Polarizing plate and polarizing plate with phase difference layer

Abstract

To provide a polarizing plate and a polarizing plate with a phase difference layer that can prevent warpage in a high temperature environment, while reducing the light transmittance T380 at a wavelength of 380 nm to 3.5% or less.SOLUTION: A polarizing plate of the present invention has a light transmittance T380 at a wavelength of 380 nm of 3.5% or less, and satisfies the following formula (1). In the formula (1), Th represents the thickness (μm) of the polarizing plate, and W represents a warpage value (mm) measured in the following heating warpage test.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and a polarizing plate with a retardation layer. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become widespread. Polarizing plates are typically used in image display devices. It is known that such polarizing plates are provided with ultraviolet absorption properties in order to protect image display elements (particularly OLED elements) from ultraviolet rays (for example, Patent Document 1). However, the polarizing plate described in Patent Document 1 has a problem in that it is prone to warping in high-temperature environments. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-203400 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a method for reducing the light transmittance T 380 The present invention provides a polarizing plate and a polarizing plate with a retardation layer that can suppress warping in a high-temperature environment while reducing the warpage to 3.5% or less. [Means for solving the problem]

[0005] [1] The polarizing plate according to the embodiment of the present invention has a light transmittance T 380 is 3.5% or less, and satisfies the following formula (1).

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[0006] According to an embodiment of the present invention, the light transmittance T 380 This can reduce the temperature and suppress warping in a high-temperature environment. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a pressure-sensitive adhesive layer-attached polarizing plate according to another aspect of the present invention. [Figure 3] FIG. 10 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to still another aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0009] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light of wavelength 550 nm at 23°C. Re(λ) is calculated by the formula: Re=(nx-ny)×d, where d (nm) is the thickness of the layer (film). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth=(nx-nz)×d, where d (nm) is the thickness of the layer (film). (4)Angle When angles are referred to herein, unless otherwise specified, the angles include angles in both clockwise and counterclockwise directions.

[0010] A. Overall structure of polarizing plate 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 1 shown in the figure has a light transmittance T 380 is 3.50% or less, preferably 2.00% or less, more preferably 1.85% or less, even more preferably 1.50% or less, particularly preferably 1.00% or less, and particularly preferably 0.80% or less. The polarizing plate 1 satisfies the following formula (1), more preferably the following formula (2), and particularly preferably the following formula (3).

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[0011] In one embodiment of the present invention, a polarizing plate 1 includes a polarizer 2, a first protective layer 3 disposed on the viewing side of the polarizer 2, and a second protective layer 4 disposed on the side opposite to the viewing side of the polarizer 2. The second protective layer 4 contains a resin and an ultraviolet absorber. The content of the ultraviolet absorber is, for example, 1 part by mass or more, preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and for example, 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 12 parts by mass or less, relative to 100 parts by mass of the resin. If the content of the ultraviolet absorber is within the above range, the light transmittance T 380 can be stably reduced. The first protective layer 3 is typically attached to the viewing side of the polarizer 2 via any appropriate adhesive layer 5a. The second protective layer 4 is typically attached to the side of the polarizer 2 opposite the viewing side via any appropriate adhesive layer 5b. That is, the polarizing plate 1 may be composed of the first protective layer 3, the adhesive layer 5a, the polarizer 2, the adhesive layer 5b, and the second protective layer 4. Each of the adhesive layer 5a and the adhesive layer 5b is typically formed from an ultraviolet-curable adhesive. The adhesive layer 5a and / or the adhesive layer 5b may be a pressure-sensitive adhesive layer.

