WO2024075658A1 - Polarizing plate and display device using same - Google Patents

Abstract

The present invention provides: a polarizing plate having durability in a high temperature and high humidity environment; and a display device using same. Provided is a polarizing plate in which a protective film A is adhered to one surface of a polarizer and a protective film B is adhered to the other surface thereof, the protective film A is a hard coat film including a hard coat layer formed on one surface of a transparent substrate, the protective film A comprises a base layer made from a resin component of the transparent substrate, an outermost layer made from a hard coat component, and a compatible layer which is formed between the base layer and the outermost layer and includes the resin component of the transparent substrate and the hard coat component mixed with each other, the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B at 40°C and 90%RH satisfy conditions (1) and (2) at the same time, and the thickness a of the outermost layer and the thickness b of the compatible layer satisfy a condition (3).　(1): 240 g/m2/day>TA>70 g/m2/day (2): 70 g/m2/day≥TB (3): 0.60≤a/b≤0.85

Description

Polarizing plate and display device using the same

The present invention relates to a polarizing plate and a display device using the same.

Polyvinyl alcohol (PVA) is mainly used for polarizing plates used in display devices. Since PVA has extremely poor water resistance, protective films are attached to both sides of the film. Conventionally, hard coat films with moisture permeability of about 300 to 1000 g/m ² /day, which are made by laminating a hard coat layer on a triacetyl cellulose (TAC) film, have been used as protective films for polarizing plates. However, under harsh conditions of high temperature and humidity, the PVA cannot completely prevent water absorption, which causes degradation.

Therefore, instead of TAC, protective films using cycloolefin polymer (COP) or polyethylene terephthalate (PET) have been developed, and the moisture permeability of the protective films has been reduced to about 5 to 100 g/m ² /day.

JP 2021-144076 A

In recent years, there has been a demand for polarizing plates that are durable under extremely high temperatures and humidity, such as for in-vehicle applications. In high-temperature and humid environments, if the water vapor barrier properties of the protective film are too high, moisture will not penetrate from the outside, but there have been observed cases where moisture generated from the base material and the adhesive used to attach the protective film remains in the polarizing plate and causes degradation.

The present invention therefore aims to provide a polarizing plate that is durable in high-temperature, high-humidity environments and a display device that uses the same.

The polarizing plate of the present invention is a polarizing plate having a protective film A bonded to one surface of a polarizer and a protective film B bonded to the other surface, wherein the protective film A is a hard coat film having a hard coat layer formed on one surface of a transparent substrate, and has a substrate layer made of a resin component of the transparent substrate, an outermost layer made of a hard coat component, and a compatible layer formed between the substrate layer and the outermost layer and in which the resin component of the transparent substrate and the hard coat component are mixed, wherein the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B at 40°C and 90% RH simultaneously satisfy the following conditions (1) and (2), and the thickness a of the outermost layer and the thickness b of the compatible layer satisfy the following condition (3).
240 g/m ² /day>TA>70 g/m ² /day ... (1)
70 g/m ² /day≧TB (2)
0.60≦a/b≦0.85 (3)

The display device according to the present invention is equipped with the above polarizing plate.

The present invention provides a polarizing plate that is durable in high-temperature, high-humidity environments, and a display device using the same.

FIG. 1 is a cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of the protective film A shown in FIG.

FIG. 1 is a cross-sectional view showing the schematic configuration of a polarizing plate according to an embodiment.

The polarizing plate 10 comprises a polarizer 1, a protective film A attached to one side of the polarizer 1, and a protective film B attached to the other side of the polarizer 1. The polarizer 1 is formed by adsorbing iodine or a dye onto a polyvinyl alcohol (PVA) film and orienting it. The PVA that constitutes the polarizer 1 has poor strength and water resistance, so protective films A and B are attached to both sides of the polarizer 1.

Protective film A is a hard coat film in which a hard coat layer is formed on one side of a transparent substrate. The hard coat layer is a functional layer that covers the flexible transparent substrate and imparts hardness and water vapor barrier properties to protective film A. A triacetyl cellulose (TAC) film, which has excellent transparency, can be suitably used as the transparent substrate.

FIG. 2 is a cross-sectional view showing the schematic configuration of protective film A shown in FIG. 1.

