JP6612191B2 - Polarizer - Google Patents

Description

  The present invention relates to a polarizing plate, and more particularly to a polarizing plate used in a liquid crystal display.

  In recent years, liquid crystal displays have been widely used as display devices for televisions, personal computers, digital cameras, mobile phones and the like. The liquid crystal display has a front-side polarizing plate // liquid crystal // rear-side polarizing plate, where the display side is the front side and the opposite side (backlight side) is the rear side. The polarizing plate usually has a configuration in which a protective film or the like is bonded to a polarizing film of a polyvinyl alcohol film which is uniaxially stretched (protective film / polarizing film / protective film). The protective films disposed on the front and rear surfaces of the polarizing film constituting the front polarizing plate are designated as protective film A and protective film B, respectively, and the protective films disposed on the front and rear surfaces of the polarizing film constituting the rear polarizing plate. Assuming that the film is a protective film C and a protective film D, respectively, the overall configuration is as follows: from the front side, protective film A / front side polarizing film / protective film B // liquid crystal // protective film C / rear side polarizing film / protective Film D is obtained.

As the protective film, a triacetyl cellulose film (hereinafter sometimes abbreviated as a TAC film) is often used because it has high transparency and optical isotropy.
However, it is inferior in dimensional stability and heat-and-moisture resistance, and has the disadvantage that the surface must be saponified beforehand with an alkaline solution in order to adhere to the polarizing film. As liquid crystal displays increase in size and quality in recent years, improvement in mechanical strength and stability under high-temperature and high-humidity environments is required. The need to avoid quality degradation has emerged. Further, since the alkali treatment uses a high-concentration alkaline solution, it is not preferable in terms of work safety and environmental protection.

  In order to solve these problems, materials other than the TAC film such as a norbornene film have been studied (Patent Documents 1 and 2). However, since a film made of another material does not use a general-purpose resin, there is a problem that the cost is high. Then, the method of using the polyester film which is general purpose resin which can ensure dimensional stability, does not require the process of the alkali treatment which has various problems, and also has no problem also in cost is also proposed.

  However, with the polyester film alone, the adhesiveness between the polarizing film and the adhesive used to bond the protective film is inferior, and the total light transmittance is low when compared with the TAC film, so that a polarizing plate is obtained. There is a drawback that the brightness is sometimes reduced. In order to improve the adhesion of the polyester film, a configuration in which an anchor layer is provided has also been proposed, but there is no specific disclosure, and depending on the adhesive, it is difficult to ensure sufficient adhesion. (Patent Documents 3 to 5).

JP-A-6-511117 JP 2006-227090 A JP 2002-116320 A JP-A-8-271733 JP-A-8-271734

  The present invention has been made in view of the above circumstances, and the problem to be solved is that it can solve various problems of a TAC film, has good adhesiveness with an adhesive, and further has a total light transmittance. The present invention is to provide a polarizing plate using a laminated polyester film which is high and can be suitably used as a protective film for a polarizing film, particularly a protective film on the rear side of the rear side polarizing plate (the protective film D described above).

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the use of a laminated polyester film having a specific configuration can easily solve the above-described problems, and have completed the present invention.

That is, the gist of the present invention is to have a coating layer formed from a coating solution containing polyvinyl alcohol and an isocyanate compound directly on one side of the polyester film, and a polarizing film on the coating layer side of the polyester film. And an adhesive layer between the coating layer and the polarizing film, and the polarizing film is a polyvinyl alcohol-iodine polarizing film, provided that self-crosslinking property in all resin constituents in the coating layer It exists in a polarizing plate except the case where content of a polyurethane resin is 50 weight% or more.

  According to the present invention, for example, when used as a protective film for a polarizing plate, particularly a protective film for the rear side of a rear polarizing plate, the adhesive strength with the adhesive for adhering the polarizing film is good, and the polarizing plate The polarizing plate using the lamination polyester film excellent in the total light transmittance after forming can be provided, and the industrial value is high.

  The polyester film constituting the laminated polyester film in the present invention may have a single layer structure or a multilayer structure, and may have four or more layers as long as it does not exceed the gist of the present invention other than a two-layer or three-layer structure. It may be a multilayer, and is not particularly limited.

  The polyester used in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyester includes polyethylene terephthalate and the like. On the other hand, the dicarboxylic acid component of the copolyester includes isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxybenzoic acid, etc.), etc. 1 type or 2 types or more are mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexane dimethanol, neopentyl glycol, is mentioned.

  The polyester film of the present invention may contain an ultraviolet absorber in order to prevent the liquid crystal of the liquid crystal display from being deteriorated by ultraviolet rays. The ultraviolet absorber is not particularly limited as long as it is a compound having ultraviolet absorbing ability and can withstand the heat applied in the production process of the polyester film.

  As the ultraviolet absorber, there are an organic ultraviolet absorber and an inorganic ultraviolet absorber. From the viewpoint of transparency, an organic ultraviolet absorber is preferable. Although it does not specifically limit as an organic type ultraviolet absorber, For example, a benzotriazole type, a cyclic imino ester type, a benzophenone type etc. are mentioned. From the viewpoint of durability, benzotriazole and cyclic imino ester are more preferable. It is also possible to use two or more ultraviolet absorbers in combination.

  Examples of the benzotriazole-based ultraviolet absorbers include, but are not limited to, 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2 '-Hydroxy-5'-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5 '-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2- [2'- Hydroxy-5 '-(methacryloyloxyhexyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-3'-tert-butyl-5'-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2 -[2'-hydroxy-5'-tert-butyl-3 '-(methacryl Yloxyethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -5-chloro-2H-benzotriazole, 2- [2′-hydroxy-5 ′ -(Methacryloyloxyethyl) phenyl] -5-methoxy-2H-benzotriazole, 2- [2'-hydroxy-5 '-(methacryloyloxyethyl) phenyl] -5-cyano-2H-benzotriazole, 2- [2 '-Hydroxy-5'-(methacryloyloxyethyl) phenyl] -5-tert-butyl-2H-benzotriazole, 2- [2'-hydroxy-5 '-(methacryloyloxyethyl) phenyl] -5-nitro-2H -Benzotriazole and the like.

