JP2010191090A - Polarizing plate, liquid crystal panel and liquid crystal display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which uses a diffusion film excellent in durability under hard environment and excellent in productivity, especially a back face side polarizing plate arranged between a liquid crystal cell and a backlight and to provide a liquid crystal panel and a liquid crystal display apparatus using the polarizing plate. <P>SOLUTION: The polarizing plate has a polarizing film which is formed of a poly(vinyl alcohol) resin film and a diffusion film which is laminated at least on one surface of the polarizing film via an adhesive layer. The diffusion film has multilayer structure comprising at least one transparent resin layer consisting of a transparent resin and at least one light diffusion layer containing a transparent binder resin and particulates and further the diffusion film is laminated on the polarizing film so that a surface of the transparent resin layer comes into contact with the adhesive layer. The polarizing plate is arranged between the liquid crystal cell and the backlight which the liquid crystal cell has. Further the liquid crystal panel and the liquid crystal display apparatus using the polarizing plate are provided. Both of the transparent resin and the transparent binder resin are an acrylic resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing plate including a light diffusing film laminated on one side or both sides of a polarizing film, and a liquid crystal panel and a liquid crystal display device using the polarizing plate.

  Applications of liquid crystal display devices are rapidly expanding as thin display devices such as liquid crystal televisions, liquid crystal monitors, and personal computers. In particular, the market for liquid crystal televisions is remarkably expanding, and the demand for cost reduction is very high.

  A normal liquid crystal display device includes a backlight composed of a cold cathode tube or an LED, a light diffusion plate, one or more light diffusion sheets, a back side polarizing plate, a liquid crystal cell, and a viewing side polarizing plate. In the use of large-screen liquid crystal televisions, the needs for wall-mounted televisions have become apparent due to thinning. In this case, it is necessary to reduce the number of members and the number of members used in response to the thinning of liquid crystal televisions. In response to such demands, one or more light diffusing sheets are omitted by reducing the number of parts by providing light diffusibility to the back side polarizing plate itself disposed between the liquid crystal cell and the backlight. The technique to do is known (for example, patent documents 1-6).

JP-A-11-183712 JP 2000-75133 A JP 2000-75134 A JP 2000-75135 A JP 2000-75136 A JP 2000-75137 A

  As a means for imparting light diffusibility to the back side polarizing plate itself, as disclosed in Patent Documents 1 to 6 above, as a transparent protective film laminated on a polarizing film, a diffusion film imparted with light diffusibility Means using are known. In the above patent document, as a method for producing such a diffusion film, for example, a method of coating a resin obtained by mixing a diffusion agent on a transparent substrate film made of triacetyl cellulose is disclosed.

  However, when a conventional diffusion film obtained by coating a transparent substrate film with a resin mixed with a diffusing agent is heated and cooled or humidified, the heat between the coated resin layer and the transparent substrate film is reduced. Due to the difference in expansion coefficient and moisture expansion coefficient, there is a problem that curling occurs and a defect occurs in the manufacturing process. In addition, since a coating process is required, there are problems such as high manufacturing costs.

  On the other hand, as disclosed in the above patent document, the transparent substrate film is not coated with a resin containing a diffusing agent, but the diffusing agent is kneaded into the transparent substrate film itself, or the transparent substrate film surface There is also known a method of producing a diffusion film by roughening the surface with a sandblast or embossing roll.

  However, a diffusion film composed of a single layer in which a diffusing agent is kneaded into the transparent base film itself often produces an unnecessary uneven shape on the surface due to the influence of the diffusing agent particles. When it is used and bonded to a polarizing film, there are problems such as inferior appearance because air bubbles easily enter the interface. In addition, there is a problem that it is difficult to control optical characteristics with a polarizing plate using a diffusion film whose surface is roughened by sandblasting or the like.

  Furthermore, when the resin material constituting the diffusion film is triacetyl cellulose, the polarizing plate using the diffusion film as a protective film often has poor heat and humidity resistance, and the polarizing film may be damaged. The reason why such a polarizing plate is often inferior in heat-and-moisture resistance is considered to be due to the high moisture permeability and water absorption rate of the triacetyl cellulose film.

  Accordingly, an object of the present invention is to provide a polarizing plate using a diffusion film excellent in durability and productivity in harsh environments, particularly a back side polarizing plate disposed between a liquid crystal cell and a backlight. That is. Another object of the present invention is to provide a liquid crystal panel and a liquid crystal display device using the polarizing plate.

  In the present invention, a polarizing film comprising a uniaxially stretched polyvinyl alcohol resin film in which iodine or a dichroic dye is adsorbed and oriented, and a haze laminated on at least one surface of the polarizing film via an adhesive layer is 1 Provided is a polarizing plate that is used as a back-side polarizing plate that is disposed between a liquid crystal cell and a backlight provided in a liquid crystal display device. Here, in the present invention, the diffusion film includes at least one transparent resin layer made of a transparent resin, and at least one light diffusion layer containing a transparent binder resin and fine particles having a refractive index different from that of the transparent binder resin. It has a multilayer structure, and both the transparent resin and the transparent binder resin are acrylic resins. The diffusion film is laminated on the polarizing film so that the surface of the transparent resin layer is in contact with the adhesive layer. The haze of the diffusion film is preferably 5% or more.

  In the polarizing plate of the present invention, the arithmetic average height Pa of the surface in contact with the adhesive layer in the transparent resin layer is preferably 0.5 μm or less.

  In one preferable embodiment of the polarizing plate of the present invention, the diffusion film has a three-layer structure of two transparent resin layers and a light diffusion layer disposed between the two transparent resin layers. In the case of using such a three-layer structure diffusion film, the surface of the transparent resin layer (the surface opposite to the light diffusion layer side) of the two transparent resin layers is bonded to the diffusion film. It is laminated | stacked on a polarizing film so that an agent layer may be contact | connected.

  The polarizing plate of this invention may be equipped with the optical compensation film or protective film laminated | stacked on the surface on the opposite side to the surface where the diffusion film in a polarizing film is laminated | stacked.

  Further, according to the present invention, there is provided a liquid crystal panel comprising a liquid crystal cell and the polarizing plate of the present invention laminated on the liquid crystal cell, wherein the polarizing plate has a surface on which the diffusion film in the polarizing film is laminated, A liquid crystal panel is provided in which the opposite surface faces the liquid crystal cell.

  Furthermore, according to the present invention, there is provided a liquid crystal display device comprising a backlight, a light diffusion plate, and the liquid crystal panel of the present invention in this order, wherein the liquid crystal panel has a diffusion film of a polarizing plate facing the light diffusion plate. Liquid crystal display device, and a liquid crystal display device comprising a backlight, a light diffusing plate, a light diffusing sheet, and the liquid crystal panel of the present invention in this order, wherein the liquid crystal panel is a polarizing plate diffusion film Is provided so as to face the light diffusion sheet.

  According to the present invention, it is possible to provide a polarizing plate and a liquid crystal panel having light diffusibility, which are excellent in durability and productivity in a harsh environment. In addition, according to the present invention, since the surface of the diffusion film facing the polarizing film can be smoothed, the durability and productivity in a harsh environment are excellent, and air bubbles are mixed during film bonding. It is possible to provide a polarizing plate and a liquid crystal panel having a good appearance effectively prevented. Furthermore, according to the present invention, it is possible to reduce the thickness of the liquid crystal display device and the number of members. Such a liquid crystal display device of the present invention can be suitably applied to a liquid crystal display device for a large-screen liquid crystal television, particularly a liquid crystal display device for a liquid crystal television that can be wall-mounted.

It is a cross-sectional schematic diagram which shows a preferable example of the polarizing plate of this invention. It is a cross-sectional schematic diagram which shows another preferable example of the polarizing plate of this invention.

  1 and 2 are schematic cross-sectional views showing preferred examples of the polarizing plate of the present invention. A polarizing plate 100 shown in FIG. 1 includes a polarizing film 101 made of a polyvinyl alcohol-based resin film and a diffusion film 102 laminated on one surface of the polarizing film 101 via an adhesive layer (not shown). The diffusion film 102 has a three-layer structure including two transparent resin layers 103 and 103 and a light diffusion layer 104 disposed between the two transparent resin layers 103 and 103. In the light diffusion layer 104, fine particles 105 having a refractive index different from that of the transparent binder resin that is the base material of the light diffusion layer 104 are dispersed.

