JP5251827B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device in which warpage of a liquid crystal panel is reduced.

  In recent years, taking advantage of its low power consumption, low voltage operation, light weight and thinness, liquid crystal displays have rapidly spread as information display devices such as mobile phones, personal digital assistants, computer monitors, and televisions. Have been doing. With the development of liquid crystal technology, liquid crystal displays in various modes have been proposed, and problems with liquid crystal displays such as response speed, contrast, and narrow viewing angle are being solved. However, since a polarizing plate is used in the liquid crystal display device, when the liquid crystal panel is placed in a humid heat environment, the liquid crystal panel warps due to water absorption by the polarizing plate, and display unevenness occurs. Is a problem.

  Japanese Unexamined Patent Publication No. 2007-292966 (Patent Document 1) proposes to improve the warpage of the liquid crystal panel under high temperature and high humidity by adjusting the dimensional change rate of the polarizing plate bonded to both sides of the liquid crystal cell. Has been. Japanese Patent Laid-Open No. 2003-50313 (Patent Document 2) uses a polarizing plate on which a pressure-sensitive adhesive layer exhibiting specific creep characteristics is used to improve the warpage of a liquid crystal panel in a humid heat environment. Has been proposed. However, in these improvements, it is necessary to subject the polarizing plate to a pretreatment such as a heat treatment, or the display unevenness due to the warp of the liquid crystal panel after being placed in a humid heat environment is insufficient.

JP 2007-292966 A JP 2003-050313 A

  An object of the present invention is to provide a liquid crystal display device in which a warp of a liquid crystal panel is small even after being placed in a humid heat environment and there is no display unevenness. As a result of intensive studies to achieve this object, the present inventors have pasted the first pressure-sensitive adhesive layer used for bonding the front side polarizing plate to the liquid crystal cell and the back side polarizing plate to the liquid crystal cell. By adjusting the storage elastic modulus of each of the second adhesive layers used for combining, the warpage of the liquid crystal panel after being placed in a humid heat environment can be suppressed, which is effective in improving display unevenness. As a result, the present invention has been completed.

That is, according to the present invention, a liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween, and a front side polarizing plate laminated on the viewing side of the liquid crystal cell via the first adhesive layer A back side polarizing plate laminated via a second pressure-sensitive adhesive layer on the side opposite to the viewing side of the liquid crystal cell, and a backlight unit disposed outside the back side polarizing plate, Each of the plate and the back-side polarizing plate has a polarizing film and transparent protective films disposed on both sides thereof, and the storage adhesive modulus at 50 ° C. of the first adhesive layer is G _f ′, and the second adhesive When the storage elastic modulus of the layer at 50 ° C. is G _r ′, a liquid crystal display device in which the ratio G _f ′ / G _r ′ of the layers is in the range of 0.01 to less than 0.5 is provided.

  In this liquid crystal display device, the transparent protective film located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate preferably has a thickness direction retardation in the range of −10 to 10 nm. Moreover, it is preferable to comprise the transparent protective film located in these liquid crystal cell sides with a cellulose resin or polyolefin resin. On the other hand, the transparent protective film located on the side farther from the liquid crystal cell of each of the front side polarizing plate and the rear side polarizing plate has a thickness of the transparent protective film located on the liquid crystal cell side and an adhesive layer attached thereto It is preferable to be larger than the total thickness.

  In these liquid crystal display devices, the polarizing film of each of the front-side polarizing plate and the rear-side polarizing plate and the transparent protective film disposed on both sides thereof contain a polyvinyl alcohol resin and a water-soluble epoxy resin in one preferred embodiment. It can be bonded via an aqueous adhesive. Moreover, in another preferable form, it can bond through the curable adhesive composition containing the epoxy compound hardened | cured by irradiation of an active energy ray. In the latter form, the epoxy compound that is cured by irradiation with active energy rays preferably includes an epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule.

  According to the present invention, it is possible to provide a liquid crystal display device in which the warp of the liquid crystal panel is small even after being placed in a humid heat environment, and thus there is no display unevenness.

It is a cross-sectional schematic diagram which shows the layer structure of the liquid crystal display device which concerns on this invention.

  Referring to FIG. 1, the liquid crystal display device of the present invention includes a liquid crystal cell 10, a front-side polarizing plate 20 laminated on the viewing side of the liquid crystal cell via a first adhesive layer 40, and the viewing of the liquid crystal cell. The back side polarizing plate 30 laminated on the opposite side to the second adhesive layer 50, and the backlight disposed outside the back side polarizing plate (that is, on the side opposite to the liquid crystal cell 10) A unit 70 is provided. The liquid crystal cell 10, the front-side polarizing plate 20 laminated on the viewing side of the liquid crystal cell via the first pressure-sensitive adhesive layer 40, and the second pressure-sensitive adhesive layer 50 laminated on the opposite side of the liquid crystal cell. A liquid crystal panel 60 is formed with the back side polarizing plate 30.

  The front-side polarizing plate 20 disposed on the viewing side of the liquid crystal cell 10 includes a polarizing film 21 and transparent protective films 25 and 26 laminated on both surfaces via an adhesive (not shown). Similarly, the back side polarizing plate 30 disposed on the side opposite to the viewing side of the liquid crystal cell 10 (that is, the backlight unit 70 side) is also provided with a polarizing film 31 and an adhesive (not shown) on both sides thereof. The transparent protective films 35 and 36 are laminated.

  A liquid crystal display device is configured by combining the liquid crystal panel 60 and the backlight unit 70. When the liquid crystal display device is placed in a humid heat environment, the liquid crystal panel 60 warps and a part of the liquid crystal panel 60 is formed. However, the display unit may become abnormally close to the backlight unit 70 or may come into contact in an extreme case, resulting in display unevenness. The liquid crystal panel 60 is fixed by a housing or a metal frame so that the liquid crystal panel 60 does not fall down to the viewing side. When the liquid crystal display device is placed in a humid heat environment, the liquid crystal panel 60 warps and the liquid crystal panel 60 is warped. Some of them contacted the case or the metal frame which fixed it, and the display nonuniformity might be caused.

Therefore, in the present invention, the storage elastic modulus at a temperature of 50 ° C. of the first pressure-sensitive adhesive layer 40 used for adhering the front side polarizing plate 20 to the liquid crystal cell 10 is G _f ′, and the back side polarizing plate 30 is used as the liquid crystal cell. When the storage elastic modulus at the same temperature of the second pressure-sensitive adhesive layer 50 used for adhering to 10 is G _r ′, the ratio G _f ′ / G _r ′ of both is in the range of 0.01 or more and less than 0.5. To be. In addition, in this specification, since the temperature when measuring a storage elastic modulus is fundamentally 50 degreeC, below, the measurement temperature (50 degreeC) when expressing a storage elastic modulus may be abbreviate | omitted. The relationship between the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40 and the storage elastic modulus G _r ′ of the second pressure-sensitive adhesive 50 corresponds to satisfying the following formula (a).

0.01 ≦ G _f ′ / G _r ′ <0.5 (a)

Thus, the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40 used for adhering the front side polarizing plate 20 and the liquid crystal cell 10 is used for adhering the rear side polarizing plate 30 and the liquid crystal cell 10. The storage adhesive modulus G _r ′ of the second pressure-sensitive adhesive layer 50 is set to a value that is 1% or more and less than half. In other words, the storage elastic modulus G _r ′ of the second pressure-sensitive adhesive layer 50 is more than twice and less than 100 times the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40. To do. That is, it is important that the second pressure-sensitive adhesive layer 50 is made of a harder material than the first pressure-sensitive adhesive layer 40. Thus, it was found that even after being placed in a moist heat environment, warpage of the liquid crystal panel 60 can be suppressed, display unevenness is not observed, and a liquid crystal display device excellent in display quality can be obtained.

