Acrylic adhesive, adhesive sheet, optical laminate, and image display device

Abstract

The present invention provides an acrylic adhesive which has a high refractive index and is capable of suppressing the occurrence of precipitates (typically white precipitates) on the surface of an adhesive sheet that is composed of the acrylic adhesive. The present invention also provides: an adhesive sheet which contains such an acrylic adhesive; an optical laminate which comprises such an adhesive sheet; and an image display device which comprises such an optical laminate.　An acrylic adhesive according to an embodiment of the present invention is formed of an acrylic adhesive composition which contains an acrylic polymer as a base polymer, wherein: the acrylic polymer is obtained by polymerizing a monomer component (M); the monomer component (M) contains 30 wt% or more of an aromatic ring-containing monomer (m1); and at least one selected from the group consisting of a xylene sulfonic acid and a xylene sulfonate is contained in an amount of 300 ppm or less in terms of solid content.

Description

Acrylic adhesive, adhesive sheet, optical laminate, and image display device

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

[0002] 2. Description of the Related Art In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices), have rapidly become widespread.

[0003] An image display device generally includes an optical laminate including optical elements such as a polarizing film and a retardation film. In such an optical laminate, a bonding layer is usually disposed between adjacent optical elements to bond them together. One example of such a bonding layer is a pressure-sensitive adhesive sheet including an acrylic pressure-sensitive adhesive formed from an acrylic pressure-sensitive adhesive composition.

[0004] The refractive index of acrylic adhesives is typically around 1.47. On the other hand, the refractive index of optical components is generally higher than this level. Therefore, when an acrylic adhesive is used to bond adjacent optical components, the difference in refractive index between the two components causes reflection at the interface, which is a problem.

[0005] Recently, an acrylic pressure-sensitive adhesive having a high refractive index has been reported (Patent Document 1). The acrylic pressure-sensitive adhesive reported in Patent Document 1 is formed from a pressure-sensitive adhesive composition containing an acrylic polymer obtained from monomer components including 75% by weight or more and 99% by weight or less of an aromatic ring-containing monomer (A1) and 1% by weight or more and 25% by weight or less of a monomer (A2) having at least one of a hydroxyl group and a carboxyl group.

[0006] Japanese Patent Application Laid-Open No. 2022-008018

[0007] However, when an adhesive sheet is produced using an acrylic adhesive formed from an adhesive composition containing an acrylic polymer obtained from a monomer component containing an aromatic ring-containing monomer, it has been found that precipitates (typically white precipitates) are often observed on the surface, posing a problem in that the quality required for adhesive sheets used for bonding optical components, particularly optical component applications, cannot be guaranteed.

[0008] An object of the present invention is to provide an acrylic pressure-sensitive adhesive having a high refractive index that can suppress the occurrence of deposits (typically white deposits) on the surface of a pressure-sensitive adhesive sheet made from the acrylic pressure-sensitive adhesive. Another object of the present invention is to provide a pressure-sensitive adhesive sheet containing such an acrylic pressure-sensitive adhesive that has a high refractive index, suppresses the occurrence of deposits (typically white deposits) on the surface, and has a beautiful appearance. A further object of the present invention is to provide an optical laminate containing such a pressure-sensitive adhesive sheet, and to provide an image display device containing such an optical laminate.

[0009] [1] An acrylic pressure-sensitive adhesive according to an embodiment of the present invention is an acrylic pressure-sensitive adhesive formed from an acrylic pressure-sensitive adhesive composition containing an acrylic polymer as a base polymer, the acrylic polymer being obtained by polymerizing a monomer component (M), the monomer component (M) containing 30 wt% or more of an aromatic ring-containing monomer (m1), and containing 300 ppm or less, calculated on solids, of at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate. [2] In the acrylic pressure-sensitive adhesive according to [1] above, the monomer component (M) may contain 50 wt% or more of an aromatic ring-containing monomer (m1). [3] In the acrylic pressure-sensitive adhesive according to [1] or [2] above, the aromatic ring-containing monomer (m1) may be phenoxybenzyl (meth)acrylate. [4] The acrylic pressure-sensitive adhesive according to any one of [1] to [3] above may contain 1,000 ppm to 18,000 ppm of residual monomer. [5] In the acrylic pressure-sensitive adhesive according to any one of [1] to [4] above, the monomer component (M) may comprise at least one selected from the group consisting of alkyl (meth)acrylates, hydroxyl group-containing monomers, carboxyl group-containing monomers, and amide group-containing monomers. [6] A pressure-sensitive adhesive sheet according to an embodiment of the present invention comprises the acrylic pressure-sensitive adhesive according to any one of [1] to [5] above. [7] The pressure-sensitive adhesive sheet according to [6] above may have an average refractive index n of 1.52 or more. [8] An optical laminate according to an embodiment of the present invention comprises the pressure-sensitive adhesive sheet according to [6] or [7] above. [9] The optical laminate according to [8] above may comprise a first liquid crystal alignment solidified layer, the pressure-sensitive adhesive sheet, and a second liquid crystal alignment solidified layer, in this order.

[10] The optical laminate according to [9] above may comprise a polarizing film on at least one side selected from the group consisting of the first liquid crystal alignment solidified layer side and the second liquid crystal alignment solidified layer side, as viewed from the pressure-sensitive adhesive sheet.

[11] An image display device according to an embodiment of the present invention includes the optical laminate according to any one of [8] to

[10] above.

[0010] According to an embodiment of the present invention, it is possible to provide an acrylic pressure-sensitive adhesive having a high refractive index, which can suppress the occurrence of precipitates (typically white precipitates) on the surface of a pressure-sensitive adhesive sheet made from the acrylic pressure-sensitive adhesive. It is also possible to provide a pressure-sensitive adhesive sheet containing such an acrylic pressure-sensitive adhesive, which has a high refractive index, suppresses the occurrence of precipitates (typically white precipitates) on the surface, and has an attractive appearance. Furthermore, it is also possible to provide an optical laminate including such a pressure-sensitive adhesive sheet, and an image display device including such an optical laminate.

[0011] 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention, a schematic cross-sectional view of an optical laminate with a polarizing film according to one embodiment of the present invention, and a schematic cross-sectional view showing one embodiment of a laminate in which a pressure-sensitive adhesive layer is provided on the surface of the second liquid crystal alignment solidified layer of the optical laminate with a polarizing film according to one embodiment of the present invention, the surface being opposite to the pressure-sensitive adhesive sheet.

[0012] [Terminology] In this specification, when the expression "weight" appears, it may be read as "mass," which is commonly used as an SI unit indicating weight, and vice versa.

[0013] As used herein, "ppm" means ppm by weight / weight (w / w), and 1 ppm is (1 x 10 －６ ) g / g = 1 μg / g.

[0014] In this specification, the expression "(meth)acrylic" means "acrylic and / or methacrylic", the expression "(meth)acrylate" means "acrylate and / or methacrylate", the expression "(meth)allyl" means "allyl and / or methallyl", and the expression "(meth)acrolein" means "acrolein and / or methacrolein".

[0015] In this specification, when simply referring to a "liquid crystal alignment solidified layer", it is a concept that includes both the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer.

[0016] In this specification, with regard to the refractive indices (nx, ny, nz), "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. In this specification, nx, ny, and nz are values ​​for light with a wavelength of 550 nm. In this specification, the average refractive index is calculated by (nx + ny + nz) / 3.

[0017] In this specification, with regard to the in-plane retardation (Re), "Re(λ)" is the in-plane retardation of a film measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation of a film measured with light having a wavelength of 550 nm at 23° C. Re(λ) can be calculated by the formula: Re=(nx-ny)×d, where d (nm) is the thickness of the film.

[0018] In this specification, with regard to the thickness direction retardation (Rth), "Rth(λ)" is the retardation in the thickness direction of a film measured with light having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction of a film measured with light having a wavelength of 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth=(nx-nz)×d, where d (nm) is the thickness of the film.

[0019] In this specification, the "Nz coefficient" is calculated by Nz=Rth / Re.

[0020] <<1. Acrylic Pressure-Sensitive Adhesive>> The acrylic pressure-sensitive adhesive according to an embodiment of the present invention is formed from an acrylic pressure-sensitive adhesive composition. The acrylic pressure-sensitive adhesive according to an embodiment of the present invention has a high refractive index, and can suppress the occurrence of deposits (typically white deposits) on the surface. A pressure-sensitive adhesive sheet that can be formed from the acrylic pressure-sensitive adhesive according to an embodiment of the present invention has a high refractive index, and can suppress the occurrence of deposits (typically white deposits) on the surface, and can have a beautiful appearance.

[0021] The acrylic pressure-sensitive adhesive according to an embodiment of the present invention may be produced by any suitable method, such as a method generally known as a method for forming a pressure-sensitive adhesive from a pressure-sensitive adhesive composition, as long as the effects of the present invention are not impaired. The acrylic pressure-sensitive adhesive according to an embodiment of the present invention may be formed by a forming method generally known as a "direct method" or a forming method generally known as a "transfer method." The direct method is a method in which an acrylic pressure-sensitive adhesive composition is applied to an appropriate substrate, and, if necessary, heated, irradiated with active energy rays (such as ultraviolet rays), dried, or the like, to form an acrylic pressure-sensitive adhesive. The transfer method is a method in which an acrylic pressure-sensitive adhesive composition is applied to a release paper or the like, dried, to form an acrylic pressure-sensitive adhesive, and the formed acrylic pressure-sensitive adhesive is then transferred to an appropriate substrate or the like.

[0022] Examples of the application method include a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, air knife coater, spray coater, comma coater, direct coater, and roll brush coater.

[0023] The acrylic pressure-sensitive adhesive composition forming the acrylic pressure-sensitive adhesive according to the embodiment of the present invention contains an acrylic polymer as a base polymer. The acrylic polymer may be one type or two or more types.

[0024] The content of the acrylic polymer in the acrylic pressure-sensitive adhesive composition is, for example, 50% by weight or more, alternatively, 60% by weight to 99.9% by weight, 70% by weight to 99% by weight, 80% by weight to 97% by weight, or 90% by weight to 95% by weight, calculated as solid content.

[0025] As mentioned above, when a pressure-sensitive adhesive sheet is prepared using an acrylic pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition containing an acrylic polymer obtained from a monomer component containing an aromatic ring-containing monomer, precipitates (typically white precipitates) are often observed on the surface of the sheet. Therefore, the present inventors have investigated technical means for suppressing the occurrence of such precipitates (typically white precipitates). After conducting a detailed investigation into the acrylic pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet that generates the precipitates (typically white precipitates), it has been found that the acrylic pressure-sensitive adhesive contains at least one substance selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts, which is an unexpected substance based on its composition. Therefore, the present inventors have conducted further investigations and found that adjusting the content of at least one substance selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in the acrylic pressure-sensitive adhesive within a specific range can suppress the occurrence of the precipitates (typically white precipitates), while conversely, departing from the specific range can cause the occurrence of the precipitates (typically white precipitates).

[0026] The acrylic pressure-sensitive adhesive according to an embodiment of the present invention contains at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts, typically in an amount of 300 ppm or less, but may be 250 ppm or less, 200 ppm or less, 180 ppm or less, 160 ppm or less, or 150 ppm or less, calculated on a solids basis. The lower limit of the content is preferably as small as possible, and may be, for example, 0 ppm or more, or may be equal to or greater than the lower limit of quantitation in measurement. For example, when the lower limit of quantitation in measurement is 40 ppm, the lower limit of the content may be 40 ppm or more.