  A polarizing plate 200 shown in FIG. 2 includes a polarizing film 201 made of a polyvinyl alcohol-based resin film and a diffusion film 202 laminated on one surface of the polarizing film 201 via an adhesive layer (not shown). The diffusion film 202 has a two-layer structure of one transparent resin layer 203 and one light diffusion layer 204 laminated on the transparent resin layer 203, and the transparent resin layer 203 faces the polarizing film 201. As described above, the polarizing film 201 is laminated. Further, in the light diffusion layer 204, fine particles 205 having a refractive index different from that of the transparent binder resin serving as the base material of the light diffusion layer 204 are dispersed.

  As shown by the above preferred examples, the polarizing plate of the present invention comprises a polarizing film made of a polyvinyl alcohol-based resin film and a diffusion film laminated on one or both sides of the polarizing film, and the diffusion film is a transparent resin layer. And a light diffusing layer. Such a polarizing plate of the present invention is used as a back-side polarizing plate disposed between a liquid crystal cell and a backlight of a liquid crystal display device. Hereinafter, the polarizing plate of the present invention will be described in more detail.

(Polarizing film)
Specifically, the polarizing film used in the polarizing plate of the present invention is obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, a saponified polyvinyl acetate resin can be used. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymers. Etc. 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 degree of saponification of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, for example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like can be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000 to 10000, preferably about 1500 to 5000.

  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 the polyvinyl alcohol-based resin is not particularly limited, and can be formed by a conventionally known appropriate method. Although the film thickness of the raw film which consists of polyvinyl alcohol-type resin is not specifically limited, For example, it is about 10-150 micrometers.

  A polarizing film is usually a process of dyeing an original film made of polyvinyl alcohol resin as described above with a dichroic dye and adsorbing the dichroic dye (dyeing process), and the dichroic dye is adsorbed. The polyvinyl alcohol-based resin film is produced through a step of treating with a boric acid aqueous solution (boric acid treatment step) and a step of washing with water after the treatment with the boric acid aqueous solution (water washing treatment step).

  Further, in the production of the polarizing film, the polyvinyl alcohol-based resin film is usually uniaxially stretched, but this uniaxial stretching may be performed before the dyeing treatment step or during the dyeing treatment step, It may be performed after the dyeing process. When uniaxial stretching is performed after the dyeing treatment step, this uniaxial stretching may be performed before the boric acid treatment step or during the boric acid treatment step. Of course, it is also possible to perform uniaxial stretching in these plural stages. Uniaxial stretching may be performed uniaxially between rolls having different peripheral speeds, or may be performed uniaxially using a hot roll. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 3 to 8 times.

  The dyeing of the polyvinyl alcohol-based resin film with the dichroic dye in the dyeing treatment step is performed, for example, by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing the dichroic dye. As the dichroic dye, for example, iodine, a dichroic dye or the like is used. Examples of dichroic dyes include C.I. I. Dichroic direct dyes composed of disazo compounds such as DIRECT RED 39, and dichroic direct dyes composed of trisazo, tetrakisazo compounds and the like are included. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to 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 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. . When iodine is used as the dichroic dye, the temperature of the aqueous solution used for dyeing is usually 20 to 40 ° C., and the immersion time (dyeing time) in this aqueous solution is usually 20 to 1800 seconds.

On the other hand, when a dichroic 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 dye is usually employed. The content of the dichroic dye in this aqueous solution, usually, 1 × 10 ^-4 to 10 parts by weight per 100 parts by weight of water, preferably 1 × 10 ^-3 to 1 parts by weight, particularly preferably 1 × 10 ^{- 3} to 1 × 10 ⁻² parts by weight. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. When using a dichroic dye as the dichroic dye, the temperature of the aqueous dye solution used for dyeing is usually 20 to 80 ° C., and the immersion time (dyeing time) in this aqueous solution is usually 10 to 1800 seconds. is there.

  The boric acid treatment step is performed by immersing a polyvinyl alcohol-based resin film dyed with a dichroic dye in a boric acid-containing aqueous solution. The amount of boric acid in the boric acid-containing aqueous solution is usually 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 in the dyeing process described above, the boric acid-containing aqueous solution used in this boric acid treatment process preferably contains potassium iodide. In this case, the amount of potassium iodide in the boric acid-containing aqueous solution is usually 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 60 to 1200 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.

  In the subsequent washing process, the polyvinyl alcohol-based resin film after the boric acid treatment described above is washed with water, for example, by immersing it in water. The water temperature in the water washing treatment is usually 5 to 40 ° C., and the immersion time is usually 1 to 120 seconds. After the water washing treatment, a drying treatment is usually performed to obtain a polarizing film. The drying process can be performed using, for example, a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually 30 to 100 ° C, preferably 50 to 80 ° C. The time for the drying treatment is usually 60 to 600 seconds, preferably 120 to 600 seconds.

  Thus, a polarizing film is obtained by subjecting the polyvinyl alcohol-based resin film to uniaxial stretching, dyeing with a dichroic dye, boric acid treatment and water washing treatment. The thickness of this polarizing film is usually in the range of 5 to 40 μm.

(Diffusion film)
The diffusion film used for the polarizing plate of the present invention is a laminated resin film having light diffusibility. By laminating a laminated resin film having light diffusibility to a polarizing film, the obtained polarizing plate is provided with a light diffusing function. Therefore, when this is used as a back side polarizing plate of a liquid crystal display device, the liquid crystal cell and back It becomes possible to omit one or a plurality of light diffusion sheets arranged between the light. In the present invention, as a diffusion film, a multilayer including at least one transparent resin layer made of a transparent resin, and at least one light diffusion layer containing a transparent binder resin and fine particles having a refractive index different from that of the transparent binder resin. A light diffusing laminated resin film having a structure is used. In the diffusion film, at least one outer surface is made of a transparent resin layer surface (that is, at least one outermost layer is a transparent resin layer), and the transparent resin layer surface is in contact with the adhesive layer (the transparent resin). The layer surface is bonded to the polarizing film using an adhesive so that the surface of the layer faces the polarizing film). In addition, the laminated resin film “has light diffusibility” means that the haze measured in accordance with JIS K 7136 is 1% or more.

  As described above, the diffusion film can have a three-layer structure in which the light diffusion layer is sandwiched between two transparent resin layers (see FIG. 1), or the transparent resin layer and the light diffusion layer laminated thereon. (See FIG. 2). In the case of a three-layer structure, the polarizing film and the diffusion film are bonded using an adhesive so that the surface of one of the two transparent resin layers is in contact with the adhesive layer. Moreover, in the case of a two-layer structure, it is bonded to a polarizing film using an adhesive so that the surface of the transparent resin layer is in contact with the adhesive layer. Of these, the diffusion film preferably has a three-layer structure. By setting it as a 3 layer structure, it is easy to manufacture a diffusion film provided with the transparent resin layer where the surface is smooth, without being influenced by the surface unevenness | corrugation of a light-diffusion layer. On the other hand, in the case of a diffusion film having a two-layer structure, the smoothness of the surface of the transparent resin layer may be relatively low due to the influence of the surface unevenness of the light diffusion layer. In addition, although it is possible to obtain a laminated resin film having four or more layers by alternately arranging transparent resin layers and light diffusion layers, a three-layer structure is preferable in view of cost and the like.

  As the transparent resin used for the transparent resin layer constituting the diffusion film and the transparent binder resin used for the light diffusion layer, a substantially optically transparent resin is used. Examples of such resins include triacetyl cellulose; polyethylene terephthalate; acrylic resins such as polymethyl methacrylate; polycarbonate resins; thermoplastic resins such as amorphous cyclic polyolefins having norbornene compounds as monomers. it can. The transparent resin constituting the transparent resin layer and the transparent binder resin used for the light diffusion layer may be the same or different materials. Among the above resins, it is preferable to use an acrylic resin having low moisture permeability, excellent transparency and weather resistance, and high surface hardness as the transparent resin and the transparent binder resin. By using an acrylic resin as the transparent resin and the transparent binder resin, a diffusion film excellent in moisture and heat resistance can be obtained, and a polarizing plate having high durability can be obtained even in a harsh environment. Further, excellent scratch resistance can be imparted to the polarizing plate. Here, the acrylic resin in the present invention means a material obtained by mixing a methacrylic resin, an additive added as necessary, etc., and melt-kneading.

