Adhesive sheet, optical laminate, and image display device

Abstract

This adhesive sheet contains a crosslinked product of a base polymer, and has a loss modulus G" of 0.002 MPa or more at 150°C and a refractive index of 1.49 or more with respect to light having a wavelength of 589 nm. The adhesive sheet has a high refractive index and yet is suitable for preventing irregularities in external appearance.

Description

Adhesive sheet, optical laminate and image display device

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

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. Image display devices generally include an optical laminate including optical substrates such as a polarizing film and a retardation film. In an optical laminate including a plurality of optical substrates, a bonding layer is usually disposed between adjacent optical substrates to bond the two together. One example of the bonding layer is a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition. Patent Document 1 discloses an example of an optical laminate including a pressure-sensitive adhesive sheet and optical substrates.

[0003] Japanese Patent Application Laid-Open No. 2020-140212

[0004] Increasing the refractive index of the pressure-sensitive adhesive sheet included in the optical laminate may be suitable for improving the optical characteristics of an image display device. For example, depending on the configuration of the optical laminate and the image display device, the brightness of the displayed image can be improved by using a pressure-sensitive adhesive sheet with a high refractive index. However, according to the inventors' studies, a pressure-sensitive adhesive sheet with a high refractive index may cause unevenness in its appearance.

[0005] An object of the present invention is to provide a pressure-sensitive adhesive sheet that has a high refractive index and is suitable for suppressing unevenness in appearance.

[0006] As a result of extensive research, the present inventors have completed the present invention by focusing on the viscosity at high temperatures of the base polymer that constitutes the pressure-sensitive adhesive sheet.

[0007] [1] A pressure-sensitive adhesive sheet according to an embodiment of the present invention comprises a crosslinked product of a base polymer, and has a loss modulus G" at 150°C of 0.002 MPa or more, and a refractive index for light with a wavelength of 589 nm of 1.49 or more. [2] In the pressure-sensitive adhesive sheet according to [1] above, the weight-average molecular weight of the base polymer may be 700,000 or more. [3] In the pressure-sensitive adhesive sheet according to [1] or [2] above, the monomer component M constituting the base polymer may contain an aromatic ring-containing monomer a1. [4] In the pressure-sensitive adhesive sheet according to [3] above, the aromatic ring-containing monomer a1 may be a high-boiling point monomer. [5] In the pressure-sensitive adhesive sheet according to [3] or [4] above, the aromatic ring-containing monomer a1 may be phenoxybenzyl acrylate. [6] In the pressure-sensitive adhesive sheet according to any of [3] to [5] above, the content of the aromatic ring-containing monomer a1 in the monomer component M may be 50 wt % or more. [7] An optical laminate according to an embodiment of the present invention includes the pressure-sensitive adhesive sheet according to any one of [1] to [6] above and an optical substrate. [8] In the optical laminate according to [7] above, the optical substrate may include a liquid crystal alignment solidified layer. [9] In the optical laminate according to [7] above, the optical substrate may include a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer, and in the optical laminate, the first liquid crystal alignment solidified layer, the pressure-sensitive adhesive sheet, and the second liquid crystal alignment solidified layer may be laminated in this order.

[10] In the optical laminate according to any one of [7] to [9] above, the optical substrate may include a polarizing film.

[11] In the optical laminate according to [7] above, the optical substrate may include a polarizing film, a first liquid crystal alignment solidified layer, and a second liquid crystal alignment solidified layer, and in the optical laminate, the polarizing film, the first liquid crystal alignment solidified layer, the pressure-sensitive adhesive sheet, and the second liquid crystal alignment solidified layer may be laminated in this order.

[12] In the optical laminate according to the above [9] or

[11] , at least one layer selected from the group consisting of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer may be a retardation layer.

[13] An image display device according to an embodiment of the present invention includes the optical laminate according to any one of the above [7] to

[12] .

[0008] According to an embodiment of the present invention, it is possible to provide a pressure-sensitive adhesive sheet that has a high refractive index and is suitable for suppressing uneven appearance.

[0009] Fig. 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. Fig. 3 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. Fig. 4 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. Fig. 5 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. Fig. 6 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention.

[0010] [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.

[0011] 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".

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention.

[0013] <<1. Pressure-Sensitive Adhesive Sheet>> An example of a pressure-sensitive adhesive sheet according to an embodiment of the present invention is shown in Fig. 1. Pressure-sensitive adhesive sheet 1 includes a crosslinked product of a base polymer.

[0014] The refractive index of the pressure-sensitive adhesive sheet 1 with respect to light having a wavelength of 589 nm is 1.49 or more. The refractive index may be 1.50 or more, 1.51 or more, 1.52 or more, 1.53 or more, 1.54 or more, 1.55 or more, 1.56 or more, 1.57 or more, or even 1.58 or more. The upper limit of the refractive index is, for example, 1.70 or less, and may be 1.69 or less, 1.68 or less, 1.67 or less, 1.66 or less, 1.65 or less, 1.64 or less, 1.63 or less, 1.62 or less, 1.61 or less, 1.60 or less, 1.59 or less, or even 1.58 or less. In this specification, the refractive index of the pressure-sensitive adhesive sheet refers to the refractive index of the surface of the pressure-sensitive adhesive sheet. The refractive index of the pressure-sensitive adhesive sheet can be measured using an Abbe refractometer at a measurement temperature of 25°C and a measurement wavelength of 589 nm. The Abbe refractometer may be, for example, a "DR-4M" model manufactured by ATAGO Co., Ltd. or an equivalent product. The refractive index of the pressure-sensitive adhesive sheet 1 can vary depending on the degree and state of crosslinking in the crosslinked body of the base polymer, as well as the composition of the monomer component M and the pressure-sensitive adhesive composition A.

[0015] The loss modulus G" (hereinafter referred to as "G"(150)") of the pressure-sensitive adhesive sheet 1 at 150°C is 0.002 MPa or more. G"(150) may be 0.003 MPa or more. The upper limit of G"(150) is, for example, 0.050 MPa or less, and may be 0.020 MPa or less, 0.018 MPa or less, 0.016 MPa or less, 0.014 MPa or less, 0.012 MPa or less, 0.010 MPa or less, 0.008 MPa or less, 0.006 MPa or less, or even 0.005 MPa or less. G"(150) can be determined as follows. First, a measurement sample made of the same adhesive as that constituting the pressure-sensitive adhesive sheet 1 is prepared. The shape of the measurement sample is a disk with a bottom diameter of 8 mm and a thickness of 1 mm. The measurement sample may also be one obtained by punching out a disk from a laminate in which a plurality of pressure-sensitive adhesive sheets 1 are stacked. Next, dynamic viscoelasticity measurement is performed on the measurement sample. G"(150) can be determined from the results of the dynamic viscoelasticity measurement. For the dynamic viscoelasticity measurement, for example, an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific can be used. The conditions for the dynamic viscoelasticity measurement are as follows. (Measurement conditions) Frequency: 1 Hz Deformation mode: Torsion Measurement temperature: -70°C to 150°C Heating rate: 5°C / min

[0016] The pressure-sensitive adhesive sheet 1 is typically formed by drying a coating film of pressure-sensitive adhesive composition A disposed on a substrate. According to the inventors' investigations, increasing the drying temperature conditions is suitable for forming a pressure-sensitive adhesive sheet 1 with a high refractive index. A high-refractive-index monomer can be used for the formation, and this may be due to the fact that high-refractive-index monomers tend to have higher boiling points than, for example, butyl acrylate, which is widely used in acrylic pressure-sensitive adhesive sheets. Furthermore, elevated temperature conditions are thought to cause deformation due to shrinkage on the surface of the substrate where the coating film is disposed, reducing the surface smoothness of the pressure-sensitive adhesive sheet formed and resulting in an uneven appearance. Ensuring a G"(150) corresponding to the viscosity at high temperatures is thought to suppress the flow of the pressure-sensitive adhesive sheet during drying and contribute to preventing a decrease in surface smoothness.

