JP2008040278A - Polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which is tough, has high surface hardness, is excellent in tight adhesion between a polarizer and a protective layer and can maintain a degree of polarization even in a high-temperature and high-humidity environment, and to provide a liquid crystal display device provided with the polarizing plate. <P>SOLUTION: The polarizing plate is obtained by stacking: a visual side protective layer at least including (a) layer and (b) layer which contain thermoplastic resin, wherein bending elastic modulus of the (a) layer is larger than the bending elastic modulus of the (b) layer and the (a) layer exists on the antireflection layer side; and the polarizer, with an active energy beam curable adhesive containing no solvent. The liquid crystal display device is obtained by using the polarizing plate together with a liquid crystal cell. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizing plate that is tough and has high surface hardness and maintains the degree of polarization even under high temperature and high humidity, and a liquid crystal display device including the polarizing plate.

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.

2. Description of the Related Art Conventionally, it is widely known to produce a multilayer film that takes advantage of the characteristics of each resin by laminating a plurality of resins.
For example, Patent Document 1 describes a thermoplastic resin sheet for molding and a molded body thereof, wherein a thermoplastic resin sheet having at least two layers, at least one of which is an amorphous polyolefin. ing. It is described that this thermoplastic resin sheet is excellent in water vapor barrier properties and transparency, has no fusion with a mold, and can be molded in a wide temperature range.

  Patent Document 2 describes a polystyrene film comprising a sandwich laminate of polystyrene layer / acrylonitrile / butadiene / styrene copolymer layer / polystyrene layer. This laminated film is considered to be a film that is inexpensive, excellent in transparency and impact resistance, and has a good balance of tear strength in the longitudinal direction or the transverse direction.

  A technique using a multilayer film as a polarizing plate protective film is also known. For example, in Patent Document 3, a resin layer having a positive photoelastic constant and a resin layer having a negative photoelastic constant, which have lower moisture absorption than triacetylcellulose, are laminated, and the photoelastic constant is lower than a specific value. A polarizing plate protective film characterized by being small is described. Further, it is described that the polarizing plate protective film does not cause display unevenness or contrast reduction even when placed in a high temperature and high humidity environment.

  Patent Document 4 is composed of a three-layer laminate in which surface layers are laminated on both sides of an intermediate layer, and at least the intermediate layer contains an ultraviolet absorber, and the concentration of the ultraviolet absorber in the intermediate layer is higher than that of the surface layer. A norbornene-based resin film having an ultraviolet transmittance of 40% or less with a wavelength of 380 nm or less is described. Moreover, it is described that this resin film does not cause an appearance defect due to volatilization of the ultraviolet absorber during extrusion molding.

  However, none of the techniques relating to the multilayer film described in the above-mentioned patent documents can provide a polarizing plate having toughness and excellent surface hardness, and further improvements are required.

JP-A-6-255053 JP-A-8-281882 JP 2000-206303 A Japanese Patent Laid-Open No. 2002-249600

  The present invention has been made in view of the above-described prior art, and provides a polarizing plate that is tough, has high surface hardness, and maintains the degree of polarization even under high temperature and high humidity, and a liquid crystal display device including the polarizing plate. The issue is to provide.

  As a result of earnest research to solve the above problems, the present inventors have found that a layer containing a thermoplastic resin having a relatively large bending elastic modulus and b layer containing a thermoplastic resin having a relatively small bending elastic modulus. When a laminated film and a polarizer are laminated via an active energy curable adhesive that does not contain a solvent, it is tough, has high surface hardness, excellent antireflection properties, and maintains the degree of polarization even at high temperatures and high humidity. It was found that a polarizing plate can be obtained. The present invention has been completed based on these findings.

Thus, the present invention includes the following.
(1) A viewing side comprising at least a layer and a b layer containing a thermoplastic resin, the bending elastic modulus of the a layer being larger than the bending elastic modulus of the b layer, and the a layer being present on the viewing side A protective layer;
A polarizing plate, wherein a polarizer is laminated via an active energy curable adhesive containing no solvent.
(2) The polarizing plate according to (1), wherein a difference in flexural modulus between the a layer and the b layer is 0.2 GPa to 2.5 GPa.

(3) The polarizing plate according to any one of (1) and (2), wherein the viewing-side protective layer is obtained by a coextrusion method.
(4) The polarizing plate according to any one of (1) to (3), wherein the viewing-side protective layer includes an ultraviolet absorber.
(5) A liquid crystal display device comprising the polarizing plate according to any one of (1) to (4).

  The polarizing plate of the present invention is tough and has high surface hardness, excellent scratch resistance, excellent adhesion between the polarizer and the protective layer, and can maintain a high degree of polarization even under high temperature and high humidity. Suitable for display devices.

Hereinafter, the present invention will be described in detail.
The polarizing plate of the present invention is formed by laminating a viewing-side protective layer and a polarizer. Moreover, the liquid crystal cell side protective layer may be laminated | stacked on the opposite side to the side by which the visual recognition side protective layer was laminated | stacked on the polarizer.
In order to laminate the viewing-side protective layer on the polarizer, an active energy ray-curable adhesive that does not contain a solvent is used.

(Active energy ray-curable adhesive without solvent)
In the present invention, the adhesive used for laminating the viewing-side protective layer and the polarizer is an adhesive that cures when irradiated with active energy rays and does not contain a solvent (solvent-free).
Here, “does not contain solvent” means that the adhesive used for applying to the adherend does not contain any solvent, or the solvent content is less than 2% by weight based on the total weight of the adhesive. Say. The solvent content in the adhesive can be measured by gas chromatography or the like.

