JP2008134396A - Polarizing plate and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which has no poor visibility due to light interference such as an interference fringe and has excellent abrasion resistance, in which a polarizer and a protection layer do not peel even under a high temperature high humidity environment and high polarization degree can be maintained and which is suitable for a liquid crystal display apparatus or the like. <P>SOLUTION: The polarizing plate is constituted by laminating the protection layer and the polarizer via a light cation curing adhesive containing aliphatic epoxy, alicyclic epoxy and/or oxetane and a photoinitiator. The protection layer is constituted by laminating k (k is an integer of ≥2) pieces of thermoplastic resin layers and has a relation expressed by formula [1]: ¾n<SB>i</SB>(λ)-n<SB>i+1</SB>(λ)¾≤0.05, wherein n<SB>i</SB>(λ) denotes a refractive index of (i-th) thermoplastic resin layer at a wavelength λ within a range between 380 nm and 780 nm, n<SB>i+1</SB>(λ) denotes a refractive index of (i+1)-th thermoplastic resin layer at the wavelength λ within the range between 380 nm and 780 nm and i denotes an integer between 1 and k-1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizing plate and a liquid crystal display device. More specifically, the polarizing plate and the liquid crystal display device are excellent in scratch resistance and anti-glare property, and are free from poor visibility due to interference of light such as interference fringes. The present invention relates to a polarizing plate capable of maintaining a high degree of polarization without peeling off from a protective layer and the liquid crystal display device.

The polarizing plate used for a liquid crystal display device etc. is a laminated body which consists of a polarizer and a protective film. As a polarizer constituting this polarizing plate, a film in which iodine or a dichroic dye is adsorbed on a film obtained by forming a film of polyvinyl alcohol by a solution casting method and stretched in a boric acid solution is usually used.
On the other hand, a triacetyl cellulose film is widely used as a protective film constituting the polarizing plate. However, since the triacetylcellulose film has poor moisture resistance and gas barrier properties, the durability, heat resistance, mechanical strength, etc. of the polarizing plate are insufficient.

In order to improve the durability and heat resistance of the polarizing plate, it has been proposed to use a protective film other than the triacetyl cellulose film. For example, Patent Document 1 proposes to use a laminated film including a norbornene-based resin layer and a resin layer having a small haze value as a protective film. And it is disclosed that a polarizing plate is obtained by attaching the protective film to a polarizer containing polyvinyl alcohol with the surface of the norbornene resin layer facing.
JP 2005-115085 A

In Patent Document 2, a resin layer having a smaller hygroscopic property than triacetyl cellulose and having a positive photoelastic constant and a resin layer having a smaller hygroscopic property than triacetyl cellulose and having a negative photoelastic constant are laminated. A protective film having a small photoelastic constant has been proposed. And the polarizing plate formed by sticking this protective film on the polarizer containing polyvinyl alcohol is disclosed.
JP 2000-206303 A

  However, in the polarizing plate obtained only by the techniques disclosed in Patent Document 1 and Patent Document 2, interference fringes are generated or scratches are caused by friction when attached to a liquid crystal display device or the like. Visibility from may be poor. In addition, the degree of polarization may change due to use under high temperature and high humidity.

  The object of the present invention is that there is no visual defect due to interference of light such as interference fringes, excellent scratch resistance and anti-glare properties, the polarizer and the protective layer do not peel off even in a high temperature and high humidity environment, and a high degree of polarization. Is to provide a polarizing plate suitable for a liquid crystal display device or the like.

As a result of intensive studies to achieve the above object, the present inventor is a film in which k thermoplastic resin layers (k is an integer of 2 or more) are laminated, and the i-th thermoplastic resin layer the refractive index n _i (λ) at the wavelength lambda in the range of 380 nm to 780 nm, the refractive index at a wavelength lambda in the range of 380 nm to 780 nm of the i + 1 th thermoplastic resin layer n _{i + 1} (lambda) and the specific relationship Interfering with a polarizing plate formed by laminating a film satisfying the above conditions and a polarizer through a photocationic curable adhesive containing an aliphatic epoxy, an alicyclic epoxy and / or oxetane, and a photopolymerization initiator It has been found that interference of light such as stripes is less likely to occur, and that the polarizer and the protective layer are not peeled off even in a high temperature and high humidity environment, and a high degree of polarization is maintained.
The present invention has been completed based on these findings.

The present invention includes the following.
(1) A refractive index n _i (λ) at a wavelength λ in the range of 380 nm to 780 nm of the i-th thermoplastic resin layer, wherein k thermoplastic resin layers (k is an integer of 2 or more) are laminated. The refractive index n _{i + 1} (λ) at a wavelength λ in the range of 380 nm to 780 nm of the i + 1 th thermoplastic resin layer is represented by the formula [1] (where i represents an integer of 1 to k−1). A protective layer having
A polarizer is laminated via a photocationically curable adhesive containing an aliphatic epoxy, an alicyclic epoxy and / or oxetane, and a photopolymerization initiator.
Polarizer.
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1]

(2) The polarizing plate according to (1), wherein the protective layer has an absolute value of a photoelastic coefficient of 10 × 10 ⁻¹² Pa ⁻¹ or less.
(3) The polarizing plate for liquid crystal displays according to (1) or (2), wherein the protective layer contains an ultraviolet absorber.
(4) A liquid crystal display device comprising the polarizing plate according to any one of (1) to (3).

The polarizing plate of the present invention is less likely to cause interference of light such as interference fringes, and is less likely to cause scratches due to friction. Therefore, it is difficult to cause poor visibility when attached to a display screen.
Since the retardation of the polarizing plate of the present invention hardly changes due to heat or stress due to deformation, even if unpredictable and undesirable stress is applied, light leakage, color unevenness, coloring, etc. hardly occur near the edge of the display screen. . Further, the polarizer and the protective layer hardly peel even under a harsh environment.
The polarizing plate of the present invention has high contrast and does not generate streaks. Moreover, since it is excellent in flexibility and scratch resistance, visibility does not become poor. The polarizing plate of the present invention is particularly suitable for a large-area liquid crystal display device and the like because the polarizer and the protective layer do not peel even in a high temperature and high humidity environment and maintains a high degree of polarization.

It is a figure which shows the refractive index n ((lambda)) of each resin layer used in the present Example. It is a figure which shows distribution of the absolute value of the difference of the refractive index n ((lambda)) of each resin layer used in the present Example. It is a figure which shows distribution of the absolute value of the difference of the refractive index n ((lambda)) of the polyvinyl alcohol used in the present Example, and the refractive index n ((lambda)) of a polymethylmethacrylate layer.

Explanation of symbols

  COP: alicyclic olefin polymer, PC: polycarbonate resin, PMMA: polymethyl methacrylate resin, PVA: polyvinyl alcohol

  In the polarizing plate of the present invention, a protective layer in which k thermoplastic resin layers (k is an integer of 2 or more) are laminated, a polarizer, an aliphatic epoxy, an alicyclic epoxy and / or oxetane, It is laminated through a photocationic curable adhesive containing a photopolymerization initiator. Further, usually, another protective layer is laminated on the polarizer on the side opposite to the side where the protective layer is laminated.

