TWI880481B - Polarizing plate and display device using the 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 the same. A polarizing plate having a protective film A attached to one side of a polarizer and a protective film B attached to the other side, wherein the protective film A is a hard coating film formed by forming a hard coating layer on one side of a transparent substrate, and 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 when the peak intensity of 1782 to 1683 cm ^-1 measured by an ATR method using a germanium prism is set as P1 and the peak intensity of 1427 to 1374 cm ^-1 is set as P2, the following condition (3) is satisfied. 240g/m ² /day＞TA＞70g/m ² /day・・・(1) 70g/m ² /day≧TB・・・(2) 0.060≦P2/P1≦0.150・・・(3)

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 in polarizing plates used in display devices. PVA has very poor water resistance, so protective films are attached to both sides. In the past, the protective film of polarizing plates used a hard coating layer laminated on a triacetate cellulose (TAC) film with a moisture permeability of about 300 to 1000 g/ ^m2 /day. However, under the harsh conditions of high temperature and high humidity, there is a problem that PVA cannot be prevented from absorbing water and causing deterioration.

Therefore, research is underway to use protective films made of cycloolefin polymer (COP) or polyethylene terephthalate (PET) to replace TAC. The moisture permeability of protective films has been reduced to about 5 to 100 g/m ² /day. [Prior Art Literature] [Patent Literature]

Patent Document 1 Japanese Patent Application Publication No. 2021-144076

[Problems to be solved by the invention]

In recent years, polarizing plates with durability under extremely high temperature and humidity have been required for automotive applications. In high temperature and humidity environments, if the water vapor barrier of the protective film is too high, although moisture from the outside will not penetrate, there are also cases where moisture generated by the adhesive used to bond the substrate and protective film is retained in the polarizing plate and deteriorates.

Therefore, the object of the present invention is to provide a polarizing plate having durability in a high temperature and high humidity environment and a display device using the same. [Means for solving the problem]

The polarizing plate of the present invention is a polarizing plate having a protective film A laminated on one side of a polarizer and a protective film B laminated on the other side, wherein the protective film A is a hard coating film formed by a hard coating layer on one side of a transparent substrate, and 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 when the peak intensity of 1782 to 1683 cm ^-1 measured by an ATR method using a germanium prism is set as P1 and the peak intensity of 1427 to 1374 cm ^-1 is set as P2, the following condition (3) is satisfied. 240g/m ² /day＞TA＞70g/m ² /day・・・(1) 70g/m ² /day≧TB・・・(2) 0.060≦P2/P1≦0.150・・・(3)

Furthermore, the display device of the present invention is equipped with the above-mentioned polarizing plate. [Effects of the invention]

According to the present invention, a polarizing plate having durability in a high temperature and high humidity environment and a display device using the same can be provided.

[Form used to implement the invention]

FIG. 1 is a cross-sectional view showing a schematic structure of a polarizing plate of an embodiment.

The polarizing plate 10 includes 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 allowing a polyvinyl alcohol (PVA) film to adsorb iodine or a dye and align it. Since the PVA constituting the polarizer 1 has poor strength and water resistance, the protective films A and B are attached to both sides of the polarizer 1.

The protective film A is a hard coating film having a hard coating layer 3 formed on one surface of a transparent substrate 2. The hard coating layer 3 covers the soft transparent substrate 2 and is a functional layer that imparts hardness and water vapor barrier properties to the protective film A. As the transparent substrate 2, a triacetate cellulose (TAC) film having good transparency can be preferably used.

The protective film A can be formed by applying a hard coating layer forming composition containing an active energy ray-curable compound, a hydrophobic material, a photopolymerization initiator, and a solvent on one surface of the transparent substrate 2, drying the composition, and curing the coating by irradiating ultraviolet rays.