[0017] G"(150) of the PSA sheet 1 can vary depending on, for example, the degree and state of crosslinking in the crosslinked body of the base polymer, the weight average molecular weight and molecular weight distribution (particularly the distribution in the low molecular weight range) of the base polymer contained in the PSA, and the composition and polymerization rate of the monomer component M.

[0018] The thickness of the pressure-sensitive adhesive sheet 1 is not particularly limited and may be, for example, 500 μm or less, 250 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or even 10 μm or less. The lower limit of the thickness of the pressure-sensitive adhesive sheet 1 may be, for example, 2 μm or more, 3 μm or more, or even 4 μm or more. When disposed between a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer described below, the thickness of the pressure-sensitive adhesive sheet 1 may be 4 μm or more, 4.5 μm or more, or even 5 μm or more. In this case, the upper limit of the thickness may be 8 μm or less, 7 μm or less, or even 6 μm or less. In this case, the thickness may be 4 μm or more and 8 μm or less, or 4 μm or more and 7 μm or less.

[0019] The adhesive sheet 1 is made of an adhesive. The adhesive is formed by curing an adhesive composition A.

[0020] <1-1. Pressure-Sensitive Adhesive Composition A> The pressure-sensitive adhesive composition A includes a base polymer. <1-1-a. Base Polymer> The weight-average molecular weight (hereinafter referred to as Mw) of the base polymer may be 700,000 or more, 750,000 or more, 800,000 or more, 850,000 or more, 900,000 or more, 950,000 or more, or even 1,000,000 or more. The upper limit of Mw is, for example, 2,000,000 or less, 1,900,000 or less, 1,800,000 or less, 1,700,000 or less, 1,600,000 or less, or even 1,500,000 or less. The Mw of the base polymer can vary depending on the composition of the base polymer, the polymerization conditions, and the amount of residual impurities in the raw material monomers. Examples of polymerization conditions include the type and amount of polymerization initiator, the type and amount of additives such as chain transfer agents, the type of polymerization solvent, and the monomer concentration in the polymerization system.

[0021] The base polymer may be a (meth)acrylic polymer. In this case, the pressure-sensitive adhesive sheet 1 becomes an acrylic pressure-sensitive adhesive sheet. A (meth)acrylic polymer refers to a polymer in which the main structural unit of the base polymer is a (meth)acrylate unit. A main structural unit refers to a structural unit having the largest weight ratio among all structural units of the base polymer. The weight ratio of the main structural unit is, for example, 50% or more, and may be 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or even 92% or more. The upper limit of this ratio is, for example, 100% or less, and may be 99% or less.

[0022] The base polymer is obtained from a monomer composition containing a monomer component M. The monomer component M contains one or more monomers.

[0023] [Monomer Composition] Monomer Component M The monomer component M, which is contained in the monomer composition and forms a base polymer by polymerization of the composition, may contain an aromatic ring-containing monomer a1. The content of the aromatic ring-containing monomer a1 in the monomer component M is, for example, 15 to 99 wt %. The main monomer contained in the monomer component M may be the aromatic ring-containing monomer a1. In other words, the content of the aromatic ring-containing monomer a1 in the monomer component M may be 50 wt % or more, 60 wt % or more, 65 wt % or more, 70 wt % or more, 75 wt % or more, 80 wt % or more, or even 85 wt % or more. The content may be 60 to 99 wt %, 70 to 95 wt %, or 80 to 90 wt %. The aromatic ring-containing monomer a1 can contribute to increasing the refractive index of the pressure-sensitive adhesive sheet 1. The aromatic ring-containing monomer a1 is a compound that contains an aromatic ring in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. Examples of aromatic rings include a benzene ring, a naphthalene ring, and a biphenyl ring. The aromatic ring-containing monomer a1 may be an aromatic ring-containing (meth)acrylate. The aromatic ring-containing monomer a1 may be used alone or in combination of two or more.

[0024] Examples of aromatic ring-containing (meth)acrylates include benzyl (meth)acrylate, phenyl (meth)acrylate, o-phenylphenol (meth)acrylate, phenoxy (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxybenzyl (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, ethylene oxide-modified cresol (meth)acrylate, and phenol ethylene oxide-modified (meth)acrylate. those having a benzene ring, such as hydroxybenzyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, methoxybenzyl (meth)acrylate, chlorobenzyl (meth)acrylate, cresyl (meth)acrylate, and polystyryl (meth)acrylate; those having a naphthalene ring, such as hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate; and those having a biphenyl ring, such as biphenyl (meth)acrylate. From the viewpoint of increasing the refractive index of the pressure-sensitive adhesive sheet 1, benzyl (meth)acrylate and phenoxybenzyl (meth)acrylate are preferred, and phenoxybenzyl acrylate (POB-A) is more preferred. The aromatic ring-containing monomer a1 may be phenoxybenzyl acrylate.

[0025] The boiling point of aromatic ring-containing monomer a1 typically tends to be higher than that of monomers that do not contain aromatic rings. This tendency, although dependent on the molecular structure, may be stronger as the number of aromatic rings contained increases. Commercially available monomers and other monomers typically used in forming the PSA sheet 1 are purified to remove impurities such as by-products. However, according to the inventors' studies, for monomers with high boiling points, the increased temperature required for distillation, a common purification method, tends to promote polymerization of impurities during purification. To avoid this, milder purification conditions are required, which tends to result in a higher amount of residual impurities. Impurities, particularly polyfunctional ones, can cause gelation during polymerization of the base polymer. For example, for high-boiling point monomers, monomers with even lower residual impurity levels than monomers typically used in forming the PSA sheet 1 may be used. Using a monomer with even lower residual impurities is suitable, for example, for increasing the Mw of the base polymer. Further purification may be performed to achieve this reduction. If purification by distillation is difficult, other purification methods, such as adsorption, may be used.

[0026] In view of the above, the aromatic ring-containing monomer a1 may be a high-boiling point monomer. In this specification, a high-boiling point monomer can be specified as a monomer that satisfies at least one condition selected from the group consisting of the following A to C. The high-boiling point monomer may also be a monomer that satisfies condition C. Phenoxybenzyl acrylate satisfies conditions A to C. A: A boiling point of 240°C or higher under a pressure of 760 mmHg B: A boiling point of 90°C or higher under a pressure of 0.2 mmHg C: A boiling point of 65°C or higher under a pressure of 0.1 mmHg

[0027] An example of an impurity that may be contained in the aromatic ring-containing (meth)acrylate is a polyfunctional acrylate such as a diacrylate. An example of the diacrylate is a compound represented by the following formula (1).