Protective film A can be formed by applying a hard coat layer-forming composition containing an active energy ray-curable compound, a hydrophobic material, a photopolymerization initiator, and a solvent to one side of a transparent substrate, drying the composition, and curing the coating by irradiating it with ultraviolet light.

When the hard coat layer forming composition is applied to the transparent substrate, a part of the transparent substrate swells or dissolves due to the solvent contained in the hard coat layer forming composition, and a layer is formed in which the components of the hard coat layer forming composition (hard coat components) and the resin components constituting the transparent substrate are mixed. After drying the coating film of the hard coat layer forming composition, the coating film is cured by ultraviolet irradiation, as shown in FIG. 2, a substrate layer 2 mainly made of the resin components of the transparent substrate, an outermost layer 3 which is a cured layer mainly made of the hard coat components, and a compatible layer 4 formed between the substrate layer 2 and the outermost layer 3 and in which the resin components of the transparent substrate and the hard coat components are mixed and cured are formed. The interface between the substrate layer 2 and the compatible layer 4, and the interface between the compatible layer 4 and the outermost layer 3 can be confirmed by observing the cross section of the protective film A using a scanning electron microscope (SEM), and the thicknesses of the substrate layer 2, the compatible layer 4, and the outermost layer 3 can be identified from the SEM image. The thickness of the compatible layer 4 can be controlled by the drying time and drying temperature after application of the hard coat layer forming composition. For example, if the drying time is extended, the swelling or dissolution of the transparent substrate by the solvent proceeds more, and the compatible layer 4 can be made thicker. In addition, if the drying temperature is increased, the drying proceeds more quickly, suppressing the swelling or dissolution of the transparent substrate by the solvent and allowing the compatible layer 4 to be made thinner.

As the active energy ray curable compound, for example, a monofunctional, difunctional, trifunctional or higher functional (meth)acrylate monomer can be used. In this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

Examples of monofunctional (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, and isodecyl (meth)acrylate. , lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene oxide modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide modified phenoxy (meth)acrylate, b-phenol (meth)acrylate, ethylene nonylphenol (meth)acrylate modified with ethylene oxide, nonylphenol (meth)acrylate modified with propylene oxide, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxyethyl hydrogen phthalate, p) Acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane, adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from adamantanediol, etc.

Examples of bifunctional (meth)acrylates include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxypivalic acid neopentyl glycol di(meth)acrylate.

Examples of trifunctional or higher (meth)acrylates include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, and glycerin tri(meth)acrylate, as well as trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. Examples of such polyfunctional (meth)acrylate compounds include trifunctional or higher polyfunctional (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, as well as polyfunctional (meth)acrylate compounds in which a portion of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

Also, as a polyfunctional monomer, urethane (meth)acrylate can be used. Examples of urethane (meth)acrylate include those obtained by reacting a polyester polyol with an isocyanate monomer or a prepolymer, and then reacting the resulting product with a (meth)acrylate monomer having a hydroxyl group.

Examples of urethane (meth)acrylates include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, etc.

The above-mentioned polyfunctional monomers may be used alone or in combination of two or more. In addition, the above-mentioned polyfunctional monomers may be monomers in the composition, or may be partially polymerized oligomers.

The hydrophobic material is a component that imparts hydrophobicity to the hard coat layer and adjusts the moisture permeability of protective film A. Cycloolefin polymers and (meth)acrylates containing an alicyclic structure can be used as hydrophobic materials contained in the hard coat layer.

As the (meth)acrylate containing an alicyclic structure, for example, a (meth)acrylate having one or more of a cyclopentane structure, a dicyclopentane structure, a cyclohexane structure, a cyclodecane structure, a tricyclodecane structure, an isobornyl structure, and an adamantane structure can be used.