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

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, tertiary butyl (meth)acrylate, glycidyl (meth)acrylate, acrylamide, phenoxyethanol, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isoborneol (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethylcarbitol (meth)acrylate ) acrylate, (meth) acrylate phosphate, ethylene oxide modified (meth) acrylate phosphate, (meth) acrylate phenoxy, ethylene oxide modified (meth) acrylate phenoxy, propylene oxide modified (meth) acrylate phenoxy, b-phenol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate, propylene oxide modified nonylphenol (meth) acrylate, methoxydiethylene glycol (meth) acrylate methacrylate), methoxypolyethyleneglycol (meth)acrylate, methoxypropyleneglycol (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)acryloyloxypropylhexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyltetrahydrohydrogen phthalate phthalate), dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane, adamantane derivative mono (meth)acrylate such as adamantane acrylate having a monovalent mono (meth)acrylate derived from adamantanediol, and the like.

Examples of bifunctional (meth)acrylates include 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, neopentyl glycol hydroxypivalate di(meth)acrylate and the like.

Examples of trifunctional or higher (meth)acrylates include trihydroxymethylpropane tri(meth)acrylate, ethoxylated trihydroxymethylpropane tri(meth)acrylate, propoxylated trihydroxymethylpropane tri(meth)acrylate, tris 2-hydroxyethyl isocyanurate tri(meth)acrylate, acrylate), tri(meth)acrylates such as glycerol tri(meth)acrylate, tri(meth)acrylate such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, ditrihydroxymethylpropane tri(meth)acrylate, or tri- or higher-functional polyfunctional (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ditrihydroxymethylpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrihydroxymethylpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrihydroxymethylpropane hexa(meth)acrylate, or polyfunctional (meth)acrylate compounds obtained by substituting a part of these (meth)acrylates with an alkyl group or ε-caprolactone.

Urethane (meth)acrylates may also be used as the polyfunctional monomer. Examples of urethane (meth)acrylates include those obtained by reacting a (meth)acrylate monomer having a hydroxyl group with a product obtained by reacting an isocyanate monomer or prepolymer with a polyester polyol.

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, and dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer.

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

The hydrophobic material is a component that makes the hard coating layer 3 hydrophobic and is used to adjust the moisture permeability of the protective film A. As the hydrophobic material contained in the hard coating layer 3, a cycloolefin polymer or a (meth)acrylate containing an alicyclic structure can be used.

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

Specific examples of the (meth)acrylate 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-trimethylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, 2-dicyclopentenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl methacrylate, and dicyclopentanyl (meth)acrylate. Ester, isoborneol (meth)acrylate, tricyclodecyl (meth)acrylate, tricyclodecane dimethanol mono(meth)acrylate, adamantyl (meth)acrylate and the like, or cyclohexanedimethanol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, dicyclopentenyl di(meth)acylate, 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, adamantyl dimethanol di(meth)acrylate, adamantyl di(meth)acrylate, adamantyl di(meth)ethanol di(meth)acrylate, dihydroxymethyl dicyclopentane di(meth)acrylate, norbornane dihydroxymethyl di(meth)acrylate, cyclohexanedimethanol tri(meth)acrylate, adamantyl tri(meth)acrylate, adamantyl trimethanol tri(meth)acrylate, norbornane trimethylol tri(meth)acrylate, tri(methacrylate)), tricyclodecane trimethanol tri(meth)acrylate, perhydro-1,4,5,8-dimethanonaphthalene-2,3,7-(oxymethyl)tri(meth)acrylate, and the like. These (meth)acrylates may be used alone or in combination of one or more.

As photopolymerization initiators, acetophenone, benzophenone, 9-oxysulfur As the polymerization initiator, for example, diphenyl (2,4,6-trimethylbenzyl) phosphine oxide, bis (2,4,6-trimethylbenzyl) phenylphosphine oxide, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxyphenyl acetophenone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, michler's ketone, acetophenone, 2-chloro-9-oxysulfur etc. You may use any one of these alone or in combination of two or more.

