Polarizing plate and polarizing plate with retardation layer

Abstract

The present application provides a polarizing plate which is excellent in durability even if it is very thin. The polarizing plate of the present application has a polarizing member and a protective layer disposed on one side of the polarizing member. The protective layer is composed of 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

Technical Field

[0001] This invention relates to polarizing plates and polarizing plates with phase retardation layers. Background Technology

[0002] In image display devices (such as liquid crystal displays and organic EL displays), a polarizing plate is usually arranged on at least one side of the display unit due to the image formation method. In recent years, with the development of thinner and more flexible image display devices, there has been a strong demand for thinner polarizing plates. However, the thinner the polarizing plate is, the more significant the durability problem of reduced optical properties under heated and humidified environments becomes.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-210474 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] The present invention was made to solve the above-mentioned problems, and its main objective is to provide a polarizing plate with excellent durability even when it is very thin and a polarizing plate with a phase difference layer.

[0008] Solution for solving the problem

[0009] The polarizing plate of the present invention has a polarizing element and a protective layer disposed on one side of the polarizing element. The protective layer is composed of a cured epoxy resin having a biphenyl backbone.

[0010] In one embodiment, the cured product is a cationic polymer cured product.

[0011] In one embodiment, the protective layer further comprises an oxetane resin.

[0012] In one embodiment, the thickness of the protective layer is less than 10 μm.

[0013] In one embodiment, the amount of iodine adsorbed in the protective layer is less than 10% by weight.

[0014] In one embodiment, the softening temperature of the protective layer is above 100°C.

[0015] In one embodiment, the total thickness of the polarizing plate is less than 10 μm.

[0016] Another aspect of the present invention provides a polarizing plate with a phase retardation layer. This polarizing plate has a phase retardation layer on the surface of the polarizing plate not provided with the aforementioned protective layer.

[0017] The effects of the invention

[0018] According to the present invention, by making the protective layer disposed on the polarizer a cured product of epoxy resin having a biphenyl backbone, a polarizing plate with excellent durability even when very thin can be obtained. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram illustrating an example of a drying and shrinkage process using heated rollers in a method for manufacturing a polarizing plate according to an embodiment of the present invention.

[0021] Figure 3 This is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to one embodiment of the present invention.

[0022] Figure 4 This is a schematic cross-sectional view of a polarizing plate with a phase difference layer, according to another embodiment of the present invention. Detailed Implementation

[0023] (Definitions of terms and symbols)

[0024] The terms and symbols used in this specification are defined as follows.

[0025] (1) Refractive index (nx, ny, nz)

[0026] “nx” is the refractive index in the direction where the in-plane refractive index reaches its maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis (i.e., the fast axis direction), and “nz” is the refractive index in the thickness direction.

[0027] (2) In-plane phase difference (Re)

[0028] “Re(λ)” represents the in-plane phase difference measured at 23°C with light of wavelength λnm. For example, “Re(550)” represents the in-plane phase difference measured at 23°C with light of wavelength 550nm. Re(λ) is obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (thin film) is set to d (nm).

[0029] (3) Phase difference (Rth) in the thickness direction

[0030] “Rth(λ)” represents the phase difference in the thickness direction measured at 23°C using light with a wavelength of λnm. For example, “Rth(550)” represents the phase difference in the thickness direction measured at 23°C using light with a wavelength of 550nm. Rth(λ) is obtained by the formula: Rth(λ)=(nx-nz)×d when the layer (thin film) thickness is set to d (nm).

[0031] (4) Nz coefficient

[0032] The Nz coefficient can be obtained by Nz = Rth / Re.

[0033] (5) Angle

[0034] When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise directions relative to a reference direction. Therefore, for example, "45°" means ±45°.

[0035] A. Overview of polarizing plates

[0036] Figure 1 This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 shown in the figure has a polarizing element 10 and a protective layer 20 disposed on one side of the polarizing element 10. The thickness of the polarizing element 10 is preferably 8 μm or less. Another protective layer (not shown) may also be disposed on the side of the polarizing element 10 opposite to the protective layer 20, as needed. When the polarizing plate 100 is applied to an image display device, it may be disposed on the visual recognition side of the display unit or on the side opposite to the visual recognition side (back side). In either case, the protective layer 20 may be disposed on the display unit side or on the side opposite to the display unit (outer side). In one embodiment, the polarizing plate 100 is disposed on the visual recognition side of the display unit (resulting in an image display device), and the protective layer 20 is disposed on the visual recognition side (the side opposite to the display unit). The polarizing plate may be strip-shaped or sheet-shaped. When the polarizing plate is strip-shaped, it is preferable to wind it into a roll to form a polarizing plate roll.

[0037] Typically, the polarizing plate has an adhesive layer as the outermost layer on one side (typically the side of the polarizing element 10 opposite to the protective layer 20), which can be adhered to the display unit. A surface protective film and / or a carrier film can be temporarily adhered to the polarizing plate in a peelable manner as needed to reinforce and / or support the polarizing plate. When the polarizing plate includes an adhesive layer, separators are temporarily adhered to the surface of the adhesive layer in a peelable manner to protect the adhesive layer during the period before actual use, and the polarizing plate can be rolled up.

[0038] In embodiments of the present invention, the protective layer 20 is composed of a cured epoxy resin having a biphenyl backbone. With such a configuration, the protective layer can be made very thin (e.g., 10 μm or less). Furthermore, the protective layer can be formed directly onto the polarizing element (i.e., without the aid of an adhesive layer or bonding agent). According to embodiments of the present invention, as described above, the polarizing element and the protective layer are very thin and the adhesive layer or bonding agent can be omitted; therefore, the total thickness of the polarizing plate can be extremely thin. Furthermore, the adhesion between the polarizing element and the protective layer is excellent. The total thickness of the polarizing plate is, for example, 40 μm or less, preferably 30 μm or less, more preferably 20 μm or less, further preferably 10 μm or less, and particularly preferably 7 μm or less. The total thickness of the polarizing plate can, for example, be 4 μm or more.

[0039] Furthermore, by constructing a protective layer from a cured epoxy resin with a biphenyl backbone, a polarizing plate with excellent durability, even when very thin, can be achieved. Specifically, a polarizing plate whose optical properties are suppressed even under heated and humidified conditions can be realized. The changes in monomer transmittance Ts (ΔTs) and polarization P (ΔP) of the aforementioned polarizing plate after being placed in an environment of 85°C and 85% RH for 120 hours are both very small. The monomer transmittance Ts can be measured using, for example, a UV-Vis spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., product name "V7100"). The polarization P is calculated using the following formula from the monomer transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) measured using a UV-Vis spectrophotometer.

[0040] Polarization (P)(%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0041] It should be noted that Ts, Tp, and Tc mentioned above are Y values ​​obtained by measuring using a 2-degree field of view (C light source) according to JIS Z 8701 and correcting for visual sensitivity. Furthermore, Ts and P are essentially characteristics of the polarizer. ΔTs and ΔP are calculated using the following formulas.

[0042] ΔTs(%)=Ts 120 -Ts0

[0043] ΔP(%)=P 120 -P0

[0044] Here, Ts0 is the monomer transmittance before placement (initial), and Ts 120 P0 is the transmittance of the monomer after placement, and P0 is the polarization before placement (initial). 120 The polarization after placement is given. ΔTs is preferably 3.0% or less, more preferably 2.7% or less, and even more preferably 2.4% or less. ΔP is preferably -0.5% to 0%, more preferably -0.3% to 0%, and even more preferably -0.1% to 0%.

[0045] In embodiments of the present invention, the polarizing plate can be extremely thin. Therefore, it is suitable for use in flexible image display devices. More preferably, the image display device has a curved shape (essentially a curved display screen), and / or is bendable or foldable. Specific examples of image display devices include liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays). Of course, the above description does not preclude the application of the polarizing plate of the present invention to general image display devices.

[0046] The following provides a detailed explanation of the polarizing element and protective layer.

[0047] B. Polarizing components

[0048] As a polarizing element, any suitable polarizing element can be used. A representative example of a polarizing element is that it can be manufactured using a laminate of two or more layers. The manufacturing method of the polarizing element is explained in section D, which describes the manufacturing method of the polarizing plate.

[0049] The thickness of the polarizing element is preferably 1μm to 8μm, more preferably 1μm to 7μm, and even more preferably 2μm to 5μm.

[0050] The boric acid content of the polarizing element is preferably 10% by weight or more, more preferably 13% to 25% by weight. As long as the boric acid content of the polarizing element is within this range, the ease of adjusting curling during bonding can be maintained well through the synergistic effect with the iodine content described later, and curling during heating can be effectively suppressed, while improving the appearance durability during heating. The boric acid content can be calculated, for example, by neutralization using the following formula as the amount of boric acid contained per unit weight of polarizing element.

