JP7740872B2 - Pressure-sensitive adhesive for optical films and pressure-sensitive adhesive layer for optical films - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive for optical films and a pressure-sensitive adhesive layer for optical films.

A surface light source device including an organic electroluminescence element (hereinafter also referred to simply as "organic EL element") typically has a surface light emitter including an organic EL element and a light extraction film provided on the light-emitting surface of this surface light emitter. The light extraction film is a film with a concave-convex structure on its surface to increase light extraction efficiency, and may also have an adhesive layer for bonding the surface light emitter and light extraction film together. With such a surface light source device, light generated in the organic EL element passes through the adhesive layer and light extraction film and is emitted outside the device.

In such surface light source devices, it is particularly advantageous for the adhesive layer to have a high refractive index in order to increase light extraction efficiency. As an adhesive for obtaining an adhesive layer with a high refractive index, for example, Patent Document 1 discloses a pressure-sensitive adhesive composition containing, as its main component, an acrylic polymer that includes an aromatic ring-containing copolymerizable monomer as a monomer unit, and which has a refractive index within a specified range after drying and/or curing.

Patent Document 2 also discloses a pressure-sensitive adhesive characterized by comprising at least an acrylic copolymer containing, as copolymerization components, an acrylic acid alkyl ester that does not contain an aromatic ring and an aromatic ring-containing monomer, with the aromatic ring-containing monomer component accounting for 40 to 90% by weight of the total monomer components.

Japanese Patent Application Laid-Open No. 2002-173656 Japanese Patent Application Laid-Open No. 2003-13029

However, the techniques described in Patent Documents 1 and 2 above were unable to ensure a high refractive index, resulting in reduced light extraction efficiency. Furthermore, the techniques described in the above patent documents also had the problem of insufficient durability and transparency in the resulting pressure-sensitive adhesive layer.

The present invention was made in consideration of the above circumstances, and aims to provide a means for obtaining an adhesive layer that has a high refractive index when obtained by performing at least one of a heat treatment and a light curing treatment, is durable in harsh environments (high temperature, high humidity, heat shock, etc.), and also has excellent transparency.

The inventors conducted extensive research to solve the above problems. As a result, they discovered that an adhesive having the following configuration solves the above problems, leading to the completion of the present invention.

That is, a pressure-sensitive adhesive for optical films according to one embodiment of the present invention comprises a (meth)acrylic acid ester copolymer (A), which comprises (a1): a structural unit derived from a (meth)acrylic acid ester monomer having an aromatic hydrocarbon group, and (a2): a structural unit derived from a hydroxy group-containing (meth)acrylic monomer, wherein the content of the structural unit derived from the hydroxy group-containing (meth)acrylic acid ester monomer (a2) is 0.1% by mass or more and 25% by mass or less of all structural units of the (meth)acrylic acid ester copolymer (A), and wherein the pressure-sensitive adhesive for optical films is cured by subjecting the pressure-sensitive adhesive for optical films to at least one of a heat treatment and a photo-curing treatment, and the pressure-sensitive adhesive layer has a refractive index of 1.58 or more and 1.80 or less.

The present invention provides a means for obtaining an adhesive layer that has a high refractive index, durability in harsh environments (high temperature, high humidity, heat shock, etc.), and excellent transparency, obtained by performing at least one of a heat treatment and a photocuring treatment.

FIG. 1 is a schematic cross-sectional view of a polarizing plate with an optical compensation layer.

Embodiments of the present invention are described below, but the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Unless otherwise specified, in this specification, operations and measurements of physical properties are performed at room temperature (20°C to 25°C) and a relative humidity of 40% RH to 50% RH. In this specification, "(meth)acrylic" is a general term for acrylic and methacrylic. In addition, in this specification, "(co)polymer" is a general term for a homopolymer formed by the polymerization of a single monomer and a copolymer formed by the polymerization of multiple types of monomers.

<Adhesives for optical films>
A pressure-sensitive adhesive for optical films according to one embodiment of the present invention (hereinafter also simply referred to as "pressure-sensitive adhesive") comprises a (meth)acrylic acid ester copolymer (A), the (meth)acrylic acid ester copolymer (A) comprising (a1): a structural unit derived from a (meth)acrylic acid ester monomer having an aromatic hydrocarbon group; and (a2): a structural unit derived from a hydroxy group-containing (meth)acrylic monomer, wherein the content of the structural unit derived from the hydroxy group-containing (meth)acrylic acid ester monomer (a2) is 0.1 mass% or more and 25 mass% or less of all structural units of the (meth)acrylic acid ester copolymer (A), and the pressure-sensitive adhesive layer cured by subjecting the pressure-sensitive adhesive for optical films to at least one of a heat treatment and a photo-curing treatment has a refractive index of 1.58 or more and 1.80 or less.

The pressure-sensitive adhesive for optical films of the present invention, having such a configuration, can be subjected to at least one of a heat treatment and a photo-curing treatment to form a pressure-sensitive adhesive layer that has a high refractive index, is durable in harsh environments (high temperature, high humidity, heat shock, etc.), and also has excellent transparency.

The present invention is described in detail below.

[(Meth)acrylic acid ester copolymer (A)]
The pressure-sensitive adhesive for optical films according to the present invention essentially contains a (meth)acrylic acid ester copolymer (a) (hereinafter also simply referred to as "copolymer (A)").

The weight-average molecular weight (Mw) of the copolymer (A) according to the present invention, as determined by gel permeation chromatography (GPC), is not particularly limited, but is preferably from 500,000 to 2,000,000, and more preferably from 700,000 to 2,000,000. If the weight-average molecular weight (Mw) is less than 500,000, durability may decrease. On the other hand, if the weight-average molecular weight (Mw) exceeds 2,000,000, the adhesive may become too viscous, preventing coatability, resulting in coating streaks and coating defects, making it difficult to obtain a normal adhesive layer.

From the viewpoint of further improving durability under harsh environments (high temperature, high humidity, heat shock, etc.), the weight-average molecular weight (Mw) of copolymer (A) determined by gel permeation chromatography (GPC) is more preferably 900,000 or more and 2,000,000 or less. The weight-average molecular weight (Mw) is particularly preferably more than 1,000,000 and 2,000,000 or less. Those skilled in the art can easily control the weight-average molecular weight (Mw) of copolymer (A) of the present invention as follows. That is, it can be easily controlled by appropriately adjusting the reaction conditions, such as the type and/or amount of polymerization initiator used in the polymerization reaction described below, the reaction temperature, and the reaction time.

The weight average molecular weight (Mw) of copolymer (A) can be measured in detail by the method described in the Examples.

In the present invention, the structural units constituting the copolymer (A) are:
(a1) a structural unit derived from a (meth)acrylic acid ester monomer having an aromatic hydrocarbon group (hereinafter also referred to simply as “component (a1)”),
(a2) a structural unit derived from a hydroxy group-containing (meth)acrylic monomer (hereinafter also referred to simply as “component (a2)”),
In addition, if necessary,
(a3) a structural unit derived from a monomer other than the above component (a1) and component (a2) and having one radically polymerizable functional group;
Includes.

In this specification, for example, the phrase "copolymer X contains a structural unit derived from monomer _Y1 and a structural unit derived from monomer _Y2 " means that when copolymer X is obtained by copolymerization, monomer _Y1 and monomer _Y2 are contained as raw material monomers used.

The structural units derived from each monomer that can constitute copolymer (A) according to the present invention are described below in order. Components (a1) and (a2) are monomers having one (meth)acryloyl group in the molecule. Monomers having two or more (meth)acryloyl groups in the molecule are classified as crosslinking agents (D), which are described below, and differ from components (a1) and (a2) and also from component (a3), which are described below.

Components (a1) to (a3) are explained below.

((Meth)acrylic acid ester monomer (a1) having an aromatic hydrocarbon group)
The copolymer (a) contains a structural unit derived from a (meth)acrylic acid ester monomer (a1) (hereinafter also referred to as "component (a1)"). In the pressure-sensitive adhesive of the present invention, the structural unit derived from component (a1) is the basic skeleton of the polymer, and increases the refractive index of the pressure-sensitive adhesive after drying or curing, and improves the durability of the pressure-sensitive adhesive. The component (a1) can be used alone or in combination of two or more. Furthermore, the component (a1) may be a commercially available product or a synthetic product.

Component (a1) is typically represented by the following formula (1):

In the above formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents an aromatic hydrocarbon group.

The aromatic hydrocarbon group is not particularly limited, but preferred examples include aromatic hydrocarbon groups having 6 to 20 carbon atoms. Specific examples include a benzene ring group, a biphenyl ring group, a phenoxybenzyl group, a naphthalene ring group, an azulene ring group, an anthracene ring group, a phenanthrene ring group, a pyrene ring group, a chrysene ring group, a naphthacene ring group, a triphenylene ring group, an o-terphenyl ring group, an m-terphenyl ring group, a p-terphenyl ring group, and a fluorene ring group.

The aromatic hydrocarbon group may further contain a sulfur element. An example of an aromatic hydrocarbon group containing a sulfur element is a dinaphthothiophene group.

More specifically, examples of (meth)acrylic acid ester monomers having an aromatic hydrocarbon group include benzyl (meth)acrylate, phenyl (meth)acrylate, benzylphenyl (meth)acrylate, p-phenylbenzyl acrylate, o-phenylphenol (meth)acrylate, ethoxylated o-phenylphenol (meth)acrylate, phenoxy (meth)acrylate, p-t-butylphenyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, ethylene oxide-modified cresol (meth)acrylate, phenol ethylene oxide-modified (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, methoxybenzyl (meth)acrylate, ) acrylate, m-phenoxybenzyl (meth)acrylate, chlorobenzyl (meth)acrylate, cresyl (meth)acrylate, polystyryl (meth)acrylate, and other monomers having a benzene ring group; hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, 1-naphthylmethyl (meth)acrylate, 2-naphthylmethyl acrylate, hydroxynaphthyl (meth)acrylate, and other monomers having a naphthalene ring group; biphenyl (meth)acrylate, and other monomers having a biphenyl ring group; fluorenyl (meth)acrylate, 9-fluorenylmethyl (meth)acrylate (9-(meth)acryloyloxymethylfluorene), hydroxyfluorenyl (meth)acrylate, and the like.

More specifically, examples of (meth)acrylic acid ester monomers having an aromatic hydrocarbon group containing elemental sulfur include monomers having a dinaphthothiophene group, such as 5-dinaphthothiophenylethyl (meth)acrylate, 6-dinaphthothiophenylethyl (meth)acrylate, and 6-dinaphthothiophenylmethyl (meth)acrylate.

Among these (a1) components, monomers having at least one group selected from the group consisting of biphenyl ring groups, phenoxybenzyl groups, naphthalene ring groups, and fluorene ring groups are preferred, as they provide a pressure-sensitive adhesive layer cured by at least one of a heat treatment and a photocuring treatment with a higher refractive index and superior durability. Furthermore, it is even more preferred to include at least one group selected from the group consisting of m-phenoxybenzyl (meth)acrylate, 1-naphthylmethyl (meth)acrylate, hydroxynaphthyl (meth)acrylate, fluorenyl (meth)acrylate, 9-fluorenylmethyl acrylate (9-acryloyloxymethylfluorene), and hydroxyfluorenyl (meth)acrylate.

The content of structural units derived from component (a1) in copolymer (A) is not particularly limited, but is preferably 10% by mass or more and 99.9% by mass or less, with the total structural units in copolymer (A) being 100% by mass.

When the content of structural units derived from component (a1) is 10% by mass or more, the refractive index after at least one of heat treatment and photocuring treatment becomes higher. On the other hand, when the content is 99.9% by mass or less, a high refractive index is more easily ensured. The content is more preferably 75% by mass or more and 99% by mass or less, and even more preferably 80% by mass or more and 99% by mass or less.

((Meth)acrylic Monomer (a2) Having a Hydroxy Group)
The copolymer (a) contains a structural unit derived from a (meth)acrylic monomer (a2) having a hydroxy group (hereinafter also referred to as "component (a2)"). The structural unit derived from the (meth)acrylic monomer (a2) having a hydroxy group is hydrophilic. Therefore, in the pressure-sensitive adhesive layer, the water retention performance of the polymer can be improved, and condensation can be prevented. Furthermore, when the pressure-sensitive adhesive layer is left at room temperature after a moist heat test, an increase in haze can be suppressed. The component (a2) can be used alone or in combination of two or more. Furthermore, the component (a2) may be a commercially available product or a synthetic product.