  Examples of the cyclic imino ester-based ultraviolet absorber include, but are not limited to, 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazine-4, for example. -One, 2-phenyl-3,1-benzoxazin-4-one, 2- (1- or 2-naphthyl) -3,1-benzoxazin-4-one, 2- (4-biphenyl) -3, 1-benzoxazin-4-one, 2-p-nitrophenyl-3,1-benzoxazin-4-one, 2-m-nitrophenyl-3,1-benzoxazin-4-one, 2-p-benzoyl Phenyl-3,1-benzoxazin-4-one, 2-p-methoxyphenyl-3,1-benzoxazin-4-one, 2-o-methoxyphenyl-3,1-benzoxazin-4-one, -Cyclohexyl-3,1-benzoxazin-4-one, 2-p- (or m-) phthalimidophenyl-3,1-benzoxazin-4-one, N-phenyl-4- (3,1-benzoxazine -4-On-2-yl) phthalimide, N-benzoyl-4- (3,1-benzoxazin-4-one-2-yl) aniline, N-benzoyl-N-methyl-4- (3,1- Benzoxazin-4-one-2-yl) aniline, 2- (p- (N-methylcarbonyl) phenyl) -3,1-benzoxazin-4-one, 2,2′-bis (3,1-benzo Oxazin-4-one), 2,2′-ethylenebis (3,1-benzoxazin-4-one), 2,2′-tetramethylenebis (3,1-benzoxazin-4-one), 2, 2'-Decame Renbis (3,1-benzoxazin-4-one, 2,2'-p-phenylenebis (3,1-benzoxazin-4-one), 2,2'-m-phenylenebis (3,1-benzo Oxazin-4-one), 2,2 ′-(4,4′-diphenylene) bis (3,1-benzoxazin-4-one), 2,2 ′-(2,6- or 1,5-naphthylene) ) Bis (3,1-benzoxazin-4-one), 2,2 ′-(2-methyl-p-phenylene) bis (3,1-benzoxazin-4-one), 2,2 ′-(2 -Nitro-p-phenylene) bis (3,1-benzoxazin-4-one), 2,2 '-(2-chloro-p-phenylene) bis (3,1-benzoxazin-4-one), 2 , 2 '-(1,4-cyclohexylene) bis (3,1-benzoo Sadin-4-one), 1,3,5-tri (3,1-benzoxazin-4-one-2-yl) benzene, 1,3,5-tri (3,1-benzoxazin-4-one) -2-yl) naphthalene, 2,4,6-tri (3,1-benzoxazin-4-one-2-yl) naphthalene, 2,8-dimethyl-4H, 6H-benzo (1,2-d; 5,4-d ′) bis (1,3) -oxazine-4,6-dione, 2,7-dimethyl-4H, 9H-benzo (1,2-d; 4,5-d ′) bis (1 , 3) -Oxazine-4,9-dione, 2,8-diphenyl-4H, 8H-benzo (1,2-d; 5,4-d ′) bis (1,3) -oxazine-4,6- Dione, 2,7-diphenyl-4H, 9H-benzo (1,2-d; 4,5-d ′) bis (1,3) -oxazine 4,6-dione, 6,6′-bis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-bis (2-ethyl-4H, 3,1-benzoxazine) -4-one), 6,6'-bis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6'-methylenebis (2-methyl-4H, 3,1-benzoxazine) -4-one), 6,6'-methylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6'-ethylenebis (2-methyl-4H, 3,1-benzo) Oxazin-4-one), 6,6′-ethylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-butylenebis (2-methyl-4H, 3,1- Benzoxazin-4-one), 6,6′-butylenebis (2- Phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-oxybis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-oxybis (2- Phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-sulfonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-sulfonylbis ( 2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-carbonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-carbonyl Bis (2-phenyl-4H, 3,1-benzoxazin-4-one), 7,7′-methylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′- Methylenebis (2-phenyl-4H 3,1-benzoxazin-4-one), 7,7′-bis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-ethylenebis (2-methyl-4H) , 3,1-benzoxazin-4-one), 7,7′-oxybis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-sulfonylbis (2-methyl-) 4H, 3,1-benzoxazin-4-one), 7,7′-carbonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,7′-bis (2-methyl) -4H, 3,1-benzoxazin-4-one), 6,7'-bis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,7'-methylenebis (2-methyl- 4H, 3,1-benzoxazin-4-one), 6,7 ′ Methylene bis (2-phenyl-4H, 3,1-benzoxazin-4-one), and the like.

  Among the above compounds, when considering the color tone, a benzoxazinone-based compound which is difficult to be yellowed is preferably used. As an example thereof, a compound represented by the following general formula (1) is more preferably used. It is done.

In the above formula, R represents a divalent aromatic hydrocarbon group, and X ¹ and X ² are each independently selected from hydrogen or the following functional group group, but are not necessarily limited thereto.

Functional group: alkyl group, aryl group, heteroaryl group, halogen, alkoxyl group, aryloxy group, hydroxyl group, carboxyl group, ester group, nitro group Among the compounds represented by the above structural formula, in the present invention, 2,2 ′-(1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] is particularly preferred.

  The amount of the ultraviolet absorber to be contained in the laminated polyester film of the present invention is usually 10.0% by weight or less, preferably 0.3 to 3.0% by weight. When an ultraviolet absorber in an amount exceeding 10.0% by weight is contained, the ultraviolet absorber may bleed out on the surface, which may cause deterioration of surface functionality such as adhesion deterioration.