[0051]

[0052] The iodine content of the polarizing element is preferably 2% by weight or more, more preferably 2% to 10% by weight. As long as the iodine content of the polarizing element is within this range, the ease of adjusting curling during bonding can be maintained well through the synergistic effect with the aforementioned boric acid content, and curling during heating can be effectively suppressed, while improving the appearance durability during heating. In this specification, "iodine content" refers to the total amount of iodine contained in the polarizing element (PVA-based resin film). More specifically, iodine in the polarizing element is expressed as iodide ions (I- ions). - ), iodine molecules (I2), polyiodide ions (I3) - I5 -Iodine ions exist in various forms, and the iodine content mentioned in this specification refers to the amount of iodine containing all of these forms. Iodine content can be calculated, for example, using a standard curve method based on fluorescence X-ray analysis. It should be noted that polyiodide ions exist in polarizing elements as PVA-iodine complexes. By forming such complexes, dichroism can be exhibited in the visible light wavelength range. Specifically, the complex of PVA and triiodide ions (PVA·I₃) - It has an absorption peak near 470 nm, and the complex of PVA and pentaiodide ions (PVA·I5) - The polyiodide ion exhibits an absorption peak near 600 nm. As a result, polyiodide ions can absorb light over a wide range of visible light depending on their morphology. On the other hand, iodide ions (I... - It has an absorption peak around 230 nm and does not actually participate in the absorption of visible light. Therefore, the polyiodide ions existing in the form of a complex with PVA are mainly related to the absorption performance of polarizers.

[0053] The polarizer preferably exhibits absorption dichroism at any wavelength within the range of 380 nm to 780 nm. The single-unit transmittance Ts of the polarizer is preferably 40% to 48%, more preferably 41% to 46%. The polarization degree P of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0054] C. Protective layer

[0055] As described above, the protective layer is composed of a cured epoxy resin having a biphenyl backbone. By including an epoxy resin with a biphenyl backbone in the protective layer, the durability of the protective layer can be further improved. The protective layer is preferably a cationic polymerized cured epoxy resin having a biphenyl backbone. By using a cationic polymerized cured layer, a polarizing plate with excellent durability even when very thin can be obtained. Hereinafter, the composition of the protective layer will be specifically described, followed by an explanation of the characteristics of the protective layer.

[0056] C-1. Epoxy resin with a biphenyl backbone

[0057] In one embodiment, the epoxy resin having a biphenyl backbone is an epoxy resin comprising the following structure. The epoxy resin having a biphenyl backbone may use only one type, or a combination of two or more types.

[0058]

[0059] (where R is in the formula) 1 ~R 8 Each of these can be independently represented by a hydrogen atom, a straight-chain or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element.

[0060] R 1 ~R8 Each of these can be independently represented by a hydrogen atom, a linear or branched hydrocarbon group having 1 to 12 carbon atoms, or a halogen element. Examples of linear or branched hydrocarbon groups having 1 to 12 carbon atoms include: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, cyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, methylcyclohexyl, n-octyl, cyclooctyl, n-nonyl, 3,3,5-trimethylcyclohexyl, n-decyl, cyclodecyl, n-undecyl, n-dodecyl, cyclododecyl, phenyl, benzyl, methylbenzyl, dimethylbenzyl, trimethylbenzyl, naphthylmethyl, phenethyl, 2-phenylisopropyl, etc. As a straight-chain or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, and n-butyl, are preferably examples. As a halogen element, fluorine and bromine are preferably examples.

[0061] In one embodiment, the epoxy resin having a biphenyl backbone is an epoxy resin shown in the following formula.

[0062]

[0063] (where R is in the formula) 1 ~R 8 As mentioned above, n represents an integer from 0 to 6.

[0064] In one embodiment, the epoxy resin having a biphenyl backbone is an epoxy resin having only a biphenyl backbone. By using an epoxy resin having only a biphenyl backbone, the durability of the resulting protective layer can be further improved.

[0065] In one embodiment, the epoxy resin having a biphenyl backbone may also contain chemical structures other than the biphenyl backbone. Examples of chemical structures other than the biphenyl backbone include bisphenol backbones, alicyclic structures, aromatic ring structures, etc. In this embodiment, the ratio (molar ratio) of chemical structures other than the biphenyl backbone is preferably less than that of the biphenyl backbone.

[0066] Commercially available epoxy resins with a biphenyl backbone can also be used. Examples of commercially available epoxy resins include those manufactured by Mitsubishi Chemical Corporation, with trade names such as jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jERYL6810, and jER YL7399.

[0067] The epoxy resin with a biphenyl backbone preferably has a glass transition temperature (Tg) of 100°C or higher. As a result, the softening temperature of the protective layer also becomes almost 100°C or higher. As long as the Tg of the epoxy resin with a biphenyl backbone is 100°C or higher, the polarizing plate containing the resulting protective layer is likely to become a polarizing plate with excellent durability. The Tg of the epoxy resin with a biphenyl backbone is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. On the other hand, the Tg of the epoxy resin with a biphenyl backbone is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 160°C or lower. As long as the Tg of the epoxy resin with a biphenyl backbone is within such a range, its formability and processability are excellent.

[0068] The epoxy equivalent of the epoxy resin having a biphenyl backbone is preferably 100 g / equivalent or more, more preferably 150 g / equivalent or more, and even more preferably 200 g / equivalent or more. Furthermore, the epoxy equivalent of the epoxy resin having a biphenyl backbone is preferably 3000 g / equivalent or less, more preferably 2500 g / equivalent or less, and even more preferably 2000 g / equivalent or less. By having the epoxy equivalent of the biphenyl backbone within the above range, a more stable protective layer (a protective layer with less residual monomer and sufficient curing) can be obtained. It should be noted that, in this specification, "epoxy equivalent" refers to "the mass of epoxy resin containing 1 equivalent of epoxy groups," which can be determined according to JIS K7236.

[0069] In embodiments of the present invention, epoxy resins having a biphenyl backbone can also be used in combination with other resins. That is, blends of epoxy resins having a biphenyl backbone with other resins can also be used for molding the protective layer. Examples of other resins include thermoplastic resins such as styrene-based resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene ether, polyacetal, polyimide, and polyetherimide, as well as acrylic resins and oxetane-based resins. Acrylic resins and oxetane-based resins are preferred. The types and amounts of resins used in combination can be appropriately set according to the purpose and the desired characteristics of the resulting film. For example, styrene-based resins can be used in combination as phase difference control agents.

[0070] As an acrylic resin, any suitable acrylic resin can be used. For example, as (meth)acrylic compounds, examples include (meth)acrylic compounds having one (meth)acryloyl group within the molecule (hereinafter also referred to as "monofunctional (meth)acrylic compounds") and (meth)acrylic compounds having two or more (meth)acryloyl groups within the molecule (hereinafter also referred to as "polyfunctional (meth)acrylic compounds"). These (meth)acrylic compounds can be used alone or in combination of two or more. Such acrylic resins are described, for example, in Japanese Patent Application Publication No. 2019-168500. The entire contents of that publication are incorporated herein by reference.

[0071] As an oxetane resin, any suitable compound having one or more oxetane alkyl groups in its molecule can be used. Examples include: oxetane compounds with one oxetyl group in the molecule, such as 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(phenoxymethyl)oxetane, 3-ethyl-3-(cyclohexyloxymethyl)oxetane, 3-ethyl-3-(epoxyethylene methoxy)oxetane, and (meth)acrylate (3-ethyloxetane-3-yl)methyl ester; and oxetane compounds with two or more oxetyl groups in the molecule, such as 3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane, 1,4-bis[(3-ethyl-3-oxetane)methoxymethyl]benzene, and 4,4'-bis[(3-ethyl-3-oxetane)methoxymethyl]biphenyl. These oxobutane resins can be used in combination of one or more types.

[0072] Preferred resins include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetane)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(epoxyethylene methoxy)oxetane, (meth)acrylate (3-ethyloxetane-3-yl)methyl ester, and 3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane. These oxetane resins are readily available and exhibit excellent dilution (low viscosity) and compatibility.

[0073] In one embodiment, from the viewpoint of compatibility and adhesion, an oxetane resin with a molecular weight of 500 or less and which is liquid at room temperature (25°C) is preferred. In one embodiment, an oxetane compound containing two or more oxetane groups, an oxetane compound containing one oxetane group and one (meth)acryloyl group or one epoxy group is preferred; more preferably, 3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane, 3-ethyl-3-(epoxyethylene methoxy)oxetane, or (meth)acrylate (3-ethyloxetane-3-yl)methyl ester are used. Using these oxetane resins improves the curability and durability of the protective layer.

[0074] Commercially available products can also be used as oxetane resins. Specifically, ARON OXETANE OXT-101, ARON OXETANE OXT-121, ARON OXETANE OXT-212, and ARON OXETANE OXT-221 (all manufactured by Toa Synthetic Co., Ltd.) can be used. ARON OXETANE OXT-101 and ARON OXETANE OXT-221 are preferred.

[0075] When using epoxy resins with a biphenyl backbone in combination with other resins, the content of the epoxy resin with a biphenyl backbone in the blend is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, even more preferably 70% to 100% by weight, and particularly preferably 80% to 100% by weight. When the content is less than 50% by weight, there is a risk that the heat resistance of the protective layer and sufficient adhesion to the polarizing element cannot be obtained.

[0076] When using a combination of an epoxy resin with a biphenyl backbone and an oxetane resin, the content of oxetane resin is preferably 1 to 50 parts by weight, more preferably 5 to 45 parts by weight, and even more preferably 10 to 40 parts by weight, relative to 100 parts by weight of the total amount of the epoxy resin with a biphenyl backbone and the oxetane resin. By setting it within the above range, curability can be improved, and the adhesion between the protective layer and the polarizing element can also be improved.

