate (2EHMA:a3), 20 parts of ethyl methacrylate (EMA:a3), and 0.45 parts of 4-methacryloyloxybenzophenone (MBP:a4) were added, and 40% of this mixture was heated under reflux in a flask. Then, 0.05 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN: 10-hour half-life temperature 52°C) and the remaining 60% of the monomer solution were added dropwise over 2 hours as polymerization initiators. After another hour, a mixture of 10 parts of ethyl acetate and 0.2 parts of ADVN was added dropwise over 1 hour to react and obtain an acrylic resin [A-1] (weight-average molecular weight: 420,000, dispersion: 4.20, solids content: 57%, viscosity: 5100 mPa·s (25°C), glass transition temperature: -3°C). Furthermore, the content of alkyl methacrylate monomers in the copolymer was 98.55%, and the average number of carbon atoms in the alkyl chain of the alkyl methacrylate monomer was 12.1. The composition and physical properties of the obtained acrylic resin [A-1] are shown in Table 1 below.

[0108] [Manufacturing Examples 2-10] Acrylic resins [A-2] to [A-10] were manufactured in the same manner as in Manufacturing Example 1, except that the copolymerization components of the acrylic resins were as shown in Table 1 below. The physical properties of the obtained acrylic resins [A-2] to [A-10] are shown in Table 1 below.

[0109] [Table 1]

[0110] Next, prior to preparing the adhesive composition, the following components were prepared.

[0111] [Hydrophilicity-imparting agent (B)] · Polyethylene glycol diacrylate (B1-1): "A400, manufactured by Shin-Nakamura Chemical Co., Ltd." [A compound containing a -(C2H4O)9- structure and two ethylenically unsaturated groups]

[0112] [Example 1] The acrylic resin (A-1) solution obtained above was adjusted to a solid content concentration of 45% with ethyl acetate. One part of polyethylene glycol diacrylate (B1-1) was mixed therein to obtain an adhesive composition solution. Such an adhesive composition solution was applied to a polyester-based release sheet so that the thickness after drying was about 75 μm, and dried at 100 °C for 5 minutes to form an adhesive composition layer. After laminating two obtained adhesive composition layers, they were sandwiched with polyester-based release sheets, and using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure amount: 1000 mJ / cm 2 (500 mJ / cm 2 ×2 passes) for ultraviolet irradiation to form an adhesive layer, and a substrate-free double-sided adhesive sheet was obtained. Also, the release sheet on one side was peeled off from the adhesive layer of the obtained substrate-free double-sided adhesive film, and it was pressed against an easily adherable treated polyethylene terephthalate (PET) sheet (thickness 125 μm) to obtain a PET sheet with an adhesive layer having a thickness of 150 μm.

[0113] [Examples 2 to 7, Comparative Examples 1 to 6] An adhesive composition was prepared in the same manner as in Example 1 with the formulation shown in Table 2 below, and then a substrate-free double-sided adhesive sheet and a PET sheet with an adhesive layer were obtained in the same manner as in Example 1.

[0114] The following evaluations were performed on the substrate-free double-sided adhesive sheets or PET sheets with an adhesive layer of the obtained Examples and Comparative Examples.

[0115] [Gel fraction] After cutting the above substrate-free double-sided adhesive sheet into 40 mm × 40 mm, using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 The sample was irradiated with UV light using four passes, left to stand for 30 minutes under conditions of 23°C and 50% RH, then one release sheet was peeled off, and the adhesive layer side was bonded to a 50mm x 100mm SUS mesh sheet (200 mesh). The other release sheet was then peeled off, and the sample was wrapped by folding it back from the center along the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was measured by the weight change after immersion for 24 hours in a sealed container containing 250g of toluene maintained at 23°C.

[0116] [Dielectric properties (low frequency: 1MHz) [relative permittivity (ε')]] For the above substrate-less double-sided adhesive sheet, after lamination until the adhesive layer thickness reached 600 μm, one release sheet was peeled off and pressed onto an untreated polyethylene terephthalate (PET) sheet (thickness 50 μm). Then, the other release sheet was peeled off and pressed onto the same untreated polyethylene terephthalate (PET) sheet as above to obtain a PET sheet with an adhesive layer for dielectric property measurement having a layer structure of "PET sheet / adhesive layer / PET sheet". The PET sheet with the adhesive layer for dielectric property measurement described above was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 The specimens were irradiated with ultraviolet light using a 4-pass method, then cut into 70mm x 70mm pieces to be used as test specimens for measuring dielectric properties (low frequency: 1MHz). For the above dielectric properties (low frequency: 1 MHz) test specimen, an HP4284A precision LCR meter (Agilent) was used to measure the impedance when the specimen was placed between electrodes and an electric field was applied at a frequency of 1 MHz in an atmosphere of 23°C × 50% RH. The dielectric constant of the adhesive layer was calculated from the change in capacitance between the electrodes. The relative permittivity (ε') was then calculated from the obtained dielectric constant and evaluated according to the following criteria. (Evaluation Criteria) ○(very good)···The relative permittivity of the adhesive layer at 1MHz is 2.7 or less. △(good)···The relative permittivity of the adhesive layer at 1MHz is greater than 2.7 and less than or equal to 3.0. ×(poor)···The relative permittivity of the adhesive layer at 1MHz is greater than 3.0

