Polarizing plates and polarizing plates with optical functional layers

Abstract

To provide a polarizing plate that is extremely thin yet possesses excellent durability and flexibility. [Solution] The polarizing plate of the present invention comprises a polarizer and a protective layer disposed on one side of the polarizer, wherein the protective layer is composed of a photocationic cured epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton, or a solidified coating film of an organic solvent solution of epoxy resin, and has a total thickness of 20 μm or less.

Description

[Technical Field]

[0001] This invention relates to polarizing plates and polarizing plates with optical functional layers. [Background technology]

[0002] In image display devices (e.g., liquid crystal displays, organic light-emitting diodes), a polarizing plate is often placed on at least one side of the display cell, due to the image formation method. In recent years, image display devices have become thinner and more flexible, and consequently, there has been a strong demand for thinner polarizing plates. However, the thinner the polarizing plate, the more pronounced the durability problem becomes, specifically the deterioration of its optical properties under heated and humidified environments.

[0003] In recent years, there has been a growing demand for curved image display devices and / or bendable or foldable image display devices. Accordingly, polarizers (and consequently, polarizers with optical functional layers) are required to have excellent mechanical properties, including flexibility, and that their optical properties do not change when bent. However, polarizers (and consequently, polarizers with optical functional layers) that satisfy these properties still require further investigation before practical application. Furthermore, improving flexibility leads to a decrease in the strength of the polarizer, resulting in reduced physical durability. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-210474 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a polarizing plate and a polarizing plate with an optical functional layer that are extremely thin yet achieve both excellent durability and excellent flexibility. [Means for solving the problem]

[0006] The polarizing plate of the present invention includes a polarizer and a protective layer disposed on one side of the polarizer. This protective layer is composed of a photocationic cured epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton, or a solidified coating film of an organic solvent solution of the epoxy resin. The total thickness of this polarizing plate is 20 μm or less. In one embodiment, the protective layer is a photocationic cured epoxy resin having at least one selected from the group consisting of the aromatic skeleton and the hydrogenated aromatic skeleton, and further comprises an oxetane resin. In one embodiment, the softening temperature of the protective layer is 100°C or higher. In one embodiment, the thickness of the protective layer is 10 μm or less. In one embodiment, the thickness of the polarizer is 10 μm or less. In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin having at least one selected from the group consisting of the above-mentioned aromatic skeleton and a hydrogenated aromatic skeleton. In another aspect of the present invention, a polarizing plate with an optical functional layer is provided. This polarizing plate with an optical functional layer includes the polarizing plate and an optical functional layer disposed on the opposite side of the polarizer from the protective layer. The total thickness of this polarizing plate with an optical functional layer is 25 μm or less. In one embodiment, the optical functional layer functions as a protective layer separate from the protective layer. In one embodiment, the optical functional layer is a phase difference layer having a circular polarization function or an elliptic polarization function. [Effects of the Invention]

[0007] According to an embodiment of the present invention, it is possible to provide a polarizing plate and a polarizing plate with an optical functional layer that achieve both excellent durability and excellent flexibility despite being very thin. In an embodiment of the present invention, the protective layer is composed of a photocation-cured product of an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton, or a solidified product of a coating film of an organic solvent solution of an epoxy resin. Therefore, it is possible to provide a polarizing plate and a polarizing plate with an optical functional layer that achieve both excellent durability and excellent flexibility.

Brief Description of Drawings

[0008] [Figure 1] It is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view of a polarizing plate with an optical functional layer according to one embodiment of the present invention. [Figure 3] It is a schematic view showing an example of a drying shrinkage treatment using a heating roll in a method for manufacturing a polarizing plate according to one embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0009] (Definitions of Terms and Symbols) The definitions of the terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) “nx” is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal 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 phase difference measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane phase difference measured with light of wavelength 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Phase Difference in the Thickness Direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using 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 using the formula Nz = Rth / Re. (5)Angle In this specification, when an angle is referred to, it encompasses both clockwise and counterclockwise directions with respect to the reference direction. Therefore, for example, "45°" means ±45°.

[0010] A. Overview of polarizing plates and polarizing plates with optical functional layers A-1. Overview of polarizing plates Figure 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 has a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10. The total thickness of the polarizing plate 100 is 20 μm or less. The protective layer 20 is a photocationically cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons, or a solidified coating film of an organic solvent solution of epoxy resin. That is, the protective layer is a layer formed by curing an epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons by photocationic polymerization, or a solidified coating film of an organic solvent solution of epoxy resin. By having such a protective layer in the polarizing plate 100, it is possible to provide a polarizing plate that achieves both excellent durability and excellent flexibility despite its very thin thickness. In one embodiment, the thickness of the polarizer 10 is preferably 10 μm or less. Also, in one embodiment, the thickness of the protective layer 20 is preferably 10 μm or less. In one embodiment, the softening temperature of the protective layer is preferably 100°C or higher. The softening temperature of the protective layer can be determined by the epoxy resin used.

[0011] The total thickness of the polarizing plate 100 is 20 μm or less, preferably 15 μm or less, and more preferably 10 μm or less. According to the present invention, even if the total thickness of the polarizing plate is within the above range, it is possible to provide a polarizing plate that achieves both excellent durability and excellent flexibility. The total thickness of the polarizing plate is, for example, 5 μm or more.

[0012] Each layer or optical film constituting the polarizing plate is typically bonded together via an adhesive layer. Examples of adhesive layers include adhesive layers and tack layers. In embodiments of the present invention, an adhesive layer can be suitably used. Such a configuration allows for further thinning of the polarizing plate. Typical adhesives constituting the adhesive layer include active energy ray curing adhesives (e.g., ultraviolet curing adhesives).

[0013] In embodiments of the present invention, the thickness of the polarizing plate can be extremely thin. Therefore, it can be suitably applied to flexible image display devices. 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 displays and electroluminescent (EL) displays (e.g., organic EL displays, inorganic EL displays). Needless to say, the above description does not prevent the polarizing plate of the present invention from being applied to ordinary image display devices.

[0014] A-2. Overview of Polarizing Plates with Optical Functional Layers Figure 2 is a schematic cross-sectional view of a polarizing plate with an optical functional layer according to one embodiment of the present invention. The illustrated polarizing plate 110 with an optical functional layer includes a polarizer 10, a protective layer 20 disposed on one side of the polarizer, and an optical functional layer 30 disposed on the other side of the polarizer. The total thickness of the polarizing plate with an optical functional layer is 25 μm or less. In one embodiment, the polarizing plate 100 is used as the polarizer 10 and the protective layer 20.

[0015] The total thickness of the optically functional polarizing plate 110 is 25 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. According to the present invention, even if the total thickness of the polarizing plate is within the above range, it is possible to provide a polarizing plate that achieves both excellent durability and excellent flexibility. The total thickness of the optically functional polarizing plate is, for example, 10 μm or more.

[0016] In one embodiment, the optical functional layer functions as a protective layer separate from the protective layer 20. Such a protective layer may also function as a phase difference layer having predetermined phase difference and optical properties. In another embodiment, the optical functional layer is a phase difference layer having circular polarization or elliptic polarization functionality. Such a phase difference layer may also function as a protective layer for a polarizer. When the optical functional layer is a phase difference layer, in one embodiment, the phase difference layer is an orientation solidification layer of a liquid crystal compound. The phase difference layer may be a single layer of orientation solidification layers, or it may have a laminated structure of a first orientation solidification layer and a second orientation solidification layer. Hereinafter, a polarizer in which the optical functional layer is a phase difference layer may be referred to as a polarizer with a phase difference layer.

[0017] Each layer or optical film constituting a polarizing plate with an optical functional layer is typically bonded together via an adhesive layer. Examples of adhesive layers include adhesive layers and tack layers. In embodiments of the present invention, an adhesive layer can be suitably used. Such a configuration makes it possible to further thin the polarizing plate with an optical functional layer. Typical adhesives constituting the adhesive layer include active energy ray curing adhesives (e.g., ultraviolet curing adhesives).

[0018] A polarizer equipped with an optical functional layer that functions as a phase difference layer may further include another phase difference layer. Typically, the other phase difference layer is provided outside the optical functional layer (phase difference layer) 30 (on the opposite side from the polarizer 10). Typically, the other phase difference layer exhibits a refractive index characteristic of nz > nx = ny. Such another phase difference layer is preferably provided when the phase difference layer is a single layer of orientation solidification layer. For convenience, the optical functional layer (phase difference layer) 30 may be referred to as the first phase difference layer, and the other phase difference layer may be referred to as the second phase difference layer. A polarizer with an optical functional layer may further include other phase difference layers. The optical properties (e.g., refractive index characteristics, in-plane phase difference, Nz coefficient, photoelastic coefficient), thickness, placement position, etc., of the other phase difference layers can be appropriately set according to the purpose.

