WO2021220741A1

WO2021220741A1 - Polarizing plate and polarizing plate with retardation layer

Info

Publication number: WO2021220741A1
Application number: PCT/JP2021/014707
Authority: WO
Inventors: 和哉三輪; 卓史上条; 大介濱本
Original assignee: 日東電工株式会社
Priority date: 2020-04-30
Filing date: 2021-04-07
Publication date: 2021-11-04
Also published as: TW202144818A; KR20230002505A; CN115485592A

Abstract

The present invention provides a polarizing plate having excellent durability despite being extremely thin. A polarizing plate according to the present invention has a polarizer, and a protective layer that is disposed on one side of the polarizer. The protective layer is formed from a cured product of an epoxy resin having a biphenyl skeleton. In one embodiment, the thickness of the protective layer is 10 µm or less.

Description

Polarizing plate and polarizing plate with retardation layer

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

In an image display device (for example, a liquid crystal display device or an organic EL display device), a polarizing plate is often arranged on at least one side of a display cell due to the image forming method. In recent years, image display devices have become thinner and more flexible, and along with this, there is a strong demand for thinner polarizing plates. However, the thinner the polarizing plate, the more remarkable the problem of durability that the optical characteristics in a heating and humidifying environment deteriorate.

JP-A-2015-210474

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a polarizing plate having excellent durability and a polarizing plate with a retardation layer, although it is very thin. be.

The polarizing plate of the present invention has a polarizing element and a protective layer arranged on one side of the polarizing element. This protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton.
In one embodiment, the cured product is a cationically polymerized cured product.
In one embodiment, the protective layer further comprises an oxetane resin.
In one embodiment, the protective layer has a thickness of 10 μm or less.
In one embodiment, the iodine adsorption amount of the protective layer is 10% by weight or less.
In one embodiment, the softening temperature of the protective layer is 100 ° C. or higher.
In one embodiment, the total thickness of the polarizing plate is 10 μm or less.
In another aspect of the present invention, a polarizing plate with a retardation layer is provided. This polarizing plate with a retardation layer has a retardation layer on a surface of the polarizing plate on which the protective layer is not arranged.

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

It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic which shows an example of the drying shrinkage treatment using the heating roll in the manufacturing method of the polarizing plate by one Embodiment of this invention. It is a schematic cross-sectional view of the polarizing plate with a retardation layer according to one Embodiment of this invention. It is a schematic cross-sectional view of the polarizing plate with a retardation layer according to another embodiment of this invention.

(Definition of terms and symbols)
Definitions of terms and symbols herein are as follows.
(1) Refractive index (nx, ny, nz)
“Nx” is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and “ny” is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advance axis direction). Is the refractive index of, and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
“Re (λ)” is an in-plane phase difference measured with light having a wavelength of λ nm at 23 ° C. For example, "Re (550)" is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C. Re (λ) is obtained by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the layer (film).
(3) Phase difference in the thickness direction (Rth)
“Rth (λ)” is a phase difference in the thickness direction measured with light having a wavelength of λ nm at 23 ° C. For example, "Rth (550)" is a phase difference in the thickness direction measured with light having a wavelength of 550 nm at 23 ° C. Rth (λ) is obtained by the formula: Rth (λ) = (nx−nz) × d, where d (nm) is the thickness of the layer (film).
(4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re.
(5) Angle When referring to an angle herein, the angle includes both clockwise and counterclockwise with respect to the reference direction. Therefore, for example, "45 °" means ± 45 °.

A. Schematic FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 of the illustrated example has a polarizing element 10 and a protective layer 20 arranged on one side of the polarizing element 10. The thickness of the polarizer 10 is preferably 8 μm or less. If necessary, another protective layer (not shown) may be provided on the opposite side of the protector 10 from the protective layer 20. When applied to an image display device, the polarizing plate 100 may be arranged on the viewing side of the display cell, or may be arranged on the side opposite to the viewing side (back side). In either case, the protective layer 20 may be arranged on the display cell side or on the opposite side (outside) of the display cell. In one embodiment, the polarizing plate 100 is arranged on the visual side of the display cell (as a result, the image display device), and the protective layer 20 is arranged on the visual side (opposite the display cell). The polarizing plate may be long or single-wafered. When the polarizing plate has a long shape, it is preferably wound into a roll to form a polarizing plate roll.

Typically, the polarizing plate has an adhesive layer as the outermost layer on one side (typically, the side opposite to the protective layer 20 of the polarizer 10), and can be bonded to the display cell. ing. If necessary, a surface protective film and / or a carrier film may be temporarily attached to the polarizing plate so as to reinforce and / or support the polarizing plate. When the polarizing plate contains a pressure-sensitive adhesive layer, a separator is temporarily attached to the surface of the pressure-sensitive adhesive layer so that the pressure-sensitive adhesive layer is protected until actual use, and the polarizing plate can be rolled.

In the embodiment of the present invention, the protective layer 20 is composed of a cured product of an epoxy resin having a biphenyl skeleton. With such a configuration, the protective layer can be made very thin (for example, 10 μm or less). In addition, the protective layer can be formed directly on the polarizer (ie, without the intervention of an adhesive 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 adhesive layer or the adhesive layer can be omitted, so that the total thickness of the polarizing plate can be made extremely thin. can. In addition, the adhesion between the polarizer and the protective layer is also excellent. The total thickness of the polarizing plate is, for example, 40 μm or less, preferably 30 μm or less, more preferably 20 μm or less, further preferably 10 μm or less, and particularly preferably 7 μm or less. The total thickness of the polarizing plate can be, for example, 4 μm or more.

Further, by forming the protective layer with a cured product of an epoxy resin having a biphenyl skeleton, it is possible to realize a polarizing plate having excellent durability even though it is very thin. Specifically, it is possible to realize a polarizing plate in which deterioration of optical characteristics is suppressed even in a heating and humidifying environment. The polarizing plate has very small changes in the simple substance transmittance Ts ΔTs and changes in the degree of polarization P ΔP after being left in an environment of 85 ° C. and 85% RH for 120 hours. The simple substance transmittance Ts can be measured using, for example, an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The degree of polarization P is calculated by the following equation from the single transmittance (Ts), the parallel transmittance (Tp) and the orthogonal transmittance (Tc) measured using an ultraviolet-visible spectrophotometer.
Polarization degree (P) (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
The Ts, Tp, and Tc are Y values measured by the JIS Z 8701 2 degree field of view (C light source) and corrected for luminosity factor. Also, Ts and P are substantially properties of the polarizer. ΔTs and ΔP are calculated by the following formulas, respectively.
ΔTs (%) = Ts ₁₂₀ _{-Ts 0}
ΔP (%) = P ₁₂₀ −P ₀
Here, Ts ₀ is the single transmittance before leaving (initial), Ts ₁₂₀ is the single transmittance after leaving, P ₀ is the degree of polarization before leaving (initial), and P ₁₂₀ is after leaving. The degree of polarization. ΔTs is preferably 3.0% or less, more preferably 2.7% or less, still more preferably 2.4% or less. ΔP is preferably −0.5% to 0%, more preferably −0.3% to 0%, and even more preferably −0.1% to 0%.

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

Hereinafter, the polarizer and the protective layer will be described in detail.

B. Polarizer As the polarizer, any suitable polarizer can be adopted. The polarizer can typically be made using a laminate of two or more layers. The method for manufacturing the polarizer will be described later in Section D as a method for manufacturing the polarizing plate.

