Adhesive composition, pressure sensitive adhesive sheet, optical laminate and picture display unit

Abstract

To provide an adhesive composition appropriate for forming a pressure sensitive adhesive sheet with durability thereof secured, as well as capable of preventing a change in a dimension of an optical film included in an optical laminate.SOLUTION: Provided is an adhesive composition including a (meth)acrylic polymer (A) as a primary component, and further including a cross-linking agent (B). The amount of blending of the cross-linking agent (B) is 5 pts.wt. or more, based on 100 pts.wt. of the (meth)acrylic polymer (A). Assuming a self-polymerization body (C) of the cross-linking agent (B), a distance Ra in Hansen solubility parameter (HSP) between the (meth)acrylic polymer (A) and the self-polymerization body (C) is 12.3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, an optical laminate, and an image display device. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. These various image display devices typically have a laminated structure of an image-forming layer, such as a liquid crystal layer or an EL light-emitting layer, and an optical laminate including an optical film and an adhesive sheet. The adhesive sheet is mainly used to bond between films included in the optical laminate or to bond between the image-forming layer and the optical laminate. Examples of optical films include polarizing plates, retardation films, and polarizing plates with retardation films, which are formed by integrating a polarizing plate and a retardation film. Patent Documents 1 and 2 disclose examples of optical laminates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-031214 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-98665 Summary of the Invention [Problem to be solved by the invention]

[0004] Excessive dimensional changes in optical films due to temperature changes can cause light leakage and color unevenness in image display devices. Light leakage and color unevenness are particularly likely to occur in relatively large image display devices that use polarizing plates with retardation films. In addition, image display devices designed with narrow bezels (narrow frame designs) are becoming more common, making it increasingly important to suppress dimensional changes. One way to suppress dimensional changes is to increase the elastic modulus of the pressure-sensitive adhesive sheet included in the optical laminate. However, simply increasing the elastic modulus can reduce the durability of the pressure-sensitive adhesive sheet, making it unable to follow dimensional changes.

[0005] An object of the present invention is to provide a pressure-sensitive adhesive composition that can reduce the dimensions of an optical film contained in an optical laminate and is suitable for forming a pressure-sensitive adhesive sheet that also ensures durability. [Means for solving the problem]

[0006] The present invention provides Contains a (meth)acrylic polymer (A) as a main component, Further comprising a crosslinking agent (B), the amount of the crosslinking agent (B) blended is 5 parts by weight or more relative to 100 parts by weight of the (meth)acrylic polymer (A); a pressure-sensitive adhesive composition, wherein, assuming a self-polymer (C) of the crosslinking agent (B), the distance Ra of the Hansen solubility parameter (HSP) between the (meth)acrylic polymer (A) and the self-polymer (C) is 12.3 or less; to provide.

[0007] In another aspect, the present invention provides a method for producing a composition comprising: A pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition of the present invention. to provide.

[0008] In another aspect, the present invention provides a method for producing a composition comprising: An optical laminate comprising the pressure-sensitive adhesive sheet of the present invention and an optical film; to provide.

[0009] In another aspect, the present invention provides a method for producing a composition comprising: An image display device comprising the optical laminate of the present invention. to provide. [Effects of the Invention]

[0010] The pressure-sensitive adhesive composition according to the present invention is suitable for forming a pressure-sensitive adhesive sheet that can suppress dimensional changes in an optical film included in an optical laminate and also ensures durability. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 5] FIG. 5 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 6] FIG. 6 is a cross-sectional view schematically showing an example of an image display device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0013] In this specification, "(meth)acrylic" means acrylic and methacrylic, and "(meth)acrylate" means acrylate and methacrylate.

[0014] [Adhesive composition] The pressure-sensitive adhesive composition (I) of this embodiment contains a (meth)acrylic polymer (A) and a crosslinking agent (B). The (meth)acrylic polymer (A) is contained in the pressure-sensitive adhesive composition (I) as a main component. In other words, the pressure-sensitive adhesive composition (I) is an acrylic pressure-sensitive adhesive composition. The main component refers to the component with the largest content in the composition. The content of the main component is, for example, 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, 73% by weight or more, or even 75% by weight or more.

[0015] The blending amount of the crosslinking agent (B) is 5 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) having a blending amount within the above range is suitable for forming a pressure-sensitive adhesive sheet having an increased elastic modulus.

[0016] According to the inventors' investigations, when the blending amount reaches the above range, crosslinkers (B) react with each other during the formation of the pressure-sensitive adhesive sheet, facilitating the formation of a self-polymer of the crosslinker (B). The formation of the self-polymer increases the cohesive strength of the pressure-sensitive adhesive sheet, thereby contributing to the formation of a pressure-sensitive adhesive sheet that can suppress dimensional changes in the optical film. However, further investigations have shown that when the compatibility between the (meth)acrylic polymer (A) and the self-polymer is low, the durability of the pressure-sensitive adhesive sheet tends to decrease. This decrease is thought to be due to the tendency for independent self-polymer-rich domains to form within the pressure-sensitive adhesive sheet. The formation of these domains can lead to the formation of voids due to peeling at the domain interfaces when the pressure-sensitive adhesive sheet is deformed by external force. In the pressure-sensitive adhesive composition of this embodiment, assuming a self-polymer (C) of the crosslinker (B), the Hansen solubility parameter (HSP) distance Ra between the (meth)acrylic polymer (A) and the self-polymer (C) is 12.3 or less. The smaller the distance Ra, the higher the compatibility between the polymers. Therefore, the adhesive composition of the present embodiment provides an adhesive sheet with ensured durability. Suitable for forming a groove.

[0017] The Hansen solubility parameter (HSP) is a solubility parameter introduced by Hildebrand, divided into three components: the dispersion term δD, the polarization term δP, and the hydrogen bonding term δH. δD represents the energy derived from the dispersion force between molecules. δP represents the energy derived from the polar force between molecules. δH represents the energy derived from the hydrogen bonding force between molecules. The units of each component are usually MPa. 1 / 2 The above three components give the Hansen equation A point (vector) in three-dimensional space known as the distance Ra is determined. The distance Ra is the distance between the point (D A , P A , H A ) and self-weight The point (D) corresponding to the union (C) C , P C , H C ) and is the distance between the A -δD B ) 2 +(δP A -δP B ) 2 +(δH A -δH B ) 2} 1 / 2 The details of the Hansen solubility parameters are disclosed in "Hansen Solubility Parameters; A Users Handbook (CRC Press, 2007)". The δD, δP and δH of a polymer can be calculated using, for example, HSPiP (version Using known software such as 5), the solubility parameters can be calculated based on the structural units of the polymer and the content of those units in the polymer. More specifically, the δD, δP, and δH of each structural unit are calculated individually, and the weighted average values ​​obtained by weighting the calculated δD, δP, and δH by the content of those units can be used as the δD, δP, and δH of the polymer. The calculations are performed at a temperature of 23°C. The calculated values ​​of δD, δP, and δH may vary slightly depending on the software used. However, these differences are usually negligible when calculating Ra. The Hansen solubility parameter for crosslinking agents is calculated only for those that form self-polymers.

