KR101811878B1 - Polarizer, method for producing polarizer, and liquid crystal display device - Google Patents

Abstract

A polarizing plate comprising a polarizing film and a transparent protective film disposed on both sides of the polarizing film, wherein a coefficient of linear expansion in a direction orthogonal to the absorption axis of the polarizing film and a coefficient of linear expansion in a direction orthogonal to the absorption axis of the polarizing plate And a coefficient of linear expansion of 1.3 10 ^-4 / 캜 or less, and a method for producing the polarizing plate. The polarizer is excellent in durability under a cold and heat shock environment.

Description

TECHNICAL FIELD [0001] The present invention relates to a polarizer, a polarizer, a method of manufacturing the polarizer, and a liquid crystal display device.

The present invention relates to a polarizing plate suitably used for a liquid crystal display device and having improved durability, and a method of manufacturing the same.

BACKGROUND ART [0002] Liquid crystal display devices are used in various display devices because of their low power consumption, low voltage operation, light weight and thinness. A liquid crystal display device generally comprises many optical members such as a liquid crystal cell, a polarizing plate, a retardation film, a condensing sheet, a diffusion film, a light guide plate, and a light reflection sheet. Therefore, production efficiency and brightness of the liquid crystal display device can be improved, and further, light weight and thinness can be achieved by reducing the number of sheets or sheets constituting these optical members and improving the film thickness. As a result of the research.

The polarizing plate is constituted by laminating a transparent protective film on at least one surface, usually both surfaces, of a polarizing film on which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin. In addition, a polarizer used for a liquid crystal display device is required to have high durability in a cold / heat shock environment test. Here, the cold / heat impact environmental test is a test in which the polarizer is bonded to a liquid crystal cell or a glass plate at a low temperature of 0 占 폚 or lower for a predetermined time, and at a high temperature of 60 占 폚 or higher for a predetermined time. In such a cold-shock environmental test, it is required that even if the temperature on the low-temperature side is lowered, a crack of the polarizing film due to the expansion and contraction of the polarizing plate is not generated even if the temperature on the high-temperature side is increased or the number of repeating cycles is increased have.

Therefore, for the purpose of improving the endurance performance of the polarizing plate, there is a proposal that the polarizing film is not exposed at the outer peripheral edge. For example, in JPH10-206633-A, when a polarizing plate in which a protective film is laminated on both surfaces of a polarizing film is chipped, it is cut using a cutting tool preheated to a temperature higher than the thermal deformation temperature of the protective film, Thereby causing thermal deformation on the end face to cover the edge of the polarizing film beneath it. In JP2004-21088-A, a polarizing plate in which a protective film is laminated on both surfaces of a polarizing film is bonded on a glass substrate. In this state, the outer peripheral edge of the polarizing plate is coated with a water- And is coated with a resin.

There is also a proposal to cut the end face of the laminated film in which the polarizing plate itself or another optical film is laminated thereon. For example, JP2001-54845-A discloses a method in which a plurality of laminated films, such as a polarizing plate, are superimposed on one another and a peripheral edge portion of the rotary blade faces the outer peripheral edge of the laminated film, have. Further, JP2003-220512-A discloses a method in which the peripheral edge portion of a workpiece, which may be a polarizing plate or the like, is continuously cut and cut by a ply cut method. However, even when these treatments were carried out, cracks sometimes occurred in the cold / heat shock environmental test.

An object of the present invention is to provide a polarizing plate excellent in durability even under a cold and heat impact environment and a method for producing the same. The inventors of the present invention have conducted intensive studies to achieve the above object and have found that the linear expansion coefficient of the polarizing film in the direction orthogonal to the absorption axis and the linear expansion coefficient in the direction orthogonal to the absorption axis of the polarizing plate of at least one transparent protective film It has been found that the durability of the polarizing plate is improved by selecting the transparent protective film so that the difference is equal to or less than a predetermined value, thereby completing the present invention.

That is, the present invention includes the following.

[1] A polarizing plate comprising a polarizing film and a transparent protective film disposed on both sides of the polarizing film, wherein a coefficient of linear expansion in a direction orthogonal to the absorption axis of the polarizing film and a coefficient of linear expansion perpendicular to the absorption axis of the polarizing plate Direction is not more than 1.3 x 10 < ^-4 > / DEG C or less.

[2] The polarizer according to [1], wherein the at least one transparent protective film is made of a cellulose resin or an olefin resin.

[3] A polarizing plate according to [1] or [2], wherein the polarizing film and the transparent protective film are bonded through a cured layer of an aqueous adhesive containing a polyvinyl alcohol resin and a water-soluble epoxy resin.

[4] A polarizing plate according to [1] or [2], wherein the polarizing film and the transparent protective film are adhered through a cured layer of a curable adhesive composition containing an epoxy compound cured by irradiation with an active energy ray.

[5] The polarizer according to [4], wherein the curable adhesive composition comprises an epoxy compound having at least one epoxy group bonded to an alicyclic ring in the molecule.

[6] A method for producing a polarizing plate by laminating a transparent protective film on both sides of a polarizing film, wherein at least one of the transparent protective films has a linear expansion coefficient of the protective film in a direction perpendicular to the absorption axis of the polarizing plate, And a coefficient of linear expansion in a direction orthogonal to the absorption axis of the film is 1.3 x 10 < ^-4 > / DEG C or less.

[7] A liquid crystal display comprising a liquid crystal cell and a polarizing plate bonded to the viewer side, wherein the polarizing plate comprises a polarizing film and a transparent protective film disposed on both sides of the polarizing film, wherein the linear expansion coefficient And a coefficient of linear expansion in a direction orthogonal to the absorption axis of the polarizing plate of one or more transparent protective films is not more than 1.3 10 ^-4 / 캜.

[8] The liquid crystal display device according to [7], wherein the transparent protective film to be bonded to the liquid crystal cell is made of a cellulose resin or a polyolefin resin.

According to the present invention, it is possible to provide a polarizing plate which is free from cracks and the like and which has excellent durability even when placed under a cold / heat shock environment.

Hereinafter, the present invention will be described in detail. First, each member constituting the polarizing plate of the present invention will be explained in order.

[Polarizing Film]

The polarizing film constituting the polarizing plate is usually produced by a process comprising uniaxially stretching a polyvinyl alcohol based resin film, a step of adsorbing a dichroic dye by staining the polyvinyl alcohol resin film with a dichroic dye, a step of adsorbing a dichroic dye to a polyvinyl A step of treating an alcoholic resin film with an aqueous solution of boric acid, and a step of washing with water after treatment with an aqueous solution of boric acid.

The polyvinyl alcohol-based resin can be produced by saponifying a polyvinyl acetate-based resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate and other monomers copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, acrylamides having an ammonium group, and the like.