[0027] By adjusting the content of at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in the acrylic pressure-sensitive adhesive according to the embodiment of the present invention to fall within the above-mentioned specific range, it is possible to suppress the occurrence of precipitates (typically white precipitates) on the surface of a pressure-sensitive adhesive sheet made from the acrylic pressure-sensitive adhesive according to the embodiment of the present invention. If the content is too large and falls outside the above-mentioned specific range, for example, when a pressure-sensitive adhesive sheet is produced using the acrylic pressure-sensitive adhesive, precipitates (typically white precipitates) may occur on the surface.

[0028] The xylene sulfonic acid may be at least one selected from the group consisting of o-xylene sulfonic acid, m-xylene sulfonic acid, and p-xylene sulfonic acid.

[0029] The salt constituting the xylene sulfonate may be any appropriate known salt, such as an alkali metal salt (e.g., sodium salt, potassium salt), an alkaline earth metal salt (e.g., calcium salt, magnesium salt), an ammonium salt, or an alkanolamine salt (e.g., methanolamine salt, ethanolamine salt).

[0030] The present inventors further investigated technical means for suppressing the formation of the above-mentioned precipitates (typically white precipitates), and as a result, they found that, in addition to adjusting the content of at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in the acrylic PSA to a specific range, further adjusting the content of residual monomers in the acrylic PSA to a specific range can further suppress the formation of the above-mentioned precipitates (typically white precipitates).

[0031] The acrylic pressure-sensitive adhesive according to an embodiment of the present invention may preferably contain 1,000 ppm to 18,000 ppm of residual monomer. The residual monomer content may be 2,000 ppm to 15,000 ppm, or may be 2,500 ppm to 12,000 ppm. By adjusting the residual monomer content in the acrylic pressure-sensitive adhesive to fall within the above-mentioned specific range, the effects of the present invention can be more effectively achieved. If the residual monomer content in the acrylic pressure-sensitive adhesive is too low and outside the above-mentioned specific range, for example, when a pressure-sensitive adhesive sheet is produced using the acrylic pressure-sensitive adhesive, precipitates (typically white precipitates) may occur on the surface of the sheet. If the residual monomer content in the acrylic pressure-sensitive adhesive is too high and outside the above-mentioned specific range, for example, the humidity durability of a pressure-sensitive adhesive sheet produced using the acrylic pressure-sensitive adhesive may be reduced.

[0032] The "residual monomer" referred to above is at least one of monomers (aromatic ring-containing monomer (m1) described below and copolymerizable monomer (m4) copolymerizable with aromatic ring-containing monomer (m1) described below) contained in monomer component (M), which is a raw material for producing an acrylic polymer as a base polymer contained in the acrylic pressure-sensitive adhesive composition that forms the acrylic pressure-sensitive adhesive.

[0033] <1-1. Acrylic Polymer> The acrylic polymer has a Tg of, for example, less than 20°C, and may be less than 15°C, less than 13°C, greater than −15°C and less than 13°C, greater than −10°C and less than 13°C, greater than −5°C and less than 13°C, or greater than −3°C and less than 13°C.

[0034] The polymer structure of the acrylic polymer may be any of a random copolymer structure, a block copolymer structure, a graft copolymer structure, and the like.

[0035] The acrylic polymer is obtained by polymerizing the monomer component (M).

[0036] The monomer component (M) contains an aromatic ring-containing monomer (m1). The aromatic ring-containing monomer (m1) may be of one type or two or more types.

[0037] The monomer component (M) typically contains 30% by weight or more of the aromatic ring-containing monomer (m1). The content of the aromatic ring-containing monomer (m1) in the monomer component (M) may be 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The upper limit of the content of the aromatic ring-containing monomer (m1) in the monomer component (M) is 100% by weight, 98% by weight or less, 96% by weight or less, 94% by weight or less, 92% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. The content of the aromatic ring-containing monomer (m1) in the monomer component (M) may be 50% by weight to 100% by weight, 60% by weight to 95% by weight, 65% by weight to 90% by weight, or 67% by weight to 88% by weight.

[0038] When the monomer component (M) contains the aromatic ring-containing monomer (m1) in the above content ratio, it is possible to provide, for example, an acrylic pressure-sensitive adhesive composition that forms an acrylic pressure-sensitive adhesive having a high refractive index. If the content ratio is too small outside the above range, for example, the refractive index of the acrylic pressure-sensitive adhesive formed from the resulting acrylic pressure-sensitive adhesive composition may be reduced.

[0039] As the aromatic ring-containing monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule can be used.

[0040] Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group.From the viewpoint of further exhibiting the effects of the present invention, the ethylenically unsaturated group is preferably a (meth)acryloyl group or a vinyl group, more preferably a (meth)acryloyl group, and more preferably an acryloyl group.Therefore, preferred embodiments of the aromatic ring-containing monomer (m1) include an aromatic ring-containing (meth)acrylate and an aromatic ring-containing vinyl compound.

[0041] From the viewpoint of being able to suppress a decrease in flexibility of the PSA, the aromatic ring-containing monomer (m1) is preferably a compound having one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer).

[0042] The number of aromatic rings contained in one molecule of the aromatic ring-containing monomer (m1) is, for example, 1 to 16, and may be 2 to 12, 2 to 8, 2 to 6, 2 to 4, 2 or 3, or 2.

[0043] The aromatic ring contained in the aromatic ring-containing monomer (m1) may be, for example, a hydrocarbon ring such as a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure); a condensed ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; or a heterocycle such as a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. Examples of heteroatoms contained in such heterocycles include nitrogen, sulfur, and oxygen, and preferably nitrogen and sulfur. The aromatic ring-containing monomer (m1) may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

[0044] The aromatic ring contained in the aromatic ring-containing monomer (m1) may have a substituent on a ring-constituting atom. The substituent may be of one type or of two or more types. Examples of the substituent include an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom, a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group.

[0045] The aromatic ring and the ethylenically unsaturated group contained in the aromatic ring-containing monomer (m1) may be bonded directly or via a linking group. Examples of such linking groups include alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, and groups in which one or more hydrogen atoms in these groups have been substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O- groups), and thiooxy groups (-S- groups). In terms of further enhancing the effects of the present invention, such linking groups are preferably groups containing at least one structure selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. The number of carbon atoms in the alkylene group and oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group is preferably 2 to 3.

[0046] From the viewpoint of further exhibiting the effects of the present invention, the aromatic ring-containing monomer (m1) may contain a monomer having two or more aromatic rings in one molecule (hereinafter, sometimes referred to as a "multiple aromatic ring-containing monomer (m2)"). Examples of the multiple aromatic ring-containing monomer (m2) include a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are directly chemically bonded, a monomer having a condensed aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure.

[0047] In one embodiment of the aromatic ring-containing monomer (m1), the content of the multiple aromatic ring-containing monomer (m2) in the aromatic ring-containing monomer (m1) may be, for example, 50% by weight or more, 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or 98% by weight or more. The upper limit of the content of the multiple aromatic ring-containing monomer (m2) in the aromatic ring-containing monomer (m1) is 100% by weight. The content of the multiple aromatic ring-containing monomer (m2) in the aromatic ring-containing monomer (m1) may be 80% by weight to 100% by weight, 85% by weight to 100% by weight, 90% by weight to 100% by weight, 95% by weight to 100% by weight, or 98% by weight to 100% by weight.

[0048] In another embodiment of the aromatic ring-containing monomer (m1), the content of the multiple aromatic ring-containing monomer (m2) in the aromatic ring-containing monomer (m1) may be, for example, less than 50% by weight, less than 40% by weight, less than 30% by weight, less than 20% by weight, less than 10% by weight, or less than 5% by weight. In this embodiment, the aromatic ring-containing monomer (m1) preferably contains a monomer (m3) having one aromatic ring per molecule, as described below.

[0049] Examples of the linking group that the aromatic ring-containing monomer (m2) may have include an oxy group (—O—), a thiooxy group (—S—), an oxyalkylene group (—O—(CH2) n - group, where n is 1 to 3, preferably 1), a thiooxyalkylene group (-S-(CH) n - group, where n is 1 to 3, preferably 1), a straight chain alkylene group (-(CH) n - group, where n is 1 to 6, preferably 1 to 3), an oxyalkylene group, a thiooxyalkylene group, and a linear alkylene group in which the alkylene group is partially or completely halogenated.

[0050] Examples of monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylate, and benzyl benzyl (meth)acrylate.

[0051] Examples of monomers having a structure in which two or more non-fused aromatic rings are directly chemically bonded include biphenyl structure-containing (meth)acrylates, triphenyl structure-containing (meth)acrylates, and vinyl group-containing biphenyls, and specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

[0052] Examples of monomers having a condensed aromatic ring structure include naphthalene ring-containing (meth)acrylates, anthracene ring-containing (meth)acrylates, vinyl group-containing naphthalenes, and vinyl group-containing anthracenes. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

[0053] Examples of monomers having a fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. Note that, since monomers having a fluorene structure contain a structural moiety in which two benzene rings are directly chemically bonded, they can be included in the concept of monomers having a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0054] Examples of monomers having a dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophenes, vinyl group-containing dinaphthothiophenes, and (meth)allyl group-containing dinaphthothiophenes. Specific examples include (meth)acryloyloxymethyl dinaphthothiophenes (e.g., dinaphthothiophenes having a CH group at the 5th or 6th position of the dinaphthothiophene ring).２ CH (R １ )C(O)OCH ２ Compounds with a structure in which - is bonded, R １ is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (for example, a dinaphthothiophene ring having a CH ２ CH (R １ )C(O)OCH(CH ３ ) - or CH ２ CH (R １ )C(O)OCH ２ CH ２ Compounds with a structure in which - is bonded, R １ is a hydrogen atom or a methyl group.), vinyl dinaphthothiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of a naphthothiophene ring), and (meth)allyloxydinaphthothiophene. Note that a monomer having a dinaphthothiophene structure can be included in the concept of a monomer having a fused aromatic ring structure by including a naphthalene structure or by having a structure in which a thiophene ring and two naphthalene structures are fused together.

[0055] Examples of monomers having a dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophenes and vinyl group-containing dibenzothiophenes. Note that, since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are fused, they can be included in the concept of monomers having a fused aromatic ring structure. Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0056] The aromatic ring-containing monomer (m1) may be a monomer (m3) having one aromatic ring per molecule. The monomer (m3) having one aromatic ring per molecule may be useful, for example, for adjusting the flexibility and adhesive properties of the PSA, improving transparency, etc.

[0057] Examples of the monomer (m3) having one aromatic ring in one molecule include carbon-containing aromatic ring (meth)acrylates such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and chlorobenzyl (meth)acrylate; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, and 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate. bromine-substituted aromatic ring-containing (meth)acrylates such as 6-(4,6-dibromo-2-s-butylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, and 2,6-dibromo-4-dodecylphenyl acrylate; carbon-containing aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0058] In one embodiment of the aromatic ring-containing monomer (m1), the content of the monomer (m3) having one aromatic ring per molecule in the aromatic ring-containing monomer (m1) may be, for example, less than 50% by weight, less than 30% by weight, less than 20% by weight, less than 15% by weight, less than 10% by weight, less than 5% by weight, or less than 2% by weight. The lower limit of the content of the monomer (m3) having one aromatic ring per molecule in the aromatic ring-containing monomer (m1) is 0% by weight.

[0059] In another embodiment of the aromatic ring-containing monomer (m1), the content of the monomer (m3) having one aromatic ring per molecule in the aromatic ring-containing monomer (m1) may be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more. In this embodiment, the aromatic ring-containing monomer (m1) may not contain the multiple aromatic ring-containing monomer (m2).