[0018] The distance Ra may be 12.25 or less, 12.2 or less, 12.15 or less, 12.1 or less, 12.05 or less, 12.0 or less, 11.95 or less, 11.9 or less, 11.85 or less, 11.8 or less, 11.75 or less, or even 11.7 or less. The lower limit of the distance Ra is, for example, 6 or more.

[0019] [(Meth)acrylic polymer (A)] The (meth)acrylic polymer (A) preferably has, as a main unit, a structural unit derived from a (meth)acrylic monomer (A1) having an alkyl group of 1 to 30 carbon atoms on the side chain. The alkyl group may be linear or branched. The (meth)acrylic polymer (A) may have one or more structural units derived from the (meth)acrylic monomer (A1). Examples of the (meth)acrylic monomer (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, and isoheptyl (meth)acrylate. acrylate, 2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-dodecyl(meth)acrylate (lauryl(meth)acrylate), n-tridecyl(meth)acrylate, and n-tetradecyl(meth)acrylate. In this specification, the term "main unit" refers to a unit that accounts for, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of all the structural units contained in the polymer.

[0020] The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) having a long-chain alkyl group on the side chain. An example of the monomer (A1) is n-dodecyl (meth)acrylate (lauryl (meth)acrylate). In this specification, the term "long-chain alkyl group" refers to an alkyl group having 6 to 30 carbon atoms.

[0021] The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) which, when made into a homopolymer, has a glass transition temperature (Tg) in the range of −70 to −20° C. An example of the monomer (A1) is n-butyl acrylate.

[0022] The (meth)acrylic polymer (A) may contain a structural unit other than the structural unit derived from the (meth)acrylic monomer (A1). The structural unit is derived from a monomer (A2) copolymerizable with the (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may contain one or more types of such structural units.

[0023] An example of the monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may be an aromatic ring-containing (meth)acrylic monomer. Examples of the aromatic ring-containing monomer include phenyl(meth)acrylate, phenoxyethyl(meth)acrylate, benzyl(meth)acrylate, phenoxydiethylene glycol(meth)acrylate, ethylene oxide-modified nonylphenol(meth)acrylate, hydroxyethylated β-naphthol(meth)acrylate, and biphenyl(meth)acrylate. The content of the structural unit derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is, for example, 0 to 50% by weight, and may be 1 to 30% by weight, 5 to 25% by weight, 8 to 20% by weight, 10 to 18% by weight, 12 to 16% by weight, or even 12 to 16% by weight. The (meth)acrylic polymer (A) having a structural unit derived from an aromatic ring-containing monomer can contribute to improving the compatibility of the (meth)acrylic polymer (A) with the crosslinking agent (B) and its self-polymer.

[0024] Another example of the monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be a hydroxyl group-containing (meth)acrylic monomer. Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. The hydroxyl group can react with various crosslinking agents. From the viewpoint of increasing the uniformity of the crosslinked structure to be formed, the content of the structural unit derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer (A) may be 1% by weight or less, 0.5% by weight or less, or even 0.1% by weight or less, or may even be 0% by weight (no such structural unit may be contained).

[0025] Monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of the carboxyl group-containing monomer are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of the amino group-containing monomer are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of the amide group-containing monomer include acrylamide-based monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam-based monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam.

[0026] Monomer (A2) may be a polyfunctional monomer. Examples of polyfunctional monomers include polyfunctional acrylates such as hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol 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, allyl (meth)acrylate, vinyl (meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; and divinylbenzene. The polyfunctional acrylate is preferably 1,6-hexanediol diacrylate or dipentaerythritol hexa(meth)acrylate.

[0027] The total content of structural units derived from carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and polyfunctional monomers in the (meth)acrylic polymer (A) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less. When the (meth)acrylic polymer (A) contains such structural units, the total content is, for example, 0.01% by weight or more, and may be 0.05% by weight or more. The (meth)acrylic polymer (A) may not contain structural units derived from polyfunctional monomers. When the (meth)acrylic polymer (A) contains structural units derived from carboxyl group-containing monomers, particularly acrylic acid, and / or structural units derived from amide group-containing monomers, the self-polymerization of the crosslinking agent (B), for example, can be enhanced. The improvement in the self-polymerization property of the crosslinking agent (B) can particularly contribute to suppressing peeling of the pressure-sensitive adhesive sheet in a humid environment and stabilizing the physical properties of the pressure-sensitive adhesive sheet in a system with a high content of the crosslinking agent (B).

[0028] Examples of other monomers (A2) include (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; vinyl sulfonate; (meth)acrylic acid esters having an alicyclic hydrocarbon group, such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; vinyl esters, such as vinyl acetate and vinyl propionate; aromatic vinyl compounds, such as styrene and vinyl toluene; olefins or dienes, such as ethylene, propylene, butadiene, isoprene, and isobutylene; vinyl ethers, such as vinyl alkyl ether; and vinyl chloride.

[0029] The total content of the structural units derived from the other monomers (A2) in the (meth)acrylic polymer (A) is, for example, 30% by weight or less, may be 10% by weight or less, and is preferably 0% by weight (not including such structural units).

[0030] The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above-mentioned monomers by a known method. A monomer and a partial polymer of the monomer may also be polymerized. The polymerization can be carried out, for example, by solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Solution polymerization and active energy ray polymerization are preferred because they allow the formation of a pressure-sensitive adhesive sheet with excellent optical transparency. The polymerization is preferably carried out while avoiding contact of the monomer and / or partial polymer with oxygen; for this purpose, for example, polymerization in an inert gas atmosphere such as nitrogen, or polymerization in a state where oxygen is blocked by a resin film or the like can be employed. The (meth)acrylic polymer (A) formed can be a random copolymer, a block copolymer, a graft copolymer, or the like. The polymer may be in any form.

[0031] The polymerization system for forming the (meth)acrylic polymer (A) may contain one or more polymerization initiators. The type of polymerization initiator can be selected depending on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

[0032] Examples of solvents used in solution polymerization include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

[0033] Examples of polymerization initiators used in solution polymerization include azo polymerization initiators, peroxide polymerization initiators, and redox polymerization initiators. Examples of peroxide polymerization initiators include dibenzoyl peroxide and t-butyl permaleate. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of the azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight, or may be 0.1 to 0.3 parts by weight, per 100 parts by weight of the total amount of monomers.

[0034] The active energy rays used in the active energy ray polymerization include, for example, ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, as well as ultraviolet rays. The active energy ray is preferably ultraviolet rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for the active energy ray polymerization typically contains a photopolymerization initiator. The polymerization conditions for the active energy polymerization are not limited as long as a (meth)acrylic polymer (A) is formed.