  Solvents include aliphatic hydrocarbons such as n-hexane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; alcohols such as methanol, ethanol, propanol, isopropanol and n-butanol; acetone and butanone , Ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters such as methyl acetate, ethyl acetate and butyl acetate; cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve; halogenation such as methylene chloride and chloroform And hydrocarbons.

Moreover, the active energy ray-curable solvent-free adhesive used in the present invention is excellent in adhesive applicability when the viscosity measured by a B-type viscometer at 23 ° C. is 200 to 5000 mPa · s.
As the solvent-free adhesive that is cured by the active energy ray, any known one can be used without particular limitation as long as it is colorless and transparent. Examples of the active energy ray-curable compound that is the main component of the active energy ray-curable solvent-free adhesive include radical polymerization by active energy rays such as compounds having a functional group such as acryloyl group, methacryloyl group, and allyl group. Cured (photo radical polymerizable compound); cured by a photocation reaction by an active energy ray of a compound having a functional group such as epoxy group, oxetane group, hydroxyl group, vinyl ether group, episulfide group, ethyleneimine group, etc. (Photo cationic polymerizable compound);

  As photoradical polymerizable compounds, hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate; hydroxyaryl acrylates such as 2-hydroxy-3-phenoxypropyl acrylate; 2-acryloyloxyethyl succinic acid, 2- Acrylic modified carboxylic acids such as acryloyloxyethylphthalic acid; polyethylene glycol diacrylates such as triethylene glycol diacrylate and tetraethylene glycol diacrylate; polypropylene glycol diacrylates such as dipropylene glycol diacrylate and tripropylene glycol diacrylate Other, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, 1,9-no Diol diacrylate, bisphenol A ethylene oxide modified diacrylate, bisphenol A propylene oxide modified diacrylate, dimethylol tricyclodecane diacrylate, trimethylol propane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate Such as epoxy acrylate, urethane acrylate, other acrylates such as acrylic benzoic acid mixed ester of neopentyl glycol; methacrylates thereof, and the like.

  Bisphenol type epoxy resin such as bisphenol A type epoxy resin and bisphenol F type epoxy resin; novolak type epoxy resin such as phenol novolac type epoxy resin and cresol novolac type epoxy resin; aliphatic epoxy resin, alicyclic Type epoxy resin, heterocyclic epoxy resin, polyfunctional epoxy resin, biphenyl type epoxy resin, glycidyl ether type epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin; alcohol such as hydrogenated bisphenol A type epoxy resin Type epoxy resin; halogenated epoxy resin such as brominated epoxy resin; rubber-modified epoxy resin, urethane-modified epoxy resin, epoxidized polybutadiene, epoxidized styrene-butadiene-styrene Compounds having an epoxy group, such as a polyblock copolymer, an epoxy group-containing polyester resin, an epoxy group-containing polyurethane resin, and an epoxy group-containing acrylic resin; phenoxymethyl oxetane, 3,3-bis (methoxymethyl) oxetane, 3,3- Bis (phenoxymethyl) oxetane, 3-ethyl-3- (phenoxymethyl) oxetane, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl-3-{[3- (triethoxysilyl) Propoxy] methyl} oxetane, di [1-ethyl (3-oxetanyl)] methyl ether, oxetanylsilsesquioxane, phenol novolac oxetane, 1,4-bis {[(3-ethyl-3-oxetanyl) methoxy] methyl} Compounds having an oxetanyl group such as benzene It is below.

  These active energy ray-curable compounds may be used alone or in combination.

  A polymerization initiator can be mix | blended with an active energy ray hardening-type adhesive in order to raise the curing reaction efficiency of the above-mentioned active energy ray hardening-type adhesive agent. The polymerization initiator is selected according to the type of active energy ray used. As the polymerization initiator, photo radical polymerization initiators such as acetophenone, benzophenone, thioxanthone, benzoin, and benzoin alkyl ethers; aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metathelone compounds, benzoin sulfones Photocationic polymerization initiators such as acid esters; and the like. These can be used individually by 1 type or in combination of 2 or more types.

  As the acetophenone photopolymerization initiator, for example, 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, diethoxyacetophenone, 1-phenyl-2-hydroxy-2-methylpropan-1-one, 1- [ 4- (2-hydroxyethyl) -phenyl] -2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone and the like.

Examples of the benzoin alkyl ether photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, and benzoin isobutyl ether.
Examples of the benzophenone photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3′-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexyl phenyl ketone, and the like.

  The cationic photopolymerization initiator may be an ionic photoacid-generating photocationic polymerization initiator or a nonionic photoacid-generating photocationic polymerization initiator. The photocationic polymerization initiator is a photocationic polymerization initiator that is activated by light having a wavelength of 350 nm or more because it can effectively initiate and advance the photocationic polymerization of the photocationically polymerizable compound. Is preferred.

  The ionic photoacid-generating photocationic polymerization initiator is not particularly limited. For example, onium salts such as aromatic diazonium salt, aromatic halonium salt, aromatic sulfonium salt; organometallic complexes such as iron-allene complex, titanocene complex, arylsilanol-aluminum complex; tetrakis (pentafluorophenyl) borate, etc. Examples thereof include a photocationic polymerization initiator having a bulky counter anion. These ionic photoacid-generating photocationic polymerization initiators may be used alone or in combination of two or more.

  Examples of commercially available ionic photoacid-generating photocationic polymerization initiators include “Adekaoptomer” series such as “Adekaoptomer SP150” and “Adekaoptomer SP170” manufactured by Asahi Denka Kogyo Co., Ltd. , A trade name “UVE-1014” manufactured by General Electronics Co., Ltd., a product name “CD-1012” manufactured by Sartomer, and a product name “Photoinitiator 2074” manufactured by Rhodia.

