Polarizing plate and polarizing plate with retardation layer

Abstract

To provide a polarizing plate excellent in durability in spite of being very thin.SOLUTION: A polarizing plate of the present invention includes a polarizer and a protective layer arranged on one side of the polarizer. The protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. In one embodiment, the protective layer has a thickness of 10 μm or less.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] Due to the image formation method used in image display devices (e.g., liquid crystal display devices and organic electroluminescence (EL) display devices), polarizing plates are often arranged on at least one side of the display cell. In recent years, image display devices have become thinner and more flexible, and as a result, there has been a strong demand for thinner polarizing plates. However, the thinner the polarizing plate, the more pronounced its durability problem becomes, namely, its optical properties deteriorate in heated and humid environments. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-210474 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned problems of the prior art, and its main object is to provide a polarizing plate and a polarizing plate with a retardation layer that are excellent in durability despite being very thin. [Means for solving the problem]

[0005] The polarizing plate of the present invention has a polarizer and a protective layer disposed on one side of the polarizer, the protective layer being made of a cured product of an epoxy resin having a biphenyl skeleton. In one embodiment, the cured product is a cationically polymerized cured product. In one embodiment, the protective layer further contains an oxetane resin. In one embodiment, the protective layer has a thickness of 10 μm or less. In one embodiment, the protective layer has an iodine adsorption amount of 10% by weight or less. In one embodiment, the protective layer has a softening temperature of 100° C. or higher. In one embodiment, the polarizing plate has a total thickness of 10 μm or less. In another aspect of the present invention, there is provided a polarizing plate with a retardation layer, which has a retardation layer on the surface of the polarizing plate on which the protective layer is not disposed. [Effects of the Invention]

[0006] According to the present invention, by forming the protective layer disposed on the polarizer from a cured product of an epoxy resin having a biphenyl skeleton, it is possible to obtain a polarizing plate that is excellent in durability despite being very thin. [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 view showing an example of a drying shrinkage treatment using a heated roll in a method for producing a polarizing plate according to one embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. [Figure 4] FIG. 2 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] (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(λ)=(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(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5)Angle When angles are referred to herein, the angles include both clockwise and counterclockwise angles relative to a reference direction, so for example, "45°" means ±45°.

[0009] A. Overview of polarizing plates FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 in the illustrated example includes a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10. The thickness of the polarizer 10 is preferably 8 μm or less. If necessary, another protective layer (not shown) may be provided on the polarizer 10 opposite the protective layer 20. When applied to an image display device, the polarizing plate 100 may be disposed on the viewing side of a display cell or on the side opposite the viewing side (rear side). In either case, the protective layer 20 may be disposed on the display cell side or on the side opposite the display cell (outside). In one embodiment, the polarizing plate 100 is disposed on the viewing side of the display cell (and thus the image display device), and the protective layer 20 is disposed on the viewing side (opposite the display cell). The polarizing plate may be in a continuous or sheet-like shape. When the polarizing plate is in a continuous shape, it is preferably wound into a roll to form a polarizing plate roll.

[0010] Typically, the polarizing plate has a pressure-sensitive adhesive layer as the outermost layer on one side (typically, the side opposite the protective layer 20 of the polarizer 10), allowing it to be attached to a display cell. If necessary, a surface protective film and / or a carrier film may be temporarily and removably attached to the polarizing plate to reinforce and / or support the polarizing plate. When the polarizing plate includes a pressure-sensitive adhesive layer, a separator may be temporarily and removably attached to the surface of the pressure-sensitive adhesive layer to protect the pressure-sensitive adhesive layer until actual use and to enable the polarizing plate to be rolled.

[0011] In an embodiment of the present invention, the protective layer 20 is made of a cured product of an epoxy resin having a biphenyl skeleton. With this configuration, the protective layer can be made very thin (for example, 10 μm or less). Furthermore, the protective layer can be formed directly on the polarizer (i.e., without an adhesive or pressure-sensitive adhesive layer). According to an embodiment of the present invention, the polarizer and protective layer are very thin as described above, and an adhesive or pressure-sensitive adhesive layer can be omitted, so the total thickness of the polarizing plate can be made extremely thin. Furthermore, the adhesion between the polarizer and the protective layer is excellent. The total thickness of the polarizing plate is, for example, 40 μm or less, preferably 30 μm or less, more preferably 20 μm or less, even more preferably 10 μm or less, and particularly preferably 7 μm or less. The total thickness of the polarizing plate can be, for example, 4 μm or more.

[0012] Furthermore, by forming the protective layer from a cured product of an epoxy resin having a biphenyl skeleton, a polarizing plate with excellent durability can be realized despite its thinness. Specifically, a polarizing plate with reduced deterioration in optical properties even in a heated and humidified environment can be realized. The polarizing plate exhibits very small changes in the single-layer transmittance Ts (ΔTs) and the degree of polarization P (ΔP) after being left in an environment of 85°C and 85% RH for 120 hours. The single-layer transmittance Ts can be measured, for example, using a UV-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The degree of polarization P can be calculated from the single-layer transmittance (Ts), parallel transmittance (Tp), and crossed transmittance (Tc) measured using the UV-visible spectrophotometer using the following formula: Degree of polarization (P)(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 The above Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Ts and P are essentially polarizer properties. ΔTs and ΔP can be calculated using the following formulas: ΔTs(%)=Ts 120 -Ts0 ΔP(%)=P 120 -P0 Here, Ts0 is the single transmittance before storage (initial), and Ts 120 is the single transmittance after storage, P0 is the degree of polarization before storage (initial), and P 120 is the degree of polarization after standing. ΔTs is preferably 3.0% or less, more preferably 2.7% or less, and even more preferably 2.4% or less. ΔP is preferably -0.5% to 0%, more preferably -0.3% to 0%, and even more preferably -0.1% to 0%.

[0013] In the embodiment of the present invention, the polarizing plate can be extremely thin. Therefore, it can be suitably applied to a flexible image display device. More preferably, the image display device has a curved shape (substantially a curved display screen) and / or is bendable or foldable. Specific examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices). Needless to say, the above description does not prevent the polarizing plate of the present invention from being applied to a typical image display device.

[0014] The polarizer and the protective layer will be described in detail below.

[0015] B. Polarizer Any appropriate polarizer can be used as the polarizer. The polarizer can typically be produced using a laminate of two or more layers. A method for producing a polarizer will be described later in Section D as a method for producing a polarizing plate.

[0016] The thickness of the polarizer is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and even more preferably 2 μm to 5 μm.

[0017] The boric acid content of the polarizer is preferably 10% by weight or more, and more preferably 13% to 25% by weight. When the boric acid content of the polarizer is within this range, a synergistic effect with the iodine content (described later) can be achieved, which favorably maintains ease of curl control during lamination and favorably suppresses curl during heating, while improving appearance durability during heating. The boric acid content can be calculated, for example, from the neutralization method using the following formula as the amount of boric acid contained in the polarizer per unit weight.

number

[0018] The iodine content of the polarizer is preferably 2% by weight or more, and more preferably 2% by weight to 10% by weight. When the iodine content of the polarizer is in this range, a synergistic effect with the boric acid content can be achieved, which favorably maintains ease of curl control during lamination, favorably suppresses curl during heating, and improves appearance durability during heating. In this specification, the "iodine content" refers to the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine in the polarizer is converted into iodine ions (I - ), molecular iodine (I2), polyiodine ion (I3 - , I5 - ), and the iodine content in this specification refers to the amount of iodine including all of these forms. The iodine content can be calculated, for example, by the calibration curve method of X-ray fluorescence analysis. Note that polyiodine ions exist in the polarizer in the form of a PVA-iodine complex. The formation of such a complex can cause absorption dichroism in the wavelength range of visible light. Specifically, a complex of PVA and triiodide ion (PVA·I3 - ) has an absorption peak around 470 nm, and the complex of PVA and pentaiodide ion (PVA·I5- ) has an absorption peak around 600 nm. As a result, polyiodide ions can absorb light in a wide range of visible light depending on their form. On the other hand, iodide ions (I - ) has an absorption peak around 230 nm and does not substantially contribute to the absorption of visible light. Therefore, polyiodide ions present in a complex state with PVA may be primarily responsible for the absorption performance of the polarizer.

