TWI876029B - Polarizing plate and polarizing plate with phase difference layer - Google Patents

Abstract

The present invention provides a polarizing plate which is very thin but has excellent durability. The polarizing plate of the present invention has a polarizing element and a protective layer arranged on one side of the polarizing element. The protective layer is made of a cured product of an epoxy resin having a biphenyl skeleton. In one embodiment, the thickness of the protective layer is less than 10 μm.

Description

Polarizing plate and polarizing plate with phase difference layer

The present invention relates to a polarizing plate and a polarizing plate with a phase difference layer.

In image display devices (such as liquid crystal display devices and organic EL display devices), due to the way the image is formed, a polarizing plate is usually arranged on at least one side of the display unit. In recent years, with the thinning and flexibility of image display devices, there is also a strong demand for thinning polarizing plates. However, the thinner the polarizing plate is, the more obvious the durability problem of reduced optical properties in a heated and humidified environment becomes. Prior art literature Patent literature

Patent document 1: Japanese Patent Publication No. 2015-210474

Problems to be solved by the invention The present invention is made to solve the above-mentioned previous problems. Its main purpose is to provide a polarizing plate and a polarizing plate with a phase difference layer that are very thin but have excellent durability.

Means for solving the problem The polarizing plate of the present invention has a polarizing element and a protective layer disposed on one side of the polarizing element. The protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. In one embodiment, the cured product is a cationic polymerization cured product. In one embodiment, the protective layer further comprises an oxycyclobutane resin. In one embodiment, the thickness of the protective layer is less than 10µm. In one embodiment, the iodine adsorption amount of the protective layer is less than 10% by weight. In one embodiment, the softening temperature of the protective layer is above 100°C. In one embodiment, the total thickness of the polarizing plate is less than 10µm. Another aspect of the present invention is to provide a polarizing plate with a phase difference layer. The polarizing plate with a phase difference layer has a phase difference layer on the surface of the polarizing plate that is not provided with the protective layer.

Effect of the invention According to the present invention, by forming the protective layer disposed on the polarizer with a cured product of an epoxy resin having a biphenyl skeleton, a polarizing plate having excellent durability even though it is very thin can be obtained.

(Definition of terms and symbols) The definitions of terms and symbols in this manual are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the in-plane refractive index reaches the maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis (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 at 23°C with light of wavelength λnm. For example, "Re(550)" is the in-plane phase difference measured at 23°C with light of wavelength 550nm. Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of wavelength 550nm. Rth(λ) can be calculated by the formula: Rth(λ)=(nx-nz)×d when the layer (film) thickness is d(nm). (4) Nz coefficient The Nz coefficient can be calculated by Nz=Rth/Re. (5) Angle When an angle is mentioned in this manual, the angle includes both the clockwise direction and the counterclockwise direction relative to the reference direction. Therefore, for example, "45°" means ±45°.

A. Overview of polarizing plate FIG1 is a schematic cross-sectional view of a polarizing plate of an embodiment of the present invention. The polarizing plate 100 of the illustrated example has a polarizing element 10 and a protective layer 20 disposed on one side of the polarizing element 10. The thickness of the polarizing element 10 is preferably 8µm or less. Another protective layer (not shown) may be disposed on the side of the polarizing element 10 opposite to the protective layer 20 as required. When the polarizing plate 100 is applied to a liquid crystal display device, it may be disposed on the visual side of the display unit or on the side opposite to the visual side (back side). In either case, the protective layer 20 may be disposed on the side of the display unit or on the side opposite to the display unit (outer side). In one embodiment, the polarizing plate 100 is disposed on the visual side of the display unit (in other words, the image display device), and the protective layer 20 is disposed on the visual side (the side opposite to the display unit). The polarizing plate can be in the form of a strip or a thin sheet. When the polarizing plate is in the form of a strip, it is preferably rolled into a roll to make a polarizing plate roll.

Typically, the polarizing plate has an adhesive layer as the outermost layer on one side (typically, the side of the polarizer 10 opposite to the protective layer 20), and can be attached to the display unit. A surface protection film and/or a carrier film can be temporarily attached to the polarizing plate in a removable manner as required to reinforce and/or support the polarizing plate. When the polarizing plate includes an adhesive layer, a separation member is temporarily attached to the surface of the adhesive layer in a removable manner to protect the adhesive layer before actual use, and the polarizing plate can be rolled up.

In the embodiment of the present invention, the protective layer 20 is composed of a cured epoxy resin having a biphenyl skeleton. As long as it is composed as described above, the protective layer can be made very thin (for example, made to be less than 10µm). Moreover, the protective layer can be formed directly on the polarizer (that is, not through a bonding agent layer or an adhesive layer). According to the embodiment of the present invention, as described above, the polarizer and the protective layer are very thin and the bonding agent layer or the adhesive layer can be omitted, so the total thickness of the polarizer can be made extremely thin. And the adhesion between the polarizer and the protective layer is also good. The total thickness of the polarizer is, for example, less than 40µm, preferably less than 30µm, more preferably less than 20µm, more preferably less than 10µm, and especially preferably less than 7µm. The total thickness of the polarizing plate can be, for example, greater than 4 μm.

Furthermore, by forming the protective layer with a cured product of an epoxy resin having a biphenyl skeleton, a polarizing plate that is extremely thin but has excellent durability can be realized. Specifically, a polarizing plate in which the degradation of optical characteristics is suppressed even in a heated and humidified environment can be realized. After the above-mentioned polarizing plate was placed in an environment of 85°C and 85% RH for 120 hours, the change ΔTs of the single transmittance Ts and the change ΔP of the polarization degree P were each very small. The single transmittance Ts is measured using, for example, an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The polarization degree P is calculated using the following formula from the single transmittance (Ts), parallel transmittance (Tp) and orthogonal transmittance (Tc) measured using an ultraviolet-visible spectrophotometer. Polarization degree (P) (%) = {(Tp-Tc)/(Tp+Tc)} ^{1 /2} × 100 In addition, the above Ts, Tp and Tc are measured with a 2-degree field of view (C light source) of JIS Z 8701 and the Y value obtained by performing a visual sensitivity correction. In addition, Ts and P are actually the characteristics of the polarizer. ΔTs and ΔP can be obtained by the following formulas. ΔTs (%) = Ts ₁₂₀ - Ts ₀ ΔP (%) = P ₁₂₀ - P ₀ Here, Ts ₀ is the single body transmittance before placement (initial), Ts ₁₂₀ is the single body transmittance after placement, P ₀ is the polarization degree before placement (initial), and P ₁₂₀ is the polarization degree after placement. ΔTs is preferably less than 3.0%, more preferably less than 2.7%, and more preferably less than 2.4%. ΔP should preferably be -0.5%~0%, more preferably -0.3%~0%, and even more preferably -0.1%~0%.

In the embodiment 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. Preferably, the image display device has a curved shape (essentially a curved display screen), and/or can be bent or folded. Specific examples of image display devices include liquid crystal display devices, electroluminescent (EL) display devices (such as organic EL display devices, inorganic EL display devices). Of course, the above description does not prevent the polarizing plate of the present invention from being applied to general image display devices.

The following is a detailed description of the polarizer and protective layer.

B. Polarizer Any suitable polarizer can be used as the polarizer. Polarizers can be typically made using a laminate of two or more layers. The manufacturing method of polarizers is described in item D after the manufacturing method of polarizing plates.

The thickness of the polarizer should be 1µm~8µm, preferably 1µm~7µm, and even more preferably 2µm~5µm.

The boric acid content of the polarizer is preferably 10% by weight or more, more preferably 13% by weight to 25% by weight. As long as the boric acid content of the polarizer is within the above range, the curling during the adjustment of the bonding can be well maintained by the multiplication effect with the iodine content described later, and the curling during heating can be well suppressed, and the appearance durability during heating can be improved. The boric acid content can be calculated by the neutralization method using the following formula based on the amount of boric acid contained per unit weight of the polarizer. [Mathematical formula 1]

The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% by weight to 10% by weight. As long as the iodine content of the polarizer is within the above range, the iodine content can be multiplied with the above-mentioned boric acid content to maintain the ease of adjusting the curling during bonding and to suppress the curling during heating, while improving the durability of the appearance during heating. The "iodine content" in this specification refers to the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine exists in the polarizer in the form of iodine ions ( ^I- ), iodine molecules ( _I2 ), polyiodine ions ( _I3- ^, _I5- ⁾ , etc., and the iodine content in this specification refers to the amount of iodine including all such forms. The iodine content can be calculated using, for example, the calibration curve method of X-ray fluorescence analysis. In addition, polyiodine ions exist in the polarizer in the state of forming a PVA-iodine complex. By forming the complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ion (PVA・I ₃ ^- ) has an absorption peak near 470nm, and the complex of PVA and pentaiodide ion (PVA・I ₅ ^- ) has an absorption peak near 600nm. As a result, polyiodine ions can absorb light in a wide range of visible light depending on their morphology. On the other hand, iodine ion (I ^- ) has an absorption peak near 230nm, which is substantially unrelated to the absorption of visible light. Therefore, polyiodine ions that exist in the state of a complex with PVA are mainly related to the absorption performance of the polarizer.