[0028] From another perspective of the above viewpoint, the monomer component M may include a monomer containing two or more aromatic rings. The monomer may be a (meth)acrylate having two or more aromatic rings in a side chain. The upper limit of the number of aromatic rings is, for example, 5 or less, and may be 4 or less, or even 3 or less. The number of aromatic rings may be 2.

[0029] From another aspect of the above viewpoint, the monomer component M may contain a high-boiling point monomer. The high-boiling point monomer may be a (meth)acrylate.

[0030] Other monomers that may be contained in the monomer component M will be described below. One example of such other monomer is alkyl(meth)acrylate a2. The number of carbon atoms in the alkyl group in the alkyl(meth)acrylate a2 is not particularly limited and may be, for example, 1 to 30. The alkyl group may be linear, branched, or cyclic. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, decyl, isodecyl, dodecyl, isomyristyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl. The alkyl(meth)acrylate a2 may be used alone or in combination of two or more. When two or more types are combined, the average carbon number of the alkyl group is preferably 3 to 9. The alkyl(meth)acrylate a2 is preferably butyl acrylate.

[0031] The content of alkyl (meth)acrylate a2 in monomer component M may be 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, 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, 15% by weight or less, or even 13% by weight or less. The lower limit of the polymerization rate is, for example, 1% by weight or more, 3% by weight or more, or even 5% by weight or more. Monomer component M may not contain alkyl (meth)acrylate a2.

[0032] Another example of the other monomer is at least one monomer selected from the group consisting of hydroxyl group-containing monomer a3, amide group-containing monomer a4, and carboxyl group-containing monomer a5. In other words, the monomer component M may contain at least one monomer selected from the group consisting of hydroxyl group-containing monomer a3, amide group-containing monomer a4, and carboxyl group-containing monomer a5. These monomers can be used alone or in combination of two or more.

[0033] The hydroxyl group-containing monomer a3 is a compound containing 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 a3 may be a hydroxyl group-containing (meth)acrylate. Examples of hydroxyl group-containing (meth)acrylates 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.

[0034] The content of the hydroxyl group-containing monomer a3 in the monomer component M may be 0.3% by weight or more, 0.5% by weight or more, 1% by weight or more, 1.5% by weight or more, or even 2% by weight or more. The upper limit of the proportion is, for example, 9% by weight or less, and may be 7% by weight or less, 5% by weight or less, 4.5% by weight or less, 4% by weight or less, 3.5% by weight or less, 3% by weight or less, 2.5% by weight or less, or even 2% by weight or less. The monomer component M may not contain a hydroxyl group-containing monomer.

[0035] The amide group-containing monomer a4 is a compound that contains an amide group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. The amide group-containing monomer a4 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.

[0036] The carboxyl group-containing monomer a5 is a compound containing a carboxyl group and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group in its structure. The carboxyl group-containing monomer a5 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.

[0037] The total content of the amide-containing monomer a4 and the carboxyl-containing monomer a5 in the monomer component M is, for example, 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, or even 3% by weight or less. The lower limit of the content is, for example, 0.5% by weight or more, and may be 1% by weight or more. The monomer component M may not contain the amide-containing monomer a4 or the carboxyl-containing monomer a5.

[0038] Another example of the other monomer is a monomer (copolymerizable monomer a6) that can be copolymerized with each of the above-mentioned monomers. The copolymerizable monomer a6 usually has a polymerizable functional group containing an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group. Examples of the copolymerizable monomer a6 include acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; sulfonic acid group-containing monomers such as allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, and sulfopropyl (meth)acrylate; phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; alkylaminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; and succinimide-based monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide. monomers; maleimide-based monomers such as N-cyclohexylmaleimide, 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; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate; 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; and 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;

[0039] The content of copolymerizable monomer a6 in monomer component M is, for example, 5% by weight or less, and may be 3% by weight or less, or even 1% by weight or less. Monomer component M may not contain copolymerizable monomer a6.

[0040] Formation of Base Polymer and Other Components Various known polymerization methods can be applied to form the base polymer from the monomer composition, such as solution polymerization, radiation polymerization using electron beams or ultraviolet (UV) rays, bulk polymerization, and emulsion polymerization. Polymerization is typically radical polymerization. The base polymer may be any of a random copolymer, block copolymer, graft copolymer, etc. of the monomer component M. However, the method for forming the base polymer is not limited to the above examples.

[0041] 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. The polymerization conditions are, for example, 50 to 70°C and 5 to 30 hours.

[0042] The polymerization initiator, chain transfer agent, emulsifier, etc. used in the radical polymerization are not particularly limited and can be selected appropriately.

[0043] 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 that combine a peroxide and a reducing agent, such as a combination of a persulfate and sodium hydrogen sulfite, or a combination of a peroxide and sodium ascorbate. However, the polymerization initiator is not limited to the above examples.

[0044] The polymerization initiators may be used alone or in combination of two or more. The total amount of the polymerization initiators used is, for example, 0.005 to 1 part by weight, or may be 0.02 to 0.5 parts by weight, relative to 100 parts by weight of the monomer component M.

[0045] Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. The chain transfer agents may be used alone or in combination of two or more. The total amount of the chain transfer agents used is, for example, 0.1 parts by weight or less per 100 parts by weight of the monomer component M.

[0046] In radiation polymerization, a monomer component M 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 it has the advantage of being able to shorten the polymerization time. The photopolymerization initiators can be used alone or in combination of two or more.

[0047] Examples of the photopolymerization initiator include various photopolymerization initiators such as benzoin ether-based, acetophenone-based, α-ketol-based, photoactive oxime-based, benzoin-based, benzil-based, benzophenone-based, ketal-based, and thioxanthone-based photopolymerization initiators. However, the photopolymerization initiator is not limited to the above examples. The amount of the photopolymerization initiator used is, for example, 0.05 to 1.5 parts by weight, or may be 0.1 to 1 part by weight, relative to 100 parts by weight of the monomer component M.

[0048] The monomer composition may contain components other than those described above.

[0049] <1-1-b. Other Components> Crosslinking Agent The pressure-sensitive adhesive composition A may contain a crosslinking agent. Examples of crosslinking agents that the pressure-sensitive adhesive composition A may contain include isocyanate-based crosslinking agents, peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. The pressure-sensitive adhesive composition A preferably contains an isocyanate-based crosslinking agent and / or a peroxide-based crosslinking agent, and more preferably contains an isocyanate-based crosslinking agent. In other words, the crosslinked product of the base polymer contained in the pressure-sensitive adhesive sheet 1 may have a crosslinked structure due to a peroxide-based crosslinking agent, or may have a crosslinked structure due to an isocyanate-based crosslinking agent, or may have both crosslinked structures.

[0050] 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.

[0051] Examples of aromatic isocyanate compounds are 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.

[0052] Examples of the alicyclic isocyanate compound are 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.