The thickness of the polarizer is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and further preferably 2 μm to 5 μm.

The boric acid content of the polarizer is preferably 10% by weight or more, more preferably 13% by weight to 25% by weight. When the boric acid content of the polarizer is in such a range, the ease of curl adjustment at the time of bonding is well maintained due to the synergistic effect with the iodine content described later, and the curl at the time of heating is maintained. It is possible to improve the appearance durability at the time of heating while satisfactorily suppressing the above. The boric acid content can be calculated as, for example, the amount of boric acid contained in the polarizer per unit weight by using the following formula from the neutralization method.

The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% by weight to 10% by weight. When the iodine content of the polarizer is in such a range, the ease of curl adjustment at the time of bonding is well maintained due to the synergistic effect with the above boric acid content, and the curl at the time of heating is maintained. It is possible to improve the appearance durability at the time of heating while satisfactorily suppressing the above. As used herein, the term "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine during polarizers iodide ion (I ^-), molecular iodine (I _2), polyiodine ion _{^{_{(I 3 -, I 5 -}}} ) where present in the form of such, herein Iodine content means the amount of iodine that includes all of these forms. The iodine content can be calculated, for example, by the calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, a complex of PVA and tri-iodide ion (PVA · _{I 3} ^-) has a light absorption peak around 470 nm, a complex of PVA and five iodide ion (PVA · _{I 5} ^-) is 600nm near Has an absorptive peak. As a result, polyiodine ions can absorb light over a wide range of visible light, depending on their morphology. On the other hand, iodine ion (I ⁻ ) has an absorption peak near 230 nm and is not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in the form of a complex with PVA may be mainly involved in the absorption performance of the polarizer.

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

C. Protective layer As described above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. By including the 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 cationically polymerized cured product of an epoxy resin having a biphenyl skeleton. Since it is a cationically polymerized cured product, a polarizing plate having excellent durability can be obtained even though it is very thin. Hereinafter, the constituent components of the protective layer will be specifically described, and then the characteristics of the protective layer will be described.

C-1. Epoxy resin having a biphenyl skeleton In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin containing the following structure. Only one type of epoxy resin having a biphenyl skeleton may be used, or two or more types may be used in combination.

(In the formula, 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 independently represent a hydrogen atom, a linear or branched hydrocarbon group having 1 to 12 carbon atoms, or a halogen element. Examples of the linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group and a sec-butyl group. tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, cyclopentyl group, n-hexyl group, isohexyl group, cyclohexyl group, n-heptyl group, cycloheptyl group, methylcyclohexyl group, n- Octyl group, cyclooctyl group, n-nonyl group, 3,3,5-trimethylcyclohexyl group, n-decyl group, cyclodecyl group, n-undecyl group, n-dodecyl group, cyclododecyl group, phenyl group, benzyl group, Examples thereof include a methylbenzyl group, a dimethylbenzyl group, a trimethylbenzyl group, a naphthylmethyl group, a phenethyl group, a 2-phenylisopropyl group and the like. The linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms preferably has 1 to 1 to 12 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group and an n-butyl group. An alkyl group of 4 can be mentioned. Preferred examples of the halogen element include fluorine and bromine.

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula.

(In the formula, 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 contain a chemical structure other than the biphenyl skeleton. Examples of the chemical structure other than the biphenyl skeleton include a bisphenol skeleton, an alicyclic structure, an aromatic ring structure and the like. In this embodiment, the proportion (molar ratio) of the chemical structure other than the biphenyl skeleton is preferably smaller than that of the biphenyl skeleton.

A commercially available product may be used as the epoxy resin having a biphenyl skeleton. Examples of commercially available products include, for example, Mitsubishi Chemical Corporation, trade names: jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, jER YL7399 and the like.

The epoxy resin having a biphenyl skeleton preferably has a glass transition temperature (Tg) of 100 ° C. or higher. As a result, the softening temperature of the protective layer is also approximately 100 ° C. or higher. When the Tg of the epoxy resin having a biphenyl skeleton is 100 ° C. or higher, the obtained polarizing plate containing the protective layer tends to have excellent durability. The Tg of the epoxy resin having a biphenyl skeleton is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, still more preferably 125 ° C. or higher. On the other hand, the Tg of the epoxy resin having a biphenyl skeleton is preferably 300 ° C. or lower, more preferably 250 ° C. or lower, still more preferably 200 ° C. or lower, and particularly preferably 160 ° C. or lower. When the Tg of the epoxy resin having a biphenyl skeleton is in such a range, moldability and processability can be 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 further preferably 200 g / equivalent or more. The epoxy equivalent of the epoxy resin having a biphenyl skeleton is preferably 3000 g / equivalent or less, more preferably 2500 g / equivalent or less, and further preferably 2000 g / equivalent or less. When the epoxy equivalent having a biphenyl skeleton is in the above range, a more stable protective layer (a protective layer having less residual monomer and sufficiently cured) can be obtained. In the present specification, the "epoxy equivalent" means "the mass of an epoxy resin containing 1 equivalent of an epoxy group" and can be measured according to JIS K7236.

In the embodiment of the present invention, an epoxy resin having a biphenyl skeleton and another resin may be used in combination. That is, a blend of an epoxy resin having a biphenyl skeleton and another resin may be used for molding the protective layer. Other resins include, for example, thermoplastic resins such as styrene resins, polyethylenes, polypropylenes, polyamides, polyphenylene sulfides, polyether ether ketones, polyesters, polysulfones, polyphenylene oxides, polyacetals, polyimides, polyetherimides, and acrylic resins. Examples thereof include curable resins such as oxetane resins. Preferably, an acrylic resin and an oxetane resin are used. The type and blending amount of the resin to be used in combination can be appropriately set according to the purpose and the desired properties of the obtained film. For example, a styrene resin can be used in combination as a retardation control agent.

As the acrylic resin, any suitable acrylic resin can be used. For example, as the (meth) acrylic compound, for example, a (meth) acrylic compound having one (meth) acryloyl group in the molecule (hereinafter, also referred to as “monofunctional (meth) acrylic compound”), in the molecule. Examples thereof include (meth) acrylic compounds having two or more (meth) acryloyl groups (hereinafter, also referred to as “polyfunctional (meth) acrylic compounds”). These (meth) acrylic compounds may be used alone or in combination of two or more. These acrylic resins are described in, for example, Japanese Patent Application Laid-Open No. 2019-168500. The entire description of the publication is incorporated herein by reference.

As the oxetane resin, any suitable compound having one or more oxetanyl groups in the molecule is used. For example, 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl-3- (phenoxymethyl) oxetane, 3-ethyl-3- (cyclohexyloxymethyl). Oxetane compound having one oxetane group in the molecule such as oxetane, 3-ethyl-3- (oxylanylmethoxy) oxetane, (meth) acrylic acid (3-ethyloxetane-3-yl) methyl; 3-ethyl- 3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, 4,4'-bis [(3-ethyl) -3-oxetanyl) methoxymethyl] An oxetane compound having two or more oxetane groups in the molecule such as biphenyl; and the like. Only one kind of these oxetane resins may be used, or two or more kinds may be combined.

Preferably 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl -3- (Oxylanylmethoxy) oxetane, (meth) acrylate (3-ethyloxetane-3-yl) methyl, 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane Etc. are used. These oxetane resins are easily available and can be excellent in dilutability (low viscosity) and compatibility.