The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified or polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The polymerization degree of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

Such a polyvinyl alcohol-based resin is used as an original film of a polarizing film. The method of forming the polyvinyl alcohol-based resin is not particularly limited, and a film can be formed by a known method. The film thickness of the polyvinyl alcohol-based resin original film is, for example, about 10 to 150 m, and preferably about 10 to 100 m.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after dyeing with a dichroic dye. When uniaxial stretching is carried out after dyeing, the uniaxial stretching may be carried out before the boric acid treatment or during the boric acid treatment. Of course, uniaxial stretching can also be performed by a plurality of steps shown here. As the uniaxial stretching, a method of uniaxially stretching between rolls having different circumferential velocities, a method of uniaxially stretching using hot roll, and the like can be adopted. The uniaxial stretching may be performed by dry stretching in air or may be performed by wet stretching in which the polyvinyl alcohol based resin film is stretched by using a solvent such as water. The stretching magnification is usually about 3 to 8 times.

The dyeing by the dichroic dye of the polyvinyl alcohol-based resin film can be performed by, for example, a method of immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a dichroic dye. As the dichroic dye, specifically iodine or a dichroic organic dye is used. On the other hand, it is preferable that the polyvinyl alcohol-based resin film is subjected to a treatment in which it is immersed in water and subjected to swelling before the dyeing treatment.

When iodine is used as the dichroic dye, a method in which a polyvinyl alcohol resin film is dipped in an aqueous solution containing iodine and potassium iodide is generally employed.

The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is normally about 20 to 40 캜. The immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method in which a polyvinyl alcohol-based resin film is dipped in an aqueous solution containing a water-soluble dichroic organic dye is employed. The content of the dichroic organic dye in the aqueous solution is usually about 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^{-3 to} 1 part by weight, per 100 parts by weight of water. The dye aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dichroic organic dye aqueous solution used for dyeing is usually about 20 to 80 캜. The immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

The boric acid treatment after dyeing with a dichroic dye can be carried out by dipping the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid. The content of boric acid in the aqueous solution containing boric acid is usually about 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, it is preferable that the aqueous solution containing boric acid contains potassium iodide. The content of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. The immersing time in the aqueous solution containing boric acid is usually about 60 to 1,200 seconds, preferably 150 to 600 seconds, more preferably 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 占 폚 or higher, preferably 50 to 85 占 폚, and more preferably 60 to 80 占 폚.

The polyvinyl alcohol resin film after boric acid treatment is usually subjected to water washing treatment. The water washing treatment can be carried out, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 캜. The immersion time is usually about 1 to 120 seconds.

After washing with water, drying treatment is carried out to obtain a polarizing film. The drying treatment may be performed using a hot-air drier or a far-infrared heater. The drying treatment temperature is usually about 30 to 100 占 폚, preferably 50 to 80 占 폚. The drying treatment time is usually about 60 to 600 seconds, preferably 120 to 600 seconds. By the drying treatment, the water content in the polarizing film is reduced to practical use. The water content thereof is usually about 5 to 20% by weight, preferably 8 to 15% by weight. If the moisture content is less than 5% by weight, the polarizing film may lose its solubility and may be damaged or broken after drying. When the moisture content exceeds 20% by weight, the thermal stability tends to become insufficient.

Thus, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film can be produced. The thickness of the resulting polarizing film may be, for example, about 5 to 40 mu m.

[Transparent protective film]

The polarizing plate of the present invention includes a polarizing film and a transparent protective film disposed on both sides thereof, as described above. The polarizing plate is bonded to the liquid crystal cell to form a member constituting a liquid crystal display device. Thus, in this polarizing plate, one transparent protective film becomes the liquid crystal cell side and the other transparent protective film becomes the side far from the liquid crystal cell.

[Transparent protective film located on the side farther from the liquid crystal cell side]

It is preferable that the transparent protective film located on the side far from the liquid crystal cell is made of a material having excellent transparency, mechanical strength, thermal stability, moisture barrier property and the like. As such a material, for example, an acrylic resin typified by methyl methacrylate resin, a chain polyolefin resin typified by polypropylene resin, a cyclic polyolefin resin, a cellulose resin, a polyethylene terephthalate resin, a polybutyl Acrylonitrile / styrene copolymer resins, acrylonitrile / butadiene / styrene copolymer resins, polyvinyl acetate resins, polyvinylidene chloride resins, polyvinylidene chloride resins, polytetrafluoroethylene resins, Amide resins, polyacetal resins, polycarbonate resins, modified polyphenylene ether resins, polysulfone resins, polyether sulfone resins, polyarylate resins, polyamideimide resins, polyimide resins, .

Each of these resins may be used alone or in combination with one or more other resins.

A resin obtained by subjecting any of these polymers to polymer modification may be used as a material for a transparent protective film. Examples of the polymer modification include copolymerization, crosslinking, molecular terminal modification, stereoregularity control, mixing involving the reaction of different polymers, and the like.

Of these resins, a methacrylate-based resin, a polypropylene-based resin, a cellulose-based resin, or a polyethylene terephthalate-based resin is preferably used as a material for a transparent protective film located on the side far from the liquid crystal cell.

The methyl methacrylate resin is a polymer containing 50% by weight or more of methyl methacrylate units. The content of the methyl methacrylate unit is preferably 70% by weight or more, and may be 100% by weight. The polymer having a methyl methacrylate unit of 100% by weight is obtained by polymerizing methyl methacrylate alone.

The methyl methacrylate resin can be usually obtained by polymerizing a monofunctional monomer containing methyl methacrylate as a main component in the presence of a radical polymerization initiator and a chain transfer agent. In some cases, a monofunctional monomer may be copolymerized with a component copolymerizable with methyl methacrylate. In some cases, a small amount of a polyfunctional monomer may be copolymerized as desired.

Examples of monofunctional monomers that can be copolymerized with methyl methacrylate include ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, Methacrylic acid esters other than methyl methacrylate such as 2-hydroxyethyl methacrylate; Acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, and 2-ethylhexyl acrylate; Acrylic acid hydroxyalkyl esters such as hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate; Unsaturated acids such as acrylic acid, methacrylic acid, and acrylic acid; Halogenated styrenes such as chlorostyrene, and bromostyrene; Substituted styrenes such as vinyltoluene, and? -Methylstyrene; Unsaturated nitriles such as acrylonitrile and methacrylonitrile, unsaturated acid anhydrides such as maleic anhydride and citraconic anhydride; Phenylmaleimide, and unsaturated imides such as cyclohexylmaleimide. Each of these monomers may be used alone or in combination with one or more other monomers.

Examples of polyfunctional monomers copolymerizable with methyl methacrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di Such as ethylene glycol or its oligomer, esterified with acrylic acid or methacrylic acid at both terminal hydroxyl groups of ethylene glycol or an oligomer thereof; Propylene glycol or its oligomer with both terminal hydroxyl groups being esterified with acrylic acid or methacrylic acid; Esterified with acrylic acid or methacrylic acid, such as neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, and butanediol di (meth) acrylate; Bisphenol A, an alkylene oxide adduct of bisphenol A, or both terminal hydroxyl groups of the halogen substituents thereof esterified with acrylic acid or methacrylic acid; Trimethylol propane, and pentaerythritol esterified with acrylic acid or methacrylic acid; An epoxy group of glycidyl acrylate or glycidyl methacrylate is added to a terminal hydroxyl group of a compound having two or more hydroxyl groups; A dibasic acid such as succinic acid, adipic acid, terephthalic acid, phthalic acid, and halogen substituents thereof, or an alkylene oxide adduct thereof with ring-opening addition of an epoxy group of glycidyl acrylate or glycidyl methacrylate; Allyl (meth) acrylate; And aromatic divinyl compounds such as divinylbenzene. When a polyfunctional monomer is copolymerized, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and neopentyl glycol dimethacrylate are preferably used.