[0077] C-2. Curing agent

[0078] Epoxy resins with a biphenyl backbone can be made into solids by using them together with any suitable curing agent. As a curing agent, any suitable curing agent capable of curing epoxy resins can be used. In one embodiment, the curing agent comprises a photocationic polymerization initiator. By comprising a photocationic polymerization initiator, a protective layer can be formed as a cationic polymerized cured product. As a photocationic polymerization initiator, any suitable compound capable of curing epoxy resins with a biphenyl backbone by irradiation with light such as ultraviolet light can be used. Only one photocationic polymerization initiator can be used, or two or more can be used in combination.

[0079] Examples of photocationic polymerization initiators include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyl diphenylsulfonium hexafluoroantimonate, p-(phenylthio)phenyl diphenylsulfonium hexafluorophosphate, 4-chlorophenyl diphenylsulfonium hexafluorophosphate, 4-chlorophenyl diphenylsulfonium hexafluoroantimonate, bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonate. Triphenylsulfonium salt-based hexafluoroantimonate type photocationic polymerization initiators and diphenyliodonium salt-based hexafluoroantimonate type photocationic polymerization initiators are preferred.

[0080] Commercially available products can also be used as photocationic polymerization initiators. Examples of commercially available products include SP-170 (manufactured by ADEKA), CPI-101A (manufactured by SAN-APRO), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), and WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.), which are triphenylsulfonium salt-based hexafluoroantimonate types.

[0081] The content of the photocationic polymerization initiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, relative to 100 parts by weight of the epoxy resin with a biphenyl backbone. When the content of the photocationic polymerization initiator is less than 0.1 parts by weight, sometimes even when irradiated with light (ultraviolet light), it is not fully cured.

[0082] C-3. Composition and characteristics of the protective layer

[0083] The protective layer, as described above, is composed of a cured epoxy resin having a biphenyl backbone. Because it is a cured material, its thickness can be much thinner than that of an extruded film. The thickness of the protective layer is preferably 10 μm or less, more preferably 7 μm or less, further preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the protective layer can, for example, be 1 μm or more. Compared to solidified aqueous coatings such as aqueous solutions or dispersions, cured epoxy resins having a biphenyl backbone have lower hygroscopicity and moisture permeability, thus offering excellent humidification durability. As a result, a polarizing plate that maintains excellent optical properties and durability even under heated and humidified conditions can be achieved. Furthermore, the protective layer, being a cured epoxy resin with a biphenyl backbone, exhibits excellent adhesion to the polarizing element. Therefore, even with the thickness described above, the polarizing element can be protected to the same extent as with protective layers using conventional films. Moreover, even with the aforementioned thickness, defects such as discoloration of the polarizing element can be prevented.

[0084] 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 polarizing plate containing the resulting protective layer is likely to become a polarizing plate with excellent durability. The softening temperature of the protective layer is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. On the other hand, the softening temperature of the protective layer is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 160°C or lower. When the softening point of the protective layer is within this range, its formability and processability are excellent.

[0085] The iodine adsorption amount of the protective layer is preferably 10% by weight or less, more preferably 6.0% by weight or less, even more preferably 3.0% by weight or less, and particularly preferably 2.0% by weight or less. Lower iodine adsorption is preferred. As long as the iodine adsorption is within such a range, a polarizing plate with superior durability can be obtained. The iodine adsorption amount can be determined by the following method.

[0086] The protective layer forming composition is applied to a substrate (PET film) using an applicator to form a protective layer (approximately 3 μm thick). The resulting PET film with the protective layer is then cut into 1 cm × 1 cm pieces. 2The sample was taken into a headspace vial (20 mL capacity) and weighed. Next, a screw-top bottle (1.5 mL capacity) containing 1 mL of iodine solution (1% wt% iodine and 7% wt% potassium iodide) was placed into the headspace vial and sealed tightly. The headspace vial was then placed in a desiccator at 65°C for 6 hours. This allowed gaseous I₂ to be adsorbed onto the sample. The sample was then transferred to a ceramic boat and burned using an automatic sample combustion device, collecting the generated gas into a 10 mL absorbent. After collection, the absorbent was prepared into 15 mL with pure water, and the original solution or appropriately diluted liquid was subjected to IC quantitative analysis. It should be noted that the iodine adsorption amount is almost zero when performing the same determination using only a PET film. The iodine adsorption amount (wt%) was calculated using the following formula based on the weight of iodine obtained from IC quantitative analysis and the weight of the protective layer itself (“weight of the PET film with protective layer” - “weight of the PET film”).

[0087] Iodine adsorption capacity (wt%) = (Iodine weight obtained by IC quantitative analysis) / (Weight of the protective layer itself) × 100

[0088] The analysis can be performed using, for example, the following measuring devices.

[0089] [Measuring Apparatus]

[0090] Automatic sample combustion device: Mitsubishi Chemical Analytech, “AQF-2100H”

[0091] IC (Anion): Manufactured by Thermo Fisher Scientific, “ICS-3000”

[0092] The protective layer is preferably substantially optically isotropic. In this specification, "substantially optically isotropic" means a phase difference of -50nm to +50nm at a wavelength of 550nm. The in-plane phase difference Re(550) is more preferably -30nm to +30nm, further preferably -10nm to +10nm, and particularly preferably 0nm to 2nm. The phase difference Rth(550) in the thickness direction is more preferably -5nm to +5nm, further preferably -3nm to +3nm, and particularly preferably -2nm to +2nm. As long as Re(550) and Rth(550) of the protective layer are within such ranges, adverse effects on display characteristics can be prevented when a polarizing plate containing the protective layer is applied to an image display device. It should be noted that Re(550) is the in-plane phase difference of the thin film measured at 23°C with light at a wavelength of 550nm. Re(550) can be obtained by the formula: Re(550) = (nx - ny) × d. Rth(550) is the phase difference in the thickness direction of the thin film measured at 23°C using light with a wavelength of 550 nm. Rth(550) can be obtained by the formula: Rth(550)=(nx-nz)×d. Here, nx is the refractive index in the direction where the in-plane refractive index reaches its maximum (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), nz is the refractive index in the thickness direction, and d is the thickness of the thin film (nm).

[0093] The higher the transmittance at 380 nm when the protective layer thickness is 3 μm, the better. Specifically, the transmittance is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. As long as the transmittance is within such a range, the desired transparency can be ensured. The transmittance can be measured, for example, using a method based on ASTM-D-1003.

[0094] The lower the haze of the protective layer, the better. Specifically, the haze is preferably 5% or less, more preferably 3% or less, further preferably 1.5% or less, and particularly preferably 1% or less. As long as the haze is 5% or less, the film can be given good transparency. Furthermore, even in the case of a polarizing plate on the visual recognition side of an image display device, the displayed content can still be visually recognized well.

[0095] When the thickness of the protective layer is 3 μm, the YI is preferably 1.27 or less, more preferably 1.25 or less, even more preferably 1.23 or less, and particularly preferably 1.20 or less. When the YI is greater than 1.3, the optical transparency sometimes becomes insufficient. It should be noted that the YI can be calculated, for example, from the tristimulus values ​​(X, Y, Z) of the color obtained by measurement using a high-speed integrating sphere spectrophotometer (trade name DOT-3C: manufactured by Murakami Color Technology Research Institute) using the following formula.

[0096] YI = [(1.28X - 1.06Z) / Y] × 100

[0097] When the thickness of the protective layer is 3 μm, the b-value (in terms of hue according to the Henry chromaticity system) is preferably less than 1.5, more preferably less than 1.0. When the b-value is greater than 1.5, undesirable hues may sometimes appear. It should be noted that the b-value can be obtained, for example, by cutting a sample of the thin film constituting the protective layer into 3 cm squares, measuring the hue using a high-speed integrating sphere spectrophotometer (trade name DOT-3C: manufactured by Murakami Color Technology Research Institute), and evaluating the hue based on the Henry chromaticity system.

[0098] The protective layer (a cured epoxy resin with a biphenyl backbone) may contain any suitable additives depending on the purpose. Specific examples of additives include: ultraviolet absorbers; leveling agents; hindered phenolic, phosphorus, and sulfur-based antioxidants; light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic fillers; resin modifiers; organic or inorganic fillers; plasticizers; lubricants; antistatic agents; and flame retardants. Additives are typically added to the solution during the formation of the protective layer. The type, quantity, combination, and amount of additives can be appropriately determined according to the purpose.

[0099] An easy-to-adhesive layer can also be formed on the polarizer side of the protective layer. This easy-to-adhesive layer may, for example, contain a water-based polyurethane and an oxazoline-based crosslinking agent. Forming such an easy-to-adhesive layer improves the adhesion between the protective layer and the polarizer. The easy-to-adhesive layer can be laminated to the polarizer using any suitable method. For example, it can also be formed directly on the polarizer, or laminated using any suitable adhesive layer or bonding agent layer. Furthermore, a hard coating layer can also be formed on the protective layer. The hard coating layer can be formed when the protective layer is used as a protective layer on the visual recognition side of a visual recognition-side polarizer. When forming both the easy-to-adhesive layer and the hard coating layer, it is representative that they can be formed on different sides of the protective layer.