In one embodiment, an oxetane resin having a molecular weight of 500 or less and liquid at room temperature (25 ° C.) is preferably used from the viewpoint of compatibility and adhesiveness. In one embodiment, it preferably contains an oxetane compound containing two or more oxetanel groups in the molecule, one oxetaneyl group and one (meth) acryloyl group or one epoxy group in the molecule. Oxetane compounds are used, more preferably 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane, 3-ethyl-3- (oxylanylmethoxy) oxetane, (meth) acrylic. Acid (3-ethyloxetane-3-yl) methyl is used. By using these oxetane resins, the curability and durability of the protective layer can be improved.

As the oxetane resin, a commercially available product 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.) can be used. Preferably, Aron Oxetane OXT-101 and Aron Oxetane OXT-221 can be used.

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

When an epoxy resin having a biphenyl skeleton and an oxetane resin are used in combination, the content of the oxetane resin is preferably 1 part by weight to 50 parts by weight with respect to 100 parts by weight of the total amount of the epoxy resin having a biphenyl skeleton and the oxetane resin. , More preferably 5 parts by weight to 45 parts by weight, still more preferably 10 parts by weight to 40 parts by weight. 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 An epoxy resin with a biphenyl skeleton can be a hardened product when used with any suitable hardener. As the curing agent, any suitable curing agent capable of curing the epoxy resin can be used. In one embodiment, the curing agent comprises a photocationic polymerization initiator. By including the photocationic polymerization initiator, a protective layer which is a cationic polymerization cured product can be formed. As the photocationic polymerization initiator, any suitable compound capable of curing an epoxy resin having a biphenyl skeleton by irradiation with light such as ultraviolet rays can be used. Only one type of photocationic polymerization initiator may be used, or two or more types may be used in combination.

Examples of the photocationic polymerization initiator include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p- (phenylthio) phenyldiphenylsulfonium hexafluoroantimonate, p- (phenylthio) phenyldiphenylsulfonium hexafluorophosphate, and the like. 4-Chlorphenyl diphenyl sulfonium hexafluorophosphate, 4-chlorophenyl diphenyl sulfonium hexafluoroantimonate, bis [4- (diphenyl sulfonio) phenyl] sulfide bishexafluorophosphate, bis [4- (diphenyl sulfonio) phenyl ] Sulfoxide bishexafluoroantimonate, (2,4-cyclopentadiene-1-yl) [(1-methylethyl) benzene] -Fe-hexafluorophosphate, diphenyliodonium hexafluoroantimonate and the like can be mentioned. Preferably, a triphenylsulfonium salt-based hexafluoroantimonate type photocationic polymerization initiator and a diphenyliodonium salt-based hexafluoroantimonate type photocationic polymerization initiator are used.

A commercially available product may be used as the photocationic polymerization initiator. Commercially available products include triphenylsulfonium salt-based hexafluoroantimonate 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. Hexafluoroantimonate type WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.) and the like can be mentioned.

The content of the photocationic polymerization initiator is preferably 0.1 parts by weight to 3 parts by weight, more preferably 0.25 parts by weight to 2 parts by weight, based on 100 parts by weight of the epoxy resin having a biphenyl skeleton. be. If the content of the photocationic polymerization initiator is less than 0.1 parts by weight, it may not be sufficiently cured even when irradiated with light (ultraviolet rays).

C-3. Composition and Characteristics of Protective Layer As described above, the protective layer is composed of a cured product of an epoxy resin having a biphenyl skeleton. With such a cured product, the thickness can be significantly reduced as compared with the extrusion-molded film. The thickness of the protective layer is preferably 10 μm or less, more preferably 7 μm or less, still more preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the protective layer can be, for example, 1 μm or more. A cured product of an epoxy resin having a biphenyl skeleton has an advantage of being excellent in humidification durability because it has lower hygroscopicity and moisture permeability than a solidified product of an aqueous coating film such as an aqueous solution or an aqueous dispersion. As a result, it is possible to realize a polarizing plate having excellent durability that can maintain the optical characteristics even in a heating and humidifying environment. Further, the protective layer, which is a cured product of an epoxy resin having a biphenyl skeleton, has excellent adhesion to a polarizer. Therefore, even with the above-mentioned thickness, the polarizer can be protected to the same extent as the protective layer using a conventional film. Further, even with the above thickness, it is possible to prevent the occurrence of problems such as color loss of the polarizer.

The softening temperature of the protective layer is preferably 100 ° C. or higher. When the softening temperature of the protective layer is 100 ° C. or higher, the obtained polarizing plate containing the protective layer tends to have excellent durability. The softening temperature of the protective layer is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, and even more preferably 125 ° C. or higher. On the other hand, the softening temperature of the protective layer is preferably 300 ° C. or lower, more preferably 250 ° C. or lower, still more preferably 200 ° C. or lower, and particularly preferably 160 ° C. or lower. When the softening point of the protective layer is within such a range, moldability and workability can be excellent.

The iodine adsorption amount of the protective layer is preferably 10% by weight or less, more preferably 6.0% by weight or less, further preferably 3.0% by weight or less, and particularly preferably 2.0% by weight or less. Is. The smaller the amount of iodine adsorbed, the more preferable. If the amount of iodine adsorbed is in such a range, a polarizing plate having even better durability can be obtained. The amount of iodine adsorbed can be measured by the following method.
The composition for forming a protective layer is applied to a base material (PET film) with an applicator to form a protective layer (thickness of about 3 μm). The obtained PET film with a protective layer ^{is cut into 1 cm × 1 cm (1 cm 2} ) to be used as a sample, and collected and weighed in a headspace vial (20 mL capacity). Next, a screw tube bottle (1.5 mL capacity) containing 1 mL of an iodine solution (iodine concentration 1% by weight, potassium iodide concentration 7% by weight) is also placed in this headspace vial and sealed. Then, the headspace vial is placed in a dryer at 65 ° C. and heated for 6 hours. As a result, I ₂ in the gas state is adsorbed on the sample. Then, the sample is collected in a ceramic boat and burned using an automatic sample combustion device, and the generated gas is collected in 10 mL of the absorbing liquid. After collection, this absorbing solution is prepared in 15 mL with pure water, and IC quantitative analysis is performed on the undiluted solution or the appropriately diluted solution. The amount of iodine adsorbed is almost 0 when the same measurement is performed only with the PET film. Based on the iodine weight obtained by IC quantitative analysis and the weight of the protective layer alone (“weight of PET film with protective layer”-“weight of PET film”), the amount of iodine adsorbed (% by weight) from the following formula. Is calculated.
Iodine adsorption amount (% by weight) = Iodine weight obtained by IC quantitative analysis / Weight of protective layer alone x 100
For the analysis, for example, the following measuring device can be used.
[measuring device]
Automatic sample combustion device: "AQF-2100H" manufactured by Mitsubishi Chemical Analytech Co., Ltd.
IC (anion): "ICS-3000" manufactured by Thermo Fisher Scientific.