As the solvent, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropanol, and isobutanol can be used; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone can be used; keto alcohols such as diacetone alcohol can be used; aromatic hydrocarbons such as benzene, toluene, and xylene can be used; glycols such as ethylene glycol, propylene glycol, and hexylene glycol can be used; glycol ethers such as ethoxylated thiocyanate, butyl thiocyanate, ethyl carbitol, butyl carbitol, diethyl thiocyanate, diethyl carbitol, and propylene glycol monomethyl ether can be used; esters such as dimethyl carbonate, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, and amyl acetate can be used; ethers such as dimethyl ether and diethyl ether can be used; and N-methylpyrrolidone, dimethylformamide, and the like can be used alone or in combination of two or more thereof.

Furthermore, various additives such as antistatic agents, defoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, photosensitizers, antifouling agents, leveling agents, oil repellents, water repellents, and anti-fingerprint adhesion agents may be added to the hard coat layer forming composition as needed.

The method for applying the hard coating layer forming composition is not particularly limited, and for example, a spin coater, a roll coater, a reverse roll coater, a gravure coater, a micro gravure coater, a knife coater, a rod coater, a wire rod coater, a die coater, a dip coater, a spray coater, an applicator, or the like can be used for application.

The coating thickness of the hard coating layer forming composition (film thickness of the coating film) is preferably 10 μm or less, more preferably 8 μm or less. If the coating thickness of the hard coating layer forming composition is greater than 10 μm, the coating film is more likely to curl due to shrinkage during curing, which is not preferred.

In addition, the pencil hardness of the protective film A (hard coating film) is preferably 3H or more. When the pencil hardness of the protective film A is 3H or more, the surface hardness of the polarizing plate is good and the durability is improved.

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

In the display device, the protective film B is disposed on the display panel side, and the hard coating layer 3 of the protective film A is disposed on the visual recognition side (the opposite side of the display panel).

The transparent substrate 2 of the protective film A is bonded to the PVA film of the polarizer 1 using glue (PVA aqueous solution) as an adhesive. In addition, in order to ensure the close adhesion between the transparent substrate 2 and the PVA film, the protective film A is subjected to a saponification treatment before bonding. Since glue is used in bonding the protective film A to the polarizer 1, moisture can be contained in the adhesive layer and the TAC film even after the drying step. In the case where both the protective films A and B are composed of films with low moisture permeability, although the intrusion of moisture from the outside is suppressed, in an extremely high temperature environment such as in a car in summer, the moisture contained in the adhesive and/or the transparent substrate 2 will continue to remain in the polarizing plate 10, causing the polarizer 1 to deteriorate.

Therefore, in the polarizing plate 10 of the present embodiment, a difference is designed between the moisture permeability of the protective film A and the moisture permeability of the protective film B, and by making the moisture permeabilities of the protective film A and the protective film B respectively within specific ranges, the deterioration of the polarizing plate 1 caused by moisture from the adhesive and/or the TAC film is suppressed.

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

The polarizing plate 10 of this embodiment satisfies the above-mentioned conditions (1) and (2) at the same time, thereby suppressing the intrusion of moisture from the outside into the interior of the polarizing plate. When exposed to a high temperature environment such as 85°C, the polarizing plate 10 can discharge to the outside the moisture generated from the adhesive used to bond the protective film A to the polarizer 1 and/or the transparent substrate 2 of the protective film A.