[0035] Examples of the photopolymerization initiator include a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, a photoactive oxime-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, a ketal-based photopolymerization initiator, and a thioxanthone-based photopolymerization initiator, although the photopolymerization initiator is not limited to the above examples.

[0036] Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. An example of a photoactive oxime-based photopolymerization initiator is 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. An example of a benzoin-based photopolymerization initiator is benzoin. An example of a benzyl-based photopolymerization initiator is benzil. An example of a benzophenone-based photopolymerization initiator is benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, or α-hydroxycyclohexylphenyl ketone. An example of a ketal-based photopolymerization initiator is benzil dimethyl ketal. Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0037] The amount of the photopolymerization initiator used is, for example, 0.01 to 1 part by weight, and may be 0.05 to 0.5 parts by weight, relative to 100 parts by weight of the total amount of the monomers.

[0038] The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1,000,000 to 2,800,000, and from the viewpoint of the durability and heat resistance of the PSA sheet, may be 1,200,000 or more, or even 1,400,000 or more. The weight average molecular weight (Mw) of the polymer and oligomer in this specification is a value (polystyrene equivalent) based on measurement by GPC (gel permeation chromatography).

[0039] The content of the (meth)acrylic polymer (A) in the pressure-sensitive adhesive composition (I) is, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, or even 80% by weight or more, in terms of solid content. The upper limit of the content is, for example, 99% by weight or less, 97% by weight or less, 95% by weight or less, 93% by weight or less, or even 90% by weight or less.

[0040] [Crosslinking agent (B)] The crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. The crosslinking agent (B) may also be a trifunctional or higher crosslinking agent having three or more crosslinking reactive groups per molecule. Trifunctional or higher crosslinking agents (B) tend to form self-polymers. The upper limit of the number of crosslinking reactive groups per molecule is, for example, five.

[0041] The crosslinking agent (B) is, for example, an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent contains an isocyanate group as a crosslinking reactive group. The isocyanate-based crosslinking agent (B) may be an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound.

[0042] Examples of aromatic isocyanate compounds that can be used in the crosslinking agent (B) include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate.

[0043] Examples of the alicyclic isocyanate compound that can be used in the crosslinking agent (B) include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

[0044] Examples of aliphatic isocyanate compounds that can be used in the crosslinking agent (B) are trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0045] The crosslinking agent (B) may be a derivative of the above-mentioned isocyanate compound. Examples of the derivative include polymers (dimers, trimers, pentamers, etc.) and derivatives of isocyanate compounds attached to polyhydric alcohols such as trimethylolpropane. These include adducts obtained by adding urethane to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc., urea-modified products, biuret-modified products, allophanate-modified products, isocyanurate-modified products, and carbodiimide-modified products, as well as urethane prepolymers obtained by adding urethane to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0046] The crosslinking agent (B) is preferably an aromatic isocyanate compound or a derivative thereof, more preferably tolylene diisocyanate or a derivative thereof (i.e., a tolylene diisocyanate (TDI) crosslinking agent). TDI crosslinking agents have better reaction uniformity than xylylene diisocyanate or a derivative thereof (i.e., a xylylene diisocyanate (XDI) crosslinking agent). An example of a TDI crosslinking agent is an adduct of tolylene diisocyanate and a polyfunctional alcohol, and a more specific example is a trimethylolpropane / tolylene diisocyanate trimer adduct.

[0047] Commercially available crosslinking agents (B) can be used, such as Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation; all trade names), and Takenate D-102, Takenate D-103, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500, and Takenate 600 (all manufactured by Mitsui Chemicals; all trade names). As the crosslinking agent (B), Coronate L, Takenate D-102 and Takenate D-103 (all of which are trimethylolpropane / tolylene diisocyanate trimer adducts) can be preferably used.

[0048] The amount of the crosslinking agent (B) in the pressure-sensitive adhesive composition (I) is 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, more than 10 parts by weight, or even 11 parts by weight or more, relative to 100 parts by weight of the (meth)acrylic polymer (A). The upper limit of the amount is, for example, 30 parts by weight or less, 28 parts by weight or less, 25 parts by weight or less, 23 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, or even 15 parts by weight or less.

[0049] The PSA composition (I) may contain one or more crosslinking agents (B). When two or more crosslinking agents (B) are contained, the distance Ra of the self-polymer (C) of at least one crosslinking agent (B), for example, the crosslinking agent (B) with the largest blending amount, may satisfy the above range. The distance Ra of the self-polymer (C) of all the crosslinking agents (B) contained may satisfy the above range.

[0050] The self-polymer (C) assumed in calculating the distance Ra is a homopolymer consisting of structural units derived from the crosslinking agent (B). However, the self-polymer of the crosslinking agent (B) actually contained in the PSA sheet formed from the PSA composition (I) may contain structural units other than those derived from the crosslinking agent (B).

[0051] The pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition (I) may have an interpenetrating network (IPN) structure of the crosslinked product of the (meth)acrylic polymer (A) and the self-polymer of the crosslinking agent (B). The IPN structure is suitable for improving the durability of the pressure-sensitive adhesive sheet.

[0052] Other examples of the crosslinking agent (B) include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. However, the crosslinking agent (B) is preferably an isocyanate-based crosslinking agent. When the pressure-sensitive adhesive composition (I) contains a crosslinking agent (B) other than an isocyanate-based crosslinking agent, the total amount of the crosslinking agent (B) added is preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, 0.1 to 2 parts by weight, and 0.1 to 1 part by weight, in that order, relative to 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) may not contain a crosslinking agent (B) other than an isocyanate crosslinking agent, for example, an epoxy crosslinking agent.

[0053] [(Meth)acrylic oligomer] The pressure-sensitive adhesive composition (I) may further contain a (meth)acrylic oligomer (D).

[0054] The (meth)acrylic oligomer (D) may have the same composition as the above-mentioned (meth)acrylic polymer (A) except for the weight-average molecular weight (Mw). The weight-average molecular weight (Mw) of the (meth)acrylic oligomer (D) may be, for example, 1,000 or more, 2,000 or more, 3,000 or more, or even 4,000 or more. The upper limit of the weight-average molecular weight (Mw) of the (meth)acrylic oligomer may be, for example, 30,000 or less, 15,000 or less, 10,000 or less, or even 7,000 or less.

[0055] The (meth)acrylic oligomer (D) has, for example, one or more structural units derived from the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, alkyl (meth)acrylates such as methyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

[0056] The (meth)acrylic oligomer (D) preferably has a structural unit derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesiveness of the pressure-sensitive adhesive sheet can be further improved. Examples of such acrylic monomers include alkyl (meth)acrylates having an alkyl group with a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; and aromatic ring-containing (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, and more preferably has two or more cyclic structures. Furthermore, when ultraviolet irradiation is carried out during polymerization of the (meth)acrylic oligomer (D) and / or during formation of the pressure-sensitive adhesive sheet, it is preferable that the above-mentioned monomer does not have an unsaturated bond, since this makes it less likely that the progress of polymerization and / or formation will be inhibited. For example, an alkyl (meth)acrylate having an alkyl group with a branched structure, or an ester of (meth)acrylic acid and an alicyclic alcohol can be used.