[0060]

[0063] From the viewpoint of further exhibiting the effects of the present invention, among the above-mentioned examples, the aromatic ring-containing monomer (m1) is preferably phenoxybenzyl (meth)acrylate, 1-naphthylmethyl (meth)acrylate, ethoxylated o-phenylphenol (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 6-(meth)acryloyloxymethyl dinaphthothiophene, 6-(meth)acryloyloxymethyl dinaphthothiophene, 5-(meth)acryloyloxyethyl dinaphthothiophene, 6-(meth)acryloyloxyethyl dinaphthothiophene, 6-vinyl dinaphthothiophene, or 5-vinyl dinaphthothiophene, and particularly preferably phenoxybenzyl (meth)acrylate.

[0061] Commercially available monomers and other monomers used to prepare base polymers contained in PSA compositions are usually purified to remove impurities such as by-products. However, the inventors' studies have revealed that when a commercially available aromatic ring-containing monomer (m1) is used as is to prepare an acrylic polymer contained in an acrylic PSA composition that forms an acrylic PSA, a precipitate (typically a white precipitate) tends to form on the surface of a PSA sheet prepared using the acrylic PSA formed from the acrylic PSA composition. In particular, it has been found that the greater the content of the aromatic ring-containing monomer (m1) in the monomer component (M), the stronger the tendency for this to occur. Therefore, the inventors have further studied the aromatic ring-containing monomer (m1) and purified a commercially available aromatic ring-containing monomer (m1), and have found that the formation of the precipitate (typically a white precipitate) can be suppressed.

[0062] The purification of the aromatic ring-containing monomer (m1) may be any suitable purification as long as it does not impair the effects of the present invention. Examples of such purification include distillation purification and adsorption purification. Since the aromatic ring-containing monomer (m1) generally has a higher boiling point than a monomer that does not contain an aromatic ring, the distillation temperature must be increased when distillation purification is performed, which may result in the generation of unintended products (impurities) due to side reactions, etc. Therefore, adsorption purification may be used as the purification of the aromatic ring-containing monomer (m1).

[0063] The monomer component (M) may contain a monomer copolymerizable with the aromatic ring-containing monomer (m1) (hereinafter, this may be referred to as "copolymerizable monomer (m4)"). The copolymerizable monomer (m4) may be one type or two or more types. Examples of the copolymerizable monomer (m4) include at least one selected from the group consisting of alkyl (meth)acrylates, hydroxyl group-containing monomers, carboxyl group-containing monomers, and amide group-containing monomers.

[0064] The content of the copolymerizable monomer (m4) in the monomer component (M) is preferably 70% by weight or less, and may be 60% by weight or less, 50% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, or 5% by weight or less, in order to further exhibit the effects of the present invention. The lower limit of the content of the copolymerizable monomer (m4) in the monomer component (M) is preferably 0% by weight, and may be 2% by weight or more, 4% by weight or more, 6% by weight or more, 8% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more. The content of the copolymerizable monomer (m4) in the monomer component (M) may be 0% by weight to 50% by weight, 5% by weight to 40% by weight, 10% by weight to 35% by weight, or 12% by weight to 33% by weight.

[0065] The number of carbon atoms in the alkyl group in the alkyl (meth)acrylate is, for example, 1 to 30. The alkyl group may be linear, branched, or cyclic. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an amyl group, a hexyl group, a cyclohexyl group, a heptyl group, a 2-ethylhexyl group, an isooctyl group, a nonyl group, a decyl group, an isodecyl group, a dodecyl group, an isomyristyl group, a lauryl group, a tridecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group. The alkyl (meth)acrylate may be of one type, or two or more types. From the viewpoint of further exhibiting the effects of the present invention, butyl acrylate is preferred as the alkyl (meth)acrylate.

[0066] The content of alkyl(meth)acrylate in monomer component (M) is preferably 50% by weight or less, and may be 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 22% by weight or less, 20% by weight or less, 17% by weight or less, or 15% by weight or less, in order to further exhibit the effects of the present invention. The lower limit of the content of alkyl(meth)acrylate in monomer component (M) is preferably 1% by weight or more, and may be 3% by weight or more, or 5% by weight or more. The content of alkyl(meth)acrylate in monomer component (M) may be 1 to 50% by weight, 1 to 40% by weight, 1 to 35% by weight, 3 to 30% by weight, 3 to 25% by weight, 3 to 22% by weight, 5 to 20% by weight, 5 to 17% by weight, or 5 to 15% by weight. In addition, alkyl(meth)acrylate does not have to be contained in monomer component (M).

[0067] The hydroxyl group-containing monomer is a compound that contains a hydroxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. The hydroxyl group-containing monomer may be a hydroxyl group-containing (meth)acrylate. Examples of the hydroxyl group-containing (meth)acrylate include hydroxyl group-containing alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; and hydroxyl group-containing cycloalkyl (meth)acrylates such as (4-hydroxymethylcyclohexyl)-methyl acrylate. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.

[0068] The content of the hydroxyl group-containing monomer in the monomer component (M) is preferably 0.2% by weight or more, and may be 0.5% by weight or more, 0.8% by weight or more, or 1% by weight or more, in order to further exhibit the effects of the present invention. The upper limit of the content of the hydroxyl group-containing monomer in the monomer component (M) is preferably 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, or 2% by weight or less. The content of the hydroxyl group-containing monomer in the monomer component (M) may be 0.2% by weight to 10% by weight, 0.2% by weight to 7% by weight, 0.5% by weight to 5% by weight, 0.5% by weight to 4% by weight, 0.8% by weight to 3% by weight, or 1% by weight to 2% by weight. In addition, the monomer component (M) may not contain a hydroxyl group-containing monomer.

[0069] The carboxyl group-containing monomer is a compound that contains a carboxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. The carboxyl group-containing monomer may be a carboxyl group-containing (meth)acrylate. Examples of the carboxyl group-containing (meth)acrylate include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0070] The content of the carboxyl group-containing monomer in the monomer component (M) is preferably 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, or 3% by weight or less, in order to further exhibit the effects of the present invention. The lower limit of the content of the carboxyl group-containing monomer in the monomer component (M) is preferably 0% by weight or more. The content of the carboxyl group-containing monomer in the monomer component (M) may be 0% by weight to 10% by weight, 0% by weight to 7% by weight, 0% by weight to 5% by weight, or 0% by weight to 3% by weight.

[0071] The amide group-containing monomer is a compound that contains an amide group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group, a vinyl group, etc. The amide group-containing monomer may be an amide group-containing (meth)acrylate. Examples of the amide group-containing (meth)acrylate include acrylamide-based monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam.

[0072] The content of the amide group-containing monomer in the monomer component (M) is preferably 10% by weight or less, or may be 7% by weight or less, 5% by weight or less, or may be 3% by weight or less, in order to further exhibit the effects of the present invention. The lower limit of the content of the amide group-containing monomer in the monomer component (M) is preferably 0% by weight or more. The content of the amide group-containing monomer in the monomer component (M) may be 0% by weight to 10% by weight, 0% by weight to 7% by weight, 0% by weight to 5% by weight, or 0% by weight to 3% by weight.

[0073] In addition to the above, examples of the copolymerizable monomer (m4) include other copolymerizable monomers, such as acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; sulfonic acid group-containing monomers such as allyl sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, and sulfopropyl (meth)acrylate; phosphate group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; aminoethyl (meth)acrylate, N,N-dimethyl Alkylaminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate and t-butylaminoethyl (meth)acrylate; alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; succinimide-based monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide; N-cyclohexylmaleimide maleimide-based monomers such as N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide-based monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide; vinyl-based monomers such as vinyl acetate and vinyl propionate; cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; glycidyl (meth)acrylate acrylate and other epoxy group-containing (meth)acrylates; glycol-based (meth)acrylates such as carbitol (meth)acrylate, ethyl carbitol (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate;Examples of such silane monomers include silane monomers containing silicon atoms, such as 3-acryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyltrimethoxysilane, 4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane, 8-vinyloctyltriethoxysilane, 10-methacryloyloxydecyltrimethoxysilane, 10-acryloyloxydecyltrimethoxysilane, 10-methacryloyloxydecyltriethoxysilane, and 10-acryloyloxydecyltriethoxysilane.

[0074] The content of the other copolymerizable monomer in the monomer component (M) is preferably 5% by weight or less, and may be 3% by weight or less, or 1% by weight or less, in order to further exhibit the effects of the present invention. The lower limit of the content of the other copolymerizable monomer in the monomer component (M) is preferably 0% by weight or more. The content of the other copolymerizable monomer in the monomer component (M) may be 0% by weight to 5% by weight, 0% by weight to 3% by weight, or 0% by weight to 1% by weight.

[0075] The acrylic polymer is obtained by polymerizing the monomer component (M). The acrylic polymer can be formed by various known polymerization methods such as solution polymerization, radiation polymerization using electron beams or ultraviolet (UV) rays, bulk polymerization, and emulsion polymerization. The polymerization is typically radical polymerization.

[0076] As the polymerization solvent for solution polymerization, known polymerization solvents such as ethyl acetate and toluene can be used. Solution polymerization can be carried out, for example, using a polymerization initiator and under a stream of an inert gas such as nitrogen. Any appropriate polymerization conditions can be adopted as long as they do not impair the effects of the present invention. Examples of such polymerization conditions include a polymerization temperature of 50°C to 70°C and a polymerization time of 5 to 30 hours.

[0077] As the polymerization initiator, chain transfer agent, and emulsifier that can be used in radical polymerization, any appropriate compounds can be used within the range that does not impair the effects of the present invention.

[0078] Examples of the polymerization initiator include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (for example, VA-057 manufactured by Wako Pure Chemical Industries, Ltd.); persulfates such as potassium persulfate and ammonium persulfate; di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-s Examples of the polymerization initiator include peroxide initiators such as ec-butyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butyl peroxyisobutyrate, 1,1-di(t-hexylperoxy)cyclohexane, t-butyl hydroperoxide, and hydrogen peroxide; and redox initiators combining peroxides and reducing agents, such as combinations of persulfates and sodium bisulfite, and combinations of peroxides and sodium ascorbate. The polymerization initiator may be a single type or two or more types. The polymerization initiator may be used in any appropriate amount as long as it does not impair the effects of the present invention. The total amount used is, for example, 0.005 to 1 part by weight, and may be 0.02 to 0.5 parts by weight, relative to 100 parts by weight of the monomer component (M).

[0079] Examples of chain transfer agents include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Only one type of chain transfer agent may be used, or two or more types may be used. The amount of chain transfer agent used may be any appropriate amount as long as it does not impair the effects of the present invention. Such an amount used is, for example, 0.1 parts by weight or less in total, relative to 100 parts by weight of the monomer component (M).

[0080] In radiation polymerization, a monomer is irradiated with radiation such as an electron beam or ultraviolet (UV) light to cause polymerization to proceed and form a base polymer. When radiation polymerization is carried out using an electron beam, the use of a photopolymerization initiator is not particularly necessary. When radiation polymerization is carried out using UV light, a photopolymerization initiator may be used because of advantages such as the ability to shorten the polymerization time. The photopolymerization initiator may be of only one type or of two or more types.

[0081] Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. The amount of the photopolymerization initiator used may be any appropriate amount as long as it does not impair the effects of the present invention. Such an amount is, for example, 0.05 to 1.5 parts by weight, or may be 0.1 to 1 part by weight, per 100 parts by weight of the monomer component (M).

[0082] <1-2. Crosslinking Agent> The acrylic pressure-sensitive adhesive composition may contain a crosslinking agent. The crosslinking agent may be of one type only, or may be of two or more types.