The modified resin may be used by carrying out a reaction between the functional groups of the methyl methacrylate resin. Examples of the reaction between these functional groups include a condensation reaction in a polymer chain between a methyl ester group of methyl acrylate and a hydroxyl group of 2- (hydroxymethyl) acrylate, a condensation reaction of a carboxyl group of acrylic acid with a hydroxyl group of 2- (hydroxymethyl) And a dehydration condensation reaction in a polymer chain.

Commercially available methyl methacrylate resins are readily available. Examples of commercially available products include "SUMIPEX" sold by Sumitomo Chemical Co., Ltd., "ACRYPET" sold by Mitsubishi Rayon Co., Ltd. (ACRYPET) "Ferpete" sold by Kuraray Co., Ltd. and "Arc Review" sold by Nihon Shokubai Co., Ltd., which are sold by Kobayashi Co., Ltd., and others.

The polypropylene-based resin is a polymer of a chain-like olefin monomer containing propylene as a main component, and is usually a chain olefin-based resin in which 80% by weight or more of the repeating units are composed of propylene. The polypropylene resin may be a homopolymer of propylene, or may be a copolymer obtained by copolymerizing propylene with a copolymerizable comonomer in an amount of 1 to 20% by weight, preferably 3 to 10% by weight.

When a copolymer containing propylene as a main component is used, the comonomer copolymerizable with propylene is preferably ethylene, 1-butene or 1-hexene. Among them, a polypropylene resin having a comparatively high transparency can be obtained. Therefore, it is preferable that ethylene is copolymerized in an amount of 1 to 20% by weight, preferably 3 to 10% by weight. When the copolymerization ratio of ethylene is 1% by weight or more, transparency is improved. On the other hand, when the copolymerization ratio of ethylene exceeds 20% by weight, the melting point of the resin is lowered, which may impair the heat resistance required for the transparent protective film.

The content of the component soluble in xylene at 20 캜 (abbreviation of CXS component: CXS component: cold xylene soluble) is preferably 1% by weight or less, more preferably 0.5% by weight or less. Among polypropylene resins, a homopolymer of propylene having a CXS content of 1% by weight or less and 0.5% by weight or less is a suitable example.

Commercially available products of polypropylene type resins are readily available. Examples of commercially available products include "Prime Polypro" sold by Prime Polymer Co., Ltd., "Nova Tech" and "WinTech" sold by Nippon Polypro Co., Ltd., Sumitomo Chemical Co., "Sumitomo nobelen" sold in Japan and "Sun Aroma" sold by Sun Aroma Co., Ltd.

The cellulose-based resin may be an organic acid ester or a mixed organic acid ester of cellulose, in which a part or all of the hydrogen atoms in the hydroxyl group of cellulose are substituted with an acetyl group, a propionyl group and / or a butyryl group. Examples thereof include acetic acid esters of cellulose, propionic acid esters, butyric acid esters, and mixed esters thereof. Among them, triacetylcellulose, diacetylcellulose, cellulose acetate propionate, cellulose acetate butyrate and the like are preferable.

The polyethylene terephthalate resin is a resin in which 80 mol% or more of the repeating units are composed of ethylene terephthalate, and may contain other dicarboxylic acid component and / or other diol component. Examples of other dicarboxylic acid components include isophthalic acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, 4-dicarboxycyclohexane, and the like. Examples of other diol components include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

These other dicarboxylic acid components and other diol components may be used in combination of two or more as necessary. Hydroxycarboxylic acids such as p-hydroxybenzoic acid and p-beta-hydroxyethoxybenzoic acid may be used in combination. As other copolymerization components, a dicarboxylic acid component or a diol component containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond or the like may also be used.

Examples of the method for producing the polyethylene terephthalate resin include a method of directly polycondensing terephthalic acid and ethylene glycol (and other dicarboxylic acids or other diols as required), a method of directly polycondensing a dialkyl ester of terephthalic acid and ethylene glycol (And optionally other diol esters) of terephthalic acid (and optionally other dicarboxylic acids) in the presence of a catalyst in the presence of a catalyst And the like. Further, if necessary, further solid phase polymerization may be carried out to increase the molecular weight or lower the low molecular weight component.

As a method for forming the above-described resin as a transparent protective film for a polarizing plate, a method according to each resin may be appropriately selected. For example, there are a solvent cast method in which a resin dissolved in a solvent is cast into a metal band or a drum and the solvent is removed by drying to obtain a film, a method in which the resin is heated to its melting temperature or higher, A melt extrusion method for obtaining a film by cooling, or the like can be used. In the melt extrusion method, the single layer film may be extruded or the multilayer film may be extruded at the same time.

Commercial products of these resin films can be easily obtained. As commercially available films, for example, methyl methacrylate resin films are available under the trade names of "Technoroy" sold by Sumitomo Chemical Co., Ltd., "Acry" sold by Mitsubishi Rayon Co., Light Glass "and" Acryprene "sold by Asahi Glass Co., Ltd.," Terra Glass "sold by Asahi Glass Co.," Paraglass "and" Como Glass "sold by Kuraray Co., Ltd., And an "arc reviewer" selling it. Examples of the polyethylene terephthalate-based resin film include "A-PET sheet" sold under the trade names "NOVA CLEAR" and "A-PET sheet" sold by Mitsubishi Kagaku Co., Ltd. and the like. As the polypropylene resin film, "FILMAX CPP film" sold by FILMAX Co., Ltd., "Sanxos" sold by SanTox Co., Ltd., and "Toxel sold by Dosselo Co., "Toyobo Pyrene Film" sold by Toyo Boseki Co., Ltd., "Toraypan" sold by Dole Film Co., Ltd., "Nippon Poly Ace Co., Ltd." "And" Taiko FC "sold by Futamura Kagaku Co., Ltd. Examples of the cellulose-based resin film include "Fuji Tech TD" sold by Fuji Film Co., Ltd. and "Konica Minolta TAC Film KC" sold by Konica Minolta Opt Co., Ltd. under trade names.

It is possible to impart haze to the transparent protective film which is disposed on the side far from the liquid crystal cell and becomes the viewing side to exhibit the anti-scattering property. Examples of the method for imparting haze include a method in which inorganic fine particles or organic fine particles are mixed into a raw material resin constituting a transparent protective film to form a film, and a method in which a resin mixed with fine particles and a resin in which fine particles are not mixed A method of forming a two-layer film or a three-layer film by using a resin mixed with fine particles as an outer layer; a method of coating a coating liquid obtained by mixing inorganic fine particles or organic fine particles with a curable binder resin on one side of the film, And a method of forming an antifogging property is adopted.