[0019] A polarizing plate with an optical functional layer may be provided with a conductive layer or an isotropic substrate with a conductive layer. Typically, the conductive layer or the isotropic substrate with a conductive layer is provided on the outside of the optical functional layer 30 (opposite side from the polarizer 10). If the polarizing plate is a polarizing plate with a phase difference layer having a phase difference layer and another phase difference layer, typically the other phase difference layer and the conductive layer or the isotropic substrate with a conductive layer are provided in this order from the side of the phase difference layer (optical functional layer) 30. When a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate or polarizing plate with a phase difference layer can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between an image display cell (e.g., an organic EL cell) and the polarizing plate.

[0020] As described above, by constructing the protective layer from a photocationic cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons, or from a solidified coating film of an organic solvent solution of epoxy resin, a polarizing plate with excellent durability can be realized despite being extremely thin. Specifically, a polarizing plate can be realized in which the deterioration of optical properties is suppressed even under heated and humidified environments. The above polarizing plate exhibits very small changes in the single-element transmittance Ts ΔTs and the polarization degree P ΔP after being left for 48 hours in an environment of 85°C and 85%RH. The single-element transmittance Ts can be measured, for example, using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The polarization degree P is calculated from the single-element transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) measured using an ultraviolet-visible spectrophotometer by the following formula. Polarization degree (P)(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 Note that the above Ts, Tp, and Tc are Y values ​​measured using a 2-degree field of view (C light source) according to JIS Z 8701 and corrected for luminous efficiency. Furthermore, Ts and P are essentially polarizer characteristics. ΔTs and ΔP are calculated using the following formulas, respectively. ΔTs(%)=Ts 48 -Ts0 ΔP(%)=P 48 -P0 Here, Ts0 is the individual transmittance before leaving it (initial), and Ts 48 P is the transmittance of the single element after standing, P0 is the polarization degree before standing (initial), and P 48 ΔTs 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 -1.0% to 0%, more preferably -0.5% to 0%, and even more preferably -0.3% to 0%.

[0021] In practical terms, an adhesive layer (not shown) is provided on the side of the optical functional layer opposite the polarizer, allowing the polarizing plate to be attached to an image display cell. Furthermore, it is preferable that a release film is temporarily attached to the surface of the adhesive layer until the polarizing plate is put into use. By temporarily attaching the release film, the adhesive layer is protected and roll formation becomes possible.

[0022] The polarizing plates and polarizing plates with optical functional layers of the present invention may be in the form of single sheets or in the form of elongated sheets. In this specification, "elongated sheet" means an elongated shape in which the length is sufficiently long relative to the width, and for example, includes an elongated shape in which the length is 10 times or more, preferably 20 times or more, relative to the width. Elongated polarizing plates can be wound into a roll.

[0023] The components of polarizers and polarizers with optical functional layers will be described in more detail below.

[0024] B. Polarizer Any suitable polarizer can be used as the polarizer. Typically, polarizers can be made using a laminate of two or more layers. The method for manufacturing polarizers will be described later in section F as a method for manufacturing polarizing plates.

[0025] The thickness of the polarizer is preferably 10 μm or less, more preferably 1 μm to 8 μm, even more preferably 1 μm to 7 μm, and particularly preferably 2 μm to 5 μm.

[0026] 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, the synergistic effect with the iodine content described later allows for good maintenance of ease of curl adjustment during bonding, good suppression of curl during heating, and improvement of appearance durability during heating. The boric acid content can be calculated, for example, as the amount of boric acid contained in the polarizer per unit weight using the following formula from the neutralization method.

number

[0027] The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% to 10% by weight. When the iodine content of the polarizer is within such a range, due to the synergistic effect with the above-mentioned boric acid content, the ease of curl adjustment during lamination can be maintained well, and while suppressing the curl during heating well, the appearance durability during heating can be improved. In this specification, the "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, in the polarizer, iodine exists in the form of iodine ions (I - ), iodine molecules (I2), polyiodine ions (I3 - , I5 - ), etc. Here, the iodine content in this specification means the amount of iodine including all these forms. The iodine content can be calculated, for example, by the calibration curve method of fluorescent X-ray analysis. Note that polyiodine ions exist in the polarizer in a state where a PVA-iodine complex is formed. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, the 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, polyiodine ions can absorb light in a wide range of visible light according to their form. On the other hand, iodine ions (I - ) have an absorption peak around 230 nm and are not substantially involved in the absorption of visible light. Therefore, polyiodine ions existing in a complex state with PVA can be mainly involved in the absorption performance of the polarizer.

[0028] The polarizer preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single transmittance Ts of the polarizer is preferably 40% to 48%, more preferably 41% to 46%. The degree of polarization P of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0029] C. Protective layer C-1. Photocationic cured product In one embodiment, the protective layer is composed of a photocationic cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons. By using such a protective layer, it is possible to provide polarizers and polarizers with optical functional layers that achieve both excellent durability and flexibility. As described above, since the protective layer is a photocationic cured product, the protective layer forming composition contains a photocationic polymerization initiator. The photocationic polymerization initiator is a photosensitive agent that functions as a photoacid generator, and a typical example is an ionic onium salt consisting of a cation part and an anion part. In this onium salt, the cation part absorbs light, and the anion part becomes the source of acid. Ring-opening polymerization of epoxy groups proceeds due to the acid generated from this photocationic polymerization initiator. The protective layer, which is a photocationic cured product, has a high softening temperature and the amount of iodine adsorption can be reduced. Therefore, it is possible to provide polarizers that achieve both excellent durability and flexibility.

[0030] C-1-1. Epoxy resin As the epoxy resin, any suitable epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons can be used. Examples of aromatic skeletons include benzene rings, naphthalene rings, and fluorene rings. Only one type of epoxy resin may be used, or two or more types may be used in combination. Preferably, an epoxy resin having a biphenyl skeleton as the aromatic skeleton is used. By using an epoxy resin having a biphenyl skeleton, a polarizing plate that achieves both superior durability and superior flexibility can be provided. Below, epoxy resins having a biphenyl skeleton will be described in detail as representative examples.

[0031] 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 two or more may be used in combination. [ka] (In the formula, R 1 ~R 8 Each of these independently represents a hydrogen atom, a linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element.

[0032] R 1 ~R 8 Each of these 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 linear or branched substituted or unsubstituted hydrocarbon groups having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, cyclopentyl group, n-hexyl group, isohexyl group, cyclohexyl group, n-heptyl group, cycloheptyl group, methylcyclohexyl group, n-octyl group, cyclooctyl group, n-nonyl group, 3,3,5-trimethylcyclohexyl group, n-decyl group, cyclodecyl group, n-undecyl group, n-dodecyl group, cyclododecyl group, phenyl group, benzyl group, methylbenzyl group, dimethylbenzyl group, trimethylbenzyl group, naphthylmethyl group, phenethyl group, and 2-phenylisopropyl group. Preferred linear or branched substituted or unsubstituted hydrocarbon groups 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 groups. Preferred halogen elements include fluorine and bromine.

[0033] 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 As described above, n represents an integer between 0 and 6.

[0034] 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 resulting protective layer can be further improved.

[0035] In one embodiment, the epoxy resin having a biphenyl skeleton may also contain chemical structures other than the biphenyl skeleton. Examples of chemical structures other than the biphenyl skeleton include a bisphenol skeleton, an alicyclic structure, an aromatic ring structure, and the like. In this embodiment, it is preferable that the proportion (molar ratio) of chemical structures other than the biphenyl skeleton is less than that of the biphenyl skeleton.

[0036] Commercially available epoxy resins having a biphenyl skeleton may be used. Examples of commercially available products include those manufactured by Mitsubishi Chemical Corporation, such as jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, and jER YL7399.

[0037] Epoxy resins having a biphenyl skeleton preferably have 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 polarizing plate containing the resulting 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, it can have excellent moldability and processability.

[0038] 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. Furthermore, 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 having the epoxy equivalent of the biphenyl skeleton within the above range, a more stable protective layer (a protective layer with less residual monomer and sufficient curing) can be obtained. In this specification, "epoxy equivalent" refers to "the mass of epoxy resin containing 1 equivalent of epoxy groups," and can be measured in accordance with JIS K7236.

[0039] In embodiments of the present invention, an epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons may be used in combination with other resins. That is, a blend of an epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons and other resins may be used to mold the protective layer. Examples of other resins include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide, as well as curable resins such as acrylic resins and oxetane resins. Preferably, acrylic resins and oxetane resins are used. The types and amounts of resins used in combination can be appropriately set according to the purpose and the desired properties of the resulting film. For example, styrene resins may be used in combination as a phase difference control agent.

[0040] Any suitable acrylic resin can be used as the acrylic resin. For example, 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 individually or in combination of two or more types. These acrylic resins are described, for example, in Japanese Patent Application Publication No. 2019-168500. The entire description of said publication is incorporated herein by reference.

[0041] As the oxetane resin, any suitable compound having one or more oxetanyl groups in its molecule can be used. Examples 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-(oxyranylmethoxy)oxetane, and (meth)acrylic acid (3-ethyloxetan-3-yl)methyl; 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 individually or in combination of two or more types.