(Photocationic curable adhesive)
The photocationically curable adhesive used in the present invention contains an aliphatic epoxy, an alicyclic epoxy and / or oxetane, and a photopolymerization initiator.
The aliphatic epoxy used in the present invention contains a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof. As aliphatic epoxy, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6- Examples include hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, trimethylolpropane diglycidyl ether, and polyethylene glycol diglycidyl ether. Trimethylolpropane triglycidyl ether and trimethylolpropane diglycidyl ether are preferable from the viewpoint of low viscosity. Commercial products of aliphatic epoxy include Epolite 100MF (manufactured by Kyoeisha Chemical Co., Ltd., trimethylolpropane triglycidyl ether), EX-321L (manufactured by Nagase ChemteX Corporation, trimethylolpropane diglycidyl ether), and the like.

  Examples of the alicyclic epoxy used in the present invention include vinylcyclohexene monooxide, 1,2-epoxy-4-vinylcyclohexane, 1,2: 8,9 diepoxy limonene, 3,4-epoxycyclohexenylmethyl-3′4. And '-epoxycyclohexenecarboxylate. Examples of commercially available products include “CEL2000”, “CEL3000”, and “CEL2021P” manufactured by Daicel Chemical Industries.

  The oxetane compound is a compound having a 4-membered ring ether, that is, an oxetane ring in the molecule. As the oxetane compound used in the present invention, 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [{(3-ethyl-3-oxetanyl) methoxy} methyl] benzene, 3-ethyl-3- (phenoxymethyl) ) Oxetane, bis (3-ethyl-3-oxetanylmethyl) ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane), 3-ethyl-[{(3-triethoxysilylpropoxy) methyl) oxetane , Oxetanylsilsesquioxane, phenol novolac oxetane and the like. Among these oxetane compounds, 3-ethyl-3-hydroxymethyloxetane, bis (3-ethyl-3-oxetanylmethyl) ether, and 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane are preferable. Examples of commercially available oxetane compounds include “OXT-101” (3-ethyl-3-hydroxymethyloxetane), “OXT-211” (3-ethyl-3- (phenoxymethyl) oxetane) manufactured by Toagosei Co., Ltd. OXT-221 "(di [1-ethyl (3-oxetanyl)] methyl ether)," OXT-212 "(3-ethyl-3- (2-ethylhexyloxymethyl) oxetane).

Examples of the photopolymerization initiator include sulfonium salts and iodonium salts.
Examples of the sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, 4,4′-bis [diphenylsulfonio] diphenyl sulfide bishexafluorophosphate, 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluoroantimonate, 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluorophosphate 7- [Di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate, 7- [Di (p-toluyl) sulfonio]- -Isopropylthioxanthone tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide hexafluorophosphate, 4- (p-tert-butylphenylcarbonyl) -4'-diphenylsulfonio-diphenyl sulfide Hexafluoroantimonate, 4- (p-tert-butylphenylcarbonyl) -4′-di (p-toluyl) sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate and the like can be mentioned.

Examples of the iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di (4-nonylphenyl) iodonium hexafluorophosphate, and the like.
These photopolymerization initiators may be used alone or in combination of two or more. Examples of commercially available products of these photopolymerization initiators include “PI-2074” manufactured by Rhodia.

Furthermore, you may make a photosensitizer contain in an adhesive agent as needed. By using a photosensitizer, the reactivity is improved, and the mechanical strength and adhesive strength of the cured product can be improved.
The photosensitizer is not particularly limited. Examples include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, and photoreductive dyes. As photosensitizers, benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether, α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, methyl o-benzoylbenzoate, 4,4 ′ A benzophenone derivative such as bis (diethylamino) benzophenone; a thioxanthone derivative such as 2-chlorothioxanthone and 2-isopropylthioxanthone; an anthraquinone derivative such as 2-chloroanthraquinone and 2-methylanthraquinone; N-methylacridone, N- Acridone derivatives such as butylacridone; other examples include α, α-diethoxyacetophenone, benzyl, fluorenone, xanthone, uranyl compounds, halogen compounds, and photoreductive dyes. . These may be used alone or in combination of two or more. Examples of commercially available photosensitizers include “Kayacure DETX-S” manufactured by Nippon Kayaku Co., Ltd.

  The polarizing plate of the present invention is obtained by laminating a protective layer on one surface of the polarizer via the above-mentioned photocation curable adhesive, then curing the adhesive, and fixing the protective layer to the polarizer.

There is no particular limitation on the method of applying the adhesive to the resin film of the substrate, and various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used.
The photocation curable adhesive is cured by light irradiation. Although the light source to be used is not particularly limited, for example, a metal halide lamp, a mercury xenon lamp, high-pressure mercury, or other light emitting light having a light emission distribution at a wavelength of 450 to 300 nm can be used. The light irradiation intensity varies depending on the target adhesive or resin film, and is not limited, but the irradiation intensity in the wavelength region effective for activation of the initiator is preferably 1 to 2000 mW / cm ² (365 nm). The light irradiation time varies depending on the adhesive or resin film to be cured, and is not limited, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 1500 to 3000 mJ / cm ² (365 nm). Is preferred.

  Prior to bonding of the protective layer to the polarizer, the bonding surface may be subjected to easy adhesion processing such as saponification treatment, corona treatment, primer treatment, and anchor coating treatment.

(Protective layer)
The protective layer is formed by laminating k thermoplastic resin layers (k is an integer of 2 or more). That is, the protective layer is laminated in this order from the first thermoplastic resin layer to the kth thermoplastic resin layer. k is usually 2 to 7, preferably 3 to 5.
This protective layer is disposed on at least one side of the polarizing plate. This protective layer may function as a viewing side protective layer of the polarizing plate, or may function as a liquid crystal cell side protective layer. When this protective layer is disposed only on one side of the polarizing plate, another protective layer (hereinafter referred to as a protective layer on the other side) is usually disposed on the opposite surface.

  The thermoplastic resin constituting the thermoplastic resin layer is, for example, polycarbonate resin, polyethersulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, polyethylene resin, polyvinyl chloride resin, diacetyl. It can be selected from cellulose, triacetyl cellulose, alicyclic olefin polymer, and the like.

Examples of the alicyclic olefin polymer include a cyclic olefin random multiple copolymer described in JP-A No. 05-310845, a hydrogenated polymer described in JP-A No. 05-97978, and JP-A No. 11-124429. And thermoplastic dicyclopentadiene-based ring-opening polymers and hydrogenated products thereof. Note that not all of the illustrated thermoplastic resins can be applied to the present invention, and some of the same kind of thermoplastic resins may or may not satisfy the following requirements. Select as appropriate.
The thermoplastic resin used in the present invention includes colorants such as pigments and dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, lubricants, and solvents. These compounding agents may be appropriately blended.

  Lubricants include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, and strontium sulfate, as well as polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, and cellulose Organic particles such as acetate propionate can be mentioned. As particles constituting the lubricant, organic particles are preferable, and among these, particles made of polymethyl methacrylate are particularly preferable.