Examples of the inorganic fine particles used for imparting haze include silica, colloidal silica, alumina, alumina sol, aluminosilicate, alumina-silica composite oxide, kaolin, talc, mica, calcium carbonate and calcium phosphate. Examples of the organic fine particles include crosslinked polyacrylic acid particles, methyl methacrylate / styrene copolymer resin particles, crosslinked polystyrene particles, crosslinked polymethyl methacrylate particles, silicone resin particles and polyimide particles.

When haze is given to the transparent protective film, it is preferable that the haze value is in the range of 6 to 45%. If the haze value of the transparent protective film is less than 6%, a sufficient antiglare effect may not be exhibited. On the other hand, when the haze value exceeds 45%, the screen of the liquid crystal display device in which the transparent protective film is disposed may be whitened and the image quality may deteriorate. The haze is a value defined as a ratio of the diffusion transmittance to the total light transmittance and can be measured using a commercially available haze meter in accordance with JIS K 7136. As a commercially available haze meter, for example, "HM-150" sold by Murakami Shikishi Suisen Co., Ltd. is available. To measure the haze value, it is preferable to use a measurement sample in which the film surface is bonded to the glass substrate so that the antiglare surface becomes the surface, for example, by using an optically transparent pressure-sensitive adhesive in order to prevent the film from warping.

A functional layer including a conductive layer, a hard coat, and a low reflection layer can be formed on the outer side of the transparent protective film that is disposed on the side far from the liquid crystal cell and becomes the viewing side. As the coating liquid containing the binder resin constituting the above-mentioned antiglare layer, a resin composition capable of exhibiting these functions may be selected.

[Transparent protective film positioned on the liquid crystal cell side]

As the resin material constituting the transparent protective film positioned on the side of the liquid crystal cell in the polarizing plate, those described above for the transparent protective film located on the side far from the liquid crystal cell can be used. Of these, a polyolefin-based resin including a cellulose resin or a chain-like polyolefin-based resin or a cyclic polyolefin-based resin is preferably used because it is easy to control the retardation value and is easily available.

The cyclic polyolefin-based resin referred to here is obtained by polymerizing a cyclic olefin monomer such as norbornene and other cyclopentadiene derivatives in the presence of a catalyst. When such an annular polyolefin-based resin is used, it is easy to obtain a transparent protective film having a predetermined retardation value.

As the cyclic polyolefin-based resin, for example, norbornene or a derivative thereof obtained by a Diels-Alder reaction in cyclopentadiene and an olefin or (meth) acrylic acid or an ester thereof is used as a monomer, ring-opening metathesis polymerization A resin obtained by subsequent hydrogenation; Ring-opening metathesis polymerization is carried out using dicyclopentadiene and tetracyclododecene or its derivative obtained by a Diels-Alder reaction in an olefin or a (meth) acrylic acid or an ester thereof as a monomer, followed by hydrogenation Suzy; At least two kinds of monomers selected from norbornene, tetracyclododecene, derivatives thereof, and other cyclic olefin monomers are similarly subjected to ring-opening metathesis copolymer followed by hydrogenation; And resins obtained by addition-copolymerizing aromatic compounds having a chain type olefin and / or vinyl group with cyclic olefins such as norbornene, tetracyclododecene or their derivatives.

Commercially available products of the cyclic polyolefin-based resin can be easily obtained. Examples of commercially available products include TOPAS, which is produced by TOPAS ADVANCED POLYMERS GmbH and sold by Polyplastics in Japan, and ATON, Nippon Zeon (sold by JSR Co., Ltd.) "Zeonoa" and "Zeonex" sold by Mitsui Chemicals, Inc. and "Apel" sold by Mitsui Gagaku Co., Ltd.

Typical examples of the chain-like polyolefin-based resin are a polyethylene-based resin and a polypropylene-based resin. Among them, a homopolymer of propylene or a copolymer mainly composed of propylene and copolymerized with a comonomer copolymerizable therewith, for example, at a ratio of 1 to 20% by weight, preferably 3 to 10% by weight, is suitably used .

As a method for forming a film of a cellulose-based resin, a polyolefin-based resin, or the like into a film, a method according to each resin may be appropriately selected. For example, a solvent cast method in which a resin dissolved in a solvent is poured into a metal band or a drum, and the solvent is removed by drying to obtain a film; a method in which the resin is heated to a temperature above its melting temperature, kneaded and extruded from the die, A melt extrusion method in which a film is obtained by cooling the melt-extruded product. Among them, the melt extrusion method is preferably employed for the polyolefin-based resin from the viewpoint of productivity. On the other hand, the cellulose resin is generally formed by a solvent casting method.

As these films, films having desired retardation values may be used by stretching and shrinking treatment depending on the application.

[Difference in coefficient of linear expansion between polarizing film and protective film]

In the present invention, as described above, when the polarizing film and at least one of the transparent protective films disposed on both sides are bonded to each other to form a polarizing plate, And the linear expansion coefficient is satisfied. That is, the polarizing film and the protective film are selected such that the difference between the coefficient of linear expansion in the direction of the polarizing film and the linear expansion coefficient in the direction of the transparent protective film is 1.3 × 10 ^-4 / ° C. or less.

The transparent protective film disposed on at least one side of the polarizing film satisfies the relationship of the linear expansion coefficient with respect to the polarizing film so that even when the polarizing plate is placed under a cold and heat shock environment, And the stress applied to the polarizing film is suppressed, so that cracks are less likely to occur in the polarizing film, and the polarizing plate is excellent in durability under a cold / heat shock environment. On the other hand, when all of the transparent protective films disposed on both surfaces of the polarizing film do not satisfy the above relationship, that is, when the difference in coefficient of linear expansion between the transparent protective film and the polarizing film in both directions exceeds 1.3 10 ^-4 / When the polarizing plate is placed under a cold shock environment, cracks are likely to occur in the polarizing film.

Here, the coefficient of linear expansion is a value measured as an average coefficient of linear expansion (also referred to as average coefficient of linear expansion) of the test piece in an arbitrary temperature range in accordance with JIS K 7197. In the present invention, Lt; RTI ID = 0.0 > 85 C. < / RTI > The difference in coefficient of linear expansion specified in the present invention means a value obtained by a coefficient of linear expansion of a film having a small coefficient of linear expansion and a coefficient of expansion of a film having a large coefficient of expansion.

As described above, the polarizing film is composed of a polyvinyl alcohol-based resin, and the polyvinyl alcohol-based resin shrinks in accordance with an increase in temperature, that is, its size is often small.

On the other hand, the thermoplastic resin film constituting the transparent protective film often expands as the temperature rises, that is, the dimension increases. In determining the coefficient of linear expansion, a positive (positive) value is obtained when the temperature rises according to the temperature rise, and a negative (negative) value is obtained when the temperature rises with the temperature rises. Based on these values, the coefficient of linear expansion .