  The methacrylic resin is a polymer mainly composed of methacrylic acid ester. The methacrylic resin may be a homopolymer of one kind of methacrylic acid ester or a copolymer of methacrylic acid ester with other methacrylic acid ester or acrylic acid ester. Examples of the methacrylic acid esters include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate. The carbon number of the alkyl group of the alkyl methacrylate is usually about 1 to 4. Moreover, as an acrylic ester which can be copolymerized with a methacrylic ester, an alkyl acrylate is preferable, and examples thereof include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and the like. Carbon number of the alkyl group of the alkyl acrylate is usually about 1 to 8.

  A copolymer mainly composed of a methacrylic acid ester is a copolymer component comprising a compound having at least one polymerizable carbon-carbon double bond in the molecule, such as an aromatic vinyl compound such as styrene and a vinylcyan compound such as acrylonitrile. May be included.

  The acrylic resin preferably contains acrylic rubber particles in order to improve the impact resistance and film forming property of the film. The amount of acrylic rubber particles that can be contained in the acrylic resin is preferably 5% by weight or more, more preferably 10% by weight or more. The upper limit of the amount of the acrylic rubber particles is not critical, but if the amount of the acrylic rubber particles is too large, the surface hardness of the film is lowered, and when the film is subjected to surface treatment, it is resistant to the organic solvent in the surface treatment agent. Solvent property decreases. Therefore, the amount of acrylic rubber particles that can be contained in the acrylic resin is preferably 80% by weight or less, and more preferably 60% by weight or less.

  The acrylic rubber particles are particles containing an elastic polymer mainly composed of an acrylate ester as an essential component. The acrylic rubber particles may have a single-layer structure consisting essentially only of the elastic polymer. It may have a multi-layer structure in which the coalescence is one layer. Specifically, as this elastic polymer, 50 to 99.9% by weight of an alkyl acrylate and at least one kind of other vinyl monomer copolymerizable therewith, 0 to 49.9% by weight, A cross-linked elastic copolymer obtained by polymerization of a monomer mixture composed of 0.1 to 10% by weight of a polymerizable cross-linkable monomer is preferably used.

  Examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like. Carbon number of the alkyl group of the alkyl acrylate is usually about 1 to 8. Examples of the other vinyl monomers copolymerizable with the alkyl acrylate include compounds having one polymerizable carbon-carbon double bond in the molecule. Methacrylic acid esters such as methyl acid; Aromatic vinyl compounds such as styrene; Vinyl cyanide compounds such as acrylonitrile. Examples of the copolymerizable crosslinkable monomer include a crosslinkable compound having at least two polymerizable carbon-carbon double bonds in the molecule. (Meth) acrylates of polyhydric alcohols such as (meth) acrylate and butanediol di (meth) acrylate; alkenyl esters of (meth) acrylic acid such as allyl (meth) acrylate and methallyl (meth) acrylate; divinylbenzene, etc. Is mentioned. In this specification, (meth) acrylate refers to methacrylate or acrylate, and (meth) acrylic acid refers to methacrylic acid or acrylic acid.

  In addition to the acrylic rubber particles, the acrylic resin contains normal additives such as ultraviolet absorbers, organic dyes, pigments, inorganic dyes, antioxidants, antistatic agents, surfactants, and the like. Also good. Among these, an ultraviolet absorber is preferably used for improving weather resistance. Examples of the ultraviolet absorber include 2,2′-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol], 2- (5 -Methyl-2-hydroxyphenyl) -2H-benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3,5-di -Tert-butyl-2-hydroxyphenyl) -2H-benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3,5 -Di-tert-butyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3,5-di-tert-amyl-2-hydroxypheny ) Benzotriazole ultraviolet absorbers such as -2H-benzotriazole and 2- (2'-hydroxy-5'-tert-octylphenyl) -2H-benzotriazole; 2-hydroxy-4-methoxybenzophenone, 2-hydroxy -4-octyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxy-4'-chlorobenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone and 2,2'-dihydroxy-4,4 Examples include 2-hydroxybenzophenone ultraviolet absorbers such as' -dimethoxybenzophenone; salicylic acid phenyl ester ultraviolet absorbers such as p-tert-butylphenyl salicylic acid ester and p-octylphenyl salicylic acid ester. Two or more kinds of ultraviolet absorbers may be used as necessary. When the acrylic resin contains an ultraviolet absorber, the amount is usually 0.1% by weight or more, preferably 0.3% by weight or more, and preferably 2% by weight or less.

  The refractive index of the fine particles dispersed in the light diffusion layer needs to have a value different from the refractive index of the transparent binder resin in order to give the diffusion film a light diffusion function. The difference is preferably 0.01 or more. Also, if this refractive index difference is made too large, strong scattering is likely to occur even when the content of the fine particles is small, and the control of scattering tends to be difficult. It is preferably 1 or less. The refractive index of the fine particles is appropriately selected in consideration of the type of the transparent binder resin used, etc., but when using the transparent binder resin as described above, the refractive index of the fine particles is 1.4 or more and 1.6 or less. It is preferable to select from a range. When the acrylic resin is used as the transparent binder resin, the refractive index of the fine particles is from about 1.39 to 1.59 because the refractive index of the acrylic resin is generally about 1.49. Preferably, the selection is made so as to satisfy the above conditions.

  The fine particles are preferably spherical or almost spherical considering the isotropic and uniformity of scattering. Also, particles having a surface with fine irregularities and amorphous particles are not preferred because unexpected scattering may occur due to structures such as fine irregularities on the surface smaller than the particle size. . The weight average particle diameter of the fine particles is preferably 1 μm or more and 50 μm or less, and more preferably 2 μm or more and 20 μm or less. When the weight average particle diameter of the fine particles is less than 1 μm, the scattered light intensity on the wide angle side increases, and the contrast tends to decrease when the polarizing plate is applied to a liquid crystal display device. If the weight average particle diameter exceeds 50 μm, the required scattering effect may not be obtained, or it may be necessary to increase the thickness of the diffusion film in order to obtain the required scattering effect.

  As the fine particles, colorless or white organic particles and inorganic particles can be used. Examples of the organic particles include melamine beads (refractive index 1.57); (meth) acrylic resin beads such as polymethyl methacrylate beads (refractive index 1.49); methyl methacrylate / styrene copolymer resin beads ( Refractive index 1.50 to 1.59); Polycarbonate beads (refractive index 1.59); Polyolefin resin beads such as polyethylene beads (refractive index 1.53) and polypropylene beads; Polyvinyl chloride beads (refractive index 1.46) ); Silicone resin beads (refractive index 1.46); polystyrene beads and the like. Resin beads made of a copolymer obtained by copolymerizing two or more monomers selected from ethylene, propylene, styrene, methyl methacrylate, benzoguanamine, formaldehyde, melamine, butadiene, and the like can also be used.

  Inorganic particles include calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica, glass, talc, mica, white carbon, magnesium oxide, zinc oxide and other inorganic particles, and these inorganic particles are surface treated with fatty acids. The ones that have been given can be listed as typical ones.

  In the light diffusion layer, the fine particles are preferably contained in an amount of 5 to 40 parts by weight with respect to 100 parts by weight of the transparent binder resin. If the content of the fine particles is less than 5 parts by weight, sufficient light diffusibility tends not to be obtained. Moreover, when content of microparticles | fine-particles exceeds 40 weight part, it exists in the tendency for the shaping | molding to a diffusion film to become difficult or the mechanical strength of a diffusion film to become low.

  The resin composition used for forming the light diffusion layer can be obtained by mixing the transparent binder resin (for example, methacrylic resin, acrylic rubber particles and other additives) and the fine particles, and melt-kneading them. .

  Examples of a method for obtaining a diffusion film used in the present invention from a resin composition containing the transparent resin constituting the transparent resin layer and the fine particles constituting the light diffusion layer include, for example, a method using a feed block, a multi-manifold die Various methods generally known, such as a method using the above, can be used. Among them, for example, a method of laminating via a feed block, multilayer melt extrusion from a T die, and forming a film by contacting at least one side of the obtained laminated film-like material with a roll or a belt has good surface properties. That is, it is preferable in that a diffusion film having a smooth transparent resin layer surface can be obtained. In particular, from the viewpoint of improving the surface smoothness and surface glossiness of the diffusion film, a method of forming a film by bringing both surfaces of the laminated film obtained by the multilayer melt extrusion molding into contact with the roll surface or the belt surface is preferable. . In the roll or belt used at this time, the roll surface or belt surface in contact with the transparent resin constituting the transparent resin layer is preferably a mirror surface in order to impart smoothness to the transparent resin layer surface. According to the multilayer melt extrusion molding (coextrusion molding) method, for example, a diffusion film can be produced with high productivity as compared with a method of coating a resin liquid containing fine particles on a base film, and the surface of the transparent resin layer is A smooth diffusion film can be easily obtained.