  For each of the front-side polarizing plate 20 and the rear-side polarizing plate 30, the thickness of the transparent protective films 25 and 35 positioned on the side far from the liquid crystal cell 10 is set to the transparent protective films 26 and 36 positioned on the liquid crystal cell 10 side. It has also been found that it is effective to make it larger than the total thickness of the pressure-sensitive adhesive layers 40 and 50 adhered thereto. Thus, for each of the front-side polarizing plate 20 and the rear-side polarizing plate 30, the transparent protective films 25, 35 positioned on the side far from the liquid crystal cell 10 are increased in thickness so that the transparent positioned on the liquid crystal cell 10 side. Even if the protective films 26 and 36 are thinned, it is possible to improve handling properties when handling a large-sized polarizing plate having a diagonal size of 32 inches (about 81 cm) or more, and it is effective for suppressing warpage of the liquid crystal panel 60. Become.

  Hereinafter, each member constituting the liquid crystal display device of the present invention will be described in detail with reference to the reference numerals attached to FIG.

[Liquid Crystal Cell]
The liquid crystal cell 10 includes two cell substrates 11 and 12 and a liquid crystal layer 15 sandwiched between the substrates. The cell substrates 11 and 12 are generally often made of glass, but may be plastic substrates. In addition, the liquid crystal cell 10 itself in the liquid crystal display device of the present invention can be composed of various types employed in this field.

[Polarized film]
The polarizing films 21 and 31 constituting the front-side polarizing plate 20 and the rear-side polarizing plate 30 are usually formed by uniaxially stretching a polyvinyl alcohol-based resin film, by dyeing the polyvinyl alcohol-based resin film with a dichroic dye. It is manufactured through a step of adsorbing a chromatic dye, a step of treating a polyvinyl alcohol-based resin film adsorbed with a dichroic dye with an aqueous boric acid solution, and a step of washing with water after the treatment with an aqueous boric acid solution.

  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 another monomer 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, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

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

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizing film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. The film thickness of the polyvinyl alcohol resin raw film is, for example, about 10 to 150 μm, preferably about 10 to 100 μm.

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

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye. In addition, it is preferable to perform the process which a polyvinyl alcohol-type resin film swells by immersing in water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually 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. It is. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, 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 of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic organic dye in this 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. This aqueous dye solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic organic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with the dichroic dye can be performed by a method of immersing the dyed polyvinyl alcohol resin film in a boric acid-containing aqueous solution. The boric acid content in the boric acid-containing aqueous solution 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, the boric acid-containing aqueous solution preferably 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 immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably 150 to 600 seconds, and more preferably 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by a method of 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 ° C. The immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain a polarizing film. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds. By the drying treatment, the moisture content in the polarizing film is reduced to a practical level. The moisture content is usually about 5 to 20% by weight, preferably 8 to 15% by weight. When the moisture content is less than 5% by weight, the polarizing film loses its flexibility, and may be damaged or broken after drying. On the other hand, if the moisture content exceeds 20% by weight, the thermal stability tends to be insufficient.

  As described above, a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol-based resin film can be produced. The resulting polarizing film can have a thickness of, for example, about 5 to 40 μm.

[Transparent protective film located far from the liquid crystal cell]
In each of the front side polarizing plate 20 and the back side polarizing plate 30, the transparent protective films 25 and 35 located on the side far from the liquid crystal cell 10 are materials having excellent transparency, mechanical strength, thermal stability, moisture shielding properties, and the like. Preferably it consists of. As such a material, for example, an acrylic resin having a methyl methacrylate resin as a representative example, a chain polyolefin resin having a polypropylene resin as a representative example, a cyclic polyolefin resin, a cellulose resin, and a polyethylene terephthalate resin , Polybutylene terephthalate resin, polyvinyl chloride resin, styrene resin, acrylonitrile / styrene copolymer resin, acrylonitrile / butadiene / styrene copolymer resin, polyvinyl acetate resin, polyvinylidene chloride resin, polyamide resin Examples include resins, polyacetal resins, polycarbonate resins, modified polyphenylene ether resins, polysulfone resins, polyether sulfone resins, polyarylate resins, polyamideimide resins, polyimide resins, and the like.

  These resins can be used alone or in combination of two or more. Moreover, resin which performed arbitrary polymer modification | denaturation with respect to these resin can also be used as the material for transparent protective films. Examples of the polymer modification include copolymerization, crosslinking, molecular terminal modification, stereoregularity control, and mixing including a case involving a reaction between different polymers.

  Among the above resins, a methyl methacrylate resin, a polypropylene resin, a cellulose resin, or a polyethylene terephthalate resin is preferably used as a material for the transparent protective films 25 and 35 located on the side far from the liquid crystal cell 10.

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

  The methyl methacrylate-based resin can be usually obtained by polymerizing a monofunctional monomer mainly composed of methyl methacrylate in the presence of a radical polymerization initiator and a chain transfer agent. A component that can be copolymerized with methyl methacrylate may be blended in the monofunctional monomer and copolymerized, and a small amount of the polyfunctional monomer may be copolymerized if desired.

  Monofunctional monomers that can be copolymerized with methyl methacrylate include, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxy methacrylate. Methacrylic acid esters other than methyl methacrylate such as ethyl; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, and 2-ethylhexyl acrylate Hydroxyacrylates such as hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate Unsaturated alkyl acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as vinyltoluene and α-methylstyrene; acrylonitrile; Examples thereof include unsaturated nitriles such as methacrylonitrile; unsaturated anhydrides such as maleic anhydride and citraconic anhydride; unsaturated imides such as phenylmaleimide and cyclohexylmaleimide. These monomers may be used alone or in combination of two or more.

  Examples of polyfunctional monomers that can be copolymerized with methyl methacrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth). Acrylate or ester of both end hydroxyl groups of ethylene glycol or its oligomer, such as acrylate; Propylene glycol or its oligomer end of hydroxyl groups esterified with acrylic or methacrylic acid; Neopentyl glycol A dihydric alcohol esterified with acrylic acid or methacrylic acid, such as di (meth) acrylate, hexanediol di (meth) acrylate, and butanediol di (meth) acrylate; Phenol A, alkylene oxide adducts of bisphenol A, or those obtained by esterifying the hydroxyl groups at both ends with acrylic acid or methacrylic acid; trimethylolpropane, and polyhydric alcohols such as pentaerythritol with acrylic acid or Those esterified with methacrylic acid; those obtained by ring-opening addition of an epoxy group of glycidyl acrylate or glycidyl methacrylate to the terminal hydroxyl group of a compound having two or more hydroxyl groups; succinic acid, adipic acid, terephthalic acid, phthalic acid, and these Dibasic acids such as halogen-substituted products, or these alkylene oxide adducts obtained by ring-opening addition of an epoxy group of glycidyl acrylate or glycidyl methacrylate; allyl (meth) acrylate; And aromatic divinyl compounds. When copolymerizing a polyfunctional monomer, among these, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and neopentyl glycol dimethacrylate are preferably used.