[0117] [Dielectric properties (high frequency: 10 GHz) [relative permittivity (ε'), dielectric loss tangent (tanδ)]] For the above substrate-less double-sided adhesive sheet, after lamination until the adhesive layer thickness reached 600 μm, one release sheet was peeled off and pressed onto an untreated polyethylene terephthalate (PET) sheet (thickness 50 μm). Then, the other release sheet was peeled off and pressed onto the same untreated polyethylene terephthalate (PET) sheet as above to obtain a PET sheet with an adhesive layer for dielectric property measurement having the configuration of "PET sheet / adhesive layer / PET sheet". The PET sheet with the adhesive layer for dielectric property measurement described above was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 The specimens were irradiated with ultraviolet light using a 4-pass method, then cut into 2mm x 80mm pieces to be used as test specimens for dielectric properties (high frequency: 10GHz). For the above-mentioned test specimens used for measuring dielectric properties (high frequency: 10 GHz), the dielectric constant (relative permittivity (ε'), dielectric loss tangent (tanδ)) of the adhesive layer at 10 GHz was calculated using the cavity resonator perturbation method with an E8361A PNA series network analyzer (manufactured by Agilent), and evaluated according to the following criteria. (Evaluation criteria for relative permittivity (ε')) ○(very good)···The relative permittivity of the adhesive layer at 10GHz is 2.2 or less. ×(poor)···The relative permittivity of the adhesive layer at 10GHz is greater than 2.2 (Evaluation criteria for dielectric loss tangent (tanδ)) ○(very good)···The dielectric loss tangent of the adhesive layer at 10GHz is 0.005 or less. ×(poor)···The dielectric loss tangent of the adhesive layer at 10GHz is greater than 0.005

[0118] [180° peel strength at 23°C] The PET sheet with the adhesive layer described above was cut to a size of 25 mm wide x 100 mm long and subjected to high-pressure mercury UV irradiation with a peak illuminance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 After UV irradiation (4 passes), the release sheet was peeled off, and the adhesive layer side was pressed onto alkali-free glass (Corning Eagle XG, 1.1 mm thick) using a 2 kg rubber roller in a 23°C, 50% RH atmosphere with two passes. After standing for 30 minutes under 23°C x 50% RH conditions, the 180° peel strength (N / 25 mm) was measured at room temperature (23°C) with a peeling speed of 300 mm / min.

[0119] [80℃ holding power] The PET sheet with the adhesive layer described above was cut to a size of 25 mm x 50 mm and subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 After UV irradiation (4 passes), the release sheet was peeled off, and the material was pressed onto a stainless steel plate (SUS304) by reciprocating a 2kg roller (attachment area 25mm x 25mm). The holding force was measured using a creep tester (BE-501, high-temperature constant-humidity chamber equipped holding force tester, manufactured by Tester Sangyo Co., Ltd.) with a load of 1kg applied under an 80°C atmosphere for 24 hours. The evaluation criteria are as follows. (Evaluation Criteria) ◎(excellent)···No misalignment ○ (very good) ... deviation of less than 0.1 mm △(good)···Misalignment of 0.1mm or more, but less than 1.0mm ×(poor)···Misalignment of 1.0mm or more, or dropping.

[0120] [Optical properties (transparency) of the adhesive layer] The PET sheet with the adhesive layer described above was cut into 25mm x 25mm pieces and treated with a high-pressure mercury UV irradiation device at a peak irradiance of 150mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 The specimen was irradiated with ultraviolet light using four passes. After that, the release sheet was peeled off one side of the adhesive layer, and the adhesive layer side was bonded to alkali-free glass (Corning Eagle XG, 1.1 mm thick). The specimen was then autoclaved (50°C x 0.5 MPa x 20 minutes) to produce a test specimen with the structure of "alkali-free glass / adhesive layer / PET".

[0121] [Haze value] The haze value was measured using the obtained test specimens. The haze value was calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and substituting the obtained values ​​of diffuse transmittance and total light transmittance into Equation 1 below. This equipment conforms to JIS K7361-1. Haze value (%) = (Diffuse transmittance / Total light transmittance) × 100 ... (Equation 1)

[0122] [Heat and humidity resistance] The PET sheet with the adhesive layer described above was cut to a size of 30 mm x 50 mm and subjected to high-pressure mercury UV irradiation with a peak illuminance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 After UV irradiation (4 passes), the release sheet was peeled off, and the adhesive layer side was bonded to alkali-free glass (Corning Eagle XG, 1.1 mm thick). Then, it was autoclaved (50°C, 0.5 MPa, 20 minutes) and left to stand for 30 minutes under conditions of 23°C x 50% RH to produce a test specimen with the structure of "alkali-free glass / adhesive layer / PET".