[0042] Preferably, 3-ethyl-3-hydroxymethyl oxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(oxyranylmethoxy)oxetane, (meth)acrylic acid (3-ethyloxetan-3-yl)methyl, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, etc. are used. These oxetane resins are readily available and can be diluted (low viscosity) and have good compatibility.

[0043] In one embodiment, an oxetane resin with a molecular weight of 500 or less and that is liquid at room temperature (25°C) is preferably used from the viewpoint of compatibility and adhesion. 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-(oxyranylmethoxy)oxetane, or (meth)acrylic acid (3-ethyloxetan-3-yl)methyl is used. By using these oxetane resins, the curability and durability of the protective layer can be improved.

[0044] Commercially available oxetane resins may be used. Specifically, Aronoxetane OXT-101, Aronoxetane OXT-121, Aronoxetane OXT-212, and Aronoxetane OXT-221 (all manufactured by Toagosei Co., Ltd.) can be used. Preferably, Aronoxetane OXT-101 and Aronoxetane OXT-221 can be used.

[0045] When using an epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons in combination with another resin, the content of the epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons in the blend of the epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, even more preferably 70% to 100% by weight, and particularly preferably 80% to 100% by weight. If the content is less than 50% by weight, sufficient heat resistance of the protective layer and adhesion to the polarizer may not be obtained.

[0046] When using an epoxy resin having a biphenyl skeleton in combination with an oxetane resin, 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, per 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, curability can be improved, and the adhesion between the protective layer and the polarizer can also be improved.

[0047] C-1-2. Photocationic polymerization initiator A photocationic polymerization initiator is a photosensitive agent that functions as a photoacid generator, and a typical example is an ionic onium salt consisting of a cationic moiety and an anionic moiety. In this onium salt, the cationic moiety absorbs light, and the anionic moiety acts as a source of acid. The acid generated from this photocationic polymerization initiator promotes ring-opening polymerization of epoxy groups. As the photocationic polymerization initiator, any suitable compound can be used that can cure epoxy resins having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons upon irradiation with light such as ultraviolet light. A single photocationic polymerization initiator may be used, or two or more may be used in combination.

[0048] Examples of photocationic polymerization initiators include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, p-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfidebishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfidebishexafluoroantimonate, (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.

[0049] Commercially available photocationic polymerization initiators may be used. Examples of commercially available products include the triphenylsulfonium salt-based hexafluoroantimonate type SP-170 (manufactured by ADEKA), CPI-101A (manufactured by Sunapro), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), and the diphenyliodonium salt-based hexafluoroantimonate type WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.).

[0050] The content of the photocationic polymerization initiator is preferably 0.1 to 3 parts by weight, and more preferably 0.25 to 2 parts by weight, per 100 parts by weight of epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons. If the content of the photocationic polymerization initiator is less than 0.1 parts by weight, curing may not be sufficient even when irradiated with light (ultraviolet light).

[0051] C-2. Solidified coating film In one embodiment, the protective layer is composed of a solidified coating film of an epoxy resin organic solvent solution.

[0052] C-2-1. Epoxy resin Epoxy resins preferably have 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 is 100°C or higher, polarizing plates containing a protective layer obtained from such a resin tend to have excellent durability. The Tg of the epoxy resin 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 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 is within this range, it can have excellent moldability and processability.

[0053] Any suitable epoxy resin can be used as the epoxy resin, as long as it has the Tg described above. Typically, an epoxy resin refers to a resin having epoxy groups in its molecular structure. Preferably, an epoxy resin having aromatic rings in its molecular structure is used. Using an epoxy resin having aromatic rings can yield an epoxy resin with a higher Tg. Examples of aromatic rings in an epoxy resin having aromatic rings in its molecular structure include benzene rings, naphthalene rings, and fluorene rings. Only one type of epoxy resin may be used, or two or more types may be used in combination. When using two or more types of epoxy resins, an epoxy resin containing aromatic rings may be used in combination with an epoxy resin not containing aromatic rings.

[0054] Epoxy resins having aromatic rings in their molecular structure include, specifically, bisphenol A diglycidyl ether type epoxy resin, bisphenol F diglycidyl ether type epoxy resin, bisphenol S diglycidyl ether type epoxy resin, resorcinol diglycidyl ether type epoxy resin, hydroquinone diglycidyl ether type epoxy resin, terephthalic acid diglycidyl ester type epoxy resin, bisphenoxyethanol full orange glycidyl ether type epoxy resin, bisphenol full orange glycidyl ether type epoxy resin, and biscresol full orange glycidyl ether. Examples include epoxy resins having two epoxy groups, such as 1-type epoxy resins; epoxy resins having three epoxy groups, such as novolac-type epoxy resins, N,N,O-triglycidyl-P- or -m-aminophenol-type epoxy resins, N,N,O-triglycidyl-4-amino-m- or -5-amino-o-cresol-type epoxy resins, and 1,1,1-(triglycidyloxyphenyl)methane-type epoxy resins; and epoxy resins having four epoxy groups, such as glycidylamine-type epoxy resins (e.g., diaminodiphenylmethane type, diaminodiphenylsulfone type, metaxylenediamine type). In addition, glycidyl ester-type epoxy resins such as hexahydrophthalic anhydride-type epoxy resins, tetrahydrophthalic anhydride-type epoxy resins, dimer acid-type epoxy resins, and p-oxybenzoic acid-type epoxy resins may also be used.

[0055] The weight-average molecular weight of the epoxy resin is preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, even more preferably 10,000 to 500,000, particularly preferably 50,000 to 500,000, and most preferably 60,000 to 150,000. The weight-average molecular weight can be determined, for example, by using a gel permeation chromatograph (GPC system, manufactured by Tosoh Corporation) and converting it to polystyrene equivalent. Tetrahydrofuran may be used as the solvent.

[0056] The epoxy equivalent of the epoxy resin is preferably 1000 g / equivalent or more, more preferably 3000 g / equivalent or more, and even more preferably 5000 g / equivalent or more. Furthermore, the epoxy equivalent of the epoxy resin is preferably 30000 g / equivalent or less, more preferably 25000 equivalent or less, and even more preferably 20000 g / equivalent or less. A more stable protective layer can be obtained by having the epoxy equivalent within the above range. In this specification, "epoxy equivalent" refers to "the mass of epoxy resin containing 1 equivalent of epoxy groups," and can be measured in accordance with JIS K7236.

[0057] In embodiments of the present invention, epoxy resin may be used in combination with other resins. That is, a blend of epoxy resin and other resins may be used to form the protective layer. Examples of other resins include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and amount of resin used in combination can be appropriately set according to the purpose and the desired properties of the resulting film. For example, styrene resin may be used in combination as a phase difference control agent.

[0058] When epoxy resin is used in combination with other resins, the epoxy resin content in the blend of epoxy resin and other resins is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, even more preferably 70% to 100% by weight, and particularly preferably 80% 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.

[0059] C-3. Composition and characteristics of the protective layer As described above, the protective layer is composed of a photocationic cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons, or a solidified coating film of an organic solvent solution of epoxy resin. With such a protective layer, the thickness can be made significantly thinner compared to an extruded film. 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 may be, for example, 1 μm or more. The photocationic cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons, or the solidified coating film of an organic solvent solution of epoxy resin, has the advantage of superior humidification durability because it has lower hygroscopicity and moisture permeability compared to solidified water-based coating films such as aqueous solutions or aqueous dispersions. As a result, a highly durable polarizing plate that can maintain its optical properties even under heated and humidified environments can be realized. Furthermore, by being a photocationic cured product of an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton, or a solidified product of a coated film of an organic solvent solution of an epoxy resin, it is possible to achieve both excellent durability and excellent flexibility.

[0060] 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 containing the protective layer tends 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, it can have excellent moldability and processability.