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

C. Protective layer As mentioned above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. By including an epoxy resin having a biphenyl skeleton in the protective layer, the durability of the protective layer can be further improved. The protective layer is preferably a cationic polymerization cured product of an epoxy resin having a biphenyl skeleton. By using a cationic polymerization cured product, a polarizing plate with excellent durability can be obtained even though it is very thin. The following is a specific description of the components of the protective layer, followed by a description of the characteristics of the protective layer.

C-1. Epoxy resin having a biphenyl skeleton In one embodiment, the epoxy resin having a biphenyl skeleton includes an epoxy resin having the following structure. The epoxy resin having a biphenyl skeleton may be used alone or in combination of two or more. [Chemical Formula 1] (wherein, R ¹ to R ⁸ independently represent a hydrogen atom, a linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element).

R ¹ to R ⁸ each independently represent a hydrogen atom, a linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element. Examples of the linear or branched substituted or unsubstituted alkyl group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, dibutyl, tertiary butyl, n-pentyl, isopentyl, neopentyl, tertiary pentyl, cyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, methylcyclohexyl, n-octyl, cyclooctyl, n-nonyl, 3,3,5-trimethylcyclohexyl, n-decyl, cyclodecyl, n-undecyl, n-dodecyl, cyclododecyl, phenyl, benzyl, methylbenzyl, dimethylbenzyl, trimethylbenzyl, naphthylmethyl, phenethyl, 2-phenylisopropyl, and the like. The linear or branched substituted or unsubstituted alkyl group with 1 to 12 carbon atoms is preferably an alkyl group with 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, or n-butyl. The halogen element may be fluorine or bromine.

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula. [Chemical Formula 2] (wherein, R ¹ to R ⁸ are as described above, and n represents an integer of 0 to 6).

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

In one embodiment, the epoxy resin having a biphenyl skeleton may also contain a chemical structure 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, etc. In this embodiment, the ratio (molar ratio) of the chemical structure other than the biphenyl skeleton is preferably less than that of the biphenyl skeleton.

Commercially available epoxy resins having a biphenyl skeleton may also be used, such as those manufactured by Mitsubishi Chemical Co., under the trade names of jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, and jER YL7399.

The glass transition temperature (Tg) of the epoxy resin having a biphenyl skeleton is preferably above 100°C. As a result, the softening temperature of the protective layer is almost above 100°C. As long as the Tg of the epoxy resin having a biphenyl skeleton is above 100°C, the polarizing plate including the obtained protective layer can easily become one with excellent durability. The Tg of the epoxy resin having a biphenyl skeleton is preferably above 110°C, more preferably above 120°C, and more preferably above 125°C. On the other hand, the Tg of the epoxy resin having a biphenyl skeleton is preferably below 300°C, more preferably below 250°C, more preferably below 200°C, and particularly preferably below 160°C. As long as the Tg of the epoxy resin having a biphenyl skeleton is within the above range, the formability and processability are excellent.

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 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 more preferably 2000 g/equivalent or less. By having the epoxy equivalent of the biphenyl skeleton in the above range, a more stable protective layer (a protective layer with less residual monomers and fully cured) can be obtained. In addition, in this specification, "epoxy equivalent" means "the mass of the epoxy resin containing 1 equivalent of epoxy group", which can be measured in accordance with JIS K7236.

In the embodiment of the present invention, epoxy resins having a biphenyl skeleton may be used in combination with other resins. That is, blends of epoxy resins having a biphenyl skeleton and other resins may be used for forming the protective layer. Other resins include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene ether, polyacetal, polyimide, polyetherimide, and acrylic resins and curing resins such as cyclohexane resins. Preferably, acrylic resins and cyclohexane resins can be used. The type and amount of the resin to be used in combination can be appropriately set according to the purpose and the desired properties of the resulting film. For example, a styrene resin can be used in combination as a phase difference control agent.

Any appropriate acrylic resin can be used as the acrylic resin. For example, the (meth)acrylic compound may include a (meth)acrylic compound having one (meth)acrylic group in the molecule (hereinafter also referred to as a "monofunctional (meth)acrylic compound"), and a (meth)acrylic compound having two or more (meth)acrylic groups in the molecule (hereinafter also referred to as a "multifunctional (meth)acrylic compound"). Such (meth)acrylic compounds may be used alone or in combination of two or more. Such acrylic resins are described, for example, in Japanese Patent Publication No. 2019-168500. The entire disclosure of the publication is cited in this specification for reference.

Any appropriate compound having one or more cyclohexyl groups in the molecule can be used as the cyclohexyloxybutane resin. Examples of the cyclohexyloxybutane resin include 3-ethyl-3-hydroxymethylcyclohexyloxybutane, 3-ethyl-3-(2-ethylhexyloxymethyl)cyclohexyloxybutane, 3-ethyl-3-(phenoxymethyl)cyclohexyloxybutane, 3-ethyl-3-(cyclohexyloxymethyl)cyclohexyloxybutane, 3-ethyl-3-(oxiranylmethoxy)cyclohexyloxybutane, and (meth)acrylate (3-ethylcyclohexyl-3-yl)methyl ester. Oxycyclobutane compounds having one oxycyclobutane group; 3-ethyl-3{[(3-ethyloxycyclobutane-3-yl)methoxy]methyl}oxycyclobutane, 1,4-bis[(3-ethyl-3-oxycyclobutane)methoxymethyl]benzene, 4,4'-bis[(3-ethyl-3-oxycyclobutane)methoxymethyl]biphenyl, and the like having two or more oxycyclobutane groups in the molecule. Such oxycyclobutane resins may be used alone or in combination of two or more.

Preferred examples include 3-ethyl-3-hydroxymethylcyclohexane, 1,4-bis[(3-ethyl-3-cyclohexane)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)cyclohexane, 3-ethyl-3-(oxiranylmethoxy)cyclohexane, (meth)acrylate (3-ethylcyclohexane-3-yl)methyl ester, and 3-ethyl-3{[(3-ethylcyclohexane-3-yl)methoxy]methyl}cyclohexane. These cyclohexane resins are easily available and have good diluting properties (low viscosity) and compatibility.

In one embodiment, from the viewpoint of compatibility or adhesion, it is preferable to use an oxycyclobutane resin having a molecular weight of 500 or less and being liquid at room temperature (25°C). In one embodiment, it is preferable to use an oxycyclobutane compound containing two or more oxycyclobutane groups in the molecule, or an oxycyclobutane compound containing one oxycyclobutane group and one (meth)acryloyl group or one epoxy group in the molecule, and preferably, 3-ethyl-3{[(3-ethyloxycyclobutane-3-yl)methoxy]methyl}oxycyclobutane, 3-ethyl-3-(oxiranylmethoxy)oxycyclobutane, and (3-ethyloxycyclobutane-3-yl)methyl (meth)acrylate. By using these cyclobutane oxychloride resins, the hardening property and durability of the protective layer can be improved.

Commercially available oxycyclobutane resins may be used. Specifically, ARON OXETANE OXT-101, ARON OXETANE OXT-121, ARON OXETANE OXT-212, and ARON OXETANE OXT-221 (all manufactured by Toagosei Co., Ltd.) may be used. Preferably, ARON OXETANE OXT-101 and ARON OXETANE OXT-221 may be used.

When the epoxy resin having a biphenyl skeleton is used together with other resins, the content of the epoxy resin having a biphenyl skeleton in the blend of the epoxy resin having a biphenyl skeleton and other resins is preferably 50 wt% to 100 wt%, more preferably 60 wt% to 100 wt%, more preferably 70 wt% to 100 wt%, and particularly preferably 80 wt% to 100 wt%. When the content is less than 50 wt%, the heat resistance of the protective layer and the sufficient adhesion with the polarizer may not be obtained.

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

C-2. Hardener The epoxy resin having a biphenyl skeleton can be used together with any appropriate hardener to form a hardened product. The hardener can be any appropriate hardener that can harden the epoxy resin. In one embodiment, the hardener includes a photo-cationic polymerization initiator. By including the photo-cationic polymerization initiator, a cationic polymerization hardened product, i.e., a protective layer, can be formed. The photo-cationic polymerization initiator can be any appropriate compound that can harden the epoxy resin having a biphenyl skeleton by irradiation with light such as ultraviolet rays. The photo-cationic polymerization initiator can be used alone or in combination of two or more.