[0083] Examples of crosslinking agents that can be contained in the acrylic pressure-sensitive adhesive composition include isocyanate-based crosslinking agents, peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. The crosslinking agent that can be contained in the acrylic pressure-sensitive adhesive composition is preferably at least one selected from the group consisting of isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and peroxide-based crosslinking agents, more preferably at least one selected from the group consisting of isocyanate-based crosslinking agents and peroxide-based crosslinking agents, and even more preferably an isocyanate-based crosslinking agent.

[0084] The crosslinking agent may be selected from one type of crosslinking agent (for example, an isocyanate crosslinking agent), or may be selected from two or more types of crosslinking agents.

[0085] As the isocyanate-based crosslinking agent, a compound having at least two isocyanate groups (isocyanate compound) can be used. The number of isocyanate groups contained in the isocyanate compound is preferably 3 or more. The upper limit of the number of isocyanate groups is not particularly limited, and is, for example, 5. Examples of the isocyanate compound include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds.

[0086] Examples of aromatic isocyanate compounds include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate.

[0087] Examples of alicyclic isocyanate compounds include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

[0088] Examples of the aliphatic isocyanate compound include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0089] Examples of the isocyanate-based crosslinking agent include polymers (dimers, trimers, pentamers, etc.) of the above-mentioned isocyanate compounds, adducts obtained by addition to polyhydric alcohols such as trimethylolpropane, urea-modified products, biuret-modified products, allophanate-modified products, isocyanurate-modified products, carbodiimide-modified products, and urethane prepolymers obtained by addition to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0090] The isocyanate-based crosslinking agent is preferably an aromatic isocyanate compound and its derivatives, more preferably tolylene diisocyanate and its derivatives, in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent. From the viewpoint of reactivity, a TDI-based crosslinking agent is more suitable than xylylene diisocyanate and its derivatives, in other words, a xylylene diisocyanate-based (XDI-based) crosslinking agent. The isocyanate-based crosslinking agent may contain an adduct of a polyhydric alcohol and tolylene diisocyanate as the TDI-based crosslinking agent. A specific example of the adduct is a trimethylolpropane / tolylene diisocyanate trimer adduct.

[0091] Commercially available isocyanate crosslinking agents may be used. Examples of such commercially available products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation), Takenate D-101E, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500, and Takenate 600 (all manufactured by Mitsui Chemicals, Inc.). Of these, Takenate D-101E and Takenate D110N are preferred.

[0092] The amount of the isocyanate crosslinking agent in the acrylic pressure-sensitive adhesive composition is, for example, 0.01 to 20 parts by weight per 100 parts by weight of the acrylic polymer. The lower limit of the amount may be 0.02 parts by weight or more, 0.03 parts by weight or more, 0.04 parts by weight or more, or 0.05 parts by weight or more. The upper limit of the amount may be 15 parts by weight or less, 13 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, 0.1 parts by weight or less, or 0.08 parts by weight or less. A typical amount may be 0.03 to 1 part by weight, or 0.05 to 0.5 parts by weight.

[0093] The amount of a crosslinking agent other than an isocyanate-based crosslinking agent (e.g., a peroxide-based crosslinking agent) blended in the acrylic pressure-sensitive adhesive composition is, for example, 2 parts by weight or less, or may be 1 part by weight or less, or may be 0.5 parts by weight or less, relative to 100 parts by weight of the base polymer. The lower limit of the blending amount is, for example, 0.1 parts by weight or more, or may be 0.2 parts by weight or more, or may be 0.3 parts by weight or more. A typical blending amount may be 0.1 to 1 part by weight, or may be 0.3 to 0.5 parts by weight. The acrylic pressure-sensitive adhesive composition may not contain a crosslinking agent other than an isocyanate-based crosslinking agent.

[0094] <1-3. Other Components> The acrylic pressure-sensitive adhesive composition may contain known additives as other components. Any appropriate additives may be used as such additives as long as they do not impair the effects of the present invention. Examples of such additives include silane coupling agents, solvents, colorants, pigments, powders, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, inorganic fillers, organic fillers, metal powders, particles, and foil-like materials. Furthermore, redox systems containing a reducing agent may be used within a controllable range. The amount of additives may be any appropriate amount as long as it does not impair the effects of the present invention. Such an amount may be, for example, 10 parts by weight or less, 5 parts by weight or less, or even 1 part by weight or less, in total, per 100 parts by weight of the acrylic polymer.

[0095] <<2. Pressure-sensitive adhesive sheet>> The pressure-sensitive adhesive sheet according to an embodiment of the present invention includes the acrylic pressure-sensitive adhesive according to an embodiment of the present invention. Because the pressure-sensitive adhesive sheet according to an embodiment of the present invention includes the acrylic pressure-sensitive adhesive according to an embodiment of the present invention, it can be a pressure-sensitive adhesive sheet with a high refractive index and an attractive appearance in which the generation of precipitates (typically white precipitates) on the surface is suppressed.

[0096] The content of the acrylic pressure-sensitive adhesive according to an embodiment of the present invention in the pressure-sensitive adhesive sheet according to an embodiment of the present invention is preferably 50% by weight to 100% by weight, or may be 70% by weight to 100% by weight, 80% by weight to 100% by weight, 90% by weight to 100% by weight, 95% by weight to 100% by weight, or 99% by weight to 100% by weight. The pressure-sensitive adhesive sheet according to an embodiment of the present invention may typically be composed of the acrylic pressure-sensitive adhesive according to an embodiment of the present invention.

[0097] The thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is typically less than 20 μm, and may be 17 μm or less, 15 μm or less, 13 μm or less, or 10 μm or less. The lower limit of the thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is typically 1 μm or more, 2 μm or more, 3 μm or more, or 4 μm or more. The thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention may be 1 μm to 20 μm, 2 μm to 17 μm, 3 μm to 15 μm, 4 μm to 13 μm, or 4 μm to 10 μm.

[0098] The average refractive index n of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is preferably 1.52 or more, and may be 1.54 or more, 1.56 or more, or 1.57 or more. The upper limit of the average refractive index n of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is preferably as high as possible from the viewpoint of having a high refractive index, but in consideration of the requirements for practical use, it is, for example, 1.70 or less.

[0099] The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be formed by any appropriate method as long as the effects of the present invention are not impaired. The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be formed, for example, by drying a coating film of an acrylic pressure-sensitive adhesive composition provided on any appropriate substrate. Heating, for example, may be used as such a drying method. The substrate may be, for example, a release liner. The release liner may be a known film that can be used when forming a pressure-sensitive adhesive sheet from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet formed on the substrate may be transferred to another layer included in the optical laminate according to the embodiment of the present invention, for example, a first liquid crystal alignment solidified layer or a second liquid crystal alignment solidified layer. The substrate may be another layer that may be included in the optical laminate according to the embodiment of the present invention.

[0100] A release liner may be provided on the surface of the PSA sheet. Examples of release liners include films, paper, woven fabrics, nonwoven fabrics, porous materials, nets, foams, foils, and laminates thereof, made of resin, paper, fiber, metal, or composite materials thereof. Examples of resins include polyethylene, polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinyl chloride, vinyl chloride copolymers, polyethylene terephthalate, polybutylene terephthalate, polyurethane, and ethylene-vinyl acetate copolymers.

[0101] The thickness of the release liner is, for example, 5 μm to 200 μm, and may be 5 to 100 μm. The surface of the release liner may be subjected to various surface treatments such as release treatment, antifouling treatment, and antistatic treatment, as necessary.

[0102] The drying temperature of the coating film may be any appropriate temperature within a range that does not impair the effects of the present invention. Such a drying temperature may be, for example, 130°C or lower, 125°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower. The drying temperature may be, for example, 60°C or higher, or 80°C or higher. The drying time of the coating film may be any appropriate time within a range that does not impair the effects of the present invention. Such a drying time may be, for example, 30 to 300 seconds, 40 to 240 seconds, or 60 to 180 seconds.

[0103] The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be useful in other applications, such as in the optical laminate according to the embodiment of the present invention, for example, in the application between the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer. The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be preferably used for bonding the liquid crystal alignment solidified layer.

[0104] Optical laminate An optical laminate according to an embodiment of the present invention includes a pressure-sensitive adhesive sheet according to an embodiment of the present invention. The optical laminate according to an embodiment of the present invention may include any appropriate other member (typically an optical member) as long as it includes a pressure-sensitive adhesive sheet according to an embodiment of the present invention.

[0105] An optical laminate according to one embodiment of the present invention includes a first liquid crystal alignment solidified layer, a pressure-sensitive adhesive sheet according to an embodiment of the present invention, and a second liquid crystal alignment solidified layer, in this order. The optical laminate according to an embodiment of the present invention may include any appropriate other components (typically optical components) as long as the effects of the present invention are not impaired, as long as the optical laminate includes a first liquid crystal alignment solidified layer, a pressure-sensitive adhesive sheet according to an embodiment of the present invention, and a second liquid crystal alignment solidified layer, in this order. Examples of such other components (typically optical components) include substrates and release liners used when forming the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer. In an optical laminate according to one preferred embodiment of the present invention, the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer each constitute the outermost layer.

[0106] The optical laminate according to an embodiment of the present invention may further include a positive C plate in addition to the first liquid crystal alignment solidified layer, the pressure-sensitive adhesive sheet, and the second liquid crystal alignment solidified layer. The positive C plate has a refractive index characteristic of nz > nx = ny. The thickness direction retardation Rth(550) of the positive C plate is preferably -20 nm to -300 nm, more preferably -30 nm to -250 nm, even more preferably -40 nm to -200 nm, and particularly preferably -50 nm to -150 nm. Here, "nx = ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the positive C plate may be less than 10 nm.

[0107] The positive C plate can be formed, for example, using a liquid crystal composition containing a side-chain liquid crystal polymer described below. Examples of methods for forming the positive C plate include those described in paragraphs

[0020] to

[0028] of JP-A No. 2002-333642. In this case, the thickness of the positive C plate is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

[0108] Fig. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. The optical laminate 100 shown in Fig. 1 has a first liquid crystal alignment solidified layer 11, an adhesive sheet 20, and a second liquid crystal alignment solidified layer 12, in this order, where the first liquid crystal alignment solidified layer 11 and the adhesive sheet 20 are directly laminated together, and the adhesive sheet 20 and the second liquid crystal alignment solidified layer 12 are directly laminated together.

[0109] The optical laminate according to an embodiment of the present invention may include a polarizing film on at least one side selected from the group consisting of the first liquid crystal alignment solidified layer side and the second liquid crystal alignment solidified layer side as viewed from the pressure-sensitive adhesive sheet. That is, the optical laminate according to an embodiment of the present invention is an optical laminate for laminating to a polarizing film, and may include a polarizing film on at least one side selected from the group consisting of the first liquid crystal alignment solidified layer side and the second liquid crystal alignment solidified layer side as viewed from the pressure-sensitive adhesive sheet. Such an embodiment is, for example, an embodiment in which a polarizing film 200 is laminated to the optical laminate 100 via an adhesive layer 30, as shown in FIG. 2 described later. Note that FIG. 2 shows an embodiment in which the polarizing film 200 is provided on the first liquid crystal alignment solidified layer 11 side as viewed from the pressure-sensitive adhesive sheet 20 in the optical laminate 100, but the polarizing film 200 may also be provided on the second liquid crystal alignment solidified layer 12 side as viewed from the pressure-sensitive adhesive sheet 20 in the optical laminate 100.