[0061] The amount of iodine adsorbed in the protective layer is preferably 25% by weight or less, more preferably 10% by weight or less, even more preferably 6.0% by weight or less, and particularly preferably 3.0% by weight or less. A smaller amount of iodine adsorbed is preferable. If the amount of iodine adsorbed is within this range, a polarizing plate with even better durability can be obtained. The amount of iodine adsorbed can be measured by the following method. The protective layer-forming composition is applied to the substrate (PET film) using an applicator to form a protective layer (approximately 3 μm thick). The resulting PET film with the protective layer is then cut into 1 cm x 1 cm (1 cm) pieces. 2 Cut out a sample from the PET film and collect and weigh it into a headspace vial (20 mL capacity). Next, place a screw-cap vial (1.5 mL capacity) containing 1 mL of iodine solution (iodine concentration 1 wt%, potassium iodide concentration 7 wt%) into the headspace vial and seal it tightly. Then, place the headspace vial in a 65°C drying oven and heat for 6 hours. This will adsorb gaseous I2 onto the sample. After that, collect the sample on a ceramic boat and burn it using an automatic sample combustion device, and collect the generated gas in 10 mL of absorption solution. After collection, prepare this absorption solution by diluting it with pure water to 15 mL, and perform IC quantitative analysis on the undiluted solution or a solution diluted as appropriate. Note that the amount of iodine adsorbed when the same measurement is performed on PET film alone is almost 0. Based on the weight of iodine obtained from the IC quantitative analysis and the weight of the protective layer alone ("weight of PET film with protective layer" - "weight of PET film"), calculate the amount of iodine adsorbed (wt%) from the following formula. Iodine adsorption amount (weight %) = 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 device] Automatic sample combustion device: Mitsubishi Chemical Analytech Co., Ltd., "AQF-2100H" IC (Anion): Thermo Fisher Scientific, "ICS-3000"

[0062] The protective layer is preferably substantially optically isotropic. In this specification, "substantially optically isotropic" means that the phase difference at a wavelength of 550 nm is between -50 nm and +50 nm. The in-plane phase difference Re(550) is more preferably between -30 nm and +30 nm, even more preferably between -10 nm and +10 nm, and particularly preferably between 0 nm and 2 nm. The phase difference in the thickness direction Rth(550) is more preferably between -5 nm and +5 nm, even more preferably between -3 nm and +3 nm, and particularly preferably between -2 nm and +2 nm. If 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 containing the protective layer is applied to an image display device. Re(550) is the in-plane phase difference of the film measured with light at a wavelength of 550 nm at 23°C. Re(550) is calculated by the formula: Re(550)=(nx-ny)×d. Rth(550) is the phase difference in the thickness direction of a film measured with light of wavelength 550 nm 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 refractive index in the plane is maximum (i.e., in the direction of the slow phase axis), ny is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., in the direction of the fast phase axis), nz is the refractive index in the thickness direction, and d is the thickness of the film (nm).

[0063] A higher light transmittance at 380 nm for a protective layer with a thickness of 3 μm is preferable. Specifically, the light transmittance is preferably 85% or higher, more preferably 88% or higher, and even more preferably 90% or higher. A light transmittance within this range ensures the desired transparency. The light transmittance can be measured, for example, by a method conforming to ASTM-D-1003.

[0064] 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 gives the film a good sense of clarity. Furthermore, even when used as a polarizing plate on the viewing side of an image display device, the displayed content can be clearly seen.

[0065] The YI value 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 YI exceeds 1.3, optical transparency may be insufficient. YI can be determined, for example, from the tristimulus values ​​(X, Y, Z) of color obtained by measurement using a high-speed integrating sphere spectrophotometer (product name DOT-3C: manufactured by Murakami Color Technology Laboratory) by the following formula. YI = [(1.28X - 1.06Z) / Y] × 100

[0066] The b value (a hue scale according to the Hunter color system) at a protective layer thickness of 3 μm is preferably less than 1.5, more preferably 1.0 or less. If the b value is 1.5 or higher, undesirable colors may appear. 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 spectrophotometer (product name DOT-3C: manufactured by Murakami Color Technology Laboratory), and evaluating the hue according to the Hunter color system.

[0067] The protective layer (for example, a photocationic cured epoxy resin having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons, and a solidified epoxy resin coating) may contain any suitable additives depending on the purpose. Specific examples of additives include: UV absorbers; leveling agents; antioxidants such as hindered phenols, phosphorus, and sulfur; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; 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; flame retardants; and so on. Additives are usually added to the solution during film formation. The type, number, combination, and amount of additives can be appropriately determined depending on the purpose.

[0068] An easy-adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer may, for example, contain a water-based polyurethane and an oxazoline-based crosslinking agent. Forming such an easy-adhesion layer can improve the adhesion between the protective layer and the polarizer. 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 the protective layer on the viewing side of a viewing-side polarizer. When both an easy-adhesion layer and a hard coat layer are formed, they can typically be formed on different sides of the protective layer.

[0069] D. Optical functional layer D-1. Protective optical functional layer When the optical functional layer 30 functions as a protective layer separate from the protective layer 20, the protective layer is preferably a thin protective layer with a thickness of 20 μm or less. The thickness of the protective layer is more preferably 18 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less. The thickness of the protective layer may be, for example, 1 μm or more.

[0070] The protective layer (optical functional layer) may be composed of a resin film or a solidified coating film. Examples of resins that make up the resin film include cycloolefin resins and acrylic resins. The solidified coating film may be, for example, a solidified coating film of an organic solvent solution of a predetermined acrylic resin, or a solidified coating film of an organic solvent solution of the epoxy resin mentioned above. When the protective layer is composed of a solidified coating film, its thickness can be made significantly thinner compared to a resin film. Furthermore, the protective layer (optical functional layer) may be a photocationic cured product of an epoxy resin having the aromatic skeleton and a hydrogenated aromatic skeleton.

[0071] The protective layer (optical functional layer) is typically placed on the image display cell side when a polarizing plate is applied to an image display device. In one embodiment, the protective layer is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0 nm to 10 nm and the phase difference Rth(550) in the thickness direction is -10 nm to +10 nm. In another embodiment, the protective layer may be a phase difference layer having any appropriate phase difference value. In this case, the in-plane phase difference Re(550) of the protective layer (phase difference layer) is, for example, 110 nm to 150 nm.

[0072] D-2. Optical functional layer which is a phase difference layer having circular polarization or elliptic polarization function. When the optical functional layer 30 is a phase difference layer having a circular polarization function or an elliptical polarization function, the phase difference layer may be a stretched film of a resin film or an oriented solidified layer of a liquid crystal compound. Preferably, it is an oriented solidified layer of a liquid crystal compound. By using a liquid crystal compound, the difference between nx and ny of the resulting phase difference layer can be made significantly larger than that of a non-liquid crystal material, so that the thickness of the phase difference layer required to obtain the desired in-plane phase difference can be made significantly smaller than that of a stretched film. As a result, further thinning of the polarizing plate with a phase difference layer can be achieved. Furthermore, a polarizing plate with a phase difference layer having extremely excellent flexibility can be realized. The oriented solidified layer of a liquid crystal compound will be described in detail below. For example, a phase difference layer composed of a stretched film of a resin film is described in Japanese Patent Application Publication No. 2017-54093 and Japanese Patent Application Publication No. 2018-60014. The descriptions in these publications are incorporated herein by reference.

[0073] In this specification, "orientation-solidified layer" refers to a layer in which liquid crystal compounds are oriented in a predetermined direction within the layer, and this orientation state is fixed. The "orientation-solidified layer" is a concept that encompasses the orientation-cured layer obtained by curing liquid crystal monomers, as described later. In this embodiment, typically, rod-shaped liquid crystal compounds are oriented in a state where they are aligned along the slow axis direction of the first phase difference layer (homogenous orientation).

[0074] Examples of liquid crystal compounds include liquid crystal compounds in which the liquid crystal phase is a nematic phase (nematic liquid crystals). Examples of such liquid crystal compounds include liquid crystal polymers and liquid crystal monomers. The mechanism of liquid crystallinity in liquid crystal compounds can be either lyotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers may be used individually or in combination.

[0075] When the liquid crystal compound is a liquid crystal monomer, it is preferable that the liquid crystal monomer is 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 oriented the liquid crystal monomer, for example, polymerizing or crosslinking the liquid crystal monomers together can thereby fix the orientation state. Here, polymers are formed by polymerization and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystal. Therefore, the formed first phase difference layer does not undergo transitions to liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is characteristic of liquid crystal compounds. As a result, the first phase difference layer becomes an extremely stable phase difference layer that is not affected by temperature changes.

[0076] The temperature range in which liquid crystal monomers exhibit liquid crystalline properties varies depending on the type. 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.

[0077] Any suitable liquid crystal monomer can be used as the above-mentioned liquid crystal monomer. For example, polymerizable mesogenic compounds described in JP 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogenic compounds include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Silicon-CC3767. As the liquid crystal monomer, nematic liquid crystal monomers are preferred.

[0078] An orientation-solidified layer of a liquid crystal compound can be formed by applying an orientation treatment to the surface of a predetermined substrate, coating the surface with a coating liquid containing the liquid crystal compound to orient the liquid crystal compound in a direction corresponding to the orientation treatment, and fixing the orientation state. In one embodiment, the substrate is any suitable resin film, and the orientation-solidified layer formed on the substrate can be transferred to the surface of the polarizer 10.

[0079] Any suitable orientation treatment can be employed as described above. Specifically, these include mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment. Specific examples of mechanical orientation treatment include rubbing and stretching. Specific examples of physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of chemical orientation treatment include oblique deposition and photo-oriented orientation treatment. The processing conditions for each orientation treatment can be any suitable conditions depending on the purpose.

[0080] The orientation of liquid crystal compounds is achieved by treating them at a temperature that exhibits the liquid crystal phase, depending on the type of liquid crystal compound. This temperature treatment causes the liquid crystal compound to enter a liquid crystal state, and it then orients according to the orientation treatment direction on the substrate surface.