[0053] Examples of aliphatic isocyanate compounds are trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0054] The isocyanate-based crosslinking agent may be a polymer (dimer, trimer, pentamer, etc.) of the above-mentioned isocyanate compound, an adduct obtained by adding the compound to a polyhydric alcohol such as trimethylolpropane, a urea-modified compound, a biuret-modified compound, an allophanate-modified compound, an isocyanurate-modified compound, a carbodiimide-modified compound, or a urethane prepolymer obtained by adding the compound to a polyether polyol, a polyester polyol, an acrylic polyol, a polybutadiene polyol, a polyisoprene polyol, or the like.

[0055] 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.

[0056] Commercially available isocyanate crosslinking agents can be used. Examples of 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 D-110N are preferred.

[0057] The isocyanate-based crosslinking agents may be used alone or in combination of two or more kinds.

[0058] The amount of the isocyanate crosslinking agent in the PSA composition A is, for example, 0.01 to 20 parts by weight relative to 100 parts by weight of the base polymer. The lower limit of the amount may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.15 parts by weight or more, 0.2 parts by weight or more, or even 0.3 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, or even 0.5 parts by weight or less.

[0059] The amount of the non-isocyanate crosslinking agent, for example, a peroxide crosslinking agent, blended in the PSA composition A may be, for example, 2 parts by weight or less, 1 part by weight or less, or even 0.5 parts by weight or less, relative to 100 parts by weight of the base polymer. The lower limit of the blending amount may be, for example, 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.15 parts by weight or more, or even 0.2 parts by weight or more. The blending amount may be 0.05 to 1 part by weight, or 0.1 to 0.5 parts by weight. The PSA composition A may not contain a non-isocyanate crosslinking agent.

[0060] Other Components The pressure-sensitive adhesive composition A may further contain known additives. Examples of additives include refractive index improvers, 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 or organic fillers, metal powders, particles, and foil-like materials. Redox systems containing a reducing agent may also be used within controllable limits. However, the additives are not limited to the above examples. The total amount of additives may be, for example, 10 parts by weight or less, 5 parts by weight or less, or even 1 part by weight or less, per 100 parts by weight of the base polymer.

[0061] The pressure-sensitive adhesive composition A may contain a refractive index improver as an additive. The refractive index improver can contribute to improving the refractive index of the pressure-sensitive adhesive sheet 1. An example of the refractive index improver is a high refractive index monomer. Examples of the high refractive index monomer include phenoxybenzyl acrylate (refractive index 1.566), 1-naphthylmethyl acrylate (refractive index 1.595), ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index 1.578), benzyl acrylate (refractive index 1.519), phenoxyethyl acrylate (refractive index 1.517), phenoxydiethylene glycol acrylate (refractive index 1.510), 6-acryloyloxymethyldinaphthothioate, Examples of suitable high refractive index monomers include 6-vinyldinaphthothiophene (6VDNT, refractive index 1.802), 5-vinyldinaphthothiophene (5VDNT, refractive index 1.793), 6-methacryloyloxymethyldinaphthothiophene (6MDNTA, refractive index 1.75), 6-methacryloyloxymethyldinaphthothiophene (6MDNTMA, refractive index 1.726), 5-acryloyloxyethyldinaphthothiophene (5EDNTA, refractive index 1.786), 6-acryloyloxyethyldinaphthothiophene (6EDNTA, refractive index 1.722), 6-vinyldinaphthothiophene (6VDNT, refractive index 1.802), and 5-vinyldinaphthothiophene (5VDNT, refractive index 1.793). The high refractive index monomer serving as the refractive index improver is preferably a monomer having a higher refractive index than the aromatic ring-containing monomer a1 contained in the monomer component M. The refractive index of the high refractive index monomer serving as the refractive index improver may be 1.6 or more, 1.65 or more, or even 1.7 or more. The upper limit of the refractive index of the high refractive index monomer is, for example, 3.0 or less, and may be 2.5 or less, 2.0 or less, or even 1.9 or less. The refractive index of the monomer can be measured using an Abbe refractometer under conditions of a measurement wavelength of 550 nm and a measurement temperature of 25°C. For example, the Abbe refractometer that can be used is the "DR-4M" model manufactured by ATAGO or an equivalent. When the nominal value of the refractive index at 25°C is provided by the manufacturer of the monomer, etc., that nominal value can be used as the refractive index.

[0062] When the pressure-sensitive adhesive composition A contains a refractive index enhancer, the blending amount thereof may be, for example, 15 parts by weight or less, 12 parts by weight or less, or even 10 parts by weight or less, relative to 100 parts by weight of the base polymer. The lower limit of the blending amount is not particularly limited, and is, for example, 0.5 parts by weight or more. The pressure-sensitive adhesive composition A does not need to contain a refractive index enhancer.

[0063] The PSA composition A may contain a silane coupling agent as an additive. Examples of the silane coupling agent include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

[0064] When the pressure-sensitive adhesive composition A contains a silane coupling agent, the amount thereof may be, for example, 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.4 parts by weight or less, 0.2 parts by weight or less, or even 0.1 parts by weight or less, relative to 100 parts by weight of the base polymer. The lower limit of the amount is not particularly limited, and is, for example, 0.02 parts by weight or more. The pressure-sensitive adhesive composition A does not need to contain a silane coupling agent.

[0065] The pressure-sensitive adhesive composition A may be substantially free of a photocuring agent such as a photopolymerization initiator.

[0066] The PSA composition A is typically a solvent-based composition that can be dried to form the PSA sheet 1. In this case, the PSA sheet 1 formed from the PSA composition A is usually a solvent-based composition. The solvent-based composition is also called a thermosetting type.

[0067] The initial gel fraction of the PSA composition A may be 10% or more, 15% or more, 18% or more, 20% or more, 25% or more, 29% or more, 30% or more, 35% or more, 40% or more, or even 43% or more. The upper limit of the initial gel fraction is, for example, 80% or less, and may be 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, or even 50% or less.

[0068] The initial gel fraction of the PSA composition A can be evaluated, for example, by the following method. First, the PSA composition A is applied to a substrate so as to form a coating film, and the coating film is dried at 120°C for 300 seconds to form a PSA sheet for evaluation. Next, a portion of the formed PSA sheet is scraped off within 2 hours of formation to obtain a small piece. Next, the obtained small piece is wrapped in a stretched porous polytetrafluoroethylene film and tied with kite string. This results in a test piece. Next, the total weight (weight A) of the PSA sheet piece, the stretched porous film, and the kite string is measured. The total weight of the stretched porous film and the kite string used is defined as weight B. Next, the test piece is immersed in a container filled with ethyl acetate and allowed to stand at 23°C for 1 week. After standing, the test piece is removed from the container and dried in a dryer set to 130°C for 2 hours, and then the weight C of the test piece is measured. The initial gel fraction can be calculated from weight A, weight B, and weight C according to the following formula. Formula: Initial gel fraction (%) = (C - B) / (A - B) x 100

[0069] <1-2. Formation of Pressure-Sensitive Adhesive Sheet> The pressure-sensitive adhesive sheet 1 can be formed, for example, by drying a coating film of the pressure-sensitive adhesive composition A provided on a substrate. Heating can be used for drying. A release film may be used as the substrate. The pressure-sensitive adhesive sheet 1 formed on the release film can be transferred to, for example, another layer that may be included in the optical laminate. The substrate may be another layer that may be included in the optical laminate. However, the method for forming the pressure-sensitive adhesive sheet 1 from the pressure-sensitive adhesive composition A is not limited to the above example.