Since the polarizing film is composed of a uniaxially stretched film of a polyvinyl alcohol-based resin as described above, when the film is stretched, the shrinkage (neck-in) in the direction perpendicular to the stretching direction is made small, The linear expansion coefficient in the orthogonal direction can be increased (the absolute value can be made small) although it is in the minus range. On the other hand, although the coefficient of linear expansion of the transparent protective film made of a thermoplastic resin laminated on the polarizing film varies depending on the type of the resin constituting it, the kind of the additives, the orientation state of the resin and the like, The coefficient may be made small. Of course, the value of the coefficient of linear expansion also varies depending on the type of the thermoplastic resin constituting the transparent protective film, so it is also effective to select a resin having a small coefficient of linear expansion. Therefore, these measures may be appropriately combined so that the linear expansion coefficient of the polarizing film and the at least one transparent protective film satisfy the above-described relationship, that is, the difference in coefficient of linear expansion between the polarizing film and the transparent protective film becomes smaller.

As described above, the coefficient of linear expansion in the direction perpendicular to the absorption axis of the polarizing film can be adjusted so as to adjust the conditions for uniaxial stretching, but once the production conditions are determined, the linear expansion coefficient becomes almost a predetermined value. When the coefficient of linear expansion in the direction orthogonal to the absorption axis of the polarizing film is almost a predetermined value, it is preferable that the transparent protective film laminated thereon be a polarizing plate having a direction perpendicular to the absorption axis The difference between the coefficient of linear expansion and the linear expansion coefficient in the same direction of the polarizing film may be selected to be 1.3 x 10 < ^-4 > / DEG C or less as described above.

The above relationship between the coefficient of linear expansion of the transparent protective film and the coefficient of linear expansion of the polarizing film is determined by the relationship between the transparent protective film and the polarizing film which is far from the liquid crystal cell in use and the polarizing film Of course, and of course it may be accomplished on both sides. The polarizing plate is usually bonded to the liquid crystal cell through the pressure sensitive adhesive layer. When the relationship of the linear expansion coefficient is achieved between the transparent protective film serving as the liquid crystal cell side and the polarizing film at the time of use, the liquid crystal cell side protective film Can be further suppressed by the pressure-sensitive adhesive layer, which is more advantageous.

The polarizing film is generally produced in the form of a long roll, and is uniaxially stretched in the longitudinal direction (machine direction MD), so that the longitudinal direction in the stretching direction becomes the absorption axis. On the other hand, even when the transparent protective films disposed on both sides thereof are different from each other on both sides of the film, they are generally supplied in the form of a long roll, and are directly adhered to the polarizing film by roll-to-roll. In the case of roll-to-roll bonding using such a long roll-shaped film as a raw material, the width direction of the polarizing film is perpendicular to the absorption axis, and the width direction of the transparent protective film is also perpendicular to the absorption axis of the polarizing plate Direction, the coefficient of linear expansion in each of the width directions may be set to satisfy the above-described relation.

[Bonding of Polarizing Film to Protective Film]

In the polarizing plate, an adhesive is usually used for bonding the polarizing film and the transparent protective film. The cured layer of the adhesive for bonding the polarizing film and the transparent protective film may have a thickness of about 0.01 to 30 mu m, preferably 0.01 to 10 mu m, more preferably 0.05 to 5 mu m. When the thickness of the cured layer of the adhesive is within the above range, it is possible to obtain an adhesive force that does not cause any floating or peeling between the transparent protective film and the polarizing film to be laminated and has no problem in practical use.

For forming the cured layer of the adhesive, an appropriate adhesive may be suitably used in accordance with the kind and purpose of the adherend, and if necessary, an anchor coat agent may also be used. Examples of the adhesive include a solvent type adhesive, an emulsion type adhesive, a pressure-sensitive adhesive, a re-wetting adhesive, a polycondensation type adhesive, a solventless type adhesive, a film type adhesive and a hot melt type adhesive.

As one of preferred adhesives, an aqueous adhesive, that is, an adhesive component is dissolved or dispersed in water, for example. Examples of the water-soluble adhesive component include a polyvinyl alcohol-based resin. Examples of the adhesive component dispersible in water include urethane-based resins having a hydrophilic group. The water-based adhesive can be prepared by mixing these adhesive components with water together with additional additives to be blended as required. Examples of a commercially available polyvinyl alcohol-based resin that can be an aqueous adhesive include "KL-318" (trade name) which is a carboxyl group-modified polyvinyl alcohol sold by Kuraray Co.,

The aqueous adhesive may contain a crosslinking agent as required. Examples of the crosslinking agent include amine compounds, aldehyde compounds, methylol compounds, water-soluble epoxy resins, isocyanate compounds, polyvalent metal salts and the like. When a polyvinyl alcohol resin is used as an adhesive component, an aldehyde compound including glyoxal, a methylol compound including methylolmelamine, a water-soluble epoxy resin, and the like can be preferably used as a crosslinking agent.

The water-soluble epoxy resin is a polyamide epoxy resin obtained by reacting epichlorohydrin with a polyamide polyamine which is a reaction product of a polyalkylene polyamine such as dimethylenetriamine or triethylenetetramine and a dicarboxylic acid such as adipic acid Resin. An example of a commercially available product of water-soluble epoxy resin is "Sumirez Resin 650 (30)" (trade name) sold by Sumika Chemical Tech.

The polarizing plate and / or the transparent protective film can be obtained by applying an aqueous adhesive to the adhesive surface of the polarizing film and / or the transparent protective film, bonding them together, and then applying a drying treatment to cure the aqueous adhesive. Prior to adhesion, it is also effective to increase the wettability of the transparent protective film by carrying out a reverse adhesion treatment such as a saponification treatment, a corona discharge treatment, or a plasma treatment. The drying temperature may be, for example, about 60 to 100 占 폚. After the drying treatment, curing at a temperature slightly higher than the room temperature, for example, about 30 to 50 占 폚 for about 1 to 10 days is preferable in further increasing the adhesive force.

Another preferable adhesive is a curable adhesive composition containing an epoxy compound which is cured by irradiation with an active energy ray or by heating. The curable epoxy compound has at least two epoxy groups in the molecule. In this case, the polarizing film and the transparent protective film may be adhered to each other by applying an active energy ray to the applied layer of the adhesive composition, or by heating, and curing the curable epoxy compound contained in the adhesive. The curing of the epoxy compound is generally carried out by cationic polymerization of an epoxy compound. From the viewpoint of productivity, the curing is preferably carried out by irradiation of active energy rays.

From the viewpoints of weatherability, refractive index, cationic polymerizability and the like, it is preferable that the epoxy compound contained in the curable adhesive composition does not contain an aromatic ring in the molecule. Examples of the epoxy compound that does not contain an aromatic ring in the molecule include hydrogenated epoxy compounds, alicyclic epoxy compounds, aliphatic epoxy compounds, and the like. Epoxy compounds suitably used in such a curable adhesive composition are well known and described in detail, for example, in JP2004-245925-A, but will also be schematically described here.