[0019] The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The polarizer has a single transmittance Ts of preferably 40% to 48%, more preferably 41% to 46%. The polarizer has a degree of polarization P of preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0020] C. Protective layer As described above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. When the protective layer contains an epoxy resin having a biphenyl skeleton, the durability of the protective layer can be further improved. The protective layer is preferably a cationic polymerization cured product of an epoxy resin having a biphenyl skeleton. By using a cationic polymerization cured product, a polarizing plate with excellent durability can be obtained despite being very thin. Below, the components of the protective layer will be specifically described, and then the properties of the protective layer will be described.

[0021] C-1. Epoxy resin with biphenyl skeleton In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin having the following structure: The epoxy resin having a biphenyl skeleton may be used alone or in combination of two or more. [ka] (In the formula, R 1 ~R 8 each independently represents a hydrogen atom, a linear or branched, substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element).

[0022] R 1 ~R 8 each independently represents a hydrogen atom, a linear or branched, substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element. Examples of the linear or branched, substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a cyclohexyl group, an n-heptyl group, a cycloheptyl group, a methylcyclohexyl group, an n-octyl group, a cyclooctyl group, an n-nonyl group, a 3,3,5-trimethylcyclohexyl group, an n-decyl group, a cyclodecyl group, an n-undecyl group, an n-dodecyl group, a cyclododecyl group, a phenyl group, a benzyl group, a methylbenzyl group, a dimethylbenzyl group, a trimethylbenzyl group, a naphthylmethyl group, a phenethyl group, and a 2-phenylisopropyl group. Preferred examples of the linear or branched, substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, and n-butyl. Preferred examples of the halogen element include fluorine and bromine.

[0023] In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula: [ka] (In the formula, R 1 ~R 8 is as above, and n represents an integer of 0 to 6).

[0024] In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin having only a biphenyl skeleton. By using an epoxy resin having only a biphenyl skeleton, the durability of the obtained protective layer can be further improved.

[0025] In one embodiment, the epoxy resin having a biphenyl skeleton may contain a chemical structure other than the biphenyl skeleton. Examples of the chemical structure other than the biphenyl skeleton include a bisphenol skeleton, an alicyclic structure, and an aromatic ring structure. In this embodiment, the proportion (molar ratio) of the chemical structure other than the biphenyl skeleton is preferably lower than that of the biphenyl skeleton.

[0026] The epoxy resin having a biphenyl skeleton may be a commercially available product, such as those manufactured by Mitsubishi Chemical Corporation under the trade names jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, and jER YL7399.

[0027] The epoxy resin having a biphenyl skeleton preferably has a glass transition temperature (Tg) of 100°C or higher. As a result, the softening temperature of the protective layer is also approximately 100°C or higher. If the Tg of the epoxy resin having a biphenyl skeleton is 100°C or higher, the resulting polarizing plate including the protective layer tends to have excellent durability. The Tg of the epoxy resin having a biphenyl skeleton is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. On the other hand, the Tg of the epoxy resin having a biphenyl skeleton is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 160°C or lower. If the Tg of the epoxy resin having a biphenyl skeleton is within this range, excellent moldability and processability can be achieved.

[0028] The epoxy equivalent of the epoxy resin having a biphenyl skeleton is preferably 100 g / equivalent or more, more preferably 150 g / equivalent or more, and even more preferably 200 g / equivalent or more. The epoxy equivalent of the epoxy resin having a biphenyl skeleton is preferably 3000 g / equivalent or less, more preferably 2500 g / equivalent or less, and even more preferably 2000 g / equivalent or less. By ensuring that the epoxy equivalent of the biphenyl skeleton is within the above range, a more stable protective layer (a protective layer with less residual monomer and sufficiently cured) can be obtained. In this specification, "epoxy equivalent" refers to the "mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0029] In an embodiment of the present invention, an epoxy resin having a biphenyl skeleton may be used in combination with another resin. That is, a blend of an epoxy resin having a biphenyl skeleton and another resin may be used to form the protective layer. Examples of the other resin include thermoplastic resins such as styrene-based resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide, and curable resins such as acrylic resins and oxetane-based resins. Acrylic resins and oxetane-based resins are preferably used. The type and amount of the resin used in combination can be appropriately determined depending on the purpose and the desired properties of the resulting film. For example, a styrene-based resin can be used in combination as a retardation control agent.

[0030] Any suitable acrylic resin can be used as the acrylic resin. Examples of (meth)acrylic compounds include (meth)acrylic compounds having one (meth)acryloyl group in the molecule (hereinafter also referred to as "monofunctional (meth)acrylic compounds") and (meth)acrylic compounds having two or more (meth)acryloyl groups in the molecule (hereinafter also referred to as "polyfunctional (meth)acrylic compounds"). These (meth)acrylic compounds may be used alone or in combination of two or more. These acrylic resins are described, for example, in JP 2019-168500 A. The entire disclosure of this publication is incorporated herein by reference.

[0031] As the oxetane resin, any suitable compound having one or more oxetanyl groups in the molecule can be used. Examples thereof include oxetane compounds having one oxetanyl group in the molecule, such as 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(phenoxymethyl)oxetane, 3-ethyl-3-(cyclohexyloxymethyl)oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, and (3-ethyloxetan-3-yl)methyl (meth)acrylate; and oxetane compounds having two or more oxetanyl groups in the molecule, such as 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, and 4,4'-bis[(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl. These oxetane resins may be used alone or in combination of two or more.

[0032] Preferably, 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (3-ethyloxetan-3-yl)methyl (meth)acrylate, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, etc. These oxetane resins are readily available and can have excellent dilutability (low viscosity) and compatibility.

[0033] In one embodiment, from the viewpoints of compatibility and adhesiveness, an oxetane resin having a molecular weight of 500 or less and being liquid at room temperature (25°C) is preferably used. In one embodiment, an oxetane compound containing two or more oxetanyl groups in the molecule, or an oxetane compound containing one oxetanyl group and one (meth)acryloyl group or one epoxy group in the molecule is preferably used, and more preferably 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, or (3-ethyloxetan-3-yl)methyl(meth)acrylate is used. Use of these oxetane resins can improve the curability and durability of the protective layer.

[0034] As the oxetane resin, commercially available products may be used. Specifically, Aron Oxetane OXT-101, Aron Oxetane OXT-121, Aron Oxetane OXT-212, and Aron Oxetane OXT-221 (all manufactured by Toagosei Co., Ltd.) may be used. Preferably, Aron Oxetane OXT-101 and Aron Oxetane OXT-221 may be used.

[0035] When an epoxy resin having a biphenyl skeleton is used in combination with another resin, the content of the epoxy resin having a biphenyl skeleton in the blend of the epoxy resin having a biphenyl skeleton and the other resin is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight, even more preferably 70% by weight to 100% by weight, and particularly preferably 80% by weight to 100% by weight. If the content is less than 50% by weight, the heat resistance of the protective layer and sufficient adhesion to the polarizer may not be obtained.

[0036] When an epoxy resin having a biphenyl skeleton and an oxetane resin are used in combination, the content of the oxetane resin is preferably 1 to 50 parts by weight, more preferably 5 to 45 parts by weight, and even more preferably 10 to 40 parts by weight, relative to 100 parts by weight of the total amount of the epoxy resin having a biphenyl skeleton and the oxetane resin. By setting the content within the above range, the curability is improved, and the adhesion between the protective layer and the polarizer can also be improved.