[0070] As the release film, a known film that can be used when forming a solvent-based pressure-sensitive adhesive sheet can be used.

[0071] The drying temperature of the coating film is, for example, 100° C. or higher, and may be 110° C. or higher, 120° C. or higher, 130° C. or higher, or even 140° C. or higher. The upper limit of the drying temperature may be, for example, 170° C. or lower, 160° C. or lower, or even 150° C. or lower. The drying time of the coating film can be appropriately adjusted depending on the composition of the pressure-sensitive adhesive composition A, and may be, for example, 30 to 300 seconds, 40 to 240 seconds, or even 60 to 180 seconds.

[0072] The pressure-sensitive adhesive sheet 1 according to the embodiment of the present invention can be used, for example, in an optical laminate or an image display device. In other words, the pressure-sensitive adhesive sheet 1 may be used for either an optical laminate or an image display device.

[0073] 2. Optical Laminate An example of an optical laminate according to an embodiment of the present invention is shown in Fig. 2. The optical laminate 20 (20A) in Fig. 2 includes an adhesive sheet 1 and an optical substrate (optical film) 2. The adhesive sheet 1 and the optical substrate 2 are in contact with each other. The optical laminate 20A can be used as an optical substrate with an adhesive sheet.

[0074] 2-1. Liquid Crystal Alignment Solidified Layer An example of the optical substrate 2 is a liquid crystal alignment solidified layer. In other words, the optical substrate 2 may include a liquid crystal alignment solidified layer.

[0075] The liquid crystal alignment solidified layer is an alignment solidified layer of a liquid crystal compound. More specifically, it refers to a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. The liquid crystal alignment solidified layer includes an alignment solidified layer obtained by curing a liquid crystal monomer. Compared to a typical optical substrate made of a resin film, the liquid crystal alignment solidified layer is suitable for obtaining desired optical properties, such as retardation, while reducing the thickness.

[0076] The liquid crystal alignment solidified layer has a higher electron density than a normal optical substrate, and therefore tends to have a high refractive index. The combination of the pressure-sensitive adhesive sheet 1 and the optical substrate 2 including the liquid crystal alignment solidified layer, particularly the configuration in which the two are arranged in contact with each other as in the optical laminate 20A, is suitable for reducing reflection in the optical laminate 20 by mitigating the mismatch in refractive index between the pressure-sensitive adhesive sheet 1 and the optical substrate 2. The reduced reflection can contribute to improving the visibility of an image display device incorporating the optical laminate 20.

[0077] Another example of an optical laminate according to an embodiment of the present invention is shown in Figure 3. The optical laminate 20 (20B) in Figure 3 includes a first liquid crystal alignment solidified layer 21, an adhesive sheet 1, and a second liquid crystal alignment solidified layer 22. The optical substrate 2 of the optical laminate 20B includes the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22. In the optical laminate 20B, the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22 are bonded together via the adhesive sheet 1. In the optical laminate 20B, the first liquid crystal alignment solidified layer 21, the adhesive sheet 1, and the second liquid crystal alignment solidified layer 22 are laminated in this order, and in the optical laminate 20B, adjacent layers are in contact with each other.

[0078] In the liquid crystal alignment solidified layers 21 and 22, rod-shaped liquid crystal compounds are typically aligned in a predetermined direction (homogeneous alignment). Examples of the liquid crystal compounds include nematic liquid crystals and discotic liquid crystals. The liquid crystal compounds may be liquid crystal polymers or liquid crystal monomers. The liquid crystal monomers may be polymerizable and / or crosslinkable.

[0079] Specific examples of the liquid crystal monomer are the polymerizable mesogenic compounds described in JP-A-2002-533742, EP 358208, EP 66137, WO 93 / 22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445. Examples of the polymerizable mesogenic compound include LC242 manufactured by BASF, E7 manufactured by Merck, and LC-Silicon-CC3767 manufactured by Wacker-Chem. The liquid crystal monomer is preferably a nematic monomer.

[0080] The liquid crystal alignment solidified layers 21, 22 can be formed by applying a coating liquid containing a liquid crystal compound to the surface of a substrate that has been subjected to an alignment treatment, orienting the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. A release film may be used as the substrate. The liquid crystal alignment solidified layers 21, 22 formed on the release film can be transferred to another layer that may be included in the optical laminate 20, such as the pressure-sensitive adhesive sheet 1. However, the method for forming the liquid crystal alignment solidified layers 21, 22 is not limited to the above example.

[0081] For further specific examples of liquid crystal compounds and details of the method for forming the liquid crystal alignment solidified layer, refer to JP-A-2006-163343, although the liquid crystal alignment solidified layers 21 and 22 and the method for forming them are not limited to those described in the publication.

[0082] The average refractive index of the first liquid crystal alignment solidified layer 21 and / or the second liquid crystal alignment solidified layer 22 may be 1.50 or more, such as 1.52 or more, 1.53 or more, 1.55 or more, 1.57 or more, or even 1.59 or more. The upper limit of the average refractive index is, for example, 1.70 or less. When incorporated into an image display device, the liquid crystal alignment solidified layer located on the viewing side, e.g., the first liquid crystal alignment solidified layer 21, and the liquid crystal alignment solidified layer located on the opposite side from the viewing side, e.g., the second liquid crystal alignment solidified layer 22, may have the same or different average refractive indexes. The average refractive index of the liquid crystal alignment solidified layer is given by the formula: average refractive index = (nx + ny + nz) / 3, where nx is the refractive index in the direction in the plane of the layer where the refractive index is maximum (slow axis), ny is the refractive index in the direction perpendicular to the slow axis (fast axis), 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.

[0083] The absolute value of the difference between the average refractive index of each of the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22 and the refractive index of the adhesive sheet 1 may be 0.08 or less, or may be 0.075 or less, 0.07 or less, 0.06 or less, 0.05 or less, or even 0.045 or less.

[0084] At least one layer selected from the group consisting of the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22 may be a retardation layer. The retardation layer has, for example, a refractive index characteristic represented by the formula nx>ny. However, the refractive index characteristic of the retardation layer is not limited to the above example. The retardation layer can have various refractive index characteristics known as retardation layers, such as a refractive index characteristic represented by the formula nz>nx=ny.

[0085] The retardation layer may have an Re(550) of 10 nm or more, 30 nm or more, 50 nm or more, 80 nm or more, or even 100 nm or more. Re(550) is the in-plane retardation of the retardation layer for light with a wavelength of 550 nm. The in-plane retardation is given by the formula Re=(nx-ny)×d, where d (nm) is the thickness of the retardation layer.