  The nonionic photoacid-generating photocationic polymerization initiator is not particularly limited. For example, nitrobenzyl ester, sulfonic acid derivative, phosphoric acid ester, phenolsulfonic acid ester, diazonaphthoquinone, N-hydroxyimidophosphonate and the like can be mentioned. These nonionic photoacid-generating photocationic polymerization initiators may be used alone or in combination of two or more.

  The compounding quantity of a polymerization initiator is 0.5-10 weight part normally with respect to 100 weight part of active energy ray hardening compounds.

  Further, the active energy ray curable adhesive contains a photosensitizer, an antistatic agent, an infrared absorber, an ultraviolet absorber, an antioxidant, organic particles, inorganic oxide particles, a pigment, a dye, and the like. Also good.

  By using a photosensitizer, the reactivity is improved, and the mechanical strength and adhesive strength of the cured adhesive can be improved. The photosensitizer is not particularly limited, and examples thereof include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreducible dyes.

  Specific examples of the photosensitizer include benzoin methyl ether, benzoin isopropyl ether, benzoin derivatives such as α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, methyl o-benzoylbenzoate, Benzophenone derivatives such as 4,4′-bis (dimethylamino) benzophenone and 4,4′-bis (diethylamino) benzophenone; thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; 2-chloroanthraquinone, 2- Anthraquinone derivatives such as methylanthraquinone; acridone derivatives such as N-methylacridone and N-butylacridone; other, α, α-diethoxyacetophenone, benzyl, fluorenone, xanthone, Examples include uranyl compounds and halogen compounds, but are not limited thereto. These may be used alone or in combination. The photosensitizer is preferably contained within a range of 0.1 to 20 parts by weight when the active energy ray-curable compound is 100 parts by weight.

  In the polarizing plate of the present invention, the visible-side protective layer is bonded to one surface of the polarizer via the active energy ray-curable adhesive and then irradiated with active energy rays to cure the visible-side protective layer. It is obtained by fixing the layer to a polarizer.

  There is no particular limitation on the method of applying the adhesive to the polarizer, 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.

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

  In the present invention, light is usually used as the active energy ray. Although the said light is not specifically limited, For example, a microwave, infrared rays, visible light, an ultraviolet-ray, X-ray | X_line, a gamma ray etc. are mentioned. In particular, ultraviolet rays are preferably used because of easy handling and relatively high energy.

The light source used for irradiating with ultraviolet rays is not particularly limited, and examples thereof include a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excitation mercury lamp, and a metal halide lamp. The irradiation intensity is not particularly limited, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is preferably 0.1 to 100 mW / cm ² . When the light irradiation intensity is less than 0.1 mW / cm ² , the reaction time becomes too long, and when it exceeds 100 mW / cm ² , the adhesive is yellowed or polarized due to radiation heat from the lamp, polymerization reaction heat, or the like. The child itself may be deteriorated. The light irradiation time is appropriately selected according to the curing state and is not particularly limited. However, the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5,000 mJ / cm ^2. It is preferable to set to.

(1) Viewing-side protective layer The viewing-side protective layer includes at least an a layer and a b layer containing a thermoplastic resin. Here, “the main component is a thermoplastic resin” means that the resin component constituting the a layer and the b layer is a thermoplastic resin and may contain a compounding agent or the like as desired. .

(I) a layer The thermoplastic resin contained in the a layer is not particularly limited as long as it is a highly transparent thermoplastic resin, but those having a light transmittance of 80% or more are preferable.

  Preferable specific examples of the thermoplastic resin contained in the layer a include vinyl aromatic polymers, polyacrylonitrile polymers, poly (meth) acrylate polymers, vinyl alicyclic hydrocarbon polymers and hydrides thereof. Can be mentioned. These can be used alone or in combination of two or more.

  Examples of the vinyl aromatic polymer include a copolymer of polystyrene, styrene and / or a styrene derivative and at least one selected from acrylonitrile, maleic anhydride, methyl methacrylate and butadiene; a copolymer of styrene and a conjugated diene Hydrides (including hydrides of aromatic rings); and the like. Here, examples of the styrene derivative include 4-methylstyrene, 3-methylstyrene, 4-chlorostyrene, 4-methoxystyrene, 4-tert-butoxystyrene, α-methylstyrene, and the like.

  Examples of the poly (meth) acrylate polymer include a homopolymer of a (meth) acrylate compound, two or more copolymers of a (meth) acrylate compound, a (meth) acrylate compound and other copolymers. Examples thereof include a copolymer with a polymerizable monomer. Here, (meth) acrylic acid ester means acrylic acid ester or methacrylic acid ester.

  Specific examples of the (meth) acrylic acid ester compound include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t -Butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, etc. are mentioned.

  Examples of the polyacrylonitrile-based polymer include acrylonitrile homopolymer, acrylonitrile, and a copolymer of acrylonitrile and a monomer copolymerizable with acrylonitrile. The monomer copolymerizable with acrylonitrile was selected from the group consisting of acrylic ester, methacrylic ester, styrene, vinyl acetate, glycidyl methacrylate, divinylbenzene, and polyethylene glycol (n = 1-9) dimethacrylate. 1 type or more is mentioned.