  The surface of the transparent resin layer of the diffusion film (when the diffusion film has a three-layer structure, the surface of at least one of the transparent resin layers) is made smooth by polarizing the surface of the transparent resin layer through the adhesive layer. When bonding to a film, it is possible to prevent problems such as bonding air bubbles occurring at the interface between the adhesive layer and the transparent resin layer, and to obtain a polarizing plate with a good appearance. Specifically, the arithmetic average height Pa measured according to JIS B 0601 on the surface of the transparent resin layer bonded to the polarizing film (in contact with the adhesive layer) is preferably 0.5 μm or less. More preferably, it is 0.1 μm or less.

  The thickness of the diffusion film is not particularly limited, but is preferably about 20 μm or more and 200 μm or less, and more preferably 30 μm or more and 100 μm or less, from the viewpoint of reducing the thickness and weight of the polarizing plate.

  The thickness of the transparent resin layer is not particularly limited, but may be, for example, 5 μm or more and 80 μm or less, and preferably 10 μm or more and 60 μm or less. The thickness of the light diffusion layer is not particularly limited, but can be, for example, 5 μm or more and 100 μm or less, and preferably 10 μm or more and 80 μm or less.

  The haze value measured in accordance with JIS K 7136 of the diffusion film is 1% or more as described above, and is preferably 5% or more in order to impart a good light diffusion function to the polarizing plate. 15% or more and 90% or less is more preferable. More preferably, it is 45% or more and 90% or less. Moreover, when a polarizing plate is arrange | positioned at a liquid crystal display device, a diffusion film with a high total light transmittance is so preferable that the brightness | luminance on a display screen becomes high enough. Specifically, the total light transmittance of the diffusion film is preferably 70% or more, more preferably 80% or more, and particularly preferably 85% or more. The total light transmittance of the diffusion film is measured according to JIS K 7361.

  An adhesive or pressure-sensitive adhesive layer for bonding the liquid crystal cell and the polarizing plate may be formed on the surface of the polarizing film opposite to the surface on which the diffusion film is bonded. In addition, a transparent film such as a protective film or an optical compensation film is laminated on the surface of the polarizing film opposite to the surface on which the diffusion film is bonded, and an adhesive or pressure-sensitive adhesive layer is formed on the transparent film. May be. Furthermore, an optical functional film described later can be laminated on the transparent film, and an adhesive or pressure-sensitive adhesive layer can be formed on the optical functional film.

  Examples of the protective film include cellulose resin films such as a triacetyl cellulose film (TAC film), olefin resin films, acrylic resin films, polycarbonate resin films, and polyester resin films such as polyethylene terephthalate. Further, as the optical compensation film, those obtained by stretching the film mentioned as the protective film to give refractive index anisotropy, those containing an optical anisotropy imparting additive, and an optical anisotropic layer on the surface And the like formed.

  The cellulose resin constituting the cellulose resin film means a partially esterified product or a completely esterified product of cellulose, and examples thereof include cellulose acetate ester, propionate ester, butyrate ester, and mixed esters thereof. be able to. More specifically, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, cellulose acetate butyrate and the like can be mentioned. When such a cellulose resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. Cellulosic resin films can be obtained commercially, for example, “Fujitac TD80” (Fuji Film Co., Ltd.), “Fujitac TD80UF” (Fuji Film Co., Ltd.), “Fujitac TD80UZ” (Fuji Film ( Co., Ltd.), “KC8UX2M” (manufactured by Konica Minolta Opto), “KC8UY” (manufactured by Konica Minolta Opto), and the like.

  As an optical compensation film comprising a cellulose resin film, for example, a film in which a compound having a retardation adjusting function is contained in the cellulose resin film; a film in which a compound having a retardation adjusting function is applied to the surface of a cellulose resin film. A film obtained by uniaxially or biaxially stretching a cellulose resin film, and the like. As an optical compensation film made of a commercially available cellulose-based resin film, for example, “WV film Wide View Film“ WV BZ 438 ””, “WV film Wide View Film“ WV EA ”” manufactured by Fuji Film Co., Ltd., Konica Minolta Examples thereof include “KC4FR-1” and “KC4HR-1” manufactured by Opto Corporation.

  The thickness of the protective film or optical compensation film made of a cellulose resin film is not particularly limited, but is preferably in the range of 20 to 90 μm, and more preferably in the range of 30 to 90 μm. When the thickness is less than 20 μm, it is difficult to handle the film. On the other hand, when the thickness exceeds 90 μm, the workability is inferior, and it is disadvantageous in reducing the thickness and weight of the resulting polarizing plate.

  Examples of the optical compensation film made of the olefin resin film include a uniaxially stretched or biaxially stretched cycloolefin resin film. When the polarizing plate of the present invention is used for a liquid crystal panel for a large-sized liquid crystal television, particularly a liquid crystal panel having a vertical alignment (VA) mode liquid crystal cell, the above-mentioned optical compensation film is a stretched product of a cycloolefin resin film, It is also suitable from the viewpoint of optical characteristics and durability. Here, the cycloolefin resin film is a film made of a thermoplastic resin having a unit of a monomer made of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene monomer. The cycloolefin-based film may be a hydrogenated product of a ring-opening polymer using a single cycloolefin or a ring-opening copolymer using two or more kinds of cycloolefins. It may also be an addition copolymer with an aromatic compound having a vinyl group. Further, those having a polar group introduced into the main chain or side chain are also effective.

  Commercially available thermoplastic cycloolefin-based resins include “Topas” sold by Ticona, Germany, “Arton” sold by JSR Corporation, and “Zeonor” sold by Nippon Zeon Corporation. ZEONOR ”and“ ZEONEX ”,“ APEL ”(both trade names) sold by Mitsui Chemicals, Inc., and the like, which can be suitably used. A cycloolefin resin film can be obtained by forming such a cycloolefin resin. As a film forming method, a known method such as a solvent casting method or a melt extrusion method is appropriately used. Also, for example, “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd., “Zeonor Film” sold by Optes Co., Ltd., “Arton Film” sold by JSR Co., Ltd. Cycloolefin-based resin films (such as trade names) are also commercially available, and these can also be suitably used.

  If the thickness of the optical compensation film made of a stretched cycloolefin-based resin film is too thick, the processability will be inferior, and the transparency will be reduced, and it will be disadvantageous in reducing the thickness and weight of the polarizing plate. It is preferable that it is about 20-80 micrometers.

  Next, the manufacturing method of the polarizing plate of this invention and the adhesive agent used for bonding of the film which comprises the polarizing plate of this invention are demonstrated. The polarizing plate of this invention is manufactured by bonding a polarizing film and a diffusion film using an adhesive agent. At this time, the diffusion film is laminated on the polarizing film so that the surface of the transparent resin layer is in contact with the adhesive layer (so that the surface of the transparent resin layer faces the polarizing film). When a transparent film such as a protective film or an optical compensation film is laminated on the surface of the polarizing film opposite to the surface on which the diffusion film is bonded, the polarizing film and the transparent film are similarly used with an adhesive. Pasted together.

  For bonding the polarizing film and the diffusion film, an adhesive made of a curable resin composition containing an epoxy resin is preferably used. By using such an adhesive, the polarizing film and the diffusion film can be bonded with high adhesive strength without adversely affecting the appearance of the polarizing plate. As an adhesive used for laminating a polarizing film and a protective film or an optical compensation film, in addition to an adhesive made of a curable resin composition containing an epoxy resin, a polyvinyl alcohol resin or a urethane resin is used as an adhesive component. Conventionally known adhesives such as aqueous adhesives can be used, but if the same type of adhesive as that used for bonding the polarizing film and the diffusion film is used, the production efficiency is improved and the raw material type Can be reduced.

