WO2025205587A1 - Adhesive composition and optical film with adhesive layer - Google Patents

Abstract

Provided is an adhesive composition which is capable of forming an adhesive layer that has excellent heat resistance durability. This adhesive composition contains a (meth)acrylic resin, a crosslinking agent, a silane compound, and an ionic compound. The (meth)acrylic resin contains, as a monomer unit, an alkyl (meth)acrylate which has a homopolymer glass transition temperature of 30°C or higher. The ionic compound contains an anion that is represented by formula (1). (In formula (1), each of R¹ to R⁴ independently represents a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent.)

Description

Pressure-sensitive adhesive composition and optical film with pressure-sensitive adhesive layer

The present disclosure relates to a pressure-sensitive adhesive composition and an optical film with a pressure-sensitive adhesive layer.

Optical films such as polarizing plates used in image display devices such as liquid crystal displays and organic electroluminescence (organic EL) displays are often attached to other components (for example, image display elements such as liquid crystal cells in liquid crystal display devices) via an adhesive layer containing an adhesive composition. Patent Document 1 discloses an adhesive composition for polarizing plates containing an acrylic resin (A) and an ionic compound (B), wherein the acrylic resin (A) contains a structural moiety derived from methyl methacrylate, and the average number of carbon atoms (α) in the side chain structural moieties of the acrylic resin (A) is 3.3 or less.

Japanese Patent Application Laid-Open No. 2022-25417

The above-mentioned pressure-sensitive adhesive layers may be used in high-temperature environments. In particular, pressure-sensitive adhesive layers applicable to optical films for automotive applications, etc., are required to be able to withstand harsh high-temperature environments (for example, environments of 100°C or higher).

One aspect of the present disclosure aims to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer with excellent heat resistance and durability.

The inventors have discovered that a pressure-sensitive adhesive layer with excellent heat resistance and durability can be formed using a pressure-sensitive adhesive composition that uses a combination of a specific (meth)acrylic resin and an ionic compound containing a borate anion.

In some aspects, the present disclosure provides the following [1] to [6].
[1] A pressure-sensitive adhesive composition comprising a (meth)acrylic resin, a crosslinking agent, a silane compound, and an ionic compound, wherein the (meth)acrylic resin comprises, as a monomer unit, an alkyl (meth)acrylate having a homopolymer glass transition temperature of 30°C or higher, and the ionic compound comprises an anion represented by the following formula (1):

[In formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, a halogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, or an optionally substituted heterocyclic group.]
[2] The pressure-sensitive adhesive composition according to [1], wherein the anion represented by formula (1) is an anion represented by the following formula (2):

[In formula (2), R ⁵ to R ⁹ each independently represent a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent, and two or more selected from the group consisting of R ⁵ to R ⁹ may be bonded to each other to form a ring.]
[3] The pressure-sensitive adhesive composition according to [2], wherein the anion represented by formula (2) is a tetrakis(pentafluorophenyl)borate anion.
[4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the (meth)acrylic resin further contains a hydroxy group-containing (meth)acrylate and a carboxy group-containing monomer as monomer units, the content of the hydroxy group-containing (meth)acrylate being from 0.3 to 5.5 mass% based on the total amount of monomer units contained in the (meth)acrylic resin, and the mass ratio of the content of the carboxy group-containing monomer to the content of the hydroxy group-containing (meth)acrylate being from 0.06 to 1.0.
[5] A pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of [1] to [4].
[6] A pressure-sensitive adhesive layer-attached optical film comprising an optical film and the pressure-sensitive adhesive layer according to [5] provided on at least one surface of the optical film.

One aspect of the present disclosure provides an adhesive composition capable of forming an adhesive layer with excellent heat resistance and durability.

FIG. 1 is a schematic cross-sectional view showing an example of a pressure-sensitive adhesive layer-attached optical film. FIG. 2 is a schematic cross-sectional view showing another example of a pressure-sensitive adhesive layer-attached optical film.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the following embodiments. In all of the drawings below, the scale has been adjusted appropriately to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

<Adhesive composition>
<(Meth)acrylic resin>
A pressure-sensitive adhesive composition according to an embodiment includes a (meth)acrylic resin. The (meth)acrylic resin includes, as a monomer unit, an alkyl (meth)acrylate having a homopolymer glass transition temperature of 30° C. or higher. Because the pressure-sensitive adhesive composition according to an embodiment includes such a (meth)acrylic resin together with an ionic compound described below, a pressure-sensitive adhesive layer including the pressure-sensitive adhesive composition has excellent durability (heat resistance durability) in high-temperature environments (e.g., environments of 100° C. or higher).

In this specification, the glass transition temperature (Tg) of homopolymers of various monomers such as alkyl (meth)acrylates is measured using a differential scanning calorimeter (DSC) (for example, an EXSTAR DSC6000 (manufactured by SII Nanotechnology, Inc.)) in a nitrogen atmosphere at a heating rate of 10°C/min over a temperature range of, for example, -80 to 150°C.

The alkyl group in an alkyl(meth)acrylate (hereinafter also referred to as "alkyl(meth)acrylate (A1)") whose homopolymer has a Tg of 30°C or higher may be linear or branched. The alkyl(meth)acrylate (A1) may also be an alkyl(meth)acrylate having an alicyclic structure (for example, a cycloalkyl(meth)acrylate). The number of carbon atoms in the alkyl group in the alkyl(meth)acrylate (A1) may be 1 or more, and may be 12 or less, 10 or less, 8 or less, 6 or less, 4 or less, or 2 or less.

Examples of alkyl (meth)acrylates (A1) include alkyl methacrylates having an alkyl group with 1 to 6 carbon atoms, such as methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, propyl methacrylate, isopropyl methacrylate, 3,3-dimethylbutyl methacrylate, and 3,3-dimethyl-2-butyl methacrylate, as well as n-stearyl methacrylate, stearyl acrylate, t-butyl acrylate, and isobornyl acrylate.

When the alkyl (meth)acrylate (A1) is an alkyl (meth)acrylate having an alicyclic structure, the alicyclic structure can be a cycloparaffin structure typically having 5 or more carbon atoms (e.g., 5 to 7). Examples of alkyl (meth)acrylates having an alicyclic structure and having a homopolymer Tg of 30°C or higher include isobornyl methacrylate, cyclohexyl methacrylate, dicyclopentanyl methacrylate, cyclododecyl methacrylate, methylcyclohexyl methacrylate, trimethylcyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, and 1-adamantyl methacrylate.

These alkyl (meth)acrylates (A1) may be used alone or in combination of two or more. The alkyl (meth)acrylate (A1) may be, for example, at least one selected from the group consisting of alkyl methacrylates having an alkyl group with 1 to 4 carbon atoms and alkyl methacrylates having an alicyclic structure, or at least one selected from the group consisting of methyl methacrylate, tert-butyl methacrylate, isobornyl methacrylate, and cyclohexyl methacrylate.

From the viewpoint of achieving superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the Tg of the alkyl (meth)acrylate (A1) may be 50°C or higher, 60°C or higher, 80°C or higher, or 100°C or higher, and may be, for example, 200°C or lower, 150°C or lower, or 120°C or lower.

From the viewpoint of excellent mechanical strength and heat resistance durability of the adhesive layer, the content of alkyl (meth)acrylate (A1) may be 1% by mass or more, 2% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 30% by mass or less, 20% by mass or less, 15% by mass or less, or 13% by mass or less, based on the total amount of monomer units contained in the (meth)acrylic resin. When the content of alkyl (meth)acrylate whose homopolymer has a Tg of 30°C or more is within the above range, the cohesiveness of the adhesive is improved, thereby further improving the mechanical strength of the adhesive layer, and the adhesive layer also has excellent flexibility and adhesiveness, which is more advantageous from the viewpoint of heat resistance durability.

The (meth)acrylic resin may contain, as a monomer unit, an alkyl (meth)acrylate (hereinafter also referred to as alkyl (meth)acrylate (A2)) whose homopolymer has a glass transition temperature of less than 30°C. The alkyl group in the alkyl (meth)acrylate (A2) may be linear or branched. The alkyl (meth)acrylate (A2) may also be an alkyl (meth)acrylate having an alicyclic structure (e.g., cycloalkyl (meth)acrylate). The number of carbon atoms in the alkyl group in the alkyl (meth)acrylate (A2) may be 1 or more, or 2 or more, and may be 12 or less, 10 or less, 8 or less, or 5 or less.

Examples of alkyl (meth)acrylates (A2) include alkyl (meth)acrylates whose homopolymer Tg is 0°C or higher and lower than 30°C, and alkyl (meth)acrylates whose homopolymer Tg is lower than 0°C.

An example of an alkyl (meth)acrylate whose homopolymer has a Tg of 0°C or higher and lower than 30°C is methyl acrylate.

Examples of alkyl (meth)acrylates whose homopolymer Tg is less than 0°C include alkyl acrylates with alkyl groups having 2 to 12 carbon atoms, such as ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, i-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, i-octyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, i-nonyl acrylate, n-decyl acrylate, i-decyl acrylate, and n-dodecyl acrylate, and alkyl methacrylates with alkyl groups having 5 to 12 carbon atoms, such as n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, and n-dodecyl methacrylate.

These alkyl (meth)acrylates (A2) may be used alone or in combination of two or more. The alkyl (meth)acrylate (A2) may include both alkyl (meth)acrylates having a homopolymer Tg of 0°C or higher and lower than 30°C, and alkyl (meth)acrylates having a homopolymer Tg of lower than 0°C.

The alkyl (meth)acrylate having a homopolymer Tg of 0°C or higher and lower than 30°C may be, for example, methyl acrylate.

The alkyl (meth)acrylate having a homopolymer Tg of less than 0°C may contain an alkyl acrylate having an alkyl group with 2 to 10 carbon atoms, an alkyl acrylate having an alkyl group with 3 to 8 carbon atoms, or an alkyl acrylate having an alkyl group with 4 to 6 carbon atoms, in order to further improve the conformability (or flexibility or adhesion) to the optical film.

The Tg of an alkyl (meth)acrylate whose homopolymer has a Tg of 0°C or higher but lower than 30°C may be 2°C or higher, or 5°C or higher, and may be 25°C or lower, 20°C or lower, or 15°C or lower.

The Tg of an alkyl (meth)acrylate whose homopolymer has a Tg of less than 0°C may be -10°C or lower, -20°C or lower, or -30°C or lower, and may be, for example, -100°C or higher, -80°C or higher, or -60°C or higher.