[0037] C-2. Hardener An epoxy resin having a biphenyl skeleton can be used together with any appropriate curing agent to form a cured product. Any appropriate curing agent capable of curing an epoxy resin can be used as the curing agent. In one embodiment, the curing agent includes a photocationic polymerization initiator. By including a photocationic polymerization initiator, a protective layer that is a cationic polymerization cured product can be formed. Any appropriate compound capable of curing an epoxy resin having a biphenyl skeleton by irradiation with light such as ultraviolet light can be used as the photocationic polymerization initiator. Only one type of photocationic polymerization initiator can be used, or two or more types can be used in combination.

[0038] Examples of the photocationic polymerization initiator include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, p-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluoroantimonate, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonate. Preferably, a triphenylsulfonium salt-based hexafluoroantimonate type photocationic polymerization initiator or a diphenyliodonium salt-based hexafluoroantimonate type photocationic polymerization initiator is used.

[0039] Commercially available photocationic polymerization initiators may be used, including triphenylsulfonium salt-based hexafluoroantimonate type SP-170 (manufactured by ADEKA Corporation), CPI-101A (manufactured by San-Apro Co., Ltd.), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), and diphenyliodonium salt-based hexafluoroantimonate type WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.).

[0040] The content of the cationic photopolymerization initiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, relative to 100 parts by weight of the epoxy resin having a biphenyl skeleton. If the content of the cationic photopolymerization initiator is less than 0.1 part by weight, the resin may not be sufficiently cured even when irradiated with light (ultraviolet rays).

[0041] C-3. Composition and characteristics of the protective layer As described above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. Such a cured product allows for a significantly thinner thickness compared to extrusion-molded films. The thickness of the protective layer is preferably 10 μm or less, more preferably 7 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the protective layer can be, for example, 1 μm or more. A cured product of an epoxy resin having a biphenyl skeleton has lower moisture absorption and moisture permeability than a solidified aqueous coating film such as an aqueous solution or aqueous dispersion, and therefore has the advantage of excellent humidity durability. As a result, a polarizing plate with excellent durability that can maintain its optical properties even in a heated and humidified environment can be realized. Furthermore, a protective layer made of a cured product of an epoxy resin having a biphenyl skeleton exhibits excellent adhesion to the polarizer. Therefore, even with the above thickness, the polarizer can be protected to the same extent as a protective layer using a conventional film. Furthermore, even with the above thickness, defects such as discoloration of the polarizer can be prevented.

[0042] The softening temperature of the protective layer is preferably 100°C or higher. If the softening temperature of the protective layer is 100°C or higher, the resulting polarizing plate including the protective layer is likely to have excellent durability. The softening temperature of the protective layer is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. On the other hand, the softening temperature of the protective layer is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 160°C or lower. If the softening point of the protective layer is within this range, excellent moldability and processability can be achieved.

[0043] The iodine adsorption amount of the protective layer is preferably 10% by weight or less, more preferably 6.0% by weight or less, even more preferably 3.0% by weight or less, and particularly preferably 2.0% by weight or less. The smaller the iodine adsorption amount, the better. If the iodine adsorption amount is within this range, a polarizing plate with even better durability can be obtained. The iodine adsorption amount can be measured by the following method. The protective layer-forming composition is applied to a substrate (PET film) using an applicator to form a protective layer (thickness: about 3 μm). The resulting PET film with the protective layer is cut into a size of 1 cm × 1 cm (1 cm 2 ) was cut into a small piece and used as a sample. It was then collected and weighed in a headspace vial (20 mL). Next, a screw cap vial (1.5 mL) containing 1 mL of iodine solution (iodine concentration 1 wt%, potassium iodide concentration 7 wt%) was placed in the same headspace vial and sealed. The headspace vial was then placed in a 65°C oven for 6 hours. This allowed the gaseous I2 to adsorb onto the sample. The sample was then placed in a ceramic boat and combusted using an automatic sample combustion device. The evolved gas was collected in 10 mL of absorption solution. After collection, this absorption solution was adjusted to 15 mL with pure water, and either the original solution or an appropriately diluted solution was subjected to IC quantitative analysis. Note that the iodine adsorption amount was nearly zero when a similar measurement was performed on the PET film alone. The iodine adsorption amount (wt%) was calculated using the following formula based on the weight of iodine obtained by IC quantitative analysis and the weight of the protective layer alone ("weight of PET film with protective layer" - "weight of PET film"): Iodine adsorption amount (wt%) = weight of iodine obtained by IC quantitative analysis / weight of protective layer alone × 100 For the analysis, for example, the following measuring devices can be used. [Measuring equipment] Automatic sample combustion device: Mitsubishi Chemical Analytech Co., Ltd., "AQF-2100H" IC (anion): Thermo Fisher Scientific, "ICS-3000"

[0044] The protective layer preferably has substantially optical isotropy. In this specification, "substantially optical isotropy" means that the retardation at a wavelength of 550 nm is -50 nm to +50 nm. The in-plane retardation Re(550) is more preferably -30 nm to +30 nm, even more preferably -10 nm to +10 nm, and particularly preferably 0 nm to 2 nm. The thickness direction retardation Rth(550) is more preferably -5 nm to +5 nm, even more preferably -3 nm to +3 nm, and particularly preferably -2 nm to +2 nm. When the Re(550) and Rth(550) of the protective layer are within these ranges, adverse effects on display characteristics can be prevented when a polarizing plate including the protective layer is used in an image display device. Note that Re(550) is the in-plane retardation of the film measured at 23°C with light having a wavelength of 550 nm. Re(550) can be calculated using the formula: Re(550)=(nx-ny)×d. Rth(550) is the retardation in the thickness direction of the film measured with light of 550 nm wavelength at 23°C. Rth(550) is calculated by the formula: Rth(550) = (nx - nz) × d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), ny is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), nz is the refractive index in the thickness direction, and d is the film thickness (nm).

[0045] The higher the light transmittance at 380 nm when the protective layer is 3 μm thick, the better. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the light transmittance is within this range, the desired transparency can be ensured. The light transmittance can be measured, for example, by a method in accordance with ASTM-D-1003.

[0046] The lower the haze of the protective layer, the better. Specifically, the haze is preferably 5% or less, more preferably 3% or less, even more preferably 1.5% or less, and particularly preferably 1% or less. A haze of 5% or less can impart a good sense of clarity to the film. Furthermore, even when used as a polarizing plate on the viewer side of an image display device, the displayed content can be clearly seen.

[0047] The YI at a protective layer thickness of 3 μm is preferably 1.27 or less, more preferably 1.25 or less, even more preferably 1.23 or less, and particularly preferably 1.20 or less. If the YI exceeds 1.3, the optical transparency may be insufficient. Note that the YI can be calculated, for example, by the following formula using the color tristimulus values ​​(X, Y, Z) obtained by measurement using a high-speed integrating sphere spectral transmittance meter (product name DOT-3C, manufactured by Murakami Color Research Laboratory). YI = [(1.28X - 1.06Z) / Y] x 100

[0048] The b-value (a measure of hue according to the Hunter color system) of the protective layer at a thickness of 3 μm is preferably less than 1.5, and more preferably 1.0 or less. If the b-value is 1.5 or more, an undesired color tone may occur. The b-value can be obtained, for example, by cutting a sample of the film constituting the protective layer into a 3 cm square, measuring the hue using a high-speed integrating sphere spectral transmittance meter (product name DOT-3C, manufactured by Murakami Color Research Laboratory), and evaluating the hue according to the Hunter color system.

[0049] The protective layer (cured product of the epoxy resin having a biphenyl skeleton) may contain any appropriate additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; stabilizers such as light stabilizers, weathering stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic fillers; resin modifiers; organic or inorganic fillers; plasticizers; lubricants; antistatic agents; and flame retardants. The additives are typically added to the solution during the formation of the protective layer. The type, number, combination, and amount of additives can be appropriately determined depending on the purpose.

[0050] An easy-adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer contains, for example, an aqueous polyurethane and an oxazoline-based crosslinking agent. Forming such an easy-adhesion layer can improve the adhesion between the protective layer and the polarizer. The easy-adhesion layer may be laminated to the polarizer by any appropriate method. For example, it may be formed directly on the polarizer, or may be laminated via any appropriate pressure-sensitive adhesive layer or adhesive layer. Furthermore, a hard coat layer may be formed on the protective layer. The hard coat layer may be formed when the protective layer is used as a protective layer on the viewer side of the viewer-side polarizing plate. When both the easy-adhesion layer and the hard coat layer are formed, they may typically be formed on different sides of the protective layer.