In addition, when the peak intensity (peak height) of 1782 to 1683 cm ^-1 measured by the ATR method using a germanium prism is defined as P1, and the peak intensity of 1427 to 1374 cm ^-1 is defined as P2 in the hard coating layer 3, P2/P1 is defined as the degree of hardness. The peak of 1782 to 1683 cm ^-1 represents the peak of the stretching vibration of the C=O bond of the (meth)acrylic group constituting the (meth)acrylate compound, and the intensity of 1427 to 1374 cm ^-1 represents the peak of the stretching vibration of the C=C bond of the (meth)acrylic group of the (meth)acrylate compound. If the value of the degree of hardness P2/P1 of the hard coating layer 3 becomes smaller, the pencil hardness increases, and if the degree of hardness P2/P1 becomes larger, the pencil hardness decreases. Furthermore, if the value of hardening degree P2/P1 decreases, the moisture permeability decreases, and if the value of hardening degree P2/P1 increases, the moisture permeability tends to increase. Therefore, there is a range of hardening degree P2/P1 that can take into account both pencil hardness and moisture permeability. Specifically, hardening degree P2/P1 preferably satisfies the following condition (3). 0.060≦P2/P1≦0.150 ･･･(3)

If the curing degree P2/P1 is less than 0.060, the moisture permeability of the protective film A becomes too low and the above condition (1) may not be satisfied. In this case, it may be impossible to discharge the moisture generated by the transparent substrate 2 of the protective film A to the outside. If the curing degree P2/P1 is greater than 0.150, the pencil hardness of the protective film A deteriorates. In addition, the moisture permeability may become too high and the above condition (1) may not be satisfied. In this case, it may be difficult to suppress the intrusion of moisture from the outside into the polarizing plate. The condition (1) is more preferably 239.7 g/m ^{2 /} day ≧ TA ≧ 93.5 g/m ² /day, more preferably 212 g/m ² /day ≧ TA ≧ 152.9 g/m ² /day, and still more preferably 191.7 g/m ² /day ≧ TA ≧ 152.9 g/m ² /day. The condition (3) is more preferably 0.067 ≦ P2/P1 ≦ 0.149, still more preferably 0.101 ≦ P2/P1 ≦ 0.137, and still more preferably 0.101 ≦ P2/P1 ≦ 0.126.

As described above, the polarizing plate 10 of the present embodiment has a protective film A and a protective film B that satisfy the above conditions (1) to (3). With this structure, the protective film B disposed on the display panel side almost blocks the entry and exit of moisture. On the other hand, the protective film A disposed on the visual recognition side can suppress the intrusion of moisture from the outside into the interior of the polarizing plate 10, and at the same time, it can release the moisture generated inside the polarizing plate 10 in an extremely high temperature environment. Therefore, when the polarizing plate 10 of the present embodiment is used in a high temperature environment, the moisture generated inside the polarizing plate 10 will not remain, so the degradation of the polarizer is suppressed, and the optical performance of the polarizing plate 10 can be maintained for a longer period of time.

Furthermore, by satisfying the above condition (3) with the hard coating layer 3 of the protective film A, the moisture permeability of the protective film A can be controlled within a preferred range while also being given a high pencil hardness. As a result, the low moisture permeability and surface hardness of the protective film A can be maintained for a long time, thereby improving the durability of the polarizing plate.

Therefore, according to this embodiment, a polarizing plate 10 having good durability in a high temperature and high humidity environment can be provided.

The polarizing plate 10 of this embodiment can be used in combination with an image display panel such as a liquid crystal panel or an OLED panel to form an image display device. The image display device may also have a touch panel. The polarizing plate 10 of this embodiment has excellent durability in a high temperature and high humidity environment, so it can be used as an image display device installed in an extremely high temperature and humid environment such as a car interior. [Example]

Hereinafter, specific examples for implementing the present invention will be described.

A hard coating layer forming composition was prepared containing a main material (polymerizable material), a hydrophobic material, a photopolymerization initiator and a solvent in the proportions shown in Table 1. Irgacure (registered trademark) 184 shown in Table 1 is 1-hydroxycyclohexyl phenyl ketone.

The prepared hard coating layer forming composition was applied to a 40 μm thick TAC film (trade name: TJ40, manufactured by Fuji Film Co., Ltd.) using a wire bar coater so as to obtain the coating thickness described in Table 2. The coating was dried by heating in an oven at 60°C for 1 minute, and then cured by irradiating with ultraviolet light in a UV curing device in a nitrogen atmosphere (oxygen concentration of 500 ppm or less), thereby preparing protective films A (hard coating films) of Examples 1 to 6 and Comparative Examples 1 to 7. In Comparative Examples 6 and 7, 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.