  The vinyl alicyclic hydrocarbon polymer is a polymer having a repeating unit derived from vinylcycloalkane or vinylcycloalkene. Examples of the vinyl alicyclic hydrocarbon polymer include polymers of vinyl alicyclic hydrocarbon compounds such as vinyl cycloalkanes such as vinyl cyclohexane, vinyl cycloalkenes such as vinyl cyclohexene, and hydrides thereof; styrene, α-methyl Examples thereof include hydrides of aromatic ring portions of polymers of vinyl aromatic hydrocarbon compounds such as styrene.

  The vinyl alicyclic hydrocarbon polymer is a random copolymer of a vinyl alicyclic hydrocarbon compound or a vinyl aromatic hydrocarbon compound and another monomer copolymerizable with these monomers, It may be a copolymer such as a block copolymer and a hydride thereof. Examples of the block copolymer include diblock, triblock, or more multiblock and gradient block copolymers, but are not particularly limited.

  Preferred resins for layer a are vinyl aromatic polymers, poly (meth) acrylate polymers, vinyl alicyclic hydrocarbon polymers, and hydrides thereof, such as polystyrene, styrene / maleic acid copolymers, More preferred are methyl methacrylate, vinyl alicyclic hydrocarbon polymer and hydride thereof.

(Ii) b layer Although it will not restrict | limit especially if it is a highly transparent thermoplastic resin as a thermoplastic resin which comprises b layer, What has a light transmittance of 80% or more is preferable.

  Preferred specific examples of the resin constituting the layer b include alicyclic structure-containing polymers, cellulose polymers, polyester polymers, polycarbonate polymers, polysulfone polymers, polyethersulfone polymers, vinyl aromas. A group polymer, a polyolefin polymer, a polyvinyl alcohol polymer, a polyvinyl chloride polymer, and a poly (meth) acrylate polymer. These polymers can be used alone or in combination of two or more.

  Among these, alicyclic structure-containing polymers; cellulose polymers such as cellulose diacetate, cellulose triacetate, and cellulose acetate butyrate; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. Polyester-based polymers are preferable, and from the viewpoints of transparency, dimensional stability, lightness, and the like, alicyclic structure-containing polymers, cellulose triacetate, and polyethylene terephthalate are more preferable. From the viewpoint of low hygroscopicity and dimensional stability, alicyclic Formula structure containing polymers are particularly preferred.

  The alicyclic structure-containing polymer has an alicyclic structure in the repeating unit of the polymer, a polymer having an alicyclic structure in the main chain and a polymer having an alicyclic structure in the side chain. Any of these can be used.

  Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and a cycloalkane structure is preferable from the viewpoint of thermal stability. Although there is no restriction | limiting in particular in carbon number which comprises an alicyclic structure, Usually, 4-30 pieces, Preferably it is 5-20 pieces, More preferably, it is 5-15 pieces. When the number of carbon atoms constituting the alicyclic structure is within this range, a base resin film excellent in heat resistance and flexibility can be obtained.

  The proportion of the repeating unit having an alicyclic structure in the alicyclic structure-containing polymer may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more. If the number of repeating units having an alicyclic structure is too small, the heat resistance is undesirably lowered. In addition, repeating units other than the repeating unit which has an alicyclic structure in an alicyclic structure containing polymer are suitably selected according to the intended purpose.

  Specific examples of the alicyclic structure-containing polymer include a norbornene polymer, a monocyclic olefin polymer, a cyclic conjugated diene polymer, and hydrides thereof. Among these, norbornene-based polymers are preferable from the viewpoints of transparency and moldability.

  Specific examples of the norbornene-based polymer include ring-opening polymers of norbornene-based monomers, ring-opening copolymers of norbornene-based monomers and other monomers capable of ring-opening copolymerization, and those Hydrides of the above, addition polymers of norbornene monomers, addition copolymers with other monomers copolymerizable with norbornene monomers, and the like. Among these, from the viewpoint of transparency, a ring-opening (co) polymer hydride of a norbornene monomer is particularly preferable.

Examples of the norbornene-based monomer include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7-diene. (Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0. 1 ^2,5 . 1 ^7,10 ] dodec-3-ene (common name: tetracyclododecene), derivatives of these compounds (for example, those having a substituent in the ring), and the like. Here, examples of the substituent include an alkyl group, an alkylene group, an alkoxycarbonyl group, and a carboxyl group. In addition, these substituents may be the same or different and a plurality may be bonded to the ring. Norbornene monomers can be used alone or in combination of two or more.

  Other monomers capable of ring-opening copolymerization with norbornene monomers include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene; Derivatives thereof; and the like.

Ring-opening polymers of norbornene monomers and ring-opening copolymers of norbornene monomers and other monomers copolymerizable therewith are polymerized in the presence of a ring-opening polymerization catalyst. Can be obtained.
As the ring-opening polymerization catalyst, a commonly used known catalyst can be used.

  Examples of other monomers that can be addition-copolymerized with norbornene-based monomers include, for example, α-olefins having 2 to 20 carbon atoms such as ethylene and propylene, and derivatives thereof; cycloolefins such as cyclobutene and cyclopentene, and these Derivatives; non-conjugated dienes such as 1,4-hexadiene and the like. These monomers can be used alone or in combination of two or more. In these, an alpha olefin is preferable and ethylene is more preferable.

  Norbornene monomer addition polymers and addition copolymers of norbornene monomers and other monomers copolymerizable therewith are obtained by polymerizing the monomers in the presence of an addition polymerization catalyst. Obtainable. As the addition polymerization catalyst, a commonly used known catalyst can be used.

  Hydrogenated ring-opening polymer of norbornene monomer, hydrogenated ring-opening copolymer of norbornene monomer and other monomers capable of ring-opening copolymerization, norbornene monomer Addition polymer hydride, and addition polymer hydride of norbornene monomer and other monomers copolymerizable therewith, add known hydrogenation catalyst, carbon-carbon unsaturated bond Can be obtained by hydrogenating preferably 90% or more.