[0051] D. Polarizing Plate Manufacturing Method D-1. Polarizer manufacturing method The method for producing a polarizer described in the above item B includes forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an auxiliary in-air stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction to shrink the laminate by 2% or more in the width direction, in this order. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60 to 120°C. According to this production method, the above-mentioned polarizer can be obtained. In particular, a laminate including a PVA-based resin layer containing a halide is prepared, and the laminate is stretched using a multi-stage process including auxiliary in-air stretching and underwater stretching. The stretched laminate is then heated using a heating roll. This process allows for the production of a polarizer with excellent optical properties (typically, single-layer transmittance and polarization degree) and reduced variations in the optical properties. Specifically, by using a heating roll in the drying shrinkage treatment process, the laminate can be uniformly shrunk throughout the laminate while being transported. This not only improves the optical properties of the resulting polarizer, but also enables stable production of polarizers with excellent optical properties and reduces variations in the polarizer's optical properties (particularly, single-layer transmittance). The following describes the halide and the drying shrinkage treatment. Details of other manufacturing methods are described, for example, in JP 2012-73580 A and JP 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0052] D-1-1. Halides A PVA-based resin layer containing a halide and a PVA-based resin can be formed by applying a coating liquid containing the halide and the PVA-based resin onto a thermoplastic resin substrate and drying the coating film. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. Such a resin concentration allows the formation of a uniform coating film that adheres closely to the thermoplastic resin substrate.

[0053] Any suitable halide may be used as the halide. For example, iodide and sodium chloride may be used. For example, iodide may be potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

[0054] The amount of the halide in the coating solution is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, based on 100 parts by weight of the PVA resin. If the amount of the halide is too large, the halide may bleed out, causing the final polarizer to become cloudy.

[0055] Generally, stretching a PVA-based resin layer increases the orientation of polyvinyl alcohol molecules in the PVA-based resin. However, immersing the stretched PVA-based resin layer in a liquid containing water can disrupt the orientation of the polyvinyl alcohol molecules, resulting in a decrease in the orientation. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate, the tendency for the degree of orientation to decrease is particularly pronounced. For example, while a PVA film alone is typically stretched in boric acid water at 60°C, a laminate of an A-PET (thermoplastic resin substrate) and a PVA-based resin layer is stretched at a high temperature of around 70°C. In this case, the orientation of the PVA at the initial stage of stretching can decrease before it increases due to underwater stretching. In response to this, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and then high-temperature stretching (auxiliary stretching) the laminate in air before stretching it in boric acid water, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, 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 by immersing the laminate in a liquid during processing steps such as dyeing and underwater stretching.

[0056] D-1-2. Drying shrinkage treatment The drying shrinkage treatment can be performed by zone heating, in which the entire zone is heated, or by heating the transport rolls (using so-called heated rolls) (heated roll drying method). Preferably, both methods are used. Drying using heated rolls efficiently suppresses heat curling of the laminate, allowing for the production of a polarizer with excellent appearance. Specifically, drying the laminate while it is aligned with heated rolls efficiently promotes crystallization of the thermoplastic resin substrate, thereby increasing the crystallinity. Even at relatively low drying temperatures, the crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the rigidity of the thermoplastic resin substrate increases, allowing it to withstand shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Furthermore, using heated rolls allows the laminate to be dried while maintaining a flat state, thereby suppressing not only curling but also wrinkling. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction through the drying shrinkage treatment. This is because the orientation of the PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heated roll, the laminate can be continuously shrunk in the width direction while being transported, thereby achieving high productivity.

[0057] 2 is a schematic diagram showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but the transport rolls R1 to R6 may also be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin substrate surface).

[0058] Drying conditions can be controlled by adjusting the heating temperature of the transport rolls (heating roll temperature), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. This satisfactorily increases the crystallinity of the thermoplastic resin, effectively suppresses curling, and produces an optical laminate with extremely excellent durability. The temperature of the heating rolls can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are multiple transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time between the laminate and the heating rolls (total contact time) is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0059] The heating rolls may be installed in a heating furnace (e.g., an oven) or in a normal production line (under room temperature). Preferably, they are installed in a heating furnace equipped with a blower. By using both heating roll drying and hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and to easily control shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The hot air speed is preferably about 10 m / s to 30 m / s. Note that this air speed is the air speed inside the heating furnace and can be measured with a mini-vane type digital anemometer.

[0060] Preferably, after the underwater stretching treatment and before the drying shrinkage treatment, a washing treatment is carried out. The washing treatment is typically carried out by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0061] In this manner, a laminate of a thermoplastic resin substrate and a polarizer can be obtained.

[0062] D-2. Polarizing plate manufacturing method A protective layer can be formed by applying a composition containing an epoxy resin having a biphenyl skeleton and a curing agent to the surface of the laminate obtained in the above section D-1 (e.g., the surface of a polarizer) to form a coating film, and then curing the coating film. In one embodiment, the protective layer is a cationically polymerized cured product. In this embodiment, a photocationic polymerization initiator is used as the curing agent. A protective layer can be formed by applying a composition containing an epoxy resin having a biphenyl skeleton and a photocationic polymerization initiator to the surface of the laminate (e.g., the surface of a polarizer) to form a coating film, and then irradiating the coating film with light (e.g., ultraviolet light).

[0063] The solvent contained in the composition may be any suitable solvent capable of dissolving or uniformly dispersing the biphenyl-based epoxy resin and curing agent. Specific examples of the solvent include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

[0064] The epoxy resin concentration in the solution is preferably 10 to 30 parts by weight relative to 100 parts by weight of the solvent. Such a resin concentration allows the formation of a uniform coating film that adheres closely to the polarizer. The content of the curing agent is as described in Section C above.

[0065] The solution may be applied to any suitable substrate or to a polarizer. When the solution is applied to a substrate, the cured coating film formed on the substrate is transferred to the polarizer. When the solution is applied to a polarizer, the coating film is cured, for example, by light irradiation, to form a protective layer directly on the polarizer. Preferably, the solution is applied to a polarizer, and a protective layer is formed directly on the polarizer. With this configuration, the adhesive layer or pressure-sensitive adhesive layer required for transfer can be omitted, thereby making it possible to further reduce the thickness of the polarizing plate. Any suitable method can be used to apply the solution. Specific examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (such as comma coating).

[0066] When the coating film is cured by light irradiation, the coating film can be irradiated with light (typically ultraviolet light) using any appropriate light source so as to achieve any appropriate irradiation dose. Examples of ultraviolet light sources that can be used include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, electrodeless lamps, carbon arc lamps, xenon lamps, metal halide lamps, chemical lamps, black lights, and LED lamps. The irradiation dose of ultraviolet light is, for example, 2 mJ / cm. 2 ~3000mJ / cm 2 , preferably 10 mJ / cm 2 ~2000mJ / cm 2 Specifically, when a high-pressure mercury lamp is used as the light source, the irradiation dose is usually 5 mJ / cm 2 ~3000mJ / cm 2 , preferably 50 mJ / cm 2 ~2000mJ / cm 2 When an electrodeless lamp is used as the light source, the irradiation dose is usually 2 mJ / cm 2 ~2000mJ / cm 2 , preferably 10 mJ / cm 2 ~1000mJ / cm 2 This is carried out under the following conditions.

[0067] The irradiation time can be set to any appropriate value depending on the type of light source, the distance between the light source and the coating surface, the coating thickness, and other conditions. The irradiation time is usually several seconds to several tens of seconds, and may be as short as a fraction of a second. Light can be irradiated from any appropriate direction. In order to prevent uneven curing, it is preferable to irradiate from the coated surface side of the composition for forming a protective layer.