Examples of the photocatalytic polymerization initiator include triphenylcopperium hexafluoroantimonylate, triphenylcopperium hexafluorophosphate, p-(phenylthio)phenyldiphenylcopperium hexafluoroantimonylate, p-(phenylthio)phenyldiphenylcopperium hexafluorophosphate, 4-chlorophenyldiphenylcopperium hexafluorophosphate, 4-chlorophenyldiphenylcopperium hexafluoroantimonylate, bis[4-(diphenylcopperium)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylcopperium)phenyl]sulfide bishexafluoroantimonylate, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonylate. It is preferable to use a triphenylsiron salt type hexafluoroanticorrosive acid salt type photocatalytic polymerization initiator or a diphenyliodonium salt type hexafluoroanticorrosive acid salt type photocatalytic polymerization initiator.

Commercially available photocatalytic polymerization initiators may be used. Examples of commercially available initiators include triphenylphosphine salt-based hexafluoroanticorrosive type SP-170 (manufactured by ADEKA), CPI-101A (manufactured by SAN-APRO), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), and diphenyliodonium salt-based hexafluoroanticorrosive type WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.).

The content of the photocatalytic polymerization initiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, relative to 100 parts by weight of the epoxy resin having a biphenyl skeleton. When the content of the photocatalytic polymerization initiator is less than 0.1 parts by weight, there is a case where the curing is not sufficient even after irradiation with light (ultraviolet rays).

C-3. Composition and characteristics of the protective layer As described above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. As long as it is the cured product, its thickness can be much thinner than the extruded film. The thickness of the protective layer is preferably 10µm or less, preferably 7µm or less, more preferably 5µm or less, and particularly preferably 3µm or less. The thickness of the protective layer can be, for example, 1µm or more. Compared with the cured product of a water-based coating film such as an aqueous solution or a water dispersion, the cured product of an epoxy resin having a biphenyl skeleton has lower moisture absorption and moisture permeability, and therefore has the advantage of excellent humidification durability. As a result, a polarizing plate with excellent durability that can maintain optical properties even in a heated and humidified environment can be achieved. In addition, the cured product of the epoxy resin having a biphenyl skeleton, i.e. the protective layer, has excellent adhesion to the polarizer. Therefore, even with the above-mentioned thickness, the polarizer can be protected to the same extent as the protective layer using the conventional film. Moreover, even with the above-mentioned thickness, the polarizer can be prevented from fading and other adverse conditions.

The softening temperature of the protective layer is preferably 100°C or higher. As long as the softening temperature of the protective layer is 100°C or higher, the polarizing plate including the obtained protective layer is likely to have excellent durability. The softening temperature of the protective layer is preferably 110°C or higher, more preferably 120°C or higher, and 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, more preferably 200°C or lower, and particularly preferably 160°C or lower. As long as the softening point of the protective layer is within the above range, the formability and processability are excellent.

The iodine adsorption amount of the protective layer is preferably less than 10% by weight, more preferably less than 6.0% by weight, more preferably less than 3.0% by weight, and particularly preferably less than 2.0% by weight. The smaller the iodine adsorption amount, the better. As long as the iodine adsorption amount is within the above range, a polarizing plate with better durability can be obtained. The iodine adsorption amount can be measured by the following method. The protective layer forming composition is applied to the substrate (PET film) with a sprinkler to form a protective layer (thickness of about 3µm). The obtained PET film with a protective layer is cut into 1cm×1cm ( ^1cm2 ) to make a sample, and is taken into a headspace vial (20mL capacity) and weighed. Next, a screw-capped bottle (1.5 mL capacity) containing 1 mL of iodine solution (iodine concentration 1 wt%, potassium iodide concentration 7 wt%) is also placed in the headspace vial and capped. Afterwards, the headspace vial is placed in a 65°C dryer and heated for 6 hours. This allows _I2 in a gaseous state to be adsorbed on the sample. Afterwards, the sample is taken into a ceramic boat and burned using an automatic sample combustion device, and the generated gas is collected into 10 mL of absorption liquid. After collection, the absorption liquid is adjusted to 15 mL with pure water, and IC quantitative analysis is performed on the original solution or the appropriately diluted liquid. In addition, the iodine adsorption amount is almost 0 when the same measurement is performed only on PET film. Based on the weight of iodine obtained by IC quantitative analysis and the weight of the protective layer monomer ("weight of the PET film with protective layer" - "weight of the PET film"), the iodine adsorption amount (weight %) is calculated from the following formula. Iodine adsorption amount (weight %) = weight of iodine obtained by IC quantitative analysis / weight of the protective layer monomer × 100 The following measuring devices can be used for analysis, for example. [Measuring device] Automatic sample combustion device: "AQF-2100H" manufactured by Mitsubishi Chemical Analytech IC (anion): "ICS-3000" manufactured by Thermo Fisher Scientific

The protective layer is preferably substantially optically isotropic. In this specification, "substantially optically isotropic" means that the phase difference at a wavelength of 550nm is -50nm~+50nm. The in-plane phase difference Re(550) is preferably -30nm~+30nm, more preferably -10nm~+10nm, and particularly preferably 0nm~2nm. The phase difference Rth(550) in the thickness direction is preferably -5nm~5nm, more preferably -3nm~3nm, and particularly preferably -2nm~2nm. As long as the Re(550) and Rth(550) of the protective layer are within the above range, when the polarizing plate including the protective layer is used in an image display device, it can prevent adverse effects on the display characteristics. In addition, Re(550) is the in-plane phase difference of the film measured at 23°C with light of a wavelength of 550nm. Re(550) can be calculated by the formula: Re(550)=(nx-ny)×d. Rth(550) is the phase difference in the thickness direction of the film measured at 23°C with light of a wavelength of 550nm. Rth(550) can be calculated by the formula: Rth(550)=(nx-nz)×d. Here, nx is the refractive index in the direction where the in-plane refractive index reaches the 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), nz is the refractive index in the thickness direction, and d is the thickness of the film (nm).

The higher the light transmittance of the protective layer at 380 nm when the thickness is 3 μm, the better. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, and more preferably 90% or more. As long as the light transmittance is within the above range, the desired transparency can be ensured. The light transmittance can be measured, for example, according to the method of ASTM-D-1003.

The lower the haze of the protective layer, the better. Specifically, the haze is preferably below 5%, more preferably below 3%, more preferably below 1.5%, and most preferably below 1%. If the haze is below 5%, the film can be given a good sense of transparency. Moreover, even when used as a side polarizer for visual identification of an image display device, the display content can still be well identified.

When the protective layer has a thickness of 3µm, the YI should be less than 1.27, preferably less than 1.25, more preferably less than 1.23, and particularly preferably less than 1.20. When the YI is greater than 1.3, the optical transparency is insufficient. In addition, the YI can be obtained from the color tristimulus values (X, Y, Z) measured using a high-speed integrating sphere spectroscopic transmittance meter (trade name DOT-3C: manufactured by Murakami Color Technology Laboratory) using the following formula. YI=[(1.28X-1.06Z)/Y]×100

The b value (in accordance with the hue scale of the Hunter colorimetric system) of the protective layer at a thickness of 3µm is preferably less than 1.5, and preferably less than 1.0. When the b value is greater than 1.5, an undesirable color tone may appear. In addition, the b value can be obtained, for example, in the following manner: a sample of the film constituting the protective layer is cut into 3 cm squares, the hue is measured using a high-speed integrating sphere spectroscopic transmittance meter (trade name DOT-3C: manufactured by Murakami Color Technology Laboratory), and the hue is evaluated in accordance with the Hunter colorimetric system.

The protective layer (cured material of epoxy resin with biphenyl skeleton) may contain any appropriate additives according to the purpose. Specific examples of additives include: ultraviolet absorber; leveler; hindered phenol, phosphorus, sulfur and other antioxidants; light stabilizer, weather stabilizer, heat stabilizer and other stabilizers; glass fiber, carbon fiber and other reinforcing materials; near infrared absorber; tris(dibromopropyl) phosphate, triallyl phosphate Flame retardants such as esters and antimony oxide; antistatic agents such as anionic, cationic, and non-ionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers or inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants, etc. Additives are usually added to the solution when the protective layer is formed. The type, amount, combination, and addition amount of additives can be appropriately set according to the purpose.

An easy-to-bond layer may also be formed on the polarizer side of the protective layer. The easy-to-bond layer, for example, includes a water-based polyurethane and an oxazoline-based crosslinking agent. By forming the easy-to-bond layer, the adhesion between the protective layer and the polarizer can be improved. The easy-to-bond layer can be laminated with the polarizer using any appropriate method. For example, it can also be formed directly on the polarizer, or it can be laminated through any appropriate adhesive layer or adhesive layer. In addition, a hard coating layer may also be formed on the protective layer. The hard coating layer can be formed when the protective layer is used as a protective layer on the visual side of the visual side polarizing plate. When both the easy-adhesion layer and the hard coating layer are formed, they can be formed on different sides of the protective layer.