The protective layer is preferably substantially optically isotropic. As used herein, the term "substantially optically isotropic" means that the phase difference at a wavelength of 550 nm is −50 nm to +50 nm. The in-plane retardation Re (550) is more preferably −30 nm to +30 nm, further preferably −10 nm to +10 nm, and particularly preferably 0 nm to 2 nm. The phase difference Rth (550) in the thickness direction is more preferably −5 nm to + 5 nm, further preferably -3 nm to + 3 nm, and particularly preferably -2 nm to + 2 nm. When Re (550) and Rth (550) of the protective layer are in such a range, it is possible to prevent adverse effects on the display characteristics when the polarizing plate including the protective layer is applied to the image display device. Re (550) is an in-plane phase difference of the film measured with light having a wavelength of 550 nm at 23 ° C. Re (550) is calculated by the formula: Re (550) = (nx-ny) × d. Rth (550) is a phase difference in the thickness direction of the film measured with light having a wavelength of 550 nm at 23 ° C. Rth (550) is calculated by the formula: Rth (550) = (nx-nz) × d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and ny is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advancing axis direction). It is the refractive index, nz is the refractive index in the thickness direction, and d is the thickness (nm) of the film.

The higher the light transmittance at 380 nm when the thickness of the protective layer is 3 μm, the more preferable. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, still more preferably 90% or more. When the light transmittance is in such a range, the desired transparency can be ensured. The light transmittance can be measured, for example, by a method according to ASTM-D-1003.

The lower the haze of the protective layer, the more preferable. Specifically, the haze is preferably 5% or less, more preferably 3% or less, still more preferably 1.5% or less, and particularly preferably 1% or less. When the haze is 5% or less, a good clear feeling can be given to the film. Further, even when the polarizing plate on the visual side of the image display device is used, the displayed contents can be visually recognized satisfactorily.

The YI at a thickness of 3 μm of the protective layer is preferably 1.27 or less, more preferably 1.25 or less, still more preferably 1.23 or less, and particularly preferably 1.20 or less. If the YI exceeds 1.3, the optical transparency may be insufficient. YI is obtained from, for example, the tristimulus values (X, Y, Z) of the color obtained by measurement using a high-speed integrating sphere type spectral transmittance measuring machine (trade name: DOT-3C: manufactured by Murakami Color Technology Laboratory). , Can be calculated by the following equation.
YI = [(1.28X-1.06Z) / Y] x 100

The b value (a measure of hue according to the hunter's color system) at a thickness of 3 μm of the protective layer is preferably less than 1.5, more preferably 1.0 or less. When the b value is 1.5 or more, an undesired color may appear. For the b value, for example, a sample of the film constituting the protective layer is cut into 3 cm squares, and a high-speed integrating sphere type spectral transmittance measuring machine (trade name: DOT-3C: manufactured by Murakami Color Technology Laboratory) is used to determine the hue. Can be obtained by measuring and evaluating the hue according to the color system of the hunter.

The protective layer (cured product of epoxy resin having a biphenyl skeleton) may contain any appropriate additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; antioxidants such as hindered phenol-based, phosphorus-based, and sulfur-based; stabilizers such as light-resistant stabilizers, weather-resistant stabilizers, and heat-stabilizing agents; glass fibers, Reinforcing materials such as carbon fibers; Near infrared absorbers; Flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; Antistatic agents such as anionic, cationic and nonionic surfactants; Inorganic pigments , Organic pigments, colorants such as dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers and inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; and the like. Additives are usually added to the solution during protective layer formation. The type, number, combination, amount of additive, etc. of the additive can be appropriately set according to the purpose.

An easy-adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer contains, for example, an aqueous polyurethane and an oxazoline-based cross-linking agent. By forming such an easy-adhesion layer, the adhesion between the protective layer and the polarizer can be improved. The easy-adhesion layer can be laminated with the polarizer by any suitable method. For example, it may be formed directly on the polarizer and may be laminated via any suitable adhesive layer or adhesive layer. Further, a hard coat layer may be formed on the protective layer. The hard coat layer can be formed when the protective layer is used as the visible protective layer of the visible polarizing plate. When both the easy-adhesion layer and the hard coat layer are formed, typically they can be formed on different sides of the protective layer, respectively.

D. Method for manufacturing polarizing plate D-1. Method for producing a polarizer The method for producing a polarizer according to the above item B is a polyvinyl alcohol-based resin containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material. A layer (PVA-based resin layer) is formed to form a laminated body, and the laminated body is heated in the width direction while being conveyed in the longitudinal direction by aerial auxiliary stretching treatment, dyeing treatment, and underwater stretching treatment. A drying shrinkage treatment for shrinking by 2% or more, and a drying shrinkage treatment, which are performed in this order, are included. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60 ° C. to 120 ° C. According to such a manufacturing method, the above-mentioned polarizer can be obtained. In particular, by preparing a laminate containing a PVA-based resin layer containing a halide, stretching the laminate to multi-step stretching including aerial auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. It is possible to obtain a polarizer having excellent optical characteristics (typically, single transmittance and degree of polarization) and suppressing variation in optical characteristics. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminated body can be uniformly shrunk over the entire laminated body while being conveyed. As a result, not only the optical characteristics of the obtained polarizer can be improved, but also a polarizer having excellent optical characteristics can be stably produced, and the variation in the optical characteristics of the polarizer (particularly, the single transmittance) can be suppressed. can do. Hereinafter, the halide and the drying shrinkage treatment will be described. Details of manufacturing methods other than these are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. The entire description of the publication is incorporated herein by reference.

D-1-1. Halide A PVA-based resin layer containing a halide and a PVA-based resin can be formed by applying a coating liquid containing a halide and a PVA-based resin onto a thermoplastic resin base material and drying the coating film. The coating liquid is typically a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film can be formed in close contact with the thermoplastic resin base material.

As the halide, any suitable halide can be adopted. For example, iodide and sodium chloride can be mentioned. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. If the amount of the halide is too large, the halide may bleed out and the finally obtained polarizer may become cloudy.

Generally, the stretching of the PVA-based resin layer increases the orientation of the polyvinyl alcohol molecules in the PVA-based resin. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin base material and the PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. When stretched, the tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in the air before being stretched in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. As a result, the optical characteristics of the polarizer obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water, can be improved.

D-1-2. Dry shrinkage treatment The dry shrinkage treatment may be carried out by heating the entire zone by zone heating, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizer having an excellent appearance. Specifically, by drying the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the thermoplastic resin base material is in a state of being able to withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminated body can be continuously contracted in the width direction while being conveyed, and high productivity can be realized.

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

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

The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using both drying with a heating roll and hot air drying together, a steep temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30 ° C to 100 ° C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

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

In this way, a laminate of a thermoplastic resin base material / polarizer can be obtained.

D-2. Method for Producing Polarizing Plate A coating film is formed by applying a composition containing an epoxy resin having a biphenyl skeleton and a curing agent to the surface of the laminate obtained in item D-1 above (for example, the surface of a polarizer). A protective layer can be formed by curing the coating film. In one embodiment, the protective layer is a cationically polymerized cured product. In this embodiment, a photocationic polymerization initiator is used as the curing agent. A composition containing an epoxy resin having a biphenyl skeleton and a photocationic polymerization initiator is applied to the surface of a laminate (for example, the surface of a polarizer) to form a coating film, and the coating film is irradiated with light (for example, ultraviolet rays). By doing so, a protective layer can be formed.

As the solvent contained in the above composition, any suitable solvent capable of dissolving or uniformly dispersing the epoxy resin having a biphenyl skeleton and the curing agent can be used. 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 parts by weight to 30 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the polarizer can be formed. The content of the curing agent is as described in Item C above.