Specific examples of (meth)acrylates containing an alicyclic structure include cyclohexyl (meth)acrylate, cyclohexanedimethanol mono(meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexanol (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentadienyl (meth)acrylate. monofunctional (meth)acrylates such as 2-dicyclopentenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl methacrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, tricyclodecane dimethanol mono(meth)acrylate, and adamantyl (meth)acrylate; cyclohexane dimethanol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, dicyclopentanyl methacrylate, and the like; dicyclopentadienyl di(meth)acrylate, bornyl di(meth)acrylate, isobornyl di(meth)acrylate, tricyclodecanyl di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, adamantyl di(meth)acrylate, adamantane dimethanol di(meth)acrylate, adamantane diethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, norborna Examples of the polyfunctional (meth)acrylates include dimethylol di(meth)acrylate, cyclohexane trimethanol tri(meth)acrylate, adamantyl tri(meth)acrylate, adamantane trimethanol tri(meth)acrylate, norbornane trimethylol tri(meth)acrylate, tricyclodecane trimethanol tri(meth)acrylate, and perhydro-1,4,5,8-dimethanonaphthalene-2,3,7-(oxymethyl) tri(meth)acrylate. These (meth)acrylates may be used alone or in combination of one or more.

As a photopolymerization initiator, radical polymerization initiators such as acetophenone, benzophenone, thioxanthone, benzoin, benzoin methyl ether, and acylphosphine oxide can be used. As a polymerization initiator, for example, diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-phenylacetophenone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, Michler's ketone, acetophenone, and 2-chlorothioxanthone can be used. One of these may be used alone, or two or more may be used in combination.

The solvent may be any solvent capable of swelling or dissolving the transparent substrate, and may be one or more of the following solvents, such as alcohols (e.g., methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropyl alcohol, isobutanol, etc.); ketones (e.g., acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, etc.); ketone alcohols (e.g., diacetone alcohol, etc.); aromatic hydrocarbons (e.g., benzene, toluene, xylene, etc.); glycols (e.g., ethylene glycol, propylene glycol, hexylene glycol, etc.); glycol ethers (e.g., ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, diethyl carbitol, propylene glycol monomethyl ether, etc.); esters (e.g., dimethyl carbonate, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, amyl acetate, etc.); ethers (e.g., dimethyl ether, diethyl ether, etc.); N-methylpyrrolidone, dimethylformamide, etc., may be used alone or in combination.

Additionally, various additives such as antistatic agents, defoamers, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, photosensitizers, antifouling agents, leveling agents, oil repellents, water repellents, and fingerprint prevention agents may be added to the composition for forming the hard coat layer as necessary.

The method for applying the composition for forming the hard coat layer is not particularly limited, and for example, it can be applied using a spin coater, roll coater, reverse roll coater, gravure coater, microgravure coater, knife coater, bar coater, wire bar coater, die coater, dip coater, spray coater, applicator, etc.

The coating thickness of the composition for forming a hard coat layer (film thickness of the coating film) is preferably 8 μm or less. If the coating thickness of the composition for forming a hard coat layer exceeds 8 μm, curling is likely to occur due to shrinkage during curing, which is not preferred. The coating thickness of the composition for forming a hard coat layer (film thickness of the coating film) is more preferably 6 to 7 μm.

Furthermore, it is preferable that the pencil hardness of protective film A (hard coat film) is 3H or more. If the pencil hardness of protective film A is 3H or more, the polarizing plate will have excellent surface hardness and improved durability.

Protective film B is a low moisture permeable film made of any one of cycloolefin polymer (COP), polyethylene terephthalate (PET), and polymethyl methacrylate (PMMA). Protective film B is attached to polarizer 1 via, for example, an ultraviolet-curable adhesive. The thickness of protective film B is not particularly limited, but is preferably 10 to 100 μm.

In addition, in the display device, protective film B is placed on the display panel side, and the hard coat layer of protective film A is placed on the viewing side (the side opposite the display panel).

The transparent substrate (substrate layer 2) of protective film A is bonded to the PVA film of polarizer 1 using water-based glue (PVA aqueous solution) as an adhesive. To ensure adhesion between the transparent substrate and the PVA film, protective film A is subjected to a saponification treatment before bonding. Because water-based glue is used to bond protective film A to polarizer 1, moisture may be present in the adhesive layer and TAC film even after a drying process. If both protective films A and B are constructed using films with low moisture permeability, the intrusion of moisture from the outside is suppressed, but in extremely high-temperature environments such as the inside of a car in summer, moisture contained in the adhesive and/or transparent substrate continues to remain in polarizer 10, causing deterioration of polarizer 1.

In the polarizing plate 10 according to this embodiment, a difference is provided between the moisture permeability of protective film A and that of protective film B, and the moisture permeability of protective film A and protective film B are each set to a specific range, thereby suppressing deterioration of the polarizer 1 due to moisture from the adhesive and/or TAC film.