D. Manufacturing method of polarizing plate D-1. Manufacturing method of polarizing element The manufacturing method of polarizing element described in item B above comprises the following steps: forming a polyvinyl alcohol resin layer (PVA resin layer) comprising a halogenated substance and a polyvinyl alcohol resin (PVA resin) on one side of a long strip of thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment and drying shrinkage treatment, wherein the drying shrinkage treatment is to heat the laminate while conveying the laminate in the longitudinal direction, thereby shrinking the laminate in the width direction by more than 2%. The halogen content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying and shrinking treatment is preferably carried out using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. According to the manufacturing method, a polarizer as described above can be obtained. In particular, after a laminate comprising a halogenated PVA-based resin layer is prepared, the laminate is stretched by a multi-stage stretching including air-assisted stretching and underwater stretching, and the stretched laminate is then heated by a heating roller, thereby obtaining a polarizer having excellent optical properties (represented by single body transmittance and polarization degree) and suppressed optical property variations. Specifically, by using a heated roller in the drying and shrinking step, the laminate can be uniformly shrunk while being transported. This not only improves the optical properties of the resulting polarizer, but also stably produces polarizers with excellent optical properties, and suppresses the variation of the optical properties of the polarizer (especially the single-body transmittance). The following describes the halides and the drying and shrinking treatment. The details of the manufacturing methods other than these are described in, for example, Japanese Patent Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire description of the publication is cited in this specification as a reference.

D-1-1. Halogenated substances The PVA resin layer containing halogenated substances and PVA resins can be formed by applying a coating liquid containing halogenated substances and PVA resins on a thermoplastic resin substrate and drying the coating film. The coating liquid is typically a solution obtained by dissolving the halogenated substances and the PVA resins in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trihydroxymethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The PVA resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film that adheres closely to the thermoplastic resin substrate can be formed.

Any appropriate halides may be used as the halides. Examples thereof include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferred.

The amount of halogen in the coating liquid is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA resin. If the amount of halogen is too much, the halogen may overflow and make the resulting polarizer white and cloudy.

Generally speaking, after the PVA resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA resin layer will become higher, but if the stretched PVA resin layer is immersed in a water-containing liquid, the orientation of the polyvinyl alcohol molecules will be disordered and the orientation will decrease. In particular, when the laminate of the thermoplastic resin substrate and the PVA resin layer is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate, the tendency of the above orientation to decrease is very obvious. For example, the stretching of a PVA film monomer in boric acid water is generally performed at 60°C. In contrast, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a relatively high temperature of around 70°C. At this time, the orientation of the PVA at the beginning of the stretching decreases before it rises by stretching in water. In contrast, by preparing a laminate of a PVA-based resin layer containing a halogenide and a thermoplastic resin substrate, and stretching the laminate at a high temperature in air (auxiliary stretching) 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 resin layer is immersed in a liquid, the orientation disorder and the reduction of orientation of the polyvinyl alcohol molecules can be suppressed more than when the PVA resin layer does not contain halides. As a result, the optical properties of the polarizer obtained by immersing the laminate in a liquid through a dyeing process and an underwater stretching process can be improved.

D-1-2. Drying and shrinking treatment Drying and shrinking treatment can be performed by heating the entire area, or by heating the conveying roller (so-called using a heating roller) (heating roller drying method). It is preferred to use both. By using a heating roller to dry it, the heat curling of the laminate can be effectively suppressed, and a polarizer with excellent appearance can be manufactured. Specifically, by drying the laminate along the state of adding a hot roller, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted to increase the crystallinity. Even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can still be well increased. As a result, the rigidity of the thermoplastic resin substrate increases and becomes a state that can withstand the shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. In addition, by using a heating roller, the laminate can be dried while maintaining a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction through a drying and shrinking treatment to improve the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate in the width direction obtained by the drying and shrinking treatment of the laminate is preferably 2%~10%, more preferably 2%~8%, and particularly preferably 4%~6%. By using heated rollers, the laminate can be continuously shrunk in the width direction while being transported, achieving high productivity.

FIG2 is a schematic diagram showing an example of a drying and shrinking process. In the drying and shrinking process, the laminate 200 is dried while being transported by conveying rollers R1 to R6 and guide rollers G1 to G4 that have been heated to a predetermined temperature. In the example of the figure, the conveying rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but, for example, the conveying rollers R1 to R6 may also be arranged to continuously heat only one surface of the laminate 200 (e.g., the surface of the thermoplastic resin substrate).

The drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, and the contact time with the heating roller. The temperature of the heating roller is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. While the crystallinity of the thermoplastic resin can be increased and the curling can be suppressed, an optical laminate with excellent durability can be produced. In addition, the temperature of the heating roller can be measured by a contact thermometer. In the example of the figure, 6 conveyor rollers are provided, but there is no particular limitation as long as there are plural conveyor rollers. The number of conveyor rollers is usually 2 to 40, and it is preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven) or in a general manufacturing line (at room temperature). It is best to install it in a heating furnace equipped with an air supply mechanism. By using the heating roller for drying and hot air drying simultaneously, the rapid temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. In addition, the hot air drying time should be 1 second~300 seconds. The wind speed of the hot air should be around 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured by a mini fan-type digital anemometer.

It is preferred to perform a cleaning treatment after the water stretching treatment and before the drying shrinkage treatment. The cleaning treatment can be performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

According to the above method, a thermoplastic resin substrate/polarizer laminate can be obtained.

D-2. Method for manufacturing polarizing plate A composition comprising an epoxy resin having a biphenyl skeleton and a curing agent can be applied on the surface of the laminate obtained in item D-1 above (e.g., the surface of a polarizer) to form a coating film, and the coating film is cured to form a protective layer. In one embodiment, the protective layer is a cation polymerization curing material. In this embodiment, a photocation polymerization initiator can be used as a curing agent. A composition comprising an epoxy resin having a biphenyl skeleton and a photocation polymerization initiator can be applied on the surface of a laminate (e.g., the surface of a polarizer) to form a coating film, and then the coating film is irradiated with light (e.g., ultraviolet rays) to form a protective layer.

The solvent contained in the above composition can be any appropriate solvent that can dissolve or uniformly disperse the epoxy resin having a biphenyl skeleton and the hardener. Specific examples of the solvent include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

The epoxy resin concentration of the solution is preferably 10 to 30 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film that adheres closely to the polarizer can be formed. In addition, the content of the hardener is as described in the above item C.

The solution can be applied to any appropriate substrate or to a polarizer. When the solution is applied to the substrate, the cured coating formed on the substrate is transferred to the polarizer. When the solution is applied to the polarizer, the coating is cured by, for example, light irradiation, thereby forming a protective layer directly on the polarizer. It is preferred that the solution is applied to the polarizer and a protective layer is formed directly on the polarizer. As long as the structure is as described above, the adhesive layer or the adhesive layer required for transfer can be omitted, so the polarizer can be made thinner. The solution can be applied by any appropriate method. Specific examples include roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, scraper coating (corner wheel coating, etc.).

When curing the coating film by light irradiation, the coating film may be irradiated with light (typically ultraviolet light) using any appropriate light source in any appropriate irradiation amount. Examples of ultraviolet light sources include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, electrodeless lamps, halogen lamps, carbon arc lamps, xenon lamps, metal halogen lamps, chemical lamps, black light lamps, LED lamps, etc. The irradiation amount of ultraviolet light is, for example, 2mJ/ ^cm2 to 3000mJ/ ^cm2 , preferably 10mJ/ ^cm2 to 2000mJ/ ^cm2 . Specifically, when using a high-pressure mercury lamp as the light source, the irradiation dose is usually 5mJ/ ^cm2 ~3000mJ/ ^cm2 , preferably 50mJ/ ^cm2 ~2000mJ/ ^cm2 . When using an electrodeless lamp as the light source, the irradiation dose is usually 2mJ/ ^cm2 ~2000mJ/ ^cm2 , preferably 10mJ/ ^cm2 ~1000mJ/ ^cm2 .

The irradiation time can be set to any appropriate value according to the type of light source, the distance between the light source and the coating surface, the coating thickness and other conditions. The irradiation time is usually several seconds to several tens of seconds, and can also be a fraction of a second. The light can be irradiated from any appropriate direction. From the perspective of preventing uneven curing, it is preferable to irradiate from the coating surface side of the protective layer forming composition.

After exposure by light irradiation such as ultraviolet irradiation, a heat treatment may be further performed to complete the hardening by the photoreaction. The heat treatment may 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.