  A resin modified by conducting a reaction between functional groups of a methyl methacrylate resin can also be used. Examples of such a reaction between functional groups include, for example, demethanol condensation reaction in a polymer chain between a methyl ester group of methyl acrylate and a hydroxyl group of methyl 2- (hydroxymethyl) acrylate, and a carboxyl group of acrylic acid and 2 Examples thereof include a dehydration condensation reaction in a polymer chain with a hydroxyl group of-(hydroxymethyl) methyl acrylate.

  A commercially available product can be easily obtained for the methyl methacrylate resin. Examples of commercial products are “Sumipex” sold by Sumitomo Chemical Co., Ltd., “Acrypet” sold by Mitsubishi Rayon Co., Ltd., and Asahi Kasei Co., Ltd. "Delpet", "Parapet" sold by Kuraray Co., Ltd., and "Acryviewer" sold by Nippon Shokubai Co., Ltd.

  The polypropylene resin is a polymer of a chain olefin monomer having propylene as a main component, and is usually a chain olefin resin in which 80% by weight or more of repeating units are composed of propylene. The polypropylene resin may be a homopolymer of propylene, or a copolymer obtained by copolymerizing 1 to 20% by weight, preferably 3 to 10% by weight of a comonomer mainly composed of propylene and copolymerizable therewith. It may be a polymer.

  When a copolymer containing propylene as a main component is used, the comonomer copolymerizable with propylene is preferably ethylene, 1-butene, or 1-hexene. Especially, since the polypropylene resin which is comparatively excellent in transparency is obtained, what copolymerized ethylene in the ratio of 1-20 weight%, preferably 3-10 weight% is preferable. By setting the copolymerization ratio of ethylene to 1% by weight or more, an effect of increasing transparency appears. On the other hand, when the copolymerization ratio of ethylene exceeds 20% by weight, the melting point of the resin is lowered, and the heat resistance required for the transparent protective film may be impaired.

  The content of a component soluble in xylene at 20 ° C. (CXS component: CXS is an abbreviation of cold xylene soluble) is preferably 1% by weight or less and preferably 0.5% by weight or less. More preferred. Among the polypropylene-based resins, a propylene homopolymer having a CXS component of 1% by weight or less, and further 0.5% by weight or less is one suitable example.

  As the polypropylene resin, a commercially available product can be easily obtained. Examples of commercial products are “Prime Polypro” sold by Prime Polymer Co., Ltd., “Novatech” and “Wintech” sold by Nippon Polypro Co., Ltd., Sumitomo Chemical Co., Ltd. "Sumitomo Noblen" sold by the company, "San Aroma" sold by Sun Allomer.

  The cellulose resin may be an organic acid ester or mixed organic acid ester of cellulose in which 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 include cellulose acetate, propionate, butyrate, and mixed esters thereof. Of these, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, cellulose acetate butyrate and the like are preferable.

  Polyethylene terephthalate resin is a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate, and may contain other dicarboxylic acid components and / or other diol components. Examples of other dicarboxylic acid components include isophthalic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 1,4 -Dicarboxycyclohexane etc. are mentioned. 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 can be used in combination of two or more if necessary. Hydroxycarboxylic acids such as p-hydroxybenzoic acid and p-β-hydroxyethoxybenzoic acid can also be used in combination. As other copolymer components, dicarboxylic acid components or diol components containing a small amount of amide bond, urethane bond, ether bond, carbonate bond, etc. can also be used.

  Polyethylene terephthalate resin can be produced by directly polycondensing terephthalic acid and ethylene glycol (and other dicarboxylic acids or other diols as required), dialkyl esters of terephthalic acid and ethylene glycol (and as required) A method of polycondensation of a dialkyl ester of another dicarboxylic acid or other diol) while undergoing a transesterification reaction, an ethylene glycol ester of terephthalic acid (and other dicarboxylic acid if necessary) (and another diol if necessary) For example, a method in which an ester) is polycondensed in the presence of a catalyst is employed. Furthermore, if necessary, additional solid phase polymerization can be performed to increase the molecular weight or reduce the low molecular weight components.

  As a method for forming the resin as described above on the transparent protective film for the polarizing plate, a method corresponding to each resin may be appropriately selected. For example, a solvent cast method in which a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling can be used. In the melt extrusion method, a single layer film can be extruded or a multilayer film can be coextruded.

  Commercially available products of these resin films can be easily obtained. Examples of commercially available films include methyl methacrylate resin films, each with the trade name “Technoloy” sold by Sumitomo Chemical Co., Ltd. and “Acrylic” sold by Mitsubishi Rayon Co., Ltd. "Light" and "Acryprene", "Delagrass" sold by Asahi Kasei Co., Ltd., "Paragrass" and "Comogras" sold by Kuraray Co., Ltd., and "Acryviewer" sold by Nippon Shokubai Co., Ltd. and so on. For polyethylene terephthalate resin films, there are “Novaclear” sold by Mitsubishi Chemical Co., Ltd. and “A-PET sheet” sold by Teijin Chemicals Ltd., respectively. For polypropylene resin films, “FILMAX CPP film” sold by FILMAX, “Santox” sold by Sun Tox Co., Ltd. "Tosero", "Toyobo Pyrene Film" sold by Toyobo Co., Ltd., "Trephan" sold by Toray Film Processing Co., Ltd., "Nihon Polyace" sold by Nippon Polyace Co., Ltd. "Dazai FC" sold by Futamura Chemical Co., Ltd. Cellulosic resin films include “Fujitac TD” sold by Fuji Film Co., Ltd. and “Konica Minolta TAC Film KC” sold by Konica Minolta Opto Co., Ltd.

  The transparent protective film 25 disposed on the side far from the liquid crystal cell 10 and serving as the viewing side can be imparted with anti-glare properties by imparting haze. 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, a resin mixed with fine particles by multilayer extrusion, and fine particles are mixed. A method of forming a two-layer film from a resin that has not been mixed, or forming a three-layer film by using a resin in which fine particles are mixed as an outer layer, a coating in which inorganic fine particles or organic fine particles are mixed with a curable binder resin on one side of the film A method of coating the liquid and curing the binder resin to provide an antiglare layer is employed.

  Examples of inorganic fine particles used for imparting haze include silica, colloidal silica, alumina, alumina sol, aluminosilicate, alumina-silica composite oxide, kaolin, talc, mica, calcium carbonate, calcium phosphate, and the like. 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 imparted to the transparent protective film, the haze value is preferably in the range of 6 to 45%. When the haze value of the transparent protective film is less than 6%, a sufficient antiglare effect may not appear. On the other hand, if the haze value exceeds 45%, the screen of the liquid crystal display device on which the transparent protective film is disposed may be whitened, resulting in a reduction in image quality. Haze is a value defined as the ratio of diffuse transmittance to total light transmittance, and can be measured using a commercially available haze meter in accordance with JIS K 7136. An example of a commercially available haze meter is “HM-150” sold by Murakami Color Research Laboratory. In measuring the haze value, in order to prevent warping of the film, for example, an optically transparent adhesive is used, and a measurement sample in which the film surface is bonded to a glass substrate so that the antiglare surface is the surface is used. Is preferred.

  A functional layer that is disposed on the side far from the liquid crystal cell and includes a conductive layer, a hard coat layer, a low reflection layer, and the like on the outside of the transparent protective film 25 on the viewing side and the transparent protective film 35 on the backlight side. Can be provided. As the coating liquid containing the binder resin constituting the antiglare layer, a resin composition capable of expressing these functions can also be selected.