[0100] D. Manufacturing method of polarizing plate

[0101] D-1. Manufacturing method of polarizing element

[0102] The method for manufacturing the polarizing element described in item B above includes: forming a polyvinyl alcohol (PVA) resin layer containing halides and polyvinyl alcohol (PVA) resin on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, wherein the drying shrinkage treatment involves heating the laminate while conveying it along its long side, thereby causing it to shrink by more than 2% along its width. The halides in the PVA resin layer are preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin. The drying shrinkage treatment is preferably performed using a heated roller, and the temperature of the heated roller is preferably 60°C to 120°C. According to this manufacturing method, the polarizing element described above can be obtained. In particular, by fabricating a laminate containing a PVA-based resin layer with halogenated compounds, and by performing a multi-stage stretching process including air-assisted stretching and underwater stretching, and by heating the stretched laminate with heated rollers, a polarizing element with excellent optical properties (typically monomer transmittance and polarization) and suppressed optical property inconsistencies can be obtained. Specifically, by using heated rollers in the drying and shrinkage process, the laminate can be uniformly shrunk while being transported. This not only improves the optical properties of the resulting polarizing element but also enables the stable production of polarizing elements with excellent optical properties and suppresses the inconsistencies in the optical properties of the polarizing element (especially monomer transmittance). The halogenation and drying and shrinkage processes will be described below. For details of manufacturing methods other than these, please refer to, for example, Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0103] D-1-1. Halides

[0104] A PVA-based resin layer comprising a halide and a PVA-based resin can be formed by applying a coating solution containing the halide and the PVA-based resin onto a thermoplastic resin substrate and drying the coating film. The coating solution is typically a solution formed by dissolving the aforementioned halide and the aforementioned PVA-based resin in a solvent. Examples of solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylenediamine, and amines such as diethylenetriamine. These can be used alone or in combination. Among these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhering to the thermoplastic resin substrate can be formed.

[0105] Any suitable halide can be used as the halide. Examples include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

[0106] The amount of halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of PVA-based resin, more preferably 10 to 15 parts by weight. If the amount of halide is too high, halide may sometimes leach out, resulting in a cloudy appearance of the final polarizing element.

[0107] Generally, after stretching, the orientation of polyvinyl alcohol molecules in PVA-based resin layers increases. However, if the stretched PVA-based resin layer is immersed in an aqueous liquid, the orientation of polyvinyl alcohol molecules can sometimes become disordered, resulting in a decrease in orientation. This is particularly true when stretching laminates of thermoplastic resin substrates and PVA-based resin layers in boric acid water. To stabilize the stretching of the thermoplastic resin substrate, the laminate is stretched at a higher temperature in boric acid water, leading to a significant tendency for a decrease in orientation. For example, the stretching of PVA film itself in boric acid water is typically performed at 60°C. In contrast, the stretching of laminates of A-PET (thermoplastic resin substrate) and PVA-based resin layers is performed at a higher temperature, around 70°C. In this case, the orientation of PVA decreases in the initial stretching stage before it increases during the water stretching process. To address this, by fabricating a laminate of a PVA-based resin layer containing halogens and a thermoplastic resin substrate, and then subjecting the laminate to high-temperature stretching in air (assisted stretching) before stretching in boric acid water, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after assisted stretching can be promoted. As a result, when the PVA-based resin layer is immersed in liquid, the orientation disorder and reduction of polyvinyl alcohol molecules are more effectively suppressed compared to the case where the PVA-based resin layer does not contain halogens. Therefore, the optical properties of polarizing elements obtained through processing steps such as dyeing and underwater stretching by immersing the laminate in liquid can be improved.

[0108] D-1-2. Drying and shrinkage treatment

[0109] The drying shrinkage treatment can be performed by area heating, which involves heating the entire area, or by heating the conveyor rollers (using so-called heated rollers) (heated roller drying method). Both methods are preferred. By using heated rollers for drying, heat curling of the laminate can be effectively suppressed, resulting in a polarizing element with excellent appearance. Specifically, by drying the laminate along the heated rollers, the crystallization of the thermoplastic resin substrate can be effectively promoted, increasing the degree of crystallinity. Even at lower drying temperatures, the degree of crystallinity of the thermoplastic resin substrate can be significantly increased. As a result, the rigidity of the thermoplastic resin substrate increases, becoming able to withstand the shrinkage of the PVA-based resin layer due to drying, thus suppressing curling. Furthermore, by using heated rollers, drying can be performed while maintaining the laminate in a flat state, thus suppressing not only curling but also wrinkle formation. At this time, the laminate shrinks in the width direction through the drying shrinkage treatment, thereby improving optical properties. This is because the orientation of PVA and PVA / iodine complexes can be effectively improved. The shrinkage rate in the width direction of the laminate based on the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rollers, the laminate can be continuously shrunk in the width direction while being conveyed, thus achieving high productivity.

[0110] Figure 2 This is a schematic diagram illustrating an example of a drying shrinkage process. In the drying shrinkage process, the laminate 200 is conveyed and dried using conveyor rollers R1 to R6 and guide rollers G1 to G4, which are heated to a specified temperature. In the example shown, the conveyor rollers R1 to R6 are configured to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate. However, for example, the conveyor rollers R1 to R6 may also be configured to continuously heat only one surface of the laminate 200 (e.g., the thermoplastic resin substrate surface).

[0111] The drying conditions can be controlled by adjusting the heating temperature of the conveyor rollers (temperature of the heating rollers), the number of heating rollers, and the contact time with the heating rollers. The temperature of the heating rollers is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. This allows for the production of optically laminated products with excellent durability while effectively increasing the crystallinity of the thermoplastic resin and suppressing curling. It should be noted that the temperature of the heating rollers can be measured using a contact thermometer. The example shown has six conveyor rollers, but there is no particular limitation on the number of conveyor rollers. Typically, 2 to 40 conveyor rollers are used, preferably 4 to 30. The contact time between the laminate and the heating rollers (total contact time) is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0112] The heating rollers can be installed inside a heating furnace (e.g., an oven) or in a general manufacturing line (at room temperature). Preferably, they are installed in a heating furnace equipped with air supply. By combining heating roller-based drying with hot air drying, abrupt temperature changes between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The preferred temperature for hot air drying is 30°C to 100°C. Furthermore, the preferred hot air drying time is 1 second to 300 seconds. The preferred air velocity is approximately 10 m / s to 30 m / s. It should be noted that this air velocity is the air velocity inside the heating furnace and can be measured using a miniature fan-blade type digital anemometer.

[0113] The cleaning process is preferably performed after the stretching treatment in water and before the drying and shrinkage treatment. A typical example of this cleaning process is immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0114] Thus, a laminate of thermoplastic resin substrate / polarizing element can be obtained.

[0115] D-2. Manufacturing method of polarizing plate

[0116] A protective layer can be formed by coating a composite containing an epoxy resin having a biphenyl backbone and a curing agent onto the surface of the laminate obtained in item D-1 above (e.g., the surface of a polarizer). In one embodiment, the protective layer is a cationic polymerized cured product. In this embodiment, a photocationic polymerization initiator can be used as the curing agent. A protective layer can be formed by coating a composite containing an epoxy resin having a biphenyl backbone and a photocationic polymerization initiator onto the surface of the laminate (e.g., the surface of a polarizer) and irradiating the coating with light (e.g., ultraviolet light).

[0117] As a solvent contained in the above composition, any suitable solvent that can dissolve or uniformly disperse the epoxy resin having a biphenyl backbone and the curing agent can be used. Specific examples of solvents include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

[0118] The epoxy resin concentration in the solution is preferably 10 to 30 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhering closely to the polarizing element can be formed. Furthermore, the content of the curing agent is as described in section C above.

[0119] The solution can be applied to any suitable substrate, or to a polarizing element. When the solution is applied to a substrate, the cured coating film formed on the substrate is transferred to the polarizing element. When the solution is applied to the polarizing element, the coating film is cured, for example, by light irradiation, thereby directly forming a protective layer on the polarizing element. Preferably, the solution is applied to the polarizing element, directly forming a protective layer on it. With this configuration, the adhesive or binder layer required for transfer can be omitted, thus allowing the polarizing plate to be thinner. Any suitable method can be used as the solution application method. Specific examples include roller coating, spin coating, wire rod coating, dip coating, mold coating, curtain coating, spray coating, and doctor blade coating (comma coating, etc.).

[0120] When curing a coated film by light irradiation, any suitable light source can be used to irradiate the film with light (ultraviolet light is representative) in any suitable amount. Examples of ultraviolet light sources include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, electrodeless lamps, carbon arc lamps, xenon lamps, metal halide lamps, chemical lamps, black lights, and LED lights. An example ultraviolet irradiation dose is 2 mJ / cm². 2 ~3000mJ / cm 2 The preferred value is 10 mJ / cm 2 ~2000mJ / cm 2 Specifically, when using a high-pressure mercury lamp as a light source, the irradiation dose is typically 5 mJ / cm². 2 ~3000mJ / cm 2 Optimal 50mJ / cm 2 ~2000mJ / cm 2 Under these conditions, it is carried out. When using an electrodeless lamp as the light source, the irradiation dose is typically 2 mJ / cm². 2 ~2000mJ / cm 2 Optimal value 10mJ / cm 2 ~1000mJ / cm 2 It is carried out under the following conditions.