[0068] After exposure to light such as ultraviolet light, a heat treatment may be further carried out to complete the curing by photoreaction. The heat treatment may be carried out at any appropriate temperature for any appropriate time. The heating temperature is, for example, 80°C to 250°C, and preferably 100°C to 150°C. The heating time is, for example, 10 seconds to 2 hours, and preferably 5 minutes to 1 hour.

[0069] In this manner, a protective layer is formed, resulting in a laminate of a thermoplastic resin substrate, a polarizer, and a protective layer. By peeling the thermoplastic resin substrate from this laminate, a polarizing plate having a polarizer 10 and a protective layer 20 as shown in FIG. 1 can be obtained. Alternatively, a resin film constituting another protective layer may be attached to the polarizer surface of the thermoplastic resin substrate / polarizer laminate, and then the thermoplastic resin substrate may be peeled off to form a protective layer on the peeled surface. In this case, a polarizing plate further having another protective layer can be obtained.

[0070] E. Polarizing plate with retardation layer E-1. Overview of polarizing plates with retardation layers In one embodiment of the present invention, a retardation layer-attached polarizing plate may be provided. This retardation layer-attached polarizing plate further includes a retardation layer on the side of the polarizing plate where the protective layer is not disposed. FIG. 3 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. The retardation layer-attached polarizing plate 110 in the illustrated example includes a polarizer 10, a protective layer 20 disposed on one side of the polarizer 10, and a retardation layer 40 disposed on the other side of the polarizer 10. The polarizer 10 and the protective layer 20 constitute the polarizing plate. Therefore, the retardation layer-attached polarizing plate includes a polarizer including a polarizer and a protective layer disposed on one side of the polarizer, and a retardation layer disposed on the polarizing plate opposite the protective layer. If necessary, the polarizing plate may further include another protective layer (not shown) on the polarizer 10 opposite the protective layer 20. In other words, the retardation layer-attached polarizing plate 110 may further include another protective layer (not shown) between the polarizer 10 and the retardation layer 40. As described above, an easy-adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer may be laminated to the polarizer by any appropriate method. For example, the easy-adhesion layer may be formed directly on the polarizer, or may be laminated via any appropriate pressure-sensitive adhesive layer or adhesive layer.

[0071] In the embodiment shown in FIG. 3, the retardation layer 40 is a single layer. In this case, Re(550) of the retardation layer 40 is, for example, 100 nm to 190 nm, and the angle between the slow axis of the retardation layer 40 and the absorption axis of the polarizer 10 is, for example, 40° to 50°. In this case, another retardation layer (not shown) is preferably provided on the outer side of the retardation layer 40 (the side opposite to the polarizer 10). The refractive index characteristic of the other retardation layer typically satisfies the relationship nz>nx=ny. Alternatively, as shown in FIG. 4, in a retardation-layer-attached polarizing plate 111 according to another embodiment, the retardation layer 40 has a laminated structure of a first layer 41 and a second layer 42. In this case, the Re(550) of the first layer 41 is, for example, 200 nm to 300 nm, and the angle between the slow axis of the first layer 41 and the absorption axis of the polarizer 10 is, for example, 10° to 20°; the Re(550) of the second layer 42 is, for example, 100 nm to 190 nm, and the angle between the slow axis of the second layer 42 and the absorption axis of the polarizer 10 is, for example, 70° to 80°. In any of the embodiments, the retardation layer 40 may be a resin film or a layer in which a liquid crystal compound is aligned and solidified. When the retardation layer 40 has a laminated structure, the first layer 41 and the second layer 42 are typically resin films or layers in which a liquid crystal compound is aligned and solidified, respectively.

[0072] E-2. Single-layer retardation layer When the retardation layer is composed of a single layer, as described above, the retardation layer has Re(550) of, for example, 100 nm to 190 nm, and the angle between the slow axis of the retardation layer 40 and the absorption axis of the polarizer 10 is, for example, 40° to 50°. The retardation layer is typically provided to impart anti-reflection properties to the polarizing plate, and in one embodiment, can function as a λ / 4 plate. As described above, the retardation layer may be a resin film or an oriented and solidified layer of a liquid crystal compound.

[0073] The retardation layer preferably exhibits a refractive index characteristic showing a relationship of nx > ny ≧ nz. The in-plane retardation Re(550) of the retardation layer is, as described above, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, more preferably 130 nm to 160 nm. Here, "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within a range that does not impair the effects of the present invention, ny < nz may occur.

[0074] The Nz coefficient of the retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the polarizing plate with a retardation layer is used in an image display device, a very excellent reflected hue can be achieved.

[0075] The angle θ formed by the slow axis of the retardation layer 40 and the absorption axis of the polarizer 10 is, as described above, for example, 40° to 50°, preferably 42° to 48°, and more preferably about 45°. If the angle θ is within such a range, by using the retardation layer as a λ / 4 plate, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained.

[0076] The retardation layer may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value hardly changes depending on the wavelength of the measurement light. In one embodiment, the retardation layer exhibits an inverse dispersion wavelength characteristic. In this case, Re(450) / Re(550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection characteristics can be realized.

[0077] The absolute value of the photoelastic coefficient of the retardation layer is preferably 2.0×10 -11 m 2 / N or less, more preferably 2.0×10-13 m 2 / N~1.5×10 -11 m 2 / N, more preferably 1.0 × 10 -12 m 2 / N~1.2×10 -11 m 2 When the absolute value of the photoelastic coefficient is within this range, the retardation is less likely to change when shrinkage stress occurs during heating. As a result, thermal unevenness in the resulting image display device can be effectively prevented.

[0078] E-2-1.Resin film When the retardation layer is a resin film, the resin film is typically a stretched film. In this case, the thickness of the retardation layer is preferably 60 μm or less, more preferably 30 μm to 55 μm. When the thickness of the retardation layer is in this range, curling during heating can be effectively suppressed and curling during lamination can be effectively adjusted.

[0079] The retardation layer can be made of any suitable resin film that can satisfy the above characteristics. Typical examples of such resins include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, and acrylic-based resins. These resins can be used alone or in combination (for example, blends or copolymers). When the retardation layer is made of a resin film that exhibits reverse dispersion wavelength characteristics, polycarbonate-based resins or polyester carbonate-based resins (hereinafter sometimes simply referred to as polycarbonate-based resins) can be suitably used.

[0080] Any suitable polycarbonate-based resin can be used as the polycarbonate-based resin as long as it can achieve the effects of the present invention. For example, the polycarbonate-based resin contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri-, or polyethylene glycols, and alkylene glycols or spiroglycols. Preferably, the polycarbonate-based resin contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, structural units derived from an alicyclic dimethanol, and / or structural units derived from di-, tri-, or polyethylene glycol; more preferably, it contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, and structural units derived from di-, tri-, or polyethylene glycol. The polycarbonate-based resin may contain structural units derived from other dihydroxy compounds as needed. Details of polycarbonate resins that can be suitably used in the present invention are described in, for example, JP-A Nos. 2014-10291, 2014-26266, 2015-212816, 2015-212817, and 2015-212818, the disclosures of which are incorporated herein by reference.

[0081] The glass transition temperature of the polycarbonate resin is preferably 110°C or higher and 150°C or lower, more preferably 120°C or higher and 140°C or lower. If the glass transition temperature is too low, heat resistance tends to be poor, which may cause dimensional changes after film formation and may degrade the image quality of the resulting organic EL panel. If the glass transition temperature is too high, molding stability during film formation may be poor and the transparency of the film may be impaired. The glass transition temperature is determined in accordance with JIS K 7121 (1987).

[0082] The molecular weight of the polycarbonate resin can be expressed by reduced viscosity. The reduced viscosity is measured using a Ubbelohde viscometer at a temperature of 20.0°C ± 0.1°C using methylene chloride as a solvent and a precisely adjusted polycarbonate concentration of 0.6 g / dL. The reduced viscosity is usually preferably 0.30 dL / g or higher, more preferably 0.35 dL / g or higher. The reduced viscosity is usually preferably 1.20 dL / g or lower, more preferably 1.00 dL / g or lower, and even more preferably 0.80 dL / g or lower. If the reduced viscosity is less than 0.30 dL / g, the mechanical strength of the molded product may be reduced. On the other hand, if the reduced viscosity exceeds 1.20 dL / g, the flowability during molding may be reduced, resulting in problems such as reduced productivity and moldability.