The content of alkyl (meth)acrylates whose homopolymer Tg is 0°C or more and less than 30°C may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total amount of monomer units contained in the (meth)acrylic resin, and may be 50% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, or 20% by mass or less.

The content of alkyl (meth)acrylates whose homopolymer Tg is less than 0°C may be 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, based on the total amount of monomer units contained in the (meth)acrylic resin, and may be 90% by mass or less, 80% by mass or less, or 75% by mass or less.

The content of alkyl (meth)acrylate (A2) may be 20% by mass or more, 40% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more, based on the total amount of monomer units contained in the (meth)acrylic resin, and may be 95% by mass or less, 93% by mass or less, or 90% by mass or less.

The (meth)acrylic resin may contain a monomer having a polar group as a monomer unit. The monomer having a polar group is a monomer that is copolymerizable with the above-mentioned alkyl (meth)acrylate (A1) and alkyl (meth)acrylate (A2), and has a polar group such as a hydroxy group, a carboxy group, a substituted or unsubstituted amino group, or a heterocyclic group such as an epoxy group. The monomer having a polar group may have, for example, at least one of a hydroxy group and a carboxy group. The monomer having a polar group may include, for example, at least one of a (meth)acrylate having a hydroxy group and a monomer having a carboxy group.

The monomer having a hydroxy group may be a (meth)acrylate having a hydroxy group (hereinafter also referred to as a "hydroxy group-containing (meth)acrylate"). The hydroxy group-containing (meth)acrylate may be, for example, a (meth)acrylate having a hydroxyalkyl group. The number of carbon atoms in the hydroxyalkyl group may be 1 or more, or 2 or more, and may be 12 or less, 10 or less, 8 or less, 5 or less, or 4 or less.

(Meth)acrylates having a hydroxy group may contain, in addition to the hydroxy group, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), a cycloalkyl group (e.g., a cyclopentyl group, a cyclohexyl group, etc.), an aryl group (e.g., a phenyl group, and an alkylphenyl group (e.g., a tolyl group, a xylyl group, etc.)), an aralkyl group (e.g., a benzyl group), an alkoxy group (e.g., an alkoxy group having 1 to 4 carbon atoms, such as a methoxy group, an ethoxy group), a polyoxyalkylene group (e.g., a dioxyethylene group), a cycloalkoxy group (e.g., For example, the (meth)acrylate may have a substituent such as a cycloalkyloxy group having 5 to 10 carbon atoms, such as a cyclohexyloxy group, an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), an alkylthio group (e.g., an alkylthio group having 1 to 4 carbon atoms, such as a methylthio group or an ethylthio group), a cycloalkylthio group (e.g., a cyclohexylthio group), an arylthio group (e.g., a thiophenoxy group), an aralkylthio group (e.g., a benzylthio group), an acyl group (e.g., an acetyl group), a nitro group, or a cyano group. The (meth)acrylate having a hydroxy group may be, for example, a (meth)acrylate having a hydroxy group and one or more groups selected from the group consisting of a halogen atom, an alkoxy group, and an aryloxy group.

Examples of hydroxy group-containing (meth)acrylates include 1-hydroxy C1-C8 alkyl (meth)acrylates such as 1-hydroxymethyl (meth)acrylate, 1-hydroxyethyl (meth)acrylate, 1-hydroxyheptyl (meth)acrylate, 1-hydroxybutyl (meth)acrylate, and 1-hydroxypentyl (meth)acrylate; 2-hydroxy C2-C9 alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxypentyl (meth)acrylate, and 2-hydroxyhexyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 3-hydroxy C3 to C10 alkyl (meth)acrylates such as acrylate, 3-hydroxypentyl (meth)acrylate, 3-hydroxyhexyl (meth)acrylate, and 3-hydroxyheptyl (meth)acrylate; 4-hydroxy C4 to C11 alkyl (meth)acrylates such as 4-hydroxybutyl (meth)acrylate, 4-hydroxypentyl (meth)acrylate, 4-hydroxyhexyl (meth)acrylate, 4-hydroxyheptyl (meth)acrylate, and 4-hydroxyoctyl (meth)acrylate; 2-chloro-2-hydroxypropyl (meth)acrylate; 3-chloro-2-hydroxypropyl (meth)acrylate; and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

These hydroxy group-containing (meth)acrylates may be used alone or in combination of two or more. From the viewpoint of providing superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the hydroxy group-containing (meth)acrylate may be a hydroxyalkyl (meth)acrylate, and may be at least one selected from the group consisting of 2-hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate; and 3-hydroxyalkyl (meth)acrylates such as 3-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 3-hydroxypentyl (meth)acrylate. From the viewpoint of providing superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the hydroxy group-containing (meth)acrylate may include a 2-hydroxyalkyl (meth)acrylate or may include 2-hydroxyethyl (meth)acrylate. 2-Hydroxyethyl (meth)acrylate is advantageous for forming a uniform crosslinked structure, which can further improve the mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer.

From the viewpoint of achieving superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the content of the hydroxy group-containing (meth)acrylate may be 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more, and may be 10% by mass or less, 8% by mass or less, 5.5% by mass or less, 4% by mass or less, 3% by mass or less, or 2.5% by mass or less, based on the total amount of monomer units contained in the (meth)acrylic resin. The content of the hydroxy group-containing (meth)acrylate may be, for example, 0.3% by mass or more and 5.5% by mass or less, 0.5% by mass or more and 3% by mass or less, or 0.5% by mass or more and 2.5% by mass or less.

Examples of monomers having a carboxy group (hereinafter also referred to as "carboxy group-containing monomers") include (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, and carboxyalkyl (meth)acrylates (e.g., carboxyethyl (meth)acrylate and carboxypentyl (meth)acrylate). These carboxy group-containing monomers may be used alone or in combination of two or more. The carboxy group-containing monomer may contain acrylic acid. Acrylic acid promotes the reaction between the hydroxy group-containing (meth)acrylate and the crosslinking agent and can contribute to the formation of a uniform crosslinked structure, thereby further improving the mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer.

The content of the carboxyl group-containing monomer may be 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, based on the total amount of monomer units contained in the (meth)acrylic resin, from the viewpoint of the mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, and may be 5.5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The mass ratio of the carboxy group-containing monomer content to the hydroxy group-containing (meth)acrylate content (carboxy group-containing monomer content/hydroxy group-containing (meth)acrylate content) may be 0.06 or more, 0.08 or more, or 0.1 or more, and may be 1.0 or less, 0.8 or less, or 0.7 or less. When the polar group-containing monomer includes a hydroxy group-containing (meth)acrylate and a carboxy group-containing monomer, and the mass ratio of the carboxy group-containing monomer content to the hydroxy group-containing (meth)acrylate content is within the above range, a crosslinked structure is likely to be formed uniformly in the adhesive, and the adhesive layer tends to have better mechanical strength and heat resistance durability. The mass ratio of the carboxy group-containing monomer content to the hydroxy group-containing (meth)acrylate content may be, for example, 0.06 or more and 1.0 or less, or 0.1 or more and 0.7 or less.

Examples of (meth)acrylates having a substituted or unsubstituted amino group include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylate. These (meth)acrylates having a substituted or unsubstituted amino group may be used alone or in combination of two or more. From the perspective of further improving the releasability of a separate film when laminated to the pressure-sensitive adhesive layer, the (meth)acrylic resin may be substantially free of a monomer having a substituted or unsubstituted amino group as a monomer unit. Note that "the (meth)acrylic resin is substantially free of a monomer having a substituted or unsubstituted amino group" means that the content of (meth)acrylates having a substituted or unsubstituted amino group, based on the total amount of monomer units contained in the (meth)acrylic resin, is less than 1.0 mass%.

Examples of (meth)acrylates having a heterocyclic group such as an epoxy group include acryloylmorpholine, vinylcaprolactam, N-vinyl-2-pyrrolidone, vinylpyridine, tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, glycidyl (meth)acrylate, and 2,5-dihydrofuran. These (meth)acrylates having a heterocyclic group may be used alone or in combination of two or more.

(Meth)acrylic resins may contain other monomers as monomer units. Examples of other monomers include substituted alkyl (meth)acrylates, (meth)acrylamide monomers, styrene monomers, vinyl monomers, and monomers having multiple (meth)acryloyl groups within the molecule.

Substituent-containing alkyl (meth)acrylates are, for example, alkyl (meth)acrylates in which a substituent (excluding polar groups such as carboxy groups) has been introduced into the alkyl group of the alkyl (meth)acrylate (i.e., the hydrogen atom of the alkyl group has been replaced with a substituent). Examples of such substituents include aryl groups (such as phenyl groups), aryloxy groups (such as phenoxy groups), and alkoxy groups (such as methoxy groups and ethoxy groups). Substituent-containing alkyl acrylates include, for example, alkoxyalkyl acrylates (such as 2-methoxyethyl acrylate and ethoxymethyl acrylate), aryloxyalkyl acrylates (such as phenoxyethyl acrylate), aryloxypolyalkylene glycol monoacrylates, and polyalkylene glycol monoacrylates. These substituent-containing alkyl (meth)acrylates may be used alone or in combination of two or more.

Examples of (meth)acrylamide monomers include N-methylol (meth)acrylamide, N-(2-hydroxyethyl) (meth)acrylamide, N-(3-hydroxypropyl) (meth)acrylamide, N-(4-hydroxybutyl) (meth)acrylamide, N-(5-hydroxypentyl) (meth)acrylamide, N-(6-hydroxyhexyl) (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, and N-isopropyl (meth)acrylamide. isopropyl(meth)acrylamide, N-(3-dimethylaminopropyl)(meth)acrylamide, N-(1,1-dimethyl-3-oxobutyl)(meth)acrylamide, N-[2-(2-oxo-1-imidazolidinyl)ethyl](meth)acrylamide, 2-(meth)acryloylamino-2-methyl-1-propanesulfonic acid, N-(methoxymethyl)(meth)acrylamide, N-(ethoxymethyl)(meth)acrylamide, N-(propoxymethyl)(meth)acrylamide N-(1-methylethoxymethyl)(meth)acrylamide, N-(1-methylpropoxymethyl)(meth)acrylamide, N-(2-methylpropoxymethyl)(meth)acrylamide [alias: N-(isobutoxymethyl)(meth)acrylamide], N-(butoxymethyl)(meth)acrylamide, N-(1,1-dimethylethoxymethyl)(meth)acrylamide, N-(2-methoxyethyl)(meth)acrylamide, N-(2-ethoxyethyl)(meth)acrylamide Examples of (meth)acrylamide monomers include N-(2-propoxyethyl)(meth)acrylamide, N-[2-(1-methylethoxy)ethyl](meth)acrylamide, N-[2-(1-methylpropoxy)ethyl](meth)acrylamide, N-[2-(2-methylpropoxy)ethyl](meth)acrylamide (also known as N-(2-isobutoxyethyl)acrylamide), N-(2-butoxyethyl)(meth)acrylamide, and N-[2-(1,1-dimethylethoxy)ethyl](meth)acrylamide. These (meth)acrylamide monomers may be used alone or in combination of two or more.