[0057] Specific examples of the (meth)acrylic oligomer (D) include a copolymer of butyl acrylate, methyl acrylate, and acrylic acid, a copolymer of cyclohexyl methacrylate and isobutyl methacrylate, a copolymer of cyclohexyl methacrylate and isobornyl methacrylate, a copolymer of cyclohexyl methacrylate and acryloylmorpholine, a copolymer of cyclohexyl methacrylate and diethylacrylamide, a copolymer of 1-adamantyl acrylate and methyl methacrylate, a copolymer of dicyclopentanyl methacrylate and copolymers with isobornyl methacrylate, dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, copolymers of methyl methacrylate with at least one selected from isobornyl acrylate and cyclopentanyl methacrylate, homopolymers of dicyclopentanyl acrylate, homopolymers of 1-adamantyl methacrylate, and homopolymers of 1-adamantyl acrylate.

[0058] For the polymerization of the (meth)acrylic oligomer (D), the above-mentioned polymerization method for the (meth)acrylic polymer (A) can be used.

[0059] When the pressure-sensitive adhesive composition (I) contains the (meth)acrylic oligomer (D), the blending amount thereof may be, for example, 70 parts by weight or less, 50 parts by weight or less, or even 40 parts by weight or less, per 100 parts by weight of the (meth)acrylic polymer (A). The lower limit of the blending amount may be, for example, 1 part by weight or more, 2 parts by weight or more, or even 3 parts by weight or more, per 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not necessarily contain the (meth)acrylic oligomer (D).

[0060] [Additives] The pressure-sensitive adhesive composition (I) may contain other additives. Examples of the additives include silane coupling agents, colorants such as pigments and dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework improvers, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (alkali metal salts, which are ionic compounds, ionic liquids, ionic solids, etc.), inorganic fillers, organic fillers, powders such as metal powders, particles, and foil-like materials. The additives may be present in an amount of, for example, 10 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer (A). The amount of the hydroxybenzoate can be in the range of 0.5 to 5 parts by weight, preferably 5 parts by weight or less, and more preferably 1 part by weight or less.

[0061] Examples of the silane coupling agent include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

[0062] When the pressure-sensitive adhesive composition (I) contains a silane coupling agent, the blending amount thereof is, for example, 5 parts by weight or less, and may be 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, or even 0.05 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not necessarily contain a silane coupling agent.

[0063] The pressure-sensitive adhesive composition (I) may be, for example, an emulsion type, a solvent type (solution type), an active energy ray curable type (photocurable type), or a hot melt type (hot melt type). From the viewpoint of forming a pressure-sensitive adhesive sheet with superior durability, the pressure-sensitive adhesive composition (I) may be a solvent type. The solvent-type pressure-sensitive adhesive composition (I) may not contain a photocuring agent such as an ultraviolet curing agent.

[0064] [Adhesive sheet] An example of the pressure-sensitive adhesive sheet of this embodiment is shown in Fig. 1. The pressure-sensitive adhesive sheet 1 in Fig. 1 is formed from a pressure-sensitive adhesive composition (I). The pressure-sensitive adhesive sheet 1 is made of, for example, a (meth)acrylic polymer The adhesive sheet 1 contains a crosslinked product of (A). The adhesive sheet 1 can be formed from the adhesive composition (I) as follows.

[0065] In the case of the solvent-curable type, for example, the pressure-sensitive adhesive composition (I) or a mixture of the pressure-sensitive adhesive composition (I) and a solvent is applied to a substrate film, and the resulting coating film is dried to form the pressure-sensitive adhesive sheet 1. The heat generated during drying causes the pressure-sensitive adhesive composition (I) to thermally cure. In the case of the active energy ray-curable type (photocurable type), for example, a mixture of a monomer(s) that will become a (meth)acrylic polymer (A) upon polymerization, a crosslinking agent (B), and, if necessary, a partially polymerized product of the monomer(s), a polymerization initiator, an oligomer (D), other crosslinking agents, additives, a solvent, and the like is applied to a substrate film, and the substrate film is then irradiated with active energy rays to form the pressure-sensitive adhesive sheet 1. The solvent may be removed by drying before irradiation with active energy rays. The substrate film may be a film (release film) whose coated surface has been subjected to a release treatment.

[0066] The pressure-sensitive adhesive sheet 1 formed on the base film can be transferred to any layer. The base film may also be an optical film, in which case an optical laminate containing the pressure-sensitive adhesive sheet 1 and the optical film is obtained.

[0067] The coating onto the substrate film can be carried out by a known method, such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, or extrusion coating using a die coater.

[0068] For the solvent-curable adhesive, the drying temperature after application is, for example, 40 to 200°C. The drying temperature may be 160°C or lower, 150°C or lower, 130°C or lower, 120°C or lower, or even 100°C or lower. By setting the drying temperature to 130°C or lower, 120°C or lower, or even 100°C or lower, a pressure-sensitive adhesive sheet 1 with superior durability can be obtained. In other words, the pressure-sensitive adhesive sheet 1 may be obtained by drying a coating film of the pressure-sensitive adhesive composition (I) at a temperature of 130°C or lower, 120°C or lower, or even 100°C or lower. The drying time may be, for example, 5 seconds to 20 minutes, 5 seconds to 10 minutes, or even 10 seconds to 5 minutes. For the active energy ray-curable adhesive, the drying temperature and drying time when drying is performed after application may be within the above ranges.

[0069] The composition or mixture to be applied to the substrate film preferably has a viscosity suitable for handling and coating. For this reason, in the case of an active energy ray curable type, the mixture to be applied preferably contains a partial polymer of the monomer(s).

[0070] In one example of the release film, the coated surface is subjected to release treatment with a silicone compound.

[0071] The thickness of the pressure-sensitive adhesive sheet 1 is, for example, 1 to 200 μm, and may be 5 to 150 μm, or even 10 to 100 μm.

[0072] The storage modulus G' (25°C) of the pressure-sensitive adhesive sheet 1 is, for example, 0.15 MPa or more, and may be 0.2 MPa or more, 0.25 MPa or more, 0.3 MPa or more, 0.4 MPa or more, 0.5 MPa or more, 0.6 MPa or more, 0.7 MPa or more, 0.8 MPa or more, 0.9 MPa or more, 1.0 MPa or more, 1.1 MPa or more, or even 1.2 MPa or more. The upper limit of the storage modulus G' (25°C) is, for example, 5 MPa or less, and may be 3.0 MPa or less, 2.5 MPa or less, or even 2.0 MPa or less. A pressure-sensitive adhesive sheet 1 having a storage modulus G' within the above range is more suitable for suppressing dimensional changes in optical films.