  As the lubricant, elastic particles made of a rubber-like elastic body can be used. Examples of the rubber-like elastic body include an acrylate-based rubber-like polymer, a rubber-like polymer containing butadiene as a main component, and an ethylene-vinyl acetate copolymer. Examples of the acrylic ester rubbery polymer include those containing butyl acrylate, 2-ethylhexyl acrylate, or the like as a main component. Of these, acrylate polymers based on butyl acrylate and rubbery polymers based on butadiene are preferred. The elastic particles may be formed by laminating two kinds of polymers. Typical examples thereof include an alkyl acrylate such as butyl acrylate, a styrene grafted rubber elastic component, and a methyl methacrylate. Examples thereof include elastic particles in which a hard resin layer made of a copolymer of a rate and / or methyl methacrylate and an alkyl acrylate forms a layer with a core-shell structure.

  The elastic particles generally have a number average particle size of 2.0 μm or less, preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.5 μm when dispersed in a thermoplastic resin. Even if the primary particle size of the elastic particles is small, if the number average particle size of the secondary particles formed by aggregation or the like is large, the protective layer has a high haze (cloudiness), and the light transmittance is low. Not suitable for display screens. Moreover, when the number average particle size becomes too small, the flexibility tends to decrease.

In the present invention, the refractive index n _p (λ) of the elastic particles at a wavelength of 380 nm to 780 nm is between the refractive index n _r (λ) of the thermoplastic resin serving as the matrix at a wavelength of 380 nm to 780 nm. It is preferable to satisfy the relationship.
| N _p (λ) −n _r (λ) | ≦ 0.05 Formula [2]
In particular, it is more preferable that | n _p (λ) −n _r (λ) | ≦ 0.045. Note that n _p (λ) and n _r (λ) are average values of the main refractive indexes at the wavelength λ. When the value of | n _p (λ) −n _r (λ) | exceeds the above value, transparency may be impaired by interface reflection caused by a difference in refractive index at the interface.

  The thermoplastic resin used in the present invention preferably has a light transmittance in the visible region of 400 to 700 nm at a thickness of 1 mm of 80% or more, more preferably 85% or more, and even more preferably 90% or more. . The thermoplastic resin is preferably an amorphous resin from the viewpoint of transparency. In addition, the thermoplastic resin preferably has a glass transition temperature of 60 to 200 ° C, more preferably 100 to 180 ° C. The glass transition temperature can be measured by differential scanning calorimetry (DSC).

  The thermoplastic resin used in the present invention is preferably selected from those having a melt flow rate value in the range of 10 to 100 g / 10 min (280 ° C., load 2.16 kgf). Moreover, it is preferable that the value of the melt flow rate of the thermoplastic resin which comprises each layer is comparable. Specifically, it is preferable that the difference in the melt flow rate value of the thermoplastic resin constituting the adjacent layers is 0 to 30 g / 10 minutes (280 ° C., load 2.16 kgf).

  Moreover, it is preferable that content of the volatile component contained in the said protective layer is small. Means for reducing the content of volatile components include: (1) reducing the amount of volatile components in the transparent resin itself; (2) molding a protective layer by melt extrusion; (3) molding the protective layer. For example, the transparent resin to be used may be pre-dried before being used. The preliminary drying is performed with a hot air dryer or the like, for example, in the form of pellets or the like. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, the amount of volatile components in the protective layer can be reduced, and foaming of the transparent resin to be extruded can be prevented.

The protective layer has a refractive index n _i (λ) at a wavelength λ in the range of 380 nm to 780 nm of the i-th thermoplastic resin layer, and a refraction at a wavelength λ in the range of 380 nm to 780 nm of the i + 1-th thermoplastic resin layer. The ratio n _{i + 1} (λ) has the relationship of the formula [1].
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1]
However, i represents the integer of 1-k-1. In particular, the protective layer more preferably satisfies the relationship | n _i (λ) −n _{i + 1} (λ) | ≦ 0.045.
Note that n _i (λ) and n _{i + 1} (λ) are average values of the main refractive indexes at the wavelength λ. If the value of | n _i (λ) −n _{i + 1} (λ) | exceeds the above value for some or all of i = 1 to k−1, the difference in refractive index at the interface Interference fringes may occur on the surface of the protective layer due to the interface reflection caused by. Note that the i-th thermoplastic resin layer and the (i + 1) -th thermoplastic resin layer adjacent to each other may be in direct contact with each other or may be in contact with each other through an adhesive layer described later.

  The protective layer can have a water absorption of at least one of the laminated thermoplastic resin layers of 0.5% or less, and more preferably 0.1% or less. The durability of the polarizing plate can be increased by using a low water absorption rate for the protective layer. The water absorption rate of the thermoplastic resin layer can be determined according to JIS K 7209.

The protective layer used in the present invention is preferably optically isotropic. Specifically, Re is preferably 10 nm or less, more preferably 5 nm or less. The absolute value of Rth is preferably 10 nm or less, more preferably 5 nm or less.
The in-plane direction retardation Re, retardation Rth in the thickness direction, the thickness of the film upon the d (nm), Re = ( n x -n y) × d, Rth = ((n _x + _ny ) / 2- _nz ) × d. _nx and _ny are in-plane main refractive indexes ( _nx ≧ _ny ); _nz is a refractive index in the thickness direction; and d is an average thickness.

  The thickness of each thermoplastic resin layer constituting the protective layer is not particularly limited, but the thickness of the kth thermoplastic resin layer is usually 5 to 100 μm, preferably 10 μm or more, and more preferably Is 10-50 μm. The thickness of the 1st thermoplastic resin layer is 5-100 micrometers normally, Preferably it is 10-50 micrometers. At this time, it is preferable that the thickness of the kth thermoplastic resin layer is substantially equal to the thickness of the first thermoplastic resin layer. Specifically, the absolute value of the difference between the thickness of the first thermoplastic resin layer and the thickness of the kth thermoplastic resin layer is preferably 20 μm or less, and more preferably 10 μm or less. .

Moreover, the thickness of the intermediate thermoplastic resin layer provided as needed between the first thermoplastic resin layer and the kth thermoplastic resin layer is usually 5 to 100 μm, preferably 10-50 μm. The ratio of the thickness of the intermediate thermoplastic resin layer to the thickness of the kth thermoplastic resin layer or the thickness of the first thermoplastic resin layer (intermediate layer thickness: first layer or first layer The thickness of the kth layer is not particularly limited, but is preferably 5: 1 to 1: 5.
The thickness of the entire protective layer is usually 20 to 200 μm, preferably 40 to 100 μm.

  The thermoplastic resin forming the first thermoplastic resin layer is preferably selected from an acrylic resin, an alicyclic olefin polymer, and a polycarbonate resin, particularly preferably selected from an acrylic resin such as a polymethyl methacrylate resin. .

  The thermoplastic resin that forms the kth thermoplastic resin layer is preferably hard. Specifically, a pencil hardness (JIS K 5600-5-4, where the test load is 500 g) is preferably harder than 2H. As the thermoplastic resin for forming the kth thermoplastic resin layer, the most preferable one is selected from acrylic resins such as polymethyl methacrylate resin.

  In addition, when a polarizing plate is formed by providing a protective layer on the polarizer, a thermoplastic resin for forming the kth thermoplastic resin layer is used to prevent the polarizing plate from warping, bending, rounding, etc. The thermoplastic resin forming the thermoplastic resin layer is preferably selected from the same kind of thermoplastic resin.