Examples of styrene-based monomers include styrene; alkyl styrenes such as methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene, and octylstyrene; halogenated styrenes such as fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene, and iodostyrene; nitrostyrene; acetylstyrene; methoxystyrene; and divinylbenzene. These styrene-based monomers may be used alone or in combination of two or more.

Examples of vinyl monomers include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, and vinyl laurate; vinyl halides such as vinyl chloride and vinyl bromide; vinylidene halides such as vinylidene chloride; nitrogen-containing aromatic vinyls such as vinylpyridine, vinylpyrrolidone, and vinylcarbazole; and conjugated dienes such as butadiene, isoprene, and chloroprene. These vinyl monomers may be used alone or in combination of two or more.

Examples of monomers having multiple (meth)acryloyl groups in their molecules include monomers having two (meth)acryloyl groups in their molecules, such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; and monomers having three (meth)acryloyl groups in their molecules, such as trimethylolpropane tri(meth)acrylate. These monomers having multiple (meth)acryloyl groups in their molecules may be used alone or in combination of two or more.

From the viewpoint of achieving superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the weight average molecular weight (Mw) of the (meth)acrylic resin may be 1 million or more, 1.1 million or more, 1.2 million or more, 1.3 million or more, or 1.5 million or more, and may be 3.2 million or less, 3.1 million or less, 3 million or less, 2.9 million or less, 2.5 million or less, or 1.7 million or less. The Mw of the (meth)acrylic resin may be, for example, 1 million to 3.2 million, 1.1 million to 3.1 million, 1.2 million to 3 million, 1.3 million to 2.9 million, 1.5 million to 2.5 million, or 1.5 million to 1.7 million.

The molecular weight distribution (Mw/Mn), expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (meth)acrylic resin, may be, for example, 1.5 or more, 2 or more, or 2.5 or more, and may be 10 or less, 8 or less, 7 or less, 5 or less, 4 or less, or 3 or less. Mw and Mn can be analyzed by gel permeation chromatography (GPC) and are values converted into standard polystyrene.

From the viewpoint of achieving superior mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer, the Tg of the (meth)acrylic resin may be -45°C or higher, -40°C or higher, -38°C or higher, or -35°C or higher, and may be -10°C or lower, -15°C or lower, -20°C or lower, or -25°C or lower. The Tg of the (meth)acrylic resin may be, for example, -45°C to -10°C, -40°C to -15°C, or -38°C to -20°C. The Tg of the (meth)acrylic resin can be determined by DSC measurement in a nitrogen atmosphere at a heating rate of 10°C/min.

A (meth)acrylic resin (or a mixture thereof when two or more types are combined) may have a viscosity of 20 Pa·s or less, or even 0.1 Pa·s or more and 7 Pa·s or less, at 25°C when dissolved in ethyl acetate to a concentration of 20% by mass. The viscosity can be measured using a Brookfield viscometer.

The (meth)acrylic resin content may be 80% by mass or more, 90% by mass or more, or 95% by mass or more, and may be 99% by mass or less, or 98% by mass or less, based on the total mass of the solids in the pressure-sensitive adhesive composition.

(Meth)acrylic resins can be produced by known methods, such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. A polymerization initiator may be used in the production of the (meth)acrylic resin. The polymerization initiator is used in an amount of, for example, 0.001 to 5 parts by mass per 100 parts by mass of the total of all monomers used in the production of the (meth)acrylic resin. (Meth)acrylic resins may also be produced by a method in which polymerization is promoted by active energy rays, such as ultraviolet rays.

Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. Examples of thermal polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-hydroxymethylpropionitrile); lauryl peroxide; Examples of suitable photopolymerization initiators include organic peroxides such as benzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, dipropyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, and (3,5,5-trimethylhexanoyl) peroxide; and inorganic peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide. Examples of photopolymerization initiators include 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone. Other examples of polymerization initiators include redox initiators that use a peroxide in combination with a reducing agent.

(Meth)acrylic resins are manufactured, for example, by solution polymerization. One example of a solution polymerization method involves mixing monomers and an organic solvent to prepare a mixed solution, adding a thermal polymerization initiator to the mixed solution under a nitrogen atmosphere, and stirring the mixture at 40 to 90°C (e.g., 60 to 80°C) for approximately 3 to 10 hours. To control the reaction, the monomers and thermal polymerization initiator may be added continuously or intermittently during polymerization. The monomers and thermal polymerization initiator may be added in a dissolved state in an organic solvent. Examples of organic solvents that can be used include aromatic hydrocarbons such as toluene and xylene; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as propyl alcohol and isopropyl alcohol; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

<Crosslinking agent>
The pressure-sensitive adhesive composition according to one embodiment includes a crosslinking agent. When the (meth)acrylic resin contains a monomer having a polar group as a monomer unit, the polar group is present in the (meth)acrylic resin. The crosslinking agent can be a compound that reacts with the polar group that may be present in the (meth)acrylic resin to form a crosslink. Examples of crosslinking agents include isocyanate-based compounds, epoxy-based compounds, aziridine-based compounds, and metal chelate-based compounds. Of these, isocyanate-based compounds, epoxy-based compounds, and aziridine-based compounds have at least two functional groups in the molecule that can react with the polar group that may be present in the (meth)acrylic resin. These crosslinking agents may be used alone or in combination of two or more.

The crosslinking agent preferably contains an isocyanate compound. Isocyanate compounds are preferably compounds having at least two isocyanato groups (-NCO) in the molecule, such as aliphatic isocyanate compounds (e.g., hexamethylene diisocyanate), alicyclic isocyanate compounds (e.g., isophorone diisocyanate), and aromatic isocyanate compounds (e.g., tolylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, etc.). The crosslinking agent may also be an adduct of an isocyanate compound with a polyhydric alcohol compound (e.g., an adduct with glycerol, trimethylolpropane, etc.), an isocyanurate, a biuret-type compound, or a derivative of a urethane prepolymer-type isocyanate compound obtained by addition reaction with a polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol, etc. These crosslinking agents may be used alone or in combination of two or more.

Epoxy compounds are compounds that contain at least two epoxy groups in their molecules. Specific examples of these compounds include bisphenol A epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, N,N-diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane. These epoxy compounds may be used alone or in combination of two or more.

Aziridine compounds, also known as ethyleneimines, are compounds that contain at least two three-membered ring structures consisting of one nitrogen atom and two carbon atoms within the molecule. Specific examples of these compounds include diphenylmethane-4,4'-bis(1-aziridinecarboxamide), toluene-2,4-bis(1-aziridinecarboxamide), triethylenemelamine, isophthaloylbis-1-(2-methylaziridine), tris-1-aziridinylphosphine oxide, hexamethylene-1,6-bis(1-aziridinecarboxamide), trimethylolpropane-tris-β-aziridinylpropionate, and tetramethylolmethane-tris-β-aziridinylpropionate.

Examples of metal chelate compounds include compounds in which acetylacetone or ethyl acetoacetate is coordinated with polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

Among these, the crosslinking agent may be, for example, at least one selected from the group consisting of aromatic isocyanate compounds, aliphatic isocyanate compounds, and adducts of these with polyhydric alcohol compounds. When the crosslinking agent contains an aromatic isocyanate compound and/or an adduct of these with polyhydric alcohol compounds, a uniform crosslinked structure is more likely to be formed, and the mechanical strength and heat resistance durability of the pressure-sensitive adhesive layer tend to be more easily improved.

The content of the crosslinking agent may be 0.01 parts by mass or more, 0.05 parts by mass or more, or 0.1 parts by mass or more, and may be 5 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less, per 100 parts by mass of the solid content of the (meth)acrylic resin (or the total amount of the (meth)acrylic resins if two or more types are used).

<Silane Compound>
The pressure-sensitive adhesive composition according to one embodiment includes a silane compound. The silane compound may include, for example, a compound represented by the following formula (1-1):

In the above formula (1-1), R ¹¹¹ represents an alkyl group having 1 to 5 carbon atoms, R ¹¹² and R ¹¹³ each independently represent an alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms, L ¹ represents an alkylene group having 1 to 20 carbon atoms or a group in which at least one —CH ₂ — contained in an alkylene group having 1 to 20 carbon atoms is substituted with —NH— or —O—, and X represents a thiol group (—SH), an amino group (—NH ₂ ), an epoxy group or an alicyclic epoxy group.

The alkyl groups having 1 to 5 carbon atoms represented by R ¹¹¹ to R ¹¹³ in formula (1-1) may each independently be an alkyl group having 1 to 4 carbon atoms, an alkyl group having 1 to 3 carbon atoms, or an alkyl group having 1 to 2 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, and a pentyl group such as an n-pentyl group, an i-pentyl group, or a t-pentyl group.

The alkoxy groups having 1 to 5 carbon atoms represented by R ¹¹² and R ¹¹³ in formula (1-1) may each independently be an alkoxy group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 2 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, a t-butoxy group, and pentyloxy groups such as an n-pentyloxy group, an i-pentyloxy group, and a t-pentyloxy group.

The alkylene group having 1 to 20 carbon atoms represented by ^L1 in formula (1-1) may be, for example, a group represented by —(CH ₂ ) _n — (n represents an integer of 1 to 20). Here, n (the number of carbon atoms in the alkylene group) may be 2 or more, 4 or more, 6 or more, or 8 or more, and may be 18 or less, 15 or less, or 12 or less.

In the group represented by L ¹ in formula (1-1), in which at least one —CH ₂ — (methylene group) contained in an alkylene group having 1 to 20 carbon atoms is substituted with —NH— or —O—, the alkylene group having 1 to 20 carbon atoms (the alkylene group before at least one —CH ₂ — is substituted with —NH— or —O—) may be, for example, a group represented by —(CH ₂ ) _n — (n represents an integer of 1 to 20). Here, n (the number of carbon atoms in the alkylene group) may be 2 or more, 4 or more, 6 or more, or 8 or more, and may be 18 or less, 15 or less, or 12 or less.