[Transparent protective film located on the liquid crystal cell side]
In the front side polarizing plate 20 and the back side polarizing plate 30 shown in FIG. 1, the resin material constituting the transparent protective films 26 and 36 located on the liquid crystal cell 10 side is located on the far side from the liquid crystal cell 10. The thing similar to what was described about the transparent protective films 25 and 35 can be used. Among these, since the retardation value is easily controlled and easily available, a cellulose resin or a polyolefin resin including a chain polyolefin resin or a cyclic polyolefin resin is preferably used.

  The cyclic polyolefin resin here is obtained by polymerizing cyclic olefin monomers such as norbornene and other cyclopentadiene derivatives in the presence of a catalyst. When such a cyclic polyolefin-based resin is used, a transparent protective film having a predetermined retardation value described later can be easily obtained.

  Examples of the cyclic polyolefin resin include ring-opening metathesis polymerization using cyclopentadiene and olefins or (meth) acrylic acid or esters thereof as a monomer with norbornene or a derivative thereof obtained by Diels-Alder reaction. Resin obtained by addition; ring-opening metathesis polymerization from dicyclopentadiene and olefins or (meth) acrylic acid or esters thereof by tetracyclododecene or its derivative obtained by Diels-Alder reaction, followed by Resin obtained by hydrogenation; at least two monomers selected from norbornene, tetracyclododecene, their derivatives, and other cyclic olefin monomers are similarly copolymerized by ring-opening metathesis, followed by Resins obtained by hydrogenation; resins obtained by addition copolymerization of aromatic compounds having chain olefins and / or vinyl groups with cyclic olefins such as norbornene, tetracyclododecene, or derivatives thereof It is done.

  As the cyclic polyolefin-based resin, a commercially available product can be easily obtained. Examples of commercial products are “TOPAS” produced by TOPAS ADVANCED POLYMERS GmbH under the trade name, and sold in Japan by Polyplastics Co., Ltd. “Arton” from JSR Co., Ltd. "Zeonor" and "Zeonex" sold by Nippon Zeon Co., Ltd., and "Appel" sold by Mitsui Chemicals.

  Typical examples of the chain polyolefin resin are a polyethylene resin and a polypropylene resin. Among them, a homopolymer of propylene, or a copolymer obtained by copolymerizing propylene as a main component and a comonomer copolymerizable therewith, for example, ethylene in a proportion of 1 to 20% by weight, preferably 3 to 10% by weight. Preferably used.

  As a method for forming a film from a cellulose resin, a polyolefin resin, or the like, a method corresponding to each resin may be selected as appropriate. For example, a solvent cast method in which a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling with a cooling drum can be used. Among these, for the polyolefin-based resin, the melt extrusion method is preferably employed from the viewpoint of productivity. On the other hand, a cellulose resin is generally formed into a film by a solvent casting method.

  When the liquid crystal cell 10 is in an in-plane switching (IPS) mode, the transparent protective films 26 and 36 positioned on the liquid crystal cell 10 side are not damaged so as not to impair the wide viewing angle characteristics inherent in the IPS mode liquid crystal cell. The thickness direction retardation Rth is preferably in the range of -10 to 10 nm. The retardation Rth in the thickness direction is a value obtained by multiplying the value obtained by subtracting the refractive index in the thickness direction from the in-plane average refractive index, and is represented by the following formula (b). The in-plane retardation Re is a value obtained by multiplying the in-plane refractive index difference by the film thickness, and is represented by the following formula (c).

Rth = _{[(n x + n y) /} 2-n z ] × d (b)
_{Re = (n x -n y)} × d (c)

Wherein, n _x is a refractive index in x-axis direction in the film plane (in-plane slow axis direction), n _y is a y-axis direction (in-plane fast axis direction in the film plane, the plane In the direction perpendicular to the x-axis), _nz is the refractive index in the z-axis direction (thickness direction) perpendicular to the film surface, and d is the thickness of the film.

  Here, the retardation value may be a value at an arbitrary wavelength in the range of about 500 to 650 nm near the center of visible light, but in this specification, the retardation value at a wavelength of 590 nm is used as a standard. The retardation Rth in the thickness direction and the in-plane retardation Re can be measured using various commercially available phase difference meters.

  As a method of controlling the retardation Rth in the thickness direction of the resin film within a range of −10 to 10 nm, a method of minimizing the distortion remaining in the thickness direction when producing the film can be mentioned. For example, in the solvent casting method, a method of relaxing residual shrinkage strain in the thickness direction generated when the cast resin solution is dried by heat treatment can be employed. On the other hand, in the melt extrusion method, the distance from the die to the cooling drum is reduced as much as possible in order to prevent the resin film from being drawn from the die and cooled, and the extrusion amount and the rotation speed of the cooling drum are reduced. A method of controlling the film so that the film is not stretched can be employed. Moreover, the method of relieving the distortion which remains in the obtained film by heat processing similarly to the solvent casting method is also employable.

[Adhesion between polarizing film and protective film]
Usually, an adhesive is used for joining the polarizing film 21 and the transparent protective films 25 and 26 in the front polarizing plate 20 and joining the polarizing film 31 and the transparent protective films 35 and 36 in the rear polarizing plate 30. . The adhesive layer for joining the polarizing film and the transparent protective film can have a thickness of about 0.01 to 30 μm, preferably 0.01 to 10 μm, and more preferably 0.05 to 5 μm. If the thickness of the adhesive layer is within this range, the adhesive layer having no practical problem can be obtained without floating or peeling between the transparent protective film and the polarizing film to be laminated.

  In forming the adhesive layer, an appropriate adhesive can be used as appropriate according to the type and purpose of the adherend, and an anchor coating agent can be used as necessary. Examples of the adhesive include a solvent-type adhesive, an emulsion-type adhesive, a pressure-sensitive adhesive, a rewet-adhesive, a polycondensation-type adhesive, a solventless-type adhesive, a film-type adhesive, and a hot-melt-type adhesive. Can be mentioned.

  One preferred adhesive is an aqueous adhesive, that is, an adhesive component in which the adhesive component is dissolved or dispersed in water. Examples of adhesive components that can be dissolved in water include polyvinyl alcohol resins. An example of an adhesive component that can be dispersed in water is a urethane resin having a hydrophilic group. The water-based adhesive can be prepared by mixing such an adhesive component with water together with an additional additive added as necessary. Examples of commercially available polyvinyl alcohol resins that can be used as water-based adhesives include “KL-318” (trade name), which is a carboxyl group-modified polyvinyl alcohol sold by Kuraray Co., Ltd.

  The water-based adhesive can contain a crosslinking agent as necessary. Examples of the crosslinking agent include amine compounds, aldehyde compounds, methylol compounds, water-soluble epoxy resins, isocyanate compounds, and polyvalent metal salts. When a polyvinyl alcohol resin is used as an adhesive component, an aldehyde compound such as glyoxal, a methylol compound such as methylol melamine, a water-soluble epoxy resin, or the like is preferably used as a crosslinking agent. Here, the water-soluble epoxy resin is, for example, a polyamide obtained by reacting epichlorohydrin with a polyamide polyamine which is a reaction product of a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine and a dicarboxylic acid such as adipic acid. It can be an epoxy resin. Examples of commercially available water-soluble epoxy resins include “Smiles Resin 650 (30)” (trade name) sold by Sumika Chemtex Co., Ltd.