The solution may be applied to any suitable substrate or to a polarizer. When the solution is applied to the substrate, the cured product of the coating film formed on the substrate is transferred to the polarizer. When the solution is applied to the polarizer, a protective layer is directly formed on the polarizer by curing the coating film by, for example, light irradiation. Preferably, the solution is applied to the polarizer and a protective layer is formed directly on the polarizer. With such a configuration, the adhesive layer or the pressure-sensitive adhesive layer required for transfer can be omitted, so that the polarizing plate can be further thinned. Any suitable method can be adopted as the method for applying the solution. Specific examples include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, and a knife coating method (comma coating method, etc.).

When the coating film is cured by light irradiation, the coating film can be irradiated with light (typically ultraviolet rays) so as to have an arbitrary appropriate irradiation amount using an arbitrary appropriate light source. As the light source of ultraviolet rays, for example, a low pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, an electrodeless lamp, a carbon arc lamp, a xenon lamp, a metal halide lamp, a chemical lamp, a black light, an LED lamp and the like can be used. The dose of ultraviolet rays, for ^{example, 2mJ / cm 2 ~ 3000mJ /} cm 2, preferably ^{10mJ / cm 2 ~ 2000mJ / cm} 2. Specifically, when using a high pressure mercury lamp as a light source, the irradiation dose is usually ^{5mJ / cm 2 ~ 3000mJ / cm} 2, preferably at the conditions of ^{50mJ / cm 2 ~ 2000mJ / cm} 2. When an electrodeless lamp is used as the light source, the irradiation amount is usually ² ^{mJ / cm 2} to 2000 mJ / cm 2, preferably 10 mJ / cm ² to 1000 mJ / cm ² .

The irradiation time can be set to an arbitrary 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 may be a fraction of a second. Irradiation of light can be performed from any suitable direction. From the viewpoint of preventing non-uniform curing, it is preferable to irradiate from the coated surface side of the protective layer forming composition.

After exposure by light irradiation such as ultraviolet irradiation, further heat treatment may be performed in order to complete curing by light reaction. The heat treatment can be carried out at any suitable 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.

As described above, the protective layer is formed, and as a result, a laminate of the thermoplastic resin base material / polarizer / protective layer can be obtained. By peeling the thermoplastic resin base material from this laminate, a polarizing plate having a polarizing element 10 and a protective layer 20 as shown in FIG. 1 can be obtained. Alternatively, a resin film constituting another protective layer is attached to the polarizer surface of the laminate of the thermoplastic resin base material / polarizer, and then the thermoplastic resin base material is peeled off to form a protective layer on the peeled surface. You may. In this case, a polarizing plate having another protective layer can be obtained.

E. Polarizing plate with retardation layer E-1. Outline of Polarizing Plate with Differential Layer In one embodiment of the present invention, a polarizing plate with a retardation layer can be provided. This polarizing plate with a retardation layer further has a retardation layer on a surface on which the protective layer of the polarizing plate is not arranged. FIG. 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate 110 with a retardation layer in the illustrated example includes a polarizing element 10, a protective layer 20 arranged on one side of the polarizer 10, and a retardation layer 40 arranged on the other side of the polarizer 10. , Have. The polarizer 10 and the protective layer 20 form the above-mentioned polarizing plate. Therefore, the polarizing plate with a retardation layer includes a polarizing plate including a polarizing element and a protective layer arranged on one side of the polarizing element, and a retardation layer arranged on the opposite side of the polarizing plate to the protective layer. And have. If necessary, the polarizing plate may further include another protective layer (not shown) on the opposite side of the polarizing element 10 from the protective layer 20. In other words, the polarizing plate 110 with a retardation layer may further include another protective layer (not shown) between the polarizer 10 and the retardation layer 40. As described above, an easy-adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer can be laminated with the polarizer by any suitable method. For example, it may be formed directly on the polarizer and may be laminated via any suitable adhesive layer or adhesive layer.

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

E-2. A retardation layer composed of a single layer When the retardation layer is composed of a single layer, the retardation layer has a Re (550) of, for example, 100 nm to 190 nm as described above, and the retard phase of the retardation layer 40 is slow. The angle formed by the shaft and the absorption shaft of the polarizer 10 is, for example, 40 ° to 50 °. The retardation layer is typically provided to impart antireflection properties to the polarizing plate and can function as a λ / 4 plate in one embodiment. As described above, the retardation layer may be a resin film or an orientation-solidified layer of a liquid crystal compound.

The retardation layer preferably shows a relationship in which the refractive index characteristic is nx> ny ≧ nz. The in-plane retardation Re (550) of the retardation layer is, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm as described above. Here, "ny = nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, ny <nz may be satisfied as long as the effect of the present invention is not impaired.

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

The angle θ formed by the slow axis of the retardation 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. Is. If the angle θ is in such a range, by using a λ / 4 plate as the retardation layer, polarized light with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics). A plate can be obtained.

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

Retardation layer is preferably the absolute value of photoelastic coefficient is 2.0 × ¹⁰ -11 ^m 2 / N or less, more preferably ^{^{^{2.0 × 10 -13 m 2 /N~1.5×10 -11}}} m ² / N, more preferably includes a resin of ^{^{^{1.0 × 10 -12 m 2 /N~1.2×10 -11}}} m 2 / N. When the absolute value of the photoelastic coefficient is in such a range, the phase difference change is unlikely to occur when a shrinkage stress during heating occurs. As a result, thermal unevenness of the obtained image display device can be satisfactorily prevented.

E-2-1. Resin film When the retardation layer is a resin film, the resin film is typically a stretched film. In this case, the thickness of the retardation layer is preferably 60 μm or less, more preferably 30 μm to 55 μm. When the thickness of the retardation layer is within such a range, it is possible to satisfactorily adjust the curl at the time of bonding while satisfactorily suppressing the curl at the time of heating.

The retardation layer may be composed of any suitable resin film that can satisfy the above characteristics. Typical examples of such resins are polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, and polyamide resins. , Polyethylene resin, polyether resin, polystyrene resin, acrylic resin and the like. These resins may be used alone or in combination (eg, blending, copolymerizing). When the retardation layer is composed of a resin film exhibiting inverse dispersion wavelength characteristics, a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter, may be simply referred to as a polycarbonate-based resin) can be preferably used.

As the above-mentioned polycarbonate-based resin, any suitable polycarbonate-based resin can be used as long as the effects of the present invention can be obtained. For example, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, an alicyclic diol, an alicyclic dimethanol, di, tri or polyethylene glycol, and an alkylene. Includes structural units derived from at least one dihydroxy compound selected from the group consisting of glycols or spiroglycols. Preferably, the polycarbonate resin is a structural unit derived from a fluorene dihydroxy compound, a structural unit derived from an isosorbide dihydroxy compound, a structural unit derived from an alicyclic dimethanol, and / or di, tri or polyethylene glycol. Includes structural units derived from; more preferably 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-based resin may contain structural units derived from other dihydroxy compounds, if necessary. Details of the polycarbonate resin that can be suitably used in the present invention are, for example, JP-A-2014-10291, JP-A-2014-226666, JP-A-2015-212816, JP-A-2015-212817. , 2015-21218, and the description is incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110 ° C. or higher and 150 ° C. or lower, more preferably 120 ° C. or higher and 140 ° C. or lower. If the glass transition temperature is excessively low, the heat resistance tends to deteriorate, dimensional changes may occur after film molding, and the image quality of the obtained organic EL panel may be deteriorated. If the glass transition temperature is excessively high, the molding stability during film molding may be deteriorated, and the transparency of the film may be impaired. The glass transition temperature is determined according to JIS K 7121 (1987).