When L ¹ is a group in which at least one —CH ₂ — contained in an alkylene group having 1 to 20 carbon atoms is substituted with —NH— or —O—, only one methylene group contained in the alkylene group having 1 to 20 carbon atoms may be substituted with —NH— or —O—, or two or more methylene groups contained in the alkylene group having 1 to 20 carbon atoms may each independently be substituted with —NH— or —O—. When two or more methylene groups are substituted, the multiple substituents (—NH— and/or —O—) may be separated from each other by an alkylene group having two or more carbon atoms.

The epoxy group represented by X in formula (1-1) can be a group represented by the following formula (a1):

In formula (a1), * represents a bond.

An example of the alicyclic epoxy group represented by X in formula (1-1) is a monovalent group in which one hydrogen atom has been removed from the structure represented by formula (a2) below.

In formula (a2), n represents an integer of 1 to 5. n may be 1 to 3, or 1 or 2.

Examples of silane compounds represented by formula (1-1) include 3-glycidoxypropyltrialkoxysilanes such as 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane; 3-glycidoxypropylalkyldialkoxysilanes such as 3-glycidoxypropylmethyldiethoxysilane and 3-glycidoxypropylmethyldimethoxysilane; 8-glycidoxyoctyltrialkoxysilanes such as 8-glycidoxyoctyltrimethoxysilane and 8-glycidoxyoctyltriethoxysilane; and 2-(3,4-epoxycyclohexyl)ethyltrialkoxysilanes such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

The silane compound may include a silane compound other than the compound represented by formula (1-1). Examples of silane compounds other than the compound represented by formula (1-1) include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 1,3-bis(3'-trimethoxypropyl)urea, 1,6-bis(trimethoxysilyl)hexane, and 1,8-bis(trimethoxysilyl)octane.

The silane compound may include a silicone oligomer. Examples of silicone oligomers include mercaptopropyl group-containing oligomers such as 3-mercaptopropyltrimethoxysilane-tetramethoxysilane oligomer (an oligomer containing 3-mercaptopropyltrimethoxysilane and tetramethoxysilane as monomer units; the same applies to similar expressions below), 3-mercaptopropyltrimethoxysilane-tetraethoxysilane oligomer, 3-mercaptopropyltriethoxysilane-tetramethoxysilane oligomer, and 3-mercaptopropyltriethoxysilane-tetraethoxysilane oligomer; mercaptomethyltrimethoxysilane-tetramethoxysilane oligomer, mercaptomethyltrimethoxysilane-tetraethoxysilane oligomer, and mercaptomethyltriethoxysilane-tetramethoxysilane. oligomers, mercaptomethyl group-containing oligomers such as mercaptomethyltriethoxysilane-tetraethoxysilane oligomer; 3-methacryloyloxypropyltrimethoxysilane-tetramethoxysilane oligomer, 3-methacryloyloxypropyltrimethoxysilane-tetraethoxysilane oligomer, 3-methacryloyloxypropyltriethoxysilane-tetramethoxysilane oligomer, 3-methacryloyloxypropyltriethoxysilane-tetraethoxysilane oligomer, 3-methacryloyloxypropylmethyldimethoxysilane-tetramethoxysilane oligomer, 3-methacryloyloxypropylmethyldimethoxysilane-tetraethoxysilane oligomer, 3-methacryloyloxypropylmethyldiethoxysilane-tetramethoxy Silane oligomers, methacryloyloxypropyl group-containing oligomers such as 3-methacryloyloxypropylmethyldiethoxysilane-tetraethoxysilane oligomer; 3-acryloyloxypropyltrimethoxysilane-tetramethoxysilane oligomer, 3-acryloyloxypropyltrimethoxysilane-tetraethoxysilane oligomer, 3-acryloyloxypropyltriethoxysilane-tetramethoxysilane oligomer, 3-acryloyloxypropyltriethoxysilane-tetraethoxysilane oligomer, 3-acryloyloxypropylmethyldimethoxysilane-tetramethoxysilane oligomer, 3-acryloyloxypropylmethyldimethoxysilane-tetraethoxysilane oligomer, 3-acryloyloxypropylmethyldiethoxysilane Examples include acryloyloxypropyl group-containing oligomers such as silane-tetramethoxysilane oligomer and 3-acryloyloxypropylmethyldiethoxysilane-tetraethoxysilane oligomer; and vinyl group-containing oligomers such as vinyltrimethoxysilane-tetramethoxysilane oligomer, vinyltrimethoxysilane-tetraethoxysilane oligomer, vinyltriethoxysilane-tetramethoxysilane oligomer, vinyltriethoxysilane-tetraethoxysilane oligomer, vinylmethyldimethoxysilane-tetramethoxysilane oligomer, vinylmethyldimethoxysilane-tetraethoxysilane oligomer, vinylmethyldiethoxysilane-tetramethoxysilane oligomer, and vinylmethyldiethoxysilane-tetraethoxysilane oligomer.

The content of the silane compound may be 0.01 parts by mass or more, 0.05 parts by mass or more, 0.1 parts by mass or more, or 0.2 parts by mass or more, relative to 100 parts by mass of the solid content of the (meth)acrylic resin (or the total amount of the resins when two or more types are used), from the viewpoint of easily improving the adhesion (or bond) between the pressure-sensitive adhesive layer and a metal layer, glass substrate, etc., and being advantageous for improving peel resistance, etc., and may be 5 parts by mass or less, 4 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less, from the viewpoint of easily suppressing bleed-out of the silane compound from the pressure-sensitive adhesive layer.

<Ionic Compounds>
The pressure-sensitive adhesive composition according to one embodiment includes an ionic compound, which includes an anion represented by the following formula (1):

In formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent.

When used in touch-input liquid crystal display devices such as smartphones, the adhesive layer may be disposed so as to come into contact with a metal layer composed of metal wiring. When an adhesive layer containing an ionic compound is applied to a metal layer, corrosion of the metal layer may progress, particularly in high-temperature, high-humidity environments. When corrosion, particularly pitting corrosion, occurs, it can cause serious problems when the metal layer is thin or the metal wiring in the metal layer has a narrow line width, as it penetrates the metal layer. However, in one embodiment of the adhesive composition, the ionic compound contains an anion represented by formula (1) above, and therefore this adhesive composition makes it possible to form an adhesive layer that inhibits corrosion of the metal layer when attached to the metal layer.

The halogen atoms represented by R ¹ to R ⁴ in formula (1) may each independently be one selected from the group consisting of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The alkyl group, alkenyl group, alkynyl group, aryl group, and heterocyclic group represented by R ¹ to R ⁴ may be unsubstituted or may have one or more substituents. Examples of substituents that these groups may have include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom; alkoxy groups such as methoxy group, ethoxy group, and t-butoxy group; aryloxy groups such as phenoxy group and p-tolyloxy group; alkoxycarbonyl groups such as methoxycarbonyl group and butoxycarbonyl group; vinyloxycarbonyl group; aryloxycarbonyl groups such as phenoxycarbonyl group and aryloxycarbonyl group; acyloxy groups such as acetoxy group, propionyloxy group, and benzoyloxy group; acyl groups such as acetyl group, benzoyl group, naphthoyl group, isobutyryl group, acryloyl group, methacryloyl group, and methoxalyl group; benzoyl groups substituted with a halogen atom, alkyl group, alkylsulfanyl group, arylsulfanyl group, dialkylamino group, nitro group, cyano group, or trifluoromethyl group; alkylsulfanyl groups such as methylsulfanyl group and t-butylsulfanyl group; phenylsulfanyl alkyl groups such as methylamino group and cyclohexylamino group; dialkylamino groups such as dimethylamino group, diethylamino group, morpholino group and piperidino group; arylamino groups such as phenylamino group and p-tolylamino group; alkyl groups such as methyl group, ethyl group, t-butyl group and dodecyl group; aryl groups such as phenyl group, p-tolyl group, xylyl group, cumenyl group, naphthyl group, anthryl group and phenanthryl group; hydroxyl group; carboxyl group; sulfonamido group; formyl group; mercapto group; sulfo group; mesyl group; p-toluenesulfonyl group; amino group; nitro group; nitroso group; cyano group; trifluoromethyl group; trichloromethyl group; trimethylsilyl group; phosphinico group; phosphono group; alkylsulfonyl group; arylsulfonyl group; trialkylammonium group; dimethylsulfoniumyl group; and triphenylphenacylphosphoniumyl group.

The substituent that the alkyl group, alkenyl group, alkynyl group, aryl group, and heterocyclic group represented by R ¹ to R ⁴ may have is preferably an electron-withdrawing substituent. By substituting with an electron-withdrawing substituent, the ionic compound is more likely to dissociate, and antistatic performance can be improved. Examples of the electron-withdrawing substituent include a halogen atom, a cyano group, a carboxyl group, a nitro group, a nitroso group, an acyl group, an alkyloxycarbonyl group, an aryloxycarbonyl group, an alkylsulfonyl group, an arylsulfonyl group, a trialkylammonium group, an amide group, a perfluoroalkyl group, a perfluoroalkylthio group, a perfluoroalkylcarbonyl group, a sulfonamide group, and a 4-cyanophenyl group.

The alkyl group which may have a substituent represented by R ¹ to R ⁴ may be, for example, an alkyl group which may have a substituent and has 1 to 30 carbon atoms. The number of carbon atoms in the alkyl group may be 1 to 20, 1 to 15, 1 to 12, or 1 to 10. Examples of the alkyl group which may have a substituent include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, an octadecyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a 1-ethylpentyl group, a cyclopentyl group, a cyclohexyl group, a trifluoromethyl group, a 2-ethylhexyl group, a phenacyl group, a 1-naphthoylmethyl group, a 2-naphthoylmethyl group, a 4-methylsulfanylphenacyl group, a 4-phenylsulfanylphenacyl group, a 4-dimethylaminophenacyl group, a 4-cyanophenacyl group, a 4-methylphenacyl group, a 2-methylphenacyl group, a 3-fluorophenacyl group, a 3-trifluoromethylphenacyl group, and a 3-nitrophenacyl group.

The optionally substituted alkenyl group represented by R ¹ to R ⁴ may be, for example, an optionally substituted alkenyl group having 2 to 10 carbon atoms. Examples of the optionally substituted alkenyl group include a vinyl group, an allyl group, and a styryl group.

The alkynyl group optionally having a substituent represented by R ¹ to R ⁴ may be, for example, an alkynyl group having 2 to 10 carbon atoms optionally having a substituent. Examples of the alkynyl group optionally having a substituent include an ethynyl group, a propynyl group, and a propargyl group.