[0123] Using the obtained test specimens, a humid and heat resistance test was conducted for 7 days (168 hours) under an atmosphere of 85°C and 85%RH. The haze value was measured before the start of the humid and heat resistance test, and after the test, and after standing for 2 hours under conditions of 23°C × 50%RH. The haze value was calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and substituting the obtained values ​​of diffuse transmittance and total light transmittance into Equation 2 below. Subsequently, the haze value increase was calculated from Equation 3 below. This equipment conforms to JIS K7361-1. Haze value (%) = (Diffuse transmittance / Total light transmittance) × 100 ... (Equation 2) Haze value increase (%) = {(Haze value after humidity and heat resistance test - Haze value before humidity and heat resistance test) / Haze value before humidity and heat resistance test} × 100 ... (Equation 3) (Evaluation Criteria) ○ (very good) ... Increase of less than 1.5% △ (good) ··· Increase of 1.5% or more but less than 2.5% × (poor) ... Increase is greater than 2.5%

[0124] [Table 2]

[0125] The adhesive sheets produced using the adhesive compositions of Examples 1 to 7 exhibited a good balance of low dielectric constant and low dielectric loss tangent in both the low-frequency and high-frequency ranges, while also possessing excellent adhesive properties and resistance to moisture and heat. On the other hand, adhesive sheets made using the adhesive compositions of Comparative Examples 1, 3-6, which do not contain a specific hydrophilicity imparting agent, exhibited inferior adhesive properties and heat and humidity resistance compared to Examples 1-7. Furthermore, adhesive sheets made using the adhesive compositions of Comparative Examples 2 and 3, which contained too much polar group-containing (meth)acrylic acid ester monomer (a2) as a copolymer component of the acrylic resin, exhibited inferior high-frequency dielectric properties compared to Examples 1-7. In addition, adhesive sheets made using the adhesive compositions of Comparative Examples 4-6, which do not contain alkyl methacrylate ester monomer (a3) ​​as a copolymer component of the acrylic resin, exhibited inferior adhesive properties compared to Examples 1-7.

[0126] While the above embodiments illustrate specific forms of the present invention, these embodiments are merely illustrative and should not be interpreted restrictively. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention. [Industrial applicability]

[0127] The adhesive composition of the present invention provides excellent adhesive properties, low dielectric constant, and low dielectric loss tangent, making it particularly useful as an adhesive for bonding optical components that constitute touch panels and image display devices, and for encapsulating organic EL displays.

Claims

1. An adhesive comprising a crosslinked adhesive composition containing an acrylic resin (A) and a hydrophilicity imparting agent (B), The acrylic resin (A) is a copolymer of a copolymer component (a) containing an alkyl methacrylate monomer (a1) having an alkyl chain having 10 to 36 carbon atoms, and a polar group-containing ethylenically unsaturated monomer (a2). The content of the alkyl methacrylate monomer (a1) having an alkyl chain with 10 to 36 carbon atoms is 50 to 95% by weight relative to the copolymer component (a). The content of the polar group-containing ethylenically unsaturated monomer (a2) is 0.01% by weight or more and less than 3% by weight relative to the copolymer component (a). The acrylic resin (A) content in the adhesive composition is 90% by weight or more. The hydrophilic agent (B) is -(C n H 2n O) Contains a compound (B1) having an m-(n is 2 to 6, m is 2 to 25) structure and containing at least one ethylenically unsaturated group, An adhesive characterized in that the content of the compound (B1) is 0.01 to 5 parts by weight per 100 parts by weight of acrylic resin (A).

2. The adhesive according to claim 1, characterized in that the alkyl methacrylate monomer (a1) having an alkyl chain having 10 to 36 carbon atoms contains an alkyl methacrylate monomer (a1-1) having an alkyl chain having 10 to 15 carbon atoms and an alkyl methacrylate monomer (a1-2) having an alkyl chain having 16 to 36 carbon atoms.

3. The adhesive according to claim 1 or 2, characterized in that the content of alkyl methacrylate monomer in copolymer component (a) is 80 to 99% by weight relative to copolymer component (a), and the average number of carbon atoms in the alkyl chain of the alkyl methacrylate monomer is 10 to 15.

4. The adhesive according to any one of claims 1 to 3, characterized in that the acrylic resin (A) has an active energy ray crosslinkable structural portion.

5. The adhesive according to claim 4, characterized in that the active energy ray crosslinkable structural site is a benzophenone-based crosslinkable structural site.

6. The adhesive according to any one of claims 1 to 5, characterized in that the weight-average molecular weight of the acrylic resin (A) is 150,000 to 1,500,000.

7. The adhesive according to any one of claims 1 to 6, characterized in that the adhesive composition is crosslinked by active energy rays.

8. An adhesive sheet characterized by having an adhesive layer made of the adhesive described in any one of claims 1 to 7.

9. An adhesive sheet for an image display device, characterized by having an adhesive layer made of the adhesive described in any one of claims 1 to 7.

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