Specifically, when the moisture permeabilities of protective films A and B at 40° C. and 90% RH are TA and TB, respectively, TA and TB simultaneously satisfy the following conditions (1) and (2). Note that both of the moisture permeabilities TA and TB are values measured in accordance with the moisture permeability test method (cup method) for moisture-proof packaging materials specified in JIS Z 0208:1976.
240 g/m ² /day>TA>70 g/m ² /day ... (1)
70 g/m ² /day≧TB (2)

The polarizing plate 10 according to this embodiment satisfies the above conditions (1) and (2) simultaneously, and thus can suppress the intrusion of moisture from the outside into the polarizing plate, while discharging moisture generated from the adhesive used to bond the protective film A to the polarizer 1 and/or the transparent substrate of the protective film A to the outside when exposed to a high-temperature environment of, for example, 85° C. The moisture permeability TA is preferably 190 to 240 g/m ² /day, and more preferably 190 to 220 g/m ² /day.

The polarizing plate 10 is exposed to light from a light source for a long period of time while being incorporated into a display device. Therefore, it is required that the hard coat layer (outermost layer 3) of the protective film A does not peel off due to deterioration even when exposed to light for a long period of time, and that the low moisture permeability and surface hardness of the protective film A can be maintained. The adhesion of the outermost layer 3 is related to the thickness of the compatible layer 4 formed on the protective film A, and if the compatible layer 4 has a certain thickness or more relative to the thickness of the outermost layer 3, the adhesion between the outermost layer 3 and the base layer 2 will be good. The thickness of the compatible layer 4 also affects the low moisture permeability of the protective film A. When the coating thickness of the composition for forming a hard coat layer is constant, the thicker the compatible layer 4, the thinner the thickness of the outermost layer 3, which contributes greatly to the low moisture permeability, and therefore the lower the moisture permeability.

Specifically, the protective film A according to this embodiment is formed so that the thickness a of the outermost layer 3 and the thickness b of the compatible layer 4 satisfy the following condition (3).
0.60≦a/b≦0.85 (3)

When a/b is less than 0.60, the thickness of the compatible layer 4 is sufficiently thick relative to the thickness of the outermost layer 3, so that the adhesion of the outermost layer 3 to the base layer 2 is good. However, since the thickness of the compatible layer 4 is formed thick, the thickness of the outermost layer 3 is insufficient, so that the moisture permeability is high, and condition (1) cannot be satisfied. On the other hand, when a/b exceeds 0.85, the outermost layer 3 becomes thick, so that the moisture permeability is low, but the thickness of the compatible layer 4 is insufficient relative to the thickness of the outermost layer 3, so that the adhesion of the outermost layer 3 to the base layer 2 is deteriorated. Even within the range of the above condition (3), a/b is more preferably 0.61 to 0.83, and more preferably 0.69 to 0.83. The thickness a of the outermost layer 3 is preferably 2.9 to 3.6 μm, and more preferably 3.1 to 3.6 μm. The thickness b of the compatible layer 4 is preferably 4.1 to 4.9 μm, and more preferably 4.1 to 4.8 μm.

As described above, the polarizing plate 10 according to this embodiment includes protective film A and protective film B that satisfy the above conditions (1) to (3). With this configuration, protective film B arranged on the display panel side almost completely blocks the ingress and egress of moisture. Meanwhile, protective film A arranged on the viewing side allows the release of moisture generated inside the polarizing plate 10 in an extremely high-temperature environment while suppressing the ingress of moisture into the polarizing plate 10 from the outside. Therefore, in the polarizing plate 10 according to this embodiment, when used in a high-temperature environment, moisture generated inside the polarizing plate 10 does not remain, suppressing deterioration of the polarizer and making it possible to maintain the optical performance of the polarizing plate 10 for a longer period of time.

Furthermore, by having the thicknesses of the outermost layer 3 and the compatible layer 4 of the protective film A satisfy the above condition (3), it is possible to suppress the moisture permeability of the protective film A, while suppressing deterioration due to light even when the film is exposed to light for a long period of time, and to maintain the adhesion of the outermost layer 3 to the base layer 2. As a result, it is possible to maintain the low moisture permeability and surface hardness of the protective film A for a long period of time, and it is possible to improve the durability of the polarizing plate.