[0110] The total thickness of the optical laminate according to the embodiment of the present invention may be any appropriate total thickness as long as the effects of the present invention are not impaired. Such a total thickness is preferably 20 μm or less, and may be 1 μm to 20 μm, 2 μm to 15 μm, or 3 μm to 10 μm.

[0111] 3-1. Liquid Crystal Alignment Solidified Layer The optical laminate according to the embodiment of the present invention includes a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer. By using the liquid crystal alignment solidified layer in this way, the optical laminate according to the embodiment of the present invention can be made thinner.

[0112] The liquid crystal alignment fixed layer may be a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer, and the alignment state is fixed.

[0113] Examples of liquid crystal compounds used in the liquid crystal alignment solidified layer include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably a polymerizable liquid crystal compound, i.e., a liquid crystal monomer. If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing it. The polymer formed by polymerization can be non-liquid crystal. Therefore, the formed liquid crystal alignment solidified layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes that are specific to liquid crystal compounds. As a result, the liquid crystal alignment solidified layer is not affected by temperature changes and has excellent stability.

[0114] In one embodiment, the liquid crystal alignment solidified layer can be formed using a liquid crystal composition containing a liquid crystal monomer. In this specification, the liquid crystal monomer contained in the liquid crystal composition refers to a compound having a polymerizable group and liquid crystallinity. The polymerizable group refers to a group that participates in a polymerization reaction, preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can participate in a polymerization reaction by an active radical or acid generated from a photopolymerization initiator. Examples of such liquid crystal monomers that can be used include polymerizable mesogen compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US Pat. No. 5,211,877), EP 66137 (US Pat. No. 4,388,453), WO 93 / 22397, EP 0,261,712, DE 19504224, DE 4408171, and GB 2,280,445. Examples of such polymerizable mesogenic compounds include LC242 (trade name) from BASF, E7 (trade name) from Merck, and LC-Silicon-CC3767 (trade name) from Wacker-Chem.

[0115] The mechanism by which the liquid crystal monomer exhibits liquid crystallinity may be thermotropic or lyotropic. The liquid crystal phase may be nematic or smectic. From the viewpoint of ease of production, the liquid crystallinity is preferably thermotropic nematic liquid crystal.

[0116] The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the type of the liquid crystal monomer, and specifically, such a temperature range is, for example, 40°C to 120°C, or may be 50°C to 100°C, or may be 60°C to 90°C.

[0117] The birefringence Δn of the liquid crystal alignment solidified layer is, for example, 0.06 or more, or may be 0.08 or more, 0.09 or more, or 0.10 or more. The upper limit of Δn is, for example, 0.13 or less, or may be 0.12 or less. If Δn is in this range, a desired in-plane retardation can be achieved with a very thin thickness. As a result, it becomes possible to further thin the liquid crystal alignment solidified layer and the optical laminate, which can ultimately contribute to, for example, significantly reducing the thickness of image display devices.

[0118] The liquid crystal alignment solidified layer may exhibit an inverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value changes little depending on the wavelength of the measurement light.

[0119] The first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer can each typically function as a λ / 2 plate or a λ / 4 plate. The first liquid crystal alignment solidified layer can typically function as a λ / 2 plate, and the second liquid crystal alignment solidified layer can typically function as a λ / 4 plate.

[0120] Specifically, Re(550) of the first liquid crystal alignment solidified layer is, for example, 150 nm to 300 nm, may be 200 nm to 270 nm, or may be 220 nm to 260 nm.

[0121] Specifically, the Re(550) of the second liquid crystal alignment solidified layer is, for example, 100 nm to 200 nm, may be 110 nm to 160 nm, or may be 120 nm to 140 nm.

[0122] The thickness of the first liquid crystal alignment solidified layer can typically be adjusted to obtain the desired in-plane retardation of the λ / 2 plate. In one embodiment, the thickness of the first liquid crystal alignment solidified layer is, for example, 0.5 μm to 5.0 μm, or may be 0.8 μm to 4.0 μm, 1.0 μm to 3.0 μm, 1.2 μm to 2.5 μm, or 1.3 μm to 2.0 μm. In another embodiment, the thickness of the first liquid crystal alignment solidified layer is, for example, 0.3 μm to 1.7 μm, or may be 0.7 μm to 1.6 μm, 1.0 μm to 1.5 μm, or 1.3 μm to 1.5 μm. Thus, according to an embodiment of the present invention, linear unevenness can be suppressed while the thickness of the first liquid crystal alignment solidified layer is thinner than conventional ones.

[0123] The thickness of the second liquid crystal alignment solidified layer can be adjusted to obtain a desired in-plane retardation of the λ / 4 plate. In one embodiment, the thickness of the second liquid crystal alignment solidified layer is, for example, 0.5 μm to 2.5 μm, or may be 0.6 μm to 2.0 μm, 0.7 μm to 1.5 μm, 0.7 μm to 1.2 μm, or 0.7 μm to 1.1 μm.

[0124] The angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer is, for example, 10° to 20°, or may be 12° to 18°, or 14° to 16°. The angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer is, for example, 70° to 80°, or may be 72° to 78°, or may be 74° to 76°. The arrangement order of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer may be reversed, and the angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer and the angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer may also be reversed.

[0125] The average refractive index of the liquid crystal alignment solidified layer can vary depending on the composition forming the liquid crystal alignment solidified layer (substantially, the type of liquid crystal compound, the type, number, combination, and amount of additives, etc.) The average refractive index n1 of the first liquid crystal alignment solidified layer and the average refractive index n2 of the second liquid crystal alignment solidified layer may be the same or different from each other (the average refractive index n1 of the first liquid crystal alignment solidified layer may be larger, and the average refractive index n2 of the second liquid crystal alignment solidified layer may be larger).

[0126] The average refractive index n1 of the first liquid crystal alignment solidified layer is, for example, 1.55 to 1.75, and may be 1.60 to 1.70.

[0127] The average refractive index n2 of the second liquid crystal alignment solidified layer is, for example, 1.45 to 1.65, and may be 1.50 to 1.60.

[0128] The average refractive index n1 of the first liquid crystal alignment solidified layer and the average refractive index n2 of the second liquid crystal alignment solidified layer may be reversed. The absolute value of the difference between the average refractive index n1 of the first liquid crystal alignment solidified layer and the average refractive index n2 of the second liquid crystal alignment solidified layer may be, for example, 0.00 to 0.20. The average refractive index of the liquid crystal alignment solidified layer will typically be determined based on the composition of the liquid crystal alignment solidified layer to obtain the desired optical characteristics. As a result, linear unevenness may occur, but according to embodiments of the present invention, such linear unevenness can be suppressed.

[0129] A side-chain thermotropic liquid crystal polymer may be introduced into the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer (essentially, the liquid crystal composition forming these layers). The introduction of a side-chain thermotropic liquid crystal polymer can induce homeotropic alignment (vertical alignment) of the liquid crystal monomer. As a result, the nz of the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer can be increased, and as a result, the Nz coefficient of the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer can be appropriately adjusted. Ultimately, the Nz coefficient of the retardation layer can be set to, for example, a range of 0.30 to 0.70 without providing a positive C plate.

[0130] A typical example of a side-chain thermotropic liquid crystal polymer is a copolymer having a monomer unit containing a thermotropic liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment side chain. When the polymer has a thermotropic liquid crystal fragment in its side chain, the side-chain liquid crystal polymer can be oriented when a liquid crystal composition containing the liquid crystal monomer is heated to a predetermined temperature. Furthermore, when the side-chain polymer has a non-liquid crystal fragment in its side chain, the non-liquid crystal fragment can interact with the photopolymerizable liquid crystal monomer, causing the photopolymerizable liquid crystal monomer to be homeotropically oriented.

[0131] As the side chain type thermotropic liquid crystal polymer, a copolymer having a liquid crystalline monomer unit represented by general formula (I) and a non-liquid crystalline monomer unit represented by general formula (II) is preferably used.

[0132] In formula (I), R １ is a hydrogen atom or a methyl group, and R ２ is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms; X １ Ha-CO ２ a is an integer of 1 to 6, and b and c are each independently 1 or 2.

[0133] In formula (II), R ３ is a hydrogen atom or a methyl group, and R ４ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or a group represented by the following general formula (III):

[0134] In formula (III), R ５ is an alkyl group having 1 to 5 carbon atoms, and d is an integer of 1 to 6.

[0135] The ratio of the liquid crystalline monomer unit to the non-liquid crystalline monomer unit in the side chain liquid crystal monomer can be appropriately set depending on the purpose. The ratio (molar ratio) of the non-liquid crystalline monomer to the total of the liquid crystalline monomer unit and the non-liquid crystalline monomer unit is, for example, 0.05 to 0.80, or may be 0.10 to 0.60, or may be 0.15 to 0.50.

[0136] The ratio of the liquid crystal monomer to the side-chain liquid crystal polymer in the liquid crystal composition can be appropriately set depending on the purpose. The content of the liquid crystal monomer relative to the content of the side-chain liquid crystal polymer is, for example, 1.2 to 20 times, or may be 1.3 to 10 times, or 1.4 to 9 times, or may be 1.5 to 8 times.

[0137] The side-chain liquid crystal polymer and the method for forming the liquid crystal alignment solidified layer are described, for example, in Japanese Patent No. 6769921, the description of which is incorporated herein by reference.

[0138] 3-2. Polarizing Film The optical laminate according to the embodiment of the present invention may include a polarizing film on at least one side selected from the group consisting of the first liquid crystal alignment solidified layer side and the second liquid crystal alignment solidified layer side when viewed from the pressure-sensitive adhesive sheet.

[0139] The polarizing film may be laminated directly to at least one selected from the group consisting of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer, or may be laminated via an interlayer adhesive (typically, an adhesive).

[0140] Fig. 2 is a schematic cross-sectional view of an optical laminate with a polarizing film according to one embodiment of the present invention. In the embodiment shown in Fig. 2, a pressure-sensitive adhesive layer is provided on the side of the first liquid crystal alignment solidified layer opposite the pressure-sensitive adhesive sheet. The optical laminate 500 with a polarizing film shown in Fig. 2 includes, in this order, a polarizing film 200, an adhesive layer 30, and an optical laminate 100 which is a laminate of a first liquid crystal alignment solidified layer 11, a pressure-sensitive adhesive sheet 20, and a second liquid crystal alignment solidified layer 12. The polarizing film 200 and the adhesive layer 30 are directly laminated together, the adhesive layer 30 and the first liquid crystal alignment solidified layer 11 are directly laminated together, the first liquid crystal alignment solidified layer 11 and the pressure-sensitive adhesive sheet 20 are directly laminated together, and the pressure-sensitive adhesive sheet 20 and the second liquid crystal alignment solidified layer 12 are directly laminated together.

[0141] 3 is a schematic cross-sectional view showing an optical laminate with a polarizing film according to another embodiment of the present invention. The laminate 600 with a polarizing film shown in FIG. 3 includes a polarizing film 200, an adhesive layer 30, an optical laminate 100 which is a laminate of a first liquid crystal alignment solidified layer 11, a pressure-sensitive adhesive sheet 20, and a second liquid crystal alignment solidified layer 12, in this order, and a pressure-sensitive adhesive layer 60. The polarizing film 200 and the adhesive layer 30 are directly laminated together, the adhesive layer 30 and the first liquid crystal alignment solidified layer 11 are directly laminated together, the first liquid crystal alignment solidified layer 11 and the pressure-sensitive adhesive sheet 20 are directly laminated together, the pressure-sensitive adhesive sheet 20 and the second liquid crystal alignment solidified layer 12 are directly laminated together, and the second liquid crystal alignment solidified layer 12 and the pressure-sensitive adhesive layer 60 are directly laminated together.