Monomers containing both a hydroxy group and an aromatic hydrocarbon group are classified as component (a1).

More specific examples of component (a2) include 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxymethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 1,4-cyclohexanedimethanol monoacrylate, N-(2-hydroxyethyl) (meth)acrylamide, N-(2-hydroxypropyl) (meth)acrylamide, and N-(2,2-dimethyl-β-hydroxyethyl) (meth)acrylamide.

Among these, 4-hydroxybutyl (meth)acrylate and N-(2-hydroxyethyl) (meth)acrylamide are preferred from the viewpoints of good transparency, low gel content in the copolymer, and good appearance.

The content of structural units derived from component (a2) in copolymer (a) is 0.1% by mass to 25% by mass, where the total structural units in copolymer (a) is 100% by mass. If the content of structural units derived from component (a2) is less than 0.1% by mass, the haze after a humidity and heat durability test decreases. On the other hand, if the content exceeds 25% by mass, humidity and heat durability decreases, coatability cannot be ensured, coating streaks and coating defects occur, and it becomes difficult to obtain a normal pressure-sensitive adhesive layer. The content of structural units derived from component (a2) is preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass, and even more preferably 0.7% by mass to 12% by mass. Furthermore, the content of structural units derived from component (a2) is even more preferably 0.7% by mass to 11% by mass, and particularly preferably 1% by mass to 10% by mass, where the total structural units in copolymer (a) is 100% by mass. It is also preferable that the content of structural units derived from component (a2) is 0.1% by mass or more and less than 12% by mass.

(Monomer (a3) other than component (a1) and component (a2) and having one radically polymerizable functional group)
The copolymer (A) according to the present invention preferably further contains a structural unit derived from a monomer (a3) (hereinafter also referred to as "component (a3)") having one radically polymerizable functional group other than the above-mentioned component (a1) and component (a2). In the pressure-sensitive adhesive layer, the structural unit derived from component (a3) has the effect of improving adhesiveness and durability. The component (a3) can be used alone or in combination of two or more types. Furthermore, the component (a3) may be a commercially available product or a synthetic product.

Examples of component (a3) include (meth)acrylic acid alkyl ester monomers, (meth)acrylic acid alkyl ester monomers having an alkoxyalkyl group or an alkoxyalkylene glycol group, (meth)acrylic acid ester monomers having an acyl group or an epoxy group, monomers having a carboxy group, (meth)acrylic monomers having a phosphate group, monomers having a sulfonic acid group, (meth)acrylic monomers having a urethane group, (meth)acrylic monomers having an amino group, (meth)acrylic monomers having an amide group, vinyl monomers having a silane group, styrene, chlorostyrene, α-methylstyrene, vinyltoluene, vinyl chloride, vinyl acetate, vinyl propionate, acrylonitrile, vinylpyridine, and 2-(meth)acryloyloxyethyl phthalate.

Specific examples of (meth)acrylic acid alkyl ester monomers include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-hexyl (meth)acrylate, and n Examples of such acrylates include n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate (n-lauryl (meth)acrylate), cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate.

Specific examples of (meth)acrylic acid alkyl ester monomers having an alkoxyalkyl group or an alkoxyalkylene glycol group include, for example, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate; ethoxydiethylene glycol (meth)acrylate, ethoxytriethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, propoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 2-ethylhexyldiglycol (meth)acrylate (2-ethylhexyloxydiethylene glycol (meth)acrylate), methoxypolyethylene glycol (meth)acrylate (n = 4 or more and 10 or less), and methoxydipropylene glycol (meth)acrylate.

Specific examples of (meth)acrylic acid ester monomers having an acyl group or an epoxy group include glycidyl (meth)acrylate and 2-acetoacetoxyethyl (meth)acrylate.

Specific examples of monomers having a carboxy group include (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, fumaric anhydride, crotonic acid, itaconic acid, itaconic anhydride, myristoleic acid, palmitoleic acid, and oleic acid.

Specific examples of (meth)acrylic monomers having a phosphate group include 2-methacryloyloxyethyl diphenyl phosphate (meth)acrylate, trimethacryloyloxyethyl phosphate (meth)acrylate, and triacryloyloxyethyl phosphate (meth)acrylate.

Specific examples of monomers having a sulfonic acid group include sodium sulfopropyl (meth)acrylate, sodium 2-sulfoethyl (meth)acrylate, and sodium 2-acrylamido-2-methylpropanesulfonate.

Specific examples of (meth)acrylic monomers having a urethane group include urethane (meth)acrylate.

Specific examples of (meth)acrylic monomers having an amino group include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, N-t-butylaminoethyl (meth)acrylate, and (meth)acryloyloxyethyl trimethylammonium chloride.

Specific examples of (meth)acrylic monomers having an amide group include N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, (meth)acrylamide, N-isopropyl(meth)acrylamide, N-t-butyl(meth)acrylamide, and diacetone(meth)acrylamide.

Specific examples of vinyl monomers having a silane group include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethyl)silane, vinyltriacetylsilane, and methacryloyloxypropyltrimethoxysilane.

Of these, n-butyl (meth)acrylate, isobornyl (meth)acrylate, N-(meth)acryloylmorpholine, and 2-ethylhexyl (meth)acrylate are preferred from the viewpoint of achieving the effects of the present invention more efficiently.

The content of structural units derived from component (a3) in copolymer (A) is not particularly limited, but is preferably 3% by mass or more and 80% by mass or less, with all structural units in copolymer (a) being 100% by mass. Furthermore, the content of structural units derived from component (a3) in copolymer (A) is more preferably 5% by mass or more and 50% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less, with all structural units in copolymer (a) being 100% by mass. When two or more types of component (a3) are used, the above content represents the total content of the components (a3).

[Method for producing copolymer (A)]
Next, a method for producing the copolymer (A) will be described. In the present invention, the method for producing the copolymer (A) is not particularly limited. Specifically, conventionally known methods such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, reverse-phase suspension polymerization, thin-film polymerization, and spray polymerization using a polymerization initiator can be used. Examples of methods for controlling polymerization include adiabatic polymerization, temperature-controlled polymerization, and isothermal polymerization. The polymerization initiator may be either a thermal polymerization initiator or a photopolymerization initiator. Furthermore, in addition to or in addition to the method of initiating polymerization using a polymerization initiator, a method of initiating polymerization by irradiation with active energy rays such as radiation, electron beams, and ultraviolet rays can also be employed. Among these, solution polymerization using a thermal polymerization initiator or bulk polymerization using a photopolymerization initiator is more preferred because it allows for easy control of molecular weight and minimizes impurities.

In solution polymerization using a thermal polymerization initiator, a thermal polymerization initiator is added to a monomer solution that serves as the raw material for copolymer (A), such as a raw material monomer solution composed of the above-mentioned monomers, and a polymerization reaction is carried out. More specifically, ethyl acetate, toluene, methyl ethyl ketone, acetone, or the like is used as a solvent, and preferably 0.01 to 1 part by mass of the thermal polymerization initiator is added per 100 parts by mass of the total raw material monomers. The reaction is then carried out in a nitrogen atmosphere, for example, at a reaction temperature of 40 to 90°C for a reaction time of 1 to 10 hours.

Examples of thermal polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile), azobiscyanovaleric acid, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile). tolyl), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2'-azobis[2-methyl-N-(2-hydrogen Examples of thermal polymerization initiators include azo compounds such as t-butyl peroxypivalate, t-butyl peroxybenzoate, t-butylperoxy-2-ethylhexanoate, di-t-butyl peroxide, cumene hydroperoxide, benzoyl peroxide, and t-butyl hydroperoxide; and inorganic peroxides such as hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate. These thermal polymerization initiators can be used alone or in combination of two or more.

Examples of bulk polymerization methods using a photopolymerization initiator include adding raw material monomers and a photopolymerization initiator, and irradiating them with active energy rays in a nitrogen atmosphere at a reaction initiation temperature of 20°C to 35°C. When the temperature in the reaction system rises by 5°C to 20°C above the reaction initiation temperature, the reaction can be stopped by introducing air into the reaction system, for example, to obtain copolymer (A).

Examples of active energy rays used in bulk polymerization methods include ultraviolet rays, laser rays, alpha rays, beta rays, gamma rays, X-rays, and electron beams. Ultraviolet rays are preferred from the standpoints of controllability, ease of handling, cost, and other factors. More preferably, ultraviolet rays with a wavelength of 200 nm or more and 400 nm or less are used. Ultraviolet rays can be irradiated using light sources such as high-pressure mercury lamps, microwave-excited lamps, chemical lamps, and black lights.

Examples of photopolymerization initiators include acetophenones such as acetophenone, 3-methylacetophenone, benzil dimethyl ketal, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2-hydroxy-2-methyl-1-phenylpropan-1-one; benzophenones such as benzophenone, 4-chlorobenzophenone, and 4,4'-diaminobenzophenone; benzoin ethers such as benzoin propyl ether and benzoin ethyl ether; thioxanthones such as 4-isopropylthioxanthone; 1-hydroxycyclohexyl phenyl ketone, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone. These photopolymerization initiators can be used alone or in combination.

The amount of photopolymerization initiator used is preferably 0.0005 parts by mass or more and 1 part by mass or less per 100 parts by mass of the total amount of raw material monomers. The amount used is more preferably 0.002 parts by mass or more and 0.5 parts by mass or less.

A chain transfer agent can also be used to adjust the molecular weight of copolymer (A). Examples of the chain transfer agent include mercaptans such as methyl mercaptan, t-butyl mercaptan, decyl mercaptan, benzyl mercaptan, stearyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, mercaptoacetic acid, mercaptopropionic acid and its esters, 2-ethylhexyl thioglycol, and octyl thioglycolate; alcohols such as methanol, ethanol, propanol, n-butanol, isopropanol, t-butanol, hexanol, benzyl alcohol, and allyl alcohol; halogenated hydrocarbons such as chloroethane, fluoroethane, and trichloroethylene; carbonyls such as acetone, methyl ethyl ketone, cyclohexanone, acetophenone, acetaldehyde, propionaldehyde, n-butylaldehyde, furfural, and benzaldehyde; and methyl-4-cyclohexene-1,2-dicarboxylic anhydride and α-methylstyrene. These chain transfer agents can be used alone or in combination of two or more.

The above-mentioned copolymer (A) can be used alone or in combination of two or more types.

[Inorganic particles (B)]
The pressure-sensitive adhesive for optical films of the present invention preferably further contains inorganic particles (B). By containing the inorganic particles (B), the refractive index of the pressure-sensitive adhesive layer after at least one of a heat treatment and a photocuring treatment becomes higher. Furthermore, by containing the inorganic particles (B), the coatability of the pressure-sensitive adhesive can be improved.

Specific examples of the inorganic particles include at least one selected from the group consisting of zirconium oxide, zinc oxide, iron oxide, copper oxide, titanium oxide, tin oxide, cerium oxide, tantalum oxide, niobium oxide, tungsten oxide, europium oxide, hafnium oxide, potassium titanate, barium titanate, strontium titanate, potassium niobate, lithium niobate, calcium tungstate, antimony-doped tin oxide (ATO), and indium tin oxide (ITO).

These inorganic particles can be used alone or in combination of two or more types. Furthermore, commercially available inorganic particles or synthetic products may be used.

From the viewpoint of having a high refractive index and excellent transparency and durability, it is more preferable that the inorganic particles be at least one type selected from the group consisting of zirconium oxide, titanium oxide, and barium titanate.

The inorganic particles are preferably coated with one or more coating agents, at least one of which is preferably a coating agent represented by the following formula (I):

In the above formula (I), R ¹ represents a hydrocarbon group having 6 or more carbon atoms.

Hydrocarbon groups with six or more carbon atoms have the effect of increasing the dispersibility of inorganic particles, particularly in non-polar solvents.