  Here, the epoxy resin refers to a compound that has an average of two or more epoxy groups in the molecule and is cured by a polymerization reaction involving the epoxy group. In addition, according to the custom in this field, even when the compound is a monomer, it is called an epoxy resin.

  As the epoxy resin contained in the curable resin composition, an epoxy resin that does not contain an aromatic ring in the molecule is suitably used from the viewpoints of weather resistance, refractive index, and cationic polymerizability. Examples of the epoxy resin that does not contain an aromatic ring in the molecule include a hydrogenated epoxy resin, an alicyclic epoxy resin, and an aliphatic epoxy resin.

  The hydrogenated epoxy resin can be obtained by selectively hydrogenating an aromatic epoxy resin under pressure in the presence of a catalyst. Examples of aromatic epoxy resins include bisphenol-type epoxy resins such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol S diglycidyl ether; phenol novolac epoxy resins, cresol novolac epoxy resins, and hydroxybenzaldehyde phenol. Examples thereof include novolak-type epoxy resins such as novolak epoxy resins; glycidyl ethers of tetrahydroxydiphenylmethane, glycidyl ethers of tetrahydroxybenzophenone, and polyfunctional epoxy resins such as epoxidized polyvinylphenol. A nuclear hydrogenated product of these aromatic epoxy resins becomes a hydrogenated epoxy resin. Among them, it is preferable to use hydrogenated bisphenol A glycidyl ether as the hydrogenated epoxy resin.

  Examples of the aliphatic epoxy resin include polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof. More specifically, 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; glycerin triglycidyl ether; trimethylolpropane triglycidyl ether; polyethylene glycol diglycidyl ether; propylene Diglycidyl ethers of glycols; polyether polyols obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin Examples thereof include polyglycidyl ether.

  The alicyclic epoxy resin means an epoxy resin having at least one epoxy group bonded to the alicyclic ring in the molecule. The “epoxy group bonded to the alicyclic ring” has a structure represented by the following formula, wherein m is an integer of 2 to 5.

Accordingly, the alicyclic epoxy resin is a compound having at least one structure represented by the above formula in the molecule. More specifically, a compound in which one or a plurality of hydrogen groups in (CH ₂ ) _m in the above formula are bonded to another chemical structure can be an alicyclic epoxy resin. One or more hydrogen atoms in (CH ₂ ) _m may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group.

  Among the alicyclic epoxy resins as described above, an alicyclic epoxy resin having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula). Is more preferably used because of its excellent adhesive strength between the polarizing film and the diffusion film. Although the structure of the alicyclic epoxy resin preferably used in this invention is specifically illustrated below, it is not limited to these compounds.

  (A) Epoxycyclohexylmethyl epoxycyclohexanecarboxylates represented by the following formula (I):

(In the formula, R ¹ and R ² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
(B) Epoxycyclohexanecarboxylates of alkanediol represented by the following formula (II):

(In the formula, R ³ and R ⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and n represents an integer of 2 to 20).
(C) Epoxycyclohexyl methyl esters of dicarboxylic acid represented by the following formula (III):

(In the formula, R ⁵ and R ⁶ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and p represents an integer of 2 to 20).
(D) Epoxycyclohexyl methyl ethers of polyethylene glycol represented by the following formula (IV):

(In the formula, R ⁷ and R ⁸ independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and q represents an integer of 2 to 10).
(E) Epoxycyclohexyl methyl ethers of alkanediols represented by the following formula (V):

(In the formula, R ⁹ and R ¹⁰ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and r represents an integer of 2 to 20).
(F) Diepoxy trispiro compound represented by the following formula (VI):

(In the formula, R ¹¹ and R ¹² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
(G) Diepoxy monospiro compound represented by the following formula (VII):

(In the formula, R ¹³ and R ¹⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
(H) Vinylcyclohexene diepoxides represented by the following formula (VIII):

(In the formula, R ¹⁵ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
(I) Epoxycyclopentyl ethers represented by the following formula (IX):

(In the formula, R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
(J) Diepoxytricyclodecanes represented by the following formula (X):

(In the formula, R ¹⁸ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.)
Among the alicyclic epoxy resins exemplified above, the following alicyclic epoxy resins are commercially available or similar, and are preferably used because they are relatively easy to obtain.

(A) Esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and (7-oxa-bicyclo [4.1.0] hept-3-yl) methanol [formula (I ) In which R ¹ = R ² = H],
(B) 4-methyl-7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and (4-methyl-7-oxa-bicyclo [4.1.0] hept-3-yl) methanol Esterified product [compound of the above formula (I), R ¹ = 4-CH ₃ , R ² = 4-CH ₃ ],
(C) Esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and 1,2-ethanediol [in the above formula (II), R ³ = R ⁴ = H, n = 2 Compound of
(D) (7-oxabicyclo [4.1.0] hept-3-yl) esterified product of methanol and adipic acid [in the above formula (III), R ⁵ = R ⁶ = H, p = 4 compound ],
(E) (4-Methyl-7-oxabicyclo [4.1.0] hept-3-yl) esterified product of methanol and adipic acid [in the above formula (III), R ⁵ = 4-CH ₃ , R _{^{6 = 4-CH 3, p}} = 4 the compound]
(F) Etherified product of (7-oxabicyclo [4.1.0] hept-3-yl) methanol and 1,2-ethanediol [in the above formula (V), R ⁹ = R ¹⁰ = H, r = 2 compounds].

  Examples of the aliphatic epoxy resin include polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof. More specifically, 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; glycerin triglycidyl ether; trimethylolpropane triglycidyl ether; polyethylene glycol diglycidyl ether; propylene Diglycidyl ethers of glycols; polyether polyols obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin Examples thereof include polyglycidyl ether.

  The epoxy resin contained in the curable resin composition may be only one type or two or more types.

  The epoxy equivalent of the epoxy resin contained in the curable resin composition is usually in the range of 30 to 3,000 g / equivalent, preferably 50 to 1,500 g / equivalent. When the epoxy equivalent is less than 30 g / equivalent, the flexibility of the adhesive layer after curing may be reduced or the adhesive strength may be reduced. On the other hand, if it exceeds 3,000 g / equivalent, the compatibility with other components may decrease.

  The curing reaction of the epoxy resin is preferably cationic polymerization from the viewpoint of reactivity. Therefore, it is preferable to incorporate a cationic polymerization initiator in the curable resin composition. 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. Regardless of the type of cationic polymerization initiator, it is preferable from the viewpoint of workability that latency is imparted. The cationic polymerization initiator is a photocationic polymerization initiator that generates a cationic species or a Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, or an electron beam, and generates a cationic species or a Lewis acid by heating. It is roughly classified into thermal cationic polymerization initiators.

  Hereinafter, the cationic photopolymerization initiator will be described. Use of a cationic photopolymerization initiator makes it possible to cure the adhesive at room temperature, reducing the need to consider the heat resistance of the polarizing film or distortion due to expansion, and bonding the diffusion film to the polarizing film with good adhesion be able to. In addition, since the photocationic polymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy resin. The photocationic polymerization initiator is not particularly limited, and examples thereof include onium salts such as aromatic diazonium salts, aromatic iodonium salts, aromatic sulfonium salts, and iron-allene complexes. .

  Examples of the aromatic diazonium salt include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate.

  Examples of the aromatic iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, and di (4-nonylphenyl) iodonium hexafluorophosphate.

  Examples of the aromatic sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, 4,4′-bis [diphenylsulfonio] diphenyl sulfide bishexa. Fluorophosphate, 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenylsulfide bishexafluoroantimonate, 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenylsulfide bis Hexafluorophosphate, 7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate, 7- [di (p-tolui) ) Sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl-4′-diphenylsulfonio-diphenyl sulfide hexafluorophosphate, 4- (p-tert-butylphenylcarbonyl) -4′-diphenyl Examples include sulfonio-diphenyl sulfide hexafluoroantimonate, and 4- (p-tert-butylphenylcarbonyl) -4′-di (p-toluyl) sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate.

  Examples of the iron-allene complex include xylene-cyclopentadienyl iron (II) hexafluoroantimonate, cumene-cyclopentadienyl iron (II) hexafluorophosphate, and xylene-cyclopentadienyl iron (II ) -Tris (trifluoromethylsulfonyl) methanide and the like.