  In the case of a multilayer film, it is preferably at least a three-layer structure, and the ultraviolet absorber is preferably blended in the intermediate layer. By blending an ultraviolet absorber in the intermediate layer, the compound can be prevented from bleeding out to the film surface, and as a result, properties such as film adhesion can be maintained.

  When used as a protective film for a polarizing film, if the laminated polyester film of the present invention prevents deterioration of the liquid crystal due to ultraviolet rays, as a guideline, the light transmittance at a wavelength of 380 nm is preferably 10% or less, more preferably. Is 5% or less. The light transmittance at a wavelength of 380 nm can be adjusted by changing the type and amount of the above-described ultraviolet absorber.

  In the polyester layer of the film of the present invention, it is preferable to blend particles mainly for the purpose of imparting slipperiness and preventing scratches in each step. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples include inorganic particles such as magnesium, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-5 micrometers normally, Preferably it is the range of 0.1-3 micrometers. If the average particle size is less than 0.01 μm, the slipperiness may not be sufficiently imparted, or the particles may be aggregated to make the dispersibility insufficient, thereby reducing the transparency of the film. On the other hand, when the thickness exceeds 5 μm, the surface roughness of the film becomes too rough, and a defect may occur in a subsequent process.

  Furthermore, the content of particles in the polyester layer is usually in the range of 0.0001 to 5% by weight, preferably 0.0003 to 3% by weight. When the particle content is less than 0.0001% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient. There is a case.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but it is preferably added after completion of esterification or transesterification.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  Although the thickness of the polyester film in this invention will not be specifically limited if it is a range which can be formed into a film as a film, Usually, 10-200 micrometers, Preferably it is the range of 25-50 micrometers.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all. That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7.0 times, preferably 3.0 to 6.0 times. Next, the film is stretched in the direction perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6 times. .0 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In the present invention, the simultaneous biaxial stretching method can be adopted for the production of the polyester film constituting the laminated polyester film. The simultaneous biaxial stretching method is a method in which the above-mentioned unstretched sheet is usually stretched and oriented in the machine direction and the width direction at a temperature controlled normally at 70 to 120 ° C., preferably 80 to 110 ° C. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Next, formation of the coating layer which comprises the laminated polyester film in this invention is demonstrated. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. Since the coating can be performed simultaneously with the film formation, the production can be handled at a low cost, and therefore in-line coating is preferably used.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed particularly before the lateral stretching after the longitudinal stretching is finished. When the coating layer is provided on the polyester film by in-line coating, it is possible to apply at the same time as the film formation, and the coating layer can be processed at a high temperature in the heat treatment process of the polyester film after stretching. Performances such as adhesion to various surface functional layers that can be formed on the layer and heat-and-moisture resistance can be improved. Moreover, when coating before extending | stretching, the thickness of an application layer can also be changed with a draw ratio, and compared with offline coating, thin film coating can be performed more easily. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

  In the present invention, the polyester film has a coating layer containing polyvinyl alcohol and an isocyanate compound (hereinafter sometimes abbreviated as a first coating layer) on one surface of the polyester film, and on the other surface of the polyester film. And having an application layer whose absolute reflectance has a minimum value in a wavelength range of 300 to 800 nm and whose minimum value is 3.5% or less (hereinafter, may be abbreviated as a second application layer). Is an essential requirement.

  The first coating layer of the film of the present invention is a coating layer for improving adhesiveness with various functional layers. For example, various adhesives used for bonding the polarizing film and the laminated polyester film of the present invention together. It can be used to improve the adhesion with the agent.

  The inventors of the present invention have studied polyester resins for improving the adhesion to the polyester film and polyvinyl alcohol for improving the adhesion to the adhesive layer. There was no adhesion. Moreover, although the coating layer by the combination of a polyester resin and polyvinyl alcohol was also examined, the big improvement in adhesiveness was not seen. Furthermore, when the combination of various materials was examined, it was possible to improve the adhesiveness by combining the polyvinyl alcohol and the isocyanate compound, and by devising the composition ratio, and the coating layer having adhesiveness for protecting the polarizing film Succeeded in forming. Furthermore, it has also been found that the adhesiveness is greatly improved by combining a polyester resin.

  The polyvinyl alcohol contained in the first coating layer of the film of the present invention has a polyvinyl alcohol moiety, and includes, for example, modified compounds partially acetalized or butyralized with respect to polyvinyl alcohol. Known polyvinyl alcohol can be used. The degree of polymerization of polyvinyl alcohol is not particularly limited, but is usually 100 or more, preferably 300 to 40,000. When the degree of polymerization is less than 100, the water resistance of the coating layer may decrease. Moreover, the saponification degree of polyvinyl alcohol is not particularly limited, but a polyvinyl acetate saponified product in a range of 70 mol% or more, preferably 70 to 99.9 mol% is practically used.

  The isocyanate compound contained in the first coating layer of the film of the present invention is a compound derived from an isocyanate derivative represented by isocyanate or blocked isocyanate. Examples of isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate, and aromatic rings such as α, α, α ′, α′-tetramethylxylylene diisocyanate. Aliphatic isocyanates such as aliphatic isocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis (4-cyclohexyl isocyanate), isopropylidene dicyclohexyl diisocyanate Ne Alicyclic isocyanates such as bets are exemplified. Further, polymers and derivatives such as burettes, isocyanurates, uretdiones, and carbodiimide modified products of these isocyanates are also included. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to avoid yellowing due to ultraviolet rays.

  When used in the state of blocked isocyanate, the blocking agent includes, for example, bisulfites, phenolic compounds such as phenol, cresol, and ethylphenol, and alcohols such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol. Compounds, active methylene compounds such as dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate and acetylacetone, mercaptan compounds such as butyl mercaptan and dodecyl mercaptan, lactam compounds such as ε-caprolactam and δ-valerolactam , Amine compounds such as diphenylaniline, aniline, ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, formaldehyde, acetoald Examples include oxime compounds such as oxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

  In addition, the isocyanate compound in the present invention may be used alone or as a mixture or bond with various polymers. In the sense of improving the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or a bond with a polyester resin or a urethane resin.