[0081] In one embodiment, the orientation state is fixed by cooling the liquid crystal compound oriented as described above. If the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the orientation state is fixed by subjecting the liquid crystal compound oriented as described above to a polymerization treatment or a crosslinking treatment.

[0082] Specific examples of liquid crystal compounds and details of the method for forming the orientation solidified layer are described in Japanese Patent Publication No. 2006-163343. The description in said publication is incorporated herein by reference.

[0083] Another example of an oriented solidified layer is a form in which the discotic liquid crystal compound is oriented in one of the following states: vertical orientation, hybrid orientation, or tilt orientation. Typically, the discotic liquid crystal compound has a disc surface that is oriented substantially perpendicular to the film surface of the first phase difference layer. Substantially perpendicular means that the average angle between the film surface and the disc surface of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°, and even more preferably 85° to 90°. A discotic liquid crystal compound generally refers to a liquid crystal compound having a disc-shaped molecular structure in which a cyclic parent core such as benzene, 1,3,5-triazine, or calixarene is positioned at the center of the molecule, and linear alkyl groups, alkoxy groups, substituted benzoyloxy groups, etc., are radially substituted as side chains. Representative examples of discotic liquid crystals include benzene derivatives, triphenylene derivatives, tolkene 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 reports by J. MLehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985) and J. Zhang et al., J. Am. Chem. Soc. Vol. 116, p. 2655 (1994). Further specific examples of discotic liquid crystal compounds include, for example, the compounds described in Japanese Patent Publication No. 2006-133652, Japanese Patent Publication No. 2007-108732, and Japanese Patent Publication No. 2010-244038. The descriptions in the above documents and publications are incorporated herein by reference.

[0084] In one embodiment, the retardation layer (optical functional layer) 30 is a single layer of an alignment cured layer of a liquid crystal compound. When the retardation layer (hereinafter sometimes referred to as the first retardation layer as described above) is composed of a single layer of an alignment cured layer of a liquid crystal compound, its thickness is preferably 0.5 μm to 7 μm, more preferably 1 μm to 5 μm. By using a liquid crystal compound, in-plane retardation equivalent to that of a resin film can be realized with a thickness much thinner than that of a resin film.

[0085] Typically, the first retardation layer shows a refractive index characteristic relationship of nx > ny = nz. The first retardation layer is typically provided to impart antireflection characteristics to a polarizing plate, and when the first retardation layer is a single layer of an alignment cured layer, it can function as a λ / 4 plate. In this case, the in-plane retardation Re(550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and still 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 not impairing the effects of the present invention, ny > nz or ny < nz may occur.

[0086] The Nz coefficient of the first retardation layer is preferably 0.9 to 1.5, more 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.

[0087] The first 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 first 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.

[0088] The angle θ between the slow axis of the first phase difference layer and the absorption axis of the polarizer 10 is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°. If the angle θ is within this range, by making the first phase difference layer a λ / 4 plate as described above, a polarizer with a phase difference layer having excellent circular polarization characteristics (and consequently, excellent anti-reflective properties) can be obtained.

[0089] In another embodiment, the first phase difference layer may have a laminated structure of a first orientation solidification layer and a second orientation solidification layer. In this case, either the first orientation solidification layer or the second orientation solidification layer may function as a λ / 4 plate and the other as a λ / 2 plate. Therefore, the thicknesses of the first orientation solidification layer and the second orientation solidification layer may be adjusted to obtain a desired in-plane phase difference between the λ / 4 plate and the λ / 2 plate. For example, when the first orientation solidification layer functions as a λ / 2 plate and the second orientation solidification layer functions as a λ / 4 plate, the thickness of the first orientation solidification layer is, for example, 2.0 μm to 3.0 μm, and the thickness of the second orientation solidification layer is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane phase difference Re(550) of the first orientation solidification layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm. The in-plane phase difference Re(550) of the second orientation solidification layer is as described above with respect to a single-layer orientation solidification layer. The angle between the slow axis of the first orientation solidification layer and the absorption axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably about 15°. The angle between the slow axis of the second orientation solidification layer and the absorption axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably about 75°. With such a configuration, it is possible to obtain characteristics close to ideal inverse wavelength dispersion characteristics, and as a result, very excellent anti-reflective properties can be realized. The liquid crystal compounds constituting the first and second orientation-solidified layers, the methods for forming the first and second orientation-solidified layers, and their optical properties are as described above with respect to a single-layer orientation-solidified layer.

[0090] D-3. Second phase difference layer The second phase difference layer may be a so-called positive C plate, as described above, whose refractive index characteristics exhibit the relationship nz>nx=ny. By using a positive C plate as the second phase difference layer, reflection in oblique directions can be effectively prevented, and the anti-reflective function can be widened to a wider viewing angle. The second phase difference layer is preferably provided when the first phase difference layer is a single layer of orientation solidification layer. The phase difference Rth(550) in the thickness direction of the second phase difference layer is preferably -50nm to -300nm, more preferably -70nm to -250nm, even more preferably -90nm to -200nm, and particularly preferably -100nm to -180nm. Here, "nx=ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the second phase difference layer may be less than 10nm.

[0091] A second phase difference layer having the refractive index characteristic nz>nx=ny can be formed from any suitable material. Preferably, the second phase difference layer consists of a film containing a liquid crystal material fixed to a homeotropic orientation. The liquid crystal material (liquid crystal compound) that can be homeotropically oriented may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the phase difference layer are described in paragraphs

[0020] to

[0028] of Japanese Patent Application Publication No. 2002-333642. In this case, the thickness of the second phase difference 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.

[0092] E. Conductive layer or isotropic substrate with conductive layer The conductive layer can be formed by depositing a metal oxide film on any suitable substrate using any appropriate film deposition method (e.g., vacuum deposition, sputtering, CVD, ion plating, spraying, etc.). Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among these, indium-tin composite oxide (ITO) is preferred.

[0093] When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, and more preferably 35 nm or less. The thickness of the conductive layer is preferably 10 nm or more.

[0094] The conductive layer may be transferred from the substrate to the optical functional layer (or, if present, the second phase difference layer) and used alone as a constituent layer of a polarizing plate with a phase difference layer, or it may be laminated to the optical functional layer (or, if present, the second phase difference layer) as a laminate with the substrate (substrate with conductive layer). Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used as a polarizing plate as an isotropic substrate with a conductive layer.

[0095] Any suitable isotropic substrate can be used as the optically isotropic substrate (isotropic substrate). Examples of materials that constitute the isotropic substrate include materials whose main backbone is a resin that does not have a conjugated system, such as norbornene resin or olefin resin, and materials that have cyclic structures such as lactone rings or glutarimide rings in the main chain of an acrylic resin. When such materials are used, the occurrence of phase difference due to the orientation of molecular chains can be suppressed to a small extent when an isotropic substrate is formed. The thickness of the isotropic substrate is preferably 50 μm or less, and more preferably 35 μm or less. The thickness of the isotropic substrate is, for example, 20 μm or more.

[0096] The conductive layer and / or the conductive layer of the isotropic substrate with the conductive layer may be patterned as needed. Patterning can create conductive and insulating portions. As a result, electrodes can be formed. These electrodes can function as touch sensor electrodes that detect contact with a touch panel. Any suitable patterning method can be used. Specific examples of patterning methods include wet etching and screen printing.

[0097] F. Method for manufacturing polarizing plates F-1. Method for manufacturing polarizers The method for manufacturing a polarizer described in Section B above involves forming a laminate on one side of a long thermoplastic resin substrate by creating a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halogenated compound and a polyvinyl alcohol-based resin (PVA-based resin), and then subjecting the laminate to the following treatments in this order: air-assisted stretching, dyeing, underwater stretching, and drying shrinkage treatment, in which the laminate shrinks by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. The halogenated compound content 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 heated roll, and the temperature of the heated roll is preferably 60°C to 120°C. By such a manufacturing method, a polarizer as described above can be obtained. In particular, by fabricating a laminate containing a PVA-based resin layer containing a halide, performing multi-stage stretching of the laminate including aerial assisted stretching and underwater stretching, and heating the stretched laminate with a heated roll, it is possible to obtain a polarizer with excellent optical properties (typically, single-element transmittance and polarization degree) and suppressed variations in optical properties. Specifically, by using a heated roll in the drying shrinkage process, the laminate can be uniformly shrunk throughout the entire laminate while being transported. This not only improves the optical properties of the obtained polarizer, but also enables the stable production of polarizers with excellent optical properties and suppresses variations in the optical properties of the polarizer (especially single-element transmittance). The following describes the halide and the drying shrinkage process. Details of other manufacturing methods are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0098] F-1-1. Halides A PVA-based resin layer containing a halide and a PVA-based resin can be formed by applying a coating solution containing the halide and PVA-based resin onto a thermoplastic resin substrate and drying the coating film. The coating solution is typically a solution obtained by dissolving the halide and the PVA-based resin 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 individually or in combination of two or more. 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 solvent. Such a resin concentration allows for the formation of a uniform coating film that adheres closely to the thermoplastic resin substrate.