Examples of the monocyclic olefin-based polymer include addition polymers such as cyclohexene, cycloheptene, and cyclooctene.
Examples of the cyclic conjugated diene polymer include polymers obtained by 1,2-addition polymerization or 1,4-addition polymerization of cyclic conjugated diene monomers such as cyclopentadiene and cyclohexadiene.

  The molecular weight of the thermoplastic resin constituting the a layer and the b layer is a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography using cyclohexane (toluene when the polymer resin is not dissolved) as a solvent. Usually in the range of 10,000 to 300,000, preferably 15,000 to 250,000, more preferably 20,000 to 200,000. When the molecular weight is in such a range, when producing a protective film serving as a visible side protective layer, the mechanical strength and moldability of the film are highly balanced, which is preferable.

  Although the glass transition temperature of the thermoplastic resin which comprises the said a layer and b layer should just be selected suitably according to a use purpose, Preferably it is 80 degreeC or more, More preferably, it exists in the range of 100-250 degreeC. When manufacturing a protective film to be a visible side protective layer when the glass transition temperature is in such a range, a film having excellent durability without deformation or stress in use under high temperature and high humidity is obtained. be able to.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the thermoplastic resin constituting the a layer and the b layer is not particularly limited, but is usually 1.0 to 10.0, preferably 1.0. ˜6.0, more preferably in the range of 1.1 to 4.0. By adjusting the molecular weight distribution within such a range, when producing a protective film serving as a viewing-side protective layer, a film in which mechanical strength and moldability are well balanced can be obtained.

(Flexural modulus)
The viewing-side protective layer includes at least an a layer and a b layer mainly composed of a thermoplastic resin, and the bending elastic modulus of the a layer is larger than the bending elastic modulus of the b layer.

  The flexural modulus is a ratio of a load and a deflection when a bending load is applied to an object. More specifically, the strains at two specified points are ε1 and ε2, and the corresponding stresses are ρ1 and ρ2. The stress difference (ρ2−ρ1) is divided by the strain difference (ε2−ε1).

  Generally, a tough polymer has a low flexural modulus, and a polymer with a high surface hardness has a high flexural modulus. As the viewing-side protective layer, a layer formed by combining a layer having a relatively large flexural modulus and high surface hardness and a b layer having a relatively small flexural modulus and excellent toughness, and the layer a Is provided on the viewer side with respect to the b-layer, thereby providing a viewer-side protective layer that is tough and has a high surface hardness.

  The bending elastic modulus of the a layer may be relatively larger than the bending elastic modulus of the b layer, but from the viewpoint of obtaining a polarizing plate that is tougher and has a higher surface hardness, the bending elastic modulus of the a layer is 3 GPa. As described above, it is preferably 3 to 4 GPa, and the flexural modulus of the b layer is less than 3 GPa, preferably 0.1 to 3 GPa. If the flexural modulus of the a layer exceeds 4 GPa, the opacity or melt viscosity becomes high, and film formation may be difficult. Moreover, when the bending elastic modulus of b layer will be less than 0.1 GPa, the viscosity at the time of a fusion | melting will become low, and there exists a possibility that film forming may become difficult.

  The difference in bending elastic modulus between the a layer and the b layer is not particularly limited as long as the bending elastic modulus of the a layer is relatively larger than the bending elastic modulus of the b layer, but is preferably 0.2 to 2.5 GPa. More preferably, it is 0.5 to 2.0 GPa. If the difference in flexural modulus between the a layer and the b layer is too small, the balance between toughness and surface hardness of the resulting polarizing plate may be deteriorated. On the other hand, if the difference in flexural modulus is too large, it may be difficult to form a uniform laminated film during film formation.

  As a preferred combination of the a layer and the b layer, moisture permeability, toughness, and surface hardness are highly balanced, and therefore, expressed as a layer / b layer, containing a vinyl aromatic polymer / alicyclic structure Examples thereof include polymers and poly (meth) acrylate polymers / alicyclic structure-containing polymers. Of these, combinations of polystyrene / alicyclic structure-containing polymer, styrene / maleic acid copolymer / alicyclic structure-containing polymer, and polymethyl methacrylate / alicyclic structure-containing polymer are particularly preferable.

  The viewing-side protective layer may be a laminate including at least an a layer and a b layer, but further includes a c layer on the opposite side of the a layer via the b layer, or between the a layer and the b layer. May be laminated via an x layer as desired.

  The c layer is provided to prevent curling of the antireflection film, and can be formed of a material having affinity for both the resin constituting the a layer and the resin constituting the b layer. For example, what consists of a thermoplastic resin with high transparency and affinity to both resin which comprises a layer and b layer is mentioned. Moreover, c layer can also be formed from the same resin as a layer or b layer.

  Although c layer is provided in order to prevent curling of the protective film used as a visual recognition side protective layer, curl cannot be prevented even if the thickness is too thin or too thick. The thickness of c layer is 5-100 micrometers normally, Preferably it is 10-50 micrometers.

  The x layer can be formed from a resin having an affinity for both the resin constituting the a layer and the b layer. For example, polyester urethane resin, polyether urethane resin, polyisocyanate resin, polyolefin copolymer, resin having a hydrocarbon skeleton in the main chain, polyamide resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, Examples thereof include chlorinated rubber, cyclized rubber, and modified products obtained by introducing polar groups into these polymers. Among these, polyolefin copolymers and modified products thereof are preferably used.