[0012] The thickness of the polarizing plate 1 is, for example, 30 μm or more, preferably 40 μm or more, and for example, 65 μm or less, preferably 50 μm or less. When the thickness of the polarizing plate is equal to or less than the upper limit, the polarizing plate can be made thinner, and warping in a high-temperature environment can be stably suppressed. In one embodiment, the thickness of the second protective layer 4 is smaller than the thickness of the first protective layer 3. The upper limit of the thickness of the second protective layer 4 is, for example, 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 5 μm or less. The lower limit of the thickness of the second protective layer 4 is typically 0.5 μm or more, preferably 1 μm or more, and more preferably 3 μm or more. When the thickness of the second protective layer is equal to or less than the upper limit, the thickness of the polarizing plate can be reduced, and the warping of the polarizing plate in a high-temperature environment can be further suppressed. When the thickness of the second protective layer is equal to or more than the lower limit, the light transmittance T 380 can be reduced more stably. The upper limit of the thickness of the first protective layer 3 is, for example, 45 μm or less, preferably 40 μm or less. The lower limit of the thickness of the first protective layer 3 is typically 20 μm or more, preferably 30 μm or more. When the first protective layer 3 is surface-treated, the thickness of the first protective layer 3 includes the thickness of the surface treatment layer. The surface treatment layer will be described later. When the thickness of the first protective layer is equal to or less than the upper limit, the thickness of the polarizing plate can be further reduced and the warping of the polarizing plate in a high-temperature environment can be further suppressed.When the thickness of the first protective layer is equal to or more than the lower limit, the polarizer can be stably protected. The thickness of the polarizer 2 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 15 μm or less, preferably 12 μm or less, more preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of each of the adhesive layer 5a and the adhesive layer 5b is, for example, 0.5 μm or more, preferably 1 μm or more, and for example, 10 μm or less, preferably 5 μm or less.

[0013] In one embodiment of the present invention, the second protective layer 4 is a solidified layer of a coating film of an organic solvent solution containing a resin and an ultraviolet absorber. The solidified layer of the coating film is formed, for example, by applying the organic solvent solution to a substrate and then drying the coating film. Therefore, even if the thickness of the solidified layer of the coating film is within the thickness range of the second protective layer described above (particularly 10 μm or less, particularly 3 μm to 5 μm), it is supported by the substrate and can be stably transported during the production of the polarizing plate. On the other hand, extrusion molding is also considered as a method for producing the second protective layer. However, when the second protective layer is an extrusion molded product, stable molding and / or transport of the second protective layer may be difficult if the thickness of the second protective layer is within the above range.

[0014] B. Overall structure of the adhesive layer-attached polarizing plate 2 is a schematic cross-sectional view of a pressure-sensitive adhesive layer-attached polarizing plate according to another aspect of the present invention. The pressure-sensitive adhesive layer-attached polarizing plate 11 includes the above-described polarizing plate 1 and a pressure-sensitive adhesive layer 6a disposed on the side opposite the viewing side of the polarizing plate 1. More specifically, the pressure-sensitive adhesive layer 6a is disposed on the opposite side of the second protective layer 4 from the polarizer 2, and is provided on the surface of the second protective layer 4. The pressure-sensitive adhesive layer 6a is typically formed from a pressure-sensitive adhesive described below. The pressure-sensitive adhesive layer 6a enables the pressure-sensitive adhesive layer-attached polarizing plate 11 to be attached to an image display panel including an image display element.

[0015] C. Overall structure of polarizing plate with retardation layer 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to yet another aspect of the present invention. The polarizing plate with a retardation layer 10 includes the polarizing plate 1 described above and a first retardation layer 7 disposed on the side opposite the viewing side of the polarizing plate 1. The polarizing plate with a retardation layer 10 may further include a second retardation layer 8 disposed on the side opposite the viewing side of the first retardation layer 7 (the side opposite the polarizing plate 1 with respect to the first retardation layer 7). A polarizing plate with a retardation layer can have a desired optical compensation function. The first retardation layer 7 is typically bonded to the second protective layer 4 via any appropriate pressure-sensitive adhesive layer 6b. The pressure-sensitive adhesive layer 6b is typically formed from a pressure-sensitive adhesive described below. The pressure-sensitive adhesive layer 6b may be an adhesive layer. The second retardation layer 8 is typically bonded to the first retardation layer 7 via any appropriate adhesive layer 5c. The adhesive layer 5c is typically formed from an ultraviolet-curable adhesive. The adhesive layer 5c may be a pressure-sensitive adhesive layer. The retardation layer-attached polarizing plate 10 may further include the above-mentioned pressure-sensitive adhesive layer 6a. In the retardation layer-attached polarizing plate 10, the pressure-sensitive adhesive layer 6a is disposed on the side opposite to the viewing side of the second retardation layer 8, and is provided on the second retardation layer 8.

[0016] The components of the polarizing plate and the pressure-sensitive adhesive layer-attached polarizing plate will be described below.

[0017] D. Polarizer Any appropriate polarizer can be adopted as the polarizer 2. For example, the resin film forming the polarizing plate 2 may be a single-layer resin film or a laminate of two or more layers.