Specific examples of coating agents represented by formula (I) above include linear carboxylic acids such as hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, and stearic acid; branched carboxylic acids such as 2-ethylhexanoic acid, 2-methylheptanoic acid, 4-methyloxanoic acid, and neodecanoic acid; and cyclic carboxylic acids such as naphthenic acid and cyclohexanedicarboxylic acid. Of these, branched carboxylic acids such as neodecanoic acid and 2-ethylhexanoic acid are preferred. The reason for this is unclear, but it is thought that hydrophobic coating agents with branched hydrocarbon chains, rather than linear hydrocarbon chains, can further enhance the particle dispersion effect in hydrophobic organic solvents and the like.

The coating agent represented by formula (I) above may be used alone or in combination of two or more types.

It is more preferable that the inorganic particles be coated with other coating agents in addition to the coating agent of formula (I) above. This allows the particles to exhibit excellent dispersibility in a variety of solvents. Examples of other coating agents include coating agents that increase the dispersibility of inorganic particles in polar solvents, coating agents that increase dispersibility in monomers and polymers, and coating agents that further increase dispersibility in non-polar solvents.

Coating agents that improve the dispersibility of inorganic particles in polar solvents can bond to the surface of inorganic particles and, by containing hydrophilic groups, can improve the dispersibility of particles in relatively polar solvents, monomers, etc. Examples include coating agents that contain multiple functional groups, including at least one selected from the group consisting of hydroxyl groups, amino groups, thiol groups, carboxyl groups, epoxy groups, and alkoxy groups. Of course, other functional groups may be present in addition to these functional groups.

Such coating agents include, for example, aluminum alkoxides such as aluminum trimethoxide, aluminum triethoxide, aluminum triisopropoxide, aluminum tri-n-butoxide, aluminum tri-sec-butoxide, and aluminum tri-t-butoxide; aluminum coupling agents such as diisopropoxyaluminum ethyl acetoacetate, diisopropoxyaluminum alkyl acetoacetate, diisopropoxyaluminum monomethacrylate, aluminum stearate oxide trimer, and isopropoxyaluminum alkyl acetoacetate mono(dioctyl phosphate); titanium-n-butoxide Titanium alkoxides such as titanium tetra-t-butoxide, titanium tetra-sec-butoxide, titanium tetraethoxide, titanium tetraisobutoxide, titanium tetramethoxide, titanium tetra(methoxypropoxide), and titanium tetra(methoxyphenoxide); isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetraisopropyl bis(dioctyl phosphate) titanate, isopropyl tris(dioctyl pyrophosphate) titanate, and bis(dioctyl pyrophosphate)oxyacetate titanate , titanium-based coupling agents such as bis(dioctyl pyrophosphate)ethylene titanate; silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; zirconium tetra n-butoxide, zirconium tetra t-butoxide, zirconium tetra(2-ethylhexoxide), zirconium tetraisobutoxide, zirconium tetraethoxide, zirconium tetraisopropoxide, Examples of suitable coating agents include zirconium alkoxides such as zirconium tetra-n-propoxide and zirconium tetra(2-methyl-2-butoxide); zirconium compounds such as zirconium di-n-butoxide (bis-2,4-pentanedionate), zirconium tri-n-butoxide pentanedionate, and zirconium dimethacrylate dibutoxide; hydroxycarboxylic acids such as hydroxystearic acid and salicylic acid; ether carboxylic acids such as 2-[2-(2-methoxyethoxy)ethoxy]acetic acid; carboxylic acid coupling agents such as carboxylated polybutadiene and carboxylated polyisoprene; and carboxylic acid polymers such as maleic acid-modified polypropylene. For example, silane coupling agents form polymers with a siloxane structure that coat inorganic particles and improve the dispersibility of inorganic particles in polar solvents. Silane coupling agents are particularly convenient because they can introduce substituents with high affinity for monomers and other compounds into the side chains. Among these coating agents, silane coupling agents, hydroxycarboxylic acids, and ether carboxylic acids are preferred.

A single coating agent that enhances dispersibility in polar solvents may be used, or a mixture of two or more may be used.

Coating agents that improve the dispersibility of inorganic particles in monomers and polymers contain groups that exhibit affinity for inorganic particles as well as groups that exhibit affinity for monomers, thereby improving the dispersibility of inorganic particles in monomers and polymers made from those monomers. For example, coating particles with a coating agent that has a vinyl group, such as (meth)acrylic acid or a (meth)acrylic acid ester, can improve the dispersibility of inorganic particles in monomers that also have a vinyl group, such as (meth)acrylic acid or a (meth)acrylic acid ester. Furthermore, coating inorganic particles with a coating agent that has an aromatic hydrocarbon group can improve the dispersibility of particles in monomers and polymers that have a phenyl group, such as the copolymer (A) of the present invention, and polymers such as styrene resins and phenolic resins.

Examples of such coating agents include aluminum-based coupling agents such as diisopropoxyaluminum monomethacrylate; and silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, p-styryltrimethoxysilane, and phenyltrimethoxysilane.

When the coating agent represented by formula (I) has a branched hydrocarbon group having 6 or more carbon atoms, an example of a coating agent other than coating agent (I) is a coating agent represented by the following formula (II).

In the above formula (II), ^R2 represents a linear hydrocarbon group having 6 or more carbon atoms.

Coating agents having a branched hydrocarbon group with six or more carbon atoms can improve dispersibility in non-polar solvents, etc., and by using them in combination with a coating agent represented by formula (II) above, this dispersibility can be further improved. Examples of coating agents of formula (II) include linear carboxylic acids such as hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, and stearic acid.

The coating agent used to coat the inorganic particles may be a total of two types, including the coating agent of formula (I) and another coating agent. However, a total of three or more types may also be used, such as the coating agent of formula (I), a coating agent that improves dispersibility in polar solvents, and a coating agent that improves dispersibility in monomers or polymers. Furthermore, for example, two or more types of each of the coating agents of formula (I) may be used.

As described above, inorganic particles are preferably coated with a coating agent other than the coating agent of formula (I) to enhance dispersibility in desired solvents, etc., along with the coating agent of formula (I). The ratio of these coating agents can be adjusted appropriately to enhance dispersibility in the dispersion medium, such as the solvent, monomer, or polymer. Generally, when two types of coating agents are used, the molar ratio of the coating agent other than the coating agent of formula (I) to the coating agent of formula (I) is preferably, for example, 0.1 to 30, more preferably 0.2 to 25, and even more preferably 0.3 to 15. A molar ratio within this range effectively improves dispersibility in solvents, etc., depending on the type of coating agent. The ratio of coating agent bonded to the surface of inorganic particles can be determined from analysis results using, for example, NMR spectroscopy, a CHN coder, an elemental analyzer, or an X-ray fluorescence analyzer.

The average particle size of the inorganic particles is not particularly limited, but from the viewpoints of dispersibility, transparency, etc., it is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 30 nm or less, and even more preferably 5 nm or more and 20 nm or less.

The average particle size can be measured using a standard method. For example, inorganic particles are magnified and observed using a transmission electron microscope (TEM), field-emission transmission electron microscope (FE-TEM), field-emission scanning electron microscope (FE-SEM), etc., and 100 inorganic particles are randomly selected and their lengths along their major axis are measured. The average of these measurements is used as the average particle size. Possible shapes of inorganic particles include spheres, ellipsoids, cubes, rectangular parallelepipeds, pyramidal, needles, columns, rods, cylinders, scales, plates, and flakes. When measuring particle size, the major axis length of each shape is measured. Taking into account factors such as dispersibility in solvents, spherical, granular, and columnar shapes are preferred for inorganic particle shapes.

The ratio of coating agent to inorganic particles is preferably 40% by mass or less, as measured by the weight loss rate when the inorganic particles are heated in an air atmosphere to remove the organic components. If the weight loss rate exceeds 40% by mass, the amount of coating agent is too high, and the inherent effects of the inorganic particles may not be fully achieved. On the other hand, if the weight loss rate is less than 5% by mass, the amount of coating agent is too low, and the dispersibility of the particles may not be sufficiently improved. Therefore, the weight loss rate is preferably 5% by mass or more, and more preferably 10% to 30% by mass.

The weight loss rate can be calculated, for example, by using a simultaneous thermogravimetry-differential thermal analyzer (TG-DTA) to heat the particles to 800°C at a rate of 10°C/min in an air atmosphere, and then dividing the mass lost by the mass before heating by 100.

The method for coating inorganic particles with the coating agent can be any conventionally known method, such as the method described in JP 2008-44835 A.

The content of inorganic particles in the pressure-sensitive adhesive of the present invention is not particularly limited, but is preferably 50 parts by mass or more and 2000 parts by mass or less, more preferably 70 parts by mass or more and 1500 parts by mass or less, and even more preferably 100 parts by mass or more and 1000 parts by mass or less, relative to 100 parts by mass of copolymer (A). By keeping the content of inorganic particles in the pressure-sensitive adhesive within the above range, it is possible to obtain a pressure-sensitive adhesive that has a high refractive index after at least one of a heat treatment and a photo-curing treatment, and also has excellent transparency and durability.

The inorganic particles of this embodiment may be in the form of a powder, or in the form of a dispersion in which the inorganic particles are dispersed in a dispersion medium. Examples of the dispersion medium include alcohols such as methanol, ethanol, n-propanol, isopropanol, and ethylene glycol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as ethyl acetate, propyl acetate, and propylene glycol monomethyl ether acetate; ethers such as ethylene glycol monomethyl ether and diethylene glycol monobutyl ether; hydrocarbons such as benzene, toluene, xylene, ethylbenzene, and cyclohexane; halogenated hydrocarbons such as dichloromethane and chloroform; amides such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; water; and oils such as mineral oil, vegetable oil, wax oil, and silicone oil. These may be used alone or in combination.

[Silane coupling agent (C)]
The pressure-sensitive adhesive for optical films of the present invention preferably further contains a silane coupling agent (C). In the pressure-sensitive adhesive composition of the present invention, the silane coupling agent (C) can mainly contribute to improving durability and, when the adherend is glass, improving adhesion to glass. In this specification, the term "silane coupling agent" refers to a silane compound that does not have a siloxane bond (Si—O—Si bond) and has two or more reactive groups in the molecule.

In the present invention, the silane coupling agent (C) is not particularly limited. Specific examples include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, n-propyltrimethoxysilane, ethyltrimethoxysilane, diethyldiethoxysilane, n-butyltrimethoxysilane, n-hexyltriethoxysilane, n-octyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, cyclohexylmethyldimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-methacryloxysilane. Examples of suitable alkylsilanes include propylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, bis-(3-[triethoxysilyl]propyl)tetrasulfide, and γ-isocyanatopropyltriethoxysilane. Further examples include silane coupling agents having functional groups such as epoxy groups (glycidoxy groups), amino groups, mercapto groups, and (meth)acryloyl groups, as well as silane coupling agents containing functional groups that can react with these functional groups. Compounds having hydrolyzable silyl groups obtained by reacting other coupling agents, polyisocyanates, etc., with each functional group in any ratio can also be used.

The silane coupling agent (C) may be a commercially available product or a synthetic product. Commercially available silane coupling agents (C) include, for example, KBM-303, KBM-403, KBE-402, KBE-403, KBE-502, KBE-503, KBM-5103, KBM-573, KBM-802, KBM-803, KBE-846, and KBE-9007 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

The above silane coupling agents (C) can be used alone or in combination of two or more.

When the pressure-sensitive adhesive for optical films of the present invention contains a silane coupling agent (C), the content of the silane coupling agent (C) is not particularly limited. However, the content is preferably 0.001 to 5 parts by mass relative to 100 parts by mass of copolymer (A). The content is more preferably 0.001 to 4 parts by mass, and even more preferably 0.01 to 3 parts by mass. A content of 0.001 parts by mass or more is preferred from the viewpoint of being able to exhibit durability effects even in harsh environments. On the other hand, a content of 5 parts by mass or less is preferred from the viewpoint of preventing deterioration of heat foaming due to low molecular weight compounds.

[Crosslinking agent (D)]
The pressure-sensitive adhesive of the present invention preferably further contains a crosslinking agent (D). The crosslinking agent reacts with the copolymer (A) to form a crosslinked structure. Thus, in the pressure-sensitive adhesive of the present invention, the crosslinking agent can mainly contribute to adhesiveness (tackiness) and durability.