[0073] The storage modulus (25°C) of the pressure-sensitive adhesive sheet 1 can be evaluated by the following method. First, a measurement sample made of the material that constitutes the pressure-sensitive adhesive sheet 1 is prepared. The shape of the measurement sample is as follows: It is disc-shaped. The measurement sample has a bottom diameter of 8 mm and a thickness of 2 mm. The measurement sample may be a disc-shaped punched-out laminate of a plurality of adhesive sheets 1. Next, dynamic viscoelasticity measurement is performed on the measurement sample. For the dynamic viscoelasticity measurement, for example, an ARES-G2 manufactured by TA Instruments can be used. From the results of the dynamic viscoelasticity measurement, the storage modulus G' of the adhesive sheet 1 at 25°C can be determined. The conditions for the dynamic viscoelasticity measurement are as follows: Measurement conditions Frequency: 1Hz Deformation mode: Torsion Measurement temperature: -70℃~150℃ Heating rate: 5°C / min

[0074] The gel fraction of the pressure-sensitive adhesive sheet 1 is, for example, 60% or more, and may be 65% or more, or even 70% or more. The upper limit of the gel fraction is, for example, 99% or less, and may be 98% or less, or even 95% or less. Pressure-sensitive adhesive sheets 1 with a gel fraction within the above range are more suitable for suppressing dimensional changes in optical films.

[0075] The gel fraction of the pressure-sensitive adhesive sheet 1 can be evaluated by the following method. First, approximately 0.2 g is scraped off from the pressure-sensitive adhesive sheet 1 to obtain a small piece. Next, the obtained small piece is wrapped in a stretched porous polytetrafluoroethylene membrane (NTF1122 manufactured by Nitto Denko, average pore size 0.2 μm) and tied with kite string to obtain a test piece. Next, the weight A of the obtained test piece is measured. Weight A is the total weight of the pressure-sensitive adhesive sheet piece, the stretched porous membrane, and the kite string. The total weight B of the stretched porous membrane and kite string used is measured in advance. Next, the test piece is immersed in a 50 mL container filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test piece is removed from the container and dried for two hours in a dryer set at 130°C, after which the weight C of the test piece is measured. The gel fraction of the pressure-sensitive adhesive sheet 1 is calculated from the measured weights A, B, and C using the formula: gel fraction (wt %)=(CB) / (AB)×100(%).

[0076] The haze of the pressure-sensitive adhesive sheet 1 when the thickness is 15 μm is, for example, 1.1% or less, and may be 1% or less, 0.9% or less, 0.8% or less, 0.7% or less, or even 0.6% or less. The lower limit of the haze is, for example, 0.1% or more.

[0077] The pressure-sensitive adhesive sheet 1 can be used, for example, for optical applications. The pressure-sensitive adhesive sheet 1 may be used in an optical laminate and / or an image display device. The pressure-sensitive adhesive sheet 1 is suitable for use in image displays in which suppression of dimensional changes in the optical film is particularly required, such as image displays with narrow frames or image displays with relatively large screen sizes. Use in these image displays, for example, suppresses peeling of the film included in the optical laminate.

[0078] [Optical laminate] An example of the optical laminate of this embodiment is shown in Fig. 2. The optical laminate 10A in Fig. 2 includes an adhesive sheet 1 and an optical film 2. The adhesive sheet 1 and the optical film 2 are laminated together. The optical laminate 10A can be used as an optical film with an adhesive sheet.

[0079] Examples of the optical film 2 include a polarizing plate, a retardation film, and a laminated film including a polarizing plate and / or a retardation film. However, the optical film 2 is not limited to the above examples. The optical film 2 may also include a glass film.

[0080] The polarizing plate includes a polarizer. A polarizer protective film may be bonded to at least one surface of the polarizer. Any pressure-sensitive adhesive or adhesive may be used to bond the polarizer and the polarizer protective film. A pressure-sensitive adhesive sheet 1 may also be used for bonding. The polarizer is typically formed by in-air stretching (drying). It is a polyvinyl alcohol (PVA) film in which iodine has been oriented by stretching such as by stretching in water or boric acid.

[0081] A retardation film is a film having birefringence in the in-plane direction and / or the thickness direction, and is, for example, a stretched resin film or a film in which a liquid crystal material is oriented and fixed.

[0082] The retardation film may be a λ / 4 plate, a λ / 2 plate, an anti-reflection retardation film (see, for example, paragraphs 0221, 0222, and 0228 of JP 2012-133303 A), a viewing angle compensation retardation film (see, for example, paragraphs 0225 and 0226 of JP 2012-133303 A), or an obliquely oriented viewing angle compensation retardation film (see, for example, paragraph 0227 of JP 2012-133303 A). The retardation film is not limited to the above examples, as long as it has birefringence in the in-plane direction and / or the thickness direction. The retardation value, arrangement angle, three-dimensional birefringence, whether the retardation film is single-layer or multi-layer, and the like are also not limited. Known films can be used as the retardation film.

[0083] The thickness of the optical film 2 is, for example, 1 to 200 μm. The thickness of the optical film 2, which is a polarizing plate, is, for example, 1 to 150 μm, and may be 100 μm or less, 75 μm or less, 50 μm or less, 20 μm or less, or even 15 μm or less. The lower limit of the thickness may be 10 μm or more, 20 μm or more, 50 μm or more, 75 μm or more, or even 100 μm or more.

[0084] The optical film 2 may be a single layer or a laminated film composed of two or more layers. When the optical film 2 is a laminated film, the pressure-sensitive adhesive sheet 1 may be used to bond the layers together.

[0085] Another example of the optical laminate of the present embodiment is shown in Fig. 3. The optical laminate 10B in Fig. 3 has a laminated structure in which a separator 3, a pressure-sensitive adhesive sheet 1, and an optical film 2 are laminated in this order. By peeling off the separator 3, the optical laminate 10B can be used as an optical film with a pressure-sensitive adhesive sheet.

[0086] The separator 3 is typically a resin film. Examples of resins that can be used to form the separator 3 include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the separator 3 that comes into contact with the pressure-sensitive adhesive sheet 1 may be subjected to a release treatment. The release treatment may be, for example, a treatment using a silicone compound. However, the separator 3 is not limited to the above examples. The separator 3 is peeled off when the optical laminate 10B is used, for example, when it is attached to the image-forming layer.

[0087] Another example of the optical laminate of this embodiment is shown in Fig. 4. The optical laminate 10C in Fig. 4 has a laminated structure in which a separator 3, a pressure-sensitive adhesive sheet 1, a retardation film 2A, an interlayer pressure-sensitive adhesive 4, and a polarizing plate 2B are laminated in this order. After peeling off the separator 3, the optical laminate 10C can be used by being attached to, for example, an image-forming layer.