Table 1 Substrate TAC HC coating Main material Material Name Pentaerythritol triacrylate Mixing quantity (weight) 39.7 Hydrophobic materials Material Name Cycloolefin polymers Mixing quantity (weight) 0.3 Photopolymerization initiator Material Name Irgacure (Registered Trademark) 184 Mixing quantity (weight) 5.0 Solvent Solvent 1 Material Name Dimethyl carbonate Mixing quantity (weight) 32.5 Solvent 2 Material Name MIBK Mixing quantity (weight) 17.5

After the TAC film surface of protective film A is bonded to the polarizer using glue and dried, protective film B is bonded to the polarizer using a UV curable adhesive, and the UV curable adhesive is cured by irradiating UV rays to obtain a polarizing plate. In Comparative Example 5, protective film A is used as protective film B.

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

(Degree of Hardening) The hard coating layer of the protective film A was subjected to FT-IR analysis by the ATR method. From the FT-IR measurement results, the peak height P1 at 1782 to 1683 cm ^-1 and the peak height P2 at 1427 to 1374 cm ^-1 were obtained, and the degree of hardening P2/P1 was obtained. At this time, the infrared spectrometer used was FT/IR-610 manufactured by JASCO Corporation, and a germanium prism was used as a prism.

(Pencil hardness) Using a pencil (uni, 3H manufactured by Mitsubishi Pencil Co., Ltd.) and a Clemens scratch tester (HA-301, manufactured by TESTER SANGYO Co., Ltd.), the hard coating surface of the protective film A was scratched at a load of 500g and a scratching speed of 0.5mm/sec. The scratch test was performed on 5 samples, and samples with more than 2 scratches on the hard coating surface were rated as NG, and the rest were rated as OK.

(Polarization degree of polarizing plate after high temperature and high humidity durability test) The polarizing plates of each embodiment and each comparative example were placed in a constant temperature 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 correcting the value measured by an absorptiophotometer with an integrating sphere (V7100, manufactured by JASCO Corporation) with a 2-degree field of view (light source C) according to JIS Z 8701.

Table 2 shows various properties of the protective films A and B of each embodiment and each comparative example, and the measured values of the polarization degree of the polarizing plate (initial value, before and after the high temperature and high humidity durability test).

Table 2 Protective Film A Characteristics Protective film B characteristics Polarizing plate characteristics Structure HC layer thickness [µm] Moisture permeability TA [g・m ² /day] Hardening degree (P2/P1) Pencil hardness (3H) Structure Moisture permeability TB [g・m ² /day] Polarization degree[%] Early days After 240 hours of operation After 500 hours of operation Embodiment 1 HC laminated TAC film 7.0 239.7 0.149 OK COP Film 5 99.510 99.441 99.367 Embodiment 2 7.0 212 0.137 OK 99.469 99.397 Embodiment 3 7.0 191.7 0.126 OK 99.483 99.409 Embodiment 4 7.0 152.9 0.101 OK 99.497 99.421 Embodiment 5 7.0 93.5 0.067 OK 99.501 99.367 Embodiment 6 7.0 70.1 0.061 OK 99.472 99.324 Comparison Example 1 7.0 239.8 0.154 NG 99.439 99.31 Comparison Example 2 7.0 69.6 0.060 OK 99.468 99.300 or less Comparison Example 3 7.0 240.5 0.155 NG 99.423 99.301 or less Comparison Example 4 7.0 68.7 0.058 OK 99.408 99.302 or less Comparison Example 5 7.0 71.3 0.062 OK Protective film A 71.2 99.426 99.303 or less Comparison Example 6 PMMA film - 40 - NG COP Film 5 99.407 99.304 or less Comparative Example 7 COP Film - 5 - NG 99.396 99.305 or less

The polarizing plates of Examples 1 to 6 are examples in which the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B satisfy the above conditions (1) and (2), and the degree of hardening of the hard coating layer of the protective film A also satisfies the above condition (3). Therefore, even after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours, they still show a high polarization value and have excellent surface hardness.