[0099] Any suitable halide can be used as the halide. Examples include iodide and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

[0100] The amount of halogen in the coating solution is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, per 100 parts by weight of the PVA resin. If the amount of halogen is too high, the halogen may bleed out, and the resulting polarizer may become cloudy.

[0101] Generally, stretching a PVA-based resin layer increases the orientation of polyvinyl alcohol molecules within the PVA-based resin. However, immersing the stretched PVA-based resin layer in a water-containing liquid can disrupt the orientation of the polyvinyl alcohol molecules, potentially reducing their degree of orientation. This tendency to decrease orientation is particularly pronounced when stretching a laminate of a thermoplastic resin substrate and a PVA-based resin layer in boric acid water. For example, while stretching a PVA film alone in boric acid water is typically performed at 60°C, stretching a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a higher temperature of around 70°C. In this case, the orientation of the PVA in the initial stages of stretching may decrease before it increases due to water stretching. In contrast, by fabricating a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and performing high-temperature stretching (auxiliary stretching) in air before stretching the laminate in boric acid water, the 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 disorder 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 polarizers obtained through processing steps that involve immersing the laminate in a liquid, such as dyeing and water stretching.

[0102] F-1-2. Drying shrinkage treatment The drying shrinkage treatment may be performed by zone heating, which involves heating the entire zone, or by heating the conveying rolls (using so-called heated rolls) (heated roll drying method). Preferably, both methods are used. By drying using heated rolls, heat curling of the laminate can be efficiently suppressed, and polarizers with excellent appearance can be manufactured. Specifically, by drying the laminate while it is aligned with the heated rolls, the crystallization of the thermoplastic resin substrate can be efficiently promoted, increasing the degree of crystallinity, and even at relatively low drying temperatures, the degree of crystallinity of the thermoplastic resin substrate can be increased well. As a result, the rigidity of the thermoplastic resin substrate increases, making it able to withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Furthermore, by using heated rolls, the laminate can be dried while maintaining a flat state, so not only curling but also wrinkles can be suppressed. 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 PVA and PVA / iodine complex can be effectively increased. The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rolls, the laminate can be continuously shrunk in the width direction while being transported, thereby achieving high productivity.

[0103] Figure 3 is a schematic diagram showing an example of a drying shrinkage process. In the drying shrinkage process, 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 to continuously heat the PVA resin layer surface and the thermoplastic resin substrate surface alternately, but for example, the transport rolls R1 to R6 may be arranged to continuously heat only one side of the laminate 200 (for example, the thermoplastic resin substrate surface).

[0104] Drying conditions can be controlled by adjusting the heating temperature of the conveying rolls (temperature of the heating rolls), the number of heating rolls, and the contact time with the heating rolls. The heating roll temperature is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. This effectively increases the crystallinity of the thermoplastic resin, effectively suppresses curling, and produces an optical laminate with extremely high durability. The heating roll temperature can be measured using a contact thermometer. In the illustrated example, six conveying rolls are provided, but there are no particular restrictions on the number of conveying rolls as long as there are multiples. Typically, 2 to 40 conveying rolls are provided, preferably 4 to 30. The contact time between the laminate and the heating rolls (total contact time) is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0105] The heating rolls may be installed inside a heating furnace (e.g., an oven) or in a normal production line (at room temperature). Preferably, they are installed inside a heating furnace equipped with a blowing mechanism. By using heating roll drying in combination with hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature for hot air drying is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m / s to 30 m / s. This wind speed is the wind speed inside the heating furnace and can be measured with a mini-vane type digital anemometer.

[0106] Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. Typically, the above washing treatment is carried out by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0107] In this way, a laminate of thermoplastic resin substrate / polarizer can be obtained.

[0108] F-2. Method for manufacturing polarizing plates The protective layer can be formed by any suitable method. For example, a protective layer can be formed by applying a composition containing an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton, and a photocationic polymerization initiator to the surface of the laminate obtained in item F-1 above (e.g., the polarizer surface), forming a coating film, and then irradiating the coating film with light (e.g., ultraviolet light).

[0109] Any suitable solvent capable of dissolving or uniformly dispersing the epoxy resin (typically an epoxy resin having a biphenyl skeleton) and the curing agent can be used as the solvent in the above composition. Specific examples of solvents include ethyl acetate, toluene, methylethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

[0110] When the protective layer is a photocationically cured product, the epoxy resin concentration in the solution is preferably 10 to 30 parts by weight per 100 parts by weight of solvent. With such a resin concentration, a uniform coating film that adheres closely to the polarizer can be formed. The curing agent content is as described in section C above.

[0111] 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, a protective layer is directly formed on the polarizer by curing the coating film, for example, by light irradiation. Preferably, the solution is applied to the polarizer and a protective layer is directly formed on the polarizer. With this configuration, the adhesive layer or tack layer required for transfer can be omitted, so the polarizer can be made even thinner. 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 (comma coating, etc.).

[0112] When curing a coated film by light irradiation, the coated film can be irradiated with light (typically ultraviolet light) using any suitable light source to achieve any appropriate irradiation dose. Examples of ultraviolet light sources 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 can be, for example, 2 mJ / cm². 2 ~3000 mJ / cm 2 Preferably 10 mJ / cm² 2 ~2000 mJ / cm 2 Specifically, when using a high-pressure mercury lamp as the light source, the irradiation dose is typically 5 mJ / cm². 2 ~3000 mJ / cm 2 Preferably 50 mJ / cm² 2 ~2000 mJ / cm 2 The procedure is carried out under these conditions. When an electrodeless lamp is used as the light source, the irradiation dose is typically 2 mJ / cm². 2 ~2000 mJ / cm 2 Preferably 10 mJ / cm² 2 ~1000 mJ / cm 2 It will be carried out under these conditions.

[0113] 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 coated surface, the coating thickness, and other conditions. The irradiation time is usually several seconds to tens of seconds, and may even be as short as a fraction of a second. Light irradiation can be performed from any appropriate direction. To prevent uneven curing, it is preferable to irradiate from the coated surface side of the protective layer forming composition.

[0114] After exposure to light, such as ultraviolet irradiation, a heat treatment may be further applied to complete the photo-reaction curing. The heat treatment can be performed at any appropriate temperature and time. The heating temperature is, for example, 80°C to 250°C, preferably 100°C to 150°C. The heating time is, for example, 10 seconds to 2 hours, preferably 5 minutes to 1 hour.

[0115] In one embodiment, a protective layer can be formed by applying a composition containing epoxy resin to the surface of the laminate obtained in section F-1 (for example, the polarizer surface) to form a coating film, and then solidifying the coating film. When the protective layer is the solidified product of the coating film, the epoxy resin concentration in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of solvent. With such a resin concentration, a uniform coating film that adheres closely to the polarizer can be formed.

[0116] The solution may be applied to any suitable substrate or to the polarizer. When the solution is applied to a substrate, the solidified coating film formed on the substrate is transferred to the polarizer. When the solution is applied to the polarizer, a protective layer is directly formed on the polarizer by drying (solidifying) the coating film. Preferably, the solution is applied to the polarizer, and a protective layer is directly formed on the polarizer. With this configuration, the adhesive layer or tack layer required for transfer can be omitted, so the polarizer can be made even thinner. Any suitable method can be used to apply the solution. Specific examples include the roll coating method, spin coating method, wire bar coating method, dip coating method, die coating method, curtain coating method, spray coating method, and knife coating method (comma coating method, etc.).

[0117] By drying (solidifying) the solution coating film, a protective layer, which is a solidified coating film, can be formed. The drying temperature is preferably 100°C or lower, and more preferably 50°C to 70°C. A drying temperature within this range can prevent adverse effects on the polarizer. The drying time can vary depending on the drying temperature. For example, the drying time may be 1 to 10 minutes.

[0118] As described above, a protective layer is formed, and as a result, a laminate of thermoplastic resin substrate / polarizer / protective layer can be obtained. By peeling the thermoplastic resin substrate from this laminate, a polarizing plate having a polarizer 10 and a protective layer 20 as shown in Figure 1 can be obtained. Alternatively, a resin film constituting another protective layer may be bonded 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 having yet another protective layer can be obtained.