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

E. Polarizing plate with phase difference layer E-1. Overview of polarizing plate with phase difference layer In one embodiment of the present invention, a polarizing plate with phase difference layer can be provided. The polarizing plate with phase difference layer further has a phase difference layer on the surface of the above-mentioned polarizing plate that is not provided with a protective layer. FIG. 3 is a schematic cross-sectional view of a polarizing plate with phase difference layer in an embodiment of the present invention. The polarizing plate with phase difference layer 110 in the figure example has: a polarizer 10, a protective layer 20 arranged on one side of the polarizer 10, and a phase difference layer 40 arranged on the other side of the polarizer 10. The polarizer 10 and the protective layer 20 constitute the above-mentioned polarizing plate. Therefore, the polarizing plate with a phase difference layer has a polarizing plate and a phase difference layer, and the polarizing plate includes a polarizer and a protective layer disposed on one side of the polarizer, and the phase difference layer is disposed on the side of the polarizer opposite to the protective layer. The polarizing plate may also include another protective layer (not shown) on the side of the polarizer 10 opposite to the protective layer 20 according to needs. In other words, the polarizing plate with a phase difference layer 110 may also include another protective layer (not shown) between the polarizer 10 and the phase difference layer 40. As mentioned above, an easy-to-bond layer may also be formed on the polarizer side of the protective layer. The easy-to-bond layer may be laminated with the polarizer using any appropriate method. For example, it can be formed directly on the polarizer, or can be laminated through any appropriate adhesive layer or bonding agent layer.

In the embodiment shown in FIG3 , the phase difference layer 40 is a single layer. At this time, Re (550) of the phase difference layer 40 is, for example, 100 nm to 190 nm, and the angle formed by the slow axis of the phase difference layer 40 and the absorption axis of the polarizer 10 is, for example, 40° to 50°. At this time, it is preferred to provide another phase difference layer (not shown) on the outside of the phase difference layer 40 (the side opposite to the polarizer 10). The refractive index characteristics of the other phase difference layer represent the relationship of nz＞nx=ny. Or as shown in FIG4 , in another embodiment of the polarizing plate 111 with a phase difference layer, the phase difference layer 40 has a layered structure of a first layer 41 and a second layer 42. At this time, the Re(550) of the first layer 41 is, for example, 200nm~300nm, and the angle formed by the slow axis of the first layer 41 and the absorption axis of the polarizer 10 is, for example, 10°~20°; the Re(550) of the second layer 42 is, for example, 100nm~190nm, and the angle formed by the slow axis of the second layer 42 and the absorption axis of the polarizer 10 is, for example, 70°~80°. Regardless of the implementation form, the phase difference layer 40 can be a resin film or a directional solidification layer of a liquid crystal compound. When the phase difference layer 40 has a layered structure, it means that the first layer 41 and the second layer 42 are respectively a resin film or a directional solidification layer of a liquid crystal compound.

E-2. Phase difference layer composed of a single layer When the phase difference layer is composed of a single layer, the Re (550) of the phase difference layer is, for example, 100nm~190nm as described above, and the angle formed by the slow axis of the phase difference layer 40 and the absorption axis of the polarizer 10 is, for example, 40°~50°. The phase difference layer is typically provided to give the polarizing plate anti-reflection properties, and in one embodiment, it can function as a λ/4 plate. The phase difference layer can be a resin film as described above, or a directional solidification layer of a liquid crystal compound.

The phase difference layer preferably has a refractive index characteristic showing a relationship of nx>ny≧nz. The in-plane phase difference Re(550) of the phase difference layer is, for example, 100nm~190nm as described above, preferably 110nm~170nm, more preferably 130nm~160nm. In addition, "ny=nz" here includes not only the case where ny and nz are completely the same, but also the case where they are substantially the same. Therefore, there may be a case where ny<nz without damaging the effect of the present invention.

The Nz coefficient of the phase difference layer is preferably 0.9-3, more preferably 0.9-2.5, more preferably 0.9-1.5, and most preferably 0.9-1.3. By satisfying the above relationship, when the obtained polarizing plate with phase difference layer is used in an image display device, a very excellent reflection color can be achieved.

The angle θ formed by the slow axis of the phase difference layer 40 and the absorption axis of the polarizer 10 is, for example, 40° to 50°, preferably 42° to 48°, and more preferably about 45°, as described above. As long as the angle θ is within the above range, by making the phase difference layer into a λ/4 plate, a polarizing plate with a phase difference layer having very excellent circular polarization characteristics (in terms of very excellent anti-reflection characteristics) can be obtained.

The phase difference layer can exhibit an inverse dispersion wavelength characteristic in which the phase difference value increases with the wavelength of the measured light, a positive wavelength dispersion characteristic in which the phase difference value decreases with the wavelength of the measured light, or a flat wavelength dispersion characteristic in which the phase difference value hardly changes with the wavelength of the measured light. In one embodiment, the phase difference layer exhibits an inverse dispersion wavelength characteristic. In this case, Re(450)/Re(550) of the phase difference layer is preferably greater than 0.8 and less than 1, and more preferably greater than 0.8 and less than 0.95. As long as it is the above-mentioned structure, a very excellent anti-reflection property can be achieved.

The phase difference layer includes a resin having an absolute value of a photoelastic coefficient of preferably 2.0×10 ^-11 m ² /N or less, more preferably 2.0×10 ^-13 m ² /N to 1.5×10 ^-11 m ² /N, and more preferably 1.0×10 ^-12 m ² /N to 1.2× ^{10 -11} m ² /N. When the absolute value of the photoelastic coefficient is within the above range, the phase difference is unlikely to change when shrinkage stress is generated during heating. As a result, thermal unevenness of the obtained image display device can be well prevented.

E-2-1. Resin film When the phase difference layer is a resin film, the resin film is typically a stretched film. In this case, the thickness of the phase difference layer is preferably 60µm or less, preferably 30µm to 55µm. As long as the thickness of the phase difference layer is within the above range, the curling during heating can be well suppressed, and the curling during bonding can be well adjusted.

The phase difference layer can be formed of any appropriate resin film that can satisfy the above-mentioned characteristics. Representative examples of the resin include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins can be used alone or in combination (e.g., blending, copolymerization). When the phase difference layer is formed of a resin film showing reverse dispersion wavelength characteristics, a polycarbonate resin or a polyester carbonate resin (hereinafter referred to as a polycarbonate resin) can be appropriately used.

As long as the effects of the present invention can be obtained, any appropriate polycarbonate resin can be used as the polycarbonate resin. For example, the polycarbonate resin includes a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri- or polyethylene glycols, and alkylene glycols or spiroglycerol. The polycarbonate resin preferably includes structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, structural units derived from alicyclic dimethanols, and/or structural units derived from di, tri or polyethylene glycol; more preferably, it includes structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from di, tri or polyethylene glycol. The polycarbonate resin may also include structural units derived from other dihydroxy compounds as needed. In addition, the details of the polycarbonate resin that can be suitably used in the present invention are described in, for example, Japanese Patent Publication No. 2014-10291, Japanese Patent Publication No. 2014-26266, Japanese Patent Publication No. 2015-212816, Japanese Patent Publication No. 2015-212817, and Japanese Patent Publication No. 2015-212818, and this specification cites these descriptions as references.

The glass transition temperature of the polycarbonate resin is preferably 110°C to 150°C, more preferably 120°C to 140°C. If the glass transition temperature is too low, the heat resistance tends to deteriorate, and there is a possibility of causing dimensional changes after film formation, or the image quality of the obtained organic EL panel may be reduced. If the glass transition temperature is too high, the forming stability during film formation may deteriorate, or the transparency of the film may be impaired. In addition, the glass transition temperature can be obtained in accordance with JIS K 7121 (1987).

The molecular weight of the above-mentioned polycarbonate resin can be expressed by concentrated viscosity. The concentrated viscosity is measured by using methylene chloride as a solvent, after the polycarbonate concentration is precisely adjusted to 0.6g/dL, using an Oodel viscometer at a temperature of 20.0℃±0.1℃. The concentrated viscosity is usually preferably above 0.30dL/g, and more preferably above 0.35dL/g. In addition, the reduced viscosity is usually preferably below 1.20dL/g, more preferably below 1.00dL/g, and more preferably below 0.80dL/g. If the concentrated viscosity is less than 0.30dL/g, there is a problem that the mechanical strength of the molded product is reduced. On the other hand, if the relative viscosity is greater than 1.20 dL/g, the fluidity during molding may decrease, which may cause problems in productivity or moldability.

Commercially available polycarbonate resin films may also be used. Specific examples of commercial products include "PURE-ACE WR-S", "PURE-ACE WR-W", and "PURE-ACE WR-M" manufactured by Teijin Co., Ltd. and "NRF" manufactured by Nitto Denko Co., Ltd.

The phase difference layer 40 can be obtained, for example, by stretching a film formed from the above-mentioned polycarbonate resin. The method of forming a film from a polycarbonate resin can adopt any appropriate molding method. Specific examples include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, casting and coating (such as casting), calendering, hot pressing, etc. Extrusion molding or casting and coating is preferred. This is because the smoothness of the obtained film can be improved, thereby obtaining good optical uniformity. The molding conditions can be appropriately set according to the composition or type of the resin used, the desired properties of the phase difference layer, etc. In addition, as mentioned above, many polycarbonate resin films are sold on the market, so the commercially available films can be directly subjected to the stretching treatment.