Therefore, this embodiment can provide a polarizing plate 10 that has excellent durability in high-temperature and high-humidity environments.

The polarizing plate 10 according to this embodiment can be used in combination with an image display panel such as a liquid crystal panel or an organic EL panel to form an image display device. The image display device may also include a touch panel. The polarizing plate 10 according to this embodiment has excellent durability in high temperature and high humidity environments, and can therefore be suitably used as an image display device to be installed in environments such as the inside of a vehicle, which can be extremely hot and humid.

The following describes specific examples of the present invention.

A composition for forming a hard coat layer was prepared containing the main material (polymerizable material), hydrophobic material, photopolymerization initiator, and solvent in the ratios shown in Table 1. Note that Irgacure (registered trademark) 184 shown in Table 1 is 1-hydroxycyclohexyl phenyl ketone, and TPO is diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide.

The prepared hard coat layer forming composition was applied to a 40 μm thick TAC film (product name: TJ40 manufactured by Fujifilm Corporation) using a wire bar coater to a coating thickness as shown in Table 2. After heating in an oven to dry the coating film, the coating film was cured by irradiating ultraviolet light in a nitrogen atmosphere (oxygen concentration 500 ppm or less) in a UV curing device so that the integrated light amount was 100 mJ/cm ² , to produce protective film A (hard coat film) according to Examples 1 to 6 and Comparative Examples 1 to 6. In Examples 7 and 8, a 60 μm thick polymethyl methacrylate (PMMA) film and a 26 μm thick cycloolefin polymer (COP) film were used as protective film A. In addition, a 26 μm thick COP film was used as protective film B.

The TAC film surface of protective film A was attached to the polarizer using water-based glue and then dried. After that, protective film B was attached to the polarizer using a UV-curable adhesive, and the UV-curable adhesive was cured by irradiating it with UV light to obtain a polarizing plate.

Before being attached to the polarizer, protective film A was cut in a direction perpendicular to the surface, and the cross section was photographed using a scanning electron microscope (SEM). The thickness a of the outermost layer and the thickness b of the compatible layer were calculated from the cross-sectional image.

(Moisture permeability)
The moisture permeability TA of protective film A and the moisture permeability TB of protective film B before being attached to the polarizer were measured under conditions of 40° C. and 90 RH % in accordance with the moisture permeability test method for moisture-proof packaging materials (cup method) specified in JIS Z 0208:1976.

(Pencil hardness)
A scratch test was performed on the hard coat layer surface of the protective film A using a pencil (uni, 3H, manufactured by Mitsubishi Pencil Co., Ltd.) and a Clemens scratch tester (HA-301, manufactured by Tester Sangyo Co., Ltd.) under conditions of a load of 500 g and a scratch speed of 0.5 mm/sec. The scratch test was performed on five samples, and samples in which scratches were found on the hard coat layer surface of two or more samples were evaluated as NG, and the rest were evaluated as OK.

(Adhesion)
A light resistance test was carried out on the hard coat surface of the protective film A before bonding to the polarizer, by irradiating light for 200 hours under conditions of 40°C, 20% RH, and radiation intensity (integrated illuminance at 300 to 700 nm) of 500±50 W/ ^m2 using an ultraviolet fade meter (U48, manufactured by Suga Test Instruments Co., Ltd.). In accordance with the checkerboard test stipulated in the old JIS K 5400 General Test Method for Paints, 100 squares of ¹ mm2 were formed on the hard coat surface of the protective film A after the light resistance test. Adhesive tape (CT405AP-24, Nichiban Co., Ltd.) was attached to the formed squares and pressed evenly with a spatula, and then the adhesive tape was peeled off in a 90° direction, and the presence or absence of peeling of the outermost layer was visually confirmed. When peeling occurred in 10% or more of the area of each square, it was judged as peeling, and when there were no squares with peeling, it was evaluated as OK, and when there were one or more squares with peeling, it was evaluated as NG.

(Polarization degree of polarizing plate after high temperature and high humidity durability test)
The polarizing plates according to each of the Examples and Comparative Examples were placed in a thermostatic chamber at 85° C. and 85% RH, and the polarization degree was measured 240 hours and 500 hours after the placement. The polarization degree was calculated by performing luminosity correction using a 2-degree visual field (C light source) according to JIS Z 8701 for a value measured using an absorptiometer with an integrating sphere (V7100, manufactured by JASCO Corporation).