The aryl group represented by R ¹ to R ⁴ , which may have a substituent, may be, for example, an aryl group having 6 to 30 carbon atoms, which may have a substituent. Examples of the aryl group which may have a substituent include a phenyl group, a biphenyl group, a 1-naphthyl group, a 2-naphthyl group, a 9-anthryl group, a 9-phenanthryl group, a 1-pyrenyl group, a 5-naphthacenyl group, a 1-indenyl group, a 2-azulenyl group, a 9-fluorenyl group, a terphenyl group, a quaterphenyl group, an o-tolyl group, a m-tolyl group, a p-tolyl group, a xylyl group, an o-cumenyl group, a m-cumenyl group, a p-cumenyl group, a mesityl group, a pentalenyl group, a binaphthalenyl group, a ternaphthalenyl group, a quaternaphthalenyl group, a heptalenyl group, a biphenylenyl group, an indacenyl group, a fluoran and phenylenyl, acenaphthylenyl, aceanthrylenyl, phenalenyl, fluorenyl, anthryl, bianthracenyl, teranthracenyl, quaternaryanthracenyl, anthraquinolyl, phenanthryl, triphenylenyl, pyrenyl, chrysenyl, naphthacenyl, pleiadenyl, picenyl, perylenyl, pentaphenyl, pentacenyl, tetraphenylenyl, hexaphenyl, hexacenyl, rubicenyl, coronenyl, trinaphthylenyl, heptaphenyl, heptacenyl, pyrantrenyl, and ovalenyl groups.

The heterocyclic group which may have a substituent represented by R ¹ to R ⁴ may be, for example, an aromatic or aliphatic heterocyclic ring containing at least one atom selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, and a phosphorus atom. Examples of the heterocyclic group which may have a substituent include a thienyl group, a benzo[b]thienyl group, a naphtho[2,3-b]thienyl group, a thianthrenyl group, a furyl group, a pyranyl group, an isobenzofuranyl group, a chromenyl group, a xanthenyl group, a phenoxathiinyl group, a 2H-pyrrolyl group, a pyrrolyl group, an imidazolyl group, a pyrazolyl group, a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolizinyl group, an isoindolyl group, a 3H-indolyl group, an indolyl group, a 1H-indazolyl group, a purinyl group, a 4H-quinolidinyl group, an isoquinolyl group, a quinolyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxanilyl group, and a quinazolinyl group. , cinnolinyl group, pteridinyl group, 4aH-carbazolyl group, carbazolyl group, β-carbolinyl group, phenanthridinyl group, acridinyl group, perimidinyl group, phenanthrolinyl group, phenazinyl group, phenarsazinyl group, isothiazolyl group, phenothiazinyl group, isoxazolyl group, furazanyl group, phenoxazinyl group, isochromanyl group, chromanyl group, pyrrolidinyl group, pyrrolinyl group, imidazolidinyl group, imidazolinyl group, pyrazolidinyl group, pyrazolinyl group, piperidyl group, piperazinyl group, indolinyl group, isoindolinyl group, quinuclidinyl group, morpholinyl group, and thioxanthryl group.

It is preferable that R ¹ to R ⁴ are each independently an alkyl group which may have a substituent or an aryl group which may have a substituent. It is particularly preferable that ^{R 1} to R ⁴ are each independently an aryl group which may have a substituent.

The anion represented by formula (1) may be an anion represented by the following formula (2):

In formula (2), R ⁵ to R ⁹ each independently represent a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent, and two or more selected from the group consisting of R ⁵ to R ⁹ may be bonded to each other to form a ring.

As the halogen atom, optionally substituted alkyl group, optionally substituted alkenyl group, optionally substituted alkynyl group, optionally substituted aryl group, and optionally substituted heterocyclic group represented by R ⁵ to R ⁹ , the same groups as those described above as the halogen atom, optionally substituted alkyl group, optionally substituted alkenyl group, optionally substituted alkynyl group, optionally substituted aryl group, and optionally substituted heterocyclic group represented by R ¹ to R ⁴ can be used without any particular limitation.

Among ^R5 to ^R9 , for ^example , ^R5 and ^R6 , R6 and ^R7 , ^R7 and ^R8 , and ^R8 and ^R9 may each independently bond to each other to form a ring together with the carbon atoms to which they are bonded, or ^R5 , R6 and ^R7 , ^R6 , ^R7 and ^R8 , and ^R7 , ^{R8 and R9} may each independently bond to each other to form a ring together with the carbon atoms to which they are bonded.

From the viewpoint of improving the antistatic performance of the ionic compound, and the metal corrosion inhibiting ability and optical durability of the pressure-sensitive adhesive layer-attached optical film and the optical laminate including the same, it is preferable that R ⁵ to R ⁹ are all halogen atoms, and more preferably all fluorine atoms. When R ⁵ to R ⁹ are all fluorine atoms, the anion represented by the above formula (2) is a tetrakis(pentafluorophenyl)borate anion.

The ionic compound contains a cation in addition to the anion represented by formula (1) above. The cation may be an inorganic cation or an organic cation. The cation is preferably an organic cation.

Examples of inorganic cations include alkali metal ions such as lithium cation [Li ⁺ ], sodium cation [Na ⁺ ], and potassium cation [K ⁺ ], and alkaline earth metal ions such as beryllium cation [Be ²⁺ ], magnesium cation [Mg ²⁺ ], and calcium cation [Ca ²⁺ ].

Examples of organic cations include pyridinium cation, N-decylpyridinium cation, imidazolium cation, 1-dodecyl-3-butylimidazolium cation, tetrahydropyrimidium cation, dihydropyrimidium cation, pyrazolium cation, pyrazolinium cation, ammonium cation, trioctylmethylammonium cation, trimethyloctylammonium cation, sulfonium cation, phosphonium cation, tributyldodecylphosphonium cation, and triphenylmethoxymethylphosphonium cation. The organic cation may be a substituted or unsubstituted pyridinium cation, or a substituted or unsubstituted imidazolium cation. The substituted pyridinium cation may be, for example, an N-alkyl-substituted pyridinium cation such as an N-decylpyridinium cation. The substituted imidazolium cation may be, for example, a 1,3-alkyl-substituted imidazolium cation such as a 1-dodecyl-3-butylimidazolium cation.

The organic cation may be, for example, a cation represented by the following formula (3):

In formula (3), R ¹⁰ to R ¹³ each independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent, and two or more selected from the group consisting of R ¹⁰ to R ¹³ may be bonded to each other to form a ring.

As the optionally substituted alkyl group, optionally substituted alkenyl group, optionally substituted alkynyl group, optionally substituted aryl group, and optionally substituted heterocyclic group represented by R ¹⁰ to R ¹³ , the same groups as those described above as the optionally substituted alkyl group, optionally substituted alkenyl group, optionally substituted alkynyl group, optionally substituted aryl group, and optionally substituted heterocyclic group represented by R ¹ to R ⁴ can be used without any particular limitation.

Among R ¹⁰ to R ¹³ , for example, R ¹⁰ and R ¹¹ , R ¹¹ and R ¹² , R ¹² and R ¹³ , and R ¹³ and R ¹⁰ may each independently bond to each other to form a ring together with the nitrogen atom to which they are bonded, or R ¹⁰ , R ¹¹ and R ¹² , R ¹¹ , R ¹² and R ¹³ , and R ¹² , R ¹³ and R ¹⁰ may each independently bond to each other to form a ring together with the nitrogen atom to which they are bonded.

It is preferred that R ¹⁰ to R ¹³ are each independently an alkyl group which may have a substituent or an aryl group which may have a substituent, and that three selected from the group consisting of R ¹⁰ to R ¹³ are bonded to each other to form, together with the N atom to which R ¹⁰ to R ¹³ are bonded, an unsaturated ring structure (including an aromatic ring structure) containing an unsaturated bond.

The organic cation may be, for example, a cation represented by the following formula (4):

In formula (4), R ¹⁴ to R ¹⁷ each independently represent a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, a heterocyclic group which may have a substituent, a hydroxyl group, an ethylene oxide group, a carboxyl group, or a carbonyl group, and may be bonded to each other to form a ring.

The ionic compound may be solid at room temperature (e.g., 23°C). Ionic compounds that are solid at room temperature can retain their antistatic properties for a longer period of time than ionic compounds that are liquid at room temperature.

The content of the ionic compound may be 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, relative to 100 parts by mass of the solid content of the (meth)acrylic resin, from the viewpoint of achieving better antistatic properties, and may be 10 parts by mass or less, 8 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less, from the viewpoint of achieving better metal corrosion inhibition ability and durability of the pressure-sensitive adhesive layer-attached optical film.

<Other ingredients>
The pressure-sensitive adhesive composition may further contain a solvent, a crosslinking catalyst, an ultraviolet absorber, a weather stabilizer, a tackifier, a plasticizer, a softener, a dye, a pigment, an inorganic filler, light-scattering fine particles, a rust inhibitor, a release agent, a resin other than a (meth)acrylic resin, etc. In addition, the pressure-sensitive adhesive composition may contain an ultraviolet-curable compound. When the pressure-sensitive adhesive composition contains an ultraviolet-curable compound, a pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive composition, and then the pressure-sensitive adhesive layer is cured by irradiation with ultraviolet light, thereby making it possible to form a harder pressure-sensitive adhesive layer.

When the adhesive composition contains a crosslinking catalyst in addition to the crosslinking agent, the adhesive layer can be prepared with shorter aging time. Furthermore, when the adhesive composition contains a crosslinking catalyst, lifting or peeling at the interface between the adhesive layer and the adjacent member, as well as foaming of the adhesive layer, can be more effectively suppressed, and the reworkability of the adhesive layer (the property of the adhesive layer being easily peeled off after being attached to an adherend) can also be further improved. Examples of crosslinking catalysts include amine-based compounds such as hexamethylenediamine, ethylenediamine, polyethyleneimine, hexamethylenetetramine, diethylenetriamine, triethylenetetramine, isophoronediamine, trimethylenediamine, polyamino resins, and melamine resins. When an amine-based compound is blended as a crosslinking catalyst in the adhesive composition, an isocyanate-based compound is preferred as the crosslinking agent.