  These photocationic polymerization initiators can be easily obtained as commercial products. For example, “Kayarad PCI-220” and “Kayarad PCI-620” (Nippon Kayaku Co., Ltd. )), “UVI-6990” (manufactured by Union Carbide), “Adekaoptomer SP-150”, “Adekaoptomer SP-170” (manufactured by ADEKA, Inc.), “CI-5102”, “ "CIT-1370", "CIT-1682", "CIP-1866S", "CIP-2048S", "CIP-2064S" (Nippon Soda Co., Ltd.), "DPI-101", "DPI-102" , “DPI-103”, “DPI-105”, “MPI-103”, “MPI-105”, “BBI-101”, “BBI-102”, “BBI” 103 "," BBI-105 "," TPS-101 "," TPS-102 "," TPS-103 "," TPS-105 "," MDS-103 "," MDS-105 "," DTS-102 " “DTS-103” (manufactured by Midori Chemical Co., Ltd.), “PI-2074” (manufactured by Rhodia), and the like. Among these, “CI-5102” manufactured by Nippon Soda Co., Ltd. is one of preferred photocationic polymerization initiators.

  The above cationic photopolymerization initiators may be used alone or in combination of two or more. Among them, aromatic sulfonium salts are particularly preferably used because they have ultraviolet absorption characteristics even in a wavelength region of 300 nm or more, and thus can provide a cured product having excellent curability and good mechanical strength and adhesive strength. .

  The compounding quantity of a photocationic polymerization initiator is 0.5-20 weight part normally with respect to 100 weight part of epoxy resins, Preferably it is 1 weight part or more, Preferably it is 15 weight part or less. When the blending amount is less than 0.5 parts by weight with respect to 100 parts by weight of the epoxy resin, curing becomes insufficient, and mechanical strength and adhesive strength are lowered. In addition, when the blending amount exceeds 20 parts by weight with respect to 100 parts by weight of the epoxy resin, the ionic substance in the cured product increases, so that the hygroscopic property of the cured product increases, and the durability performance of the polarizing plate may decrease. There is sex.

  When a photocationic polymerization initiator is added to the curable resin composition, a photosensitizer can be used in combination as necessary. By using a photosensitizer, the reactivity is 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 and diazo compounds, halogen compounds, and photoreductive dyes. Specific photosensitizers include, for example, benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether and α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, methyl o-benzoylbenzoate Benzophenone derivatives such as 4,4′-bis (dimethylamino) benzophenone and 4,4′-bis (diethylamino) benzophenone; thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; 2-chloroanthraquinone and 2-methyl Anthraquinone derivatives such as anthraquinone; acridone derivatives such as N-methylacridone and N-butylacridone; other, α, α-diethoxyacetophenone, benzyl, fluorenone, Sandton, uranyl compounds, halogen compounds and the like can be mentioned, but are not limited thereto. These photosensitizers may be used alone or in combination. The content of the photosensitizer is preferably in the range of 0.1 to 20 parts by weight in 100 parts by weight of the curable resin composition.

  Next, the thermal cationic polymerization initiator will be described. Examples of thermal cationic polymerization initiators that generate cationic species or Lewis acids upon heating include benzylsulfonium salts, thiophenium salts, thiolanium salts, benzylammonium, pyridinium salts, hydrazinium salts, carboxylic acid esters, sulfonic acid esters, and amine imides. Can do. These initiators can be easily obtained as commercial products. For example, “ADEKA OPTON CP77” and “ADEKA OPTON CP66” (manufactured by Asahi Denka Kogyo Co., Ltd.), “CI” -2639 "and" CI-2624 "(manufactured by Nippon Soda Co., Ltd.)," Sun-Aid SI-60L "," Sun-Aid SI-80L "and" Sun-Aid SI-100L "(Sanshin Chemical Industry Co., Ltd.) Manufactured).

  It is also a useful technique to combine the photocationic polymerization and the thermal cationic polymerization described above. The curable resin composition containing an epoxy resin may further contain a compound that promotes cationic polymerization, such as oxetanes and polyols.

  Oxetanes are compounds having a 4-membered ring ether structure in the molecule, such as 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, Examples include 3-ethyl-3- (phenoxymethyl) oxetane, di [(3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, and phenol novolak oxetane. It is done. These oxetanes can be easily obtained as commercial products. For example, all of these oxetanes are trade names such as “Aron Oxetane OXT-101”, “Aron Oxetane OXT-121”, “Aron Oxetane OXT-211”. , “Aron Oxetane OXT-221”, “Aron Oxetane OXT-212” (both manufactured by Toagosei Co., Ltd.) and the like. Although the compounding quantity of oxetane is not restrict | limited in particular, It is 5-95 weight% normally in curable resin composition, Preferably it is 30-70 weight%.

  As the polyols, those having no acidic groups other than phenolic hydroxyl groups are preferable. For example, polyol compounds having no functional groups other than hydroxyl groups, polyester polyol compounds, polycaprolactone polyol compounds, polyol compounds having phenolic hydroxyl groups, polycarbonates A polyol etc. can be mentioned. The molecular weight of these polyols is usually 48 or more, preferably 62 or more, more preferably 100 or more, and preferably 1,000 or less. The blending amount of these polyols is usually 50% by weight or less, preferably 30% by weight or less in the curable resin composition.

  Furthermore, unless the effects of the present invention are impaired, the curable resin composition used as an adhesive has other additives such as an ion trap agent, an antioxidant, a chain transfer agent, a sensitizer, and a tackifier. , Thermoplastic resins, fillers, flow regulators, plasticizers, antifoaming agents, and the like can be blended. Examples of the ion trapping agent include powdery bismuth-based, antimony-based, magnesium-based, aluminum-based, calcium-based, titanium-based and mixed compounds thereof, and examples of the antioxidant include hinders. Dophenol-based antioxidants and the like are included.

  In pasting the polarizing film and the diffusion film, first, an adhesive made of the curable resin composition containing the epoxy resin is applied to the bonding surface of the polarizing film and / or the diffusion film. There are no particular limitations on the method of applying the adhesive, and various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. Moreover, since each coating system has an optimum viscosity range, it is also a useful technique to adjust the viscosity using a solvent. As the solvent for this purpose, a solvent that dissolves the curable resin composition satisfactorily without reducing the optical performance of the polarizing film is used, but there is no particular limitation on the type of the solvent. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used. The thickness of the layer which consists of the coated curable resin composition is 0.1-20 micrometers normally, Preferably it is 0.2-10 micrometers, More preferably, it is 0.5-5 micrometers.

  The laminated film in which the diffusion film is bonded to the polarizing film through the uncured adhesive layer is then irradiated with active energy rays or heated to form an adhesive layer made of the curable resin composition. Curing and fixing the diffusion film on the polarizing film. The thickness of the adhesive layer after curing is usually 0.1 to 20 μm, preferably 0.2 to 10 μm, and more preferably 0.5 to 5 μm.

  In addition, also when bonding a protective film or an optical compensation film on the opposite side to the side by which the diffusion film in a polarizing film is laminated | stacked, it can carry out similarly to the above.

  Prior to the bonding of the diffusion film, the protective film, and the optical compensation film to the polarizing film, the bonding surfaces of these films may be subjected to easy adhesion processing such as corona treatment, primer treatment, and anchor coating treatment.

When polymerization curing is performed by irradiation with active energy rays, the light source used is not particularly limited, but has a light emission distribution at a wavelength of 400 nm or less, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light A lamp, a microwave excitation mercury lamp, a metal halide lamp, or the like can be used. The light irradiation intensity to the curable resin composition is determined for each curable resin composition, and is not particularly limited, but the irradiation intensity in the wavelength region effective for activation of the initiator is 0.1 to It is preferably 100 mW / cm ² . When the light irradiation intensity to the curable resin composition is less than 0.1 mW / cm ² , the reaction time becomes too long, and when it exceeds 100 mW / cm ² , the heat radiated from the lamp and the curable resin composition The heat generated during the polymerization may cause yellowing of the curable resin composition and deterioration of the polarizing film. The light irradiation time to the curable resin composition is controlled for each curable resin composition and is not particularly limited, but the integrated light amount expressed as the product of irradiation intensity and irradiation time is 10 to 5. it is preferably set to be 000mJ / cm ^2. When the integrated light amount to the curable resin composition is less than 10 mJ / cm ² , the generation of the active species derived from the initiator is not sufficient, and the adhesive layer may be insufficiently cured, while that When integrated quantity of light exceeds 5,000 mJ / cm ^2, the irradiation time is very long, becomes disadvantageous in improving productivity.