  A polarizing plate can be obtained by applying a water-based adhesive on the adhesive surface of the polarizing film and / or the transparent protective film, bonding them together, and then subjecting them to a drying treatment. Prior to adhesion, it is also effective to give the transparent protective film an easy adhesion treatment such as a saponification treatment, a corona discharge treatment, or a plasma treatment to enhance wettability. A drying temperature can be about 60-100 degreeC, for example. After the drying treatment, curing at a temperature slightly higher than room temperature, for example, at a temperature of about 30 to 50 ° C. for about 1 to 10 days is preferable for further enhancing the adhesive force.

  Another preferred adhesive is a curable adhesive composition containing an epoxy compound that is cured by irradiation with active energy rays or heating. Here, the curable epoxy compound has at least two epoxy groups in the molecule. In this case, the adhesion between the polarizing film and the transparent protective film is performed by irradiating an active energy ray to the coating layer of the adhesive composition or heating it to apply a curable epoxy compound contained in the adhesive. It can be carried out by a curing method. Curing of the epoxy compound is generally performed by cationic polymerization of the epoxy compound. Further, from the viewpoint of productivity, this curing is preferably performed by irradiation with active energy rays.

  From the viewpoint of weather resistance, refractive index, cationic polymerizability, etc., the epoxy compound contained in the curable adhesive composition is preferably one that does not contain an aromatic ring in the molecule. Examples of epoxy compounds that do not contain an aromatic ring in the molecule include hydrogenated epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds. The epoxy compound suitably used in such a curable adhesive composition is described in detail in, for example, Japanese Patent Application Laid-Open No. 2004-245925, but the outline is also described here.

  The hydrogenated epoxy compound is a glycidyl compound obtained by subjecting an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound, to a nuclear hydrogenated polyhydroxy compound obtained by selectively performing a nuclear hydrogenation reaction in the presence of a catalyst and under pressure. It can be etherified. Examples of the aromatic polyhydroxy compound that is a raw material of the aromatic epoxy compound include bisphenols such as bisphenol A, bisphenol F, and bisphenol S; phenol novolac resins, cresol novolac resins, and hydroxybenzaldehyde phenol novolac resins. And novolak type resins; polyhydroxy compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone, and polyvinylphenol. A glycidyl ether can be obtained by performing a nuclear hydrogenation reaction on such an aromatic polyhydroxy compound and reacting the resulting hydrogenated polyhydroxy compound with epichlorohydrin. Suitable hydrogenated epoxy compounds include hydrogenated glycidyl ether of bisphenol A.

  An alicyclic epoxy compound is a compound having at least one epoxy group bonded to an alicyclic ring in the molecule. The “epoxy group bonded to the alicyclic ring” means a bridged oxygen atom —O— in the structure represented by the following formula, and 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 removed and bonded to another chemical structure can be an alicyclic epoxy compound. Further, one or more hydrogen atoms in (CH ₂ ) _m forming the alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula) has excellent adhesion. It is preferably used from the indication. Specific examples of the alicyclic epoxy compound are listed below. Here, the compound names are given first, and then the chemical formulas corresponding to each are shown, and the same reference numerals are given to the compound names and the chemical formulas corresponding thereto.

A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
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-epoxycyclohexyl methyl ether),
G: ethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.5.2.2] henicosane,
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 can 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; ethylene Polyglycidyl ether of polyether polyol (for example, diglycidyl ether of polyethylene glycol) obtained by adding alkylene oxide (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohol such as glycol, propylene glycol, and glycerin Can be mentioned.

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

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

  From the viewpoint of reactivity, cationic polymerization is preferably used as the curing reaction of the epoxy compound. For that purpose, it is preferable to mix | blend a cationic polymerization initiator with the curable adhesive composition containing an epoxy compound. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation or heating with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and initiates an epoxy group polymerization reaction. From the viewpoint of workability, it is preferable that the cationic polymerization initiator is provided with latency. Hereinafter, a cationic polymerization initiator that generates a cationic species or Lewis acid by irradiation of active energy rays and initiates a polymerization reaction of an epoxy group is referred to as a “photo cationic polymerization initiator”, and generates a cationic species or a Lewis acid by heat. The cationic polymerization initiator that initiates the polymerization reaction of the epoxy group is referred to as “thermal cationic polymerization initiator”.

  The method of curing the adhesive composition by irradiation with active energy rays using a cationic photopolymerization initiator enables curing at room temperature, reducing the need to consider the heat resistance of the polarizing film or distortion due to expansion, This is advantageous in that the transparent protective film and the polarizing film can be favorably bonded. In addition, since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy compound.

  Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts, and iron-allene complexes. The compounding quantity of a photocationic polymerization initiator is 0.5-20 weight part normally with respect to 100 weight part of epoxy compounds, Preferably it is 1 weight part or more, Preferably it is 15 weight part or less. When the blending amount of the cationic photopolymerization initiator is less than 0.5 parts by weight with respect to 100 parts by weight of the epoxy compound, curing becomes insufficient, and the mechanical strength and adhesive strength of the cured product tend to decrease. On the other hand, when the blending amount of the cationic photopolymerization initiator exceeds 20 parts by weight with respect to 100 parts by weight of the epoxy compound, the ionic substance in the cured product increases, resulting in an increase in the hygroscopic property of the cured product and durability performance. May be reduced.

  When using a photocationic polymerization initiator, the curable adhesive composition may further contain a photosensitizer as necessary. By using a photosensitizer, the reactivity of cationic polymerization can be improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreducible dyes. When mix | blending a photosensitizer, it is preferable to make the quantity into the range of 0.1-20 weight part with respect to 100 weight part of curable adhesive compositions.

  On the other hand, examples of the thermal cationic polymerization initiator include benzylsulfonium salt, thiophenium salt, thioranium salt, benzylammonium, pyridinium salt, hydrazinium salt, carboxylic acid ester, sulfonic acid ester, and amine imide.

  The curable adhesive composition containing the epoxy compound is preferably cured by photocationic polymerization as described above, but can be cured by thermal cationic polymerization in the presence of the above-mentioned thermal cationic polymerization initiator. Cationic polymerization and thermal cationic polymerization can be used in combination. When photocationic polymerization and thermal cationic polymerization are used in combination, the curable adhesive composition preferably contains both a photocationic polymerization initiator and a thermal cationic polymerization initiator.

  The curable adhesive composition may further contain a compound that promotes cationic polymerization, such as an oxetane compound or a polyol compound. An oxetane compound is a compound having a 4-membered ring ether in the molecule. When mix | blending an oxetane compound, the quantity is 5 to 95 weight% normally in a curable adhesive composition, Preferably it is 5 to 50 weight%. The polyol compound may be alkylene glycol including ethylene glycol, hexamethylene glycol, polyethylene glycol or the like, or an oligomer thereof, polyester polyol, polycaprolactone polyol, polycarbonate polyol and the like. When a polyol compound is blended, the amount is usually 50% by weight or less, preferably 30% by weight or less in the curable adhesive composition.

  In addition, the curable adhesive composition may have other additives such as ion trapping agents, antioxidants, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillers, as long as the adhesiveness is not impaired. Agents, flow modifiers, plasticizers, antifoaming agents, and the like. Examples of the ion trapping agent include inorganic compounds including powdered bismuth-based, antimony-based, magnesium-based, aluminum-based, calcium-based, titanium-based, and mixed systems thereof. Examples of the antioxidant include And hindered phenolic antioxidants.