[0083] Commercially available polycarbonate resin films may be used, including, for example, "Pure Ace WR-S," "Pure Ace WR-W," and "Pure Ace WR-M" manufactured by Teijin Limited, and "NRF" manufactured by Nitto Denko Corporation.

[0084] The retardation layer 40 can be obtained, for example, by stretching a film formed from the polycarbonate-based resin. Any appropriate molding method can be used to form a film from a polycarbonate-based resin. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., casting), calendar molding, and heat pressing. Extrusion molding or cast coating is preferred because it enhances the smoothness of the resulting film and provides good optical uniformity. The molding conditions can be appropriately set depending on the composition and type of the resin used, the properties desired for the retardation layer, and the like. As mentioned above, many polycarbonate-based resin film products are commercially available, and the commercially available film may be directly subjected to the stretching treatment.

[0085] The thickness of the resin film (unstretched film) can be set to any appropriate value depending on the desired thickness of the retardation layer, the desired optical properties, the stretching conditions described below, etc. It is preferably 50 μm to 300 μm.

[0086] Any appropriate stretching method and conditions (e.g., stretching temperature, stretching ratio, stretching direction) may be employed for the stretching. Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage may be used alone, simultaneously, or sequentially. Stretching may be performed in various directions or dimensions, such as the length direction, width direction, thickness direction, and oblique direction. The stretching temperature is preferably Tg-30°C to Tg+60°C, more preferably Tg-10°C to Tg+50°C, relative to the glass transition temperature (Tg) of the resin film.

[0087] By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (for example, refractive index properties, in-plane retardation, Nz coefficient) can be obtained.

[0088] In one embodiment, the retardation film is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. A specific example of fixed-end uniaxial stretching is a method in which a resin film is stretched in the width direction (transverse direction) while running in the longitudinal direction. The stretching ratio is preferably 1.1 to 3.5 times.

[0089] In another embodiment, the retardation film can be produced by continuously obliquely stretching a long resin film in the direction of the angle θ relative to the longitudinal direction. By employing oblique stretching, a long stretched film having an orientation angle of θ relative to the longitudinal direction of the film (slow axis in the direction of the angle θ) can be obtained, which, for example, enables roll-to-roll lamination with a polarizer, thereby simplifying the manufacturing process. The angle θ may be the angle between the absorption axis of the polarizer and the slow axis of the retardation layer in a retardation layer-attached polarizing plate. As described above, the angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°.

[0090] Examples of stretching machines used for oblique stretching include tenter-type stretching machines that can apply feeding forces, pulling forces, or take-up forces at different speeds in the transverse and / or longitudinal directions. Tenter-type stretching machines include transverse uniaxial stretching machines and simultaneous biaxial stretching machines, but any appropriate stretching machine can be used as long as it can continuously obliquely stretch a long resin film.

[0091] By appropriately controlling the left and right speeds in the stretching machine, a retardation layer (essentially, a long retardation film) having the desired in-plane retardation and the slow axis in the desired direction can be obtained.

[0092] The stretching temperature of the film can vary depending on the in-plane retardation value and thickness desired for the retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, etc. Specifically, the stretching temperature is preferably Tg-30°C to Tg+30°C, more preferably Tg-15°C to Tg+15°C, and most preferably Tg-10°C to Tg+10°C. By stretching at such a temperature, a retardation layer having properties suitable for the present invention can be obtained. Tg is the glass transition temperature of the constituent material of the film.

[0093] E-2-2. Solidified alignment layer of liquid crystal compounds When the retardation layer is a layer of a liquid crystal compound with a fixed orientation, the use of a liquid crystal compound can significantly increase the difference between nx and ny of the resulting retardation layer compared to non-liquid crystal materials, thereby significantly reducing the thickness of the retardation layer required to obtain a desired in-plane retardation. As a result, a polarizing plate with a retardation layer can be further thinned. In this specification, the term "fixed orientation layer" refers to a layer in which the liquid crystal compound is oriented in a predetermined direction within the layer and the orientation state is fixed. Note that the term "fixed orientation layer" encompasses a concept including a hardened orientation layer obtained by hardening a liquid crystal monomer, as described below. In this embodiment, typically, rod-shaped liquid crystal compounds are oriented in the slow axis direction of the retardation layer (homogeneous orientation).

[0094] Examples of liquid crystal compounds include liquid crystal compounds whose liquid crystal phase is a nematic phase (nematic liquid crystals). For example, liquid crystal polymers and liquid crystal monomers can be used as such liquid crystal compounds. The mechanism by which liquid crystallinity is expressed by liquid crystal compounds may be either lyotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers may be used alone or in combination.

[0095] When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After the liquid crystal monomer is aligned, for example, the alignment state can be fixed by polymerizing or crosslinking the liquid crystal monomers with each other. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystals. Therefore, the formed retardation layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is specific to liquid crystal compounds. As a result, the retardation layer is an extremely stable retardation layer that is not affected by temperature changes.

[0096] The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the type of the liquid crystal monomer. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

[0097] Any suitable liquid crystal monomer can be used as the liquid crystal monomer. For example, polymerizable mesogenic compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US 5,211,877), EP 66137 (US 4,388,453), WO 93 / 22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445 can be used. Specific examples of such polymerizable mesogenic compounds include BASF's product name LC242, Merck's product name E7, and Wacker-Chem's product name LC-Sillicon-CC3767. Nematic liquid crystal monomers are preferred as the liquid crystal monomer.

[0098] The alignment and solidification layer of the liquid crystal compound can be formed by performing an alignment treatment on the surface of a predetermined substrate, applying a coating liquid containing a liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. In one embodiment, the substrate is any appropriate resin film, and the alignment and solidification layer formed on the substrate can be transferred to the surface of the polarizer 10. In another embodiment, the substrate can be another protective layer. In this case, the transfer step is omitted, and lamination can be performed by roll-to-roll processing continuously from the formation of the alignment and solidification layer (retardation layer), further improving productivity.

[0099] Any appropriate alignment treatment can be adopted as the alignment treatment. Specific examples include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique deposition and photoalignment treatment. Any appropriate treatment conditions can be adopted for the various alignment treatments depending on the purpose.

[0100] The alignment of liquid crystal compounds is achieved by treating them at a temperature at which they exhibit a liquid crystal phase depending on the type of liquid crystal compound. By performing such temperature treatment, the liquid crystal compounds assume a liquid crystal state and are aligned in accordance with the alignment treatment direction of the substrate surface.

[0101] In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to a polymerization treatment or a crosslinking treatment.

[0102] Specific examples of liquid crystal compounds and details of the method for forming the alignment solidified layer are described in JP-A-2006-163343, the disclosure of which is incorporated herein by reference.

[0103] Another example of the alignment-solidified layer is a mode in which a discotic liquid crystal compound is aligned in any one of vertical alignment, hybrid alignment, and tilt alignment. The discotic liquid crystal compound is typically aligned such that its discotic plane is substantially perpendicular to the film plane of the retardation layer. The term "substantially perpendicular" means that the average angle between the film plane and the discotic plane of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°, and even more preferably 85° to 90°. Discotic liquid crystal compounds generally refer to liquid crystal compounds having a discotic molecular structure in which a cyclic core such as benzene, 1,3,5-triazine, or calixarene is located at the center of the molecule and linear alkyl groups, alkoxy groups, substituted benzoyloxy groups, or the like are radially substituted as side chains. Representative examples of discotic liquid crystals include benzene derivatives, triphenylene derivatives, truxene derivatives, and phthalocyanine derivatives described in the research report by C. Destrade et al., Mol. Cryst. Liq. Cryst., Vol. 71, p. 111 (1981); cyclohexane derivatives described in the research report by B. Kohne et al., Angew. Chem., Vol. 96, p. 70 (1984); and azacrown and phenylacetylene macrocycles described in the research report by J. M. Lehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985) and the research report by J. Zhang et al., J. Am. Chem. Soc., Vol. 116, p. 2655 (1994). Further specific examples of discotic liquid crystal compounds include compounds described in JP-A Nos. 2006-133652, 2007-108732, and 2010-244038, the disclosures of which are incorporated herein by reference.