  Examples of polyolefin copolymers include ethylene- (meth) acrylic acid ester copolymers such as ethylene- (meth) methyl acrylate copolymer and ethylene- (meth) ethyl acrylate copolymer; ethylene and (meth) A terpolymer obtained by copolymerizing an acrylic ester with another copolymerizable monomer (propylene, maleic acid, vinyl acetate, etc.); ethylene-vinyl acetate copolymer; ethylene-styrene copolymer; And ethylene- (meth) acrylic acid glycidyl ester copolymer;

  Examples of the method for introducing a polar group into these polyolefin copolymers include oxidation, saponification, chlorination, chlorosulfonation, addition of unsaturated carboxylic acid, and the like. Of these, unsaturated carboxylic acid addition is preferably used.

  Examples of the resin having a hydrocarbon skeleton in the main chain include a polybutadiene skeleton or a resin having a polybutadiene skeleton hydrogenated to at least a part thereof, specifically, polybutadiene resin, hydrogenated polybutadiene resin, styrene / butadiene / styrene. Examples thereof include a block copolymer (SBS copolymer), a hydrogenated product thereof (SESB copolymer), and the like. Among them, a modified product of a hydrogenated product of styrene / butadiene / styrene block copolymer is preferable.

  As a compound for introducing a polar group used for obtaining a modified product of these polymers, a carboxylic acid or a derivative thereof is preferable. For example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and fumaric acid; halides, amides, imides, anhydrides and esters of unsaturated carboxylic acids such as maleyl chloride, maleimide, maleic anhydride and citraconic anhydride And the like; and the like. Among these, a polymer-modified product with an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride is excellent in adhesion, and thus can be suitably used. Among the unsaturated carboxylic acids or anhydrides thereof, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are more preferable, and maleic acid and maleic anhydride are particularly preferable. These unsaturated carboxylic acids and the like can be modified by mixing two or more kinds.

  The method for producing the viewer-side protective layer is not particularly limited. For example, (i) a method in which the a layer and the b layer are separately formed and laminated by dry lamination via the x layer to form a laminate, ii) A method of obtaining a laminate by forming a film by a coextrusion method, and the like. Of these, the coextrusion method (ii) is preferred because a laminate having a high delamination strength can be obtained and the production efficiency is excellent. Specifically, a method of obtaining a laminate by a coextrusion method is to form a film by extruding a resin material constituting the a layer and a resin material constituting the b layer from a multilayer die using a plurality of extruders. Is.

In the case of co-extrusion, the compounding agent can be added to the a layer, the b layer and / or the c layer as long as the object of the present invention is not impaired.
The compounding agent to be used is not particularly limited. For example, a lubricant; a layered crystal compound; an inorganic fine particle; a stabilizer such as an antioxidant, a heat stabilizer, a light stabilizer, a weather stabilizer, an ultraviolet absorber, a near infrared absorber; Plasticizers; coloring agents such as dyes and pigments; antistatic agents; These compounding agents can be used alone or in combination of two or more. The compounding quantity of a compounding agent can be suitably determined in the range which does not impair the objective of this invention.

  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.

  By using elastic particles made of a rubber-like elastic body as a lubricant, flexibility can be imparted. 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 viewing-side protective layer has a high haze (cloudiness) and a low light transmittance. Therefore, it becomes unsuitable for a display screen. Moreover, when the number average particle size becomes too small, the flexibility tends to decrease.

  The thickness of the entire viewing-side protective layer obtained is usually 30 to 200 μm, preferably 40 to 150 μm, particularly preferably 50 to 100 μm.

  Moreover, the thickness of the a layer contained in a visual recognition side protective layer is 5-100 micrometers normally, Preferably it is 10-50 micrometers. If the thickness of the a layer is less than 5 μm, the surface hardness cannot be increased. On the other hand, if the thickness is greater than 100 μm, the viewing-side protective layer becomes fragile, which is not preferable.

  The thickness of b layer is 5-100 micrometers normally, Preferably it is 10-50 micrometers. If the thickness of the b layer is less than 5 μm, the viewing-side protective layer becomes fragile, which is not preferable. On the other hand, if the thickness is greater than 100 μm, the transparency of the viewing-side protective layer may be reduced. In addition, the thickness of the entire polarizing plate increases, which may hinder the miniaturization of the display.

  When the visual recognition side protective layer has x layer, the thickness of x layer is 1-20 micrometers normally, Preferably it is 1-10 micrometers, More preferably, it is 2-7 micrometers. If the thickness of the x layer is greater than 20 μm, the surface hardness may not be increased.

In the polarizing plate of the present invention, it is preferable that the viewing side protective layer has a low moisture permeability. As will be described later, the polarizer has the property of absorbing moisture in the air and gradually decreasing the degree of polarization. Therefore, it is excellent in durability by attaching a viewing-side protective layer with low moisture permeability to the polarizer. A polarizing plate can be obtained.
The moisture permeability can be measured by a method based on JIS Z 0208.

  Moreover, as a visual recognition side protective layer, what carried out the surface modification process to the single side | surface or both surfaces can also be used. By performing the surface modification treatment, adhesion to the low refractive index layer and other layers described later can be improved. Examples of the surface modification treatment include energy beam irradiation treatment and chemical treatment.

  Examples of the energy ray irradiation treatment include corona discharge treatment, plasma treatment, electron beam irradiation treatment, ultraviolet ray irradiation treatment, and the like. From the viewpoint of treatment efficiency, corona discharge treatment and plasma treatment are preferred, and corona discharge treatment is particularly preferred. Examples of the chemical treatment include a method of immersing in an aqueous oxidizing agent solution such as a potassium dichromate solution or concentrated sulfuric acid and then thoroughly washing with water. In chemical treatment, it is effective to shake in an immersed state, but there is a problem that the surface dissolves or transparency decreases when treated for a long time, depending on the reactivity, concentration, etc. of the chemical used, It is necessary to adjust the processing time.