In the present invention, the crosslinking agent (D) preferably contains at least one selected from the group consisting of isocyanate compounds, carbodiimide compounds, oxazoline compounds, epoxy compounds, polyfunctional (meth)acrylic acid ester monomers, and peroxides. These various crosslinking agents are described below.

[Isocyanate Compound]
Specific examples of the isocyanate compound used as the crosslinking agent (D) in the present invention include dimer acid diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 1,4-phenylene diisocyanate, xylylene diisocyanate (XDI), tetramethylxylidene diisocyanate (TMXDI), tolidine diisocyanate (TODI), and 1,5-naphthalene diisocyanate (NDI). aliphatic diisocyanates such as allyl isocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, and norbornane diisocyanatomethyl (NBDI); alicyclic diisocyanates such as transcyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), H6-XDI (hydrogenated XDI), and H12-MDI (hydrogenated MDI); carbodiimide-modified diisocyanates of the above diisocyanates; and isocyanurate-modified diisocyanates thereof. Adducts of the above isocyanate compounds with polyol compounds such as trimethylolpropane, polytetramethylene ether glycol (PTMG) and polypropylene glycol (PPG), as well as biurets and isocyanurates of these isocyanate compounds can also be suitably used.

These isocyanate compounds may be commercially available or synthetic products.

Commercially available products include, for example, Coronate (registered trademark) L, Coronate (registered trademark) HL, Coronate (registered trademark) HX, Coronate (registered trademark) 2030, Coronate (registered trademark) 2031 (all manufactured by Tosoh Corporation), Takenate (registered trademark) D-102, Takenate (registered trademark) D-110N, Takenate (registered trademark) D-200, Takenate (registered trademark) D-202 (all manufactured by Mitsui Chemicals, Inc.), Duranate (registered trademark) 24A-100, Duranate (registered trademark) TPA-100, Duranate (registered trademark) TKA-100, Duranate (registered trademark) P301-75E, Duranate (registered trademark) E402-90T, Duranate (registered trademark) E405-80T, Duranate (registered trademark) TSE-100, Duranate (registered trademark) D-101, Duranate (registered trademark) Lanate (registered trademark) D-201 (all manufactured by Asahi Kasei Corporation), Sumidur (registered trademark) N-75, N-3200, N-3300 (all manufactured by Sumika Covestro Urethane Co., Ltd.), Sanpren (registered trademark) P-6090 (PTMG/MDI type), Sanpren (registered trademark) P-663L (PTMG/TDI type), Sanpren (registered trademark) P-664 (PTMG/TDI type), Sanpren Examples of such additives include, but are not limited to, Sanprene (registered trademark) P-665 (PTMG/TDI system), Sanprene (registered trademark) P-667 (PTMG/TDI system), Sanprene (registered trademark) P-868 (PTMG/HMDI system), Sanprene (registered trademark) P-870 (PTMG/HMDI system), and Sanprene (registered trademark) C-810 (PPG/TDI system) (all manufactured by Sanyo Chemical Industries, Ltd.).

The isocyanate compound may be used in the form of an unblocked isocyanate compound. Alternatively, it may be used in the form of a blocked isocyanate compound obtained by reacting an isocyanate compound with a blocking agent that protects the isocyanate group. Such blocked isocyanate compounds may be commercially available products or synthetic products. Commercially available blocked isocyanate compounds include, for example, Duranate (registered trademark) MF-B60X (blocked 1,6-hexamethylene diisocyanate) and Duranate (registered trademark) MF-K60X (blocked 1,6-hexamethylene diisocyanate) manufactured by Asahi Kasei Corporation, Coronate (registered trademark) AP-M, 2503, 2507, 2513, 2515, and Millionate (registered trademark) MS-50 manufactured by Tosoh Corporation, and Takenate (registered trademark) B-830 (blocked tolylene diisocyanate), B-815N (blocked 4,4'-methylenebis(cyclohexyl isocyanate)), and B-842N (blocked 1,3-bis(isocyanate)) manufactured by Mitsui Chemicals, Inc. Examples of suitable urethane-modified polyisocyanates include B-846N (blocked 1,3-bis(isocyanatomethyl)cyclohexane), B-874N (blocked isophorone diisocyanate), B-882N (blocked 1,6-hexamethylene diisocyanate), DIC Corporation's Burnock (registered trademark) D-500 (blocked tolylene diisocyanate) and D-550 (blocked 1,6-hexamethylene diisocyanate), and Dai-ichi Kogyo Seiyaku Co., Ltd.'s Elastron (registered trademark) BN-P17 (blocked 4,4'-diphenylmethane diisocyanate), BN-04, BN-08, BN-44, and BN-45 (all of which are blocked urethane-modified polyisocyanates). Of these, Duranate (registered trademark) MF-K60X is preferred.

In order to further improve the durability of the adhesive, it is preferable to use the isocyanate compound in the form of an unblocked isocyanate compound.

[Carbodiimide Compound]
In the present invention, the carbodiimide compound used as the crosslinking agent is not particularly limited. For example, a high molecular weight polycarbodiimide produced by subjecting a diisocyanate to a decarboxylation condensation reaction in the presence of a carbodiimidization catalyst is used.

Examples of diisocyanates that can be used in the decarboxylation condensation reaction include 4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 3,3'-dimethyl-4,4'-diphenylether diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate.

In addition, examples of carbodiimidization catalysts used in the above-mentioned decarboxylation condensation reaction include phospholene oxides such as 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, and 3-phospholene isomers of these.

The high-molecular-weight polycarbodiimide may be a commercially available product or a synthetic product. Examples of commercially available products include the Carbodilite® series manufactured by Nisshinbo Chemical Inc. Among these, Carbodilite® V-01, V-03, V-05, V-07, and V-09 are preferred due to their excellent compatibility with organic solvents.

[Oxazoline compounds]
In the present invention, the oxazoline compound used as a crosslinking agent is not particularly limited. However, an oxazoline group-containing acrylic/styrene polymer having a main chain composed of an acrylic skeleton or a styrene skeleton and having an oxazoline group on a side chain of the main chain is preferred. Also preferred are oxazoline group-containing polymers, such as an oxazoline group-containing acrylic polymer having a main chain composed of an acrylic skeleton and having an oxazoline group on a side chain of the main chain.

Examples of oxazoline groups include 2-oxazoline groups, 3-oxazoline groups, and 4-oxazoline groups, with the 2-oxazoline group being preferred.

The oxazoline group-containing polymer may also contain a polyoxyalkylene group in addition to the oxazoline group.

Specific examples of oxazoline group-containing polymers include oxazoline group-containing acrylic polymers such as EPOCROS (registered trademark) WS-300, EPOCROS (registered trademark) WS-500, and EPOCROS (registered trademark) WS-700, all manufactured by Nippon Shokubai Co., Ltd., and oxazoline group-containing acrylic/styrene polymers such as the EPOCROS (registered trademark) K-1000 series and EPOCROS (registered trademark) K-2000 series, all manufactured by Nippon Shokubai Co., Ltd.

[Epoxy Compound]
In the present invention, the epoxy compound used as the crosslinking agent (D) is not particularly limited, and known epoxy-based crosslinking agents can be appropriately used. Commercially available epoxy compounds include liquid epoxy resins such as "TETRAD (registered trademark)-C" and "TETRAD (registered trademark)-X" manufactured by Mitsubishi Gas Chemical Company, Inc., "ADEKA RESIN (registered trademark) EPU series" and "ADEKA RESIN (registered trademark) EPR series" manufactured by ADEKA Corporation, and "CELLOXIDE (registered trademark)" manufactured by Daicel Corporation. These liquid epoxy resins are preferred in that they facilitate mixing operations when producing pressure-sensitive adhesives for optical films.

[Polyfunctional (meth)acrylic acid ester monomer]
The polyfunctional (meth)acrylic acid ester monomer used as the crosslinking agent (D) of the present invention is a (meth)acrylic acid ester monomer having multiple (two or more) radically polymerizable functional groups. Examples of such monomers include hydrocarbon-based or hydrocarbon ether-based polyfunctional monomers. The hydrocarbon-based or hydrocarbon ether-based polyfunctional monomer is a compound in which the hydroxy group of a polyhydric alcohol having a hydrocarbon group or hydrocarbon ether group with 10 to 100 carbon atoms as its main skeleton is (meth)acrylated. This compound is preferred from the viewpoint of improving adhesion through crosslinking. Examples of the hydrocarbon group of the polyhydric alcohol include linear or branched aliphatic hydrocarbon groups, aromatic hydrocarbon groups, alicyclic hydrocarbon groups, and hydrocarbon groups combining these hydrocarbon groups. Examples of the hydrocarbon ether group include etherified hydrocarbon groups. Examples of polyhydric alcohols having a hydrocarbon ether group as their main skeleton include compounds in which alkylene oxides with 2 to 4 carbon atoms are added to the polyhydric alcohols (addition number: 1 to 30). Further examples include polyalkylene glycols (addition number 1 to 30) obtained from alkylene oxides having 2 to 4 carbon atoms.

Specific examples of the above-mentioned hydrocarbon-based bifunctional monomers include di(meth)acrylates of alkylene glycols such as ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate; di(meth)acrylates of diol compounds having alicyclic hydrocarbon groups such as cyclohexanedimethanol di(meth)acrylate and tricyclodecanedimethanol di(meth)acrylate (dimethylol-tricyclodecane diacrylate); and di(meth)acrylates of diol compounds having aromatic hydrocarbon groups such as bisphenol A di(meth)acrylate.

Specific examples of hydrocarbon ether-based bifunctional monomers include di(meth)acrylates of compounds in which alkylene oxide is added to the alkylene glycols or diol compounds described above for the hydrocarbon-based bifunctional monomers, such as alkoxylated hexanediol di(meth)acrylate, alkoxylated cyclohexanedimethanol di(meth)acrylate, alkoxylated di(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate, and alkoxylated bisphenol A di(meth)acrylate. More specific examples of hydrocarbon ether-based bifunctional monomers include di(meth)acrylates of polyalkylene glycols, such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and dipropylene glycol di(meth)acrylate, as well as dioxane glycol di(meth)acrylate.

Furthermore, examples of hydrocarbon or hydrocarbon ether trifunctional or tetrafunctional monomers include tri(meth)acrylates or tetra(meth)acrylates of tri- or tetraol compounds such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, glyceryl tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and trimethylolpropane tetra(meth)acrylate, as well as tri(meth)acrylates or tetra(meth)acrylates of compounds obtained by adding alkylene oxide to the above tri- or tetraol compounds.

Furthermore, examples of monomers other than the above hydrocarbon-based or hydrocarbon ether-based monomers include polyester poly(meth)acrylates and epoxy (meth)acrylates having two or more (meth)acryloyl groups at their terminals.

[Polyfunctional Allyl Monomer]
The polyfunctional allyl monomer used as the crosslinking agent (D) of the present invention is a monomer having at least one allyl group and a plurality (two or more) of radically polymerizable functional groups including the allyl group, such as allyl (meth)acrylate, diallyl phthalate (DAP), trimethylolpropane diallyl ether, pentaerythritol triallyl ether, and triallyl isocyanurate.

[Peroxide]
In the present invention, the peroxide used as the crosslinking agent (D) is not particularly limited, and known peroxides can be used. Furthermore, taking productivity and stability into consideration, peroxides having a one-minute half-life temperature of 80°C or higher and 160°C or lower are preferred. Peroxides having a one-minute half-life temperature of 80°C or higher and 140°C or lower are more preferred. The one-minute half-life temperature is still more preferably 80°C or higher and 125°C or lower, and particularly preferably 90°C or higher and 125°C or lower. The "half-life of a peroxide" is an index representing the decomposition rate of a peroxide, and refers to the time it takes for the remaining amount of peroxide to be reduced to half. The decomposition temperature required to achieve a half-life in a certain time and the half-life time at a certain temperature are described in manufacturer catalogs, etc., for example, in the 9th edition of the Organic Peroxide Catalog (May 2003) published by NOF Corporation.