[0086] The Re(550) of the retardation layer may be 100 nm to 180 nm, 110 to 170 nm, 120 to 160 nm, or even 135 nm to 155 nm, in which case the retardation layer can function as a so-called λ / 4 plate. The Re(550) of the retardation layer may be 180 nm to 320 nm, 200 to 290 nm, or even 230 to 280 nm, in which case the retardation layer can function as a so-called λ / 2 plate. The first liquid crystal alignment solidified layer 21 and / or the second liquid crystal alignment solidified layer 22 may be a layer that can function as a λ / 4 plate or a λ / 2 plate. The first liquid crystal alignment solidified layer 21 may be a layer that can function as a λ / 4 plate (or a λ / 2 plate), and the second liquid crystal alignment solidified layer 22 may be a layer that can function as a λ / 2 plate (or a λ / 4 plate). The optical laminate 20 in which the first liquid crystal alignment solidified layer 21 and / or the second liquid crystal alignment solidified layer 22 are layers that can function as a λ / 4 plate or a λ / 2 plate and further includes a polarizing film may be an elliptically polarizing film or a circularly polarizing film.

[0087] The first liquid crystal alignment solidified layer 21 and / or the second liquid crystal alignment solidified layer 22 may be an anti-reflection retardation layer, a viewing angle compensation retardation layer, or an obliquely aligned retardation layer for viewing angle compensation.

[0088] The thickness of the liquid crystal alignment solidified layers 21, 22 is, for example, 5 μm or less, and may be 4 μm or less, or even 3 μm or less. The lower limit of the thickness is, for example, 0.5 μm or more, and may be 1 μm or more. The thickness may be 0.5 μm or more and 5 μm or less, or 1 μm or more and 4 μm or less.

[0089] The first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22 may have the same structure or different structures.

[0090] The optical laminate 20B including the first liquid crystal alignment solidified layer 21, the adhesive sheet 3, and the second liquid crystal alignment solidified layer 22 can function as a retardation layer as a whole.

[0091] The optical laminate 20 according to the embodiment of the present invention may include a retardation layer other than the liquid crystal alignment solidified layer which is a retardation layer.

[0092] 2-2. Polarizing Film A polarizing film is another example of the optical substrate 2. In other words, the optical substrate 2 may include a polarizing film.

[0093] A polarizing film typically includes a polarizer and protective layers disposed on both sides of the polarizer. Depending on the purpose, at least one of the protective layers 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.

[0094] 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.

[0095] The PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin, and the amount of the acetoacetyl-modified PVA-based resin is preferably 5 to 20% by weight, and more preferably 8 to 12% by weight, based on 100% by weight of the total PVA-based resin.

[0096] 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).

[0097] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 41.0% to 46.0%, more preferably 42.0% to 45.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0098] The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 1 μm to 8 μm, and even more preferably 3 μm to 7 μm. For example, 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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 makes it possible to increase the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing 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 achieving 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 steps 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.

[0104] 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. Representative examples of (meth)acrylic resins include (meth)acrylic resins 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.

[0105] 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.

[0106] 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.

[0107] The thickness of each protective layer is preferably 10 μm to 80 μm, more preferably 12 μm to 40 μm, and even more preferably 15 μm to 35 μm. When the protective layer is surface-treated, the thickness of the protective layer includes the thickness of the surface-treated layer.

[0108] The optical laminate 20 may include a liquid crystal alignment solidified layer and a polarizing film. In other words, the optical substrate 2 may include a liquid crystal alignment solidified layer and a polarizing film.

[0109] Another example of an optical laminate according to an embodiment of the present invention is shown in Figure 4. The optical laminate 20 (20C) in Figure 4 includes a polarizing film 23, a first liquid crystal alignment solidified layer 21, an adhesive sheet 1, and a second liquid crystal alignment solidified layer 22. The optical substrate 2 of the optical laminate 20C includes the polarizing film 23, the first liquid crystal alignment solidified layer 21, and the second liquid crystal alignment solidified layer 22. In the optical laminate 20C, the polarizing film 23, the first liquid crystal alignment solidified layer 21, the adhesive sheet 1, and the second liquid crystal alignment solidified layer 22 are laminated in this order, and in the optical laminate 20C, adjacent layers are in contact with each other.

[0110] <2-3. Other Layers> The optical laminate 20 may include an additional adhesive sheet other than the adhesive sheet 1. An example of the optical laminate 20 including an additional adhesive sheet is shown in FIG. 5. The optical laminate 20 (20D) in FIG. 5 includes, in this order, a polarizing film 23, a first liquid crystal alignment solidified layer 21, an adhesive sheet 2, a second liquid crystal alignment solidified layer 22, and an additional adhesive sheet 3. The adhesive sheet 3 constitutes one exposed surface of the optical laminate 20D. When the optical laminate 20D is bonded to another member, the adhesive sheet 3 can constitute the bonding surface with the other member.

[0111] The pressure-sensitive adhesive sheet 3 may be a known pressure-sensitive adhesive sheet including an optical laminate that can be used in an image display device. The pressure-sensitive adhesive sheet 3 is, for example, a (meth)acrylic pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet 3 can be formed by a known method. The configuration of the pressure-sensitive adhesive sheet 3 may be the same as the configuration of the pressure-sensitive adhesive sheet 1.

[0112] The optical laminate 20 may include a release liner. An example of an optical laminate 20 including a release liner is shown in Figure 6. The optical laminate 20 (20E) in Figure 6 is the same as the optical laminate 20D in Figure 5, except that it is provided with a release liner 4 on the side of the pressure-sensitive adhesive sheet 3 opposite to the side of the second liquid crystal alignment solidified layer 22. The release liner 4 in Figure 6 is in contact with the pressure-sensitive adhesive sheet 3. The optical laminate 20E can be used by peeling off the release liner 4.

[0113] The release liner 4 is, for example, a film, paper, woven fabric, nonwoven fabric, porous material, net, foam, foil, or laminate thereof, made of resin, paper, fiber, metal, or a composite material thereof. Examples of resins include polyethylene, polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinyl chloride, vinyl chloride copolymer, polyethylene terephthalate, polybutylene terephthalate, polyurethane, ethylene-vinyl acetate copolymer, and polyester. However, the release liner 4 is not limited to the above examples. Furthermore, the materials and resins that can be used to make the release liner 4 are not limited to the above examples.

[0114] The thickness of the release liner 4 is, for example, 5 to 200 μm, and may be 5 to 100 μm. The surface of the release liner 4 may be subjected to various surface treatments such as release treatment, antifouling treatment, and antistatic treatment as needed. For the release treatment, various release agents such as silicone-based, fluorine-based, long-chain alkyl-based, and fatty acid amide-based release agents, or particles such as silica powder can be used.

[0115] The release film used in forming the pressure-sensitive adhesive sheet 3 may also be used as the release liner 4 .

[0116] The optical laminate 20 may include a surface protective film. The surface protective film is disposed, for example, on the outermost layer on the viewing side of the optical laminate 20. The surface protective film may be a known surface protective film included in an optical laminate that can be used in an image display device. The surface protective film may be a glass film.

[0117] The optical laminate 20 according to the embodiment of the present invention can be distributed and stored, for example, as a rolled body in which the strip-shaped optical laminate 20 is rolled up, or as a sheet-shaped optical laminate 20 .

[0118] The optical laminate 20 according to the embodiment of the present invention is typically used in an image display device. In other words, the optical laminate 20 may be used for an image display device. The image display device is, for example, an EL display such as a liquid crystal display, an organic EL display, or an inorganic EL display. The use of the optical laminate 20 is not limited to the above examples. Furthermore, the image display device in which the optical laminate 20 can be used is not limited to the above examples.