[0018] Specific examples of polarizers composed of a single-layer resin film include PVA-based resin films that have been subjected to a dyeing treatment with iodine and a stretching treatment (typically, uniaxial stretching). The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an iodine aqueous solution. The stretching ratio in the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the film may be dyed after stretching. If necessary, the PVA-based resin 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 resin film in water and washing it before dyeing, it is possible to clean off stains and antiblocking agents on the surface of the PVA-based film and also to swell the PVA-based resin film, thereby preventing uneven dyeing.

[0019] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a 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 the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In one embodiment of the present invention, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. Additionally, in one embodiment of the present invention, the laminate is preferably 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 manufacturing method of this embodiment includes 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. By introducing auxiliary stretching, it is possible to increase the crystallinity of PVA, even when PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of polyvinyl alcohol molecules and the decrease in 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 drying shrinkage treatment.The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as the first protective layer of the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such polarizer manufacturing methods are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0020] The polarizer 2 is preferably composed of a polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate, and more preferably composed of a polarizer obtained by peeling the resin substrate from a laminate of the resin substrate / polarizer.

[0021] The polarizer 2 preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer 2 is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer 2 is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0022] E. 1st protective layer The first protective layer 3 is disposed on one side of the polarizer 2 in the thickness direction. The first protective layer 3 is formed of any appropriate film that can be used as a protective layer for the polarizer 2. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting resins or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. The term "(meth)acrylic resin" refers to an acrylic resin and / or a methacrylic resin. Other examples include glassy polymers such as siloxane polymers. The polymer film described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials for this film include resin compositions containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups in its side chains. Examples include a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. These materials, which are the main components of the film, can be used alone or in combination. The polymer film can be, for example, an extrusion molded product of the resin composition.

[0023] The first protective layer 3 preferably contains a cellulose-based resin, and more preferably contains triacetyl cellulose. In one embodiment of the present invention, the first protective layer 3 is disposed on the outermost surface of the polarizing plate 1 on the viewing side. The first protective layer 3 may be subjected to a surface treatment such as a hard coat treatment, an anti-reflection treatment, an anti-sticking treatment, or an anti-glare treatment, as necessary. Among such surface treatments, a hard coat treatment is preferable. That is, the first protective layer 3 preferably includes a substrate formed from the above-mentioned material and a hard coat layer disposed on the substrate. The hard coat layer can impart excellent pencil hardness to the polarizing plate 1.

[0024] F.Second protective layer The second protective layer 4 is disposed on the opposite side of the polarizer 2 from the first protective layer 3. As described above, the second protective layer 4 contains a resin and an ultraviolet absorber. Resins contained in the second protective layer 4 include, for example, cellulose-based resins such as triacetyl cellulose (TAC); polyester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyolefin (PO)-based resins such as polyethylene (PE) and polypropylene (PP); polyamide (PA)-based resins; (meth)acrylic-based resins; polystyrene (PS)-based resins; polyoxymethylene (polyacetal, POM)-based resins; polyurethane (PU)-based resins; and cycloolefin-based resins. The resin contained in the second protective layer 4 is preferably a cycloolefin resin or a (meth)acrylic resin, more preferably a norbornene resin or a polymethyl methacrylate (PMMA) resin, and even more preferably a norbornene resin. Specific examples of norbornene resins include the "cycloolefin resin obtained by hydrogenating a ring-opening polymer of a norbornene monomer" described in JP-A-2006-208925. Examples of commercially available products of such cycloolefin resins include "ARTON" manufactured by JSR Corporation, "ZEONEX" manufactured by Zeon Corporation, "APEL" manufactured by Mitsui Chemicals, Inc., and "TOPAS" manufactured by Polyplastics Co., Ltd. Commercially available products of polymethyl methacrylate (PMMA) resin include, for example, "Acrypellet" manufactured by Mitsubishi Chemical Corporation, "Parapet" manufactured by Kuraray Co., Ltd., "Sumipex" manufactured by Sumitomo Chemical Co., Ltd., and "Delpet" manufactured by Asahi Kasei Corporation.

[0025] The UV absorber contained in the second protective layer 4 may be any appropriate UV absorber. Examples of UV absorbers include benzotriazole-based UV absorbers, triazine-based UV absorbers, and benzophenone-based UV absorbers. The UV absorbers may be used alone or in combination. Among UV absorbers, triazine-based UV absorbers are preferred. The content of the UV absorber in the second protective layer 4 is as described in Section A above.