Table 2 shows the characteristics of protective films A and B for each example and comparative example, as well as the measured polarization degree of the polarizing plate (initial value, before and after the high temperature and high humidity durability test).

The polarizing plates according to Examples 1 to 6 have a moisture permeability TA of protective film A and a moisture permeability TB of protective film B that satisfy the above conditions (1) and (2), and furthermore, the thickness a of the outermost layer and the thickness b of the compatible layer satisfy the above condition (3). As a result, even after being placed in a thermostatic chamber at 85°C and 85% RH for 500 hours, they exhibited a high degree of polarization, and the adhesion of the outermost layer after the light resistance test was excellent, and the surface hardness was also good.

In contrast, in Comparative Examples 1 and 3, the a/b value of Protective Film A exceeded the range of Condition (3), and the thickness of the compatible layer was insufficient relative to the thickness of the outermost layer, resulting in poor adhesion of the outermost layer to the base layer.

In Comparative Examples 2 and 4, the a/b value of Protective Film A was below the range of Condition (3), and the outermost layer was thin instead of the compatible layer being thick, resulting in a high moisture permeability TA of Protective Film A. As a result, the intrusion of moisture from the outside could not be sufficiently suppressed, and the polarization degree deteriorated after being placed in a thermostatic chamber at 85°C and 85% RH for 500 hours.

In Comparative Examples 5 and 6, the hard coat layer was formed using a composition for forming a hard coat layer that did not contain a hydrophobic material, so the moisture permeability TA of protective film A was high. As a result, the intrusion of moisture from the outside could not be sufficiently suppressed, and the polarization degree after being placed in a thermostatic chamber at 85°C and 85% RH for 500 hours was lower than in the Examples.

In Comparative Examples 7 and 8, a PMMA film and a COP film with extremely low moisture permeability TA were used as protective film A, respectively, but the polarization degree deteriorated after being placed in a thermostatic chamber at 85°C and 85% RH for 500 hours. This is thought to be because the moisture permeability TA of protective film A was too low, and when exposed to high temperature and humidity, the moisture contained in protective film A and/or the adhesive (water glue) continued to remain in the polarizing plate, causing deterioration of the polarizer. In addition, protective film A in Comparative Examples 7 and 8 had inferior surface hardness compared to the Examples because it did not have a hard coat layer.

The present invention can be used as a polarizing plate for display devices, and is particularly suitable as a polarizing plate for display devices used in high-temperature environments such as in-vehicle applications.

A Protective Film A
B Protective film B
1 Polarizer 2 Base layer 3 Outermost layer 4 Compatibility layer 10 Polarizing plate

Claims (6)

A polarizing plate in which a protective film A is bonded to one surface of a polarizer and a protective film B is bonded to the other surface of the polarizer,
the protective film A is a hard coat film having a hard coat layer formed on one surface of a transparent substrate, the hard coat film having a substrate layer made of a resin component of the transparent substrate, an outermost layer made of a hard coat component, and a compatible layer formed between the substrate layer and the outermost layer and in which the resin component of the transparent substrate and the hard coat component are mixed;
The moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B at 40° C. and 90% RH simultaneously satisfy the following conditions (1) and (2),
A polarizing plate, wherein the thickness a of the outermost layer and the thickness b of the compatible layer satisfy the following condition (3):
240 g/m ² /day>TA>70 g/m ² /day ... (1)
70 g/m ² /day≧TB (2)
0.60≦a/b≦0.85 (3) The polarizing plate according to claim 1, wherein the transparent substrate is a triacetyl cellulose film. 2. The polarizing plate according to claim ¹ , wherein the hard coat layer does not peel off after a weathering test in which the hard coat layer of the protective film is irradiated with light for 200 hours under conditions of 40° C., 20% RH, and a radiation intensity of 500±50 W/m 2. The polarizing plate according to claim 1, wherein the pencil hardness of the protective film A is 3H or more. The polarizing plate according to claim 1, wherein the protective film B is a film made of one of cycloolefin polymer, polyethylene terephthalate, and polymethyl methacrylate. A display device comprising the polarizing plate according to any one of claims 1 to 5.