[0142] The polarizing film 200 typically includes a polarizer 40 and protective layers 51 and 52 arranged on both sides of the polarizer 40 (see FIG. 2; these reference numerals are omitted in FIG. 3). Depending on the purpose, at least one of the protective layers 51 and 52 may be omitted. Therefore, the polarizing film may be a so-called double-protected polarizing film, a so-called single-protected polarizing film, or may be composed of a polarizer alone.

[0143] <3-2-a. Polarizer> A polarizer is typically made of a film made of a polyvinyl alcohol (PVA)-based resin containing a dichroic substance (e.g., iodine). Examples of PVA-based resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified ethylene-vinyl acetate copolymer.

[0144] The PVA-based resin preferably includes an acetoacetyl-modified PVA-based resin, and the amount of the acetoacetyl-modified PVA-based resin is, for example, 5% by weight to 20% by weight, or may be 8% by weight to 12% by weight, based on 100% by weight of the entire PVA-based resin.

[0145] The polarizer preferably contains iodide or sodium chloride (sometimes collectively referred to as a halide). Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. The content of the halide in the polarizer is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA-based resin. In the manufacturing method described below, the halide is blended into a coating liquid that forms a PVA-based resin layer, which is a precursor of the polarizer, and can be finally introduced into the polarizer. Introducing a halide into the polarizer can improve the orientation of PVA molecules in the polarizer, thereby realizing a polarizer with excellent optical properties (typically, both a high degree of polarization and a high single-unit transmittance).

[0146] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The polarizer has a single transmittance of, for example, 41.0% to 46.0%, or may be 42.0% to 45.0%. The polarizer has a degree of polarization of, for example, 97.0% or more, or may be 99.0% or more, or may be 99.9% or more.

[0147] The thickness of the polarizer is, for example, 12 μm or less, or may be 10 μm or less, or may be 1 μm to 8 μm, or may be 3 μm to 7 μm. By combining such a thin polarizer with a liquid crystal alignment solidified layer, it is possible to significantly reduce the thickness of the optical laminate.

[0148] The polarizer can be produced by any appropriate method. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0149] Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as PVA films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Preferably, a polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching it is used because of its excellent optical properties.

[0150] The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA-based film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA-based film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents from the surface of the PVA-based film and also to swell the PVA-based film, thereby preventing uneven dyeing and the like.

[0151] Specific examples of laminate polarizers include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. Preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate.

[0152] The stretching typically involves immersing the laminate polarizer in a boric acid aqueous solution and stretching it. Furthermore, the stretching may further include, if necessary, in-air stretching of the laminate at a high temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution. Preferably, the laminate is subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the method involves subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. The introduction of auxiliary stretching can enhance the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby enabling the achievement of high optical properties. Furthermore, by simultaneously enhancing the orientation of the PVA in advance, problems such as a decrease in orientation or dissolution of the PVA can be prevented when the PVA is immersed in water in the subsequent dyeing or stretching steps, thereby enabling the achievement of high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment processes in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through a drying shrinkage treatment. The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may serve as a protective layer for the polarizer). Alternatively, any suitable protective layer may be laminated on the peeled surface of the resin substrate / polarizer laminate after peeling the resin substrate from the resin substrate / polarizer laminate, or on the surface opposite to the peeled surface. Details of such a polarizer manufacturing method are described, for example, in JP-A-2012-73580 and JP-A-6470455. The entire disclosures of these publications are incorporated herein by reference.

[0153] <3-2-b. Protective Layer> The protective layers that can be disposed on both sides of the polarizer are typically composed of any appropriate resin film. Typical materials for such resin films include cellulose-based resins such as triacetyl cellulose (TAC), cycloolefin-based resins such as polynorbornene, (meth)acrylic resins, polyester-based resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin-based resins such as polyethylene, and polycarbonate-based resins. A typical example of a (meth)acrylic resin is a (meth)acrylic resin having a lactone ring structure. Examples of (meth)acrylic resins having a lactone ring structure are described in, for example, JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544 A, and JP 2005-146084 A. These publications are incorporated herein by reference. From the viewpoint of ease of processing into modified shapes, etc., cellulose-based resins are preferred, and TAC is more preferred. From the viewpoint of obtaining a polarizing plate with low moisture permeability and excellent durability, cycloolefin-based resins and (meth)acrylic resins are preferred.

[0154] The protective layer may be subjected to a surface treatment as needed. Examples of surface treatments include hard coating, anti-reflection, anti-sticking, and anti-glare treatments. The protective layer may be subjected to a treatment to improve visibility when viewed through polarized sunglasses (typically, by imparting an (elliptically) circular polarization function or an ultra-high phase difference) as needed. By performing such treatments, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses.

[0155] The protective layer may be optically isotropic, for example, the in-plane retardation Re(550) may be 0 nm to 10 nm, and the thickness direction retardation Rth(550) may be −10 nm to +10 nm.

[0156] The thickness of each protective layer is, for example, 10 μm to 80 μm, or may be 12 μm to 40 μm, or 15 μm to 35 μm. If the protective layer is surface-treated, the thickness of the protective layer includes the thickness of the surface-treated layer.

[0157] <3-3. Adhesive Layer> In the optical laminate according to one embodiment of the present invention, any suitable adhesive layer can be used as the adhesive layer that can be provided between the polarizing film and the optical laminate, as long as the effects of the present invention are not impaired. Such an adhesive layer is usually adhered via an ultraviolet-curable adhesive or an aqueous adhesive. Examples of aqueous adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl-based latex adhesives, aqueous polyurethanes, and aqueous polyesters. In addition to the above, examples of the adhesive layer include electron beam-curable adhesives. The adhesive layer may contain a metal compound filler.

[0158] <3-4. Pressure-sensitive adhesive layer> Any appropriate pressure-sensitive adhesive layer can be used as the pressure-sensitive adhesive layer as long as the effects of the present invention are not impaired. For example, a pressure-sensitive adhesive layer made of a known pressure-sensitive adhesive that can be used for bonding optical components can be used as such a pressure-sensitive adhesive layer. A preferred example of such a pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer made of a known acrylic pressure-sensitive adhesive.

[0159] A release liner may be provided on the surface of the pressure-sensitive adhesive layer. Examples of the release liner include films, paper, woven fabrics, nonwoven fabrics, porous materials, nets, foams, foils, and laminates thereof, made of resin, paper, fiber, metal, or composite materials thereof. Examples of resins include polyethylene, polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinyl chloride, vinyl chloride copolymers, polyethylene terephthalate, polybutylene terephthalate, polyurethane, and ethylene-vinyl acetate copolymers.

[0160] The thickness of the release liner is, for example, 5 μm to 200 μm, and may be 5 to 100 μm. The surface of the release liner may be subjected to various surface treatments such as release treatment, antifouling treatment, and antistatic treatment, as necessary.

[0161] <<4. Image Display Device>> An image display device according to an embodiment of the present invention includes an optical laminate according to an embodiment of the present invention.

[0162] Representative examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention typically includes an optical laminate according to an embodiment of the present invention on the viewing side thereof.

[0163] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The test and evaluation methods used in the examples are as follows. The term "parts" means "parts by weight" unless otherwise specified, and the term "%" means "% by weight" unless otherwise specified.

[0164] <Measurement of the content of at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in an acrylic adhesive> The content of at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in an acrylic adhesive was measured by LC / MS. Approximately 0.05 g of the acrylic adhesive (adhesive sheet) obtained in the Examples and Comparative Examples was sampled, 5 mL of THF was added, and the mixture was shaken overnight. 5 mL of acetonitrile was added to the extract to reprecipitate the polymer component, and the supernatant was filtered through a membrane filter with a pore size of 0.45 μm. The resulting solution was measured by LC / MS. The lower limit of quantitation in the LC / MS measurement was 40 ppm. (LC / MS apparatus) Vanquish Orbitrap Explorer MX, manufactured by Thermo Fisher Scientific (LC / MS analysis conditions) Column: Waters Atlantis T3 (3.0 mmφ×150 mm, packing particle size: 3 μm) Eluent composition: 0.05% trifluoroacetic acid / methanol gradient conditions Column temperature: 50° C. Column flow rate: 0.5 mL / min Injection volume: 1 μL Detector: MS (ESI-Neg.) Measurement m / z range: 100 to 250 Detected m / z: 185.0278

[0165] <Measurement of Residual Monomer Content in Acrylic Pressure-Sensitive Adhesive> The residual monomer content in the acrylic pressure-sensitive adhesive was measured by GC. Approximately 0.1 g of the acrylic pressure-sensitive adhesive (adhesive sheet) obtained in the Examples and Comparative Examples was collected in a screw bottle, 5 mL of acetone was added, and the bottle was shaken overnight. The resulting solution was filtered through a membrane filter with a pore size of 0.45 μm, and 1 μL of the resulting solution was injected into a GC for GC measurement. (GC device) Agilent Technologies, GC7890A (GC measurement conditions) Column: HP-1 (0.250 mmφ x 30 m, df = 1.0 μm) Column temperature: 40°C (3 min) → +10°C / min → 120°C → +20°C / min → 300°C (hold) Column flow rate: 1 mL / min (N2) Column pressure: 75 kPa (constant flow mode) Injection port temperature: 200°C Injection volume: 1 μL Injection method: Split (20:1) Detector: FID Detector temperature: 250°C

[0166] <Measurement of Thickness> Measurement was carried out using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800").

[0167] <Measurement of refractive index of pressure-sensitive adhesive sheet> The refractive index of the pressure-sensitive adhesive sheet was measured using an Abbe refractometer (manufactured by ATAGO, product name "DR-M2 / 1550") for the laminates having a release liner / pressure-sensitive adhesive sheet configuration obtained in the Examples and Comparative Examples (pressure-sensitive adhesive sheets (1) to (7), (C1) to (C3) as pressure-sensitive adhesive sheets) from which the release liners had been peeled. The measurement wavelength was 589 nm, and the measurement temperature was 25°C. [Refractive index of liquid crystal alignment solidified layer] The refractive index of the liquid crystal alignment solidified layer was determined in the transmission axis direction as follows. The in-plane retardation Re(550) and thickness direction retardation Rth(550) were measured using an Axoscan (manufactured by Axometrics). nx, ny, and nz were calculated from the following simultaneous equations. Re(550) = (nx - ny) x d Nz = Rth(550) / Re(550) = (nx - nz) / (nx - ny) Furthermore, the formula of the ellipse (x ２ / a ２ ) + (y ２ / b ２ ) = 1, a is nx, b is ny, x and y are the refractive indices in the x and y directions in the angle θ direction on the ellipse, and the refractive index in the transmission axis direction is calculated by solving a simultaneous equation using y = tan θ and the above nx and ny.

[0168] <Evaluation of Appearance of Pressure-Sensitive Adhesive Sheet Surface> The adhesive sheet surface of each of the laminates having a release liner / pressure-sensitive adhesive sheet configuration obtained in the Examples and Comparative Examples (pressure-sensitive adhesive sheets (1) to (7), (C1) to (C3) as the pressure-sensitive adhesive sheets) was bonded to the surface of a glass plate (Corning, Eagle XG), and then the release liner was peeled off. The bonding was carried out in an atmosphere at a temperature of 23°C and a humidity of 50% RH. Next, the laminate was treated for 15 minutes in an autoclave at a temperature of 50°C and 5 atmospheres (absolute pressure), and then left to cool to 23°C, thereby stabilizing the bonding of the laminate to the glass plate. Next, the entire product was left in an atmosphere at a temperature of 20°C and a humidity of 98% RH for 24 hours. After leaving the laminate, it was returned to an atmosphere at a temperature of 23°C and a humidity of 50% RH, and the appearance of the pressure-sensitive adhesive sheet surface was evaluated according to the following criteria: ○: No defects in appearance. △: Some deposits were observed, but the level was practically acceptable. ×: Deposits occurred over the entire surface.