[0088] A known adhesive can be used for the interlayer adhesive 4. The adhesive sheet 1 may be used as the interlayer adhesive 4.

[0089] Another example of the optical laminate of this embodiment is shown in Fig. 5. The optical laminate 10D in Fig. 5 has a laminated structure in which a separator 3, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are laminated in this order. After peeling off the separator 3, the optical laminate 10D can be used by being attached to, for example, an image forming layer.

[0090] The protective film 5 has the function of protecting the optical film 2 (polarizing plate 2B), which is the outermost layer, during distribution and storage of the optical laminate 10D and when the optical laminate 10D is incorporated into an image display device. The protective film 5 may also function as a window to the external space when incorporated into an image display device. The protective film 5 is typically a resin film. Examples of resins constituting the protective film 5 include polyesters such as PET, polyolefins such as polyethylene and polypropylene, acrylics, cycloolefins, polyimides, and polyamides, with polyesters being preferred. However, the protective film 5 is not limited to the above examples. The protective film 5 may also be a glass film or a laminated film including a glass film. The protective film 5 may be subjected to surface treatments such as anti-glare, anti-reflection, and anti-static.

[0091] The protective film 5 may be bonded to the optical film 2 by any adhesive. Bonding by an adhesive sheet 1 is also possible.

[0092] The optical laminate of this embodiment can be distributed and stored, for example, as a rolled body obtained by rolling up a strip-shaped optical laminate, or as a sheet-shaped optical laminate.

[0093] The optical laminate of this embodiment is typically used in image display devices, such as liquid crystal displays, organic EL displays, and inorganic EL displays.

[0094] [Image display device] An example of an image display device of this embodiment is shown in Fig. 6. The image display device 11 in Fig. 6 has a laminated structure in which a substrate 7, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 6, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are laminated in this order. The image display device 11 has the optical laminates 10A, 10B, 10C, and 10D shown in Figs. 2 to 5 (excluding the separator 3). The substrate 7 and the image forming layer 6 may have the same configurations as the substrate and the image forming layer, respectively, of known image display devices.

[0095] The image display device 11 in Fig. 6 may be an organic EL display or a liquid crystal display. However, the image display device 11 is not limited to this example. The image display device 11 may also be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 11 may be used for home appliances, in-vehicle applications, public information displays (PID), and the like.

[0096] The image display device of this embodiment can have any configuration as long as it includes the optical laminate of this embodiment. [Example]

[0097] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0098] First, the evaluation methods for the (meth)acrylic polymers and pressure-sensitive adhesive sheets produced in the examples and comparative examples will be described.

[0099] [Weight average molecular weight (Mw)] The weight average molecular weight (Mw) of the (meth)acrylic polymer was evaluated by GPC under the following conditions. Analytical equipment: Waters, Acquity APC Column: Tosoh G7000HXL+GMHXL+GMHXL Column temperature: 40℃ Eluent: tetrahydrofuran (acid added) ·Flow rate: 0.8mL / min ·Injection volume: 100μL Detector: Differential refractometer (RI) Standard sample: Agilent, polystyrene (PS)

[0100] [Distance Ra] The distance Ra was calculated using the method described above. The software used was HSPiP (version 5 ) was used.

[0101] [Storage modulus G' (25℃)] The storage modulus G' (25°C) of the PSA sheet was evaluated using the method described above. However, the measurement sample was prepared by punching out a disc from a laminate obtained by stacking the manufactured PSA sheets. The dynamic viscoelasticity of the measurement sample was measured using an ARES-G2 manufactured by TA Instruments.

[0102] [Hayes] The haze of the pressure-sensitive adhesive sheet (15 μm thick) was measured in accordance with JIS K7136:1981 using a haze meter HZ-V3 manufactured by Suga Test Instruments in an atmosphere at 25° C. The measurement was carried out with the pressure-sensitive adhesive sheet (15 μm thick) to be evaluated attached to a slide glass S012140 (1.3 mm thick) manufactured by Matsunami Glass Industry Co., Ltd.

[0103] [Humidity durability] The humidity durability (corresponding to an accelerated durability test) of the pressure-sensitive adhesive sheet was evaluated using the following method. First, a circularly polarizing plate with a pressure-sensitive adhesive sheet was formed, with one exposed surface of each of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples. Next, the circularly polarizing plate was fixed to the surface of a glass plate (Corning Eagle XG) via the pressure-sensitive adhesive sheet. The circularly polarizing plate was fixed in an atmosphere of 23°C and 50% RH. Next, the plate was treated in an autoclave at 50°C and 5 atmospheres (absolute pressure) for 15 minutes, and then left to cool to 23°C to stabilize the bonding of the circularly polarizing plate to the glass plate. After that, the plate was left in a heated and humidified atmosphere at 60°C and 95% RH for 500 hours. After leaving the plate, the atmosphere was returned to 23°C and 50% RH, and the presence of peeling of the circularly polarizing plate from the glass plate and the formation of bubbles between the glass plate and the circularly polarizing plate were visually confirmed, and the humidity durability was evaluated as follows. A: No changes in appearance such as foaming or peeling are observed. B: A small amount of isolated peeling or bubbling was observed at the edge, but this was within the range that would not cause any problems in practical use. C: Slight continuous peeling or bubbling is observed at the edge, but is within a range that does not cause any practical problems. D: Significant peeling or foaming is observed at the edge, and there is a problem in practical use.

[0104] The method for forming the circularly polarizing plate with the adhesive sheet used for evaluating the humidity durability is described below.

[0105] <Preparation of Polarizing Plate P1> (Fabrication of polarizer) A long polyvinyl alcohol (PVA) resin film (manufactured by Kuraray, product name "PE3000", thickness 30 μm) was uniaxially stretched in the longitudinal direction (total stretching ratio 5.9 times) using a roll stretching machine, and at the same time, the resin film was subjected to each treatment of swelling, dyeing, crosslinking, washing and drying in that order to produce a polarizer with a thickness of 12 μm. The resin film was stretched 2.2 times while being treated with pure water at 20°C. In the dyeing treatment, the resin film was stretched 1.4 times while being treated with an aqueous solution at 30°C containing iodine and potassium iodide at a weight ratio of 1:7. The iodine concentration in the aqueous solution was adjusted so that the single transmittance of the polarizer to be produced would be 45.0%. A two-stage crosslinking treatment was used. In the first stage of crosslinking treatment, the resin film was stretched 1.2 times while being treated with an aqueous solution at 40°C containing boric acid and potassium iodide. The aqueous solution used in the first stage of crosslinking treatment contained 5.0 wt% boric acid and 3.0 wt% potassium iodide. In the second stage of crosslinking treatment, the resin film was stretched 1.6 times while being treated with an aqueous solution at 65°C containing boric acid and potassium iodide. The aqueous solution used in the second crosslinking treatment had a boric acid content of 4.3 wt % and a potassium iodide content of 5.0 wt %. A potassium iodide aqueous solution at 20°C was used for the cleaning treatment. The potassium iodide content in the aqueous solution used for the cleaning treatment was 2.6 wt %. The drying treatment was carried out at 70°C for 5 minutes.