  The laminated thermoplastic resin layers may be in direct contact with each other or may be in contact with each other through an adhesive layer. The average thickness of the adhesive layer is usually 0.01 to 30 μm, preferably 0.1 to 15 μm. The adhesive layer is a layer having a tensile fracture strength according to JIS K 7113 of 40 MPa or less. Adhesives constituting the adhesive layer include acrylic adhesives, urethane adhesives, polyester adhesives, polyvinyl alcohol adhesives, polyolefin adhesives, modified polyolefin adhesives, polyvinyl alkyl ether adhesives, rubber Adhesive, ethylene-vinyl acetate adhesive, vinyl chloride-vinyl acetate adhesive, SEBS (styrene-ethylene-butylene-styrene block copolymer) adhesive, SIS (styrene-isoprene-styrene block copolymer) ) Adhesives, ethylene adhesives such as ethylene-styrene copolymers, acrylic ester adhesives such as ethylene- (meth) methyl acrylate copolymers, ethylene- (meth) ethyl acrylate copolymers, etc. Is mentioned. Among these, those that maintain a predetermined elasticity after curing are more preferable, and examples of such adhesives include SEBS adhesives, SIS adhesives, and ethylene-vinyl acetate adhesives.

The moisture permeability of the protective layer used in the present invention is preferably 5 g · m ⁻² day ⁻¹ or more and 400 g · m ⁻² day ⁻¹ or less, more preferably 10 g · m ⁻² day ⁻¹ or more, 200 g · m ⁻² day ⁻¹ or less. The moisture permeability can be measured by the cup method described in JIS Z 0208 under the test conditions for 24 hours in an environment of 40 ° C. and 92% RH.
By setting the moisture permeability of the protective layer within the above range, it is possible to obtain a polarizing plate excellent in durability even in a high temperature and high humidity environment.

The protective layer has all values of i when the tensile modulus of elasticity of the i-th thermoplastic resin layer is A _i and the tensile modulus of elasticity of the i + 1-th thermoplastic resin layer is A _{i + 1.} On the other hand, | A _{i + 1} −A _i | ≧ 0.5 GPa. By setting it as such a structure, the intensity | strength and flexibility of a polarizing plate provided with the said protective film can be improved, preventing the fall of the optical performance by an interference fringe etc. The tensile modulus of elasticity Ak of the _kth thermoplastic resin layer can be 3.0 GPa or more. Tensile modulus A _k of the k th thermoplastic resin layer may be a larger than the tensile modulus A _k-1 of the k-1 th thermoplastic resin layer adjacent thereto. Further, the tensile modulus A _{1 of the first} thermoplastic resin layer can be 3.0 GPa or more.

In addition to the thermoplastic resin layer containing an amorphous thermoplastic resin, the humidity expansion coefficient β _i of the i-th thermoplastic resin layer and the humidity expansion coefficient β _{i + 1 of} the i + 1-th thermoplastic resin layer are included. The polarizing plate formed by laminating a film satisfying a specific relationship and a polarizer can maintain a high degree of polarization without peeling off the polarizer and the protective layer even in a high temperature and high humidity environment.

  In addition, the total number of laminated thermoplastic resin layers is preferably 7 layers or less, and more preferably 5 layers or less. When the number is larger than the number of layers, it may be difficult to control the surface shape and thickness of each layer.

  In the protective layer, it is preferable that the surface of the kth thermoplastic resin layer is not formed with linear concave portions or linear convex portions, and the surface is flat. Even if linear concave portions or linear convex portions are formed, linear concave portions having a depth of less than 50 nm or a width of more than 500 nm, or lines having a height of less than 50 nm or a width of more than 500 nm. It is preferable that it is a convex part. More preferably, it is a linear concave portion having a depth of less than 30 nm or a width of 700 nm, and a linear convex portion having a height of less than 30 nm or a width of greater than 700 nm. Further, it is preferable that the above-described linear concave portions and linear convex portions are not formed on the surface of the first thermoplastic resin layer as well as the kth thermoplastic resin. By not forming the linear concave portion or the linear convex portion, it is possible to prevent light leakage or optical interference.

  The depth of the linear concave portion described above, the height of the linear convex portion, and the width thereof can be obtained by the following method. The protective layer is irradiated with light, the transmitted light is projected onto the screen, and the light or dark stripes of light appearing on the screen (this part has a large depth of linear recesses and a large height of linear protrusions) Cut out at 30 mm square. The surface of the cut film piece is observed using a three-dimensional surface structure analysis microscope (field region 5 mm × 7 mm), converted into a three-dimensional image, and a cross-sectional profile in the MD direction is obtained from the three-dimensional image. The cross-sectional profile is obtained at 1 mm intervals in the visual field region. In this cross-sectional profile, an average line is drawn, the length from the average line to the bottom of the linear recess is the linear recess depth, or the length from the average line to the top of the linear protrusion is the linear protrusion height. It becomes. The distance between the intersection of the average line and the profile is the width. The maximum values are obtained from the measured values of the linear concave portion depth and the linear convex portion height, respectively, and the width of the linear concave portion or the linear convex portion showing the maximum value is obtained. The maximum value of the linear recess depth and the height of the linear convex portion obtained from the above, the width of the linear concave portion and the width of the linear convex portion showing the maximum value, the depth of the linear concave portion of the film Let the height of the linear protrusions and their widths.

  The thermoplastic resin layer having no linear convex part and linear concave part having such a size is formed, for example, in a lip tip part which reduces the surface roughness of the lip part of the die in a T-die type extrusion molding method. Coating with chromium, nickel, titanium, etc., spraying ceramics on the tip of the lip, coating of TiN, TiAlN, TiC, CrN, DLC (diamond-like carbon) on the inner surface of the lip by the PVD (Physical Vapor Deposition) method, etc. The temperature distribution around the molten resin immediately after being extruded from the die, the air flow, etc. are uniformly adjusted, and the resin that forms the thermoplastic resin layer is selected to have the same melt flow rate value, etc. Cast support film having a small surface roughness in the cast molding method. Can be obtained by reducing the surface roughness of the coating machine, adjusting the temperature distribution during drying of the coating layer, the drying temperature, and the drying time.

  As another means for setting the size of the linear concave portion or the linear convex portion within the above range, in the T-die type extrusion molding method, the one attached to the die lip (for example, burns or dust) is used. Examples include removing, improving die lip releasability, making die lip wettability uniform over the entire surface, reducing resin powder, reducing the amount of dissolved oxygen in resin pellets, and installing a polymer filter in the melt extruder. It is done.

  The protective layer is not particularly limited by the production method thereof, for example, one obtained by laminating a single layer thermoplastic resin film, one obtained by co-extrusion molding of a plurality of thermoplastic resins, thermoplastic resin Examples thereof include those obtained by casting a thermoplastic resin solution on a film. Among these, from the viewpoint of productivity, the protective layer is preferably obtained by coextrusion molding. In the case of coextrusion molding, since a complicated process (for example, a drying process or a coating process) is not required, there is an advantage that it is possible to provide a film with less external foreign matters such as dust and excellent optical characteristics.