The thickness of the resin film (unstretched film) can be set to any appropriate value according to the desired thickness of the phase difference layer, the desired optical properties, the stretching conditions described below, etc. It is preferably 50µm to 300µm.

The above-mentioned stretching can adopt any appropriate stretching method and stretching conditions (such as stretching temperature, stretching ratio, stretching direction). Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinkage, fixed end shrinkage, etc. can be used alone, or they can be used simultaneously or successively. Regarding the stretching direction, it can also be carried out along various directions or dimensions such as length direction, width direction, thickness direction, oblique direction, etc. The stretching temperature is preferably Tg-30℃~Tg+60℃ relative to the glass transition temperature (Tg) of the resin film, and preferably Tg-10℃~Tg+50℃.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (such as refractive index properties, in-plane phase difference, Nz coefficient) can be obtained.

In one embodiment, the phase difference film can be produced by uniaxially stretching a resin film or by uniaxially stretching a fixed end. A specific example of uniaxially stretching a fixed end is a method of stretching the resin film in the width direction (lateral direction) while moving the resin film in the long direction. The stretching ratio is preferably 1.1 to 3.5 times.

In another embodiment, the phase difference film can be produced by continuously extending a long strip of resin film obliquely in the direction of the above-mentioned angle θ relative to the long side direction. By adopting the oblique stretching, a long strip of stretched film having an orientation angle of angle θ relative to the long side direction of the film (having a slow axis in the direction of angle θ) can be obtained. For example, when layered with a polarizer, it can be rolled to roll, thereby simplifying the manufacturing steps. In addition, the angle θ can be the angle formed by the absorption axis of the polarizer in the polarizing plate with a phase difference layer and the slow axis of the phase difference layer. As mentioned above, the angle θ is preferably 40°~50°, more preferably 42°~48°, and more preferably about 45°.

The stretching machine used for the oblique stretching may be a tenter-type stretching machine, which is a machine that applies a conveying force or a stretching force or a pulling force at different speeds in the transverse and/or longitudinal directions. The tenter-type stretching machine includes a transverse single-axis stretching machine, a simultaneous double-axis stretching machine, etc. Any appropriate stretching machine may be used as long as it can continuously and obliquely stretch a long strip of resin film.

By appropriately controlling the left and right speeds in the stretching machine, a phase difference layer (substantially a long strip phase difference film) having the desired in-plane phase difference and a slow axis in the desired direction can be obtained.

The stretching temperature of the above film can be changed according to the desired in-plane phase difference value and thickness of the phase difference layer, the type of resin used, the thickness of the film used, the stretching ratio, etc. Specifically, the stretching temperature is preferably Tg-30℃~Tg+30℃, more preferably Tg-15℃~Tg+15℃, and most preferably Tg-10℃~Tg+10℃. By stretching at the above temperature, a phase difference layer having characteristics suitable for the present invention can be obtained. In addition, Tg is the glass transition temperature of the constituent material of the film.

E-2-2. Oriented solidified layer of liquid crystal compound When the phase difference layer is an oriented solidified layer of liquid crystal compound, by using liquid crystal compound, the difference between nx and ny of the obtained phase difference layer can be made much larger than that of non-liquid crystal material, so the thickness of the phase difference layer used to obtain the desired in-plane phase difference can be much smaller. As a result, the polarizing plate with phase difference layer can be further thinned. The so-called "oriented solidified layer" in this specification refers to a layer in which the liquid crystal compound is oriented in a predetermined direction within the layer and its orientation state has been fixed. In addition, the concept of "oriented solidified layer" includes an oriented solidified layer obtained by curing the liquid crystal monomer as described later. In this embodiment, the rod-shaped liquid crystal compound is oriented in the slow axis direction of the phase difference layer (oriented along the plane).

Examples of the liquid crystal compound include liquid crystal compounds having a nematic phase (nematic liquid crystal). Such liquid crystal compounds may be liquid crystal polymers or liquid crystal monomers. The liquid crystal compound may have a lyotropic or thermotropic mechanism of expression of liquid crystallinity. Liquid crystal polymers and liquid crystal monomers may be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer and a cross-linking monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or cross-linking (i.e., hardening) the liquid crystal monomer. After the liquid crystal monomer is oriented, the orientation state can be fixed by, for example, polymerizing or cross-linking the liquid crystal monomers. Here, the polymer is formed by polymerization, and the three-dimensional mesh structure is formed by cross-linking, and these are non-liquid crystal. Therefore, the phase difference layer formed, for example, will not undergo the transformation into a liquid crystal phase, a glass phase, or a crystalline phase due to temperature changes that is unique to liquid crystal compounds. As a result, the phase difference layer will become a phase difference layer that is not affected by temperature changes and has extremely excellent stability.

The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on its 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.

The above-mentioned liquid crystal monomer can be any appropriate liquid crystal monomer. For example, the polymerizable liquid crystal original compound described in Japanese Patent Publication No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171 and GB2280445 can be used. Specific examples of the polymerizable liquid crystal original compound include BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Sillicon-CC3767. The liquid crystal monomer is preferably, for example, a nematic liquid crystal monomer.

The oriented solidified layer of the liquid crystal compound can be formed by the following method: performing an oriented treatment on the surface of a predetermined substrate, and applying a coating liquid containing the liquid crystal compound on the surface, so that the liquid crystal compound is oriented in the direction corresponding to the above-mentioned oriented treatment, and the oriented state is fixed. In one embodiment, the substrate is any appropriate resin film, and the oriented solidified layer formed on the substrate can be transferred to the surface of the polarizer 10. In another embodiment, the substrate can be another protective layer. In this case, the transfer step is omitted, and after the oriented solidified layer (phase difference layer) is formed, the lamination can be carried out in a roll-to-roll manner, thereby further improving productivity.

The above-mentioned orientation treatment can adopt any appropriate orientation treatment. Specifically, mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment can be mentioned. Specific examples of mechanical orientation treatment include friction treatment and stretching treatment. Specific examples of physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of chemical orientation treatment include oblique evaporation method and light orientation treatment. The treatment conditions of various orientation treatments can adopt any appropriate conditions according to the purpose.

The alignment of the liquid crystal compound can be performed by treating the liquid crystal compound at a temperature that can exhibit a liquid crystal phase according to the type of the liquid crystal compound. By performing the temperature treatment, the liquid crystal compound changes to a liquid crystal state, and the liquid crystal compound is aligned according to the alignment treatment direction of the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned in the above manner. When the liquid crystal compound is a polymerizable monomer or a crosslinking monomer, the alignment state is fixed by subjecting the liquid crystal compound aligned in the above manner to a polymerization treatment or a crosslinking treatment.

Specific examples of liquid crystal compounds and details of the method for forming an oriented solidified layer are described in Japanese Patent Application Publication No. 2006-163343, and the contents of the publication are incorporated herein by reference.

Another example of an oriented solidified layer is a discotic liquid crystal compound oriented in any state of vertical orientation, mixed orientation, and tilted orientation. The discotic liquid crystal compound is typically oriented substantially vertically with respect to the film surface of the phase difference layer. The discotic liquid crystal compound being substantially vertical means that the average value of the angle formed by 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°. Discotic liquid crystal compounds generally refer to liquid crystal compounds with a discotic molecular structure, wherein a cyclic mother nucleus such as benzene, 1,3,5-trioxane, calixarene, etc. is arranged at the center of the molecule, and straight-chain alkyl, alkoxy, substituted benzyloxy, etc. are radially substituted on the side chains. Representative examples of discotic liquid crystals include: benzene derivatives, triphenylene derivatives, indenylene derivatives, and phthalocyanine derivatives described in the research report of C. Destrade et al., Mol. Cryst. Liq. Cryst., Vol. 71, p. 111 (1981); cyclohexane derivatives described in the research report of B. Kohne et al., Angew. Chem., Vol. 96, p. 70 (1984); and nitrogen-doped crown ether-based or phenylacetylene-based macrocycles described in the research report of J. M. Lehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985) and in the research report of J. Zhang et al., J. Am. Chem. Soc., Vol. 116, p. 2655 (1994). More specific examples of discotic liquid crystal compounds include compounds described in Japanese Patent Application Publication No. 2006-133652, Japanese Patent Application Publication No. 2007-108732, and Japanese Patent Application Publication No. 2010-244038. The descriptions of the above documents and publications are incorporated herein by reference.

When the phase difference layer is a directional solidified layer of a liquid crystal compound, its thickness is preferably 0.5µm~7µm, more preferably 1µm~5µm. By using a liquid crystal compound, the same in-plane phase difference as the resin film can be achieved with a much thinner thickness than the resin film.