  After applying the curable adhesive composition containing the epoxy compound to the adhesive surface of the polarizing film or the transparent protective film, or to the adhesive surface of both of them, it is bonded to the adhesive-coated surface and activated energy. The polarizing film and the transparent protective film can be bonded by curing the uncured adhesive layer by irradiating the wire or heating. As an adhesive coating method, for example, 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 that does not substantially contain a solvent, but each coating system has an optimum viscosity range, so that the viscosity is adjusted. For this purpose, a solvent may be contained. The solvent is preferably an organic solvent that dissolves each component including an epoxy compound well without degrading the optical performance of the polarizing film. For example, hydrocarbons typified by toluene, typified by ethyl acetate, etc. Esters can be used.

  When the adhesive composition is cured by irradiation with active energy rays, the above-mentioned various types of active energy rays can be used, but since the handling is easy and the amount of irradiation light is easy to control, ultraviolet rays are not emitted. Preferably used. Active energy rays such as ultraviolet irradiation intensity and dose do not affect various optical performance including polarization degree of polarizing film, and various optical performance including transparency and retardation characteristics of transparent protective film. Within a range, it is determined as appropriate so that moderate productivity is maintained.

  When the adhesive composition is cured by heat, it can be heated by a generally known method. Usually, heating is performed at a temperature higher than the temperature at which the thermal cationic polymerization initiator compounded in the curable adhesive composition generates cationic species and Lewis acid, and the specific heating temperature is, for example, about 50 to 200 ° C. .

[Adhesive layer]
On the transparent protective film 26 which becomes the liquid crystal cell side of the front side polarizing plate 20 demonstrated above, the 1st adhesive layer 40 is laminated | stacked, and on the transparent protective film 36 which becomes the liquid crystal cell side of the back side polarizing plate 30 The second pressure-sensitive adhesive layer 50 is laminated. These pressure-sensitive adhesive layers 40 and 50 are provided for bonding the front side polarizing plate 20 and the back side polarizing plate 30 to both sides of the liquid crystal cell 10, respectively.

  The pressure-sensitive adhesive forming each pressure-sensitive adhesive layer may be any material that has excellent optical transparency and excellent pressure-sensitive adhesive properties including moderate wettability, cohesiveness, adhesiveness, etc. An excellent material is preferably used. Specifically, an adhesive containing an acrylic resin (acrylic adhesive) is preferably used as the adhesive forming the adhesive layer.

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

  The acrylic pressure-sensitive adhesive usually contains a crosslinking agent together with the acrylic resin. A typical example of the crosslinking agent is an isocyanate compound having at least two isocyanato groups (—NCO) in the molecule.

  Various additives may be further blended in the adhesive. Suitable additives include silane coupling agents and antistatic agents. A silane coupling agent is effective in increasing the adhesive strength with glass. Antistatic agents are effective in reducing or preventing the generation of static electricity. In general, when attaching a polarizing plate to a liquid crystal cell via an adhesive layer, the surface protective film (separator) that has been temporarily protected by covering the adhesive layer is peeled off and then attached to the liquid crystal cell. The static electricity generated when the surface protective film is peeled off causes the alignment failure of the liquid crystal in the liquid crystal cell, and this phenomenon may cause the display failure of the liquid crystal display device. As a means for reducing or preventing the generation of static electricity, it is effective to add an antistatic agent to the adhesive.

  The pressure-sensitive adhesive layers 40 and 50 are prepared by preparing a pressure-sensitive adhesive composition in which the above pressure-sensitive adhesive components are dissolved in an organic solvent, and applying the composition directly onto the transparent protective films 26 and 36 of the polarizing plate. Apply the above-mentioned pressure-sensitive adhesive composition to the release-treated surface of the base film made of a resin film that has been subjected to a release treatment by drying and removing directly, and dry-removing the solvent to form a pressure-sensitive adhesive layer. The film can be formed by a transfer method in which this is stuck on the transparent protective films 26 and 36 of the polarizing plate. When the pressure-sensitive adhesive layers 40 and 50 are formed on the transparent protective films 26 and 36 by the former direct coating method, a resin film (also referred to as a separator) subjected to a release treatment is bonded to the surface and used. Usually, the surface of the pressure-sensitive adhesive layer is temporarily protected. The latter transfer method is often employed from the viewpoint of the handleability of the pressure-sensitive adhesive composition that is an organic solvent solution. In this case, the release-treated base film used for forming the pressure-sensitive adhesive layer first is used. It is also advantageous in that it can be used as a separator after being attached to a polarizing plate.

[Storage modulus of adhesive layer]
In the present invention, referring to FIG. 1, the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40 used for adhering the front side polarizing plate 20 to the liquid crystal cell 10 and the back side polarizing plate 30 are liquid crystal. The ratio G _f ′ / G _r ′ to the storage elastic modulus G _r ′ of the second pressure-sensitive adhesive layer 50 used for adhering to the cell 10 is in the range of 0.01 or more and less than 0.5. That is, the relationship between G _f ′ and G _r ′ satisfies the formula (a).

  Here, the storage elastic modulus is a term used in general dynamic viscoelasticity measurement. When a strain or stress that changes (vibrates) with time is applied to a sample, the stress or strain generated thereby is measured. Therefore, the value is obtained by a method for measuring the mechanical properties of the sample. Specifically, the elastic modulus is calculated from the strain having the same phase as the stress when the strain is divided into a component having the same phase as the stress and a component having a phase shifted by 90 degrees.

After the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40 and the storage elastic modulus G _r ′ of the second pressure-sensitive adhesive 50 satisfy the above relationship, Warpage of the liquid crystal panel 60 can be suppressed. As a result, the back side polarizing plate 30 comes into contact with the backlight unit 70, the back side polarizing plate 30 approaches the backlight unit 70 abnormally, or the liquid crystal panel 60 comes into contact with a casing or a metal frame for fixing the same. Since such a problem does not occur, a liquid crystal display device without display unevenness can be obtained.

  As can be seen from the above description, the first pressure-sensitive adhesive layer 40 has a relatively low storage elastic modulus, in other words, is relatively soft. The storage elastic modulus of the first pressure-sensitive adhesive layer 40 can be set to about 0.01 to 0.1 mPa · sec, for example. Therefore, the acrylic pressure-sensitive adhesive described above can be used as it is for the first pressure-sensitive adhesive layer 40.

  On the other hand, the second pressure-sensitive adhesive layer 50 has a relatively high storage elastic modulus. In order to give a high storage elastic modulus to the pressure-sensitive adhesive layer, for example, an active energy ray-curable compound is blended in the pressure-sensitive adhesive composition mainly composed of the acrylic resin described above, and the pressure-sensitive adhesive composition is Applying on a transparent protective film or a substrate film that has been subjected to a release treatment, drying and removing the solvent to form a pressure-sensitive adhesive layer, and then irradiating it with an active energy ray to cure Can do. In this case, the pressure-sensitive adhesive composition usually contains a photopolymerization initiator in addition to the active energy ray-curable compound.