  Furthermore, in the polarizing plate of the present invention, functional layers such as a hard coat layer, an antireflection layer, and an antifouling layer may be formed on the outer surface of the protective layer. In particular, these layers exhibit their functions when the protective layer is the viewer side protective layer.

(Hard coat layer)
The hard coat layer is preferably formed from a heat or photo-curing material that exhibits a hardness of 1H or higher in a pencil hardness test (test plate is a glass plate) shown in JIS K 5600-5-4. The pencil hardness of the protective layer provided with the hard coat layer is preferably 4H or harder. When the surface layer of the protective layer is made of an acrylic resin, it is easy to adjust the pencil strength of the surface to 4H or harder with the hard coat layer.

  Examples of the hard coat layer material include organic hard coat materials such as organic silicone, melamine, epoxy, acrylic, and urethane acrylate; and inorganic hard coat materials such as silicon dioxide. Of these, urethane acrylate-based and polyfunctional acrylate-based hard coat materials are preferably used from the viewpoint of good adhesive strength and excellent productivity.

This hard coat layer has a refractive index n _H between the refractive index n _L of the low refractive index layer laminated thereon, n _H ≧ 1.53, and n _H ^1/2 −0.2 <. It is preferable to have a relationship of n _L <n _H ^1/2 +0.2 in order to develop the antireflection function.

  This hard coat layer contains various fillers for the purpose of adjusting the refractive index, improving the flexural modulus, stabilizing the volume shrinkage, improving heat resistance, antistatic properties, antiglare properties, etc., as desired. You may squeeze it. Furthermore, various additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, an antistatic agent, a leveling agent, and an antifoaming agent can be blended.

(Antireflection layer)
When using the polarizing plate of this invention for the display screen of a display, for example, it is preferable that the antireflection layer is further laminated | stacked on the said hard-coat layer. The antireflection layer is a layer for preventing the transfer of external light. The polarizing plate on which such an antireflection layer is laminated preferably has a reflectance at an incident angle of 5 ° and 430 to 700 nm of 2.0% or less and a reflectance at 550 nm of 1.0% or less. . The thickness of the antireflection layer is preferably 0.01 μm to 1 μm, more preferably 0.02 μm to 0.5 μm. As such an antireflection layer, for example, a layer in which a low refractive index layer having a refractive index smaller than that of the hard coat layer, preferably a refractive index of 1.30 to 1.45, is laminated, or a low layer made of an inorganic compound. Examples thereof include those obtained by repeatedly laminating a refractive index layer and a high refractive index layer made of an inorganic compound.

  The material for forming the low refractive index layer is not particularly limited as long as the refractive index is lower than that of the protective layer or the hard coat layer. For example, a resin material such as an ultraviolet curable acrylic resin, colloidal silica in the resin, and the like. Examples thereof include hybrid materials in which inorganic fine particles such as sol are dispersed, and sol-gel materials using metal alkoxides such as tetraethoxysilane. The material for forming the exemplified low refractive index layer may be a polymerized polymer, or a monomer or oligomer serving as a precursor. Moreover, it is preferable that each material contains the compound containing a fluorine group in order to provide the surface with antifouling property.

Examples of the sol-gel material containing a fluorine group include perfluoroalkylalkoxysilane. As perfluoroalkyl alkoxysilane, for example, general formula: CF ₃ (CF ₂ ) _n CH ₂ CH ₂ Si (OR) ₃ (wherein R represents an alkyl group having 1 to 5 carbon atoms, n is And an integer of 0 to 12). Specifically, for example, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltri And ethoxysilane. Among these, the compound wherein n is 2 to 6 is preferable.

  The low refractive index layer is preferably made of a cured product of a thermosetting fluorine-containing compound or an ionizing radiation curable fluorine compound. The dynamic friction coefficient of the cured product is preferably 0.03 to 0.15, and the contact angle with water is preferably 90 to 120 degrees. Examples of the curable fluorine-containing polymer compound include a perfluoroalkyl group-containing silane compound (for example, (heptadecafluoro-1,1,2,2-tetradecyl) triethoxysilane) and the like, and a fluorine-containing fluorine-containing polymer having a crosslinkable functional group. A copolymer is mentioned.

  The fluorine-containing polymer having a crosslinkable functional group is obtained by copolymerizing a fluorine-containing monomer and a monomer having a crosslinkable functional group, or by copolymerizing a fluorine-containing monomer and a monomer having a functional group, and then in the polymer. It can be obtained by adding a compound having a crosslinkable functional group to the functional group.

  Examples of the fluorine-containing monomer include fluoroolefins such as fluoroethylene, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoro-2,2-dimethyl-1,3-dioxole; “Biscoat 6FM” ( (Organic Organic Chemicals Co., Ltd.), “M-2020” (Daikin Co., Ltd.) and other (meth) acrylic acid partial or fully fluorinated alkyl ester derivatives, and fully or partially fluorinated vinyl ethers.

  Monomers having a crosslinkable functional group or compounds having a crosslinkable functional group include monomers having a glycidyl group such as glycidyl acrylate and glycidyl methacrylate; monomers having a carboxyl group such as acrylic acid and methacrylic acid; hydroxyalkyl acrylate and hydroxyalkyl Monomers having a hydroxyl group such as methacrylate; methylol acrylate, methylol methacrylate; monomers having a vinyl group such as allyl acrylate and allyl methacrylate; monomers having an amino group; monomers having a sulfonic acid group;

  As a material for forming the low refractive index layer, a material containing a sol in which fine particles such as silica, alumina, titania, zirconia, magnesium fluoride and the like are dispersed in an alcohol solvent is used because it can improve scratch resistance. Can do. From the viewpoint of antireflection properties, the fine particles preferably have a lower refractive index. Such fine particles may have voids, and silica hollow fine particles are particularly preferable. The average particle size of the hollow fine particles is preferably 5 nm to 2,000 nm, and more preferably 20 nm to 100 nm. Here, the average particle diameter is a number average particle diameter obtained by observation with a transmission electron microscope.

  The thickness of the low refractive index layer is not particularly limited, but is preferably about 0.05 to 0.3 μm, particularly preferably 0.1 to 0.3 μm.

(Anti-fouling layer)
In order to improve the antifouling property of the low refractive index layer, an antifouling layer may be further provided on the low refractive index layer. The antifouling layer is a layer that can impart water repellency, oil repellency, sweat resistance, antifouling properties and the like to the surface. As a material used for forming the antifouling layer, a fluorine-containing organic compound is suitable. Examples of the fluorine-containing organic compound include fluorocarbon, perfluorosilane, or a polymer compound thereof. As a method for forming the antifouling layer, a physical vapor deposition method such as vapor deposition or sputtering, a chemical vapor deposition method, a wet coating method, or the like can be used depending on the material to be formed. The average thickness of the antifouling layer is preferably 1 to 50 nm, more preferably 3 to 35 nm.

  In addition to these layers, other layers such as an antiglare layer, a gas barrier layer, a transparent antistatic layer, a primer layer, an electromagnetic wave shielding layer, and an undercoat layer may be further provided in the viewing side protective layer.