E-2-3. Another phase difference layer As described above, when the phase difference layer is composed of a single layer, it is preferred to set another phase difference layer. As described above, the other phase difference layer can be a so-called positive C-plate whose refractive index characteristics show the relationship of nz＞nx=ny. By using a positive C-plate as another phase difference layer, oblique reflection can be well prevented, and the anti-reflection function can be widened to a wide viewing angle. At this time, the phase difference Rth(550) in the thickness direction of the other phase difference layer is preferably -50nm~-300nm, more preferably -70nm~-250nm, more preferably -90nm~-200nm, and particularly preferably -100nm~-180nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the other phase difference layer can be less than 10nm.

Another phase difference layer having a refractive index characteristic of nz＞nx=ny can be formed of any appropriate material. The other phase difference layer is preferably composed of a film containing a liquid crystal material fixed in a homeotropic alignment. The liquid crystal material (liquid crystal compound) that can achieve homeotropic alignment can be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the method for forming the liquid crystal compound and the phase difference layer include the method for forming the liquid crystal compound and the phase difference layer described in paragraphs [0020] to [0028] of Japanese Patent Gazette No. 2002-333642. At this time, the thickness of the other phase difference layer is preferably 0.5µm~10µm, more preferably 0.5µm~8µm, and more preferably 0.5µm~5µm.

E-3.2-layer phase difference layer When the phase difference layer 40 has a layered structure including a first layer 41 and a second layer 42, either the first layer 41 or the second layer 42 can function as a λ/4 plate, and the other can function as a λ/2 plate. For example, when the first layer 41 functions as a λ/2 plate and the second layer 42 functions as a λ/4 plate, the in-plane phase difference Re(550) of the first layer is, for example, 200nm~300nm as described above, preferably 230nm~290nm, and more preferably 250nm~280nm. The in-plane phase difference Re(550) of the second layer is, for example, 100nm~190nm, preferably 110nm~170nm, and more preferably 130nm~160nm, as described above. The angle formed by the slow axis of the first layer and the absorption axis of the polarizer is, for example, 10°~20°, preferably 12°~18°, and more preferably about 15°, as described above. The angle formed by the slow axis of the second layer and the absorption axis of the polarizer is, for example, 70°~80°, preferably 72°~78°, and more preferably about 75°, as described above. As long as the above-mentioned structure is used, characteristics close to the ideal reverse wavelength dispersion characteristics can be obtained, and as a result, very excellent anti-reflection characteristics can be achieved.

The first layer 41 and the second layer 42 may be either a resin film or a liquid crystal compound oriented solidified layer. Preferably, the first layer 41 and the second layer 42 are both resin films or liquid crystal compound oriented solidified layers.

The thickness of the first layer 41 and the second layer 42 can be adjusted to obtain the desired in-plane phase difference of the λ/4 plate or the λ/2 plate. For example, when the first layer 41 functions as a λ/2 plate and the second layer 42 functions as a λ/4 plate, and the first layer 41 and the second layer 42 are resin films, the thickness of the first layer 41 is, for example, 40µm to 75µm, and the thickness of the second layer 42 is, for example, 30µm to 55µm. When the first layer 41 and the second layer 42 are directional solidification layers of liquid crystal compounds, the thickness of the first layer 41 is, for example, 2.0µm to 3.0µm, and the thickness of the second layer 42 is, for example, 1.0µm to 2.0µm.

The resin films, liquid crystal compounds, methods for forming the first and second layers, optical properties, etc., which constitute the first and second layers, are as described above with respect to the single layer.

Examples The present invention is specifically described below using examples, but the present invention is not limited to these examples. The measurement methods of various properties are as follows. In addition, unless otherwise specified, the "parts" and "%" in the examples are based on weight.

(1) Fading and shrinkage of protective layer A test piece (50 mm × 50 mm) was cut out from the polarizing plate obtained in the embodiment and the comparative example. The test piece formed two sides opposite to the direction perpendicular to the absorption axis of the polarizer and the absorption axis. The protective layer was made to be the inner side, and the test piece was adhered to a glass plate with an adhesive to prepare a test sample. The test sample was placed in an oven at 85°C and 85% RH for 120 hours for heating and humidification. After being arranged in a state of orthogonal polarization with a standard polarizing plate, the fading state of the humidified polarizing plate was visually inspected and evaluated according to the following criteria. In addition, the shrinkage of the protective layer after heating and humidification was also confirmed with the naked eye. No problem: No fading observed Partial fading: Fading observed at the end Overall fading: The polarizing plate as a whole is obviously faded (2) Single transmittance and polarization degree For fading evaluation, single transmittance and polarization degree are measured for those not suffering from overall fading. A test piece (50 mm × 50 mm) is cut out from the polarizing plate obtained in the embodiment and the comparative example. The test piece is formed with two sides opposite to the direction perpendicular to the absorption axis direction of the polarizer and the absorption axis direction. The test piece is made by adhering the test piece to an alkali-free glass plate with the protective layer on the outside using an adhesive, and the single transmittance (Ts), parallel transmittance (Tp) and orthogonal transmittance (Tc) of the test sample are measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), and the polarization degree (P) is calculated using the following formula. At this time, the measured light is incident from the protective layer side. Polarization degree (P) (%) = {(Tp-Tc)/(Tp+Tc)} ^{1 /2} ×100 In addition, the above Ts, Tp and Tc are the Y values obtained by measuring the 2-degree field of vision (C light source) of JIS Z 8701 and performing visual sensitivity correction. In addition, Ts and P are actually the characteristics of the polarizer. Then, the polarizing plate was placed in an oven at 85°C and 85%RH for 120 hours for heating and humidification (heating test). The single transmittance _Ts0 before the heating test and the single transmittance _Ts120 after the heating test were used to calculate the single transmittance change ΔTs using the following formula. ΔTs(%)= _Ts120 - _Ts0 Similarly, the polarization degree _P0 before the heating test and the polarization degree _P120 after the heating test were used to calculate the polarization degree change ΔP using the following formula. ΔP(%)= _P120 - _P0 In addition, the heating test was conducted by preparing the test sample in the same manner as the above-mentioned fading test.

(3) Iodine adsorption amount A protective layer (thickness: about 3µm) was formed on one side of the PET film in the same manner as the protective layer in each of the examples and comparative examples. The obtained PET film with a protective layer was cut into 1cm×1cm ( ^1cm2 ) to prepare a sample, which was taken into a headspace vial (20mL capacity) and weighed. Then, a screw-capped bottle (1.5mL capacity) containing 1mL of iodine solution (iodine concentration 1 wt%, potassium iodide concentration 7 wt%) was also placed in the headspace vial and tightly capped. Thereafter, the headspace vial was placed in a desiccator at 65°C and heated for 6 hours (thereby, _I2 in a gaseous state will be adsorbed on the sample). Afterwards, the sample is taken into a ceramic boat and burned using an automatic sample combustion device, and the generated gas is collected into 10 mL of absorption liquid. After collection, the absorption liquid is adjusted to 15 mL with pure water, and IC quantitative analysis is performed on the original solution or the appropriately diluted liquid. In addition, the iodine adsorption amount after the same measurement is performed on the PET film alone is almost 0, so the iodine adsorption amount (weight %) is calculated from the following formula based on the iodine weight obtained by IC quantitative analysis and the weight of the protective layer monomer ("weight of PET film with protective layer" - "weight of PET film"). Iodine adsorption amount (weight %) = iodine weight obtained by IC quantitative analysis / weight of protective layer monomer × 100 In addition, the measurement device and measurement conditions are as follows. [Measurement equipment] Automatic sample combustion device: Mitsubishi Chemical Analytech, "AQF-2100H" IC (anion): Thermo Fisher Scientific, "ICS-3000"

(4) Softening temperature of protective layer Local thermal analysis (Nano-TA measurement) was performed on the surface of the protective layer of the polarizing plate obtained in the embodiment and the comparative example to calculate the softening temperature of the protective layer. The measuring device and measuring conditions are as follows. Measuring device: manufactured by Hitachi High-Tech Science Co., product name "AFM5300E//Nano-TA2" Measuring mode: contact mode Probe: AN2-200 Measuring area: 8µm□ scanning Measuring gas environment: atmospheric pressure

(5) Evaluation The obtained polarizing plate was evaluated according to the following criteria. Good: ΔP value is 0% to -4.0% Acceptable: ΔP value is greater than -4.0% and -10.0% Poor: ΔP value is greater than -10% and -99.9% (completely discolored)

<Example 1> 1. Preparation of polarizer/resin substrate laminate The resin substrate is a long strip of amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100µm) with a water absorption rate of 0.75% and a Tg of about 75°C. One side of the resin substrate is subjected to a corona treatment. 13 parts by weight of potassium iodide is added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetyl acetyl modified PVA (Mitsubishi Chemical Co., trade name "GOHSEFIMER Z410") in a ratio of 9:1, and a PVA aqueous solution (coating liquid) is prepared. The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13µm, thereby producing a laminate. The obtained laminate was subjected to free-end uniaxial stretching to 2.4 times in the longitudinal direction (long side direction) between rollers of different circumferential speeds in an oven at 130°C (air-assisted stretching treatment). Then, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment). Next, the dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 relative to 100 parts by weight of water) with a liquid temperature of 30°C was adjusted while being immersed in it for 60 seconds so that the monomer transmittance (Ts) of the polarizer finally obtained became 41.5%±0.1% (dyeing treatment). Next, it was immersed in a crosslinking bath (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) with a liquid temperature of 40°C for 30 seconds (crosslinking treatment). Then, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide 5 wt%) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (long side direction) between rollers of different circumferential speeds to a total stretching ratio of 5.5 times (in-water stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment). Thereafter, it was dried in an oven maintained at 90°C while contacting a SUS heating roller maintained at a surface temperature of 75°C for about 2 seconds (drying shrinkage treatment). The shrinkage rate in the width direction obtained by drying and shrinking the laminate is 5.2%. According to the above method, a polarizer with a thickness of 5µm is formed on the resin substrate to produce a polarizer/resin substrate laminate. The single unit transmittance (initial single unit transmittance) Ts0 of the polarizer is 42.0%, and the polarization degree (initial polarization degree) P0 is 99.996%.