  When the polymerization is carried out by heat, it can be heated by a generally known method, and the conditions thereof are not particularly limited, but the thermal cationic polymerization initiator compounded in the curable resin composition is usually a cationic species. And heating is performed at a temperature higher than the temperature at which Lewis acid is generated, and is usually performed at 50 to 200 ° C.

  It should be noted that the polarizing plate functions such as the degree of polarization of the polarizing film, the transmittance and the hue, and the transparency of the diffusion film, protective film, and optical compensation film, even when cured under the conditions of irradiation with active energy rays or heating. It is preferable to cure within a range that does not decrease.

  In the polarizing plate of the present invention, the surface of the polarizing film opposite to the side on which the diffusion film is laminated (on the film when a protective film or an optical compensation film is laminated) has an adhesive layer. It is preferable. As the pressure-sensitive adhesive used for such a pressure-sensitive adhesive layer, a conventionally known appropriate pressure-sensitive adhesive can be used without particular limitation, and examples thereof include an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, and a silicone pressure-sensitive adhesive. Among these, an acrylic pressure-sensitive adhesive is preferably used from the viewpoints of transparency, adhesive strength, reliability, reworkability, and the like. The pressure-sensitive adhesive layer can be provided by a method in which such a pressure-sensitive adhesive is, for example, an organic solvent solution, which is applied on a base film (for example, a polarizing film) by a die coater or a gravure coater and dried. The sheet-like pressure-sensitive adhesive formed on a plastic film (referred to as a separate film) that has been subjected to a release treatment can also be provided by a method of transferring it to a base film. Although there is no restriction | limiting in particular also about the thickness of an adhesive layer, Generally it is preferable to exist in the range of 2-40 micrometers.

  An optical functional film may be attached to the surface of the polarizing plate on which the pressure-sensitive adhesive layer is formed via the pressure-sensitive adhesive layer. As an optical functional film, for example, an optical compensation film in which a liquid crystal compound is coated on a substrate surface and oriented; a reflection type that transmits a certain kind of polarized light and reflects polarized light that shows the opposite property Polarizing film; Retardation film made of polycarbonate-based resin; Retardation film made of cyclic polyolefin-based resin; Film with anti-glare function having uneven shape on surface; Film with surface anti-reflection function; Reflecting film having reflection function on surface; And a transflective film having both a reflection function and a transmission function. Commercially available products corresponding to an optical compensation film coated with a liquid crystal compound on the surface of the base material are “WV film” (Fuji Film Co., Ltd.), “NH film” (Shin Nippon Oil Co., Ltd.) And “NR Film” (manufactured by Nippon Oil Corporation). For example, “DBEF” (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) is a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties. Can be obtained), “APF” (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan), and the like. Moreover, as a commercial item corresponding to the phase difference film which consists of cyclic polyolefin resin, for example, "Arton film" (made by JSR Corporation), "Essina" (made by Sekisui Chemical Co., Ltd.), "Zeonor film" ( (Manufactured by Optes Co., Ltd.).

  The polarizing plate of this invention can be used suitably as a back side polarizing plate arrange | positioned between the liquid crystal cell with which a liquid crystal display device is equipped, and a backlight.

<Liquid crystal panel and liquid crystal display device>
The liquid crystal panel of the present invention comprises a liquid crystal cell and the polarizing plate of the present invention laminated on the liquid crystal cell, and the liquid crystal cell and the polarizing plate are a surface on which a diffusion film in a polarizing film is laminated. Are bonded via an adhesive layer so that the opposite surface faces the liquid crystal cell (that is, the diffusion film forms the outer surface of the liquid crystal panel). Such a liquid crystal panel of the present invention is applied to a liquid crystal display device such that the diffusion film is on the backlight side (so that the polarizing plate of the present invention is disposed between the liquid crystal cell and the backlight). . In the liquid crystal panel of the present invention, a polarizing plate is provided on the front side of the liquid crystal cell (the viewing side when applied to a liquid crystal display device and the side opposite to the side on which the polarizing plate of the present invention is laminated). The polarizing plate provided on the front side of the liquid crystal cell is not particularly limited, and any conventionally known appropriate polarizing plate can be used. For example, the polarizing plate etc. which the glare-proof process, the hard-coat process, and the antireflection process were given are mentioned. Moreover, the polarizing plate by which the polyethylene terephthalate film, the acrylic film, and the polypropylene film were laminated | stacked on the single side | surface of the polarizing film may be sufficient.

  The liquid crystal display device of the present invention comprises a liquid crystal panel arranged so that the diffusion film of the polarizing plate is on the backlight side. Such a liquid crystal display device of the present invention is provided with a liquid crystal panel in which the polarizing plate of the present invention is bonded to the back side of the liquid crystal cell, so that the adhesive strength between the polarizing film and the diffusion film is excellent, It has high durability even in the environment and has sufficient mechanical strength while adapting to thinning. Moreover, since the diffusion film of the polarizing plate of the present invention is disposed on the back side of the liquid crystal panel, adhesion between the liquid crystal panel and the backlight system can be prevented, and the visibility is further improved.

  In the liquid crystal display device of the present invention, as the configuration other than the liquid crystal panel, an appropriate configuration of a conventionally known liquid crystal display device can be adopted. For example, a backlight, a light diffusion plate, and the liquid crystal panel of the present invention The structure provided in this order, and the structure provided with the backlight, the light diffusing plate, the light diffusing sheet, and the liquid crystal panel of the present invention in this order can be given. In the former case, the liquid crystal panel is arranged so that the diffusion film of the polarizing plate faces the light diffusion plate, and in the latter case, the liquid crystal panel is arranged so that the diffusion film of the polarizing plate faces the light diffusion sheet. . Further, another optical member such as a light collecting sheet may be disposed between the backlight and the liquid crystal panel as necessary.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified.

  In the following examples, the haze of the diffusion film and the polarizing plate, and the arithmetic average height Pa of the surface of the diffusion film that is bonded to the polarizing film are measured by the following methods.

(Haze)
For the haze of the diffusion film, the transparent resin layer surface is bonded to a glass substrate using an optically transparent adhesive or glycerin, and a haze meter “HM” manufactured by Murakami Color Research Laboratory in accordance with JIS K 7136 is used. -150 "type was used for measurement. Light was incident from the diffusion film side (the side opposite to the glass substrate side). The haze of the polarizing plate is a haze meter manufactured by Murakami Color Research Laboratory Co., Ltd. in accordance with JIS K 7136, with the protective film surface bonded to a glass substrate using an optically transparent adhesive or glycerin. Measurement was performed using “HM-150” type. Light was incident from a polarizing plate (the side opposite to the glass substrate side).

(Arithmetic mean height Pa)
The shape of the surface of the diffusion film that is bonded to the polarizing film was measured by the following method. That is, after bonding to a glass substrate using an adhesive so that the surface to be measured of the diffusion film becomes the surface, three-dimensional information of the surface shape using a confocal microscope (“PLμ2300” manufactured by Sensofar) Got. In the measurement, three or more areas of 200 μm × 200 μm or more were performed, and the average value was used as the measurement value. At the time of measurement, the magnification of the objective lens was 50 times. Subsequently, based on the measurement data, the arithmetic average height Pa in the cross-sectional curve was obtained by calculation based on JIS B 0601.

<Example 1>
(A) Production of Polarizing Film After immersing a 75 μm thick polyvinyl alcohol film made of polyvinyl alcohol having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more in pure water at 30 ° C., iodine / potassium iodide It was immersed at 30 ° C. in an aqueous solution having a weight ratio of / water of 0.02 / 2/100. Then, it was immersed at 56.5 ° C. in an aqueous solution having a potassium iodide / boric acid / water weight ratio of 12/5/100. Subsequently, after washing with pure water at 8 ° C., it was dried at 65 ° C. to obtain a polarizing film in which iodine was adsorbed and oriented on a polyvinyl alcohol film. Stretching was mainly performed in the iodine staining and boric acid treatment steps, and the total stretching ratio was 5.3 times.