When the functional layer as described above is formed, it is preferable to perform chemical treatment on the surface to be formed. Examples of the chemical treatment include corona discharge treatment, sputtering treatment, low-pressure UV irradiation treatment, and plasma treatment. In addition to the chemical treatment, the viewing-side protective layer may be subjected to mechanical treatment such as etching, sandblasting, embossing roll, etc. for the purpose of enhancing adhesion with the functional layer and imparting antiglare properties. .
There is no particular limitation on the method for forming these functional layers, and a general method may be employed for forming each functional layer.

(Polarizer)
The polarizer used in the present invention is obtained by adsorbing iodine or dichroic dye on a polyvinyl alcohol film and then uniaxially stretching in a boric acid bath, or iodine or dichroic dye on a polyvinyl alcohol film. And the like obtained by adsorbing and stretching, and further modifying a part of the polyvinyl alcohol unit in the molecular chain into a polyvinylene unit. In addition, a polarizer having a function of separating polarized light into reflected light and transmitted light, such as a grid polarizer, a multilayer polarizer, and a cholesteric liquid crystal polarizer, can also be used as the polarizer. Among these, a polarizer comprising polyvinyl alcohol is preferable. The polarization degree of the polarizer is preferably 98% or more, more preferably 99% or more. The thickness (average thickness) of the polarizer is preferably 5 μm to 80 μm.

(Protective layer on the other side)
When a protective layer (protective layer on the other surface) is laminated on the surface opposite to the surface on which the protective layer is formed on the polarizing plate, the protective layer on the other surface may be the same as the protective layer described above. Alternatively, it may be a protective layer conventionally used for polarizing plates. One of the protective layer formed on the protective layer and the protective layer on the other surface functions as a viewing-side protective layer, and the other functions as a liquid crystal cell-side protective layer.
The protective layer is preferably formed of a material having a light transmittance of 80% or more, more preferably 85% or more, and still more preferably 90% or more in the visible region of 400 to 700 nm at a thickness of 1 mm.

The moisture permeability of the protective layer on the other side used in the present invention is preferably 5 g · m ⁻² day ⁻¹ or more, 400 g · m ⁻² day ⁻¹ or less, more preferably 10 g · m ⁻² day ⁻¹ or more. 200 g · m ⁻² day ⁻¹ or less.
By setting the moisture permeability of the protective layer within the above range, it is possible to obtain a polarizing plate excellent in durability even in a high temperature and high humidity environment.

  As the resin constituting the protective layer conventionally used for polarizing plates, polycarbonate resin, polyethersulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, polyethylene resin, polystyrene Examples thereof include resins, polyvinyl chloride resins, cellulose esters, and alicyclic olefin polymers. Examples of the alicyclic olefin polymer include cyclic olefin random multi-component copolymers described in JP-A No. 05-310845 or US Pat. No. 5,179,171, JP-A No. 05-97978 or US Pat. No. 5,202,388. Examples thereof include the hydrogenated polymers described, the thermoplastic dicyclopentadiene ring-opened polymers described in JP-A-11-124429, and WO99 / 20676, and hydrogenated products thereof.

  There is no particular limitation on the method of laminating the protective layer on the other side of the polarizer, for example, a general method of laminating a protective film that becomes the protective layer on the other side with a polarizer as necessary. Can be adopted. As an adhesive for bonding the protective layer on the other surface to the polarizer, a photocation curable adhesive containing the above-described aliphatic epoxy, alicyclic epoxy and / or oxetane, and photopolymerization initiator is used. It may be used or a conventionally known adhesive may be used.

The polarizing plate of this invention can laminate | stack the film which shows birefringence other than the above-mentioned protective layer, polarizer, and the protective layer of the other surface. At this time, the film showing birefringence is generally laminated on the liquid crystal cell side protective layer side.
In this case, the liquid crystal cell-side protective layer is preferably optically isotropic. Specifically, Re is preferably 10 nm or less, more preferably 5 nm or less. The absolute value of Rth is preferably 10 nm or less, more preferably 5 nm or less.

  Birefringent films include those obtained by stretching a film containing a thermoplastic resin, those obtained by forming an optically anisotropic layer on an unstretched thermoplastic resin film, and optical on a film containing a thermoplastic resin. After forming the anisotropic layer, it can be further stretched. The film showing birefringence may be a single layer film or a laminated film.

Moreover, you may use the film which shows the above birefringence as a liquid crystal cell side protective layer.
When a birefringent film is used as the liquid crystal cell side protective layer, or when a birefringent film is laminated on the liquid crystal cell side protective layer, optical compensation functions such as color compensation and viewing angle compensation are provided. The visibility of the liquid crystal display device is improved.

In a preferred polarizing plate of the present invention, the viewing-side protective layer is laminated with the first thermoplastic resin layer facing the polarizer side, and the first thermoplastic resin layer has a range of 380 nm to 780 nm. The refractive index n ₁ (λ) at a wavelength of ₁ and the refractive index n _b (λ) at a wavelength in the range of 380 nm to 780 nm of polyvinyl alcohol satisfy the relationship of the formula [3].
| N ₁ (λ) −n _b (λ) | ≦ 0.05 Formula [3]

In the preferable polarizing plate of the present invention, the first thermoplastic resin layer of the viewing-side protective layer is laminated facing the polarizer side, and the first thermoplastic resin layer is refracted at a wavelength of 380 nm. A refractive index n ₁ (380), a refractive index n ₁ (780) at a wavelength of 780 nm, a refractive index n _b (380) at a wavelength of 380 nm and a refractive index n _b (780) at a wavelength of 780 nm of the polyvinyl alcohol contained in the polarizer, However, the relationship of Formula [4] is satisfied.
|| n ₁ (380) −n _b (380) |
− | N ₁ (780) −n _b (780) || ≦ 0.02 Formula [4]

That is, the difference between the refractive index of the first thermoplastic resin layer at a wavelength near the upper limit of the visible light region and the refractive index of polyvinyl alcohol contained in the polarizer is not so different from the difference at the wavelength near the lower limit. That's what it means. In particular, it is preferable that || n ₁ (380) −n _b (380) | − | n ₁ (780) −n _b (780) || ≦ 0.01. Note that n ₁ (380) and n ₁ (780) are average values of the main refractive indexes at the respective wavelengths. n _b (380) and n _b (780) are the refractive indices of non-oriented polyvinyl alcohol.

  The polarizing plate of the present invention preferably exhibits a hardness of 3H or higher in a pencil hardness test (test plate is a glass plate) shown in JIS K 5600-5-4, more preferably a hardness of 4H or higher. .

<Liquid crystal display device>
The liquid crystal display device of the present invention can be manufactured using the polarizing plate of the present invention. In the liquid crystal display device, a light source, an incident side polarizing plate, a liquid crystal cell, and an output side polarizing plate are usually arranged in this order. The polarizing plate of the present invention can be provided on the emission side (viewing side) and / or the incident side (light source side) of the device, but it is preferable to dispose the polarizing plate of the present invention at least on the emission side. The liquid crystal display device of the present invention may further include a retardation plate, a brightness enhancement film, a light guide plate, a light diffusion plate, a light diffusion sheet, a light collection sheet, a reflection plate, and the like.