[0106] (Preparation of polarizing plate P1) A triacetyl cellulose (TAC) film (Konica Minolta, product name "KC2UA", thickness 25 μm) was attached to each main surface of the prepared polarizer using a polyvinyl alcohol adhesive. However, the TAC film attached to one main surface had a hard coat (thickness 7 μm) formed on the main surface opposite the polarizer side. In this way, a polarizing plate P1 having a configuration of protective layer with hard coat / polarizer / protective layer (without hard coat) was obtained.

[0107] <Preparation of Retardation Film R1> (Preparation of First Retardation Film) 26.2 parts by weight of isosorbide (ISB), 100.5 parts by weight of 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), 10.7 parts by weight of 1,4-cyclohexanedimethanol (1,4-CHDM), 105.1 parts by weight of diphenyl carbonate (DPC), and 0.591 parts by weight of cesium carbonate (0.2 wt % aqueous solution) as a catalyst were charged into a reaction vessel and dissolved under a nitrogen atmosphere (approximately 15 minutes). The heat transfer temperature in the reaction vessel was set to 150°C, and stirring was performed as necessary. Next, the pressure inside the reaction vessel was reduced to 13.3 kPa, and the heat transfer temperature was increased to 190°C over 1 hour. Phenol evolved as the heat transfer temperature increased was removed from the reaction vessel (the same applies below). Next, the temperature inside the reaction vessel was maintained at 190°C for 15 minutes, after which the pressure inside the reaction vessel was changed to 6.67 kPa and the heat transfer medium temperature was increased to 230°C over 15 minutes. When the stirring torque of the reactor's agitator increased, the heat transfer medium temperature was increased to 250°C over 8 minutes, and the pressure inside the reaction vessel was further reduced to 0.200 kPa or less. After reaching the predetermined stirring torque, the reaction was terminated, and the resulting reaction product was extruded into water and pelletized. In this way, a polycarbonate resin with a composition of BHEPF / ISB / 1,4-CHDM = 47.4 mol% / 37.1 mol% / 15.5 mol% was obtained. The glass transition temperature of the resulting polycarbonate resin was 136.6°C and the reduced viscosity was 0.395 dL / g.

[0108] The prepared polycarbonate resin pellets were vacuum-dried at 80°C for 5 hours, and then a long resin film with a thickness of 120 μm was obtained using a film-forming device equipped with a single-screw extruder (manufactured by Isuzu Chemical Engineering, screw diameter 25 mm, cylinder temperature setting 220°C), a T-die (width 200 mm, temperature setting 220°C), a chill roll (temperature setting 120-130°C), and a winder. Next, the obtained resin film was stretched in the width direction using a tenter stretching machine at a stretching temperature of 137-139°C and a stretch ratio of 2.5 times to obtain a first retardation film.

[0109] (Preparation of second retardation film) 20 parts by weight of a side-chain liquid crystal polymer (weight average molecular weight 5000) represented by the following chemical formula (I) (wherein 65 and 35 represent the mol % of each structural unit), a polymerizable polymer exhibiting a nematic liquid crystal phase A liquid crystal coating solution was prepared by dissolving 80 parts by weight of liquid crystal (manufactured by BASF, trade name "Paliocolor LC242") and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name "Irgacure 907") in 200 parts by weight of cyclopentanone. The prepared liquid crystal coating solution was then applied to the surface of a norbornene-based resin film (manufactured by Zeon Corporation, trade name "Zeonex"), which served as a substrate film, using a bar coater. The coating was then heated and dried at 80°C for 4 minutes to align the liquid crystal contained in the coating film. The coating film was then cured by irradiation with ultraviolet light, forming a liquid crystal solidified layer (thickness 0.58 μm) on the substrate film, which served as a second retardation film. The in-plane retardation Re of the liquid crystal solidified layer for light with a wavelength of 550 nm was 0 nm, and the retardation Rth in the thickness direction was -71 nm (nx=1.5326, ny=1.5326, nz=1.6550), and the liquid crystal solidified layer exhibited refractive index characteristics of nz>nx=ny.

[0110] [ka]

[0111] (Preparation of retardation film R1) One surface of the first retardation film prepared above was attached to the liquid crystal solidified layer of the second retardation film via an adhesive to prepare a retardation film R1.

[0112] <Preparation of a circularly polarizing plate with an adhesive sheet> (Preparation of interlayer adhesive) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with a monomer mixture containing 79.9 parts by weight of butyl acrylate, 15 parts by weight of benzyl acrylate, 5 parts by weight of acrylic acid, and 0.1 parts by weight of 4-hydroxybutyl acrylate. Next, 0.1 parts by weight of 2,2'-azoisobutyronitrile as a polymerization initiator was added to 100 parts by weight of the monomer mixture along with ethyl acetate. Nitrogen gas was introduced into the flask with gentle stirring to replace the atmosphere with nitrogen. The temperature in the flask was maintained at around 55°C, and the polymerization reaction was allowed to proceed for 7 hours. Ethyl acetate was then added to the resulting reaction solution to adjust the solids concentration to 30% by weight, yielding a (meth)acrylic polymer solution for use as an interlayer adhesive. The weight-average molecular weight of the resulting polymer was 2.2 million.

[0113] Next, 0.5 parts by weight of a trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh, trade name "Coronate L"), 0.1 parts by weight of benzoyl peroxide, a peroxide-based crosslinking agent, 0.2 parts by weight of an epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403"), and 0.5 parts by weight of a polyether compound having a reactive silyl group (manufactured by Kaneka, Silyl SAT10) were mixed with the resulting (meth)acrylic polymer solution relative to 100 parts by weight of the solids content of the solution to obtain an adhesive composition PSA1 used as an interlayer adhesive for bonding the polarizing plate P1 and the retardation film R1.

[0114] (Preparation of polarizing plate with interlayer adhesive layer) The pressure-sensitive adhesive composition PSA1 prepared above was applied to a release film whose release surface was treated with silicone. The adhesive was applied to the release surface of a 38 μm-thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film, MRF38) so that the dried layer would be 12 μm thick, and then dried at 155° C. for 1 minute to form an interlayer adhesive layer. Next, the formed interlayer adhesive layer was transferred to the protective layer (without hard coat) side of polarizing plate P1 to obtain a polarizing plate with an interlayer adhesive layer.