[0119] G. Method for manufacturing polarizing plates with optical functional layer A polarizing plate with an optical functional layer can be manufactured by any suitable method. For example, it can be manufactured by preparing a polarizing plate by the method described in item F above, and then laminating or transferring any suitable optical functional layer onto the polarizer side of the polarizing plate. The optical functional layer may be laminated onto the polarizer via any suitable adhesive layer, or it may be formed directly onto the polarizer. [Examples]

[0120] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0121] (1) Softening temperature of the protective layer Local thermal analysis (nano-TA measurement) was performed on the protective layer surface of the polarizers and polarizers with optical functional layers obtained in the examples and comparative examples, and the softening temperature of the protective layer was calculated. The measurement apparatus and measurement conditions are as follows. Measurement device: Hitachi High-Tech Science Co., Ltd., product name "AFM5300E / / Nano-TA2" Measurement mode: Contact mode Probe: AN2-200 Measurement area: 8 μm² (scan) Measurement atmosphere: Atmospheric pressure

[0122] (2) Amount of iodine adsorbed A protective layer (thickness: approximately 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 example and comparative example. The resulting PET film with the protective layer was measured to 1 cm × 1 cm (1 cm 2 The sample was cut out and collected in a headspace vial (20 mL capacity). Next, a screw-cap vial (1.5 mL capacity) containing 1 mL of iodine solution (iodine concentration 1 wt%, potassium iodide concentration 7 wt%) was placed in the headspace vial and sealed tightly. The headspace vial was then placed in a 65°C drying oven and heated for 6 hours (this allows gaseous I2 to be adsorbed onto the sample). After that, the sample was collected on a ceramic boat and burned using an automatic sample combustion device, and the generated gas was collected in 10 mL of absorption solution. After collection, this absorption solution was prepared to 15 mL with pure water, and IC quantitative analysis was performed on the undiluted solution or the solution diluted as appropriate. Since the amount of iodine adsorbed when the same measurement was performed on PET film alone was almost 0, the amount of iodine adsorbed (wt%) was calculated from the following formula based on the weight of iodine obtained from the 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 (weight %) = Weight of iodine obtained by IC quantitative analysis / Weight of protective layer alone × 100 Furthermore, the measuring device and measurement conditions are as follows: [Measuring device] Automatic sample combustion device: Mitsubishi Chemical Analytech Co., Ltd., "AQF-2100H" IC (Anion): Thermo Fisher Scientific, "ICS-3000"

[0123] (3) Transmittance and polarization of a single unit From the optically functional layered polarizer plates obtained in the examples and comparative examples, test pieces (50 mm × 50 mm) were cut out with two sides perpendicular to the absorption axis direction of the polarizer and two sides facing the absorption axis direction, respectively. The test pieces were bonded to an alkali-free glass plate with adhesive so that the protective layer was on the outside to form a test sample. The single-element transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) of the test sample were measured using a UV-Vis spectrophotometer (JASCO Corporation, product name "V7100"), and the degree of polarization (P) was calculated using the following formula. At this time, the measurement light was incident from the protective layer side. Polarization degree (P)(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 Note that the above Ts, Tp, and Tc are Y values ​​measured using a 2-degree field of view (C light source) according to JIS Z 8701, and corrected for luminous efficiency. Furthermore, Ts and P are essentially polarizer characteristics. Next, the polarizing plate with the optical functional layer was heated and humidified in an oven at 85°C and 85%RH for 48 hours (heating test), and the transmittance Ts0 before the heating test and the transmittance Ts0 after the heating test were obtained. 48 Therefore, the change in single-component transmittance ΔTs was calculated using the following formula. ΔTs(%)=Ts 48 -Ts0 Similarly, the degree of polarization P0 before the heating test and the degree of polarization P after the heating test 48 Therefore, the change in polarization degree ΔP was calculated using the following formula. ΔP(%)=P 48 -P0 For the heating test, test pieces (50 mm x 50 mm) were cut from the optical functional layer polarizer plates obtained in the examples and comparative examples, with two sides perpendicular to the absorption axis direction of the polarizer and two sides facing the absorption axis direction. The test pieces were then bonded to an alkali-free glass plate with adhesive so that the protective layer was on the outside to create the test samples. The obtained ΔTs and ΔP results were evaluated according to the following criteria. Good: ΔTs less than 2.0%, ΔP between -1.0% and 0% Acceptable: ΔTs is between 2.0% and less than 5.0%, and ΔP is between -3.0% and less than -1.0%. Defective: ΔTs is 5.0% or higher, ΔP is less than -3.0%, or discoloration occurs.

[0124] (4) Bending test The optical functional layer polarizers obtained in the examples and comparative examples were cut to a size of 30 mm (perpendicular to the absorption axis direction of the polarizer) × 120 mm (along the absorption axis direction) to be used as measurement samples. These measurement samples were subjected to continuous bending tests using a no-load U-shaped stretch mode continuous bending test apparatus (Yuasa System Equipment Co., Ltd., product name "DLDMLH-FS"). The bending speed was 60 rpm, the bending amplitude was 20 mm, the bending radius was 0.5 mm, and the number of bending cycles was 50,000. Bending was performed by gripping the longitudinal end of the measurement sample and sliding the gripping part so that the optical functional layer or phase difference layer of the measurement sample was facing inward. The following criteria were used for evaluation. Good: No cracks appeared after 50,000 folds. Defect: Cracks and / or creases appear in any of the components after fewer than 50,000 bends. Furthermore, when cracks occurred in the measurement sample, these cracks were along a direction perpendicular to the absorption axis (the width direction of the measurement sample).

[0125] <Example 1> 1. Fabrication of a polarizer / resin substrate laminate As the resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) in a long length, with a water absorption rate of 0.75% and a Tg of approximately 75°C was used. One side of the resin substrate was subjected to 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 (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "Gosephymer Z410") in a 9:1 ratio. A PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60°C to form a 13 μm thick PVA-based resin layer, thereby creating a laminate. The resulting laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130°C (air-assisted stretching). Next, the laminate was immersed for 30 seconds in an insolubilization bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) (insolubilization treatment). Next, the polarizers were immersed for 60 seconds in a staining bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) while adjusting the concentration so that the final transmittance (Ts) of the polarizers obtained was 41.5% ± 0.1% (staining treatment). Next, the material was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) (crosslinking treatment). Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to achieve a total stretch ratio of 5.5 times (underwater stretching treatment). Subsequently, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (washing treatment). Subsequently, the laminate was dried in an oven maintained at 90°C while being brought into contact with a SUS (stainless steel) heated roll with a surface temperature 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 manner, a polarizer with a thickness of 5 μm was formed on a resin substrate, and a polarizer / resin substrate laminate was fabricated. The transmittance of the polarizer (initial transmittance) Ts0 was 42.0%, and the degree of polarization (initial degree of polarization) P0 was 99.996%.

[0126] 2. Preparation of the first oriented solidified layer and the second oriented solidified layer constituting the phase difference layer A liquid crystal composition (coating solution) was prepared by dissolving 10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (BASF: trade name "Paliocolor LC242", represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (BASF: trade name "Irgacure 907") in 40 g of toluene. [ka] The surface of a polyethylene terephthalate (PET) film (38 μm thick) was rubbed using a rubbing cloth to perform an orientation treatment. The orientation direction was set so that, when bonded to a polarizing plate, it was at a 15° angle to the direction of the polarizer's absorption axis as viewed from the viewing side. The liquid crystal coating solution was applied to this orientation-treated surface using a bar coater and heated and dried at 90°C for 2 minutes to orient the liquid crystal compound. The liquid crystal layer thus formed was subjected to a 100 mJ / cm³ treatment using a metal halide lamp. 2 A liquid crystal alignment solidified layer A was formed on a PET film by irradiating it with light and curing the liquid crystal layer. The thickness of the liquid crystal alignment solidified layer A was 2.5 μm, and the in-plane phase difference Re(550) was 270 nm. Furthermore, the liquid crystal alignment solidified layer A exhibited refractive index characteristics of nx>ny=nz. A liquid crystal alignment solidification layer B was formed on a PET film in the same manner as described above, except that the coating thickness was changed and the orientation direction was set to 75° from the viewing side relative to the direction of the polarizer's absorption axis. The thickness of the liquid crystal alignment solidification layer B was 1.3 μm, and the in-plane phase difference Re(550) was 140 nm. Furthermore, the liquid crystal alignment solidification layer B exhibited refractive index characteristics of nx>ny=nz.

[0127] 3. Fabrication of polarizing plates with phase difference layer The liquid crystal alignment solidification layer A and liquid crystal alignment solidification layer B obtained in 2. above were transferred in that order to the polarizer surface of the polarizer / resin substrate laminate obtained in 1. above. At this time, the transfer (lamination) was performed so that the angle between the absorption axis of the polarizer and the slow axis of alignment solidification layer A was 15°, and the angle between the absorption axis of the polarizer and the slow axis of alignment solidification layer B was 75°. Each transfer (lamination) was performed via an ultraviolet-curing adhesive (thickness 1.0 μm). Subsequently, an adhesive substrate was bonded to the surface of alignment solidification layer B for reinforcement. Next, the resin substrate was peeled off to obtain a polarizer with a phase difference layer having the configuration of polarizer / adhesive layer / phase difference layer (first alignment solidification layer / adhesive layer / second alignment solidification layer) / adhesive substrate.

[0128] 4. Preparation of the protective layer Fifteen parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) YX4000) were dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the obtained epoxy resin solution, 1.2 parts of a photocationic polymerization initiator (manufactured by Sunapro, trade name: CPI(registered trademark)-100P) were added to obtain a protective layer forming composition. The obtained protective layer forming composition was applied to the polarizer surface of the polarizer plate with a phase difference layer obtained above using a wire bar, and the coated film was dried at 60°C for 3 minutes. Then, an integrated light intensity of 600 mJ / cm² was measured using a high-pressure mercury lamp. 2 A protective layer was formed by irradiating with ultraviolet light to achieve the desired result. The thickness of the protective layer was 3 μm. Finally, the substrate with the adhesive layer was peeled off to obtain a polarizing plate with an optical functional layer (protective layer (photocationic cured epoxy resin layer) / polarizer / phase difference layer). The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the evaluation described above. The results are shown in Table 1.