[0121] The irradiation time can be set to any appropriate value depending on the type of light source, the distance between the light source and the coating surface, the coating thickness, and other conditions. The irradiation time is usually a few seconds to tens of seconds, or it can be a fraction of a second. The light can be irradiated from any appropriate direction. From the viewpoint of preventing uneven curing, it is preferable to irradiate from the coating surface side of the composition for forming the protective layer.

[0122] After exposure to light such as ultraviolet light, a further heat treatment can be performed to complete the photo-based curing process. 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.

[0123] The above steps form a protective layer, resulting in a laminate of thermoplastic resin substrate / polarizer / protective layer. By peeling the thermoplastic resin substrate from this laminate, a product can be obtained as follows: Figure 1 The polarizing plate shown has a polarizing element 10 and a protective layer 20. Alternatively, a resin film forming another protective layer can be laminated onto the surface of the polarizing element in a laminate of thermoplastic resin substrate / polarizing element, and then the thermoplastic resin substrate can be peeled off, forming a protective layer on the peeled surface. In this case, a polarizing plate with another protective layer can be obtained.

[0124] E. Polarizing plate with phase retardation layer

[0125] E-1. Overview of a polarizing plate with a phase retardation layer

[0126] In one embodiment of the present invention, a polarizing plate with a phase retardation layer is provided. This polarizing plate with a phase retardation layer also has a phase retardation layer on the surface of the polarizing plate that is not provided with a protective layer. Figure 3 This is a schematic cross-sectional view of a polarizing plate with a phase retardation layer according to one embodiment of the present invention. The polarizing plate 110 with a phase retardation layer shown in the figure includes: a polarizing element 10, a protective layer 20 disposed on one side of the polarizing element 10, and a phase retardation layer 40 disposed on the other side of the polarizing element 10. The polarizing element 10 and the protective layer 20 constitute the aforementioned polarizing plate. Therefore, the polarizing plate with a phase retardation layer has a polarizing plate and a phase retardation layer, the polarizing plate including a polarizing element and a protective layer disposed on one side of the polarizing element, and the phase retardation layer disposed on the side of the polarizing plate opposite to the protective layer. The polarizing plate may also, as needed, include another protective layer (not shown) on the side of the polarizing element 10 opposite to the protective layer 20. In other words, the polarizing plate 110 with a phase retardation layer may also include another protective layer (not shown) between the polarizing element 10 and the phase retardation layer 40. As described above, an easy-to-adhere layer may also be formed on the polarizing element side of the protective layer. The easy-to-bond layer can be laminated to the polarizing element using any suitable method. For example, it can also be formed directly on the polarizing element, and can be laminated using any suitable adhesive layer or bonding agent layer.

[0127] Figure 3 In the illustrated embodiment, 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 between the slow axis of the retardation layer 40 and the absorption axis of the polarizer 10 is, for example, 40° to 50°. Preferably, another retardation layer (not shown) is provided on the outer side of the retardation layer 40 (the side opposite to the polarizer 10). The other retardation layer is characterized by a refractive index characteristic showing a relationship of nz > nx = ny. Alternatively, as... Figure 4As shown, in the polarizing plate 111 with a retardation layer according to another embodiment, the retardation layer 40 has a stacked structure of a first layer 41 and a second layer 42. At this time, 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°; 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 embodiment, the retardation layer 40 can be a resin film or an orientation cured layer of a liquid crystal compound. When the retardation layer 40 has a stacked structure, typically, the first layer 41 and the second layer 42 are respectively a resin film or an orientation cured layer of a liquid crystal compound.

[0128] E-2. Retardation layer composed of a single layer

[0129] When the retardation layer is composed of a single layer, Re(550) of the retardation layer is, for example, 100 nm to 190 nm as described above, 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°. Typically, the retardation layer is provided to impart an antireflection property to the polarizing plate and can function as a λ / 4 plate in one embodiment. The retardation layer can be a resin film or an orientation cured layer of a liquid crystal compound as described above.

[0130] The retardation layer preferably shows a relationship of nx > ny ≥ nz in refractive index characteristics. The in-plane retardation Re(550) of the retardation layer is, for example, 100 nm to 190 nm as described above, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm. It should be noted that here, "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within the range that does not impair the effects of the present invention, there may be a case where ny < nz.

[0131] The Nz coefficient of the retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, further preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflected hue can be achieved.

[0132] 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° as described above, preferably 42° to 48°, and further preferably about 45°. As long as the angle θ is within such a range, by making the retardation layer into a λ / 4 plate, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (resulting in very excellent antireflection characteristics) can be obtained.

[0133] The phase retardation layer can exhibit anomalous dispersion wavelength characteristics where the phase difference increases with the wavelength of the measurement light, normal wavelength dispersion characteristics where the phase difference decreases with the wavelength of the measurement light, or flat wavelength dispersion characteristics where the phase difference hardly changes with the wavelength of the measurement light. In one embodiment, the phase retardation layer exhibits anomalous dispersion wavelength characteristics. In this case, the Re(450) / Re(550) ratio of the phase retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and less than 0.95. With such a configuration, very excellent anti-reflection properties can be achieved.

[0134] The absolute value of the photoelastic coefficient of the phase retardation layer is preferably 2.0 × 10⁻⁶. -11 m 2 / N or less, more preferably 2.0×10 -13 m 2 / N~1.5×10 -11 m 2 / N, further preferably 1.0×10 -12 m 2 / N~1.2×10 -11 m 2 A resin with a photoelastic modulus of / N. As long as the absolute value of the photoelastic modulus is within this range, phase difference changes are less likely to occur under shrinkage stress during heating. As a result, thermal unevenness in the resulting image display device can be effectively prevented.

[0135] E-2-1. Resin film

[0136] 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. As long as the thickness of the retardation layer is within this range, curling during heating can be well suppressed, and curling during bonding can be well adjusted.

[0137] The retardation layer can be composed of any suitable resin film that satisfies the above-mentioned characteristics. Representative examples of such resins include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyaryl ester resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins can be used alone or in combination (e.g., blending, copolymerization). When the retardation layer is composed of a resin film exhibiting anomalous dispersion wavelength characteristics, polycarbonate resins or polyester carbonate resins (hereinafter sometimes simply referred to as polycarbonate resins) are suitable.

[0138] As the aforementioned polycarbonate resin, any suitable polycarbonate resin can be used as long as the effects of the present invention are achieved. For example, the polycarbonate resin comprises structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic diethanols, di-, tri-, or polyethylene glycols, and alkylene diols or spirodiols. Preferably, the polycarbonate resin comprises structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, structural units derived from alicyclic diethanols, and / or structural units derived from di-, tri-, or polyethylene glycols; more preferably, it comprises structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from di-, tri-, or polyethylene glycols. The polycarbonate resin may also, as needed, comprise structural units derived from other dihydroxy compounds. It should be noted that detailed descriptions of the polycarbonate resins suitable for use in this invention are described, for example, in Japanese Patent Application Publication Nos. 2014-10291, 2014-26266, 2015-212816, 2015-212817, and 2015-212818, which are incorporated herein by reference.

[0139] The glass transition temperature of the aforementioned polycarbonate resin is preferably 110°C or higher and 150°C or lower, more preferably 120°C or higher and 140°C or lower. If the glass transition temperature is too low, the heat resistance tends to deteriorate, there is a possibility of dimensional changes after film forming, or sometimes the image quality of the resulting organic EL panel may be reduced. If the glass transition temperature is too high, the forming stability during film forming may deteriorate, or sometimes the transparency of the film may be compromised. It should be noted that the glass transition temperature can be obtained according to JIS K 7121 (1987).

[0140] The molecular weight of the aforementioned polycarbonate resin can be expressed by its specific viscosity. Specific viscosity is measured using dichloromethane as a solvent, with the polycarbonate concentration precisely prepared to 0.6 g / dL, and measured using an Ubbelohde viscometer at a temperature of 20.0℃ ± 0.1℃. Specific viscosity is generally preferably 0.30 dL / g or higher, more preferably 0.35 dL / g or higher. Furthermore, specific viscosity is generally preferably 1.20 dL / g or lower, more preferably 1.00 dL / g or lower, and even more preferably 0.80 dL / g or lower. If the specific viscosity is less than 0.30 dL / g, the mechanical strength of the molded article may decrease. On the other hand, if the specific viscosity is greater than 1.20 dL / g, the flowability during molding may decrease, resulting in reduced productivity or moldability.

[0141] Commercially available films can also be used as polycarbonate-based resin films. Specific examples of commercially available products include "PURE-ACE WR-S", "PURE-ACE WR-W", and "PURE-ACE WR-M" manufactured by Teijin Corporation, and "NRF" manufactured by Nitto Denko Corporation.