[0115] (Preparation of a circular polarizing plate with an adhesive sheet) Each adhesive sheet prepared in the Examples and Comparative Examples was transferred from the release film to the second retardation film side of the retardation film R1 (the norbornene-based resin film used as the substrate film when preparing the second retardation film was peeled off). Next, the polarizing plate with the interlayer adhesive layer prepared above was attached to the first retardation film side of the retardation film R1 via the interlayer adhesive layer to obtain a circular polarizing plate with an adhesive sheet. The retardation film R1 and the polarizing plate with the interlayer adhesive layer were attached so that the angle between the slow axis of the first retardation film and the absorption axis of the polarizer was 45 degrees counterclockwise when viewed from the side of the first retardation film.

[0116] Next, the method for producing each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples will be described.

[0117] The correspondence between the abbreviations or names shown in the following explanation and the compounds is as follows: BA: n-butyl acrylate BzA: benzyl acrylate AA: acrylic acid HBA: 4-hydroxybutyl acrylate NVP: N-vinylpyrrolidone AIBN: 2,2'-azobisisobutyronitrile C / L: Trimethylolpropane / tolylene diisocyanate trimer adduct (isocyanate-based crosslinking agent; Tosoh, Coronate L) TetradC: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (multifunctional epoxy crosslinker; TetradC, manufactured by Mitsubishi Gas Chemical Company) KBM403: 3-glycidoxypropyltriethoxysilane (silane coupling agent; Shin-Etsu Chemical Co., Ltd., KBM403)

[0118] [Preparation of (meth)acrylic polymer (A)] (Synthesis Example 1) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 94.9 parts by weight of BA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. Next, 0.1 parts by weight of AIBN as a polymerization initiator was added to 100 parts by weight of the mixture of BA, AA, and HBA. Nitrogen gas was introduced into the flask with gentle stirring to replace the atmosphere with nitrogen. The liquid temperature in the flask was maintained at around 55°C, and the polymerization reaction was allowed to proceed for 7 hours. Ethyl acetate was then added to the resulting reaction solution to adjust the solids concentration to 12% by weight, yielding a solution of (meth)acrylic polymer (A-1). The weight-average molecular weight (Mw) of the (meth)acrylic polymer (A-1) was 2.2 million.

[0119] (Synthesis Example 2) A solution of (meth)acrylic polymer (A-2) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 79.9 parts by weight of BA, 15.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-2) was 2,200,000.

[0120] (Synthesis Example 3) A solution of (meth)acrylic polymer (A-3) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 74.9 parts by weight of BA, 20.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-3) was 2,300,000.

[0121] (Synthesis Example 4) Except for changing the monomers used to 92.9 parts by weight of BA, 5.0 parts by weight of AA, 0.1 part by weight of HBA, and 2 parts by weight of NVP, a solution of (meth)acrylic polymer (A-4) was obtained in the same manner as in Synthesis Example 1. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-4) was 2.5 million.

[0122] (Synthesis Example 5) A solution of (meth)acrylic polymer (A-5) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 90.9 parts by weight of BA, 5.0 parts by weight of AA, 0.1 part by weight of HBA, and 4 parts by weight of NVP. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-5) was 2,600,000.

[0123] (Synthesis Example 6) Except for changing the monomers used to 89.9 parts by weight of BA, 10.0 parts by weight of AA, and 0.1 parts by weight of HBA, a solution of (meth)acrylic polymer (A-6) was obtained in the same manner as in Synthesis Example 1. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-6) was 2,600,000.

[0124] The types and amounts of the monomers and polymerization initiators used in Synthesis Examples 1 to 6, as well as the weight average molecular weights (Mw) of the resulting polymers, are summarized in Table 1 below.

[0125] [Table 1]

[0126] [Preparation of Pressure-Sensitive Adhesive Composition and Pressure-Sensitive Adhesive Sheet] (Examples 1 to 7, Comparative Examples 1 to 3) As shown in Table 2 below, a crosslinking agent and the like were mixed with 100 parts by weight of the solid content of the (meth)acrylic polymer (A) to obtain a solvent-based pressure-sensitive adhesive composition.

[0127] [Table 2]

[0128] Next, the resulting pressure-sensitive adhesive composition was applied to the release surface of a 38 μm thick PET film (Mitsubishi Chemical Polyester Film Co., Ltd., MRF38), a release film whose release surface had been silicone-treated, and then dried for 60 seconds in an air-circulating thermostatic oven set at 155°C to form pressure-sensitive adhesive sheets (15 μm thick) for Examples 1 to 7 and Comparative Examples 1 to 3. A fountain coater was used to apply the pressure-sensitive adhesive composition. The HSP components (ΔD, ΔP, ΔH) and the HSP distance Ra between the (meth)acrylic polymer (A) and the self-polymer (C) of the crosslinking agent (B), as well as the evaluation results of each pressure-sensitive adhesive sheet produced, are shown in Table 3 below. Note that Tetrad-C did not form a self-polymer.

[0129] [Table 3]

[0130] As shown in Table 3, the adhesive sheets of the examples, which contained 5 parts by weight or more of crosslinking agent (B) and had a distance Ra of 12.3 or less, were more suitable for suppressing dimensional changes and showed higher durability than the adhesive sheets of the comparative examples. [Industrial Applicability]

[0131] The pressure-sensitive adhesive composition of the present invention can be used to form a pressure-sensitive adhesive sheet for use in, for example, an image display device. [Explanation of symbols]

[0132] 1 adhesive sheet 2 Optical Film 10A, 10B, 10C, 10D Optical laminate 11 Image display devices

Claims

1. Contains a (meth)acrylic polymer (A) as a main component, Further comprising a crosslinking agent (B), the blending amount of the crosslinking agent (B) is 5 parts by weight or more based on 100 parts by weight of the (meth)acrylic polymer (A); A pressure-sensitive adhesive composition, wherein, assuming a self-polymer (C) of the crosslinking agent (B), the distance Ra of the Hansen solubility parameter (HSP) between the (meth)acrylic polymer (A) and the self-polymer (C) is 12.3 or less.

2. The pressure-sensitive adhesive composition according to claim 1 , wherein the crosslinking agent (B) is an isocyanate-based crosslinking agent.

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the crosslinking agent (B) is a tolylene diisocyanate-based crosslinking agent.

4. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the crosslinking agent (B) is tri- or higher functional.

5. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the (meth)acrylic polymer (A) contains a structural unit derived from an aromatic ring-containing monomer.

6. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the (meth)acrylic polymer (A) contains a structural unit derived from a hydroxyl group-containing monomer in a content of 1 wt% or less.

7. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, which is a solvent-based composition.

8. A pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 7.

9. The pressure-sensitive adhesive sheet according to claim 8, which has a storage modulus G' at 25°C of 0.5 MPa or more.

10. An optical laminate comprising the pressure-sensitive adhesive sheet according to claim 8 or 9 and an optical film.

11. An image display device comprising the optical laminate according to claim 10.

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