[0104] When the retardation layer is a layer of a liquid crystal compound with a fixed alignment, its thickness is preferably 0.5 μm to 7 μm, more preferably 1 μm to 5 μm. By using a liquid crystal compound, it is possible to achieve an in-plane retardation equivalent to that of a resin film with a thickness that is significantly thinner than that of a resin film.

[0105] E-2-3. Another retardation layer As described above, when the retardation layer is composed of a single layer, preferably, another retardation layer is provided. The another retardation layer may be a so-called positive C plate, whose refractive index characteristics satisfy the relationship nz>nx=ny, as described above. By using a positive C plate as the another retardation layer, reflection in oblique directions can be effectively prevented, enabling the anti-reflection function to have a wide viewing angle. In this case, the thickness direction retardation Rth(550) of the another retardation layer is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, even more preferably −90 nm to −200 nm, and particularly preferably −100 nm to −180 nm. Here, “nx=ny” encompasses not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the another retardation layer may be less than 10 nm.

[0106] The separate retardation layer having the refractive index characteristic of nz > nx = ny can be formed from any appropriate material. The separate retardation layer is preferably made of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in paragraphs

[0020] to

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

[0107] E-3. Two-layer retardation layer When the retardation layer 40 has a laminated structure of a first layer 41 and a second layer 42, one of the first layer 41 and the second layer 42 can function as a λ / 4 plate, and the other can function as a λ / 2 plate. For example, when the first layer 41 functions as a λ / 2 plate and the second layer 42 functions as a λ / 4 plate, the in-plane retardation Re(550) of the first layer is, as described above, for example, 200 nm to 300 nm, preferably 230 nm to 290 nm, and more preferably 250 nm to 280 nm. The in-plane retardation Re(550) of the second layer is, as described above, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm. The angle between the slow axis of the first layer and the absorption axis of the polarizer is, as described above, for example, 10° to 20°, preferably 12° to 18°, and more preferably about 15°. As described above, the angle between the slow axis of the second layer and the absorption axis of the polarizer is, for example, 70° to 80°, preferably 72° to 78°, and more preferably about 75°. With this configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, it is possible to realize very excellent antireflection characteristics.

[0108] One of the first layer 41 and the second layer 42 may be a resin film and the other may be a layer of a liquid crystal compound with a fixed orientation, or both may be resin films, or both may be layers of a liquid crystal compound with a fixed orientation. Preferably, both the first layer 41 and the second layer 42 are resin films or layers of a liquid crystal compound with a fixed orientation.

[0109] The thicknesses of the first layer 41 and the second layer 42 can be adjusted to obtain the desired in-plane retardation of the λ / 4 plate or λ / 2 plate. For example, when the first layer 41 functions as a λ / 2 plate and the second layer 42 functions as a λ / 4 plate, and the first layer 41 and the second layer 42 are resin films, the thickness of the first layer 41 is, for example, 40 μm to 75 μm, and the thickness of the second layer 42 is, for example, 30 μm to 55 μm. When the first layer 41 and the second layer 42 are alignment-solidified layers of a liquid crystal compound, the thickness of the first layer 41 is, for example, 2.0 μm to 3.0 μm, and the thickness of the second layer 42 is, for example, 1.0 μm to 2.0 μm.

[0110] The resin films constituting the first and second layers, the liquid crystal compound, the method for forming the first and second layers, the optical properties, etc. are as described above for the single layer. [Example]

[0111] 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. Unless otherwise specified, "parts" and "%" in the examples are by weight.

[0112] (1) Color loss and shrinkage of the protective layer Test pieces (50 mm × 50 mm) were cut from the polarizing plates obtained in the Examples and Comparative Examples, with two sides facing each other in a direction perpendicular to the absorption axis direction of the polarizer and the absorption axis direction. Each test piece was attached to a glass plate with an adhesive, with the protective layer facing inward, to prepare a test sample. The test sample was then heated and humidified by leaving it in an oven at 85°C and 85% RH for 120 hours. The polarizing plate was then placed in a crossed Nicol position with a standard polarizing plate. The color loss of the polarizing plate after humidification was visually inspected and evaluated according to the following criteria. The presence or absence of shrinkage of the protective layer after heating and humidification was also visually confirmed. No problem: No color loss was observed Partial loss: Color loss was observed at the edge Total loss: Significant loss of color across the entire polarizing plate (2) Single unit transmittance and polarization degree For those whose color loss evaluation did not result in complete color loss, the single transmittance and polarization degree were measured. Test pieces (50 mm × 50 mm) were cut out from the polarizing plates obtained in the Examples and Comparative Examples, with two sides perpendicular to the absorption axis direction of the polarizer and the absorption axis direction facing each other. The test pieces were attached to alkali-free glass plates with an adhesive, with the protective layer facing outward, to prepare test samples. The single transmittance (Ts), parallel transmittance (Tp), and crossed transmittance (Tc) of the test samples were measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), and the polarization degree (P) was calculated using the following formula. The measurement light was incident from the protective layer side. Polarization degree (P)(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 The above Ts, Tp, and Tc are Y values ​​measured under a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Ts and P are essentially characteristics of the polarizer. Next, the polarizing plate was heated and humidified by being left in an oven at 85°C and 85% RH for 120 hours (heating test), and the single transmittance Ts0 before the heating test and the single transmittance Ts after the heating test were measured. 120 From this, the amount of change in single transmittance ΔTs was calculated using the following formula. ΔTs(%)=Ts 120 -Ts0 Similarly, the polarization degree P0 before the heating test and the polarization degree P after the heating test 120 From this, the change in the degree of polarization ΔP was calculated using the following formula. ΔP(%)=P 120 -P0 The heating test was carried out by preparing test samples in the same manner as in the case of the above-mentioned color loss test.

[0113] (3) Iodine adsorption amount A protective layer (thickness: about 3 μm) was formed on one side of the PET film in the same manner as in the formation of the protective layer in each of the Examples and Comparative Examples. The obtained PET film with the protective layer was cut into a size of 1 cm × 1 cm (1 cm 2A sample was cut out and placed in a headspace vial (20 mL) and weighed. Next, a screw cap vial (1.5 mL) containing 1 mL of iodine solution (iodine concentration 1 wt %, potassium iodide concentration 7 wt %) was placed in the same headspace vial and sealed. The headspace vial was then placed in a 65°C oven for 6 hours (this allows gaseous I2 to adsorb to the sample). The sample was then placed in a ceramic boat and combusted using an automatic sample combustion device. The generated gas was collected in 10 mL of absorption solution. After collection, the absorption solution was adjusted to 15 mL with pure water, and either the original solution or an appropriately diluted solution was subjected to IC quantitative analysis. Since the iodine adsorption amount was nearly zero when a similar measurement was performed on the PET film alone, the iodine adsorption amount (wt %) was calculated using the following formula based on the weight of iodine obtained by IC quantitative analysis and the weight of the protective layer alone ("weight of PET film with protective layer" - "weight of PET film"): Iodine adsorption amount (wt%) = weight of iodine obtained by IC quantitative analysis / weight of protective layer alone × 100 The measurement device and conditions are as follows: [Measuring equipment] Automatic sample combustion device: Mitsubishi Chemical Analytech Co., Ltd., "AQF-2100H" IC (anion): Thermo Fisher Scientific, "ICS-3000"