Examples of such peroxides include diisopropyl peroxydicarbonate (one-minute half-life temperature: 88.3°C; hereafter, the temperatures in parentheses indicate one-minute half-life temperatures), di(2-ethylhexyl)peroxydicarbonate (90.6°C), bis(4-t-butylcyclohexyl)peroxydicarbonate (92.1°C), di-sec-butyl peroxydicarbonate (92.4°C), t-butyl peroxyneodecanoate (103.5°C), t-hexyl peroxypivalate (109.1°C), and t-butyl peroxypivalate (110 .3°C), dilauroyl peroxide (116.4°C), bis-n-octanoyl peroxide (117.4°C), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (124.3°C), di(4-methylbenzoyl) peroxide (128.2°C), dibenzoyl peroxide (benzoyl peroxide) (130.0°C), a mixture of dibenzoyl peroxide, benzoyl m-methylbenzoyl peroxide, and m-toluoyl peroxide (131.1°C), and t-butyl peroxybutyrate (136.1°C). Among these, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, and t-butyl peroxyneodecanoate are preferred. These may be used alone, but from the viewpoint of adjusting the reactivity, it is also preferred to use two or more of them in combination. An example of a combination of two or more compounds is di(4-t-butylcyclohexyl) peroxydicarbonate and dilauroyl peroxide.

Commercially available peroxides may be used, or synthetic products may be used. Commercially available peroxides include, for example, NOF Corporation's products under the trade names: "Perloyl (registered trademark, the same hereinafter) IB" (85.1°C), "Percumyl (registered trademark, the same hereinafter) ND" (94.0°C), "Perloyl NPP" (94.0°C), "Perloyl IPP" (88.3°C), "Perloyl SBP" (92.4°C), "Perocta (registered trademark, the same hereinafter) ND" (92.4°C), "Perloyl TCP" (92.1°C), and "Perloyl OPP" (9 0.6°C), "Perhexyl (registered trademark, the same below) ND" (100.9°C), "Perbutyl (registered trademark, the same below) ND" (103.5°C), "Perbutyl NHP" (104.6°C), "Perhexyl PV" (109.1°C), "Perbutyl PV" (110.3°C), "Peroyl 355" (112.6°C), "Peroyl L" (116.4°C), "Perocta O" (124.3°C), "Peroyl SA" (131.8°C), "Perhexa (registered trademark, the same below) 25O" (118.8°C), "Perhexyl O" (132.6°C), "Niper (registered trademark, the same below) PMB" (128.2°C), "Perbutyl O" (134.0°C), "Niper BMT" (131.1°C), "Niper BW" (130.0°C), "Niper BMT-K40" (131.1°C), "Niper BMT-M" (131.1°C), "Perhexa MC" (142.1°C), "Per Examples include Hexa TMH (147.1°C), Perhexa HC (149.2°C), Perhexa C (153.8°C), Pertetra (registered trademark, same below) A (153.8°C), Perhexyl I (155.0°C), Perbutyl L (159.4°C), Perbutyl I (158.8°C), Perhexa 25Z (158.2°C), Perbutyl A (159.9°C), and Perhexa 22 (159.9°C).

In the present invention, the crosslinking agent (D) may be used alone or in combination of two or more. When combining two or more types, two or more crosslinking agents of the same type (for example, two types of isocyanate compounds) may be combined, or one or more crosslinking agents of different types (for example, one type of isocyanate compound and one type of peroxide) may be combined.

The content of crosslinking agent (D) in the pressure-sensitive adhesive for optical films of the present invention is not particularly limited, but is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of (meth)acrylic acid ester copolymer (A). The content is more preferably 0.02 parts by mass or more and 4 parts by mass or less, and even more preferably 0.03 parts by mass or more and 3 parts by mass or less. It is particularly preferably 0.05 parts by mass or more and 2 parts by mass or less. When the content of crosslinking agent (D) is within the above range, durability can be ensured.

[Other added ingredients]
The pressure-sensitive adhesive for optical films of the present invention may contain, as necessary, other known additives such as solvents, crosslinking accelerators, antioxidants, fillers, colorants (pigments, dyes, etc.), UV absorbers, antioxidants, plasticizers, softeners, surfactants, and antistatic agents, within the range that does not impair the effects of the present invention.

<Solvent>
The pressure-sensitive adhesive for optical films of the present invention may contain a solvent. By containing a solvent, the effect of significantly improving productivity during coating can be obtained. The solvent is not particularly limited, but examples thereof include organic solvents such as 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, methyl isobutyl ketone and acetone. These solvents can be used alone or in combination of two or more.

<Method for producing (preparing) adhesive>
The pressure-sensitive adhesive of the present invention can be prepared by mixing the copolymer (A) and, if necessary, other components such as inorganic particles (B), a silane coupling agent (C), a crosslinking agent (D), etc. The mixing order and mixing temperature of the components are not particularly limited and can be appropriately adjusted by a person skilled in the art.

[Application]
The pressure-sensitive adhesive for optical films of the present invention described above is suitable for various applications. For example, it is preferably used for optical components such as optical films, and particularly for thin pressure-sensitive adhesive optical films used in large liquid crystal panels. Examples of such optical films include polarizing plates, retardation plates for preventing coloration, optical compensation films such as viewing angle expansion films for improving the viewing angle of liquid crystal displays, brightness improvement films for increasing the contrast of displays, light extraction films for increasing the light extraction efficiency of surface light emitters, and laminates of these films.

The present invention also provides various forms, such as a pressure-sensitive adhesive layer formed from the above-mentioned pressure-sensitive adhesive for optical films, an optical component in which the pressure-sensitive adhesive layer is formed on an optical film, an optical component in which the optical film is a polarizing plate, or an optical component in which the optical component is used in an image display device such as a liquid crystal display, an organic EL display, a plasma display (PDP), a micro LED display, a curved display, or a flexible display. Each of these forms is described below.

[Adhesive layer for optical film]
According to another aspect of the present invention, there is provided a pressure-sensitive adhesive layer for an optical film (hereinafter also simply referred to as "pressure-sensitive adhesive layer") obtained by curing the pressure-sensitive adhesive for an optical film by at least one of a heat treatment and a photo-curing treatment.

The thickness of the adhesive layer is not particularly limited, but is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, and even more preferably 15 μm or more and 250 μm or less. When the thickness of the adhesive layer is within the above range, coatability and uniformity of the adhesive layer thickness can be ensured, and the adhesive layer also has excellent transparency and durability.

[Method for producing pressure-sensitive adhesive layer]
According to another aspect of the present invention, there is also provided a method for producing a pressure-sensitive adhesive layer for an optical film, comprising a crosslinking step of applying the above-mentioned pressure-sensitive adhesive for an optical film of the present invention onto a release sheet that has been subjected to a release treatment, and then carrying out at least one of a heat treatment and a photocuring treatment to crosslink the pressure-sensitive adhesive.

When using an adhesive on an optical film, the adhesive may be coated directly onto the optical film to form an adhesive layer. However, it is preferable to coat the adhesive on a film with release properties to form an adhesive layer, and then transfer the layer to various optical films for use. The release film with an adhesive layer produced in this manner can also be wound up into a roll during the manufacturing process. After cutting and processing as needed, the release film can be removed and used when adhering to various optical films, liquid crystal panels, etc. Furthermore, the release film can also serve to protect the adhesive layer until it is put into practical use. In this specification, such release films are also referred to as release sheets (separators).

Examples of materials that can be used to make the release sheet include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film; porous materials such as paper, cloth, and nonwoven fabric; nets, foam sheets, metal foils, and laminates of these, as well as other suitable thin sheets. Plastic films are preferred due to their excellent surface smoothness.

The thickness of the release sheet is typically 5 μm or more and 200 μm or less, and preferably 5 μm or more and 100 μm or less.

If necessary, the release sheet may be further subjected to release treatment using a silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based release agent, silica powder, or other antifouling treatment, or antistatic treatment such as coating, kneading, or vapor deposition. In particular, from the perspective of further improving releasability from the adhesive layer, it is preferable to subject the surface of the release sheet to a release treatment such as silicone treatment, long-chain alkyl treatment, or fluorine treatment.

In the present invention, the coating method for applying the pressure-sensitive adhesive for optical films of the present invention to a release-treated release sheet is not particularly limited, and various known methods can be used. Examples include 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, and extrusion coating using a die coater, etc.

In the method for producing a pressure-sensitive adhesive layer of the present invention, the above-mentioned pressure-sensitive adhesive for optical films is applied to a release sheet, and then a crosslinking step is carried out in which the pressure-sensitive adhesive is crosslinked by carrying out at least one of a heat treatment and a photocuring treatment.

The heat treatment not only dries and removes the solvent in the coating film obtained by application, but also serves the purpose of causing a crosslinking reaction in the pressure-sensitive adhesive for optical films described above. The heat treatment temperature is preferably 40°C or higher and 150°C or lower, more preferably 50°C or higher and 130°C or lower, and even more preferably 80°C or higher and 120°C or lower. By setting the heat treatment temperature within the above range, a pressure-sensitive adhesive layer with excellent adhesive properties can be obtained.

The heat treatment time can be set as appropriate, but is preferably from 5 seconds to 20 minutes, more preferably from 5 seconds to 10 minutes, and even more preferably from 10 seconds to 5 minutes.

There are no particular restrictions on the means of heat treatment, and various known methods can be used. Examples include a parallel drying method in which hot air is blown in the same direction above and below the film in the transport direction, a counter drying method in which hot air is blown in different directions above and below the film in the transport direction, and a float drying method in which hot air is blown directly above and below the film.

In addition, ultraviolet light is generally used as the irradiation light in the photocuring process. UV irradiation sources include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, LEDs, black lights, and chemical lamps. To promote the photopolymerization reaction, light irradiation is preferably carried out in an inert gas atmosphere such as nitrogen gas.

The cumulative amount of irradiation light during the photocuring treatment is preferably 300 mJ/cm ² or more and 3000 mJ/cm ² or less, and more preferably 500 mJ/cm ² or more and 2000 mJ/cm ² or less.

When photocuring is performed, the pressure-sensitive adhesive of the present invention may contain a photopolymerization initiator. Examples of photopolymerization initiators include photoradical initiators such as hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. The photoradical initiators may be used alone or in combination of two or more.

When forming the adhesive layer, the adhesive may be subjected to either the heat treatment or the light curing treatment described above, or both the heat treatment and the light curing treatment.

<Refractive index>
In the pressure-sensitive adhesive for optical films of the present invention, the refractive index of the pressure-sensitive adhesive layer obtained by at least one of the heat treatment and photo-curing treatment described above is 1.58 or more and 1.80 or less. If the refractive index of the pressure-sensitive adhesive layer is less than 1.58, the properties of the optical film or optical component will be degraded. On the other hand, pressure-sensitive adhesives in which the refractive index of the pressure-sensitive adhesive layer obtained by at least one of the heat treatment and photo-curing treatment exceeds 1.80 cannot be substantially produced. The refractive index is preferably 1.59 or more and 1.78 or less, more preferably greater than 1.60 and 1.76 or less, even more preferably greater than 1.60 and 1.75 or less, and even more preferably greater than 1.60 and 1.73 or less.

The refractive index of the pressure-sensitive adhesive layer can be controlled by appropriately selecting the type and amount of monomers constituting the copolymer (A), the type and amount of inorganic particles (B), the type and amount of crosslinking agent (D), etc. Furthermore, the refractive index can be measured specifically by the method described in the Examples.

<HAZE>
The pressure-sensitive adhesive layer according to the present invention has excellent transparency, with a haze of 0.05% to 1.0% at a thickness of 20 μm, preferably 0.05% to 0.8%, more preferably 0.05% to 0.6%, and even more preferably 0.05% to 0.4%.

The haze of the adhesive layer can be measured by the method described in the examples.

[Optical components]
According to one embodiment of the present invention, there is provided an optical member having the above-mentioned pressure-sensitive adhesive layer for an optical film and a first optical film provided on one surface of the pressure-sensitive adhesive layer.

The optical member of the present invention can further include glass or a second optical film on the surface of the pressure-sensitive adhesive layer of the present invention opposite the surface on which the first optical film is provided. The "first optical film" and the "second optical film" may be films having the same configuration (material, function, etc.), or may be films having different configurations (material, function, etc.). The present invention also provides an embodiment in which the first optical film (or second optical film) is a polarizing plate.