(B) Preparation of diffusion film Acrylic resin in which 30 parts by weight of acrylic rubber particles are contained in 70 parts by weight of a copolymer of methyl methacrylate / methyl acrylate = 96/4 (weight ratio) (refractive index 1.49). The composition and the Henschel such that methyl methacrylate / styrene copolymer beads (refractive index 1.505, weight average particle diameter 8 μm) are 15 parts by weight with respect to 100 parts by weight of the acrylic resin composition. After mixing with a mixer, the mixture was melt-kneaded with a first extruder (screw diameter: 65 mm, uniaxial, vented (manufactured by Toshiba Machine Co., Ltd.)) and supplied to the feed block. In addition, an acrylic resin composition in which 30 parts by weight of acrylic rubber particles is contained in 70 parts by weight of a copolymer (refractive index 1.49) of methyl methacrylate / methyl acrylate = 96/4 (weight ratio) is the second. Were melt-kneaded with an extruder (screw diameter: 45 mm, uniaxial, with vent (manufactured by Hitachi Zosen)), and supplied to the feed block. The resin supplied to the feed block from the first extruder becomes a light diffusion layer (intermediate layer), and the resin supplied to the feed block from the second extruder becomes a transparent resin layer (surface layer: both sides) Co-extrusion molding was performed at 265 ° C., and a diffusion film having a three-layer structure with a thickness of 80 μm (intermediate layer 50 μm, surface layer 15 μm × 2) was produced through a roll unit set at 85 ° C. The haze of the obtained diffusion film was 15.0%.

(C) Preparation of Adhesive Trade name “Epicoat YX8000”, a hydrogenated epoxy resin manufactured by Japan Epoxy Resins Co., Ltd. (diglycidyl ether of nuclear hydrogenated bisphenol A, having an epoxy equivalent of about 205 g / equivalent Product) 10.0 g, 4.0 g of the product name “CI5102” which is a photocationic polymerization initiator manufactured by Nippon Soda Co., Ltd., and the product name “CS7001” which is a photosensitizer manufactured by Nippon Soda Co., Ltd. 1 0.0 g was weighed into a 100 ml disposable cup, mixed and defoamed to prepare an adhesive composed of a curable resin composition containing an epoxy resin.

(D) Production of polarizing plate The diffusion film produced in (B) above is formed on one surface of the polarizing film obtained in (A), and the norbornene system as a protective film is formed on the other surface of the polarizing film. A resin film ("ZEONOR FILM" from Optes Co., Ltd.) is bonded via the UV curable adhesive obtained in (C), and irradiated with UV light from the norbornene resin film surface to obtain a polarizing plate. It was. The haze of the obtained polarizing plate was 15.2%.

<Example 2>
A polarizing plate was obtained in the same manner as in Example 1 except that methyl methacrylate / styrene copolymer beads (refractive index 1.51, weight average particle diameter 4 μm) were used as fine particles to be contained in the light diffusion layer. The haze of the diffusion film was 30.7%, and the haze of the polarizing plate was 31.3%.

<Comparative Example 1>
Example 1 except that the diffusion film has a two-layer structure of a light diffusion layer (thickness 30 μm) and a transparent resin layer (thickness 50 μm), and is bonded to the polarizing film so that the light diffusion layer is in contact with the adhesive layer. A polarizing plate was obtained in the same manner. The haze of the diffusion film was 74.0%, and the haze of the polarizing plate was 17.3%.

<Comparative example 2>
For the diffusion film, one surface of a 80 μm thick triacetyl cellulose film (Fuji film) was roughened by sandblasting, and a polarizing film was adhered to the opposite surface of the roughened surface. A polarizing plate was obtained. The haze of the diffusion film was 67.9%, and the haze of the polarizing plate was 68.0%.

[Evaluation of polarizing plate]
About the polarizing plate obtained from the said Example and comparative example, the visibility when it was set as the external appearance, warm water resistance, and a liquid crystal display device was evaluated. The results are shown in Table 1. Evaluation methods and evaluation criteria are as follows. Table 1 also shows the arithmetic average height Pa of the surface of the diffusion film that is bonded to the polarizing film.

(appearance)
The case where a bonding bubble was not seen in the interface of an adhesive bond layer and a diffusion film was set to A, and the case where a bonding bubble was seen was set to B.

(Hot water resistance)
The polarizing plate was immersed in warm water heated to 60 ° C. for 8 hours and observed for significant discoloration or deformation. The case where no discoloration or deformation was observed was indicated as A, and the case where discoloration or deformation was observed as B.

(Visibility)
An acrylic pressure-sensitive adhesive layer having a thickness of 25 μm was provided on the norbornene-based resin film surface of the polarizing plate, and then this polarizing plate was disposed on the back surface of the liquid crystal cell via the pressure-sensitive adhesive layer. A liquid crystal panel was assembled by placing a commercially available polarizing plate on the front surface of the liquid crystal cell, and this was combined with a commercially available light diffusion plate and backlight to produce a liquid crystal display device. The display of this liquid crystal display device was visually observed. The case where the display image is bright and the visibility is good is A, and the case where the display image is relatively dark and the visibility is poor is B.

  As shown in Table 1, the polarizing plates of Examples 1 and 2 had no appearance of bonding bubbles in the adhesive layer, and the appearance was good. In addition, when the polarizing plates of Examples 1 and 2 were immersed in a hot water resistance test for 8 hours, the color of the polarizing film was not changed or the polarizing plate was not significantly deformed. Furthermore, when the display of the liquid crystal display device produced using the polarizing plate of Example 1 and 2 was observed visually, a bright image was obtained when viewed from the front, and the visibility was good.

  On the other hand, in the polarizing plate of Comparative Example 1, many bubbles were observed at the interface between the adhesive layer and the diffusion film. Moreover, the liquid crystal display device produced using this polarizing plate had a dark display image, and the visibility was extremely poor.

  The polarizing plate of Comparative Example 2 had a good appearance without bonding bubbles. However, when immersed in warm water of 60 ° C. for 8 hours, the triacetyl cellulose was remarkably deformed and the color of the polarizing film was slightly changed. Moreover, when the display of the liquid crystal display device produced using the sample after this hot water resistance test was observed, it became a whitish display at the time of black display, and the contrast was remarkably low.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100,200 Polarizing plate, 101,201 Polarizing film, 102,202 Diffusing film, 103,203 Transparent resin layer, 104,204 Light diffusing layer, 105,205 Fine particles.

Claims (8)

A polarizing film composed of a uniaxially stretched polyvinyl alcohol-based resin film in which iodine or a dichroic dye is adsorbed and oriented, and a haze laminated on at least one surface of the polarizing film via an adhesive layer is 1% or more. With diffusion film,
The diffusion film has a multilayer structure including at least one transparent resin layer made of a transparent resin, and at least one light diffusion layer containing fine particles having a refractive index different from that of the transparent binder resin and the transparent binder resin. ,
The transparent resin and the transparent binder resin are both acrylic resins,
The said diffusion film is a polarizing plate for arrange | positioning between the liquid crystal cell with which a liquid crystal display device is equipped and a backlight laminated | stacked on the said polarizing film so that the surface of the said transparent resin layer may contact | connect the said adhesive bond layer.   2. The polarizing plate according to claim 1, wherein an arithmetic average height Pa of a surface in contact with the adhesive layer in the transparent resin layer is 0.5 μm or less.   The polarizing plate according to claim 1 or 2, wherein the diffusion film has a three-layer structure including two transparent resin layers and a light diffusion layer disposed between the two transparent resin layers.   The haze of the said diffusion film is 5% or more, The polarizing plate in any one of Claims 1-3.   The polarizing plate in any one of Claims 1-4 provided with the optical compensation film or protective film laminated | stacked on the surface on the opposite side to the surface where the said diffusion film in the said polarizing film is laminated | stacked. A liquid crystal panel comprising a liquid crystal cell and the polarizing plate according to any one of claims 1 to 5 laminated on the liquid crystal cell,
The said polarizing plate is a liquid crystal panel arrange | positioned so that the surface on the opposite side to the surface where the said diffusion film in the said polarizing film is laminated | stacked may oppose the said liquid crystal cell. A liquid crystal display device comprising a backlight, a light diffusion plate and the liquid crystal panel according to claim 6 in this order,
The liquid crystal panel is a liquid crystal display device in which the diffusion film of the polarizing plate is disposed so as to face the light diffusion plate. A liquid crystal display device comprising a backlight, a light diffusion plate, a light diffusion sheet and the liquid crystal panel according to claim 6 in this order,
The liquid crystal panel is a liquid crystal display device in which the diffusion film of the polarizing plate is disposed so as to face the light diffusion sheet.

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