The molecular weight of the above-mentioned polycarbonate resin can be expressed by the reduced viscosity. The reduced viscosity is measured by using methylene chloride as a solvent, precisely adjusting the polycarbonate concentration to 0.6 g / dL, and using an Ubbelohde viscous tube at a temperature of 20.0 ° C. ± 0.1 ° C. The reduced viscosity is usually preferably 0.30 dL / g or more, and more preferably 0.35 dL / g or more. The reduced viscosity is usually preferably 1.20 dL / g or less, more preferably 1.00 dL / g or less, and further preferably 0.80 dL / g or less. If the reduced viscosity is less than 0.30 dL / g, there may be a problem that the mechanical strength of the molded product is reduced. On the other hand, if the reduced viscosity exceeds 1.20 dL / g, there may be a problem that the fluidity at the time of molding is lowered and the productivity and the moldability are lowered.

A commercially available film may be used as the polycarbonate resin film. Specific examples of commercially available products include the product names "Pure Ace WR-S", "Pure Ace WR-W", "Pure Ace WR-M" manufactured by Teijin Limited, and the product name "NRF" manufactured by Nitto Denko. Be done.

The retardation layer 40 can be obtained, for example, by stretching a film formed of the above-mentioned polycarbonate resin. As a method for forming a film from a polycarbonate-based resin, any suitable molding processing method can be adopted. Specific examples include a compression molding method, a transfer molding method, an injection molding method, an extrusion molding method, a blow molding method, a powder molding method, an FRP molding method, a cast coating method (for example, a casting method), a calendar molding method, and a hot press. Law etc. can be mentioned. Extrusion molding method or cast coating method is preferable. This is because the smoothness of the obtained film can be improved and good optical uniformity can be obtained. The molding conditions can be appropriately set according to the composition and type of the resin used, the characteristics desired for the retardation layer, and the like. As described above, since many film products of the polycarbonate resin are commercially available, the commercially available film may be subjected to the stretching treatment as it is.

The thickness of the resin film (unstretched film) can be set to an arbitrary appropriate value according to the desired thickness of the retardation layer, desired optical characteristics, stretching conditions described later, and the like. It is preferably 50 μm to 300 μm.

For the above stretching, any appropriate stretching method and stretching conditions (for example, stretching temperature, stretching ratio, stretching direction) can be adopted. Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end contraction, and fixed-end contraction can be used alone or simultaneously or sequentially. As for the stretching direction, it can be performed in various directions and dimensions such as a length direction, a width direction, a thickness direction, and an oblique direction. The stretching temperature is preferably Tg-30 ° C. to Tg + 60 ° C., more preferably Tg-10 ° C. to Tg + 50 ° C., relative to the glass transition temperature (Tg) of the resin film.

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

In one embodiment, the retardation film is produced by uniaxially stretching or fixed end uniaxially stretching the resin film. Specific examples of the fixed-end uniaxial stretching include a method of stretching the resin film in the width direction (lateral direction) while running the resin film in the longitudinal direction. The draw ratio is preferably 1.1 times to 3.5 times.

In another embodiment, the retardation film can be produced by continuously obliquely stretching a long resin film in the direction of the above angle θ with respect to the longitudinal direction. By adopting oblique stretching, a long stretched film having an orientation angle of an angle θ with respect to the longitudinal direction of the film (a slow axis in the direction of the angle θ) can be obtained. Roll-to-roll is possible, and the manufacturing process can be simplified. The angle θ may be an angle formed by the absorption axis of the polarizer and the slow axis of the retardation layer in the polarizing plate with the retardation layer. As described above, the angle θ is preferably 40 ° to 50 °, more preferably 42 ° to 48 °, and even more preferably about 45 °.

Examples of the stretching machine used for diagonal stretching include a tenter type stretching machine capable of applying a feeding force, a pulling force, or a pulling force at different speeds in the horizontal and / or vertical directions. The tenter type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable stretching machine can be used as long as the long resin film can be continuously and diagonally stretched.

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

The stretching temperature of the film can change depending on the in-plane retardation value and thickness desired for the retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature is preferably Tg-30 ° C. to Tg + 30 ° C., more preferably Tg-15 ° C. to Tg + 15 ° C., and most preferably Tg-10 ° C. to Tg + 10 ° C. By stretching at such a temperature, a retardation layer having appropriate characteristics in the present invention can be obtained. 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 retarded layer is the oriented solidified layer of the liquid crystal compound, the difference between nx and ny of the obtained retardation layer is significantly increased as compared with the non-liquid crystal material by using the liquid crystal compound. Therefore, the thickness of the retardation layer for obtaining a desired in-plane retardation can be remarkably reduced. As a result, it is possible to further reduce the thickness of the polarizing plate with a retardation layer. As used herein, the term "aligned solidified layer" refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within the layer and the oriented state is fixed. The "oriented solidified layer" is a concept including an oriented cured layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, the rod-shaped liquid crystal compounds are typically oriented in a state of being aligned in the slow axis direction of the retardation layer (homogeneous orientation).

Examples of the liquid crystal compound include a liquid crystal compound (nematic liquid crystal) in which the liquid crystal phase is a nematic phase. As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystal expression mechanism of the liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer 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 crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or cross-linking (that is, curing) the liquid crystal monomer. After the liquid crystal monomers are oriented, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the oriented state can be fixed. Here, the polymer is formed by polymerization, and the three-dimensional network structure is formed by cross-linking, but these are non-liquid crystal. Therefore, the formed retardation layer does not undergo a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to a liquid crystal compound, for example. As a result, the retardation layer becomes an extremely stable retardation layer that is not affected by temperature changes.

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

Any suitable liquid crystal monomer can be adopted as the liquid crystal monomer. For example, the polymerizable mesogen compounds described in Special Tables 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP02671712, DE19504224, DE4408171 and GB2280445 can be used. Specific examples of such a polymerizable mesogen compound include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Silicon-CC3767. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

Orientation of liquid crystal compound The solidified layer is subjected to an orientation treatment on the surface of a predetermined base material, and a coating liquid containing the liquid crystal compound is applied to the surface to orient the liquid crystal compound in a direction corresponding to the orientation treatment. It can be formed by fixing the orientation state. In one embodiment, the substrate is any suitable 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 the stacking can be performed continuously by roll-to-roll from the formation of the orientation solidification layer (phase difference layer), so that the productivity is further improved.

As the orientation treatment, any appropriate orientation treatment can be adopted. Specific examples thereof include mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment. Specific examples of the mechanical orientation treatment include a rubbing treatment and a stretching treatment. Specific examples of the physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of the chemical alignment treatment include an orthorhombic deposition method and a photoalignment treatment. As the treatment conditions for various orientation treatments, any appropriate conditions can be adopted depending on the purpose.

The orientation of the liquid crystal compound is performed by treating at a temperature indicating the liquid crystal phase according to the type of the liquid crystal compound. By performing such temperature treatment, the liquid crystal compound takes a liquid crystal state, and the liquid crystal compound is oriented according to the orientation treatment direction of the surface of the base material.

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

Specific examples of the liquid crystal compound and details of the method for forming the oriented solidified layer are described in JP-A-2006-163343. The description of this publication is incorporated herein by reference.