[0114] (4) Softening temperature of the protective layer The surface of the protective layer of the polarizing plate obtained in the examples and comparative examples was subjected to local thermal analysis (nano TA measurement) to calculate the softening temperature of the protective layer. The measurement device and measurement conditions are as follows. Measurement equipment: Hitachi High-Tech Science, product name "AFM5300E / / Nano-TA2" Measurement mode: Contact mode Probe: AN2-200 Measurement area: 8μm□scan Measurement atmosphere: atmospheric pressure

[0115] (5) Judgment The obtained polarizing plate was evaluated according to the following criteria. Good: ΔP value is between 0% and -4.0% Acceptable: ΔP value exceeds -4.0% and is -10.0% Unacceptable: ΔP value exceeds -10% and reaches -99.9% (complete decolorization)

[0116] Example 1 1. Preparation of a polarizer / resin substrate laminate The resin substrate was a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of about 75° C. One side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "GOHSEFFIMER Z410") in a ratio of 9:1. 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 at its free end to 2.4 times its original size in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the final polarizer would be 41.5%±0.1% (dyeing treatment). Next, the sample was immersed 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) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). The laminate was then immersed in an aqueous boric acid solution (boric acid concentration 4.0 wt %, potassium iodide 5 wt %) 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 weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, while drying in an oven maintained at 90°C, the laminate was brought into contact with a SUS heated roll whose surface temperature was maintained at 75°C for approximately 2 seconds (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 5.2%. In this way, a 5 μm-thick polarizer was formed on the resin substrate, and a laminate of polarizer / resin substrate was produced. The polarizer had a single transmittance (initial single transmittance) Ts0 of 42.0% and a polarization degree (initial polarization degree) P0 of 99.996%.

[0117] 2. Preparation of Polarizing Plates A cycloolefin film (ZT-12, manufactured by Zeon Corporation, thickness 23 μm) was attached to the surface of the polarizer obtained above as a film constituting a second protective layer via a UV-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness was 1.0 μm, and the films were attached using a roller. The adhesive was then cured by irradiating it from the film side with UV light. The resin substrate was then peeled off to obtain a polarizing plate having a second protective layer (ZT-12) / polarizer configuration.

[0118] 3. Preparation of the Protective Layer 15 parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) YX4000) was dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. 1.2 parts of a photocationic polymerization initiator (manufactured by San-Apro Co., Ltd., product name: CPI (registered trademark)-100P) was added to the obtained epoxy resin solution to obtain a protective layer-forming composition. The obtained protective layer-forming composition was applied to the polarizer surface of the polarizing plate obtained above using a wire bar, and the coating film was dried at 60°C for 3 minutes. Next, a high-pressure mercury lamp was used to apply an integrated light dose of 600 mJ / cm. 2The film was irradiated with ultraviolet light so that a protective layer was formed. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the evaluations (1) to (4) above.

[0119] <Example 2> An epoxy resin solution was obtained by dissolving 15 parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) and 10 parts of an oxetane resin (manufactured by Toagosei Co., Ltd., trade name: Aronoxetane (registered trademark) OXT-221) in 73 parts of methyl ethyl ketone. Two parts of a photocationic polymerization initiator (manufactured by San-Apro Co., Ltd., trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer-forming composition. A protective layer was formed in the same manner as in Example 1, except that the protective layer-forming composition was obtained using this epoxy resin solution. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the evaluations (1) to (4) above.

[0120] (Comparative Example 1) A protective layer was formed in the same manner as in Example 1, except that a hydrogenated bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) YX8000) was used instead of the epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the examples. The results are shown in Table 1.

[0121] (Comparative Example 2) A protective layer was formed in the same manner as in Example 2, except that a hydrogenated bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) YX8000) was used instead of the epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the examples. The results are shown in Table 1.

[0122] (Comparative Example 3) A protective layer was formed in the same manner as in Example 1, except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) 828) was used instead of the epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the examples. The results are shown in Table 1.

[0123] Comparative Example 4 A protective layer was formed in the same manner as in Example 2, except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) 828) was used instead of the epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the examples. The results are shown in Table 1.

[0124] (Comparative Example 5) 20 parts of polyester resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name: Nichigo Polyester WR905) was dissolved in 80 parts of pure water to obtain a coating resin solution (20%). This coating resin solution was applied to the polarizer surface of the polarizing plate used in the examples using a wire bar, and the coating film was dried at 60°C for 5 minutes to form a protective layer constituted by the solidified coating film. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the examples. The results are shown in Table 1.

[0125] (Comparative Example 6) A polarizing plate having a protective layer / polarizer / another protective layer (ZT-12) structure was obtained in the same manner as in Comparative Example 5, except that a urethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Superflex 210) was used instead of the polyester resin. The obtained polarizing plate was subjected to the same evaluations as in Examples. The results are shown in Table 1.

[0126] (Comparative Example 7) A polyurethane-based aqueous dispersion resin (Superflex SF210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was applied to the polarizer surface of a polarizing plate having a second protective layer (ZT-12) / polarizer configuration to a thickness of 0.1 μm to form an easy-adhesion layer. Separately, 20 parts of an acrylic resin (B-734, manufactured by Kusumoto Chemicals Co., Ltd.), a copolymer of methyl methacrylate and butyl methacrylate (molar ratio 35 / 65), was dissolved in 80 parts of methyl ethyl ketone to obtain a 20% acrylic resin solution. This acrylic resin solution was then applied to the easy-adhesion layer using a wire bar, and the coating was dried at 60°C for 5 minutes to form a solidified protective layer. The protective layer had a thickness of 3 μm, a softening temperature of 80.4°C, and an iodine adsorption of 30.4 wt%. In this way, a polarizing plate having a protective layer / polarizer / another protective layer (ZT-12) configuration was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0127] (Comparative Example 8) A protective layer was formed in the same manner as in Comparative Example 8, except that an acrylic resin (manufactured by Kusumoto Chemicals Co., Ltd., product name "B-722"), which is a copolymer of methyl methacrylate and ethyl acrylate (molar ratio 55 / 45), was used. The protective layer had a thickness of 3 μm, a softening temperature of 57.2°C, and an iodine adsorption of 1.3 wt%. In this way, a polarizing plate having a configuration of protective layer / polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluations as in the Examples. The results are shown in Table 1.

[0128] [Table 1]

[0129] <Evaluation> As is clear from Table 1, the polarizing plates obtained in the examples were very thin, but the deterioration of optical properties was suppressed even in a heated and humidified environment, and they had excellent durability. [Industrial Applicability]

[0130] The polarizing plate of the present invention is suitably used in image display devices. Examples of image display devices include portable devices such as personal digital assistants (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game consoles; office automation equipment such as personal computer monitors, notebook computers, and copy machines; home electrical appliances such as video cameras, televisions, and microwave ovens; in-vehicle devices such as backup monitors, car navigation system monitors, and car audio; exhibition devices such as digital signage and commercial store information monitors; security devices such as surveillance monitors; and nursing and medical devices such as nursing monitors and medical monitors. [Explanation of symbols]

[0131] 10 Polarizer 20 protective layer 40 Retardation layer 100 Polarizer 110,111 Polarizing plate with retardation layer

Claims

1. a polarizer and a protective layer disposed on one side of the polarizer; The polarizing plate, wherein the protective layer is made of a cured product of an epoxy resin having a biphenyl skeleton.

2. The polarizing plate according to claim 1 , wherein the cured product is a cationically polymerized cured product.

3. The polarizing plate according to claim 1 , wherein the protective layer further comprises an oxetane resin.

4. 4. The polarizing plate according to claim 1, wherein the protective layer has a thickness of 10 [mu]m or less.

5. 5. The polarizing plate according to claim 1, wherein the protective layer has an iodine adsorption amount of 10% by weight or less.

6. 6. The polarizing plate according to claim 1, wherein the protective layer has a softening temperature of 100°C or higher.

7. 7. The polarizing plate according to claim 1, which has a total thickness of 10 [mu]m or less.

8. A polarizing plate with a retardation layer, comprising the polarizing plate according to claim 1 , and a retardation layer on the surface of the polarizing plate on which the protective layer is not disposed.

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