[0026] As described above, the second protective layer 4 is preferably a solidified layer of a liquid coating film in which a resin and an ultraviolet absorber are dispersed and / or dissolved in an organic solvent. Such a liquid is preferably an organic solvent solution in which the resin and the ultraviolet absorber are dissolved. In other words, the second protective layer is preferably a dry coating film (coating film) containing a resin and an ultraviolet absorber that are dispersible and / or soluble in an organic solvent, and more preferably a dry coating film (coating film) containing a resin and an ultraviolet absorber that are soluble in an organic solvent. To form the solidified layer of the coating film as the second protective layer 4, first, the above-mentioned resin and ultraviolet absorber are added to an organic solvent to prepare the above-mentioned liquid. Examples of organic solvents include aliphatic hydrocarbons such as isooctane, heptane, hexane, and isohexane; alicyclic hydrocarbons such as methylcyclohexane and ethylcyclohexane; aromatic hydrocarbons such as primary xylene and toluene; ethers such as cyclopentyl methyl ether (CPME) and 1,3-dioxolane; ketones such as acetone, acetylacetone, methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), cyclohexanone, and cyclopentanone; esters such as butyl acetate, ethyl acetate, methyl acetate, and propylene glycol monomethyl ether acetate; alcohols such as 1-methoxy-2-propanol and isopropanol (IPA); halogenated aliphatic hydrocarbons such as methylene chloride; halogenated aromatic hydrocarbons such as 1,2,4-trichlorobenzene; and terpenes such as limonene. The organic solvents can be used alone or in combination. Among the organic solvents, cyclopentyl methyl ether and ethyl acetate are preferred. The organic solvent is appropriately selected depending on the type of resin used. When the resin is a cycloolefin resin (norbornene resin), cyclopentyl methyl ether is preferably selected, and when the resin is a (meth)acrylic resin (PMMA resin), ethyl acetate is preferably selected. The concentration of the resin in the liquid is, for example, 1% by mass or more and 20% by mass or less. The amount of the ultraviolet absorber added to the liquid is the same as the content of the ultraviolet absorber described in Section A above. Next, the liquid (preferably an organic solvent solution) is applied to any suitable substrate (e.g., a PET substrate) and dried at any suitable temperature for any suitable time. This results in a solidified layer of the coating film serving as a second protective layer being formed on the substrate. After that, the solidified layer of the coating film (second protective layer 4) is bonded to the surface of the polarizer 2 (the surface opposite to the first protective layer) via an adhesive layer 5b, and the substrate is then peeled off from the solidified layer of the coating film (second protective layer 4).

[0027] G.Adhesive layer Each of the adhesive layers 6a and 6b is formed from an adhesive (pressure-sensitive adhesive). The adhesive forming the adhesive layer can also be used to bond the test sample to a test glass plate in the heat warpage test described above. The pressure-sensitive adhesive typically contains a (meth)acrylic polymer as a base polymer. The (meth)acrylic polymer contains a polymer of a monomer component (raw material monomer) whose main component is alkyl (meth)acrylate. The alkyl (meth)acrylate preferably accounts for 50 mass% or more of the total monomer components that serve as raw materials for the (meth)acrylic polymer, and can be arbitrarily set as the remainder of the monomers other than the alkyl (meth)acrylate. Note that (meth)acrylate refers to acrylate and / or methacrylate.

[0028] The alkyl (meth)acrylate constituting the main skeleton of the (meth)acrylic polymer may be a linear or branched alkyl group having 1 to 18 carbon atoms. The alkyl (meth)acrylates may be used alone or in combination. The average number of carbon atoms in the alkyl group is preferably 3 to 10.

[0029] The (meth)acrylic polymer may contain, in addition to the structural unit derived from the alkyl (meth)acrylate, a structural unit derived from a copolymerizable monomer polymerizable with the alkyl (meth)acrylate. That is, the monomer component serving as the raw material for the (meth)acrylic polymer may further contain a copolymerizable monomer in addition to the alkyl (meth)acrylate.

[0030] Examples of copolymerizable monomers include carboxyl group-containing monomers, hydroxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, cyclopolymerizable monomers, epoxy group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, polyfunctional acrylates, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, vinyl esters, aromatic vinyl compounds, dienes, vinyl ethers, and vinyl chloride.