  It is preferable to use a polyester resin in combination with the first coating layer of the present invention in order to improve adhesion.

  The polyester resin that can be contained in the first coating layer in the present invention comprises, for example, the following polyvalent carboxylic acid and polyvalent hydroxy compound as main constituent components. That is, as the polyvalent carboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4′-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 2,6 -Naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid , Trimellitic anhydride, pyromellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt and ester-forming derivatives thereof can be used. 1,2-propylene glycol, 1 3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexane Dimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetra Methylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, potassium dimethylolpropionate and the like can be used. One or more compounds may be appropriately selected from these compounds, and a polyester resin may be synthesized by a conventional polycondensation reaction.

  When the polyester resin is used after being dispersed in water, a hydrophilic functional group is generally contained in the polyester resin. Examples of the hydrophilic functional group include a carboxylic acid group and a sulfonic acid group. A dispersion with a carboxylic acid group is preferable in terms of improving adhesiveness.

  The content of polyvinyl alcohol in the first coating layer of the present invention is usually 10 to 80% by weight, preferably 15 to 60% by weight, and more preferably 20 to 50% by weight. If it is less than 10% by weight, the adhesiveness with the adhesive layer may not be sufficient due to a small amount of the polyvinyl alcohol component, and if it exceeds 80% by weight, it may be in close contact with the polyester film due to a small amount of other components. Sexuality may not be sufficient.

  The content of the isocyanate compound in the first coating layer of the present invention is usually 10 to 80% by weight, preferably 15 to 60% by weight, and more preferably 20 to 40% by weight. When the amount is less than 10% by weight, the coating layer becomes brittle due to a small amount of the crosslinking component, and the heat-and-moisture resistance may be lowered. When the amount exceeds 80% by weight, the other component is small, and the adhesion to the polyester film is reduced. And adhesiveness with the adhesive layer may not be sufficient.

  The content of the polyester resin that can be contained in the first coating layer of the film of the present invention is preferably 80% by weight or less, more preferably 15 to 65% by weight, and further preferably 20 to 40% by weight.

  The weight ratio of polyvinyl alcohol: isocyanate compound contained in the first coating layer of the present invention is usually in the range of 1.0 to 8.0: 1.0 to 8.0, preferably 1.0 to 4.0: It is 1.0-4.0, More preferably, it is the range of 1.0-2.5: 1.0-2.5.

  In the first coating layer in the film of the present invention, a polymer other than a polyester resin or polyvinyl alcohol can be used in combination in order to improve the coating surface state and transparency.

  Specific examples of the polymer include acrylic resin, urethane resin, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches.

  Furthermore, a crosslinking agent other than the isocyanate compound can be used in combination in the first coating layer within the range not impairing the gist of the present invention. Various known compounds can be used as the crosslinking agent, and examples thereof include oxazoline compounds, melamine compounds, epoxy compounds, carbodiimide compounds, and the like.

  An oxazoline compound is a compound having an oxazoline group in the molecule. In particular, a polymer containing an oxazoline group is preferable, and it can be prepared by polymerization of an addition polymerizable oxazoline group-containing monomer alone or with another monomer. Addition polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not limited as long as it is a monomer copolymerizable with an addition polymerizable oxazoline group-containing monomer. For example, alkyl (meth) acrylate (the alkyl group includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, (meth) acrylic acid esters such as n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene Unsaturated carboxylic acids such as sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile, methacrylonitrile; (meth) acrylamide, N-alkyl ( (Meth) acrylamide, N, N-dialkyl (meth) acrylamide, As the alkyl group, unsaturated amides such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group and cyclohexyl group); vinyl acetate Vinyl esters such as vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α, β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride And α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and the like, and one or more of these monomers can be used.

  The melamine compound is a compound having a melamine skeleton in the compound. For example, an alkylolated melamine derivative, a compound partially or completely etherified by reacting an alcohol with an alkylolated melamine derivative, and a mixture thereof can be used. As alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used. Moreover, as a melamine compound, either a monomer or a multimer more than a dimer may be sufficient, or a mixture thereof may be used. Further, a product obtained by co-condensing urea or the like with a part of melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

  Examples of the epoxy compound include a compound containing an epoxy group in the molecule, a prepolymer and a cured product thereof. Examples include condensates of epichlorohydrin with hydroxyl groups and amino groups such as ethylene glycol, polyethylene glycol, glycerin, polyglycerin, and bisphenol A, and polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like. is there. Examples of the polyepoxy compound include sorbitol, polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylol. Examples of the propane polyglycidyl ether and diepoxy compound include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether. Ether, polypropylene glycol diglycidyl ether, Ritetramethylene glycol diglycidyl ether and monoepoxy compounds include, for example, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl amine compounds such as N, N, N ′, N ′,-tetraglycidyl-m. -Xylylenediamine, 1,3-bis (N, N-diglycidylamino) cyclohexane and the like.

  These cross-linking agents preferably have water solubility or water dispersibility in consideration of application to in-line coating.

  Further, the first coating layer preferably contains particles for the purpose of improving the blocking property and slipperiness of the coating layer, and the average particle size is preferably in the range of 1 μm or less from the viewpoint of the transparency of the film. Is 0.7 μm or less, more preferably 0.2 μm or less. From the viewpoint of blocking properties and slipperiness, the average particle size is preferably in the range of 0.01 μm or more, more preferably in the range of 0.03 μm or more, and still more preferably in the range of 0.05 μm or more. Specific examples of the particles include silica, alumina, kaolin, calcium carbonate, titanium oxide, and organic particles. Among them, silica is particularly preferable. The content of the particles in the coating layer depends on the average particle diameter, but is preferably in the range of 0.1 to 30% by weight, more preferably in the range of 0.5 to 10% by weight, and further preferably 1 to 6%. It is in the range of wt%.