In the present invention, the above-mentioned pressure-sensitive adhesive may be used by directly applying it to one or both sides of the optical film to form a pressure-sensitive adhesive layer. However, for the reasons mentioned above, it is preferable to form a pressure-sensitive adhesive layer in advance on a separator or the like and then transfer this to one or both sides of the optical film. Furthermore, before transfer, the surface of the optical film may be subjected to a surface treatment such as the formation of an easy-adhesion treatment layer, or an antistatic layer, depending on the material of the optical film. Furthermore, the surface of the pressure-sensitive adhesive layer may also be subjected to an easy-adhesion treatment. From the viewpoint of firmly adhering the optical film and the pressure-sensitive adhesive layer, it is preferable to have an easy-adhesion treatment layer between the optical film and the pressure-sensitive adhesive layer for optical films of the present invention.

<Easy-adhesion treated layer (easy-adhesion layer)>
The optical member of the present invention preferably further comprises at least one adhesion-facilitating treatment layer between the first optical film and the pressure-sensitive adhesive layer for an optical film.

In a more preferred embodiment, the easy-adhesion treatment layer comprises a first easy-adhesion treatment layer and a second easy-adhesion treatment layer. The optical member has a first optical film, a first easy-adhesion treatment layer, a second easy-adhesion treatment layer, and a pressure-sensitive adhesive layer for the optical film laminated in this order. In this manner, a configuration in which the optical member has both a first and a second easy-adhesion treatment layer is preferred from the viewpoint of more firmly adhering the optical film and the pressure-sensitive adhesive layer.

The adhesion-enhancing treatment layer may be a treatment such as corona treatment or plasma treatment applied to the surface of the member that comes into contact with the adhesive layer. Alternatively, a separate layer such as a primer layer may be applied to the surface of the member that comes into contact with the adhesive layer.

The material constituting the primer layer preferably has good adhesion to the member that comes into contact with the primer layer and forms a film with excellent cohesion. For example, various polymers, metal oxide sols, silica sols, etc. are used, with polymers being particularly preferred. The primer layer may also have antistatic properties.

Polymers that can be used to form the primer layer include oxazoline group-containing polymers, polyurethane resins, polyester resins, and polymers containing amino groups in the molecule. Of these, polyurethane resins and oxazoline group-containing polymers are more preferably used.

Commercially available oxazoline group-containing polymers can be used. Examples include, but are not limited to, the EPOCROS® series (e.g., EPOCROS® WS700) manufactured by Nippon Shokubai Co., Ltd. Furthermore, polyurethane resins, polyester resins, and polymers containing amino groups in the molecule can be selected from those disclosed in paragraphs "0107" to "0113" of JP 2011-105918 A.

The thickness of the primer layer is preferably 10 nm or more and 5,000 nm or less, and more preferably 50 nm or more and 500 nm or less. Within this range, the layer can exhibit sufficient strength and adhesion while maintaining its optical properties.

The method for forming the primer layer is not particularly limited, and examples include a method in which the raw material for the primer layer (undercoat agent) is applied using a coating method such as coating, dipping, or spraying, followed by drying.

<Optical film>
In the present invention, examples of the optical film (first optical film or second optical film) include polarizing plates, retardation plates for preventing coloration, optical compensation films such as viewing angle widening films for improving the viewing angle of liquid crystal displays, brightness enhancement films for increasing the contrast of displays, light extraction films for increasing the light extraction efficiency of surface light emitters, and laminates of these. However, the optical film (first optical film or second optical film) is preferably a polarizing plate with an optical compensation layer. The polarizing plate with an optical compensation layer will be described below.

[Polarizing plate with optical compensation layer]
FIG. 1 is a schematic cross-sectional view of a polarizing plate with an optical compensation layer according to one embodiment of the present invention. Note that in FIG. 1 , the thickness ratios of the layers and optical films constituting the polarizing plate with an optical compensation layer differ from the actual thickness ratios. The polarizing plate with an optical compensation layer 100 of this embodiment includes a polarizer 10, a first protective layer 21 disposed on one side of the polarizer 10, a second protective layer 22 disposed on the other side of the polarizer 10, a first optical compensation layer 30 disposed on the side of the second protective layer 22 opposite the polarizer 10, and a second optical compensation layer 40, in this order. That is, the polarizing plate with an optical compensation layer 100 includes a polarizer 10, a first retardation layer 30, and a second retardation layer 40, in this order. Depending on the purpose and the configuration of the image display device to which the polarizing plate with an optical compensation layer is applied, at least one of the first protective layer 21 and the second protective layer 22 may be omitted.

(Polarizer)
Any appropriate polarizer can be adopted as the polarizer 10. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers made from a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, as well as polyene-based oriented films such as dehydrated PVA and dehydrochlorinated polyvinyl chloride. Because of their excellent optical properties, polarizers obtained by dyeing PVA films with iodine and uniaxially stretching them are preferred.

The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio for the uniaxial stretching is preferably 3 to 7 times. Stretching may be carried out after the dyeing process, or may be carried out while dyeing. Alternatively, the PVA-based film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to swelling, crosslinking, washing, drying, or other treatments. For example, by immersing the PVA-based film in water and rinsing it before dyeing, it is possible to wash away dirt and anti-blocking agents from the surface of the PVA-based film, and also to swell the PVA-based film, thereby preventing uneven dyeing.

Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, stretching typically involves immersing the laminate in an aqueous boric acid solution to stretch it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The resulting resin substrate/polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled from the resin substrate/polarizer laminate and any suitable protective layer depending on the purpose may be laminated on the peeled surface. Details of the method for producing such a polarizer are described, for example, in JP-A-2012-73580.

The thickness of the polarizer is preferably 25 μm or less, and more preferably 1 μm or more and 12 μm or less. A polarizer thickness within this range effectively suppresses curling when heated and provides good appearance durability when heated.

The polarizer preferably exhibits absorption dichroism at wavelengths between 380 nm and 780 nm.

(First Protective Layer)
The first protective layer 21 is formed of any appropriate film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicone resins. Other examples include glassy polymers such as siloxane polymers. The polymer films described in JP 2001-343529 A (WO 01/37007 A) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, and an example of such a resin composition includes an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer.

As described below, the polarizing plate with an optical compensation layer of this embodiment is typically placed on the viewing side of an image display device, and the first protective layer 21 is typically placed on that viewing side. Therefore, the first protective layer 21 may be subjected to surface treatments such as hard coating, anti-reflection, anti-sticking, and anti-glare, as needed. Furthermore, the first protective layer 21 may be subjected to treatments to improve visibility when viewed through polarized sunglasses (typically, by imparting (elliptically) circular polarization functionality or ultra-high phase difference).

The first protective layer 21 may have any appropriate thickness. The thickness of the first protective layer 21 is, for example, 10 μm or more and 50 μm or less, and preferably 15 μm or more and 40 μm or less. If a surface treatment has been applied, the thickness of the first protective layer includes the thickness of the surface treatment layer.

(Second Protective Layer)
The second protective layer 22 is also formed of any appropriate film that can be used as a protective layer for a polarizer. The material that is the main component of this film is as described in the section on the first protective layer. The second protective layer 22 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm or more and 10 nm or less, and the retardation Rth(550) in the thickness direction is -10 nm or more and +10 nm or less.

The thickness of the second protective layer 22 is, for example, 15 μm or more and 35 μm or less, and preferably 20 μm or more and 30 μm or less. The difference in thickness between the first protective layer 21 and the second protective layer 22 is preferably 15 μm or less, and more preferably 10 μm or less. A thickness difference within this range can effectively suppress curling during lamination. The thicknesses of the first protective layer 21 and the second protective layer 22 may be the same, or the first protective layer 21 may be thicker, or the second protective layer 22 may be thicker. Typically, the first protective layer 21 is thicker than the second protective layer 22.

(First Optical Compensation Layer)
The first optical compensation layer 30 can function as a λ/2 plate. The in-plane retardation Re(550) of the first optical compensation layer 30 is usually 220 nm or more and 320 nm or less, and preferably 240 nm or more and 300 nm or less.

The first optical compensation layer 30 is a liquid crystal alignment solidification layer, more specifically, a layer in which a discotic liquid crystal compound is fixed in a vertically aligned state. Discotic liquid crystal compounds generally refer to liquid crystal compounds with a discotic molecular structure in which a cyclic core such as benzene, 1,3,5-triazine, or calixarene is located at the center of the molecule and linear alkyl groups, alkoxy groups, substituted benzoyloxy groups, or the like are radially substituted as side chains. Conventionally known compounds can be used as discotic liquid crystals.

The first optical compensation layer 30 can be formed, for example, by the following procedure. Here, we will describe the formation of a long-length first optical compensation layer on a long-length polarizer. First, while transporting a long-length substrate, a coating liquid for forming an alignment film is applied to the substrate and dried to form a coating film. The coating film is rubbed in a predetermined direction to form an alignment film on the substrate. This predetermined direction corresponds to the slow axis direction of the resulting first optical compensation layer, and is, for example, approximately 15° relative to the longitudinal direction of the substrate. Next, a coating liquid for forming a first optical compensation layer (a solution containing a discotic liquid crystal compound and, if necessary, a crosslinkable monomer) is applied to the formed alignment film and heated. Heating removes the solvent from the coating liquid and promotes the alignment of the discotic liquid crystal compound. Heating can be performed in a single step or in multiple steps at different temperatures. Next, ultraviolet light is irradiated to crosslink (or polymerize) the crosslinkable (or polymerizable) monomer, thereby fixing the alignment of the discotic liquid crystal compound. In this manner, a first optical compensation layer is formed on the substrate. Finally, the first optical compensation layer is attached to the polarizer via the adhesive layer, and the substrate is peeled off (i.e., the first optical compensation layer is transferred from the substrate to the polarizer). In this manner, the first optical compensation layer can be laminated on the polarizer. Note that a method for vertically aligning a discotic liquid crystal compound is described, for example, in paragraph [0153] of JP-A 2006-133652.

The thickness of the first optical compensation layer 30 is typically 1.5 μm or more, and preferably 1.6 μm or more and 2.0 μm or less.

(Second Optical Compensation Layer)
The second optical compensation layer 40 can function as a λ/4 plate. The in-plane retardation Re(550) of the second optical compensation layer 40 is typically 100 nm or more and 200 nm or less, and preferably 110 nm or more and 180 nm or less.

In the second optical compensation layer 40, rod-shaped liquid crystal compounds are typically aligned in the slow axis direction of the second optical compensation layer (homogeneous alignment). Examples of liquid crystal compounds include liquid crystal compounds whose liquid crystal phase is a nematic phase (nematic liquid crystals). Examples of such liquid crystal compounds that can be used include liquid crystal polymers and liquid crystal monomers. The mechanism by which the liquid crystallinity of liquid crystal compounds is expressed may be either lyotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers may be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking the liquid crystal monomer. After orienting the liquid crystal monomer, for example, the orientation state can be fixed by polymerizing or crosslinking the liquid crystal monomers themselves. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystals. Therefore, the formed second optical compensation layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is typical of liquid crystal compounds. As a result, the second optical compensation layer 40 becomes a retardation layer with excellent stability that is not affected by temperature changes.

The temperature range in which a liquid crystal monomer exhibits liquid crystallinity varies depending on the type of monomer. Specifically, this temperature range is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower.

Any suitable liquid crystal monomer known in the art can be used as the liquid crystal monomer.

The second optical compensation layer 40 can be formed by performing an alignment treatment on the surface of a predetermined substrate, applying a coating liquid containing a liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. In one embodiment, the substrate is any appropriate resin film, and the second optical compensation layer 40 formed on the substrate can be transferred to the surface of the first optical compensation layer 30 via an adhesive layer.

Any appropriate alignment treatment can be used as the alignment treatment. Specific examples include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique evaporation and photo-alignment treatment. Any appropriate treatment conditions can be used for the various alignment treatments depending on the purpose. In embodiments of the present invention, photo-alignment treatment is preferred. This is because photo-alignment treatment does not generate foreign matter such as rubbing debris. By forming a thin λ/4 plate using photo-alignment treatment, display defects caused by foreign matter can be suppressed.