  As the layer structure of the viewer side protective layer, a viewer side protective layer having a tough and excellent surface hardness can be obtained. Therefore, a viewer side protective layer having a three-layer structure of a layer-x layer-b layer, a layer-x layer A viewing-side protective layer having a five-layer structure of -b layer-x layer-a layer is preferable.

  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 viewing side protective layer.

(Hard coat layer)
The hard coat layer is preferably formed of 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 K5600-5-4. The pencil hardness of the viewing-side protective layer provided with the hard coat layer is preferably 4H or more. When the surface layer of the viewing side protective layer is made of an acrylic resin, it becomes easy to adjust the pencil strength of the surface to 4H or more by 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 nH between the refractive index n _L of the low refractive index layer laminated thereon and n _H ≧ 1.53 and n _H ^1/2 −0.2 <nL. It is preferable to have a relationship of <n _H ^1/2 +0.2 in order to exhibit 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, and 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 it has a refractive index lower than that of the base material or the hard coat layer. For example, a resin material such as an ultraviolet curable acrylic resin, or colloidal silica in the resin. 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 the fluorine group for providing antifouling property to the surface.

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.

  Fluoroolefins such as fluoroethylene, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoro-2,2-dimethyl-1,3-dioxole; biscoat 6FM (Osaka Organic) Chemical), M-2020 (manufactured by Daikin), (meth) acrylic acid partial or fully fluorinated alkyl ester derivatives, fully or partially fluorinated vinyl ethers, and the like.

  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 (observation side). 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 visual side protective layer of the present invention is subjected to mechanical treatment by etching, sandblasting, embossing roll, etc. for the purpose of enhancing adhesion with the functional layer and imparting antiglare property. May be.
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 not particularly limited as long as it has a function as a polarizer. For example, a polyvinyl alcohol (PVA) type or polyene type polarizer can be used.
The manufacturing method of a polarizer is not specifically limited. As a method for producing a PVA polarizer, a method of stretching uniaxially after adsorbing iodine ions on a PVA film, a method of adsorbing iodine ions after stretching a uniaxially stretched PVA film, A method of simultaneously performing iodine ion adsorption and uniaxial stretching, a method of stretching a uniaxial film after dyeing a PVA film with a dichroic dye, a method of stretching a uniaxial film and then adsorbing with a dichroic dye, a PVA system The method of performing simultaneously dyeing | staining with a dichroic dye and uniaxial stretching to a film is mentioned. In addition, as a method for producing a polyene-based polarizer, a method of heating and dehydrating in the presence of a dehydration catalyst after stretching a PVA film uniaxially, a method of stretching a polyvinyl chloride film uniaxially and then in the presence of a dehydrochlorination catalyst And publicly known methods such as heating and dehydrating.

(Liquid crystal cell side protective layer)
The liquid crystal cell side protective layer used in the present invention may be the same as the above-mentioned viewing side protective layer, or may be a protective layer conventionally used for polarizing plates.

  The liquid crystal cell-side protective layer is preferably formed of a material having 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.

  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, thermoplastic dicyclopentadiene ring-opening polymers described in JP-A No. 11-124429 (WO 99/20676), and hydrogenated products thereof. .

  There is no particular limitation on the method of laminating the liquid crystal cell side protective layer on the polarizer, for example, a general method of laminating a protective film to be the liquid crystal cell side protective layer with the polarizer through an adhesive as necessary. Can be adopted. As an adhesive for bonding the liquid crystal cell-side protective layer to the polarizer, the above-mentioned active energy ray-curable adhesive may be used, or a conventionally known adhesive may be used.

  The polarizing plate of the present invention may be obtained by laminating a film showing birefringence on the liquid crystal cell side protective layer side in addition to the above-mentioned viewing side protective layer, polarizer and liquid crystal cell side protective layer. 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 [1].
| N ₁ (λ) −n _b (λ) | ≦ 0.05 Formula [1]

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 [2] is satisfied.
|| n ₁ (380) −n _b (380) |
− | N ₁ (780) −n _b (780) || ≦ 0.02 Formula [2]

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, more preferably a hardness of “4H” or higher, in a pencil hardness test (test plate is a glass plate) shown in JIS K5600-5-4.

<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 is provided on the emission side (viewing side) of the device. 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.

<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.

<Measurement of flexural modulus>
The bending elastic modulus of the a layer and the b layer of the base resin layer is measured using a tensile tester (Autograph AG-100kNIS, manufactured by Shimadzu Corp.) according to JIS K 7171.
The results are shown in Table 1.

(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)
Polymethylmethacrylate resin (glass transition temperature Tg = 110 ° C .; hereinafter sometimes referred to as “PMMA1”) is introduced into a double flight type single screw extruder having a leaf disk-shaped polymer filter having an opening of 10 μm. At an outlet temperature of 260 ° C., the molten resin was supplied to one of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm.

At the same time, an alicyclic olefin polymer (“ZEONOR 1060R” manufactured by Nippon Zeon Co., Ltd .; water absorption of less than 0.01%, hereinafter sometimes referred to as “NB”) was installed on a leaf disk-shaped polymer filter having an aperture of 10 μm. The resin was introduced into a double flight type single screw extruder, and the molten resin was supplied to the other of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm at an extruder outlet temperature of 260 ° C.
Similarly, an ethylene-vinyl acetate copolymer (“EVAFLEX” manufactured by Mitsui DuPont Chemicals; hereinafter referred to as “EVA”) was also supplied to the other side of the multi-manifold die.