  The second coating layer of the film of the present invention is designed to have a low reflectance, and when used as a protective film on the rear surface side of the rear surface side polarizing plate, to improve the total light transmittance when the polarizing plate is used. It is a coating layer that can be applied. The total light transmittance of the laminated polyester film is based on the optical characteristics of the polyester film, the first coating layer, and the second coating layer. Since the characteristic does not greatly contribute to the total light transmittance of the entire polarizing plate, the most important optical characteristic is the side not bonded to the polarizing film, that is, the second coating layer side. As the total light transmittance of the laminated polyester film, there is also an influence of the first coating layer, so it cannot be accurately discussed, but in general, it is 90.0% or more, preferably 90.5% or more, more preferably It is 91.0% or more.

  As a result of various investigations in order to grasp the optical characteristics of only the second coating layer more accurately and consider the total light transmittance when the polarizing plate is used, consider the absolute reflectance of only the second coating layer. Turned out to be important. It was noted that the reflectance and the transmittance are mutually related characteristics, and in general, a polyester film having high light transparency and low transparency exhibits high reflectance with low reflectance.

  In the present invention, in order to increase the total light transmittance when a polarizing plate is used, the second coating layer has one minimum value in the range of the wavelength of 300 to 800 nm in absolute reflectance, and the minimum value is It is essential that it is 3.5% or less. More preferable conditions for the minimum wavelength are in the range of 400 to 700 nm, and more preferably in the range of 450 to 650 nm. The minimum value is preferably 3.0% or less, and more preferably 2.5% or less.

  When the absolute reflectance of the second coating layer of the laminated polyester film does not satisfy the above conditions, the total light transmittance is reduced when the polarizing plate is used, thereby lowering the luminance of the polarizing plate, resulting in a liquid crystal display. The screen becomes darker.

  Acrylic resin and urethane resin generally have a low refractive index, so that they are suitable for achieving the absolute reflectance as described above, that is, for increasing the total light transmittance when a polarizing plate is used. The material is effective for forming the second coating layer in the present invention. Moreover, the total light transmittance can be more effectively improved by controlling the film thickness in the range of 0.04 to 0.15 μm.

  The acrylic resin is a polymer composed of a polymerizable monomer having a carbon-carbon double bond, as typified by acrylic and methacrylic monomers. These may be either a homopolymer or a copolymer. Moreover, the copolymer of these polymers and other polymers (for example, polyester, polyurethane, etc.) is also included. For example, a block copolymer or a graft copolymer. Alternatively, a polymer (possibly a mixture of polymers) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyester solution or a polyester dispersion is also included. Similarly, a polymer (in some cases, a mixture of polymers) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyurethane solution or polyurethane dispersion is also included. Similarly, a polymer obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in another polymer solution or dispersion (in some cases, a polymer mixture) is also included. In order to improve the total light transmittance more efficiently, it is also possible to use a fluorine atom-containing compound having a low refractive index.

  The polymerizable monomer having a carbon-carbon double bond is not particularly limited, but particularly representative compounds include, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, citracone. Various carboxyl group-containing monomers such as acids, and salts thereof; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutyl hydroxyl fumarate, Various hydroxyl group-containing monomers such as monobutylhydroxy itaconate; various monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate ( (Meth) acrylic acid esters; Various nitrogen-containing compounds such as meth) acrylamide, diacetone acrylamide, N-methylol acrylamide or (meth) acrylonitrile; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, vinyl acetate, propion Various vinyl esters such as vinyl acid; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, etc .; phosphorus-containing vinyl monomers; vinyl chloride, biliden chloride, Various vinyl halides such as vinyl fluoride, vinylidene fluoride, trifluorochloroethylene, tetrafluoroethylene, chlorotrifluoroethylene and hexafluoropropylene; various conjugated dienes such as butadiene That.

  A urethane resin is a high molecular compound which has a urethane resin in a molecule | numerator. Usually, urethane resin is prepared by reaction of polyol and isocyanate. Examples of the polyol include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

  Polycarbonate polyols are obtained from a polyhydric alcohol and a carbonate compound by a dealcoholization reaction. Examples of the polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane. Diol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decane Diol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like can be mentioned. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate. Examples of polycarbonate polyols obtained from these reactions include poly (1,6-hexylene) carbonate, poly (3- And methyl-1,5-pentylene) carbonate.

  Polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides. Product and polyhydric alcohol (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol 2-methyl-2-propyl-1 3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexane Diol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyl dialkanolamine, lactone diol, etc.).

  Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and the like.

  Examples of the polyisocyanate compound used to obtain the urethane resin include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate, α, α, α ′, α ′. -Aliphatic diisocyanates with aromatic rings such as tetramethylxylylene diisocyanate, aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl Methanzi Cyanate, alicyclic diisocyanates such as isopropylidene dicyclohexyl diisocyanates. These may be used alone or in combination.

  A chain extender may be used when synthesizing the urethane resin, and the chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group. Alternatively, a chain extender having two amino groups can be mainly used.