The hydrogenated epoxy compound may be a glycidyl etherified naphtha hydrogenated polyhydroxy compound obtained by subjecting an aromatic polyhydroxy compound as a raw material of an aromatic epoxy compound to a nucleation hydrogenation reaction selectively in the presence of a catalyst and under pressure . Examples of the aromatic polyhydroxy compound as a raw material of the aromatic epoxy compound include bisphenols such as bisphenol A, bisphenol F and bisphenol S; Novolak type resins such as phenol novolak resin, cresol novolak resin, and hydroxybenzaldehyde phenol novolac resin; Tetrahydroxydiphenylmethane, tetrahydroxybenzophenone, and polyvinylphenol, and the like can be given. By subjecting such an aromatic polyhydroxy compound to a nucleus hydrogenation reaction and then reacting the resultant nucleus-hydrogenated polyhydroxy compound with epichlorohydrin, glycidyl etherification can be carried out. Suitable hydrogenated epoxy compounds include glycidyl ethers of hydrogenated bisphenol A.

The alicyclic epoxy compound is a compound having at least one epoxy group bonded to the alicyclic ring in the molecule. The "epoxy group bonded to an alicyclic ring" means a bridging oxygen atom -O- in the structure represented by the following formula, wherein m is an integer of 2 to 5.

A compound in which one or more hydrogen atoms in (CH ₂ ) _m in this formula are bonded to other chemical structures may be an alicyclic epoxy compound. Furthermore, one or more hydrogen atoms in (CH ₂ ) _m forming an alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among the alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (in the above formula, m = 4) exhibits excellent adhesion And is preferably used. Specific examples of the alicyclic epoxy compound are given below. Here, the name of the compound is taken as an example, and then the corresponding chemical formula is shown, and the chemical name and the chemical formula corresponding thereto are given the same reference numerals.

A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 3,4-

B: 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate,

C: Ethylene bis (3,4-epoxycyclohexanecarboxylate),

D: bis (3,4-epoxycyclohexylmethyl) adipate,

E: bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate,

F: diethylene glycol bis (3,4-epoxycyclohexylmethyl ether),

G: ethylene glycol bis (3,4-epoxycyclohexylmethyl ether),

H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispyro [5.2.2.5.2.2] hexocycline,

I: 3- (3,4-epoxycyclohexyl) -8,9-epoxy-1,5-dioxaspiro [5.5] undecane,

J: 4-vinylcyclohexene dioxide,

K: limonene dioxide,

L: bis (2,3-epoxycyclopentyl) ether,

M: dicyclopentadiene dioxide and the like.

The aliphatic epoxy compound may be a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof. More specifically, diglycidyl ether of propylene glycol; Diglycidyl ether of 1,4-butanediol; Diglycidyl ether of 1,6-hexanediol; Triglycidyl ether of glycerin; Triglycidyl ether of trimethylolpropane; A polyglycidyl ether of a polyether polyol (for example, a diglycidyl ether of polyethylene glycol) obtained by adding an alkylene oxide (ethylene oxide or propylene oxide) to an aliphatic polyhydric alcohol such as ethylene glycol, propylene glycol and glycerin .

In the curable adhesive composition, only one epoxy compound may be used alone, or two or more epoxy compounds may be used in combination. Among them, the curable adhesive composition preferably contains an alicyclic epoxy compound having at least one epoxy group bonded to an alicyclic ring in the molecule.

The epoxy compound used in the curable adhesive composition usually has an epoxy equivalent weight in the range of 30 to 3,000 g / equivalent, and the epoxy equivalent weight is preferably in the range of 50 to 1,500 g / equivalent. When an epoxy compound having an epoxy equivalent of less than 30 g / equivalent is used, the flexibility of the polarizing plate after curing may be lowered or the adhesive strength may be lowered. On the other hand, in a compound having an epoxy equivalent of more than 3,000 g / equivalent, there is a possibility that compatibility with other components contained in the adhesive composition is lowered.

From the viewpoint of reactivity, cationic polymerization is preferably used as a curing reaction of an epoxy compound. To this end, it is preferable to incorporate a cationic polymerization initiator into the curable adhesive composition containing an epoxy compound. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation or heating of an active energy ray such as visible light, ultraviolet ray, X-ray and electron beam to start the polymerization reaction of the epoxy group. From the viewpoint of workability, it is preferable that the cationic polymerization initiator is given a potential. Hereinafter, a cationic polymerization initiator which generates a cationic species or a Lewis acid by irradiation of an active energy ray to initiate a polymerization reaction of an epoxy group is referred to as a " photocationic polymerization initiator ", and a cationic species or a Lewis acid is generated by heat, Quot; thermal cationic polymerization initiator " is referred to as " thermal cationic polymerization initiator ".

The method of curing the adhesive composition by irradiation of an active energy ray using a cationic ion polymerization initiator enables curing at room temperature and reduces the need to consider the heat resistance or distortion caused by the expansion of the polarizing film, And the polarizing film can be favorably adhered. Further, since the photocationic polymerization initiator acts catalytically with light, even when mixed with an epoxy compound, the storage stability and workability are excellent.

Examples of the photocationic polymerization initiator include aromatic diazonium salts; Onium salts such as aromatic iodonium salts and aromatic sulfonium salts, iron-allene complexes and the like. The blending amount of the photocationic polymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 part by weight or more, and more preferably 15 parts by weight or less, based on 100 parts by weight of the epoxy compound.

If the blending amount of the photocationic polymerization initiator is less than 0.5 parts by weight based on 100 parts by weight of the epoxy compound, the curing becomes insufficient, and the mechanical strength and the adhesive strength of the cured product tend to be lowered.

On the other hand, if the blending amount of the photocationic polymerization initiator is more than 20 parts by weight based on 100 parts by weight of the epoxy compound, the ionic substance in the cured product increases, thereby increasing the hygroscopicity of the cured product and possibly lowering the durability.

When a photocationic polymerization initiator is used, the curable adhesive composition may further contain a photosensitizer, if necessary. By using a photosensitizer, the reactivity of the cationic polymerization can be improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include a carbonyl compound, an organic sulfur compound, a persulfide compound, a redox compound, an azo compound, a diazo compound, a halogen compound, a light reducing pigment and the like. When the photosensitizer is blended, the amount thereof is preferably within a range of 0.1 to 20 parts by weight based on 100 parts by weight of the curable adhesive composition.

On the other hand, examples of thermal cationic polymerization initiators include benzylsulfonium salts, thiophenium salts, thioronium salts, benzylammonium, pyridinium salts, hydradinium salts, carboxylic acid esters, sulfonic acid esters and amine imides.

The curable adhesive composition containing an epoxy compound is preferably cured by photocationic polymerization as described above, but may be cured by thermal cationic polymerization in the presence of the thermal cationic polymerization initiator described above, Polymerization may be used in combination. When the cationic ion polymerization and the thermal cationic polymerization are used in combination, it is preferable that the curable adhesive composition contains both a cationic polymerization initiator and a thermal cationic polymerization initiator.

Further, the curable adhesive composition may further contain a compound that promotes cation polymerization such as an oxetane compound or a polyol compound. The oxetane compound is a compound having a 4-membered ring ether in the molecule. When the oxetane compound is compounded, the amount thereof is usually 5 to 95% by weight, preferably 5 to 50% by weight, in the curable adhesive composition. The polyol compound may be an alkylene glycol or an oligomer thereof, such as ethylene glycol, hexamethylene glycol, or polyethylene glycol, a polyester polyol, a polycaprolactone polyol, a polycarbonate polyol, or the like. When the polyol compound is compounded, the amount thereof is generally 50% by weight or less, preferably 30% by weight or less, in the curable adhesive composition.