  The active energy ray-curable compound may be a (meth) acrylate-based compound, in particular, a monomer or oligomer having at least two (meth) acryloyl groups in the molecule. Since such a (meth) acrylate-based active energy ray-curable compound is radically polymerizable, a photoradical polymerization initiator is used as a photopolymerization initiator to be blended at the same time. The active energy rays used for curing can be ultraviolet rays or electron beams. Among them, ultraviolet rays are preferably used because they are easy to handle and the amount of irradiation light can be easily controlled.

A soft adhesive having a low storage elastic modulus is sold by an adhesive manufacturer in the form of an adhesive sheet formed on a base film that has been subjected to a release treatment as described above. In addition, adhesives hardened by increasing the storage elastic modulus are currently sold by adhesive manufacturers in the form of an adhesive sheet formed on a base film that has been subjected to a release treatment. Therefore, the ratio G _f ′ / G _r ′ between the storage elastic modulus G _f ′ of the first pressure-sensitive adhesive layer 40 and the storage elastic modulus G _r ′ of the second pressure-sensitive adhesive layer 50 as defined in the present invention is In order to achieve a value of 0.01 or more and less than 0.5, two types of pressure-sensitive adhesive sheets suitable for satisfying this condition may be selected from such commercially available pressure-sensitive adhesives.

[Thickness of each member constituting the polarizing plate]
Moreover, about the front side polarizing plate 20, the thickness of the transparent protective film 25 located in the side far from the liquid crystal cell 10 is made the transparent adhesive film 26 located in the liquid crystal cell 10 side, and the 1st adhesion | attachment stuck there. The thickness of the transparent protective film 35 positioned on the liquid crystal cell 10 side is set to be larger than the total thickness of the agent layer 40 and the thickness of the transparent protective film 35 positioned on the side far from the liquid crystal cell 10 is also set. It is preferable to make it larger than the total thickness of the second pressure-sensitive adhesive layer 50 adhered thereto. Thus, by increasing the thickness of the transparent protective films 25 and 35 located on the side far from the liquid crystal cell 10 for each of the front side polarizing plate 20 and the back side polarizing plate 30, the liquid crystal cell 10 is located. Even if the transparent protective films 26 and 36 are thinned, the handling property when handling a large-size polarizing plate having a diagonal size of 32 inches (about 81 cm) or more can be improved, and the warpage of the liquid crystal panel 60 can be further suppressed. The effect of is expressed.

  The transparent protective films 26 and 36 located on the liquid crystal cell 10 side of the polarizing plates 20 and 30 are preferably set to have a thickness of about 20 to 50 μm. The pressure-sensitive adhesive layers 40 and 50 attached thereto can be set to a thickness of about 10 to 30 μm. Therefore, the transparent protective films 25 and 35 positioned on the side farther from the liquid crystal cell 10 of the polarizing plates 20 and 30 have their thicknesses compared to the thicknesses of the transparent protective films 26 and 36 positioned on the liquid crystal cell 10 side. What is necessary is just to make it enlarge at least 30 micrometers or more so that it may become large exceeding at least 10 micrometers. In addition, as described above, if the transparent protective film 25 is located on the side far from the liquid crystal cell of the front side polarizing plate 20, the thickness thereof is the transparent protective film 26 on the liquid crystal cell side and the first attached thereto. If the transparent protective film 35 is located on the side farther from the liquid crystal cell of the back side polarizing plate 30 so as to be larger than the total thickness of the pressure-sensitive adhesive layer 40, the thickness thereof is the transparent protective film 36 on the liquid crystal cell side and What is necessary is just to set so that it may become larger than the total thickness of the 2nd adhesive layer 50 stuck on there. The thickness of the transparent protective films 26 and 36 located on the liquid crystal cell side is about 40 μm, and the thickness of the first adhesive layer 40 and the second adhesive layer 50 is about 25 μm, respectively. It is one preferable form that the thickness of the transparent protective films 25 and 26 located in each is about 80 μm.

[Backlight unit]
The backlight unit 70 includes at least a light source member for supplying light for display to the liquid crystal cell 10. This light source member is arranged in a form called a side light type composed of a light guide plate and a light source arranged on one side surface or two opposite side surfaces, or on a plurality of light sources and on the side (toward the liquid crystal cell 10). It is possible to use a type called a direct type composed of a light diffusing plate. In any form, the light reflecting layer is usually provided in the form of a sheet or a coating layer on the back surface (the side far from the liquid crystal cell 10) of the light source member. Further, one or more optical members such as a light collecting sheet and a diffusion film may be further arranged on the light emitting side of the light source member (the side facing the liquid crystal cell 10). The backlight unit 70 itself has the members described here, and can have any configuration employed in this field.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the examples, the parts and% representing the content or amount used are based on weight unless otherwise specified. In addition, each physical property in the following examples was measured by the following method.

(1) Measurement of thickness:
Measurement was performed using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(2) Measurement of in-plane retardation and thickness direction retardation:
In-plane retardation and thickness direction retardation at a wavelength of 590 nm were measured at a temperature of 23 ° C. using a phase difference meter “KOBRA-21ADH” based on the parallel Nicol rotation method manufactured by Oji Scientific Instruments.

(3) Storage modulus measurement:
The storage elastic modulus (G ′) of the pressure-sensitive adhesive layer was measured according to the following (I) to (III).
(I) Two samples of 25 ± 1 mg are taken out from the pressure-sensitive adhesive layer and molded into a substantially ball shape.
(II) The two samples obtained in the above (I) are attached to the upper and lower surfaces of the I-shaped jig, and the upper and lower surfaces are sandwiched between the L-shaped jigs. The configuration of the measurement sample is L-shaped jig / adhesive / I-shaped jig / adhesive / L-shaped jig.
(III) The storage modulus (G ′) of the sample thus prepared was measured using a dynamic viscoelasticity measuring device “DVA-220” manufactured by IT Measurement Control Co., Ltd., at a temperature of 50 ° C., a frequency of 1 Hz, and an initial value. The measurement was performed under a stress of 1N.

(4) Measurement of the amount of warpage of the liquid crystal panel:
With the liquid crystal panel warped, the projection was placed on a flat plate and the height of the four corners was measured with a ruler, and the maximum value among the four points was taken as the amount of warpage.

  In the following examples, the following two types of pressure-sensitive adhesive sheets obtained from pressure-sensitive adhesive manufacturers were used.

-Adhesive sheet A: A polyethylene terephthalate film (separator) that has been subjected to a release treatment, on which a release treatment surface is provided with an acrylic adhesive layer having a thickness of 25 μm. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.04_MPa at 50 ° C.
-Adhesive sheet B: A polyethylene terephthalate film (separator) that has been subjected to a release treatment, on which a release treatment surface is provided with an acrylic adhesive layer having a thickness of 25 μm. This acrylic pressure-sensitive adhesive layer was subjected to a hardening treatment, and its storage elastic modulus was 0.97 MPa at 50 ° C.

[Example 1]
(Preparation of aqueous adhesive)
3 parts of “KL-318” (trade name) which is a carboxyl group-modified polyvinyl alcohol obtained from Kuraray Co., Ltd. is dissolved in 100 parts of water, and the aqueous solution obtained from Sumika Chemtex Co., Ltd. is dissolved in the aqueous solution. A water-based adhesive was prepared by adding 1.5 parts of “Smilease Resin 650 (30)” (trade name, aqueous solution having a solid content concentration of 30%), which is a conductive polyamide epoxy resin.