[0031] Among such copolymerizable monomers, preferred are reactive group-containing monomers containing a reactive group capable of reacting with the crosslinking agent described below, and more preferred are carboxyl group-containing monomers and hydroxyl group-containing monomers. When the PSA contains a crosslinking agent described below, the reactive group-containing monomer serves as a reaction site with the crosslinking agent. Carboxyl group-containing monomers and hydroxyl group-containing monomers are highly reactive with intermolecular crosslinking agents and are therefore preferably used to improve the cohesiveness and heat resistance of the resulting PSA layer. Furthermore, carboxyl group-containing monomers are preferred in terms of achieving both durability and reworkability, and hydroxyl group-containing monomers are preferred in terms of improving reworkability. The copolymerizable monomers can be used alone or in combination as raw material monomers for (meth)acrylic polymers.

[0032] The carboxyl group-containing monomer is preferably (meth)acrylic acid, more preferably acrylic acid. When the carboxyl group-containing monomer is used as a raw material monomer, the content of the carboxyl group-containing monomer is usually 0.01 mass % or more and 10 mass % or less of the total monomer components that are raw materials for the (meth)acrylic polymer.

[0033] The hydroxyl group-containing monomer is preferably 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate, more preferably 4-hydroxybutyl (meth)acrylate. When the hydroxyl group-containing monomer is used as a raw material monomer, the content of the hydroxyl group-containing monomer is usually 0.01 mass% or more and 10 mass% or less of the total monomer components that are raw materials for the (meth)acrylic polymer.

[0034] The weight-average molecular weight Mw of the (meth)acrylic polymer is, for example, 200,000 to 3,000,000, preferably 1,000,000 to 2,500,000, and more preferably 1,200,000 to 2,500,000. If the weight-average molecular weight Mw is within this range, a pressure-sensitive adhesive layer with excellent durability (particularly heat resistance) can be obtained. If the weight-average molecular weight Mw exceeds 3,000,000, an increase in viscosity and / or gelation during polymer polymerization may occur.

[0035] The pressure-sensitive adhesive may contain a crosslinking agent. Examples of crosslinking agents that can be used include organic crosslinking agents and polyfunctional metal chelates. Examples of organic crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, and imine crosslinking agents. Polyfunctional metal chelates are compounds in which a polyvalent metal is covalently or coordinately bonded to an organic compound. The crosslinking agents may be used alone or in combination. The crosslinking agent preferably includes an isocyanate crosslinking agent and a peroxide crosslinking agent. When a crosslinking agent is blended into the pressure-sensitive adhesive, the blending amount of the crosslinking agent is usually 0.01 to 15 parts by mass per 100 parts by mass of the (meth)acrylic polymer (base polymer).

[0036] The pressure-sensitive adhesive may contain a reactive functional group-containing silane coupling agent. The reactive functional group of the reactive functional group-containing silane coupling agent is typically a functional group other than an acid anhydride group. The reactive functional group-containing silane coupling agents may be used alone or in combination. When a reactive functional group-containing silane coupling agent is blended into the pressure-sensitive adhesive, the blending amount of the reactive functional group-containing silane coupling agent is typically 0.001 to 5 parts by mass per 100 parts by mass of the (meth)acrylic polymer.

[0037] H. First retardation layer and second retardation layer Each of the first retardation layer 7 and the second retardation layer 8 can be composed of a retardation film having any appropriate optical and / or mechanical properties depending on the purpose. The first retardation layer 7 typically exhibits the relationship nx>ny≧nz. Here, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. The first retardation layer 7 can function as a so-called λ / 4 plate. The in-plane retardation Re(550) of the first retardation layer 7 is, for example, 100 nm to 200 nm, and preferably 130 nm to 150 nm. The angle formed by the slow axis of the first retardation layer 7 and the absorption axis of the polarizer 2 is preferably 40° to 50°, more preferably 42° to 48°, even more preferably 44° to 46°, and particularly preferably about 45°. The second retardation layer 8 typically exhibits refractive index characteristics of nz>nx=ny. Here, "nx=ny" does not only mean that nx and ny are completely equal, but also includes cases where they are substantially equal. The thickness direction retardation Rth(550) of the second retardation layer 8 is preferably -50 nm to -300 nm, more preferably -100 nm to -180 nm.