[0142] The retardation layer 40 can be obtained, for example, by stretching a film formed from the aforementioned polycarbonate resin. Any suitable forming process can be used as a method for forming the film from the polycarbonate resin. Specific examples include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, casting coating (e.g., casting), calendering, and hot pressing. Extrusion molding or casting coating is preferred. This is because it improves the smoothness of the resulting film, thereby achieving good optical uniformity. The forming conditions can be appropriately set according to the composition and type of the resin used, the desired characteristics of the retardation layer, etc. It should be noted that, as mentioned above, many film products made from polycarbonate resins are commercially available; therefore, these commercially available films can be directly subjected to stretching processing.

[0143] The thickness of the resin film (unstretched film) can be set to any appropriate value according to the desired thickness of the retardation layer, the desired optical properties, and the stretching conditions described later. Preferably, it is 50 μm to 300 μm.

[0144] The stretching described above can be performed using any suitable stretching method and conditions (e.g., stretching temperature, stretching ratio, stretching direction). Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage can be used individually, or simultaneously or sequentially. Regarding the stretching direction, it can also be performed along various directions or dimensions such as the length direction, width direction, thickness direction, and oblique direction. The stretching temperature relative to the glass transition temperature (Tg) of the resin film is preferably Tg-30℃ to Tg+60℃, more preferably Tg-10℃ to Tg+50℃.

[0145] By appropriately selecting the stretching method and stretching conditions described above, a phase difference film with the desired optical properties (e.g., refractive index characteristics, in-plane phase difference, Nz coefficient) can be obtained.

[0146] In one embodiment, the phase retardation film can be fabricated by uniaxial stretching or fixed-end uniaxial stretching of a resin film. A specific example of fixed-end uniaxial stretching is a method in which the resin film is moved along its long side while being stretched along its width (lateral direction). The stretching ratio is preferably 1.1 to 3.5 times.

[0147] In another embodiment, the retardation film can be fabricated by continuously stretching a strip-shaped resin film obliquely along an angle θ relative to its long side. By employing oblique stretching, a strip-shaped stretched film with an orientation angle θ relative to the long side of the film (having a slow axis in the direction of angle θ) can be obtained. For example, when laminated with a polarizer, roll-to-roll processing can be performed, thereby simplifying the manufacturing process. It should be noted that angle θ can be the angle formed by the absorption axis of the polarizer in the polarizer plate with the retardation layer and the slow axis of the retardation layer. As described above, angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°.

[0148] Examples of stretching machines used for oblique stretching include tenter frame stretching machines, which can apply conveying, stretching, or traction forces at different speeds in the transverse and / or longitudinal directions. Tensioner frame stretching machines include transverse single-axis stretching machines and simultaneous biaxial stretching machines. Any suitable stretching machine can be used as long as it can continuously stretch long strip resin films obliquely.

[0149] By appropriately controlling the left and right speeds in the stretching machine, a phase difference layer (essentially a strip-shaped phase difference film) with the desired in-plane phase difference and a slow axis in the desired direction can be obtained.

[0150] The stretching temperature of the aforementioned film can be varied depending on the desired in-plane phase difference value and thickness of the retardation layer, the type of resin used, the thickness of the film used, and the stretching ratio. Specifically, the stretching temperature is preferably Tg-30℃ to Tg+30℃, more preferably Tg-15℃ to Tg+15℃, and most preferably Tg-10℃ to Tg+10℃. By stretching at such temperatures, a retardation layer with properties suitable for the present invention can be obtained. It should be noted that Tg is the glass transition temperature of the constituent material of the film.

[0151] E-2-2. Orientation-cured layer of liquid crystal compound

[0152] When the retardation layer is an alignment-cured layer of a liquid crystal compound, by using the liquid crystal compound, the difference between nx and ny in the resulting retardation layer can be made much larger than that of a non-liquid crystal material. Therefore, the thickness of the retardation layer used to obtain the desired in-plane retardation can be made much smaller. As a result, further thinning of the polarizer with the retardation layer is possible. In this specification, "alignment-cured layer" refers to a layer in which the liquid crystal compound is aligned in a predetermined direction and its alignment state is fixed. Furthermore, "alignment-cured layer" includes the concept of an alignment-cured layer obtained by curing liquid crystal monomers as described later. In this embodiment, a representative example is a rod-shaped liquid crystal compound aligned in the slow axis direction of the retardation layer (plane alignment).

[0153] Examples of liquid crystal compounds include those where the liquid crystal phase is a nematic phase (nematic liquid crystals). Liquid crystal polymers and liquid crystal monomers can be used as such liquid crystal compounds. The liquid crystal properties of liquid crystal compounds can be lyotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers can be used individually or in combination.

[0154] When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer or a crosslinking monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing). After the liquid crystal monomer is oriented, for example, if the liquid crystal monomer is polymerized or crosslinked with each other, the orientation state can be fixed thereby. Here, polymers are formed by polymerization, and three-dimensional network structures are formed by crosslinking; these are non-liquid crystals. Therefore, the resulting retardation layer does not undergo the transformation into a liquid crystal phase, glassy phase, or crystalline phase due to temperature changes, as is characteristic of liquid crystal compounds. As a result, the retardation layer becomes a retardation layer with excellent stability unaffected by temperature changes.

[0155] The temperature range for liquid crystal display properties varies depending on the type of liquid crystal. Specifically, this temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

[0156] Any suitable liquid crystal monomer can be used as the aforementioned liquid crystal monomer. For example, polymerizable liquid crystal precursor compounds described in Japanese Patent Application Publication No. 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable liquid crystal precursor compounds include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Sillicon-CC3767. Nematic liquid crystal monomers are preferred as the liquid crystal monomer.

[0157] The alignment-cured layer of the liquid crystal compound can be formed as follows: an alignment treatment is performed on the surface of a specified substrate, and a coating liquid containing the liquid crystal compound is applied to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and the alignment state is fixed, thereby forming the layer. In one embodiment, the substrate is any suitable resin film, and the alignment-cured 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 process can be omitted, and roll-to-roll lamination can be performed continuously after the alignment-cured layer (phase retardation layer) is formed, thus further improving productivity.

[0158] As for the aforementioned orientation treatment, any suitable orientation treatment can be adopted. Specific examples include mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment. Specific examples of mechanical orientation treatment include friction treatment and stretching treatment. Specific examples of physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of chemical orientation treatment include oblique vapor deposition and photo-orientation treatment. The processing conditions for each orientation treatment can be any suitable condition depending on the purpose.

[0159] The orientation of a liquid crystal compound can be achieved by treating it at a temperature suitable for display liquid crystal phases, depending on the type of liquid crystal compound. Through this temperature treatment, the liquid crystal compound enters a liquid crystal state and is oriented in accordance with the orientation treatment direction of the substrate surface.

[0160] In one embodiment, the orientation state is fixed by cooling the liquid crystal compound that has been oriented as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinking monomer, the orientation state is fixed by performing a polymerization treatment or a crosslinking treatment on the liquid crystal compound that has been oriented as described above.

[0161] Specific examples of liquid crystal compounds and detailed methods for forming alignment curing layers are described in Japanese Patent Application Publication No. 2006-163343. This specification incorporates the information described in that publication by way of reference.

[0162] As another example of an orientation-cured layer, a disc-shaped liquid crystal compound can be oriented in any of the following states: vertical orientation, mixed orientation, and tilted orientation. A representative example of a disc-shaped liquid crystal compound is that the disc surface of the compound is substantially perpendicular to the thin film surface of the retardation layer. "Substantially perpendicular" means that the average angle formed by the thin film surface and the disc surface of the liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°, and even more preferably 85° to 90°. Generally speaking, a disc-shaped liquid crystal compound refers to a liquid crystal compound having a disc-shaped molecular structure in which a cyclic core, such as benzene, 1,3,5-triazine, or calixarene, is positioned at the center of the molecule, and straight-chain alkyl, alkoxy, or substituted benzoyloxy groups are radially substituted as side chains. Representative examples of disk-shaped liquid crystals include: benzene derivatives, triphenylene derivatives, triindene derivatives, and phthalocyanine derivatives described in the research report of C. Destrade et al., Mol. Cryst. Liq. Cryst., Vol. 71, p. 111 (1981); cyclohexane derivatives described in the research report of B. Kohne et al., Angew. Chem., Vol. 96, p. 70 (1984); and nitrogen-crown or phenylacetylene macrocyclic compounds described in the research reports of J. M. Lehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985) and J. Zhang et al., J. Am. Chem. Soc., Vol. 116, p. 2655 (1994). Further specific examples of disc-shaped liquid crystal compounds include those described in Japanese Patent Application Publication Nos. 2006-133652, 2007-108732, and 2010-244038. Reference is made to the descriptions in the aforementioned documents and publications in this specification.

[0163] When the phase retardation layer is an alignment-cured layer of a liquid crystal compound, its thickness is preferably 0.5 μm to 7 μm, more preferably 1 μm to 5 μm. By using a liquid crystal compound, an in-plane phase retardation equivalent to that of a resin film can be achieved with a thickness much thinner than that of the resin film.