[0119] The optical laminate 20 according to the embodiment of the present invention can be formed by laminating each of the layers included therein. Layers that have been subjected to a surface modification treatment may be laminated. The surface modification treatment is, for example, at least one selected from the group consisting of corona treatment, plasma treatment, excimer UV light treatment, and flame treatment, and may be corona treatment and / or plasma treatment, or may be corona treatment. Each surface modification treatment can be performed using a corresponding known treatment device.

[0120] <<3. Image Display Device>> An example of an image display device according to an embodiment of the present invention is shown in Fig. 7. The image display device 30 of Fig. 7 has a layered structure in which a polarizing film 23, a first liquid crystal alignment solidified layer 21, an adhesive sheet 1, a second liquid crystal alignment solidified layer 22, an adhesive sheet 3, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 5, and a substrate 6 are layered in this order. The image display device 30 has the optical laminate 20D of Fig. 5. The image forming layer 5 and the substrate 6 may have the same configurations as the substrate and the image forming layer, respectively, provided in known image display devices.

[0121] The image display device 30 in Fig. 7 may be an organic EL display or a liquid crystal display. However, the image display device 30 is not limited to the above examples. The image display device 30 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 30 can be used for home appliances, in-vehicle applications, public information displays (PID), and the like.

[0122] The image display device of the present invention may have any configuration as long as it includes the optical layered body of the present invention.

[0123] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0124] In this example, the refractive index, G"(150), and appearance of the produced pressure-sensitive adhesive sheet were evaluated. In addition, an optical laminate including a polarizing film, a first liquid crystal alignment solidified layer, a pressure-sensitive adhesive sheet, and a second liquid crystal alignment cured layer was produced, and its reflectance was evaluated.

[0125] [Preparation of Pressure-Sensitive Adhesive Sheet] (Preparation of (Meth)Acrylic Polymer P1) 85 parts by weight of phenoxybenzyl acrylate (POB-A), 2 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 13 parts by weight of n-butyl acrylate (BA) were 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 (AIBN) as a polymerization initiator was charged together with ethyl acetate relative to 100 parts by weight of the monomer mixture. Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the liquid temperature in the flask was maintained at around 55°C, allowing the polymerization reaction to proceed for 7 hours. The monomer concentration during polymerization was 35% by weight. Ethyl acetate was then added to the resulting reaction solution to adjust the solids concentration to 30%, yielding a solution of (meth)acrylic polymer P1. A commercially available monomer (manufactured by Kyoeisha Chemical Co., Ltd., purity 94%) was further purified by adsorption for POB-A.

[0126] (Preparation of (meth)acrylic polymers P2 to P9) Solutions of (meth)acrylic polymers P2 to P9 were obtained in the same manner as for (meth)acrylic polymer P1, except that the type and amount of monomer and the monomer concentration during polymerization were changed as shown in Table 1 below. Mw was determined as the Mw at the peak top position by gel permeation chromatography (GPC) under the following conditions. Analytical device: Acquity APC manufactured by Waters Column: G7000HXL+GMHXL+GMHXL manufactured by Tosoh Column temperature: 40°C Eluent: tetrahydrofuran (acid added) Flow rate: 0.8 mL / min Injection volume: 100 μL Detector: differential refractometer (RI) Standard sample: polystyrene (PS) manufactured by Agilent

[0127]

[0128] The abbreviations and refractive indices of the monomers shown in Table 1 are as follows. The refractive index of a monomer is the refractive index of a homopolymer of the monomer at a wavelength of 550 nm. POB-A: phenoxybenzyl acrylate (refractive index 1.566) 4HBA: 4-hydroxybutyl acrylate (refractive index 1.452) BA: n-butyl acrylate (refractive index: 1.420) ACMO: acryloylmorpholine (refractive index: 1.510) BzA: benzyl acrylate (refractive index 1.519) AA: acrylic acid (refractive index: 1.421)

[0129] (Preparation of Pressure-Sensitive Adhesive Compositions) Solvent-based Pressure-Sensitive Adhesive Compositions A1 to A9 were obtained by mixing the (meth)acrylic polymer prepared above as a base polymer with a crosslinking agent and additives so as to obtain the compositions shown in Table 2. The blending amounts of the crosslinking agent and additives shown in Table 2 are values ​​(unit: parts by weight) when the weight of the base polymer is taken as 100 parts by weight.

[0130] (Preparation of Pressure-Sensitive Adhesive Sheets) A pressure-sensitive adhesive composition was applied to the surface of a release liner PET film (Mitsubishi Chemical Corporation, MRF38-NS2) so that the thickness of the pressure-sensitive adhesive sheet after drying would be a predetermined thickness. A fountain coater was used to apply the pressure-sensitive adhesive composition. The coating film formed by application was subjected to a drying treatment at 120°C for 1 minute in an air-circulating constant-temperature oven to prepare pressure-sensitive adhesive sheets S1 to S9.

[0131]

[0132] The abbreviations in Table 2 are as follows: D-110N: Trimethylolpropane / xylylene diisocyanate trimer adduct (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.); isocyanate-based crosslinking agent BPO: Benzoyl peroxide; peroxide-based crosslinking agent 6MDNTA: 6-acryloyloxymethyldinaphthothiophene (manufactured by Sugai Chemical Co., Ltd.); refractive index improver

[0133] [Preparation of Liquid Crystal Alignment Solidified Layer] (Preparation of First Liquid Crystal Alignment Solidified Layer) A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF, Paliocolor LC242) was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30 wt %. A surfactant (BYK-360, BYK-Chemie) and a photopolymerization initiator (IGM Resins, Omnirad 907) were added to this solution to prepare a liquid crystal composition solution. The amounts of the surfactant and polymerization initiator added were 0.01 parts by weight and 3 parts by weight, respectively, per 100 parts by weight of the photopolymerizable liquid crystal compound. A biaxially stretched norbornene-based film (Zeonor Film, Nippon Zeon Corporation, thickness 33 μm, Re(550) = 135 nm) was prepared as a substrate film. The liquid crystal composition solution was applied to a substrate film using a bar coater so that 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 liquid crystal was aligned by irradiating the substrate with an integrated light intensity of 400 mJ / cm under a nitrogen atmosphere. 2 The first liquid crystal alignment solidified layer was homogeneously aligned, had a thickness of 1.7 μm, and had an average refractive index of 1.590.

[0134] (Preparation of second liquid crystal alignment solidified layer) A laminate of substrate film / second liquid crystal alignment solidified layer (homogeneous alignment, thickness 0.92 μm, Re(550)=130 nm) was obtained in the same manner as in preparation of the first liquid crystal alignment solidified layer, except that the coating thickness was changed. The average refractive index of the second liquid crystal alignment solidified layer was 1.590.

[0135] [Preparation of Polarizing Film] (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 corona treatment. A PVA-based resin (100 parts by weight of 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 dissolved in water to prepare an aqueous PVA solution (coating solution). The PVA aqueous solution 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%.