[0169] <Evaluation of Interference Unevenness> For each of the polarized film-attached optical laminates (1b) to (7b) and (C1b) to (C3b) obtained in the Examples and Comparative Examples, the release liner was peeled off and the exposed pressure-sensitive adhesive sheet was attached to a V3 reflector (manufactured by NEODIS) with a hand roller to prepare a test sample. The obtained test samples were visually observed under a three-wavelength fluorescent lamp and evaluated according to the following criteria: ⊚: No interference unevenness was observed. ◯: Slight interference unevenness was observed. Δ: Interference unevenness was observed, but it was at a level acceptable for practical use. ×: Interference unevenness was noticeable.

[0170] <Evaluation of Durability> The acrylic pressure-sensitive adhesive composition (A) obtained in Production Example 6 was applied to a release liner (Mitsubishi Chemical Corporation, MRF38-NS2) to a dried thickness of 25 μm, and cured and dried at a drying temperature of 155°C for 90 seconds to obtain a pressure-sensitive adhesive sheet (A). For each of the polarized film-attached optical laminates (1b) to (7b) and (C1b) to (C3b) obtained in the Examples and Comparative Examples, the release liner was peeled off, and the exposed pressure-sensitive adhesive sheet was bonded to the surface of a glass plate (Corning, Eagle XG) using a hand roller. The lamination was performed in an atmosphere of 23°C and 50% RH. Next, the laminate was treated in an autoclave at 50°C and 5 atmospheres (absolute pressure) for 15 minutes, and then left to cool to 23°C to stabilize the bonding of the laminate to the glass plate. The entire laminate was then left in a heated atmosphere at 105°C for 24 hours. After leaving, the sample was returned to an atmosphere of 23°C and 50% RH, and it was visually confirmed whether the laminate had peeled off from the glass plate, and durability at high temperature was evaluated according to the following criteria: ∘: No bubbling or peeling was observed. ×: Bubbling or peeling was observed.

[0171] [Production Example 1] Preparation of First Liquid Crystal Alignment Solidified Layer A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF's "Paliocolor LC242," chemical formula shown below) was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30 wt %. A surfactant (BYK-Chemie's "BYK-360") and a photopolymerization initiator (IGM Resins' "Omnirad 907") were added to this solution to prepare a liquid crystal composition solution. The surfactant and polymerization initiator were added in amounts of 0.01 and 3 parts by weight, respectively, per 100 parts by weight of the photopolymerizable liquid crystal compound. A biaxially stretched norbornene-based film (Zeon Corporation's "ZEONORFILM," thickness 33 μm, Re(550) = 135 nm) was prepared as a substrate. The liquid crystal composition was applied to the substrate using a bar coater so that the Re(550) was 240 nm, and the liquid crystal was aligned by heating at 100°C for 3 minutes. After cooling to room temperature, the substrate was photocured by irradiating with ultraviolet light at an integrated dose of 400 mJ / cm2 under a nitrogen atmosphere, yielding a laminate having a substrate / first liquid crystal alignment solidified layer configuration. The first liquid crystal alignment solidified layer was homogeneously aligned, had a thickness of 1.7 μm, and an average refractive index of 1.590.

[0172] [Production Example 2]: Preparation of second liquid crystal alignment solidified layer A laminate having a structure of substrate / second liquid crystal alignment solidified layer (Re(550)=130 nm) was obtained in the same manner as in the production of the first liquid crystal alignment solidified layer in Production Example 1, except for changing the coating thickness. The second liquid crystal alignment solidified layer was homogeneously aligned, had a thickness of 0.92 μm, and had an average refractive index of 1.590.

[0173] [Manufacturing Example 3]: Preparation of Polarizer A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) with a Tg of approximately 75°C was used as the thermoplastic resin substrate. One side of the resin substrate was subjected to a corona treatment. A PVA-based resin (a 9:1 mixture of polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIRM") was mixed with 100 parts by weight of the PVA-based resin, and 13 parts by weight of potassium iodide was added and dissolved in water to prepare an aqueous PVA solution (coating solution). The PVA-based resin was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13 μm-thick PVA-based resin layer, producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (in-air auxiliary stretching treatment). Next, the laminate was immersed for 30 seconds in an insolubilizing bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) having a liquid temperature of 40°C (insolubilization treatment), then immersed for 60 seconds in a dyeing bath (an iodine aqueous solution obtained by blending iodine and potassium iodide with 100 parts by weight of water in a weight ratio of 1:7) having a liquid temperature of 30°C while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment), then immersed for 30 seconds in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) having a liquid temperature of 40°C (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls operating at different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). The laminate was then immersed in a cleaning bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20°C (washing treatment). The laminate was then dried in an oven maintained at approximately 90°C and brought into contact with a SUS heated roll maintained at a surface temperature of approximately 75°C (drying shrinkage treatment). In this way, a polarizer approximately 5 μm thick was formed on the resin substrate, yielding a laminate having a resin substrate / polarizer configuration. The polarizer's single transmittance Ts was 43.3%.

[0174] [Production Example 4]: Preparation of Polarized Film An HC-COP film was bonded to the surface of the polarizer obtained in Production Example 3 (the surface opposite to the resin substrate) via a UV-curable adhesive. The HC-COP film was a cycloolefin resin (COP) film (thickness 25 μm) with an HC layer (thickness 4 μm) formed thereon, and the COP film was bonded to the polarizer side. The COP film had an Re(550) of 135 nm. Next, the resin substrate was peeled off, and a triacetyl cellulose (TAC) film (thickness 25 μm) was bonded to the peeled surface via a UV-curable adhesive. In this way, a polarized film having a configuration of HC layer / COP film (protective layer) / polarizer / TAC film (protective layer) was obtained.

[0175] [Production Example 5]: Adhesive for laminating polarizing film and first liquid crystal alignment solidified layer Hydroxyethyl acrylamide (trade name "HEAA", manufactured by KJ Chemicals) 10 parts by weight, 2-acetoacetoxyethyl methacrylate (trade name "AAEM", manufactured by Mitsubishi Chemicals) 4 parts by weight, acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals) 60 parts by weight, tripropylene glycol diacrylate (trade name "Aronix M-220", 1 part by weight of 4-vinylphenylboronic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) manufactured by Toagosei Co., Ltd.) 11 parts by weight, acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.) 10 parts by weight, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins) An adhesive was prepared by stirring 1 part by weight of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.) 2 parts by weight of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.) and 1 part by weight of diethyl thioxanthone (trade name "KAYACUREDETX-S", manufactured by Nippon Kayaku Co., Ltd.) at 50°C for 1 hour.

[0176] [Production Example 6]: Acrylic polymer (A) and acrylic pressure-sensitive adhesive composition (A) A monomer mixture containing 94.9 parts by weight of butyl acrylate (BA), 5 parts by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate (HEA) was charged into a four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser. Furthermore, 0.1 parts by weight of 2,2'-azobisisobutyronitrile as a polymerization initiator and 100 parts by weight of ethyl acetate were charged to 100 parts by weight of this monomer mixture. Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the temperature in the flask was maintained at around 55°C, allowing the polymerization reaction to proceed for 8 hours to prepare a solution of acrylic polymer (A) having a weight average molecular weight (Mw) of 2,200,000. An acrylic pressure-sensitive adhesive composition (A) was prepared by blending 0.6 parts by weight of an isocyanate crosslinking agent (trimethylolpropane / tolylene diisocyanate adduct: manufactured by Tosoh Corporation, trade name "Coronate L"), 0.2 parts by weight of a peroxide crosslinking agent (benzoyl peroxide, manufactured by NOF Corporation, trade name "Niper BMT"), and 0.2 parts by weight of an epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403") relative to 100 parts by weight of the solids content of the solution of acrylic polymer (A).

[0177] [Production Example 7]: Production of purified phenoxybenzyl acrylate (1) 50 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical, purity 94%) was added to 100 parts by weight of cyclohexane and stirred. Furthermore, 60 parts by weight of an adsorbent (Mizusawa Industrial Chemicals, Mizuka Life F-1G) was added and stirred, and the stirring was stopped after 10 hours. Filter paper was placed in a Kiriyama funnel, and the adsorbent was removed by suction filtration under reduced pressure. The filtrate was concentrated in an evaporator to remove the solvent, yielding purified phenoxybenzyl acrylate (1).

[0178] [Production Example 8]: Production of purified phenoxybenzyl acrylate (2) 50 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical, purity 94%) was added to 100 parts by weight of cyclohexane and stirred. Furthermore, 5 parts by weight of an adsorbent (Mizuka Life F-1G, Mizusawa Industrial Chemicals) was added and stirred, and the stirring was stopped after 10 hours. Filter paper was placed in a Kiriyama funnel, and the adsorbent was removed by suction filtration under reduced pressure. The filtrate was concentrated in an evaporator to remove the solvent, yielding purified phenoxybenzyl acrylate (2).

[0179] Example 1 Acrylic Polymer (1), Acrylic Pressure-Sensitive Adhesive Composition (1) A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 85 parts by weight of the purified phenoxybenzyl acrylate (1) (purified POB-A (1)) obtained in Production Example 7, 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 14 parts by weight of butyl acrylate (BA). To 100 parts by weight of this monomer mixture, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was charged together with ethyl acetate. Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the liquid temperature in the flask was maintained at around 58°C, and a polymerization reaction was carried out for 8 hours. The monomer concentration during polymerization was 40% by weight. Thereafter, ethyl acetate was added to the resulting reaction solution to adjust the solids concentration to 30%, thereby preparing a solution of acrylic polymer (1). Solids content of acrylic polymer (1): 100 parts by weight, 0.3 parts by weight of an isocyanate-based crosslinking agent (trimethylolpropane / xylylene diisocyanate trimer adduct, Mitsui Chemicals, Takenate D-110N): and ethyl acetate was added as a dilution solvent to a solids content of 15%, and the mixture was mixed and stirred to prepare an acrylic pressure-sensitive adhesive composition (1). <Adhesive sheet (1) and optical laminates (1a), (1b) with polarized film> The first liquid crystal alignment solidified layer side of the laminate having the structure of substrate / first liquid crystal alignment solidified layer obtained in Production Example 1 was bonded to the TAC film side of the polarized film via the adhesive (thickness 1 μm) obtained in Production Example 5, and then the substrate was peeled off to obtain a laminate having the structure of polarized film / adhesive / first liquid crystal alignment solidified layer. Next, the acrylic pressure-sensitive adhesive composition (1) obtained above was applied to a release liner (Mitsubishi Chemical Corporation, MRF38-NS2) so as to give a thickness after drying of 5 μm, and the applied composition was cured and dried under conditions of a drying temperature of 120°C and a drying time of 90 seconds to form a pressure-sensitive adhesive sheet (1) on the release liner, thereby obtaining a laminate having a release liner / pressure-sensitive adhesive sheet (1) configuration.Next, the exposed surface of the first liquid crystal alignment solidified layer of the laminate having a polarizing film / adhesive / first liquid crystal alignment solidified layer configuration was plasma-treated, and then the exposed surface was bonded to the exposed surface of a pressure-sensitive adhesive sheet (1) formed on a release liner to obtain a laminate having a polarizing film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (1) / release liner configuration. After peeling the release liner, the second liquid crystal alignment solidified layer side of the laminate having a substrate / second liquid crystal alignment solidified layer configuration obtained in Production Example 2 was bonded to the pressure-sensitive adhesive sheet (1) side of the laminate. Before bonding, the exposed surface of the second liquid crystal alignment solidified layer of the laminate was subjected to corona irradiation. Next, the substrate was peeled off to obtain an optical laminate (1a) with a polarizing film having a polarizing film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (1) / second liquid crystal alignment solidified layer configuration. Separately, the acrylic pressure-sensitive adhesive composition (A) obtained in Production Example 6 was applied to a release liner (Mitsubishi Chemical Corporation, MRF38-NS2) to a dried thickness of 25 μm, and the coating was cured and dried at a drying temperature of 155°C for 90 seconds to obtain a pressure-sensitive adhesive sheet (A) / release liner laminate. The surface of the second liquid crystal alignment solidified layer of a polarized film-attached optical laminate (1a) having a configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (1) / second liquid crystal alignment solidified layer was subjected to corona irradiation, and the pressure-sensitive adhesive sheet (A) side of the pressure-sensitive adhesive sheet (A) / release liner laminate was bonded to the corona-treated surface. This resulted in a polarized film-attached optical laminate (1b) having a configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (1) / second liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (A) / release liner. In the optical laminate (1b) with polarizing film, the angle between the transmission axis of the polarizer of the polarizing film and the slow axis of the first liquid crystal alignment solidified layer was 15°, and the angle between the transmission axis of the polarizer of the polarizing film and the slow axis of the second liquid crystal alignment solidified layer was 75°. The average refractive index of each of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer was 1.59. The results are shown in Table 1.