Liquid crystal compounds are aligned by treating them at a temperature that allows them to exhibit a liquid crystal phase, depending on the type of liquid crystal compound. By performing this temperature treatment, the liquid crystal compounds assume a liquid crystal state and are aligned in accordance with the alignment treatment direction on the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. If the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to a polymerization treatment or crosslinking treatment.

The thickness of the second optical compensation layer 40 is preferably 0.5 μm or more and 1.2 μm or less. With this thickness, it can function properly as a λ/4 plate.

(Conductive layer or substrate-attached conductive layer)
The conductive layer can be formed by depositing a metal oxide film on any suitable substrate by any appropriate film-forming method (e.g., vacuum deposition, sputtering, CVD, ion plating, spraying, etc.). After deposition, a heat treatment (e.g., 100°C or higher and 200°C or lower) may be performed as needed. Heat treatment can crystallize an amorphous film. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Indium oxide may be doped with divalent metal ions or tetravalent metal ions. Indium-based composite oxides are preferred, and indium-tin composite oxide (ITO) is more preferred. Indium-based composite oxides are characterized by high transmittance (e.g., 80% or higher) in the visible light region (wavelength 380 nm or higher and 780 nm or lower) and low surface resistance per unit area.

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, and more preferably 35 nm or less. The lower limit of the conductive layer thickness is preferably 10 nm or more.

The surface resistance of the conductive layer is preferably 300 Ω/□ or less, more preferably 150 Ω/□ or less, and even more preferably 100 Ω/□ or less.

The conductive layer can be formed as an electrode by patterning the metal oxide film using an etching method or the like. The electrode can function as a touch sensor electrode that detects contact with the touch panel.

The conductive layer may be transferred from the substrate to the second optical compensation layer and used alone as a constituent layer of the polarizing plate with optical compensation layers, or it may be laminated to the second optical compensation layer as a laminate with the substrate (a substrate-attached conductive layer, i.e., a conductive film or sensor film). Typically, as described above, the conductive layer and substrate can be incorporated into the polarizing plate with optical compensation layers as a substrate-attached conductive layer.

The material constituting the substrate may be any suitable resin. Preferably, it is a resin with excellent transparency. Specific examples include cyclic olefin resins, polycarbonate resins, cellulose resins, polyester resins, and acrylic resins.

Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used in a polarizing plate with an optical compensation layer as an isotropic substrate-attached conductive layer. Examples of materials that constitute an optically isotropic substrate (isotropic substrate) include materials whose main skeleton is a resin that does not have a conjugated system, such as a norbornene resin or an olefin resin, and materials that have a cyclic structure, such as a lactone ring or a glutarimide ring, in the main chain of an acrylic resin. Using such materials can minimize the occurrence of retardation due to molecular chain orientation when an isotropic substrate is formed.

The thickness of the substrate is preferably 10 μm or more and 200 μm or less, and more preferably 20 μm or more and 60 μm or less.

(others)
Any suitable adhesive (adhesive layer) is used for laminating each layer constituting the polarizing plate with optical compensation layers according to the present invention. A water-based adhesive (e.g., a PVA-based adhesive) can be typically used for laminating the polarizer and the protective layer. An active energy ray (e.g., ultraviolet) curable adhesive is typically used for laminating the optical compensation layer. The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less.

Although not shown, a pressure-sensitive adhesive layer of the present invention is provided on the second optical compensation layer 40 side of the polarizing plate with optical compensation layers 100 (on the substrate side if a conductive layer and substrate are provided), resulting in the pressure-sensitive adhesive layer and polarizing plate with optical compensation layers according to this embodiment. The pre-provided pressure-sensitive adhesive layer of the present invention allows for easy attachment to other optical components (e.g., image display cells). For practical purposes, a separator is temporarily and removably attached to the pressure-sensitive adhesive layer to protect the pressure-sensitive adhesive layer until actual use and enable roll formation.

[Image display device]
The present invention also provides an image display device using at least one of the optical members described above.

The image display device is not particularly limited, and examples include liquid crystal display devices, organic EL display devices, plasma displays (PDPs), micro LED displays, etc. Furthermore, from the viewpoint of more significantly demonstrating the effects of the pressure-sensitive adhesive for optical films of the present invention, thin image display devices are particularly preferred.

The present invention will be explained in more detail below using examples, but these examples are not intended to limit the present invention in any way. In the following explanation, all "parts" mean "parts by mass." Unless otherwise specified, operations and measurements of physical properties were carried out at room temperature of 23°C and a relative humidity of 55% RH.

<Measurement of weight average molecular weight (Mw)>
The weight average molecular weight (Mw) of the (meth)acrylic acid ester copolymer (A) was measured by GPC (gel permeation chromatography) under the following conditions:
Analytical equipment: HLC-8120GPC, manufactured by Tosoh Corporation
Column: Tosoh Corporation, G7000H _XL + GMH _XL + GMH _XL
Column size: 7.8 mm diameter x 30 cm each, total 90 cm
Column temperature: 40°C
Flow rate: 0.8ml/min
Injection volume: 100μl
Eluent: tetrahydrofuran Detector: differential refractometer (RI)
Standard sample: polystyrene.

<Preparation of (Meth)acrylic Acid Ester Copolymer (A1)>
[Production Example 1]
A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 99 parts by mass of m-phenoxybenzyl acrylate (Light Acrylate POB-A, manufactured by Kyoeisha Chemical Co., Ltd.), 1% by mass of 4-hydroxybutyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), and 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, along with 100 parts by mass of ethyl acetate, and nitrogen gas was introduced while gently stirring. After nitrogen gas substitution, the liquid temperature in the flask was controlled to around 55°C, and a polymerization reaction was carried out for 5 hours to prepare a solution of (meth)acrylic acid ester copolymer (A1) having a weight average molecular weight (Mw) of 1,020,000 and Mw/Mn = 2.5.

[Production Examples 2 to 28]
(Meth)acrylic acid ester copolymers (A-2) to (A-28) were obtained in the same manner as in Production Example 1, except that the types and ratios of monomers and the amount of photopolymerization initiator were changed as shown in Table 1. The compositions and weight average molecular weights (Mw) of (meth)acrylic acid ester copolymers (A-1) to (A-28) are shown in Table 1.

The monomers in Table 1 are as follows. Note that blank spaces in Table 1 indicate that the monomer was not used.

POB-A: Phenoxybenzyl acrylate (Light Acrylate POB-A, manufactured by Kyoeisha Chemical Co., Ltd.)
A-LEN-10: Ethoxylated o-phenylphenol acrylate (A-LEN-10, manufactured by Shin-Nakamura Chemical Co., Ltd.)
NMT-A: 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.)
A-BPML: p-phenylbenzyl acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.)
PhEA: Phenoxyethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.)
BzA: benzyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd.)
FLM-A: 9-fluorenylmethyl acrylate (synthesized based on JP 2013-181097 A)
4HBA: 4-hydroxybutyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd.)
HEAA (registered trademark): N-hydroxyethyl acrylamide (manufactured by KJ Chemicals Co., Ltd.)
IBXA: Isobornyl acrylate (Osaka Organic Chemical Industry Ltd.)
ACMO (registered trademark): N-acryloylmorpholine (manufactured by KJ Chemicals Co., Ltd.)
BA: n-butyl acrylate (manufactured by Nippon Shokubai Co., Ltd.)
MEA: methoxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.).

<Preparation of Pressure-Sensitive Adhesive, Pressure-Sensitive Adhesive Layer, and Optical Component>
[Example 1]
(Preparation of Pressure-Sensitive Adhesive for Optical Film)
To 100% by mass of the solids content of the (meth)acrylic acid ester copolymer (A1) solution obtained in Production Example 1 (i.e., 100 parts by mass of the (meth)acrylic acid ester copolymer (A1)), 0.1 parts by mass (active ingredient equivalent) of Takenate (registered trademark) D-110N (75% ethyl acetate solution of an adduct of xylylene diisocyanate (XDI) and trimethylolpropane, number of isocyanate groups per molecule: 3, manufactured by Mitsui Chemicals, Inc., number average molecular weight Mn=700) as a crosslinking agent and 0.1 parts by mass of a silane coupling agent (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane) were added and mixed, to prepare a pressure-sensitive adhesive for optical films (solids content 25% by mass, solvent 75% by mass).

(Formation of pressure-sensitive adhesive layer for optical film)
The pressure-sensitive adhesive obtained above was applied to one side of a release-treated (silicone-treated) 38 μm-thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Corporation, MRF38, no oligomer blocking layer) so that the thickness of the pressure-sensitive adhesive layer after drying would be 20 μm. The resulting film was then heated at 120° C. for 2 minutes to form a pressure-sensitive adhesive layer for an optical film.

The heat treatment was carried out using the float drying method, in which hot air is blown directly from above and below the film.

(Preparation of Optical Member (Polarizing Plate with Pressure-Sensitive Adhesive Layer and Optical Compensation Layer))
1-1. Preparation of Polarizing Plate An A-PET (amorphous polyethylene terephthalate) film (manufactured by Mitsubishi Chemical Corporation, product name: Novaclear (registered trademark) SH046, thickness 200 μm) was prepared as a substrate, and its surface was subjected to a corona treatment (corona discharge amount 58 W·min/m ² ). Separately, polyvinyl alcohol (PVA, polymerization degree 4200, saponification degree 99.2%) to which 1% by mass of acetoacetyl-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, product name: Gohsefimer (trademark) Z200, polymerization degree 1200, saponification degree 99.0% or more, acetoacetyl-modification degree 4.6%) was added was prepared. This polyvinyl alcohol was applied to the corona-treated surface of the A-PET film so that the film thickness after drying would be 12 μm, and the film was dried by hot air drying for 10 minutes at 60°C. In this way, a laminate having a polyvinyl alcohol (PVA)-based resin layer provided on the substrate was prepared.

Next, this laminate was first stretched 2.0 times in air at 130°C to obtain a stretched laminate. Next, the stretched laminate was immersed in a boric acid insolubilizing solution at 30°C for 30 seconds to insolubilize the PVA-based resin layer in which the polyvinyl alcohol molecules contained in the stretched laminate were oriented. This boric acid insolubilizing solution contained 3% boric acid by mass relative to 100% water by mass. A colored laminate was produced by dyeing this stretched laminate. The colored laminate was produced by immersing the stretched laminate in a dye solution containing iodine and potassium iodide at 30°C, thereby adsorbing iodine to the PVA-based resin layer contained in the stretched laminate. The iodine concentration and immersion time were adjusted so that the resulting polarizer had a single-piece transmittance of 44.5%. Specifically, the dye solution contained water as the solvent, had an iodine concentration in the range of 0.08% by mass to 0.25% by mass, and a potassium iodide concentration in the range of 0.56% by mass to 1.75% by mass. The ratio of the iodine and potassium iodide concentrations was 1:7.

Next, the colored laminate was immersed in a boric acid crosslinking aqueous solution at 30°C for 60 seconds to crosslink the PVA molecules of the iodine-adsorbed PVA-based resin layer. The boric acid crosslinking aqueous solution used in this step had a boric acid content of 3% by mass relative to 100% by mass of water and a potassium iodide content of 3% by mass relative to 100% by mass of water. The resulting colored laminate was then stretched 2.7 times in the boric acid aqueous solution at a stretching temperature of 70°C in the same direction as the stretching in air described above, resulting in a final stretch ratio of 5.4 times, thereby obtaining a substrate/polarizer laminate. The polarizer had a thickness of 5 μm. The boric acid crosslinking aqueous solution used in this step had a boric acid content of 6.5% by mass relative to 100% by mass of water and a potassium iodide content of 5% by mass relative to 100% by mass of water. The resulting laminate was removed from the boric acid aqueous solution, and the boric acid adhering to the polarizer surface was washed with an aqueous solution containing 2% by mass of potassium iodide relative to 100% by mass of water. The washed laminate was dried with hot air at 60°C.

A 40 μm thick acrylic film was attached to the polarizer surface of the substrate/polarizer laminate obtained above via a PVA adhesive. Furthermore, a polarizing plate having a protective layer/polarizer/resin substrate structure was obtained.