The present invention will be described in more detail with reference to examples and comparative examples. Parts and% are based on mass unless otherwise specified.
The protective films obtained in Examples and Comparative Examples were evaluated by the following methods.

<Refractive index of thermoplastic resin layer>
A resin is formed into a single layer, and a prism coupler (manufactured by Metricon, model 2010) is used. From the refractive index values at wavelengths of 633 nm, 407 nm, and 532 nm under the conditions of temperature 20 ° C. ± 2 ° C. and humidity 60 ± 5%, Caucy The refractive indexes of 380 nm and 780 nm are calculated according to the dispersion formula. FIG. 1 shows the distribution of the refractive index of each resin layer with respect to wavelength. Figure 2 shows the distribution of refractive index difference between polymethyl methacrylate resin (PMMA) and alicyclic olefin polymer (COP), and the distribution of refractive index difference between polymethyl methacrylate resin (PMMA) and polycarbonate (PC). ing. FIG. 3 shows the distribution of the difference in refractive index between polymethyl methacrylate resin (PMMA) and polyvinyl alcohol (PVA).

<Thickness of each resin layer>
The protective film was embedded in an epoxy resin, sliced using a microtome (RUB-2100, manufactured by Yamato Kogyo Co., Ltd.), and the cross section was observed and measured using a scanning electron microscope.

<Water permeability of protective film>
The measurement was performed by a method according to the cup method described in JIS Z 0208 under the test conditions of leaving for 24 hours in an environment of 40 ° C. and 92% RH. The unit of moisture permeability is g · m ⁻² · day ⁻¹ .

<Melt flow rate>
According to JIS K 7210, measurement was performed with a melt indexer F-B01 manufactured by Toyo Seiki Seisakusho under the conditions of 280 ° C. and 2.16 kgf (Condition S).

<Tensile modulus>
A thermoplastic resin is formed into a single layer to obtain a film having a thickness of 100 μm, a 1 cm × 25 cm test piece is cut out, and a tensile tester (manufactured by Toyo Baldwin, Tensilon UTM-10T-PL) is used based on ASTM D882. Then, the measurement was performed under the condition of a tensile speed of 25 mm / min. The same measurement is performed 5 times, and the arithmetic average value is set as the representative value of the tensile elastic modulus.

(Production of polarizer)
A polyvinyl alcohol film having a refractive index of 1.545 at a wavelength of 380 nm and a refractive index of 1.521 at a wavelength of 780 nm and a thickness of 75 μm is uniaxially stretched 2.5 times to obtain 0.2 g of iodine and 60 g of potassium iodide. Was immersed in an aqueous solution containing 30 g / L for 30 seconds and then immersed in an aqueous solution containing 70 g / L of boric acid and 30 g / L of potassium iodide and simultaneously uniaxially stretched 6.0 times and held for 5 minutes. Finally, it was dried at room temperature for 24 hours to obtain a polarizer P having an average thickness of 30 μm and a polarization degree of 99.95%.

(Preparation of protective film 1)
Polymethylmethacrylate resin (melt flow rate 18 g / 10 min (280 ° C., 2.16 kgf), tensile elastic modulus 3.3 GPa, Tg = 110 ° C., water absorption 0.3%; hereinafter sometimes referred to as “PMMA 1”) Is introduced into a double flight type single screw extruder having a leaf disk-shaped polymer filter with an opening of 10 μm, and a molten resin is melted at an extruder outlet temperature of 260 ° C. and the surface roughness Ra of the die slip is 0.1 μm. Feeded to one of the dies.

  At the same time, polymethyl methacrylate resin (melt flow rate 20 g / 10 min (280 ° C., 2.16 kgf), elastic modulus 2.8 GPa, Tg = 100 ° C., water absorption rate, containing elastic particles having a number average particle size of 0.4 μm 0.3%) is added 2 wt% of an ultraviolet absorber, and this ultraviolet absorber-containing polymethyl methacrylate resin (hereinafter sometimes referred to as “PMMA2”) is added to a leaf disk-shaped polymer filter having an opening of 10 μm. The molten resin was introduced into the installed double flight type single-screw extruder at an extruder outlet temperature of 260 ° C. and supplied to the other of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm.

Then, each of the molten polymethyl methacrylate resin (PMMA1) and the UV-absorbing polymethyl methacrylate resin (PMMA2) is discharged from the multi-manifold die at 260 ° C., and cast to a cooling roll adjusted to 130 ° C., Thereafter, the protective film 1 having a width of 600 mm and a thickness of 80 μm composed of three layers of PMMA1 layer (15 μm) -PMMA2 layer (50 μm) -PMMA1 layer (15 μm) is passed through a cooling roll whose temperature is adjusted to 50 ° C. Obtained by coextrusion. The depth of the linear concave portion or the height of the linear convex portion of the protective film 1 is 20 nm or less and the width is in the range of 800 nm or more, and the moisture permeability is 51 g · m ⁻² · day ^−1. It was.

(Preparation of protective film 2)
Polymethylmethacrylate resin (melt flow rate 18 g / 10 min (280 ° C., 2.16 kgf), tensile elastic modulus 3.3 GPa, Tg = 110 ° C., water absorption 0.3%; hereinafter referred to as “PMMA” .) Is introduced into a hopper mounted on a double flight type single screw extruder (ratio of screw effective length L to screw diameter D L / D = 28) provided with a leaf filter-shaped polymer filter having an opening of 10 μm. The molten resin was supplied to one of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm at an extruder outlet temperature of 260 ° C. and an extruder gear pump speed of 6 rpm.

  At the same time, cycloaliphatic olefin polymer (hydrogenated ring-opening polymer of norbornene monomer; melt flow rate 20 g / 10 min (280 ° C., 2.16 kgf), tensile modulus 2.4 GPa, Tg = 110 ° C., water absorption Less than 0.01%; hereinafter referred to as “COP”) is introduced into a double flight type single screw extruder provided with a leaf disk-shaped polymer filter having an opening of 10 μm, and the outlet temperature of the extruder is 260 ° C. The molten resin was supplied to the other of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm.

The polymethyl methacrylate resin, the alicyclic olefin polymer, and the ethylene-vinyl acetate copolymer as an adhesive are each discharged from a multi-manifold die at 260 ° C. in a molten state, and are cooled to 130 ° C. Cast, and then passed through a cooling roll adjusted to 50 ° C., and three layers of PMMA layer (20 μm) / adhesive layer (4 μm) / COP layer (32 μm) / adhesive layer (4 μm) / PMMA layer (20 μm) A protective film 2 having a configuration (excluding the adhesive layer) and having a width of 600 mm and a thickness of 80 μm was obtained by coextrusion molding.
The refractive index of the PMMA layer at a wavelength of 380 nm was 1.512, and the refractive index at a wavelength of 780 nm was 1.488. The COP layer had a refractive index of 1.555 at a wavelength of 380 nm, and a refractive index of 1.529 at a wavelength of 780 nm. The obtained protective film 2 had a haze of 0.1% or less, a total light transmittance of 93%, and a moisture permeability of 3.5 g · m ⁻² · day ⁻¹ .