  Examples of the chain extender having two hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol and butanediol, aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene, and esters such as neopentyl glycol hydroxypivalate. And glycols such as glycols. Examples of the chain extender having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine, ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3- Propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10- Aliphatic diamines such as decane diamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isoprobilitincyclohexyl-4,4′-diamine, 1,4-diaminocyclohexane, 1 , 3-Bisaminomethylcyclohexa And alicyclic diamines such as

The urethane resin used in the present invention may use a solvent as a medium, but preferably uses water as a medium. In order to disperse or dissolve the urethane resin in water, there are a forced emulsification type using an emulsifier, a self-emulsification type in which a hydrophilic group is introduced into the urethane resin, and a water-soluble type. In particular, a self-emulsification type in which an ionic group is introduced into the skeleton of a urethane resin to form an ionomer is preferable because of excellent storage stability of the liquid and water resistance, transparency, and adhesion of the resulting coating layer. Examples of the ionic group to be introduced include various groups such as a carboxyl group, sulfonic acid, phosphoric acid, phosphonic acid, quaternary ammonium salt, and the like, and a carboxyl group is preferable. As a method for introducing a carboxyl group into a urethane resin, various methods can be taken in each stage of the polymerization reaction. For example, there are a method of using a carboxyl group-containing resin as a copolymer component during prepolymer synthesis, and a method of using a component having a carboxyl group as one component such as polyol, polyisocyanate, and chain extender. In particular, a method in which a desired amount of carboxyl groups is introduced using a carboxyl group-containing diol depending on the amount of this component charged.
For example, dimethylolpropionic acid, dimethylolbutanoic acid, bis- (2-hydroxyethyl) propionic acid, bis- (2-hydroxyethyl) butanoic acid, etc. are copolymerized with a diol used for polymerization of urethane resin. Can do. The carboxyl group is preferably in the form of a salt neutralized with ammonia, amine, alkali metal, inorganic alkali or the like. Particularly preferred are ammonia, trimethylamine and triethylamine. In such a polyurethane resin, a carboxyl group from which the neutralizing agent has been removed in the drying step after coating can be used as a crosslinking reaction point by another crosslinking agent. Thereby, it is possible to further improve the durability, solvent resistance, water resistance, blocking resistance, and the like of the obtained coating layer, as well as excellent stability in a liquid state before coating.

  In the film of the present invention, the content of the acrylic resin or the urethane resin in the second coating layer cannot be unconditionally discussed because it depends on the refractive index of the acrylic resin or the urethane resin, but preferably 40% by weight or more. More preferably, it is the range of 50 weight% or more, More preferably, it is the range of 60 weight% or more. If it is less than 40% by weight, the total light transmittance may not be sufficiently improved.

  In the second coating layer in the film of the present invention, a polymer other than an acrylic resin or a urethane resin can be used in combination in order to improve the coating surface state and transparency. As the polymer used in combination, it is preferable not to use many polymers having a high refractive index in consideration of the influence on the total light transmittance.

  Specific examples of the polymer include polyester resin, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches and the like.

  Furthermore, it is also possible to use a crosslinking agent in the second coating layer as long as the gist of the present invention is not impaired. By using a cross-linking agent, the coating layer becomes strong, so that the heat and moisture resistance and the scratch resistance may be further improved. Examples of the crosslinking agent include melamine compounds, epoxy compounds, oxazoline compounds, isocyanate compounds, carbodiimide compounds, and the like. These cross-linking agents may be used alone or in combination of two or more. Furthermore, when consideration is given to application to in-line coating, it is preferable to have water solubility or water dispersibility.

  Further, the second coating layer may contain particles for the purpose of improving the blocking property and slipperiness of the coating layer, and the same particles as those used in the first coating layer can be used.

  Furthermore, as long as the gist of the present invention is not impaired, the first coating layer and the second coating layer have an antifoaming agent, coating property improving agent, thickening agent, organic lubricant, antistatic agent, ultraviolet absorption as necessary. Agents, antioxidants, foaming agents, dyes, pigments and the like may be contained.

  Analysis of various components in the coating layer can be performed by surface analysis such as TOF-SIMS.

  When providing a coating layer by in-line coating, the above-mentioned series of compounds is applied as an aqueous solution or dispersion, and the coating solution adjusted to a solid content concentration of about 0.1 to 50% by weight as a guide is applied onto the polyester film. It is preferable to produce a laminated polyester film. Moreover, in the range which does not impair the main point of this invention, a small amount of organic solvents may be contained in the coating liquid for the purpose of improving dispersibility in water, improving film-forming properties, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

  The thickness of the first coating layer of the laminated polyester film in the present invention is usually in the range of 0.002 to 1.0 μm, more preferably 0.03 to 0.5 μm, and still more preferably 0.04 to 0.2 μm. . If the film thickness is less than 0.002 μm, sufficient adhesion may not be obtained, and if it exceeds 1.0 μm, the appearance, transparency, and film blocking properties may be deteriorated.

  The film thickness of the second coating layer of the laminated polyester film in the present invention is usually in the range of 0.04 to 0.15 μm, more preferably in the range of 0.06 to 0.13 μm. Since it depends on the refractive index of the coating layer, it cannot be said unconditionally. However, when the film thickness is out of this range, a high total light transmittance may not be obtained when a polarizing plate is used.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used.

  In the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 3 to 40 at 80 to 200 ° C. The heat treatment may be performed for 2 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds.

  On the other hand, when the coating layer is provided by in-line coating, heat treatment is usually performed at 70 to 280 ° C. for 3 to 200 seconds as a guide.

  Further, irrespective of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as required. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  When the laminated polyester film of the present invention is used as, for example, a protective film for a polarizing film in a polarizing plate, generally, the polarizing film is bonded to the first coating layer via an adhesive for adhering the polarizing film. . As the adhesive, conventionally known ones can be used, for example, acrylic compounds such as polyvinyl alcohol, polyvinyl butyral and polybutyl acrylate, and epoxy having an alicyclic epoxy group exemplified by glycidyl group and epoxycyclohexane. System compounds and the like.

  On the prepared adhesive layer, for example, polyvinyl alcohol that is uniaxially stretched and dyed with iodine or the like is bonded as a polarizing film. A protective film, a retardation film, or the like can be bonded to the opposite side of the polarizing film to form a polarizing plate. That is, when the laminated polyester film of the present invention is used for a polarizing plate, the layer configuration exemplified above is protective film / polarizing film / adhesive / first coating layer / polyester film / second coating layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement method and evaluation method used in the present invention are as follows.