The pressure-sensitive adhesive composition described above can be prepared by mixing the above components. The pressure-sensitive adhesive composition may have a gel fraction of, for example, 50% to 98%, preferably 60% to 95%, or 70% to 90%. The gel fraction can be measured according to the measurement method described in the Examples section below.
<Adhesive Layer>

In one embodiment, the adhesive layer includes the above-mentioned adhesive composition. The adhesive layer may consist of the above-mentioned adhesive composition. The adhesive layer can be obtained, for example, by a method including: dissolving or dispersing each component contained in the above-mentioned adhesive composition in a solvent to prepare a solvent-containing adhesive composition; and applying the adhesive composition onto a substrate film and drying it. The adhesive layer has excellent heat resistance and durability.

The base film may be a plastic film. The plastic film may be a release film (separator) with a release treatment applied to its surface. The release film may be, for example, a film made of various resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyacrylate, with a release treatment such as silicone treatment applied to the surface on which the adhesive layer is formed.

Alternatively, the pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition to the surface of an optical film (details of which will be described later). When forming the pressure-sensitive adhesive layer on the surface of the optical film, the bonding surface of the optical film and/or the bonding surface of the pressure-sensitive adhesive layer may be subjected to a surface activation treatment (e.g., plasma treatment, corona treatment, etc.) as necessary.

The thickness of the adhesive layer may be, for example, 10 μm or more, 15 μm or more, or 18 μm or more, and may be 50 μm or less, 40 μm or less, or 35 μm or less.

<Optical film with pressure-sensitive adhesive layer>
A pressure-sensitive adhesive layer-attached optical film according to one embodiment includes an optical film and the pressure-sensitive adhesive layer provided on at least one surface of the optical film.

Examples of optical films include polarizers; protective films provided to protect the surface of polarizers, etc.; polarizing plates in which a protective film is laminated on one or both sides of a polarizer; retardation films; optical compensation films other than retardation films; anti-glare films with an uneven surface, films with surface anti-reflection functions; reflective films with a reflective surface; semi-transparent reflective films that combine reflective and transparent functions; light diffusion films; hard-coated films, etc.

The pressure-sensitive adhesive layer-attached optical film may comprise one or more types of optical film, or may comprise two or more optical films of the same type. When the pressure-sensitive adhesive layer-attached optical film comprises two or more optical films, an adhesive layer (described below) may be used between the optical films to laminate the two or more optical films. In this case, the adhesive layer may also be part of the optical film. The thickness of the optical film is not particularly limited, but may be, for example, 5 μm or more and 300 μm or less. In this specification, a polarizing plate in which a protective film is laminated on one or both sides of a polarizer is also referred to as a linear polarizing plate.

Examples of polarizers include those in which iodine is oriented (e.g., adsorption orientation) in a polyvinyl alcohol resin layer (e.g., uniaxially stretched polyvinyl alcohol film), and those in which a liquid crystal compound and a dichroic dye are oriented.

The protective film is not particularly limited, but is preferably a translucent (preferably optically transparent) thermoplastic resin film. Examples of thermoplastic resins that can be used to form the protective film include polyolefin resins such as linear polyolefin resins (e.g., polyethylene resins, polypropylene resins, etc.) and cyclic polyolefin resins; cellulose ester resins; polyester resins; polycarbonate resins; (meth)acrylic resins; vinyl alcohol resins such as polyvinyl alcohol and polyvinyl acetate; polystyrene resins; and mixtures and copolymers thereof. In this specification, "(meth)acrylic" refers to "at least one of acrylic and methacrylic resins." These resins may contain one or more additives (e.g., lubricants, plasticizers, dispersants, heat stabilizers, ultraviolet absorbers, infrared absorbers, antistatic agents, antioxidants, light diffusing agents such as fine particles, etc.).

Examples of linear polyolefin resins include linear olefin homopolymers such as polyethylene resin and polypropylene resin, and copolymers containing two or more types of olefins as monomer units.

Cyclic polyolefin resin is a general term for resins polymerized using cyclic olefins as monomer units. Examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers (typically random copolymers) of cyclic olefins with linear olefins such as ethylene or propylene, graft polymers modified with unsaturated carboxylic acids or their derivatives, and hydrogenated versions of these. Of these, norbornene resins using norbornene monomers such as norbornene and polycyclic norbornene monomers as the cyclic olefin are preferred.

Cellulose-based resins are partially or completely esterified products of cellulose, such as cellulose acetate, propionate, and butyrate esters, as well as mixed esters of these. Examples of cellulose-based resins include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

Polyester-based resins are resins other than the above-mentioned cellulose-based resins that have ester bonds and may be composed, for example, of a polycondensation product of a polycarboxylic acid or its derivative with a polyhydric alcohol. Dicarboxylic acids or their derivatives can be used as the polycarboxylic acid or its derivative, and examples of polycarboxylic acids or their derivatives include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. Diols can be used as the polyhydric alcohol, and examples of polyhydric alcohols include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol.

Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexane dimethyl terephthalate, and polycyclohexane dimethyl naphthalate.

Polycarbonate-based resins consist of polymers in which monomer units are bonded via carbonate groups. Polycarbonate-based resins may also be modified polycarbonates, which are resins in which the polymer backbone has been modified, or copolymer polycarbonates.

The (meth)acrylic resin used as the thermoplastic resin constituting the protective film can be a polymer containing primarily (meth)acrylic acid esters as monomer units, and is preferably a copolymer obtained by copolymerizing a (meth)acrylic acid ester with a small amount of other comonomers. The (meth)acrylic resin used as the thermoplastic resin constituting the protective film may contain, as monomer units, methyl methacrylate and methyl acrylate, or may contain methyl methacrylate, methyl acrylate, and a third monofunctional monomer.

Examples of the third monofunctional monomer include methacrylic acid esters other than methyl methacrylate, such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate; acrylic acid esters other than methyl acrylate, such as ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; 2-(hydroxymethyl)methyl acrylate, 2 Examples of suitable third monofunctional monomers include hydroxyalkyl acrylates such as methyl (1-hydroxyethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, and butyl 2-(hydroxymethyl)acrylate; unsaturated acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as vinyltoluene and α-methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated acid anhydrides such as maleic anhydride and citraconic anhydride; and unsaturated imides such as phenylmaleimide and cyclohexylmaleimide. These third monofunctional monomers may be used alone or in combination of two or more.

The (meth)acrylic resin used as the thermoplastic resin constituting the protective film may further contain a polyfunctional monomer as a monomer unit. Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, nonaethylene glycol di(meth)acrylate, and tetradecaethylene glycol di(meth)acrylate, which are esterified at both terminal hydroxyl groups of ethylene glycol or its oligomers with acrylic acid or methacrylic acid; propylene glycol or its oligomers with acrylic acid or methacrylic acid, which are esterified at both terminal hydroxyl groups of propylene glycol or its oligomers with acrylic acid or methacrylic acid; and dihydric alcohol hydroxyl groups of neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate, and butanediol di(meth)acrylate, which are esterified at both terminal hydroxyl groups of dihydric alcohols with acrylic acid or methacrylic acid. Examples of suitable esters include those obtained by esterifying both terminal hydroxyl groups of bisphenol A, alkylene oxide adducts of bisphenol A, or halogen-substituted derivatives thereof with acrylic acid or methacrylic acid; those obtained by esterifying polyhydric alcohols such as trimethylolpropane or pentaerythritol with acrylic acid or methacrylic acid, and those obtained by ring-opening addition of epoxy groups of glycidyl acrylate or glycidyl methacrylate to the terminal hydroxyl groups of these esters; those obtained by ring-opening addition of epoxy groups of glycidyl acrylate or glycidyl methacrylate to dibasic acids such as succinic acid, adipic acid, terephthalic acid, phthalic acid, and halogen-substituted derivatives thereof, and alkylene oxide adducts thereof; aryl (meth)acrylates; and aromatic divinyl compounds such as divinylbenzene. Among these, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and neopentyl glycol dimethacrylate are preferred.

The (meth)acrylic resin used as the thermoplastic resin constituting the protective film may be modified by promoting a reaction between functional groups possessed by the copolymer. Examples of such reactions include an intrapolymer chain demethanolization condensation reaction between the methyl ester group of methyl acrylate and the hydroxyl group of methyl 2-(hydroxymethyl)acrylate, and an intrapolymer chain dehydration condensation reaction between the carboxyl group of acrylic acid and the hydroxyl group of methyl 2-(hydroxymethyl)acrylate. Furthermore, the (meth)acrylic resin used as the thermoplastic resin constituting the protective film may have the structure of a glutarimide derivative, a glutaric anhydride derivative, or a lactone ring.

The Tg of the (meth)acrylic resin used as the thermoplastic resin constituting the protective film is preferably 90 to 160°C, more preferably 110 to 160°C, and even more preferably 120 to 150°C.

The (meth)acrylic resin used as the thermoplastic resin constituting the protective film may contain additives as needed. Examples of additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light-resistant agents, impact modifiers, surfactants, etc.

The (meth)acrylic resin used as the thermoplastic resin constituting the protective film may contain acrylic rubber particles, which act as an impact modifier, from the perspective of film formability and impact resistance. Acrylic rubber particles are particles whose essential component is an elastomeric polymer primarily composed of acrylic esters. Examples include single-layer structures consisting essentially of this elastomeric polymer, and multi-layer structures with this elastomeric polymer as one layer. Examples of such elastomeric polymers include cross-linked elastomeric copolymers in which alkyl acrylate is the main component and is copolymerized with other copolymerizable vinyl monomers and cross-linking monomers. Examples of alkyl acrylates that are the main component of elastomeric polymers include those with alkyl groups containing 1 to 8 carbon atoms, such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Acrylic acids with alkyl groups containing 4 or more carbon atoms are particularly preferred. Other vinyl monomers copolymerizable with this alkyl acrylate include compounds having one polymerizable carbon-carbon double bond in the molecule, more specifically methacrylic acid esters such as methyl methacrylate, aromatic vinyl compounds such as styrene, and vinyl cyanide compounds such as acrylonitrile. Crosslinkable monomers include crosslinkable compounds having at least two polymerizable carbon-carbon double bonds in the molecule, more specifically (meth)acrylates of polyhydric alcohols such as ethylene glycol di(meth)acrylate and butanediol di(meth)acrylate, alkenyl esters of (meth)acrylic acid such as allyl (meth)acrylate, and divinylbenzene.

The protective film can also be a laminate of a film made of acrylic resin that does not contain rubber particles and a film made of acrylic resin that does contain rubber particles.