[0038] I. Image display device The polarizing plate, adhesive layer-attached polarizing plate, and retardation layer-attached polarizing plate described in the above items A to H can be applied to an image display device. Therefore, one embodiment of the present invention also includes an image display device using any of the polarizing plate, adhesive layer-attached polarizing plate, and retardation layer-attached polarizing plate. Typical examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention typically includes the polarizing plate described in the above items A to F on its viewing side. The image display device includes an image display panel. The image display panel includes an image display element. Note that the image display device may be referred to as an optical display device, the image display panel may be referred to as an optical display panel, and the image display element may be referred to as an optical display element. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows.

[0040] (1) Heat warpage test The acrylic adhesive obtained in Production Example 1 was applied to the silicone-treated surface of a release film (PET film, MRF38, manufactured by Mitsubishi Chemical Polyester Film Corporation), and then dried in an air-circulating constant-temperature oven set to a predetermined temperature to form an adhesive layer (adhesive sheet) with a thickness of 15 μm. Next, the adhesive layer was transferred from the release film to the surface of the second protective layer of the polarizing plate obtained in the Examples and Comparative Examples. The polarizing plate provided with the adhesive layer (adhesive layer-attached polarizing plate) was then cut into a size of 70 mm x 150 mm to prepare a test sample. In the test sample, the absorption axis direction of the polarizer was parallel to the long side direction of the test sample. Next, the test sample was attached to a test glass plate (manufactured by Matsunami Glass Co., Ltd.) via the adhesive layer. The test glass plate had a size of 80 mm x 170 mm and a thickness of 0.2 mm. The test sample attached to the test glass plate was then placed in an oven and heated at 85°C for 24 hours, and then left to stand at room temperature (23°C) and 55% RH for 1 hour. When the test sample was observed with the test glass plate facing downwards, it had a concave (U-shaped) shape that opened upwards. The height of the warpage of the test sample was then measured. Specifically, the test sample was placed on a horizontal surface so that the test glass plate was in contact with the horizontal surface, and the vertical dimension between the horizontal surface and the edge of the short side of the bottom surface (the surface facing the horizontal surface) of the test glass plate to which the test sample was attached was measured with a ruler, and this was taken as the height of the warpage of the test sample. The results are shown in Table 1.

[0041] (2) Light transmittance T 380 measurement The polarizing plates obtained in each of the examples and comparative examples were set in a spectrophotometer (trade name "LPF-200", manufactured by Otsuka Electronics Co., Ltd.) so that incident light was perpendicular to the first protective layer, and the light transmittance T 380 The results are shown in Table 1.

[0042] [Manufacturing Example 1] A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 75.1 parts of butyl acrylate, 19 parts of benzyl acrylate, 4.8 parts of acrylic acid, 0.1 parts of 2-hydroxyethyl acrylate, and 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, along with 100 g of ethyl acetate. Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the liquid temperature in the flask was maintained at around 55°C for 8 hours to carry out a polymerization reaction, yielding a solution containing an acrylic polymer with a weight-average molecular weight of 2,200,000. 3 parts of an isocyanate crosslinking agent (Coronate L, manufactured by Tosoh Corporation), 0.2 parts of a peroxide crosslinking agent (benzoyl peroxide), and 0.075 parts of a silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) were blended with 100 parts of the solid content of the obtained acrylic polymer solution to obtain an acrylic adhesive, which is a solution of an acrylic adhesive composition (solid content 11% by mass).

[0043] [Examples 1 to 7] 1. Polarizer Fabrication A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating liquid) was prepared by dissolving 100 parts by mass of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by mass of potassium iodide was added, in water. The above PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60° C. to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by mass of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment). Next, the substrate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4% by mass, potassium iodide concentration 5% by mass) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this way, a polarizer having a thickness of about 5 μm was formed on the resin substrate.