Another example of the oriented solidified layer is a form in which the discotic liquid crystal compound is oriented in any of vertical orientation, hybrid orientation, and inclined orientation. In the discotic liquid crystal compound, typically, the disk surface of the discotic liquid crystal compound is oriented substantially perpendicular to the film surface of the retardation layer. When the discotic liquid crystal compound is substantially vertical, the average value of the angles formed by the film surface and the disk surface of the discotic liquid crystal compound is preferably 70 ° to 90 °, more preferably 80 ° to 90 °. , More preferably, it means that it is 85 ° to 90 °. A discotic liquid crystal compound generally has a cyclic mother nuclei such as benzene, 1,3,5-triazine, and calix arene in the center of the molecule, and has a linear alkyl group, an alkoxy group, and a substituted benzoyl. A liquid crystal compound having a disk-like molecular structure in which an oxy group or the like is radially substituted as its side chain. Typical examples of discotic liquid crystals include C.I. Research report by Destrade et al., Mol. Cryst. Liq. Cryst. Benzene derivatives, triphenylene derivatives, tolucene derivatives, phthalocyanine derivatives, and B.I. Research report by Kohne et al., Angew. Chem. Cyclohexane derivatives described in Volume 96, p. 70 (1984), and J. Mol. M. Research report by Lehn et al., J. Mol. Chem. Soc. Chem. Commun. , 1794 (1985), J. Mol. Research report by Zhang et al., J. Mol. Am. Chem. Soc. Examples thereof include the aza-crown-based and phenylacetylene-based macrocycles described in Volume 116, p. 2655 (1994). Further specific examples of the discotic liquid crystal compound include the compounds described in JP-A-2006-133652, JP-A-2007-108732, and JP-A-2010-244038. The above references and publications are incorporated herein by reference.

When the retardation layer is an orientation-solidified layer of a liquid crystal compound, its thickness is preferably 0.5 μm to 7 μm, and more preferably 1 μm to 5 μm. By using the liquid crystal compound, it is possible to realize an in-plane phase difference equivalent to that of the resin film with a thickness much thinner than that of the resin film.

E-2-3. Another retardation layer As described above, when the retardation layer is composed of a single layer, another retardation layer is preferably provided. Another retardation layer can be a so-called positive C plate, as described above, in which the refractive index characteristics show a relationship of nz> nx = ny. By using the positive C plate as another retardation layer, it is possible to satisfactorily prevent reflection in the oblique direction, and it is possible to widen the viewing angle of the antireflection function. In this case, the phase difference Rth (550) in the thickness direction of another retardation layer is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, still more preferably −90 nm to −200 nm, and particularly preferably −. It is 100 nm to −180 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of another retardation layer can be less than 10 nm.

Another retardation layer with a refractive index characteristic of nz> nx = ny can be formed of any suitable material. Another retardation layer preferably consists of a film containing a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) that can be homeotropically oriented may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the methods for forming the liquid crystal compound and the retardation layer described in [0020] to [0028] of JP-A-2002-333642. In this case, the thickness of another retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

E-3.2 Layer difference layer When the retardation layer 40 has a laminated structure of the first layer 41 and the second layer 42, either one of the first layer 41 and the second layer 42 is λ / 4 It can function as a plate and the other as a λ / 2 plate. For example, when the first layer 41 functions as a λ / 2 plate and the second layer 42 functions as a λ / 4 plate, the in-plane retardation Re (550) of the first layer is, for example, 200 nm to 300 nm as described above. It is preferably 230 nm to 290 nm, and more preferably 250 nm to 280 nm. The in-plane retardation Re (550) of the second layer is, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm 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 ° to 20 °, preferably 12 ° to 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 ° to 80 °, preferably 72 ° to 78 °, and more preferably about 75 ° as described above. With such a configuration, it is possible to obtain characteristics close to the ideal reverse wavelength dispersion characteristic, and as a result, it is possible to realize extremely excellent antireflection characteristics.

One of the first layer 41 and the second layer 42 may be a resin film and the other may be an orientation-solidified layer of a liquid crystal compound, both may be a resin film, and both are orientation-solidified layers of a liquid crystal compound. You may. Preferably, both the first layer 41 and the second layer 42 are oriented solidified layers of a resin film or a liquid crystal compound.

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

The resin film constituting the first layer and the second layer, the liquid crystal compound, the method for forming the first layer and the second layer, the optical characteristics, and the like are as described above for the single layer.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Color loss and shrinkage of protective layer From the polarizing plates obtained in Examples and Comparative Examples, a test piece (50 mm ×) having two sides facing each other in the direction orthogonal to the absorption axis direction of the polarizer and the absorption axis direction. 50 mm) was cut out. The test piece was attached to a glass plate with an adhesive so that the protective layer was on the inside to form a test sample, and the test sample was left in an oven at 85 ° C. and 85% RH for 120 hours to be heated and humidified, and a standard polarizing plate was used. The state of color loss of the polarizing plate after humidification was visually inspected when the polarizing plate was placed in the state of cross-nicol, and evaluated according to the following criteria. In addition, the presence or absence of shrinkage of the protective layer after heating and humidification was also visually confirmed.
No problem: No color loss was observed Partial loss: Color loss was observed at the edges Total loss: Color loss was remarkable throughout the polarizing plate (2) Single transmittance and degree of polarization Color loss evaluation For those that were not completely missing, the single transmittance and the degree of polarization were measured. From the polarizing plates obtained in Examples and Comparative Examples, test pieces (50 mm × 50 mm) having two sides opposite to each other in the direction orthogonal to the absorption axis direction of the polarizer and the absorption axis direction were cut out. The test piece was attached to a non-alkali glass plate with an adhesive so that the protective layer was on the outside to form a test sample, and an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100") was used for the test sample. Then, the single transmittance (Ts), the parallel transmittance (Tp) and the orthogonal transmittance (Tc) were measured, and the degree of polarization (P) was calculated by the following equation. At this time, the measurement light was incident from the protective layer side.
Polarization degree (P) (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
The Ts, Tp, and Tc are Y values measured by the JIS Z 8701 2 degree field of view (C light source) and corrected for luminosity factor. Also, Ts and P are substantially properties of the polarizer.
Next, the polarizing plate was left in an oven at 85 ° C. and 85% RH for 120 hours to heat and humidify (heating test), _{and from the single transmittance Ts 0} before the heating test and the single transmittance Ts ₁₂₀ after the heating test, The amount of change in single transmittance ΔTs was determined using the following formula.
ΔTs (%) = Ts ₁₂₀ _{-Ts 0}
Similarly, from the degree of polarization P ₀ before the heating test and the degree of polarization P ₁₂₀ after the heating test, the amount of change in degree of polarization ΔP was determined using the following formula.
ΔP (%) = P ₁₂₀ −P ₀
The heating test was carried out by preparing a test sample in the same manner as in the case of color loss described above.