(1) Measuring method of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. And dissolved at 30 ° C.

(2) Measuring method of average particle size (d ₅₀ : μm) Integration (weight basis) 50 in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type, manufactured by Shimadzu Corporation) % Was defined as the average particle size.

(3) Method for measuring film thickness of coating layer The surface of the coating layer was dyed with RuO ₄ and embedded in an epoxy resin. Thereafter, the section prepared by ultramicrotomy stained with RuO _4, a coating layer cross-section was measured by using a TEM (Hitachi Ltd. H-7650, accelerating voltage 100 V).

(4) Adhesive evaluation method A 5% by weight aqueous solution of polyvinyl alcohol having a polymerization degree of 1000 and a saponification degree of 98.5 mol% as an adhesive was applied to the first coating layer surface of the laminated polyester film so that the dry film thickness was 2 μm. It dried and it was set as the adhesive bond layer. A tape of 18 mm width (Cellotape (registered trademark), Elpac (registered trademark) LP-18, manufactured by Nichiban Co., Ltd.) is pasted on the adhesive layer, peeled off rapidly at a peeling angle of 180 degrees, and then peeled off. The surface was observed. If the peeled area was 5% or less, ◎ if over 5% and 20% or less, ○, if over 20% and 50% or less, Δ, if over 50%, x.

(5) Method of measuring the absolute reflectance minimum value from the surface of the second coating layer in the polyester film In advance, a black tape (vinyl tape VT-50 manufactured by Nichiban Co., Ltd.) is applied to the measurement back surface (first coating layer surface) of the polyester film. , Using a spectrophotometer (UV-spectrophotometer V-570 and automatic absolute reflectance measuring device AM-500N manufactured by JASCO Corporation), synchronous mode, incident angle 5 °, N-polarization, response Fast, data collection The absolute reflectance in the wavelength range of 300 to 800 nm was measured on the coating layer surface at an interval of 1.0 nm, a bandwidth of 10 nm, and a scanning speed of 1000 m / min, and the wavelength (bottom wavelength) and absolute reflectance at the minimum value were evaluated.

(6) Measuring method of total light transmittance It measured by JIS K 7361 using Murakami Color Research Laboratory make haze meter HM-150.

(7) Evaluation method of total light transmittance when made into polarizing plate On the first coating layer surface side of the laminated polyester film, a 5% by weight aqueous solution of polyvinyl alcohol having a polymerization degree of 1000 and a saponification degree of 98.5 mol% was applied. A polarizing film of polyvinyl alcohol-iodine was bonded using a roll machine and dried at 70 ° C. for 4 minutes to obtain a polarizing plate. On the other hand, as a reference, a polarizing plate was prepared in the same manner for a triacetyl cellulose film (TAC film). In the prepared polarizing plate, the total light transmittance was measured according to JIS K 7361 using a haze meter HM-150 manufactured by Murakami Color Research Laboratory, and the total light transmittance of the polarizing plate formed from the laminated polyester film was evaluated. did. That is, compared with the total light transmittance of the polarizing plate formed from the TAC film, when the reduction amount is 1% or less, the case where the reduction amount exceeds 1% and there is a concern about the reduction of the brightness. It was.

(8) Measurement of transmittance at a wavelength of 380 nm Using a spectrophotometer (UV-3100PC type manufactured by Shimadzu Corporation), the light transmittance is continuously measured in a scanning speed of a low speed, a sampling pitch of 2 nm, and a wavelength of 300 to 700 nm. The light transmittance at a wavelength of 380 nm was detected.

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part by weight of ethyl acid phosphate to this reaction mixture, 0.04 part by weight of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.63.

<Method for producing polyester (B)>
In the method for producing polyester (A), after adding 0.04 part by weight of ethyl acid phosphate, 0.2 part by weight of silica particles dispersed in ethylene glycol having an average particle diameter of 2 μm and 0.04 part by weight of antimony trioxide And polyester (B) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.65. The obtained polyester (B) had an intrinsic viscosity of 0.65.

<Method for producing polyester (C)>
Polyester (A) is subjected to a vented twin screw extruder and 2,2 ′-(1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] (manufactured by CYTEC Co., Ltd.) as an ultraviolet absorber. CYASORB UV-3638 (molecular weight 369 benzoxazinone type) was supplied to a concentration of 10% by weight and melt-kneaded to form chips, thereby preparing an ultraviolet absorber master batch polyester (C). The intrinsic viscosity of the obtained polyester (C) was 0.59.

Examples of compounds constituting the coating layer are as follows.
(Compound example)
・ Polyvinyl alcohol: (I)
Polyvinyl alcohol having a saponification degree of 88 mol% and a polymerization degree of 500

・ Isocyanate compounds: (II)
33.6 parts by weight of hexamethylene diisocyanate was added to 200 parts by weight of a polyester (molecular weight 2000) of bisphenol A ethylene oxide 2 mol adduct and maleic acid, and reacted at 100 ° C. for 2 hours. Next, the blocked isocyanate compound diluted with 718 parts by weight of water after the temperature of the system was once lowered to 50 ° C, 73 parts by weight of a 30% aqueous sodium bisulfite solution was added and stirred at 45 ° C for 60 minutes.