[0136] (Preparation of Polarizing Film) An HC-COP film was bonded to the surface of the polarizer prepared above (the surface opposite to the resin substrate) via a UV-curable adhesive. The HC-COP film was a film in which an HC layer (4 μm thick) was formed on a cycloolefin resin (COP) film (25 μm thick), 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 (25 μm thick) was bonded to the peeled surface via a UV-curable adhesive. In this way, a polarizing film having a configuration of HC layer / COP film (protective layer) / polarizer / TAC film (protective layer) was obtained.

[0137] [Preparation of Optical Laminate] (Preparation of Adhesive for Laminating Polarizing Film and First Liquid Crystal Alignment Solidified Layer) 10 parts by weight of hydroxyethyl acrylamide (trade name "HEAA", manufactured by KJ Chemicals), 4 parts by weight of 2-acetoacetoxyethyl methacrylate (trade name "AAEM", manufactured by Mitsubishi Chemicals), 60 parts by weight of acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals), 11 parts by weight of 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.), 10 parts by weight of acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM) 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.

[0138] (Preparation of Optical Laminate) The first liquid crystal alignment solidified layer side of a laminate having a substrate film / first liquid crystal alignment solidified layer configuration was bonded to the TAC film side of the polarizing film prepared above via the adhesive (thickness: 1 μm), and then the substrate film was peeled off to obtain a laminate having a polarizing film / adhesive / first liquid crystal alignment solidified layer configuration. Next, the exposed surface of the first liquid crystal alignment solidified layer was plasma-treated, and then this exposed surface was bonded to the exposed surface of the pressure-sensitive adhesive sheet formed on a release liner to obtain a laminate having a polarizing film / adhesive / first liquid crystal alignment solidified layer / pressure-sensitive adhesive sheet / release liner configuration. Next, the release liner was peeled off from the pressure-sensitive adhesive sheet, and the second liquid crystal alignment solidified layer side of a laminate having a substrate film / second liquid crystal alignment solidified layer configuration was bonded to the exposed surface of the pressure-sensitive adhesive sheet exposed by the peeling. Prior to bonding, the exposed surface of the second liquid crystal alignment solidified layer in the laminate was corona-treated. Next, the substrate film was peeled off to obtain an optical laminate having a structure of polarizing film / adhesive / first liquid crystal alignment solidified layer / adhesive sheet / second liquid crystal alignment solidified layer. 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 refractive index of the first liquid crystal alignment solidified layer in the transmission axis direction of the polarizer was 1.66, and the refractive index of the second liquid crystal alignment solidified layer in the transmission axis direction of the polarizer was 1.56.

[0139] [Evaluation] (Refractive index of adhesive sheet) The refractive index of the adhesive sheet was measured using an Abbe refractometer at a measurement temperature of 25°C and a measurement wavelength of 589 nm. The Abbe refractometer used was a "DR-4M" model manufactured by ATAGO. When measuring the refractive index of the adhesive sheet, only the adhesive sheet was set against a prism with an Abbe refractive index diameter (the release liner was removed).

[0140] (G"(150) of Pressure-Sensitive Adhesive Sheet) The G"(150) of the pressure-sensitive adhesive sheet 1 was measured by the method described above. A measurement sample was prepared by punching out a disc from a laminate (1 mm thick) in which a plurality of pressure-sensitive adhesive sheets 1 were laminated. For the dynamic viscoelasticity measurement, an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific was used. The conditions for the dynamic viscoelasticity measurement were as follows. (Measurement conditions) Frequency: 1 Hz Deformation mode: Torsion Measurement temperature: -70°C to 150°C Heating rate: 5°C / min

[0141] (Appearance of Pressure-Sensitive Adhesive Sheet) The appearance of the produced pressure-sensitive adhesive sheets was evaluated by the following method. First, a pressure-sensitive adhesive sheet formed on a release liner was attached to the surface of a blackboard (CLAREX (flat board, black) manufactured by Nitto Jushi Kogyo Co., Ltd.). Next, after peeling off the release liner, the exposed surface of the pressure-sensitive adhesive sheet was visually inspected. If no unevenness was observed in the appearance, it was rated A, and if unevenness was observed, it was rated D.

[0142] (Reflectance of Optical Laminate) The reflectance of each prepared optical laminate was evaluated by the following method. First, the optical laminate was bonded to a reflector (V3, manufactured by NEODIS) using an acrylic adhesive (thickness 25 μm). The bonding was performed so that the second liquid crystal alignment solidified layer of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer faced the reflector. Next, a glass plate (Eagle XG, manufactured by Corning) was bonded to the first liquid crystal alignment solidified layer side of the optical laminate using an acrylic adhesive sheet (thickness 150 μm) to prepare a test sample. The spectral reflectance of the prepared sample was measured under the following measurement conditions using a spectrophotometer (CM-26d, manufactured by Konica Minolta), and the reflectance was evaluated according to the following criteria. <Measurement conditions> Type of light receiving optical system: SCI (specular reflection included method) Measurement wavelength range: 360 to 740 nm Light source: D65 Measurement diameter (diameter of opening on sample surface): φ8 mm <Criteria> A: Reflectance less than 4.9% B: Reflectance 4.9% or more but less than 4.95% D: Reflectance 4.95% or more but less than 5.0% DD: Reflectance 5.0% or more

[0143] The evaluation results are shown in Table 3 below.

[0144]

[0145] The pressure-sensitive adhesive sheets of the examples were able to suppress the occurrence of uneven appearance despite having a refractive index of 1.49 or more.

[0146] The optical laminate of the present invention can be used in image display devices such as EL displays and liquid crystal displays.

Claims

1. A pressure-sensitive adhesive sheet comprising a crosslinked base polymer, having a loss modulus G" of 0.002 MPa or more at 150°C, and a refractive index of 1.49 or more for light with a wavelength of 589 nm.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the weight-average molecular weight of the base polymer is 700,000 or more.

3. The pressure-sensitive adhesive sheet according to claim 1, wherein the monomer component M constituting the base polymer includes an aromatic ring-containing monomer a1.

4. The pressure-sensitive adhesive sheet according to claim 3, wherein the aromatic ring-containing monomer a1 is a high-boiling point monomer.

5. The adhesive sheet according to claim 3, wherein the aromatic ring-containing monomer a1 is phenoxybenzyl acrylate.

6. The pressure-sensitive adhesive sheet according to claim 3, wherein the content of the aromatic ring-containing monomer a1 in the monomer component M is 50% by weight or more.

7. An optical laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 6 and an optical substrate.

8. The optical laminate according to claim 7, wherein the optical substrate comprises a liquid crystal alignment solidified layer.

9. The optical laminate according to claim 7, wherein the optical substrate comprises a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer, and the first liquid crystal alignment solidified layer, the adhesive sheet, and the second liquid crystal alignment solidified layer are laminated in this order in the optical laminate.

10. The optical laminate according to claim 7, wherein the optical substrate comprises a polarizing film.

11. The optical laminate described in claim 7, wherein the optical substrate comprises a polarizing film, a first liquid crystal alignment solidified layer, and a second liquid crystal alignment solidified layer, and in the optical laminate, the polarizing film, the first liquid crystal alignment solidified layer, the adhesive sheet, and the second liquid crystal alignment solidified layer are laminated in this order.

12. The optical laminate according to claim 9, wherein at least one layer selected from the group consisting of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer is a retardation layer.

13. An image display device comprising the optical laminate according to claim 7.

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