A retardation film is an optical film that exhibits optical anisotropy. Retardation films can be, for example, stretched films obtained by stretching (e.g., 1.01 to 6 times) resin films made from resins such as polyvinyl alcohol resins, polyarylate resins, polyimide resins, polyethersulfone resins, polyvinylidene fluoride/polymethyl methacrylate resins, liquid crystal polyester resins, saponified ethylene-vinyl acetate copolymers, and polyvinyl chloride resins, in addition to the resins that can be used for the protective films described above. Among these, stretched films obtained by uniaxially or biaxially stretching polycarbonate resin films, cycloolefin resin films, (meth)acrylic resin films, or cellulose resin films are preferred. Furthermore, zero retardation films are also included in the retardation film definition in this specification (however, zero retardation films can also be used as protective films). Other films that can be used as retardation films include uniaxial retardation films, wide-viewing-angle retardation films, and low-photoelasticity retardation films.

The retardation film may be a film having an optically anisotropic layer made of a polymer formed by polymerizing a polymerizable liquid crystal compound in an oriented state on a substrate. The substrate may be the same thermoplastic resin film used in the protective film described above.

The retardation film can be, for example, a quarter-wave retardation layer with reverse wavelength dispersion, a positive C plate, a half-wave retardation layer with positive wavelength dispersion, or a quarter-wave retardation layer with positive wavelength dispersion. The retardation film may be composed of two or more retardation layers, for example, a combination of a quarter-wave retardation layer with reverse wavelength dispersion and a positive C plate, or a combination of a half-wave retardation layer with positive wavelength dispersion and a quarter-wave retardation layer with positive wavelength dispersion.

The retardation film and the protective film may each have a moisture permeability of 500 g/(m ² ·24 hr) or less, measured by the cup method specified in JIS Z 0208 at a temperature of 40° C. and a relative humidity of 90%.

Optical films for liquid crystal display devices, such as polarizers, protective films, retardation films, light diffusion sheets, and reflective sheets, are typically distributed with a surface protection film attached to their surface (or the surface opposite the adhesive layer, if the surface has an adhesive layer on one side). Surface protection films are used to protect the surface of the object being protected, such as an optical film, from scratches and dirt. Surface protection films are typically peeled off and removed from the optical film after the optical film has been attached to a liquid crystal cell or the like.

Examples of substrates for surface protection films include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; fluorinated polyolefin resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyester resins such as polyethylene naphthate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/isophthalate copolymer; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as triacetyl cellulose, diacetyl cellulose, and cellophane; (meth)acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; and others such as polystyrene, polycarbonate, polyarylate, and polyimide.

The attachment layer may be a pressure-sensitive adhesive layer or an adhesive layer. When the attachment layer is a pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer other than the pressure-sensitive adhesive layers described above may be used for the attachment layer. When the attachment layer is a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer may be composed of a pressure-sensitive adhesive composition whose main component is a resin such as a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin. Among these, pressure-sensitive adhesive compositions whose base polymer is a (meth)acrylic resin are preferred from the standpoint of excellent transparency, weather resistance, heat resistance, etc. The pressure-sensitive adhesive composition may be an active energy ray-curable type or a heat-curable type.

When the laminating layer is a pressure-sensitive adhesive layer, the (meth)acrylic resin (base polymer) used in the pressure-sensitive adhesive composition is preferably a polymer or copolymer containing one or more (meth)acrylic acid esters as monomers, such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. It is preferable to copolymerize a polar monomer into the base polymer. Examples of polar monomers include monomers having a carboxyl group, hydroxyl group, amide group, amino group, or epoxy group, such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

When the attachment layer is a pressure-sensitive adhesive layer, the pressure-sensitive adhesive composition used may contain only the base polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form metal carboxylates with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; polyepoxy compounds or polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Of these, polyisocyanate compounds are preferred.

When the attachment layer is a pressure-sensitive adhesive layer, the thickness of the attachment layer is preferably 1 μm or more and 200 μm or less, more preferably 2 μm or more and 100 μm or less, even more preferably 2 μm or more and 80 μm or less, and particularly preferably 3 μm or more and 50 μm or less.

When the attachment layer is an adhesive layer, the adhesive layer can be made using any suitable adhesive. Examples of adhesives that can be used include water-based adhesives and active energy ray-curable adhesives.

The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer with the desired thickness is obtained after curing or heating (drying). 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, even more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

Examples of water-based adhesives include aqueous polyvinyl alcohol resin solutions and water-based two-component urethane emulsion adhesives.

An active energy ray-curable adhesive is an adhesive containing a curable compound that cures when exposed to active energy rays such as ultraviolet light, visible light, electron beams, or X-rays, and is preferably an ultraviolet ray-curable adhesive.

The curable compound can be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of cationically polymerizable curable compounds include epoxy compounds (compounds having one or more epoxy groups in the molecule), oxetane compounds (compounds having one or more oxetane rings in the molecule), and combinations thereof. Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having radically polymerizable double bonds, and combinations thereof. A cationically polymerizable curable compound and a radically polymerizable curable compound may be used in combination. Active energy ray-curable adhesives typically further contain at least one of a cationic polymerization initiator and a radical polymerization initiator to initiate the curing reaction of the curable compound.

For the purpose of improving adhesion, a surface activation treatment may be applied to the bonding surface of at least one of the bonding layer and the optical film. Examples of surface activation treatments include dry treatments such as corona treatment, plasma treatment, discharge treatment (e.g., glow discharge treatment), ozone treatment, UV ozone treatment, and ionizing active ray treatment (e.g., ultraviolet treatment, electron beam treatment). These surface activation treatments may be applied alone or in combination of two or more. Corona treatment is preferred as the surface activation treatment. Corona treatment can be performed, for example, at an output of 1 kJ/ ^m2 or more and 50 kJ/m2 or ^less . The time for performing the corona treatment may be, for example, 1 second or more and 1 minute or less.

In one embodiment of the optical film with a pressure-sensitive adhesive layer, it is preferable to apply the above-mentioned release film to the surface of the pressure-sensitive adhesive layer and provide temporary protection until use. An optical film with a pressure-sensitive adhesive layer to which a release film is applied can be produced, for example, by a method of applying a pressure-sensitive adhesive composition onto a release film to form a pressure-sensitive adhesive layer, and then laminating a resin film on top of the pressure-sensitive adhesive layer, or by a method of applying a pressure-sensitive adhesive composition onto a resin film to form a pressure-sensitive adhesive layer, and then laminating a release film onto the surface of the pressure-sensitive adhesive layer.

The optical film with a pressure-sensitive adhesive layer can be used in displays such as organic electroluminescence (organic EL) displays and liquid crystal displays, and can be used, for example, by being attached to the viewing side of the image display element of the display device.

There are no particular restrictions on the laminate structure of the optical film with a pressure-sensitive adhesive layer, as long as it includes an optical film and a pressure-sensitive adhesive layer provided on at least one surface of the optical film.

FIG. 1 is a schematic cross-sectional view showing one embodiment of an optical film with a pressure-sensitive adhesive layer. The optical film 10 with a pressure-sensitive adhesive layer shown in FIG. 1 comprises a linear polarizer 11 and a pressure-sensitive adhesive layer 12 provided on one side of the linear polarizer 11. The linear polarizer 11 comprises, in this order, a first protective film 13, an adhesive layer 14, a polarizer 15, an adhesive layer 16, and a second protective film 17. The pressure-sensitive adhesive layer 12 can be used to attach to a liquid crystal cell, which is the image display element of a liquid crystal display device. A separator (release film), not shown, may be provided on the side of the pressure-sensitive adhesive layer 12 opposite the linear polarizer 11.

Figure 2 is a schematic cross-sectional view showing another embodiment of an optical film with a pressure-sensitive adhesive layer. The optical film 20 with a pressure-sensitive adhesive layer shown in Figure 2 comprises, in this order, a pressure-sensitive adhesive layer 21, a retardation film 22, an attachment layer 23, and a linear polarizer 24. The linear polarizer 24 comprises, in this order, a first protective film 25, an adhesive layer 26, a polarizer 27, an adhesive layer 28, and a second protective film 29. The pressure-sensitive adhesive layer 21 can be used to attach to a liquid crystal cell, which is the image display element of a liquid crystal display device. A separator (release film), not shown, may be provided on the surface of the pressure-sensitive adhesive layer 21 opposite the retardation film 22.

The pressure-sensitive adhesive layer-attached optical films 10 and 20 shown in Figures 1 and 2 are merely examples, and the pressure-sensitive adhesive layer-attached optical film may have a layered structure other than those described above. For example, the pressure-sensitive adhesive layer-attached optical film may further include a hard coat film, a film with antiglare functionality, a film with surface antireflection functionality, etc.

<Display device>
The above-mentioned pressure-sensitive adhesive layer-attached optical film can be suitably used in display devices such as organic EL display devices, liquid crystal display devices, inorganic electroluminescence (inorganic EL) display devices, electron emission display devices, etc. One example of the display device includes the above-mentioned pressure-sensitive adhesive layer-attached optical film.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples. Below, parts and percentages representing amounts used or contents are by weight unless otherwise specified.

<Production Example 1>
A mixed solution containing 86.4 parts of ethyl acetate, 68.7 parts of butyl acrylate, 20.0 parts of methyl acrylate, 10.0 parts of methyl methacrylate, 1.0 parts of 2-hydroxyethyl acrylate, and 0.3 parts of acrylic acid was charged into a reaction vessel equipped with a condenser, a nitrogen inlet tube, a thermometer, and a stirrer. Subsequently, the temperature of the mixed solution was raised from room temperature to 60°C while the air in the reaction vessel was replaced with nitrogen gas to ensure an oxygen-free atmosphere in the reaction vessel. Thereafter, a solution of 0.10 parts of 2,2'-azobisisobutyronitrile (polymerization initiator) dissolved in 13.7 parts of ethyl acetate was added to the mixed solution in its entirety. This concentration was maintained for 4 hours after the addition of the polymerization initiator, allowing a (meth)acrylic resin to form in the reaction vessel. Finally, ethyl acetate was added to the reaction vessel to adjust the concentration of the (meth)acrylic resin to 20% by mass, thereby preparing an ethyl acetate solution of the (meth)acrylic resin of Production Example 1. The monomer composition (mass %) of the (meth)acrylic resin of Production Example 1 is shown in Table 1.

<Production Example 2>
An ethyl acetate solution of a (meth)acrylic resin of Production Example 2 was prepared in the same manner as in Production Example 1, except that the monomer composition was as shown in Table 1.