[0164] E-2-3. Another phase difference layer

[0165] As described above, when the retardation layer is composed of a single layer, it is preferable to provide another retardation layer. This other retardation layer, as described above, can be a so-called positive C-plate exhibiting a refractive index characteristic of nz > nx = ny. By using a positive C-plate as the other retardation layer, oblique reflections can be effectively prevented, and the anti-reflection function can be widened. In this case, the phase difference Rth(550) in the thickness direction of the other retardation layer is preferably -50nm to -300nm, more preferably -70nm to -250nm, even more preferably -90nm to -200nm, and particularly preferably -100nm to -180nm. Here, "nx = ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the other retardation layer can be less than 10nm.

[0166] The other phase retardation layer, having a refractive index characteristic of nz > nx = ny, can be formed from any suitable material. The other phase retardation layer is preferably formed from a thin film containing a liquid crystal material fixed in a vertical orientation. The vertically oriented liquid crystal material (liquid crystal compound) can be a liquid crystal monomer or a liquid crystal polymer. As a specific example of the liquid crystal compound and the method for forming the phase retardation layer, the liquid crystal compound and the method for forming the phase retardation layer described in Japanese Patent Application Publication No. 2002-333642,

[0020] to

[0028] , can be cited. In this case, the thickness of the other phase 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.

[0167] Phase retardation layer of E-3.2 layer structure

[0168] When the phase retardation layer 40 has a stacked structure of a first layer 41 and a second layer 42, either the first layer 41 or the second layer 42 can function as a λ / 4 plate, and the other can function as a λ / 2 plate. For example, when the first layer 41 functions as a λ / 2 plate and the second layer 42 functions as a λ / 4 plate, the in-plane phase difference Re(550) of the first layer is, for example, 200nm to 300nm, preferably 230nm to 290nm, and more preferably 250nm to 280nm. The in-plane phase difference Re(550) of the second layer is, for example, 100nm to 190nm, preferably 110nm to 170nm, and more preferably 130nm to 160nm. The angle formed between 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°. The angle between the slow axis of the second layer and the absorption axis of the polarizer is, for example, 70° to 80°, preferably 72° to 78°, and more preferably about 75°, as described above. With this configuration, near-ideal anomalous wavelength dispersion characteristics can be obtained, resulting in very excellent anti-reflection properties.

[0169] The first layer 41 and the second layer 42 may be either a resin film or an alignment-cured layer of a liquid crystal compound, or both may be resin films or both may be alignment-cured layers of a liquid crystal compound. Preferably, both the first layer 41 and the second layer 42 are either resin films or alignment-cured layers of a liquid crystal compound.

[0170] The thicknesses of the first layer 41 and the second layer 42 can be adjusted to obtain the desired in-plane phase difference of the λ / 4 plate or the λ / 2 plate. For example, when the first layer 41 functions as a λ / 2 plate and the second layer 42 functions as a λ / 4 plate, and when the first layer 41 and the second layer 42 are resin films, the thickness of the first layer 41 is, for example, 40 μm to 75 μm, and the thickness of the second layer 42 is, for example, 30 μm to 55 μm. When the first layer 41 and the second layer 42 are alignment and curing layers of a liquid crystal compound, the thickness of the first layer 41 is, for example, 2.0 μm to 3.0 μm, and the thickness of the second layer 42 is, for example, 1.0 μm to 2.0 μm.

[0171] Regarding the resin film constituting the first and second layers, the liquid crystal compound, the formation method of the first and second layers, optical properties, etc., as described above for the single layer.

[0172] Example

[0173] The present invention will now be described in detail with reference to specific embodiments, but the present invention is not limited to these embodiments. The methods for measuring each characteristic are as described below. It should be noted that, unless otherwise specified, "parts" and "%" in the embodiments are based on weight.

[0174] (1) Decolorization and shrinkage of the protective layer

[0175] Test pieces (50mm × 50mm) were cut from the polarizing plates obtained in the examples and comparative examples. These test pieces were formed with two sides opposite to the direction perpendicular to the absorption axis of the polarizer and the absorption axis direction, respectively. The test pieces were adhered to a glass plate with the protective layer facing inwards using adhesive to create test specimens. These specimens were then placed in an oven at 85°C and 85% RH for 120 hours for heating and humidification, arranged in a cross-prism configuration with a standard polarizing plate. The decolorization state of the humidified polarizing plate was visually observed and evaluated according to the following criteria. Furthermore, the shrinkage of the protective layer after heating and humidification was also visually confirmed.

[0176] No problem: No discoloration observed.

[0177] Partial decolorization: Decolorization was observed at the tip.

[0178] Overall discoloration: The polarizing plate showed obvious overall discoloration.

[0179] (2) Monomer transmittance and polarization

[0180] For those undergoing decolorization evaluation that are not overall decolorization, the individual transmittance and polarization were measured. Test pieces (50mm × 50mm) were cut from the polarizing plates obtained in the examples and comparative examples, forming two sides opposite to the direction perpendicular to the absorption axis of the polarizer and the absorption axis direction, respectively. The test pieces were adhered to an alkali-free glass plate with the protective layer facing outwards using adhesive to create a test specimen. The individual transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) of this test specimen were measured using a UV-Vis spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., product name "V7100"). The polarization (P) was then calculated using the following formula. At this time, the measurement light was incident from the protective layer side.

[0181] Polarization (P)(%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0182] It should be noted that Ts, Tp, and Tc mentioned above are Y values ​​obtained by measuring a 2-degree field of view (C light source) according to JIS Z 8701 and undergoing visual sensitivity correction. Furthermore, Ts and P are essentially characteristics of the polarizer.

[0183] Then, the polarizing plate was placed in an oven at 85°C and 85% RH for 120 hours for heating and humidification (heating test). The monomer transmittance Ts0 before the heating test and the monomer transmittance Ts after the heating test were recorded. 120 The change in monomer transmittance ΔTs is calculated using the following formula.

[0184] ΔTs(%)=Ts 120-Ts0

[0185] Similarly, the polarization P0 before the heating test and the polarization P after the heating test... 120 The change in polarization ΔP can be calculated using the following formula.

[0186] ΔP(%)=P 120 -P0

[0187] It should be noted that the heating test is conducted by preparing test samples in the same manner as the decolorization test described above.

[0188] (3) Iodine adsorption capacity

[0189] The protective layer was formed on one side of the PET film in the same manner as in the embodiments and comparative examples (thickness: approximately 3 μm). The resulting PET film with the protective layer was cut into 1 cm × 1 cm pieces. 2 The sample was taken into a headspace vial (20 mL capacity) and weighed. Next, a screw-top bottle (1.5 mL capacity) containing 1 mL of iodine solution (1% wt% iodine and 7% wt% potassium iodide) was placed into the headspace vial and sealed tightly. The headspace vial was then placed in a desiccator at 65°C for 6 hours (to allow gaseous I₂ to adsorb onto the sample). The sample was then transferred to a ceramic boat and burned using an automatic sample combustion device, collecting the generated gas into 10 mL of absorbent. After collection, the absorbent was prepared to 15 mL with pure water, and the original solution or appropriately diluted solution was subjected to IC quantitative analysis. It should be noted that the iodine adsorption amount is almost zero when performing the same determination using only a PET film. The iodine adsorption amount (wt%) was calculated using the following formula based on the weight of iodine obtained from IC quantitative analysis and the weight of the protective layer itself (“weight of the PET film with protective layer” - “weight of the PET film”).

[0190] Iodine adsorption capacity (wt%) = (Iodine weight obtained by IC quantitative analysis) / (Weight of the protective layer itself) × 100

[0191] In addition, the measuring apparatus and measuring conditions are as follows.

[0192] [Measuring Apparatus]

[0193] Automatic sample combustion device: Mitsubishi Chemical Analytech, “AQF-2100H”

[0194] IC (Anion): Manufactured by Thermo Fisher Scientific, “ICS-3000”

[0195] (4) Softening temperature of the protective layer

[0196] Local thermal analysis (Nano-TA measurement) was performed on the surface of the protective layer of the polarizing plates obtained in the examples and comparative examples to calculate the softening temperature of the protective layer. The measuring apparatus and measuring conditions are described below.

[0197] Measuring apparatus: Manufactured by Hitachi High-Tech Science Co., product name "AFM5300E / / Nano-TA2"

[0198] Measurement mode: Contact mode

[0199] Probe: AN2-200

[0200] Measurement area: 8μm □ scan

[0201] Atmosphere being measured: Atmospheric pressure

[0202] (5)Judgment

[0203] The resulting polarizing plate is judged according to the following criteria.

[0204] Good: ΔP value is -4.0% to 0%.

[0205] It is possible that the value of ΔP is -10.0% to less than -4.0%.

[0206] Not allowed: ΔP value is -99.9% (complete decolorization) to less than -10%.

[0207] <Example 1>

[0208] 1. Fabrication of a laminate of polarizing element / resin substrate

[0209] As the resin substrate, a strip-shaped amorphous polyethylene terephthalate copolymer film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75 °C was used. One side of the resin substrate was subjected to corona treatment.

[0210] A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "GOHSEFIMER Z410") in a 9:1 ratio.

[0211] The above-mentioned PVA aqueous solution is coated on the corona-treated surface of the resin substrate and dried at 60°C, thereby forming a PVA-based resin layer with a thickness of 13 μm, and a laminate is produced.

[0212] The resulting laminate was subjected to uniaxial stretching at the free end to 2.4 times its original length in a 130°C oven between rollers with different circumferential speeds (air-assisted stretching treatment).