(Preparation of polarizing plate)
Transparent protective films 25 and 35 disposed on the side far from the liquid crystal cell by applying saponification treatment to “KC8UX” (trade name), a 80 μm thick triacetyl cellulose film obtained from Konica Minolta Opto Co., Ltd. did. “KC4UEW” (trade name), a 40 μm thick triacetylcellulose film also obtained from Konica Minolta Opto Co., Ltd., has an in-plane retardation of 0.7 nm and a thickness direction retardation of −0.1 nm. there were. This was subjected to saponification treatment to obtain transparent protective films 26 and 36 disposed on the liquid crystal cell side.

  The transparent protective film having a thickness of 80 μm is pasted on one surface of a polarizing film having a thickness of about 28 μm on which iodine is adsorbed and oriented on a polyvinyl alcohol film through the aqueous adhesive prepared above. On the surface, the transparent protective film having a thickness of 40 μm was bonded through the same aqueous adhesive, and then dried at 80 ° C. for 5 minutes to prepare a polarizing plate.

(Preparation of polarizing plate A with adhesive layer)
Using the polarizing plate prepared above, a soft pressure-sensitive adhesive sheet A was bonded to the surface of the transparent protective film having a thickness of 40 μm to prepare a polarizing plate A with a pressure-sensitive adhesive layer.

(Preparation of polarizing plate B with adhesive layer)
Similarly, a polarizing plate B with a pressure-sensitive adhesive layer was prepared by bonding the hard pressure-sensitive adhesive sheet B to the surface of the transparent protective film having a thickness of 40 μm using the polarizing plate prepared above.

(Cutting of polarizing plate with adhesive layer)
The polarizing plate A with pressure-sensitive adhesive layer and the polarizing plate B with pressure-sensitive adhesive layer produced above were each cut into a wide 32 type size (diagonal 32 inches (about 81 cm), width about 71 cm × length about 40 cm). These polarizing plates showed good handling properties during handling.

(Production of liquid crystal display device)
Disassembled Panasonic's IPS mode wide 32 type [diagonal 32 inches (approx. 81cm) width approx. 71cm x length approx. 40cm] LCD TV “VIERA” (model number: VIERA TH-L32X1) The polarizing plate A with the pressure-sensitive adhesive layer prepared above is used for the front side (viewing side) of the liquid crystal cell, and the polarizing plate B with the pressure-sensitive adhesive layer is used for the back side (backlight). The liquid crystal panel 60 was produced by bonding to each side of the pressure-sensitive adhesive layer so as to be in a crossed Nicol state. At this time, the absorption axis of the front-side polarizing plate 20 was arranged so as to be parallel to the alignment direction when no voltage was applied to the liquid crystal molecules in the liquid crystal cell 10 (black display). The storage elastic modulus at 50 ° C. of the first pressure-sensitive adhesive layer 40 that bonds the front-side polarizing plate 20 to the liquid crystal cell 10 and the second pressure-sensitive adhesive layer 50 that bonds the back-side polarizing plate 30 to the liquid crystal cell 10. The ratio G _f ′ / G _r ′ is 0.04. The liquid crystal panel 10 was left in an environment of a temperature of 40 ° C. and a relative humidity of 95% for 96 hours, taken out, and the amount of warpage of the panel one day later was measured. The amount of warpage was 0.4 mm. When this liquid crystal panel was used to reassemble the IPS mode liquid crystal display device and the backlight was turned on, no display unevenness was found.

[Comparative Example 1]
A polarizing plate A with an adhesive layer is bonded to each of the front side (viewing side) and the back side (backlight side) of the liquid crystal cell 10, and the others are produced in the same manner as in Example 1, Evaluation was performed in the same manner. The storage elastic modulus at 50 ° C. of the first pressure-sensitive adhesive layer 40 that bonds the front-side polarizing plate 20 to the liquid crystal cell 10 and the second pressure-sensitive adhesive layer 50 that bonds the back-side polarizing plate 30 to the liquid crystal cell 10. The ratio G _f ′ / G _r ′ is 1. The amount of warpage of the panel at this time was 1.1 mm. When this liquid crystal panel was used to reassemble the IPS mode liquid crystal display device and the backlight was turned on, display unevenness was observed.

[Comparative Example 2]
A polarizing plate B with an adhesive layer is bonded to each of the front side (viewing side) and the back side (backlight side) of the liquid crystal cell 10, and the others are produced in the same manner as in Example 1, Evaluation was performed in the same manner. The storage elastic modulus at 50 ° C. of the first pressure-sensitive adhesive layer 40 that bonds the front-side polarizing plate 20 to the liquid crystal cell 10 and the second pressure-sensitive adhesive layer 50 that bonds the back-side polarizing plate 30 to the liquid crystal cell 10. The ratio G _f ′ / G _r ′ is 1. The amount of warpage of the panel at this time was 1.1 mm. When this liquid crystal panel was used to reassemble the IPS mode liquid crystal display device and the backlight was turned on, display unevenness was observed.

  Table 1 shows the storage elastic modulus and evaluation results of the pressure-sensitive adhesive layers in the above Examples and Comparative Examples.

10 ... Liquid crystal cell,
11, 12 ... cell substrate,
15 …… Liquid crystal layer
20 …… Front-side polarizing plate,
21 …… Polarizing film,
25, 26 ... Transparent protective film,
30 …… Back polarizing plate,
31: Polarizing film,
35, 36 ... Transparent protective film,
40 …… First adhesive layer,
50 …… Second adhesive layer,
60 …… LCD panel,
70 …… Backlight unit.

Claims (7)

A liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween,
A front-side polarizing plate laminated via a first pressure-sensitive adhesive layer on the viewing side of the liquid crystal cell,
A back side polarizing plate laminated via a second pressure-sensitive adhesive layer on the side opposite to the viewing side of the liquid crystal cell, and a backlight unit disposed outside the back side polarizing plate,
The front side polarizing plate and the back side polarizing plate each have a polarizing film and transparent protective films disposed on both sides thereof, and
When the storage elastic modulus at 50 ° C. of the first pressure-sensitive adhesive layer is G _f ′ and the storage elastic modulus at 50 ° C. of the second pressure-sensitive adhesive layer is G _r ′, the ratio G _f ′ / A liquid crystal display device characterized in that G _r ′ is in the range of 0.01 or more and less than 0.5.   2. The liquid crystal display device according to claim 1, wherein the transparent protective film located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate has a thickness direction retardation in a range of −10 to 10 nm.   3. The liquid crystal display device according to claim 1, wherein the transparent protective film positioned on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate is made of a cellulose resin or a polyolefin resin.   The transparent protective film located on the side far from the liquid crystal cell of each of the front side polarizing plate and the rear side polarizing plate has a thickness that is the transparent protective film located on the liquid crystal cell side and the adhesive adhered thereto. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is larger than the total thickness of the layers.   The polarizing film of each of the front side polarizing plate and the back side polarizing plate and the transparent protective film disposed on both surfaces thereof are bonded via a water-based adhesive containing a polyvinyl alcohol resin and a water-soluble epoxy resin. The liquid crystal display device according to claim 1.   The polarizing film of each of the front side polarizing plate and the back side polarizing plate and the transparent protective film disposed on both surfaces thereof are pasted via a curable adhesive composition containing an epoxy compound that is cured by irradiation with active energy rays. The liquid crystal display device according to any one of claims 1 to 4.   The liquid crystal display device according to claim 6, wherein the epoxy compound includes an epoxy compound having at least one epoxy group bonded to an alicyclic ring in a molecule.

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