The curable adhesive composition may contain other additives such as an ion trap agent, an antioxidant, a chain transfer agent, a sensitizer, a tackifier, a thermoplastic resin, a filler, a flow regulator, a plasticizer and a defoaming agent can do. Examples of the ion trap agent include inorganic compounds including powdery bismuth, antimony, magnesium, aluminum, calcium, titanium, and mixtures thereof. Examples of the antioxidant include hindered phenol Based antioxidant and the like.

A curable adhesive composition containing an epoxy compound is coated on the adhesive surface of a polarizing film or a transparent protective film or both of these adhesive surfaces and then bonded with a surface coated with an adhesive to irradiate or heat the active energy ray, The polarizing film and the transparent protective film can be bonded by curing the cured adhesive layer. As the coating method of the adhesive, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be adopted.

This curable adhesive composition can basically be used as a solvent-free adhesive agent substantially not containing a solvent. However, since each coating method has an optimum viscosity range, a solvent may be added for viscosity adjustment. The solvent is preferably an organic solvent that dissolves each component including the epoxy compound well without deteriorating the optical performance of the polarizing film. For example, hydrocarbons typified by toluene, esters typified by ethyl acetate, and the like can be used .

When the adhesive composition is cured by irradiation of an active energy ray, various kinds of the above-mentioned active energy rays can be used, but ultraviolet rays are preferably used since they are easy to handle and easily control the irradiation light amount and the like. The irradiation intensity or irradiation amount of an active energy ray, for example, ultraviolet ray is suitably adjusted so as not to affect various optical performances including the degree of polarization of the polarizing film and various optical performances including transparency and retardation characteristics of the transparent protective film .

When the adhesive composition is cured by heat, it may be heated by a generally known method. Normally, the thermal cationic polymerization initiator compounded in the curable adhesive composition is heated to a temperature higher than the temperature at which the cationic species or Lewis acid is generated, and the heating temperature is, for example, about 50 to 200 캜.

[Pressure-sensitive adhesive layer]

The pressure-sensitive adhesive layer is usually laminated on the transparent protective film to be the liquid crystal cell side of the polarizing plate described above. This pressure-sensitive adhesive layer is provided for bonding the polarizing plate to the liquid crystal cell.

The pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer should be excellent in optical transparency, excellent in wettability, cohesiveness, adhesiveness, etc., and excellent in durability. Specifically, as the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer, a pressure-sensitive adhesive containing an acrylic resin (acrylic pressure-sensitive adhesive) is preferably used.

The acrylic resin contained in the acrylic pressure-sensitive adhesive is a resin containing acrylic acid alkyl ester such as butyl acrylate, ethyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate as main monomers. A polar monomer is usually copolymerized with the acrylic resin. The polar monomer is generally a compound having a polymerizable unsaturated bond and a polar functional group, and the polymerizable unsaturated bond is derived from a (meth) acryloyl group, and the polar functional group is a carboxyl group, a hydroxyl group, an amide group, An epoxy group and the like. Specific examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylamide, 2-N, ) Acrylate, and glycidyl (meth) acrylate.

Further, a crosslinking agent is usually mixed with an acrylic resin in the acrylic pressure-sensitive adhesive.

As typical examples of the crosslinking agent, there can be mentioned isocyanate compounds having at least two isocyanate groups (-NCO) in the molecule.

The pressure-sensitive adhesive may also be blended with various additives. Suitable additives include silane coupling agents and antistatic agents. The silane coupling agent is effective for enhancing adhesion to glass. The antistatic agent is effective for reducing or preventing the generation of static electricity. In general, when a polarizing plate is attached to a liquid crystal cell through a pressure-sensitive adhesive layer, the surface protective film (separator) covered with the pressure-sensitive adhesive layer until it is temporarily adhered thereto is peeled and then bonded to the liquid crystal cell. The static electricity may cause a defective orientation of the liquid crystal in the liquid crystal cell, and this phenomenon may cause defective display of the liquid crystal display device. As means for reducing or preventing the generation of such static electricity, it is effective to add an antistatic agent to the pressure-sensitive adhesive.

The pressure-sensitive adhesive layer can be prepared by a direct method in which the pressure-sensitive adhesive component as described above is dissolved in an organic solvent to prepare a pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition is applied directly onto the transparent protective film of the polarizing plate, The pressure-sensitive adhesive composition may be applied to the releasably treated surface of a base film made of a film and the solvent is removed by drying to form a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is adhered onto the transparent protective film of the polarizing plate. When a pressure-sensitive adhesive layer is formed on a transparent protective film by a direct method using an electron, a resin film (also referred to as a separator) subjected to a release treatment is bonded to the surface of the pressure-sensitive adhesive layer, and the surface of the pressure- It is common practice.

The latter transfer method is widely used in view of the handling property of the pressure-sensitive adhesive composition which is an organic solvent solution. In this case, after the release-treated base film used for forming the pressure-sensitive adhesive layer at the beginning is adhered to the polarizing plate, It is also suitable for being able to be.

[Suitable mode of use of the polarizing plate]

The thus obtained polarizing plate is bonded to the liquid crystal cell through the pressure-sensitive adhesive layer to constitute a liquid crystal panel and can be used in a liquid crystal display device. In this case, the liquid crystal cell may be of various types such as an IPS mode, a VA mode, and a TN mode. On the opposite side of the liquid crystal panel to which the polarizing plate of the present invention is bonded, a polarizing plate of the same kind or a known polarizing plate can be bonded.

The polarizing plate provided with the transparent protective film imparted with the above-mentioned antiglare property is usually bonded to the viewer side of the liquid crystal cell.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, parts and percentages indicating contents or amounts are based on weight unless otherwise specified. On the other hand, the respective properties in the following examples were measured by the following methods.

(1) Measurement of thickness:

(Manufactured by Nikon Corporation) using a digital micrometer "MH-15M ".

(2) Measurement of coefficient of linear expansion:

Based on JIS K 7197, using a thermo-mechanical analyzer (TMA) "EXSTAR-6000" manufactured by SII AI Nanotechnology Co., , And the amount of deformation at each temperature of the test film was measured. The coefficient of linear expansion of the film was determined from the deformation amount in the temperature range of 40 ° C to 85 ° C. On the other hand, the case where the film dimension increases (expands) as the temperature rises is taken as positive (positive), and the case where the film dimension decreases (shrinks) as the temperature rises becomes negative (negative).

In the following examples, the following materials were used as the polarizing film and the protective film thereof. In the following, each symbol is indicated.

Polarizing film: polyvinyl alcohol film having a thickness of about 28 탆 in which iodine is adsorbed and oriented. The coefficient of linear expansion in the direction perpendicular to the absorption axis of the polarizing film was -7.38 × 10 ^-5 / ℃.