(3) Iodine Adsorption Amount A protective layer (thickness: about 3 μm) was formed on one side of the PET film in the same manner as in the formation of the protective layer in each Example and Comparative Example. The obtained PET film with a protective layer ^{was cut into 1 cm × 1 cm (1 cm 2} ) to be used as a sample, and collected and weighed in a headspace vial (20 mL capacity). Next, a screw tube bottle (1.5 mL capacity) containing 1 mL of an iodine solution (iodine concentration 1% by weight, potassium iodide concentration 7% by weight) was also placed in this headspace vial and sealed. Then, the headspace vial was placed in a dryer at 65 ° C. and heated for 6 hours (this causes I _{2 in} the gas state to be adsorbed on the sample). Then, the sample was collected in a ceramic boat and burned using an automatic sample combustion device, and the generated gas was collected in 10 mL of the absorbing liquid. After collection, this absorbed solution was prepared in 15 mL with pure water, and IC quantitative analysis was performed on the undiluted solution or the appropriately diluted solution. Since the amount of iodine adsorbed when the same measurement was performed only with the PET film was almost 0, the iodine weight obtained by the IC quantitative analysis and the weight of the protective layer alone (“weight of the PET film with the protective layer””. -The iodine adsorption amount (% by weight) was calculated from the following formula based on "weight of PET film").
Iodine adsorption amount (% by weight) = Iodine weight obtained by IC quantitative analysis / Weight of protective layer alone x 100
The measuring device and measuring conditions are as follows.
[measuring device]
Automatic sample combustion device: "AQF-2100H" manufactured by Mitsubishi Chemical Analytech Co., Ltd.
IC (anion): "ICS-3000" manufactured by Thermo Fisher Scientific.

(4) Softening temperature of protective layer Local thermal analysis (nano TA measurement) was performed on the protective layer surface of the polarizing plate obtained in Examples and Comparative Examples, and the softening temperature of the protective layer was calculated. The measuring device and measuring conditions are as follows.
Measuring device: Hitachi High-Tech Science Corporation, product name "AFM5300E // Nano-TA2"
Measurement mode: Contact mode Probe: AN2-200
Measurement area: 8 μm □ Scan Measurement atmosphere: Atmospheric pressure

(5) Judgment The obtained polarizing plate was judged according to the following criteria.
Good: ΔP value is 0% to -4.0%
Possible: The value of ΔP exceeds -4.0% and -10.0%
Impossible: ΔP value exceeds -10% to -99.9% (completely decolorized)

<Example 1>
1. 1. Fabrication of Laminate of Polarizer / Resin Base Material Amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) as a resin base material, which is long, has a water absorption rate of 0.75%, and has a Tg of about 75 ° C. Was used. One side of the resin substrate was corona-treated.
Polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Co., Ltd., trade name "Gosefimer Z410") are mixed in a ratio of 9: 1 to 100 parts by weight of PVA-based resin. , 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminate.
The obtained laminate was uniaxially stretched at the free end 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water), the polarizer finally obtained Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 41.5% ± 0.1% (dyeing treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight, potassium iodide 5% by weight) at a liquid temperature of 70 ° C., in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so that the total stretching ratio was 5.5 times (underwater stretching treatment).
Then, the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminated body by the drying shrinkage treatment was 5.2%.
In this way, a polarizer having a thickness of 5 μm was formed on the resin substrate to prepare a laminate of the polarizer / resin substrate. The simple substance transmittance (initial simple substance transmittance) Ts0 of the polarizer was 42.0%, and the degree of polarization (initial degree of polarization) P0 was 99.996%.

2. Fabrication of Polarizing Plate A cycloolefin-based film (ZEON Corporation, ZT-12, thickness 23 μm) is applied to the surface of the polarizer obtained above as a film constituting the second protective layer, and an ultraviolet curable adhesive is applied. It was pasted together. Specifically, the curable adhesive was coated so as to have a total thickness of 1.0 μm, and bonded using a roll machine. Then, UV light was irradiated from the film side to cure the adhesive. Next, the resin base material was peeled off to obtain a polarizing plate having a second protective layer (ZT-12) / polarizer configuration.

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

<Example 2>
15 parts of epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Co., Ltd., trade name: jER (registered trademark) YX4000) and 10 parts of oxetane resin (manufactured by Toagosei Co., Ltd., trade name: Aron Oxetane (registered trademark) OXT-221) Was dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the obtained epoxy resin solution, two parts of a photocationic polymerization initiator (manufactured by San-Apro Co., Ltd., trade name: CPI (registered trademark) -100P) was added to obtain a protective layer forming composition. A protective layer was formed in the same manner as in Example 1 except that a protective layer forming composition was obtained using this epoxy resin solution. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a structure of a protective layer / a polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was used for the evaluations (1) to (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 Corporation, trade name: jER (registered trademark) YX8000) was used instead of the epoxy resin having a biphenyl skeleton. .. The thickness of the protective layer was 2 μm to 3 μm. In this way, a polarizing plate having a structure of a protective layer / a polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Examples. The results are shown in Table 1.

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

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

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

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

(Comparative Example 7)
A polyurethane-based water-based dispersion resin (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Superflex SF210) as an easy-adhesion layer on the polarizing element surface of a polarizing plate having a second protective layer (ZT-12) / polarizer configuration. Was applied so as to have a thickness of 0.1 μm to form an easy-adhesion layer. Separately, 20 parts of an acrylic resin (manufactured by Kusumoto Kasei Co., Ltd., product name "B-734"), which is a copolymer of methyl methacrylate / butyl methacrylate (molar ratio 35/65), is dissolved in 80 parts of methyl ethyl ketone to dissolve the acrylic resin. A solution (20%) was obtained. Next, this acrylic resin solution was applied onto the easy-adhesion layer using a wire bar, and the coating film was dried at 60 ° C. for 5 minutes to form a protective layer formed as a solidified product of the coating film. The thickness of the protective layer was 3 μm, the softening temperature was 80.4 ° C., and the amount of iodine adsorbed was 30.4% by weight. In this way, a polarizing plate having a structure of a protective layer / a polarizer / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Examples. The results are shown in Table 1.

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

<Evaluation>
As is clear from Table 1, although the polarizing plate obtained in the examples was very thin, the deterioration of the optical characteristics was suppressed even in a heating and humidifying environment, and the polarizing plate was excellent in durability.

The polarizing plate of the present invention is suitably used for an image display device. Examples of image display devices include portable devices such as mobile information terminals (PDAs), smartphones, mobile phones, clocks, digital cameras, and portable game machines; OA devices such as personal computer monitors, laptop computers, and copiers; video cameras and televisions. , Home appliances such as microwave ovens; Back monitors, car navigation system monitors, car audio and other in-vehicle devices; Digital signage, commercial store information monitors and other exhibition devices; Surveillance monitors and other security devices; Nursing care Nursing care / medical equipment such as monitors for medical use and monitors for medical use;

10 Polarizer 20 Protective layer 40 Phase difference layer 100

Polarizing plate

110, 111 Polarizing plate with retardation layer

Claims

It has a polarizer and a protective layer arranged on one side of the polarizer.
A polarizing plate in which the protective layer is made of a cured product of an epoxy resin having a biphenyl skeleton.
The polarizing plate according to claim 1, wherein the cured product is a cationically polymerized cured product.
The polarizing plate according to claim 1 or 2, wherein the protective layer further contains an oxetane resin.
The polarizing plate according to any one of claims 1 to 3, wherein the protective layer has a thickness of 10 μm or less.
The polarizing plate according to any one of claims 1 to 4, wherein the amount of iodine adsorbed in the protective layer is 10% by weight or less.
The polarizing plate according to any one of claims 1 to 5, wherein the softening temperature of the protective layer is 100 ° C. or higher.
The polarizing plate according to any one of claims 1 to 6, wherein the total thickness is 10 μm or less.
A polarizing plate with a retardation layer, which has a retardation layer on a surface of the polarizing plate according to any one of claims 1 to 7 on which the protective layer is not arranged.