(Preparation of Photocationic Curable Adhesive Composition 1)
Epolite 100MF (manufactured by Kyoeisha Chemical Co., Ltd., aliphatic epoxy compound) 100 parts by mass, CEL3000 (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy compound) 7.5 parts by mass, OXT-221 (manufactured by Toagosei) .5 parts by mass, PI 2074 (manufactured by Rhodia, photopolymerization initiator) 3.8 parts by mass, and DETX-S (manufactured by Nippon Kayaku Co., Ltd., photosensitizer) 2.3 parts by mass in a uniform liquid The mixture was stirred until the photocation curable adhesive composition 1 was prepared.

(Preparation of Photocationic Curable Adhesive Composition 2)
Epolite 100MF (manufactured by Kyoeisha Chemical Co., Ltd., aliphatic epoxy compound) 100 parts by mass, CEL3000 (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy compound) 7.5 parts by mass, OXT-221 (manufactured by Toagosei Co., Ltd., oxetane compound) 7 0.5 parts by mass, 7.5 parts by mass of OXT-211 (manufactured by Toagosei Co., Ltd., oxetane compound), 5 parts by mass of OXT-101 (manufactured by Toagosei Co., Ltd., oxetane compound), PI 2074 (manufactured by Rhodia, photopolymerization initiator) 3.8 parts by mass and 2.3 parts by mass of DETX-S (manufactured by Nippon Kayaku Co., Ltd., photosensitizer) are stirred in a container until a uniform liquid is prepared to prepare a photocationically curable adhesive composition 2 did.

Example 1
The above-mentioned photocationic curable adhesive composition 1 is applied to both surfaces of the polarizer P, then the protective film 1 is overlaid, pressed by a roller, and then irradiated with light of 3000 mJ / cm ² (365 nm metal halide lamp). Thus, a polarizing plate 1 was obtained.

Example 2
A polarizing plate 2 was obtained in the same manner as in Example 1 except that the protective film 2 was used instead of the protective film 1.

Example 3
A polarizing plate 3 was obtained in the same manner as in Example 1 except that the photocation curable adhesive composition 2 was used instead of the photo cation curable adhesive composition 1.

Comparative Example 1
Epicoat YX8000 (Japan Epoxy Resin, Aromatic Epoxy Compound) 100 parts by mass, PI 2074 (Rhodia, photopolymerization initiator) 3.8 parts by mass, and DETX-S (Nippon Kayaku Co., Ltd., photosensitizer) ) 2.3 parts by mass of the mixture was stirred until it became a uniform liquid in the container to prepare an adhesive composition 3.
A polarizing plate 4 was obtained in the same manner as in Example 1 except that the adhesive composition 3 was used instead of the photocationically curable adhesive composition 1.

<Peel test>
A test piece having a width of 15 mm and a length of 40 mm was cut out from the polarizing plate, and the protective film and the polarizer were peeled off by hand to confirm the state of peeling. In the table, “destruction” means that the film was not peeled but was broken with an applied force.

<Change in polarization degree>
Two polarizing plates cut out in a size of 10 inches square are prepared, and the transmittance (H ₀ ) at the intersection of diagonal lines of the overlapping polarizing plates so that the polarization axes are parallel to each other is shown in the JIS Z 8701 2 ° field of view (C The light source was measured using a spectrophotometer. Next, the transmittance (H ₉₀ ) at the diagonal intersection of the stacked polarizing plates was measured in the same manner so that the polarization axes were orthogonal. The polarization degree was calculated from the measured value based on the following formula.
Polarization degree (%) = [(H ₀ −H ₉₀ ) / (H ₀ + H ₉₀ )] ^1/2 × 100
(H ₀ and H ₉₀ are Y values with corrected visibility.)
Next, the two polarizing plates were sequentially exposed to the following environment, and the degree of polarization at the diagonal intersection of the polarizing plate was determined in the same manner, and the change in the degree of polarization before and after being left under high temperature and high humidity was determined.
1. 1. High temperature environment: 80 ° C., humidity 50%, 500 hours 2. High temperature and high humidity environment 1: Temperature 60 ° C, humidity 90%, 500 hours High-temperature and high-humidity environment 2: temperature 80 ° C, humidity 90%, 100 hours Low temperature environment: −30 ° C., humidity 10%, 500 hours Water-resistant environment: A wet tissue is placed on a laminated film at a temperature of 80 ° C. and a humidity of 90% and left for 30 minutes.
○: The change width of the polarization degree is 0.5 or less ×: The change width of the polarization degree exceeds 0.5

<Moisture resistance>
From the commercially available liquid crystal monitor (IPS mode 20V type liquid crystal monitor), the polarizing plate and viewing angle compensation film installed on the viewing side among the polarizing plate and viewing angle compensation film sandwiching the liquid crystal cell are peeled off, The polarizing plates 1 to 3 obtained in Examples and Comparative Examples were re-bonded to the liquid crystal cell.
The reassembled liquid crystal display device was allowed to stand in a constant temperature and humidity chamber at 80 ° C. and 95% RH for 24 hours, and then left in a constant temperature and humidity chamber at 20 ° C. and 40% RH for 24 hours. Each layer of the protective layer and the laminated state between the polarizer and the protective layer are visually observed, and if the part that peels off and appears white is 1 mm or longer from the end of the polarizing plate, the length is less than 1 mm. Evaluated as ○ if any.

<Pencil hardness>
According to JIS K 5600-5-4 except that the load was changed to 500 g, the surface of the protective film (the surface in contact with the antiglare film) was scratched about 5 mm with 5H pencil, and the degree of damage was confirmed. .
○: No damage was found in any part.
X: Scratched or more in one place.

<Observation of interference fringes on polarizing plate>
A polarizing plate is placed on a black cloth that does not transmit light, such as a black curtain, and illuminated with a three-wavelength fluorescent lamp (Matsushita Electric Industrial Co., Ltd., National FL20SS / ENW / 18), and the surface of the polarizing plate protective film is visually observed. The evaluation was based on the following criteria.
○: Interference fringes are not visible △: Interference fringes are slightly visible ×: Interference fringes are noticeable

<Color reproducibility>
The reassembled liquid crystal television was installed in an environment with an ambient brightness of 500 lux, and when the screen display was black, the display screen was visually observed and evaluated according to the following criteria.
○: Display screen color is black ×: Display screen color is blue

Claims (4)

The refractive index n _i (λ) and the (i + 1) th of the i-th thermoplastic resin layer at a wavelength λ ranging from 380 nm to 780 nm, wherein k thermoplastic resin layers (k is an integer of 2 or more) are laminated. The thermoplastic resin layer has a refractive index n _{i + 1} (λ) at a wavelength λ in the range of 380 nm to 780 nm and a protection having a relationship of the formula [1] (where i represents an integer of 1 to k−1). Layers,
With a polarizer,
Laminated via a photocationic curable adhesive containing an aliphatic epoxy, an alicyclic epoxy and / or oxetane, and a photopolymerization initiator,
Polarizer.
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1] The polarizing plate according to claim 1, wherein the protective layer has an absolute value of a photoelastic coefficient of 10 × 10 ⁻¹² Pa ⁻¹ or less.   The polarizing plate for liquid crystal display according to claim 1, wherein the protective layer contains an ultraviolet absorber.   A liquid crystal display provided with the polarizing plate as described in any one of Claims 1-3.

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