80 TAC: Triacetylcellulose film "TD80UL" (trade name) having a thickness of 80 mu m and obtained from Fuji Film. When this film was attached to a polarizing film as a transparent protective film to form a polarizing plate, the linear expansion coefficient (value of this film itself) in the direction orthogonal to the absorption axis of the polarizing plate was 6.91 x 10 < ^-5 >

40AC1: Acetic acid cellulose film "KC4FR-T" (trade name) having a thickness of 40 μm obtained from Konica Minolta Opt. Linear expansion coefficient (the value of the film itself) in a direction perpendicular to the absorption axis of the polarizer when the film as a transparent protective film to a polarizing plate attached to the polarizing film was 2.54 × 10 ^-5 / ℃.

40AC2: a triacetylcellulose film "KC4UEW" (trade name) having a thickness of 40 μm obtained from Konica Minolta Opt. The coefficient of linear expansion in a direction perpendicular to the film on the absorption axis of the polarizing plate when the polarizing plate attached to the polarizing film as a transparent protective film (the value of the film itself) was 6.O9 × 10 ^-5 / ℃.

[Example 1]

(Preparation of aqueous adhesive)

Three parts of "KL-318" (trade name), which is a carboxyl group-modified polyvinyl alcohol obtained from Kuraray Co., Ltd., was dissolved in 100 parts of water. To the aqueous solution was added a water-soluble polyamide obtained from Sumika- 1.5 parts of "Sumirez Resin 650 (30)" (trade name, aqueous solution having a solid content concentration of 30%), which is an epoxy resin, was added to prepare an aqueous adhesive.

(Production of polarizing plate)

The 80 TAC was subjected to a saponification treatment to obtain a transparent protective film disposed on the side far from the liquid crystal cell. 40AC1 was subjected to saponification treatment to obtain a transparent protective film disposed on the liquid crystal cell side. The above-mentioned 80 TAC was bonded to one side of the polarizing film through the water-based adhesive prepared above, and 40 AC1 was bonded to the other side through the same water-based adhesive, followed by drying at 80 ° C for 5 minutes To prepare a polarizing plate.

In this example, the difference between the linear expansion coefficient in the direction orthogonal to the absorption axis of the polarizing film and the linear expansion coefficient in the direction orthogonal to the polarizing plate absorption axis of 80 TAC and the linear expansion coefficient in the direction perpendicular to the absorption axis of the polarizing film is 40AC1 And the coefficient of linear expansion in the direction orthogonal to the polarizing plate absorption axis are calculated as follows, and the 40AC1 side satisfies the requirements of the present invention.

80 TAC side: 6.91 x 10 ^-5 / C ^{- (} -7.38 x 10 ^-5 / C) = 1.43 x 10 ^-4 / C

40AC1 ^{side: 2.54 × 10 -5 /℃-(-7.38×10 -5 /℃)=9.92×10} -5 / ℃

(Production and Evaluation of Polarizer Having Pressure-Sensitive Adhesive Layer)

An acrylic pressure sensitive adhesive sheet was bonded to the 40AC1 side of the polarizing plate prepared above to prepare a polarizing plate having a pressure sensitive adhesive layer. The polarizing plate having the pressure-sensitive adhesive layer was cut into a wide 32-inch size (diagonal 32 inches (about 81 cm), width of about 71 cm, length of about 40 cm). The pressure-sensitive adhesive layer side was bonded to a glass plate and maintained at 65 ° C and 85% relative humidity for 24 hours, followed by holding at -35 ° C for 30 minutes and holding at 85 ° C for 30 minutes. Impact environment test was conducted. As a result, the polarizing film did not break even after repeating 300 cycles.

[Comparative Example 1]

A polarizing plate was produced in the same manner as in Example 1 except that one of the transparent protective films 40AC1 was changed to 40AC2. In this example, the difference between the linear expansion coefficient in the direction orthogonal to the absorption axis of the polarizing film and the linear expansion coefficient in the direction orthogonal to the polarizing plate absorption axis of 80 TAC and the linear expansion coefficient in the direction perpendicular to the absorption axis of the polarizing film, And the linear expansion coefficient in the direction orthogonal to the absorption axis of the polarizing plate are respectively calculated as follows, and they did not satisfy the requirements of the present invention.

80 TAC side: 6.91 x 10 ^-5 / C ^{- (} -7.38 x 10 ^-5 / C) = 1.43 x 10 ^-4 / C

40AC2 side: 6.09 占 10-5 / 占 폚 ^- ( ^- 7.38 占 0-5 / C) = 1.35 占^0-4 /

An acrylic pressure sensitive adhesive sheet was bonded to the 40AC2 side of the polarizing plate to prepare a polarizing plate having a pressure sensitive adhesive layer. The obtained polarizing plate having a pressure-sensitive adhesive layer was cut into a wide 32-inch size, and the pressure-sensitive adhesive layer was bonded to a glass plate, and maintained at the same temperature of 65 캜 and relative humidity of 85% as in Example 1, and subjected to a cold / As a result, breakage of the polarizing film was caused by repetition of 50 cycles.

Claims (8)

A polarizing plate comprising a polarizing film and a transparent protective film disposed on both sides of the polarizing film,
Wherein a difference between a coefficient of linear expansion in a direction orthogonal to an absorption axis of the polarizing film and a coefficient of linear expansion in a direction orthogonal to the absorption axis of the polarizing plate of one or more transparent protective films is 1.3 x ^10-4 / The polarizing plate according to claim 1, wherein the at least one transparent protective film is made of a cellulose resin or a polyolefin resin. The polarizing plate according to claim 1 or 2, wherein the polarizing film and the transparent protective film are adhered through a cured layer of an aqueous adhesive containing a polyvinyl alcohol-based resin and a water-soluble epoxy resin. The polarizing plate according to claim 1 or 2, wherein the polarizing film and the transparent protective film are adhered through a cured layer of a curable adhesive composition containing an epoxy compound which is cured by irradiation of an active energy ray. The polarizing plate according to claim 4, wherein the curable adhesive composition comprises an epoxy compound having at least one epoxy group bonded to an alicyclic ring in the molecule. A method for producing a polarizing plate by laminating a transparent protective film on both surfaces of a polarizing film,
And the coefficient of linear expansion in the direction perpendicular to the absorption axis of the transparent protective film has at least one transparent protective film and the linear expansion coefficient, the polarizing film in the direction perpendicular to the absorption axis of the polarizing plate of the car is not more than 1.3 × 10 ^-4 / ℃ Wherein the polarizing plate is selected to be a polarizing plate. A liquid crystal display comprising a liquid crystal cell and a polarizing plate bonded to the viewer side,
The polarizing plate includes a polarizing film and a transparent protective film disposed on both sides of the polarizing film and has a linear expansion coefficient in a direction orthogonal to the absorption axis of the polarizing film and a linear expansion coefficient in a direction perpendicular to the absorption axis of the polarizing plate of one or more transparent protective films Is 1.3 x 10 < ^-4 > / DEG C or less. The liquid crystal display device according to claim 7, wherein the transparent protective film to be bonded to the liquid crystal cell is made of a cellulose resin or a polyolefin resin.