2. Preparation of polarizing plate A cycloolefin film (ZT-12, manufactured by Zeon Co., Ltd., Japan, with a thickness of 23µm) is bonded to the surface of the polarizing element obtained above as a film constituting the second protective layer through a UV curing adhesive. Specifically, the curing adhesive is applied to a total thickness of 1.0µm and bonded using a roller. After that, UV rays are irradiated from the film side to cure the adhesive. Then, the resin substrate is peeled off to obtain a polarizing plate having a second protective layer (ZT-12)/polarizing element structure.

3. Preparation of protective layer 15 parts of epoxy resin having a biphenyl skeleton (Mitsubishi Chemical Co., trade name: jER (registered trademark) YX4000) were dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. 1.2 parts of a photocatalytic polymerization initiator (San-Apro Ltd., trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. The obtained protective layer forming composition was applied to the surface of the polarizer of the polarizing plate obtained above with a wire rod, and the coated film was dried at 60°C for 3 minutes. Next, a high-pressure mercury lamp was used to irradiate ultraviolet light at a cumulative light intensity of 600 mJ/ ^cm2 to form a protective layer. The thickness of the protective layer was 2µm to 3µm. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was used for the evaluations of (1) to (4) above.

<Example 2> 15 parts of an epoxy resin having a biphenyl skeleton (Mitsubishi Chemical Co., trade name: jER (registered trademark) YX4000) and 10 parts of an oxycyclobutane resin (Toagosei Co., trade name: ARON OXETANE (registered trademark) OXT-221) were dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. 2 parts of a photocatalytic polymerization initiator (San-Apro Ltd., trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. The epoxy resin solution is used to obtain a protective layer forming composition, and the protective layer is formed in the same manner as in Example 1. The thickness of the protective layer is 2µm~3µm. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) is obtained in the above manner. The obtained polarizing plate is provided for the evaluations of (1)~(4) above.

(Comparative Example 1) A protective layer was formed in the same manner as in Example 1 except that a hydrogenated bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Co., trade name: jER (registered trademark) YX8000) was used instead of an epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2µm to 3µm. A polarizing plate having a structure of a protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example. The results are listed in Table 1.

(Comparative Example 2) Hydrogenated bisphenol-type epoxy resin (Mitsubishi Chemical Co., trade name: jER (registered trademark) YX8000) was used to replace the epoxy resin having a biphenyl skeleton, and the protective layer was formed in the same manner as in Example 2. The thickness of the protective layer was 2µm~3µm. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example. The results are listed in Table 1.

(Comparative Example 3) A bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Co., trade name: jER (registered trademark) 828) was used to replace the epoxy resin having a biphenyl skeleton, and a protective layer was formed in the same manner as in Example 1. The thickness of the protective layer was 2µm to 3µm. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example. The results are listed in Table 1.

(Comparative Example 4) A protective layer was formed in the same manner as in Example 2 except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Co., trade name: jER (registered trademark) 828) was used to replace the epoxy resin having a biphenyl skeleton. The thickness of the protective layer was 2µm to 3µm. A polarizing plate having a structure of a protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example. The results are listed in Table 1.

(Comparative Example 5) 20 parts of polyester resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Nichigo-POLYESTER WR905) were dissolved in 80 parts of pure water to obtain a coating resin solution (20%). The coating resin solution was applied to the surface of the polarizer of the polarizing plate used in the embodiment using a wire rod, and the coating film was dried at 60°C for 5 minutes to form a protective layer composed of a cured product of the coating film. The thickness of the protective layer is 2µm~3µm. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in the embodiment. The results are listed in Table 1.

(Comparative Example 6) Except that urethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: SUPERFLEX 210) was used instead of polyester resin, a polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Comparative Example 5. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

(Comparative Example 7) On the polarizer surface of the polarizing plate having a second protective layer (ZT-12)/polarizer structure, a polyurethane aqueous dispersion resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: SUPERFLEX SF210) was applied to a thickness of 0.1µm as an easy-adhesion layer to form an easy-adhesion layer. In addition, 20 parts of an acrylic resin (manufactured by Kusumoto Chemicals Co., Ltd., product name "B-734") of a copolymer of methyl methacrylate/butyl methacrylate (molar ratio 35/65) was dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). Next, the acrylic resin solution was applied to the easy-to-bond layer using a wire rod, and the coated film was dried at 60°C for 5 minutes to form a protective layer composed of a cured product of the coated film. The thickness of the protective layer was 3µm, the softening temperature was 80.4°C, and the iodine adsorption amount was 30.4% by weight. A polarizing plate having a structure of a protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in the embodiment. The results are listed in Table 1.

(Comparative Example 8) Except for using an acrylic resin of a copolymer of methyl methacrylate/ethyl acrylate (molar ratio 55/45) (manufactured by Kusumoto Chemicals Co., Ltd., product name "B-722"), a protective layer was formed in the same manner as in Comparative Example 8. The thickness of the protective layer was 3µm, the softening temperature was 57.2°C, and the iodine adsorption amount was 1.3% by weight. A polarizing plate having a structure of protective layer/polarizer/another protective layer (ZT-12) was obtained in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Table 1]

<Evaluation> It is clear from Table 1 that the polarizing plate obtained in the embodiment is very thin, and the degradation of optical properties is suppressed in a heated and humidified environment, and the durability is excellent.

Industrial applicability The polarizing plate of the present invention can be used in image display devices. Examples of image display devices include: portable devices such as PDAs, smart phones, mobile phones, clocks, digital cameras, and portable game consoles; OA devices such as computer monitors, laptops, and copiers; home electrical devices such as video cameras, televisions, and microwave ovens; vehicle-mounted devices such as rear-view monitors, car navigation system monitors, and car stereos; display devices such as digital signs and information guide screens for commercial stores; alarm devices such as surveillance screens; nursing and medical devices such as nursing monitors and medical monitors, etc.

10: Polarizer 20: Protective layer 40: Phase difference layer 41: First layer 42: Second layer 100: Polarizer 110,111: Polarizer with phase difference layer 200: Laminated body G1~G4: Guide rollers R1~R6: Transport rollers

FIG. 1 is a schematic cross-sectional view of a polarizing plate of an embodiment of the present invention. FIG. 2 is a schematic view showing an example of a drying and shrinking treatment using a heating roller in a method for manufacturing a polarizing plate of an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a polarizing plate with a phase difference layer of an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a polarizing plate with a phase difference layer of another embodiment of the present invention.

10: Polarizer

20: Protective layer

100: Polarizing plate

Claims (7)

A polarizing plate has a polarizing element and a protective layer disposed on one side of the polarizing element; the protective layer is formed of a hardened material of an epoxy resin having a biphenyl skeleton; the protective layer further comprises an oxycyclobutane resin; relative to a total of 100 parts by weight of the epoxy resin having a biphenyl skeleton and the oxycyclobutane resin, the content of the oxycyclobutane resin is 10 parts by weight to 40 parts by weight. As in claim 1, the polarizing plate, wherein the aforementioned hardened material is a cationic polymerization hardened material. For example, in the polarizing plate of claim 1 or 2, the thickness of the protective layer is less than 10 μm. As in claim 1 or 2, the polarizing plate, wherein the iodine adsorption amount of the aforementioned protective layer is less than 10% by weight. As in claim 1 or 2, the polarizing plate, wherein the softening temperature of the protective layer is above 100°C. For polarizing plates in claim 1 or 2, the total thickness is less than 10μm. A polarizing plate with a phase difference layer comprises a phase difference layer on the surface of the polarizing plate of any one of claims 1 to 6 where the protective layer is not disposed.