[0180] Example 2 Acrylic Polymer (2), Acrylic Pressure-Sensitive Adhesive Composition (2) An acrylic polymer (2) and an acrylic pressure-sensitive adhesive composition (2) were prepared in the same manner as in Example 1, except that 85 parts by weight of purified phenoxybenzyl acrylate (2) (purified POB-A (2)) obtained in Production Example 8 was used instead of 85 parts by weight of purified phenoxybenzyl acrylate (1) (purified POB-A (1)) obtained in Production Example 7. <Adhesive sheet (2) and polarized film-attached optical laminates (2a), (2b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (2) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (2) configuration, a polarized film-attached optical laminate (2a) having a polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (2) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (2b) having a polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (2) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner configuration. The results are shown in Table 1.

[0181] Example 3 Acrylic Polymer (3), Acrylic Pressure-Sensitive Adhesive Composition (3) A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 70 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 29 parts by weight of butyl acrylate (BA). To 100 parts by weight of this monomer mixture, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was charged together with ethyl acetate. Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the temperature in the flask was maintained at around 58°C, allowing the polymerization reaction to proceed for 8 hours. The monomer concentration during polymerization was 40% by weight. Thereafter, ethyl acetate was added to the obtained reaction solution to adjust the solid content concentration to 30%, thereby preparing a solution of acrylic polymer (3). 0.3 parts by weight of an isocyanate crosslinking agent (trimethylolpropane / xylylene diisocyanate trimer adduct, manufactured by Mitsui Chemicals, Inc., Takenate D-110N) and ethyl acetate as a dilution solvent were added to adjust the solid content to 15%, and the mixture was mixed and stirred to prepare an acrylic pressure-sensitive adhesive composition (3). <Adhesive sheet (3) and polarized film-attached optical laminates (3a), (3b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (3) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (3) configuration, a polarized film-attached optical laminate (3a) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (3) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (3b) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (3) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0182] Example 4 Acrylic Polymer (4), Acrylic Pressure-Sensitive Adhesive Composition (4) An acrylic polymer (4) and an acrylic pressure-sensitive adhesive composition (4) were prepared in the same manner as in Example 3, except that 50 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 49 parts by weight of butyl acrylate (BA) were charged instead of charging 70 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 29 parts by weight of butyl acrylate (BA). <Adhesive sheet (4) and polarized film-attached optical laminates (4a), (4b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (4) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (4) configuration, a polarized film-attached optical laminate (4a) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (4) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (4b) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (4) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0183] Example 5 Acrylic Polymer (5), Acrylic Pressure-Sensitive Adhesive Composition (5) Acrylic polymer (5) and acrylic pressure-sensitive adhesive composition (5) were prepared in the same manner as in Example 2, except that the pressure-sensitive adhesive sheet was cured and dried at a drying temperature of 155°C for 90 seconds. Pressure-Sensitive Adhesive Sheet (5) and Polarized Film-Attached Optical Laminates (5a), (5b) Except that the acrylic pressure-sensitive adhesive composition (5) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, a laminate having a release liner / pressure-sensitive adhesive sheet (5), a polarized film-attached optical laminate (5a) having a polarized film-attached structure of polarized film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (5) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (5b) having a polarized film-attached structure of polarized film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (5) / second liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet (A) / release liner were obtained. The results are shown in Table 1.

[0184] Example 6 Acrylic Pressure-Sensitive Adhesive Composition (6) The procedure of Example 2 was repeated except that, in the preparation of the acrylic pressure-sensitive adhesive composition, 0.3 parts by weight of an isocyanate crosslinking agent (trimethylolpropane / xylylene diisocyanate trimer adduct, manufactured by Mitsui Chemicals, Inc., Takenate D-110N), 0.6 parts by weight of purified phenoxybenzyl acrylate (1) (purified POB-A (1)), and ethyl acetate were added as a dilution solvent so that the solids content was 15%, relative to 100 parts by weight of the solids content of the acrylic polymer (2), and the mixture was stirred to prepare the acrylic pressure-sensitive adhesive composition (6). <Adhesive sheet (6) and polarized film-attached optical laminates (6a), (6b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (6) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (6), a polarized film-attached optical laminate (6a) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (6) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (6b) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (6) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0185] Example 7 Acrylic Pressure-Sensitive Adhesive Composition (7) The procedure of Example 2 was repeated except that, in the preparation of the acrylic pressure-sensitive adhesive composition, 0.3 parts by weight of an isocyanate crosslinking agent (trimethylolpropane / xylylene diisocyanate trimer adduct, manufactured by Mitsui Chemicals, Inc., Takenate D-110N), 1.6 parts by weight of purified phenoxybenzyl acrylate (1) (purified POB-A (1)), and ethyl acetate were added as a dilution solvent so that the solids content was 15%, relative to 100 parts by weight of the solids content of the acrylic polymer (2), and the mixture was stirred to prepare the acrylic pressure-sensitive adhesive composition (7). <Adhesive sheet (7) and polarized film-attached optical laminates (7a), (7b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (7) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (7), an optical laminate (7a) with a polarized film having a configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (7) / second liquid crystal alignment solidified layer, and an optical laminate (7b) with a polarized film having a configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (7) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0186] Comparative Example 1 Acrylic polymer (C1), acrylic pressure-sensitive adhesive composition (C1) An acrylic polymer (C1) and an acrylic pressure-sensitive adhesive composition (C1) were prepared in the same manner as in Example 1, except that 85 parts by weight of commercially available phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Industry Co., Ltd., purity 94%) was used instead of 85 parts by weight of the purified phenoxybenzyl acrylate (1) (purified POB-A (1)) obtained in Production Example 7. <Adhesive Sheet (C1) and Polarized Film-Attached Optical Laminates (C1a), (C1b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (C1) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (C1) configuration, a polarized film-attached optical laminate (C1a) having a polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C1) / second liquid crystal alignment solidified layer configuration, and a polarized film-attached optical laminate (C1b) having a polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C1) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner configuration. The results are shown in Table 1.

[0187] Comparative Example 2 Acrylic Polymer (C2), Acrylic Pressure-Sensitive Adhesive Composition (C2) An acrylic polymer (C2) and an acrylic pressure-sensitive adhesive composition (C2) were prepared in the same manner as in Example 3, except that 15 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 84 parts by weight of butyl acrylate (BA) were charged instead of charging 70 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 29 parts by weight of butyl acrylate (BA). <Adhesive Sheet (C2) and Polarized Film-Attached Optical Laminates (C2a), (C2b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (C2) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (C2) configuration, a polarized film-attached optical laminate (C2a) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C2) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (C2b) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C2) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0188] Comparative Example 3 Acrylic Polymer (C3), Acrylic Pressure-Sensitive Adhesive Composition (C3) An acrylic polymer (C3) and an acrylic pressure-sensitive adhesive composition (C3) were prepared in the same manner as in Example 3, except that 95 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%) and 5 parts by weight of 4-hydroxybutyl acrylate (4HBA) were used instead of charging 70 parts by weight of commercially available phenoxybenzyl acrylate (Kyoeisha Chemical Industry Co., Ltd., purity 94%), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 29 parts by weight of butyl acrylate (BA). <Adhesive Sheet (C3) and Polarized Film-Attached Optical Laminates (C3a), (C3b)> The same procedure as in Example 1 was carried out, except that the acrylic pressure-sensitive adhesive composition (C3) obtained above was used instead of the acrylic pressure-sensitive adhesive composition (1) obtained in Example 1, to obtain a laminate having a release liner / adhesive sheet (C3) configuration, a polarized film-attached optical laminate (C3a) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C3) / second liquid crystal alignment solidified layer, and a polarized film-attached optical laminate (C3b) having a polarized film-attached configuration of polarized film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet (C3) / second liquid crystal alignment solidified layer / adhesive sheet (A) / release liner. The results are shown in Table 1.

[0189]

[0190] The acrylic pressure-sensitive adhesive, pressure-sensitive adhesive sheet, and optical laminate according to the embodiment of the present invention can be suitably used in image display devices (typically, liquid crystal display devices and organic EL display devices).

Claims

1. An acrylic pressure-sensitive adhesive formed from an acrylic pressure-sensitive adhesive composition containing an acrylic polymer as a base polymer, the acrylic polymer being obtained by polymerizing a monomer component (M), the monomer component (M) containing 30% by weight or more of an aromatic ring-containing monomer (m1), and the acrylic pressure-sensitive adhesive containing at least one selected from the group consisting of xylene sulfonic acid and xylene sulfonate salts in an amount of 300 ppm or less, calculated as solid content.

2. The acrylic pressure-sensitive adhesive according to claim 1, wherein the monomer component (M) contains 50% by weight or more of an aromatic ring-containing monomer (m1).

3. The acrylic pressure-sensitive adhesive according to claim 1, wherein the aromatic ring-containing monomer (m1) is phenoxybenzyl (meth)acrylate.

4. The acrylic pressure-sensitive adhesive according to claim 1, which contains 1,000 ppm to 18,000 ppm of residual monomer.

5. The acrylic pressure-sensitive adhesive according to claim 1, wherein the monomer component (M) comprises at least one selected from the group consisting of alkyl (meth)acrylates, hydroxyl group-containing monomers, carboxyl group-containing monomers, and amide group-containing monomers.

6. A pressure-sensitive adhesive sheet comprising the acrylic pressure-sensitive adhesive according to any one of claims 1 to 5.

7. The pressure-sensitive adhesive sheet according to claim 6, wherein the average refractive index n is 1.52 or more.

8. An optical laminate comprising the pressure-sensitive adhesive sheet according to claim 6.

9. The optical laminate according to claim 8, comprising a first liquid crystal alignment solidified layer, the adhesive sheet, and a second liquid crystal alignment solidified layer in this order.

10. The optical laminate according to claim 9, further comprising a polarizing film on at least one side selected from the group consisting of the first liquid crystal alignment solidified layer side and the second liquid crystal alignment solidified layer side, as viewed from the pressure-sensitive adhesive sheet.

11. An image display device comprising the optical laminate according to any one of claims 8 to 10.

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