・ Polyester resin: (IIIA)
Carboxylic acid aqueous dispersion monomer composition of polyester resin copolymerized with the following composition: (acid component) isophthalic acid / trimellitic acid // (diol component) diethylene glycol / neopentyl glycol = 96/4 // 80/20 (mol %)
・ Polyester resin: (IIIB)
Carboxylic acid aqueous dispersion monomer composition of polyester resin copolymerized with the following composition: (acid component) terephthalic acid / isophthalic acid // (diol component) ethylene glycol / diethylene glycol / neopentyl glycol / dimethylolpropionic acid = 20/80 /// 16/64/12/8 (mol%)
・ Polyester resin: (IIIC)
Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / 1,4-butanediol / Diethylene glycol = 56/40/4 // 70/20/10 (mol%)

Acrylic resin: (IV) Acrylic resin aqueous dispersion polymerized with the following composition: ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylol acrylamide / acrylic acid = 65/21/10/2/2 (% by weight) Emulsion polymer (emulsifier: anionic surfactant)

-Urethane resin: (V)
Hydran AP-40 (manufactured by DIC), which is a water-dispersible polyester polyurethane resin

Melamine compound: (VIA) hexamethoxymethyl melamine Epoxy compound: (VIB) Denacol EX-521 (manufactured by Nagase ChemteX), which is polyglycerol polyglycidyl ether.
-Particles: (VII) silica sol with an average particle size of 65 nm

Example 1:
A mixed raw material obtained by mixing polyester (A) and (B) at a ratio of 90% and 10%, respectively, is used as a raw material for the outermost layer (surface layer), and polyesters (A) and (C) are at a ratio of 85% and 15%, respectively. Each of the mixed raw materials is fed to two extruders as a raw material for the intermediate layer, melted at 285 ° C., and then two types and three layers (surface layer / intermediate layer / The unstretched sheet was obtained by coextrusion and cooling and solidification in the layer structure of the surface layer. Next, the film was stretched 3.4 times in the machine direction at a film temperature of 85 ° C. using the roll peripheral speed difference, and then the coating liquid A1 shown in Table 1 below was applied to one side of the longitudinally stretched film (first coating layer). The coating liquid B1 shown in Table 2 below is applied to the opposite surface (formation of the second coating layer), led to a tenter, stretched 4.3 times at 120 ° C in the transverse direction, and heat-treated at 225 ° C. Thereafter, the polyester is loosened by 2% in the lateral direction and has a thickness of 38 μm (surface layer: 4 μm, intermediate layer: 30 μm) having a first coating layer of 0.05 μm and a second coating layer of 0.10 μm (after drying). A film was obtained. When the obtained polyester film was evaluated, the adhesiveness of the first coating layer was good, the minimum absolute reflectance of the second coating layer was kept as low as 2.5%, and the transmittance at 380 nm was 4%. It was confirmed that it absorbs ultraviolet rays. The properties of this film are shown in Table 3 below.

Examples 2 to 17:
In Example 1, it manufactured like Example 1 except having changed the coating composition into the coating composition shown in Table 1 and Table 2, and obtained the polyester film. The finished polyester film was as shown in Table 3.

Example 18:
A mixed raw material obtained by mixing polyester (A) and (B) at a ratio of 90% and 10%, respectively, is used as a raw material for the outermost layer (surface layer), and polyesters (A) and (C) are at a ratio of 80% and 20%, respectively. A polyester film was obtained in the same manner as in Example 1 except that the mixed raw material was used as a raw material for the intermediate layer. The completed polyester film is as shown in Table 3. Further, the transmittance at 380 nm was 1%, and it was confirmed that ultraviolet rays were absorbed.

Example 19:
A mixed raw material in which polyesters (A) and (B) are mixed at a ratio of 90% and 10%, respectively, is used as a raw material for the outermost layer (surface layer), and polyesters (A) and (C) are respectively at a ratio of 90% and 10%. A polyester film was obtained in the same manner as in Example 1 except that the mixed raw material was used as a raw material for the intermediate layer. The completed polyester film is as shown in Table 3. Further, the transmittance at 380 nm was 9%, and it was confirmed that ultraviolet rays were absorbed.

Example 20:
Example 1 except that a mixed raw material in which polyesters (A) and (B) are mixed at a ratio of 90% and 10%, respectively, is used as a raw material for the outermost layer (surface layer) and polyester (A) is used as a raw material for the intermediate layer. In the same manner, a polyester film was obtained. The finished polyester film was as shown in Table 3.

Comparative Examples 1-10:
In Example 1, it manufactured like Example 1 except having changed the coating composition into the coating composition shown in Table 1 and Table 2, and obtained the polyester film. When the completed laminated polyester film was evaluated, it was as shown in Table 4, and it was as shown in Table 4 that the adhesiveness was weak, the minimum value of the reflectance was not seen, or the minimum value of the reflectance was high.

  The polarizing plate of the present invention can be suitably used for applications that require high total light transmittance, such as a polarizing film used in a liquid crystal display.

Claims (7)

Having a coating layer formed from a coating solution containing polyvinyl alcohol and an isocyanate compound directly on one side of the polyester film, having a polarizing film on the coating layer side of the polyester film, the coating layer and the polarization An adhesive layer is provided between the film and the polarizing film is a polyvinyl alcohol-iodine polarizing film, provided that the content of the self-crosslinkable polyurethane resin in all the resin constituents in the coating layer is 50% by weight. A polarizing plate, excluding the case where it is at least%. The polarizing plate of claim 1 having a coating layer on the polyester film surface on the opposite side to the polyvinyl alcohol and an isocyanate-based compound coating layer formed from a coating solution containing a. The coating layer of the polyester film surface opposite to the coating layer formed from the coating solution containing polyvinyl alcohol and an isocyanate compound has one minimum value in the wavelength range of 300 to 800 nm in absolute reflectance, The polarizing plate according to claim 2 , wherein the minimum value is 3.5% or less. The polarizing plate according to any one of claims 1 to 3 , wherein the saponification degree of polyvinyl alcohol is 70 mol% or more. The polarization ratio according to any one of claims 1 to 4 , wherein a weight ratio of polyvinyl alcohol to an isocyanate compound in all nonvolatile components in the coating solution is in the range of 1.0 to 8.0: 1.0 to 8.0. Board. The polarizing plate according to any one of claims 1 to 5 , wherein the coating liquid contains a polyester resin. The polarizing plate according to claim 6 , wherein the polyester resin in the coating solution contains a hydrophilic functional group.