[0213] Next, the laminate was immersed in an insoluble bath (an aqueous solution of boric acid prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment).

[0214] Next, while adjusting the concentration so that the final polarizer's monomer transmittance (Ts) is 41.5% ± 0.1%, it is immersed in a staining bath (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds (staining treatment).

[0215] Next, it is immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous solution of boric acid prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) for 30 seconds (crosslinking treatment).

[0216] Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0 wt% and potassium iodide 5 wt%) at a liquid temperature of 70°C, uniaxial stretching is performed along the longitudinal direction (long side direction) between rollers with different circumferential speeds to achieve a total stretch ratio of 5.5 times (water stretching treatment).

[0217] The laminate was then immersed in a cleaning bath at 20°C (an aqueous solution of 4 parts by weight of potassium iodide mixed with 100 parts by weight of water) (cleaning treatment).

[0218] Subsequently, while drying in an oven maintained at 90°C, the laminate is heated by SUS rollers at a surface temperature of 75°C for approximately 2 seconds (drying shrinkage treatment). The width-direction shrinkage rate of the laminate based on the drying shrinkage treatment is 5.2%.

[0219] Following the above steps, a 5 μm thick polarizer is formed on a resin substrate, creating a laminate of the polarizer and the resin substrate. The polarizer has a monomer transmittance (initial monomer transmittance) Ts0 of 42.0% and a polarization degree (initial polarization degree) P0 of 99.996%.

[0220] 2. Fabrication of polarizing plates

[0221] Using a UV-curable adhesive, a cycloolefin-based film (ZT-12, 23 μm thick, manufactured by Zeon Corporation, Japan) was laminated onto the surface of the obtained polarizer as a second protective layer. Specifically, the total thickness of the adhesive coating was 1.0 μm, and the film was laminated using a rolling mill. Then, UV light was irradiated from the film side to cure the adhesive. Next, the resin substrate was peeled off to obtain a polarizing plate having the second protective layer (ZT-12) and the polarizer.

[0222] 3. Fabrication of the protective layer

[0223] 15 parts of an epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) with a biphenyl backbone were dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. 1.2 parts of a photocationic polymerization initiator (San-Apro Ltd., trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. The obtained protective layer forming composition was coated onto the surface of the polarizer of the obtained polarizing plate using a wire rod, and the coated film was dried at 60°C for 3 minutes. Then, a high-pressure mercury lamp was used to achieve a cumulative light intensity of 600 mJ / cm². 2 Ultraviolet light is irradiated in a manner that forms a protective layer. The thickness of the protective layer is 2 μm to 3 μm. Thus, a polarizing plate with a structure of a protective layer / polarizing element / another protective layer (ZT-12) is obtained. The obtained polarizing plate is subjected to the evaluation described in (1) to (4) above.

[0224] <Example 2>

[0225] 15 parts of an epoxy resin with a biphenyl backbone (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) and 10 parts of an oxetane resin (manufactured by Toa Synthetic Co., Ltd., trade name: ARON OXETANE (registered trademark) OXT-221) were dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. 2 parts of a photocationic polymerization initiator (San-Apro Ltd., trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. Using this epoxy resin solution to obtain the protective layer forming composition, a protective layer was formed in the same manner as in Example 1. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of a protective layer / polarizing element / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the evaluation described in (1) to (4) above.

[0226] (Comparative Example 1)

[0227] A hydrogenated bisphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) was used instead of the epoxy resin with a biphenyl backbone, and the protective layer was formed in the same manner as in Example 1. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of protective layer / polarizing element / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in the Example. The results are shown in Table 1.

[0228] (Comparative Example 2)

[0229] Hydrogenated bisphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) was used instead of the epoxy resin with a biphenyl backbone. Otherwise, the procedure was the same as in Example 2 to form a protective layer. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of protective layer / polarizer / another protective layer (ZT-12) was obtained. The resulting polarizing plate was subjected to the same evaluation as in the Example. The results are shown in Table 1.

[0230] (Comparative Example 3)

[0231] A bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) 828) was used instead of the epoxy resin with a biphenyl backbone. Otherwise, the procedure was the same as in Example 1 to form a protective layer. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of protective layer / polarizing element / another protective layer (ZT-12) was obtained. The resulting polarizing plate was subjected to the same evaluation as in the Example. The results are shown in Table 1.

[0232] (Comparative Example 4)

[0233] A bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) 828) was used instead of the epoxy resin with a biphenyl backbone. Otherwise, the procedure was the same as in Example 2 to form a protective layer. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of protective layer / polarizing element / another protective layer (ZT-12) was obtained. The resulting polarizing plate was subjected to the same evaluation as in the Example. The results are shown in Table 1.

[0234] (Comparative Example 5)

[0235] 20 parts of a polyester resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Nichigo-POLYESTER WR905) were dissolved in 80 parts of pure water to obtain a coating resin solution (20%). This coating resin solution was applied to the surface of the polarizing element of the polarizing plate used in the example using a wire rod, and the coating film was dried at 60°C for 5 minutes to form a protective layer in the form of a solidified coating film. The thickness of the protective layer was 2 μm to 3 μm. Thus, a polarizing plate with a structure of protective layer / polarizing element / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in the example. The results are shown in Table 1.

[0236] (Comparative Example 6)

[0237] Except that an urethane resin (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., trade name: SUPERFLEX 210) was used instead of a polyester resin, the same procedure as in Comparative Example 5 was followed to obtain a polarizing plate having a protective layer / polarizing element / another protective layer (ZT-12). The obtained polarizing plate was subjected to the same evaluation as in the Examples. The results are shown in Table 1.

[0238] (Comparative Example 7)

[0239] On the polarizing element surface of a polarizing plate having a second protective layer (ZT-12) / polarizing element, a polyurethane-based aqueous dispersion resin (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., product name: SUPERFLEX SF210) with a thickness of 0.1 μm is coated as an easy-to-adhere layer. Additionally, 20 parts of an acrylic resin (manufactured by Kusunoki Kasei Co., Ltd., product name "B-734"), a copolymer of methyl methacrylate and butyl methacrylate (molar ratio 35 / 65), are dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). Next, this acrylic resin solution is coated onto the easy-to-adhere layer using a wire rod, and the coated film is dried at 60°C for 5 minutes to form a protective layer in the form of a solidified coated film. The protective layer has a thickness of 3 μm, a softening temperature of 80.4°C, and an iodine adsorption capacity of 30.4% by weight. Thus, a polarizing plate with a protective layer / polarizing element / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in the embodiment. The results are shown in Table 1.

[0240] (Comparative Example 8)

[0241] Except for the use of an acrylic resin (manufactured by Kusunoki Chemical Co., Ltd., product name "B-722") which is a copolymer of methyl methacrylate and ethyl acrylate (molar ratio 55 / 45), the protective layer was formed in the same manner as in Comparative Example 8. The thickness of the protective layer was 3 μm, the softening temperature was 57.2 °C, and the iodine adsorption amount was 1.3% by weight. Thus, a polarizing plate with a structure of protective layer / polarizing element / another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the same evaluation as in the Example. The results are shown in Table 1.

[0242] [Table 1]

[0243]

[0244] <Evaluation>

[0245] As can be clearly seen from Table 1, even though the polarizing plate obtained in the embodiment is very thin, the reduction of optical properties under heating and humidification environment is still suppressed and the durability is excellent.

[0246] Industrial availability

[0247] The polarizing plate of the present invention is suitable for use in image display devices. Examples of image display devices include portable devices such as portable information terminals (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game consoles; office automation (OA) equipment such as computer monitors, laptops, and copiers; household electrical appliances such as cameras, televisions, and microwave ovens; in-vehicle equipment such as rear-view monitors, monitors for car navigation systems, and car audio systems; display equipment such as digital signage and information displays for commercial shops; security equipment such as surveillance monitors; and care and medical equipment such as nursing monitors and medical monitors.

[0248] Explanation of reference numerals in the attached figures

[0249] 10: Polarizer

[0250] 20: Protective layer

[0251] 40: Phase difference layer

[0252] 100: Polarizing plate

[0253] 110, 111: Polarizing plates with phase retardation layers

Claims

1. A polarizing plate having a polarizing element and a protective layer disposed on one side of the polarizing element. The protective layer is composed of a cured epoxy resin with a biphenyl backbone. in, The total thickness of the polarizing plate is less than 20 μm. The protective layer also includes oxetane resin, with the content of oxetane resin being 10 to 50 parts by weight relative to the total amount of epoxy resin with biphenyl backbone and oxetane resin of 100 parts by weight.

2. The polarizing plate according to claim 1, wherein, The cured product is a cationic polymer cured product.

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

4. The polarizing plate according to claim 1 or 2, wherein, The iodine adsorption amount of the protective layer is less than 10% by weight.

5. The polarizing plate according to claim 1 or 2, wherein, The softening temperature of the protective layer is above 100°C.

6. The polarizing plate according to claim 1 or 2, wherein the total thickness is less than 10µm.

7. A polarizing plate with a phase retardation layer, wherein the polarizing plate of any one of claims 1 to 6 has a phase retardation layer on the side of the polarizing plate not provided with the protective layer.

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