[0044] 2. Applying the first protective layer A TAC film (thickness: 32 μm) with a hard coat layer (HC) as a first protective layer was bonded to the surface of the obtained polarizer (the surface opposite to the resin substrate) via a UV-curable adhesive. Specifically, the UV-curable adhesive layer was coated to a thickness of approximately 2.0 μm, and the films were bonded using a roller. Thereafter, UV light was irradiated from the TAC film side to cure the adhesive. The resin substrate was then peeled off. 3. Preparation of the second protective layer A cycloolefin resin (trade name: Arton, manufactured by JSR Corporation) was dissolved in cyclopentyl methyl ether to prepare an organic solvent solution of the cycloolefin resin (concentration: 10% by mass). Next, an ultraviolet absorber (UVA, trade name: Adekastab LA-F70, manufactured by ADEKA Corporation) was added to the organic solvent solution in the amount shown in Table 1, relative to 100 parts by mass of the cycloolefin resin, to prepare an organic solvent solution of the cycloolefin resin and UVA. Next, the organic solvent solution was applied onto a PET substrate using an applicator so that the thickness after drying would be the value shown in Table 1, and then dried at 110°C for 3 minutes. In this way, a solidified layer of the applied film of the organic solvent solution of the cycloolefin resin and UVA was prepared as the second protective layer (UVA-COP / PET). Next, a second protective layer was attached to the surface of the polarizer (the surface opposite to the first protective layer) via a UV-curable adhesive. Specifically, the UV-curable adhesive layer was applied to a thickness of approximately 2.0 μm, and the layers were attached using a roller. After that, UV light was irradiated from the second protective layer side to cure the adhesive. Next, the PET substrate was peeled off from the second protective layer. In this way, a polarizing plate having a structure of first protective layer (HC / TAC film) / polarizer / second protective layer (UVA-COP) was obtained.

[0045] [Example 8] A polarizing plate having a structure of first protective layer (HC / TAC film) / polarizer / second protective layer (UVA-PMMA) was obtained in the same manner as in Example 1, except that the second protective layer (UVA-COP) was changed to a second protective layer (UVA-PMMA) prepared as follows. <Preparation of second protective layer> PMMA resin (trade name NeoCryl B-728, manufactured by DSM Coating Resins) was dissolved in ethyl acetate to prepare an organic solvent solution of PMMA resin (concentration 10% by mass). Next, an ultraviolet absorber (UVA, trade name Adekastab LA-F70, manufactured by ADEKA Corporation) was added to the organic solvent solution in the amounts shown in Table 1 per 100 parts by mass of PMMA resin to prepare an organic solvent solution of PMMA resin and UVA. Next, the organic solvent solution was applied onto a PET substrate using an applicator so that the thickness after drying would be the value shown in Table 1, and then dried at 60°C for 3 minutes. In this way, a solidified layer of the coated film of the organic solvent solution of PMMA resin and UVA was prepared as the second protective layer (UVA-PMMA / PET).

[0046] [Comparative Example 1] Except for not using an ultraviolet absorber (UVA), a polarizing plate was obtained in the same manner as in Example 1. That is, in the polarizing plate of Comparative Example 1, the second protective layer did not contain UVA.

[0047] Comparative Example 2 A polarizing plate was obtained in the same manner as in Example 1, except that a 25 μm-thick cycloolefin resin film (trade name G+, manufactured by Zeon Corporation) prepared by extrusion molding was used instead of the solidified layer of the coating film of the organic solvent solution of the cycloolefin resin and UVA.

[0048] [Table 1]

[0049] [evaluation] As is clear from Table 1, by adjusting the thickness of the second protective layer so that the polarizing plate thickness Th (μm) / warpage value (mm) in the heat warpage test is 10 or more, the light transmittance T 380 It can be seen that a polarizing plate can be obtained that can reduce the warp in a high-temperature environment while reducing the warp ratio to 3.5% or less. [Industrial Applicability]

[0050] The polarizing plate and retardation layer-attached polarizing plate of the present invention can be suitably used in image display devices (typically, liquid crystal display devices and organic EL display devices). [Explanation of symbols]

[0051] 1 Polarizing plate 2 polarizers 3 1st protective layer 4 Second protective layer 7 First retardation layer 8 Second retardation layer 10 Polarizing plate with retardation layer

Claims

[Claim 1] Light transmittance T at a wavelength of 380 nm ３８０ is 3.5% or less, A polarizing plate that satisfies the following formula (1): [Equation 1] In formula (1), Th represents the thickness (μm) of the polarizing plate, and W represents the warpage value (mm) measured in the following heat warpage test: Heat warpage test; A test sample was prepared by cutting the polarizing plate to a size of 70 mm x 150 mm, and the test sample was attached to a test glass plate via an adhesive layer. The test sample was then heated at 85°C for 24 hours, and then allowed to stand at room temperature (23°C) for at least 1 hour, after which the height of the warpage of the test sample was measured.

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