[0129] [Example 2] A polarizing plate (protective layer (cured epoxy resin layer) / polarizer / protective layer (COP film)) was fabricated in the same manner as in Example 1, except that a cycloolefin resin (COP) film (thickness 13 μm) was used as a protective layer instead of a phase difference layer as the optical functional layer. The total thickness of the polarizing plate was 22 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0130] [Example 3] A polarizing plate (protective layer (cured epoxy resin layer) / polarizer) was prepared in the same manner as in Example 1, except that a protective layer-forming composition was applied to the polarizer of the polarizer / resin substrate laminate obtained in 1 above. The total thickness of the polarizing plate was 8 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0131] [Example 4] Fifteen parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) YX4000) and ten parts by weight of an oxetane resin (manufactured by Toagosei Co., Ltd., trade name: Aronoxetane(registered trademark) OXT-221) were dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. Two parts of a photocationic polymerization initiator (manufactured by Sunapro Co., Ltd., trade name: CPI(registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. A polarizing plate with an optical functional layer (protective layer (photocationic cured epoxy resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 1, except that the protective layer forming composition was obtained using this epoxy resin solution. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0132] [Example 5] A polarizing plate with an optical functional layer (protective layer (cured epoxy resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 1, except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) 828) was used instead of an epoxy resin having a biphenyl skeleton. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0133] [Example 6] A polarizing plate with an optical functional layer (protective layer (photocationic cured epoxy resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 4, except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) 828) was used instead of an epoxy resin having a biphenyl skeleton. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0134] [Example 7] A polarizing plate with an optical functional layer (protective layer (cured epoxy resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 1, except that a hydrogenated bisphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) YX8000) was used instead of an epoxy resin having a biphenyl skeleton. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0135] [Example 8] A polarizing plate with an optical functional layer (protective layer (cured epoxy resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 4, except that a hydrogenated bisphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) YX8000) was used instead of an epoxy resin having a biphenyl skeleton. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0136] [Example 9] A polarizing plate equipped with an optical functional layer was prepared in the same manner as in Example 1, except that the protective layer was prepared as described below. 20 parts of epoxy resin 1 (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) 1256B40, weight-average molecular weight: 40000, epoxy equivalent: 7350) were dissolved in 80 parts of methyl ethyl ketone to obtain an epoxy resin solution (20%). This epoxy resin solution was applied to the polarizer surface of the polarizing plate with a phase difference layer used in Example 1 (polarizer / adhesive layer / phase difference layer / substrate with adhesive for reinforcement) using a wire bar, and the coated film was dried at 60°C for 3 minutes to form a protective layer composed of solidified coated film. The thickness of the protective layer was 3 μm. In this way, a polarizing plate equipped with an optical functional layer (protective layer (solidified layer of epoxy resin coating) / polarizer / phase difference layer) was obtained. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0137] [Example 10] A protective layer was formed in the same manner as in Example 9, except that epoxy resin 2 (manufactured by Mitsubishi Chemical Corporation, trade name: jER(registered trademark) YX6954BH30, weight-average molecular weight: 36000, epoxy equivalent: 13000) was used instead of epoxy resin 1. The thickness of the protective layer was 3 μm. A polarizing plate with an optical functional layer (protective layer (solidified layer of epoxy resin coating) / polarizer / phase difference layer) was obtained in the same manner as in Example 9, except that this protective layer was used. The total thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0138] (Comparative Example 1) After peeling off the resin substrate and before applying the protective layer-forming composition, a polyurethane-based water-dispersible resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Superflex SF210) was applied to the polarizer to a thickness of 0.1 μm to form an easily adhesive layer. Separately, instead of an acrylic resin that is a polymethyl methacrylate having lactone ring units, 20 parts of an acrylic resin that is a copolymer of methyl methacrylate / ethyl acrylate (molar ratio 55 / 45) (manufactured by Kusumoto Kasei Co., Ltd., product name "B-722") were dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). Next, this acrylic resin solution was applied to the polarizer surface of the polarizer plate obtained in Example 1 using a wire bar, and the coating film was dried at 60°C for 5 minutes to form a protective layer composed of the solidified coating film. In addition, a polarizer plate with an optical functional layer (protective layer (solidified acrylic resin layer) / polarizer / phase difference layer) was obtained in the same manner as in Example 1. The thickness of the polarizer plate was 14 μm. The obtained polarizing plates were subjected to the same evaluation as in Example 1. The results are shown in Table 1. Note that ΔTs and ΔP could not be measured because the polarizing plates had lost their color after the humidification test.

[0139] (Comparative Example 2) A polarizing plate with an optical functional layer having a protective layer was obtained in the same manner as in Comparative Example 1, except that an acrylic resin copolymer of methyl methacrylate / butyl methacrylate (molar ratio 35 / 65) (manufactured by Kusumoto Chemical Co., Ltd., product name "B-734") was used instead of an acrylic resin copolymer of methyl methacrylate / ethyl acrylate (molar ratio 55 / 45). The thickness of the polarizing plate was 14 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Note that ΔTs and ΔP could not be measured because the polarizing plate had lost its color after the humidification test.

[0140] (Comparative Example 3) A protective layer (solidified coating film) was formed in the same manner as in Example 1, except that a water-based polyester resin (manufactured by Mitsubishi Chemical Corporation, product name: Nichigo Polyester WR905) was used. A polarizing plate with a phase difference layer was prepared in the same manner as in Example 1, except that this protective layer was used. The thickness of the polarizing plate was 14 μm. Note that ΔTs and ΔP could not be measured because the polarizing plate had lost its color after the humidification test. The results are shown in Table 1.

[0141] (Comparative Example 4) A protective layer (solidified coating film) was formed in the same manner as in Example 1, except that a water-based polyurethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "Superflex SF210") was used. A polarizing plate with a phase difference layer was prepared in the same manner as in Example 1, except that this protective layer was used. Note that ΔTs and ΔP could not be measured because the polarizing plate had lost its color after the humidification test. The results are shown in Table 1.

[0142] (Comparative Example 5) An acrylic film (refractive index: 1.50, thickness: 20 μm) with an easy-adhesion treatment on one side was bonded to the polarizer surface via an ultraviolet-curing adhesive. Specifically, the curing adhesive was applied to a total thickness of 1.0 μm and bonded using a roll press. Then, UV light was irradiated from the acrylic film side to cure the adhesive. A polarizing plate with a phase difference layer was fabricated in the same manner as in Example 1, except that a protective layer was laminated in this way. The thickness of the polarizing plate was 31 μm. The obtained polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0143] (Comparative Example 6) A polarizing plate with a phase difference layer was fabricated in the same manner as in Comparative Example 5, except that the thickness of the acrylic film was changed to 40 μm. The thickness of the polarizing plate was 51 μm. The obtained polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0144] [Table 1]

[0145] <Rating> As is clear from Table 1, the polarizing plates obtained in the examples, despite being very thin, showed excellent durability and suppressed degradation of optical properties even under heated and humidified environments. Furthermore, they also exhibited excellent flexibility, demonstrating a balance between excellent durability and flexibility. [Industrial applicability]

[0146] 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, laptops, and photocopiers; household electrical appliances such as video cameras, televisions, and microwave ovens; in-vehicle equipment such as backup monitors, car navigation system monitors, and car audio systems; display equipment such as digital signage and information monitors for commercial stores; security equipment such as surveillance monitors; and nursing and medical equipment such as nursing monitors and medical monitors. [Explanation of Symbols]

[0147] 10 Polarizers 20 protective layer 30 Optical functional layer 100 polarizing plates 110 Polarizing plate with optical functional layer

Claims

1. A polarizer comprising a polyvinyl alcohol-based resin layer stained with iodine, and a protective layer with a thickness of 10 μm or less disposed on one side of the polarizer, The protective layer is composed of a photocationically cured epoxy resin having an aromatic skeleton, or a solidified coating film of an organic solvent solution of an epoxy resin having an aromatic ring in its molecular structure. The protective layer is a blend of epoxy resin having an aromatic skeleton and other resins, or contains 50% by weight or more of epoxy resin having an aromatic skeleton as a resin component. A polarizing plate with a total thickness of 20 μm or less.

2. The polarizing plate according to claim 1, wherein the protective layer is a photocationic cured product of an epoxy resin having the aromatic skeleton, and the protective layer further comprises an oxetane resin.

3. The polarizing plate according to claim 1 or 2, wherein the thickness of the polarizer is 10 μm or less.

4. The polarizing plate according to any one of claims 1 to 3, wherein the epoxy resin having an aromatic skeleton is an epoxy resin having a biphenyl skeleton.

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