In contrast, in Comparative Example 1, the degree of hardening P2/P1 exceeds the range of condition (3), and since the pencil hardness of the surface of the protective film A decreases, the surface hardness also decreases.

In Comparative Example 2, the moisture permeability TA of the protective film A is lower than the range of condition (1), and the moisture permeability TA of the protective film A becomes lower. Therefore, moisture continues to remain in the polarizing plate, and the polarization degree after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours is lower than that of the example.

In Comparative Example 3, the moisture permeability TA of the protective film A exceeds the range of condition (1), and the moisture permeability TA of the protective film A becomes high. Therefore, it is not possible to fully suppress the intrusion of moisture from the outside, and the polarization degree after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours is worse than that of the example. In addition, because the curing degree P2/P1 exceeds the range of condition (3), the pencil hardness of the surface of the protective film A decreases, and the surface hardness also decreases.

In Comparative Example 4, since the hardening degree P2/P1 is lower than the range of condition (3), on the one hand, the pencil hardness of the surface of the protective film A is sufficient, on the other hand, the moisture permeability TA of the protective film A is lower than the range of condition (1). Therefore, moisture continues to remain in the polarizing plate, and the polarization degree after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours is lower than that of the example.

In Comparative Example 5, the moisture permeability TB of the protective film A exceeded the range of condition (2), and the moisture permeability TB of the protective film B became high. Therefore, the intrusion of moisture from the outside could not be sufficiently suppressed, and the polarization degree after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours was lower than that of the example.

In Comparative Examples 6 and 7, although PMMA film and COP film with extremely low moisture permeability TA were used as protective film A, respectively, the polarization degree deteriorated after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours. It is believed that this is because the moisture permeability TA of protective film A is too low, and when exposed to high temperature and high humidity, the moisture contained in protective film A and/or adhesive (glue) will continue to remain in the polarizing plate, causing the polarizer to deteriorate. In addition, since the protective film A of Comparative Examples 6 and 7 does not have a hard coating layer, the surface hardness is worse than that of the embodiment. [Possibility of industrial use]

The present invention can be used as a polarizing plate used in a display device, and is particularly suitable as a polarizing plate for a display device used in a high temperature environment such as a vehicle-mounted application.

1: Polarizer 2: Transparent substrate 3: Hard coating 10: Polarizer A: Protective film A B: Protective film B

FIG. 1 is a cross-sectional view showing a schematic structure of a polarizing plate of an embodiment.

1: Polarizer

2: Transparent substrate

3: Hard coating

10: Polarizing plate

A: Protective film A

B: Protective film B

Claims (5)

A polarizing plate, wherein a protective film A is laminated on one surface of a polarizer and a protective film B is laminated on the other surface. The protective film A is a hard coating film formed on one surface of a transparent substrate. 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). When the peak intensity of 1782 to 1683 cm ^-1 measured by an ATR method using a germanium prism is defined as P1 and the peak intensity of 1427 to 1374 cm ^-1 is defined as P2, the following condition (3) is satisfied: 240 g/m ² /day＞TA＞70 g/m ² /day ･･･(1) 70 g/m ² /day≧TB ･･･(2) 0.060≦P2/P1≦0.150 ･･･(3). The polarizing plate of claim 1, wherein the transparent substrate is a cellulose triacetate film. As for the polarizing plate of claim 1, the pencil hardness of the protective film A is above 3H. A polarizing plate as claimed in claim 1, wherein the protective film B is a film made of any one of cycloolefin polymer, polyethylene terephthalate and polymethyl methacrylate. A display device comprising a polarizing plate as claimed in any one of claims 1 to 4.