  Then, as a molten polymethyl methacrylate resin (PMMA1), an alicyclic olefin polymer (NB), and an adhesive, an ethylene-vinyl acetate copolymer (EVA) is discharged from the multi-manifold die at 260 ° C., respectively. It casts to the cooling roll temperature-controlled at 130 degreeC, Then, it passes through the cooling roll temperature-controlled at 50 degreeC, a layer (15 micrometers) which consists of PMMA1, adhesive layer (4 micrometers), b layer which consists of NB (32 micrometers) ) -Adhesive layer (4 [mu] m) -Protective film having a width of 600 mm and a thickness of 80 [mu] m comprising a layer (15 [mu] m) composed of PMMA1 was obtained by coextrusion molding. The bending elastic modulus of the a layer of the protective film was 3.3 GPa, and the bending elastic modulus of the b layer was 2.0 GPa.

(Preparation of active energy ray-curable adhesive 1)
Terminal energy-modified polybutadiene (Nippon Soda Co., Ltd., "R-45ACR") 35 parts by weight, isobornyl acrylate 60 parts by weight, and 1-hydroxy-cyclophenyl-phenyl ketone 3 parts by weight are mixed to form an active energy ray curable type. Adhesive 1 was obtained.

(Preparation of active energy ray-curable adhesive 2)
95 parts by weight of 3-ethyl-3 [(phenoxy) methyl] oxetane (“PhOX” manufactured by Toagosei Co., Ltd.), 3 parts by weight of a polybutadiene-based epoxy compound, 3 parts by weight of an alicyclic epoxy compound (“ERL4206” manufactured by Union Carbide) And 3 parts by weight of an antimony sulfonium salt compound (“SP-170” manufactured by Asahi Denka Kogyo Co., Ltd.) were mixed to obtain an active energy ray-curable adhesive 2.

Example 1
A protective film was bonded to both surfaces of the polarizer P via an active energy ray-curable adhesive 1, and ultraviolet rays with an integrated light amount of 3000 mJ / cm ² were irradiated to obtain a polarizing plate 1.

Example 2
A polarizing plate 2 was obtained in the same manner as in Example 1 except that the active energy ray curable adhesive 1 was used instead of the active energy ray curable adhesive 1.

Comparative Example 1
A 10% aqueous solution of polyvinyl alcohol (manufactured by Kuraray Co., “PVA203”) was dropped onto both surfaces of the polarizer P, a protective film was bonded thereto, and heated at 130 ° C. for 10 minutes to obtain a polarizing plate 3.

<Flexibility test>
A polarizing plate was punched into 1 cm × 5 cm to obtain a test film. The obtained test film was wound around a 3 mmφ steel rod, and it was tested whether the wound film was broken at the rod. The test was conducted a total of 10 times, and the flexibility was expressed by the following index according to the number of times the test was not broken.
○: No broken film pieces △: One broken film piece ×: Two or more broken film pieces

<Liquid crystal display performance evaluation test>
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, Polarizing plates 1 to 3 obtained in Examples and Comparative Examples were installed in the liquid crystal cell. Next, white characters are displayed with a black background, and the line of sight is moved up and down, left and right from the front, and the angle at which white characters cannot be read is measured.

(Adhesion)
Adhesiveness was determined by the cross-cut method described in JIS-K5600-5-6. Specifically, 100 square cuts were made using a cutter guide with a gap interval of 2 mm. Next, an adhesive tape (manufactured by Nichiban Co., Ltd., trade name: CT24) was attached to the grid-shaped cut surface and rubbed with an eraser to be completely attached. The adhesive tape was then peeled off vertically. The tape peeling surface was visually observed and evaluated according to the following criteria.
○: The cut edge is smooth and there is no peeling ×: peeling is seen

(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 diagonal line intersection of the overlapping polarizing plates so that the polarization axes are parallel to each other is a two-degree field of view (C light source) of JIS Z8701. ) 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 are attached as follows. ~ 5. Then, the degree of polarization at the diagonal intersection of the polarizing plate was obtained in the same manner, and the change in the degree of polarization before and after being left under high temperature and high humidity was obtained in the same manner.
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.
○: Change in polarization degree is 0.5% or less ×: Change in polarization degree is greater than 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.

<Scratchability test>
With reference to JIS K5600-5-4, with a 4H test pencil specified in JIS S 6006 tilted at an angle of 45 degrees, a load of 500 g was applied to the surface of the protective film constituting the polarizing plate (polarized light The test was conducted by scratching the surface opposite to the child side) by about 5 mm. This test was conducted five times, and the degree of scratching was determined according to the following criteria.
○: All 5 times were not scratched △: 1 time out of 5 times was scratched ×: 2 times out of 5 times were scratched

Claims (5)

A viewing-side protective layer comprising at least a layer and a b layer containing a thermoplastic resin, wherein the bending elastic modulus of the a layer is larger than the bending elastic modulus of the b layer, and the a layer is present on the viewing side; ,
The polarizer is laminated via an active energy curable adhesive containing no solvent.
Polarizer.   The polarizing plate according to claim 1, wherein a difference in flexural modulus between the a layer and the b layer is 0.2 GPa to 2.5 GPa.   The polarizing plate according to claim 1, wherein the viewing-side protective layer is obtained by a coextrusion method.   The polarizing plate according to any one of claims 1 to 3, wherein the viewing-side protective layer contains an ultraviolet absorber. A liquid crystal display provided with the polarizing plate as described in any one of Claims 1-4.