The abbreviations in Table 1 represent the following monomers.
BA: n-butyl acrylate (homopolymer Tg: -54°C)
MA: methyl acrylate (homopolymer Tg: 10°C)
MMA: methyl methacrylate (homopolymer Tg: 105°C)
HEA: 2-hydroxyethyl acrylate AA: acrylic acid

The Tg of the resulting (meth)acrylic resin was measured as follows. Tg was measured using an EXSTAR DSC6000 differential scanning calorimeter (DSC) manufactured by SII Nanotechnology, Inc., under conditions of a nitrogen atmosphere, a measurement temperature range of -80 to 150°C, and a heating rate of 10°C/min. The Tg of the (meth)acrylic resin of Production Example 1 was -29°C.

The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the resulting (meth)acrylic resin were measured as follows. Mw and Mn were measured in standard polystyrene equivalents using a GPC system with three columns connected in series: one "TSKgel guard column HHR-H(S)" manufactured by Tosoh Corporation and two "TSKgel GMHHR-H" columns. Tetrahydrofuran was used as the eluent, with a sample concentration of 2 mg/mL, a sample introduction volume of 100 μL, a temperature of 40°C, and a flow rate of 1 mL/min. The Mw of the (meth)acrylic resin of Production Example 1 was 1.62 million, and the molecular weight distribution (Mw/Mn) was 2.7.

<Examples 1 to 6, Comparative Example 1>
(1) Preparation of Pressure-Sensitive Adhesive Compositions Solutions of pressure-sensitive adhesive compositions were prepared by adding and mixing the types and amounts (parts by mass) of crosslinker, silane compound, and ionic compound shown in Table 2 relative to 100 parts by mass of the solid content of the solution to the ethyl acetate solution of the (meth)acrylic resin (resin concentration: 20%) obtained in the above Production Example, and then adding ethyl acetate to adjust the solid content concentration to 14% by mass. In Table 2, the amounts (parts by mass) of the (meth)acrylic resin, crosslinker, silane compound, and ionic compound are calculated as solid content amounts.

Details of each compounding component indicated by its abbreviation in Table 2 are as follows:
[Crosslinking agent]
Crosslinking agent: D-103 (ethyl acetate solution of trimethylolpropane adduct of tolylene diisocyanate: solids concentration 75% by mass, manufactured by Mitsui Chemicals, Inc.)
[Silane Compound]
Silane compound: 8-glycidoxyoctyltrimethoxysilane "KBM-4803", manufactured by Shin-Etsu Chemical Co., Ltd. [ionic compound]
A1: N-decylpyridinium tetrakis(pentafluorophenyl)borate A2: trioctylmethylammonium tetrakis(pentafluorophenyl)borate A3: trimethyloctylammonium tetrakis(pentafluorophenyl)borate A4: 1-dodecyl-3-butylimidazolium tetrakis(pentafluorophenyl)borate A5: tributyldodecylphosphonium tetrakis(pentafluorophenyl)borate A6: triphenylmethoxymethylphosphonium tetrakis(pentafluorophenyl)borate

(2) Preparation of Pressure-Sensitive Adhesive Layer The solution of each pressure-sensitive adhesive composition prepared in (1) above was applied to the release-treated surface of a release-treated polyethylene terephthalate film (Diafoil MRV38 (V04)", manufactured by Mitsubishi Chemical Corporation) using an applicator so that the thickness after drying would be 25 μm, and the coating was dried at 100° C. for 1 minute to prepare a pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) with a separate film.

(3) Measurement of gel fraction of pressure-sensitive adhesive layer The separate film was peeled off from the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) with separate film prepared in (2), and the resulting pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) was stored for 7 days in an environment at a temperature of 23°C and a relative humidity of 60%. The gel fraction [gel fraction at 23°C (G23)] of the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) after storage was measured. The gel fraction was measured according to the following [a] to [d]. The results are shown in Table 3.
[a] An adhesive layer having an area of approximately 8 cm x approximately 8 cm is placed approximately in the center of a metal mesh (whose mass is Wm) made of SUS304 having an area of approximately 10 cm x approximately 10 cm, and the adhesive layer and the metal mesh are bonded together.
[b] The bonded product obtained in [a] above is weighed, and its mass is designated as Ws. Subsequently, the metal mesh of the bonded product is folded four times so as to enclose the pressure-sensitive adhesive layer, and the folded metal mesh is stapled to prepare a measurement sample. The measurement sample is weighed, and its mass is designated as Wb.
[c] The measurement sample prepared in [b] above is placed in a glass container, 60 mL of ethyl acetate is added to immerse the measurement sample, and the glass container is then stored at room temperature for 3 days.
[d] The measurement sample is taken out of the glass container, dried at 120°C for 4 hours, and then weighed. The mass is designated as Wa, and the weight is calculated using the following formula:
Gel fraction (mass%)=[{Wa−(Wb−Ws)−Wm}/(Ws−Wm)]×100
Calculate the gel fraction based on

(4) Preparation of Polarizing Plate A 12 μm-thick polarizer was prepared by aligning iodine adsorbed onto a uniaxially stretched polyvinyl alcohol film. A 40 μm-thick protective film made of a saponified triacetyl cellulose resin was attached to both sides of the polarizer using a water-based adhesive to prepare a polarizing plate.

(5) Preparation of polarizing plate with adhesive layer The surface of the adhesive layer with separate film prepared in (2) above opposite to the separate film (the surface on the adhesive layer side) was bonded to the outer surface of one of the protective films of the polarizing plate prepared in (4) above using a laminator, and then aged for 7 days under conditions of a temperature of 23°C and a relative humidity of 60% to obtain a laminate (laminated optical film) of the separate film and the polarizing plate with adhesive layer.

(6) Heat Resistance Durability Evaluation Two laminated optical films prepared in (5) above were prepared. For each laminated optical film, the separate film was peeled off from the polarizing plate with the adhesive layer, and then the two polarizing plates with adhesive layers were attached to both sides of an alkali-free glass substrate ("Eagle XG" manufactured by Corning Incorporated) in a crossed Nicol configuration so that the exposed adhesive layer surface of each polarizing plate with adhesive layer was in contact with the surface of the alkali-free glass substrate. The obtained test piece (glass substrate with adhesive layer attached) was pressurized in an autoclave at a temperature of 50°C and a pressure of 5 kg/cm ² (490.3 kPa) for 20 minutes to prepare an evaluation sample. The following heat resistance durability test was performed using this evaluation sample.
[Heat resistance durability test]
The prepared evaluation sample was kept under dry conditions at a temperature of 110° C. for 500 hours.

After the test, each evaluation sample was visually inspected for lifting or peeling at the interface between the pressure-sensitive adhesive layer and the glass substrate, and for foaming in the pressure-sensitive adhesive layer, and the heat resistance durability was evaluated according to the following evaluation criteria. The results are shown in Table 3.
A: Almost no changes in appearance such as lifting, peeling, cracking, or bubbling were observed (the maximum length of the part where lifting, peeling, cracking, or bubbling was observed was less than 1 mm).
B: Changes in appearance such as lifting, peeling, cracking, or bubbling were observed (the maximum length of the part where lifting, peeling, cracking, or bubbling was observed was 1 mm or more and less than 3 mm).
C: Significant changes in appearance such as lifting, peeling, cracking, or bubbling were observed (the maximum length of the part where lifting, peeling, cracking, or bubbling was observed was 3 mm or more).

(7) Evaluation of Metal Corrosion Inhibition Ability A metal-layered glass substrate (manufactured by Geomatec Co., Ltd.) was prepared by forming a titanium-aluminum alloy layer approximately 500 nm thick on the surface of an alkali-free glass substrate by sputtering. The laminated optical film obtained in (5) above was cut into a size of 60 mm x 50 mm. The separate film was peeled off from the polarizing plate with the adhesive layer in the cut laminated optical film, and the polarizing plate with the adhesive layer and the glass substrate with the metal layer were bonded together so that the exposed adhesive layer was in contact with the metal layer of the glass substrate with the metal layer to prepare a sample. The obtained sample was autoclaved at a temperature of 50 ° C and a pressure of 0.49 MPa to prepare a test specimen for metal corrosion evaluation. This test specimen for metal corrosion evaluation was stored in an environment of a temperature of 85 ° C and a relative humidity of 85% for 250 hours.

The state of the metal layer of each test piece after storage was visually observed by irradiating light from the glass side of the metal-layered glass substrate. The metal layer to which the pressure-sensitive adhesive layer-attached polarizing plate was attached was examined for the presence or absence of areas through which light was transmitted due to corrosion, and the metal corrosion inhibition ability was evaluated according to the following evaluation criteria. The results are shown in Table 3.
A: No light transmission due to corrosion was observed.
B: Light transmission due to corrosion was confirmed.

10, 20... Optical film with adhesive layer, 11, 24... Linear polarizing plate, 12... Adhesive layer, 13, 25... First protective film, 14, 16, 26, 28... Adhesive layer, 15, 27... Polarizer, 17, 29... Second protective film, 21... Adhesive layer, 22... Retardation film, 23... Bonding layer.

Claims (6)

The composition includes a (meth)acrylic resin, a crosslinking agent, a silane compound, and an ionic compound,
The (meth)acrylic resin contains, as a monomer unit, an alkyl (meth)acrylate having a glass transition temperature of 30°C or higher in the form of a homopolymer,
The pressure-sensitive adhesive composition, wherein the ionic compound contains an anion represented by the following formula (1):

[In formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, a halogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, or an optionally substituted heterocyclic group.] The pressure-sensitive adhesive composition according to claim 1 , wherein the anion represented by formula (1) is an anion represented by the following formula (2):

[In formula (2), R ⁵ to R ⁹ each independently represent a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent, and two or more selected from the group consisting of R ⁵ to R ⁹ may be bonded to each other to form a ring.] The pressure-sensitive adhesive composition according to claim 2, wherein the anion represented by formula (2) is a tetrakis(pentafluorophenyl)borate anion. the (meth)acrylic resin further contains a hydroxy group-containing (meth)acrylate and a carboxy group-containing monomer as monomer units,
the content of the hydroxy group-containing (meth)acrylate is 0.3 mass% or more and 5.5 mass% or less based on the total amount of monomer units contained in the (meth)acrylic resin,
The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the mass ratio of the content of the carboxy group-containing monomer to the content of the hydroxy group-containing (meth)acrylate is 0.06 or more and 1.0 or less. A pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of claims 1 to 3. An optical film with a pressure-sensitive adhesive layer, comprising an optical film and the pressure-sensitive adhesive layer described in claim 5 provided on at least one surface of the optical film.