1-2. Preparation of Liquid Crystal Alignment Solidified Layer Constituting the First Optical Compensation Layer A liquid crystal alignment solidified layer (first optical compensation layer) was formed on a substrate (TAC film) according to the procedure described in paragraphs [0151] to [0156] of JP 2006-133652 A. Note that the direction of the rubbing treatment was such that, when attached to the polarizer, it was at a 15° counterclockwise angle relative to the direction of the absorption axis of the polarizer as viewed from the viewing side. The thickness of the first optical compensation layer was 1.7 μm, and the in-plane retardation Re(550) was 270 nm. Furthermore, the first optical compensation layer was a negative A plate exhibiting refractive index characteristics of nx = nz > ny. Furthermore, no protrusions with a height of 0.4 μm or more were observed on the surface of the first optical compensation layer (negative A plate).

1-3. Preparation of Liquid Crystal Alignment Solidified Layer Constituting Second Optical Compensation Layer 10 g of a polymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (manufactured by BASF, trade name "Paliocolor (registered trademark) LC242", a compound represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (Omnirad (registered trademark) 907; manufactured by IGM Resins B.V.) were dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

A photo-alignment film was coated on the surface of a polyethylene terephthalate (PET) film (38 μm thick) and subjected to a photo-alignment treatment. The photo-alignment treatment direction was such that, when attached to the polarizer, it was at a 75° counterclockwise angle relative to the absorption axis of the polarizer as viewed from the viewing side. The liquid crystal composition was applied to this photo-alignment-treated surface using a bar coater and then heated and dried at 90°C for 2 minutes to align the liquid crystal compound. The liquid crystal layer thus formed was irradiated with ¹ mJ/cm2 of light using a metal halide lamp to harden the liquid crystal layer, thereby forming a liquid crystal alignment solidified layer (second optical compensation layer) on the substrate (PET film). The second optical compensation layer had a thickness of 1.2 μm and an in-plane retardation Re(550) of 140 nm. Furthermore, the second optical compensation layer was a positive A plate exhibiting a refractive index characteristic of nx>ny=nz.

1-4. Preparation of Polarizing Plate with Optical Compensation Layer The A-PET film substrate was peeled from the polarizing plate obtained above, and the first optical compensation layer was transferred from the substrate/first optical compensation layer laminate to the peeled surface via a UV-curable adhesive. Furthermore, the second optical compensation layer was transferred from the substrate/second optical compensation layer laminate to the surface of the first optical compensation layer via a UV-curable adhesive. In this way, a polarizing plate with optical compensation layers was obtained having a configuration of protective layer/polarizer/first optical compensation layer (negative A plate: λ/2 plate)/second optical compensation layer (positive A plate: λ/4 plate).

1-5. Preparation of Pressure-Sensitive Adhesive Layer and Polarizing Plate with Optical Compensation Layer Corona treatment was performed on the polarizing plate side (opposite the protective film side) on which the pressure-sensitive adhesive layer of the polarizing plate with optical compensation layer obtained above was formed at a corona discharge rate of 80 W min/ ^m2 to form an easy-adhesion treated layer. Next, a PET film on which the pressure-sensitive adhesive layer had been formed was attached so that the easy-adhesion treated layer and the pressure-sensitive adhesive layer were in contact with each other, thereby preparing an optical member, i.e., a pressure-sensitive adhesive layer and a polarizing plate with an optical compensation layer.

(Fabrication of Organic EL Display Device)
The obtained pressure-sensitive adhesive layer and polarizing plate with an optical compensation layer were cut into a size of 100 mm x 50 mm.

A smartphone (Galaxy-S10) manufactured by Samsung Electronics Co., Ltd. was disassembled and the organic EL display device was removed. The polarizing film attached to this organic EL display device was peeled off, and the polarizing plate with optical compensation layer cut out above was attached instead to obtain an organic EL display device.

[Examples 2 to 30, Comparative Examples 1 to 5]
In the <Preparation of adhesive composition> of Example 1, an adhesive, an adhesive layer, and a polarizing plate with an optical compensation layer were obtained in the same manner as in Example 1, except that the type of (meth)acrylic acid ester copolymer (A) and the type and amount of additive were changed as shown in Table 2 below.

The inorganic particles used in Table 2 were two types of particles (compatibility improved product 1 and compatibility improved product 2) made of zirconium oxide coated with a coating agent. The amount added shown in Table 2 is the amount of zirconium oxide particles (amount of active ingredient) per 100 parts by mass of copolymer (A).

Also, KBE-403, the silane coupling agent (C) in Table 2, is 3-glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.).

<Evaluation>
(Refractive index of pressure-sensitive adhesive layer)
The refractive index of the adhesive layer at sodium D line was measured at 25°C using an Abbe refractometer.

(Hayes)
A pressure-sensitive adhesive layer was formed in the same manner as in (Formation of pressure-sensitive adhesive layer for optical film) above, and then a release film was attached to the exposed surface of the pressure-sensitive adhesive layer to prepare a pressure-sensitive adhesive sheet.

The release film on one side of the resulting pressure-sensitive adhesive sheet was peeled off, and the exposed adhesive surface was roll-pressed onto alkali-free glass (82 mm x 53 mm x 0.5 mm thick). The PET film on the other side was then peeled off, and alkali-free glass (82 mm x 53 mm x 0.5 mm thick) was laminated using a roll. The sheet was then autoclaved (50°C, 0.4 MPa gauge pressure, 20 minutes) for final lamination, producing an evaluation sample.

The haze of the obtained evaluation samples was measured in accordance with JIS K7136 (2000) using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in an environment of 25°C and relative humidity of 55% RH.

(durability)
The organic EL display device to which the polarizing plate with an optical compensation layer having the pressure-sensitive adhesive layer prepared above was attached was used as a sample for durability evaluation. The obtained sample was subjected to the following tests, and its appearance was evaluated visually:
(1) Treated at 85°C for 500 hours (heating test)
(2) Treated for 500 hours in an atmosphere of 60°C and 95% RH (humidification test)
(3) The test was performed for 300 cycles (300 hours), with one cycle consisting of leaving the sample in an 85°C environment for 30 minutes and then leaving it in a -40°C environment for 30 minutes. This cycle lasted for 1 hour (heat shock (HS) test).
- Visual evaluation -
◎: No bubbles at all at the edge ○: There are a few bubbles at the edge, but this does not pose a problem in practical use △: There are bubbles at the edge, but this does not pose a problem in practical use unless it is for a special purpose ×: There are a significant number of bubbles at the edge, which poses a problem in practical use.

(Haze value after 500 hours of humidification test and 1 hour of standing at room temperature (23°C, 55% RH))
The sample subjected to the durability humidification test was taken out and left to stand in a room temperature (23°C, 55% RH) environment for 3 hours, and then the haze was measured using the method described in the above (Haze) section. The measured haze value was evaluated on the following 5-point scale. 5 is the best, and 3 or more is usable:
5: Less than 1.0% 4: 1.0% or more and less than 2.0% 3: 2.0% or more and less than 3.0% 2: 3.0% or more and less than 5.0% 1: 5.0% or more.

(Coatability)
The surface condition of the pressure-sensitive adhesive layer formed in the above (Formation of pressure-sensitive adhesive layer for optical film) immediately after formation was visually observed and evaluated according to the following criteria. In a 5-point scale, 5 is the best and 3 or more is practical:
5: No coating streaks or coating unevenness 4: Weak coating streaks or coating unevenness in parts 3: Weak coating streaks or coating unevenness over the entire surface 2: Strong coating streaks or coating unevenness over the entire surface 1: A uniformly coated surface cannot be formed.

The composition and evaluation results of each adhesive are shown in Table 2 below. Note that a "-" in the inorganic particles column indicates that no inorganic particles were used.

The results in Table 2 above show that the adhesive of the present invention in the examples provides an adhesive layer that has a high refractive index, durability in harsh environments (high temperature, high humidity, heat shock), and excellent transparency after undergoing at least one of a heat treatment and a photocuring treatment.

Furthermore, in Examples 13 to 30, which used inorganic particles, a tendency for improved coatability was observed.

10 polarizer,
21 first protective layer,
22 second protective layer;
30 First optical compensation layer (first retardation layer),
40 second optical compensation layer (second retardation layer),
100 Polarizing plate with optical compensation layer.

Claims (13)

A pressure-sensitive adhesive for optical films, comprising a (meth)acrylic acid ester copolymer (A) and inorganic particles (B),
The (meth)acrylic acid ester copolymer (A) is
(a1): a structural unit derived from a (meth)acrylic acid ester monomer having an aromatic hydrocarbon group; and (a2): a structural unit derived from a (meth)acrylic monomer having a hydroxy group,
the content of the structural units derived from the component (a1) is 65% by mass or more and 99% by mass or less, with the total amount of all structural units of the (meth)acrylic acid ester copolymer (A) being 100% by mass;
the content of the structural units derived from the component (a2) is 0.1% by mass or more and 25% by mass or less, with the total amount of all structural units of the (meth)acrylic acid ester copolymer (A) being 100% by mass;
the weight average molecular weight of the (meth)acrylic acid ester copolymer (A) is 500,000 or more and 2,000,000 or less,
The average particle diameter of the inorganic particles (B) is 1 nm or more and 100 nm or less,
the content of the inorganic particles (B) is more than 100 parts by mass and not more than 2,000 parts by mass relative to 100 parts by mass of the (meth)acrylic acid ester copolymer (A);
The pressure-sensitive adhesive for optical films, wherein the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive for optical films through at least one of a heat treatment and a photo-curing treatment has a refractive index of 1.58 or more and 1.80 or less. The pressure-sensitive adhesive for optical films according to claim 1, wherein the weight-average molecular weight of the (meth)acrylic acid ester copolymer (A) is 700,000 or more and 2,000,000 or less. The pressure-sensitive adhesive for optical films according to claim 1 or 2, wherein the weight-average molecular weight of the (meth)acrylic acid ester copolymer (A) is 900,000 or more and 2,000,000 or less. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 3, wherein the content of the structural units derived from component (a2) is 0.1% by mass or more and less than 12% by mass, with the total structural units of the (meth)acrylic acid ester copolymer (A) being 100% by mass. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 4, wherein the (meth)acrylic acid ester copolymer (A) further contains a structural unit derived from a monomer (a3) having one radically polymerizable functional group other than the component (a1) and the component (a2). The pressure-sensitive adhesive for optical films according to claim 5, wherein the content of the structural units derived from component (a3) is 3% by mass or more and 80% by mass or less, with the total structural units of the (meth)acrylic acid ester copolymer (A) being 100% by mass. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 6, wherein the (a1) (meth)acrylic acid ester monomer having an aromatic hydrocarbon group has at least one group selected from the group consisting of a biphenyl ring group, a phenoxybenzyl group, a naphthalene ring group, and a fluorene ring group. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 7, wherein the (a1) (meth)acrylic acid ester monomer having an aromatic hydrocarbon group includes at least one selected from the group consisting of phenoxybenzyl (meth)acrylate, naphthyl (meth)acrylate, hydroxynaphthyl (meth)acrylate, fluorenyl (meth)acrylate, and hydroxyfluorenyl (meth)acrylate. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 8, wherein the content of the inorganic particles (B) is 300 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of the (meth)acrylic acid ester copolymer (A). The pressure-sensitive adhesive for optical films according to any one of claims 1 to 9, wherein the inorganic particles (B) are at least one selected from the group consisting of zirconium oxide, zinc oxide, iron oxide, copper oxide, titanium oxide, tin oxide, cerium oxide, tantalum oxide, niobium oxide, tungsten oxide, europium oxide, hafnium oxide, potassium titanate, barium titanate, strontium titanate, potassium niobate, lithium niobate, calcium tungstate, antimony-doped tin oxide (ATO), and indium tin oxide (ITO). The pressure-sensitive adhesive for optical films according to any one of claims 1 to 10 , wherein the inorganic particles (B) are at least one selected from the group consisting of zirconium oxide, titanium oxide, and barium titanate. The pressure-sensitive adhesive for optical films according to any one of claims 1 to 11 , wherein the inorganic particles (B) are coated with one or more coating agents. A pressure-sensitive adhesive layer for an optical film, which is obtained by curing the pressure-sensitive adhesive for an optical film according to any one of claims 1 to 12 by at least one of a heat treatment and a photo-curing treatment ,
A pressure-sensitive adhesive layer for an optical film, having a haze value of 0.05% or more and 1.0% or less when the layer has a thickness of 20 μm.