JP6717342B2 - Polarizer - Google Patents

Description

The present invention relates to a polarizing plate, and particularly to a polarizing plate used for 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 configuration of front side polarizing plate//liquid crystal//rear side polarizing plate when the display side is the front side and the opposite side (backlight side) is the rear side. The polarizing plate usually has a structure in which a protective film or the like is attached to a polarizing film of a polyvinyl alcohol film that has been dyed uniaxially stretched (protective film/polarizing film/protective film). Protective films arranged on the front side and the rear side of the polarizing film constituting the front-side polarizing plate are protective film A and protective film B, respectively, and protection arranged on the front side and the rear side of the polarizing film constituting the rear-side polarizing plate. Assuming that the films are protective film C and protective film D, respectively, the overall structure is from the front side to protective film A/front side polarizing film/protective film B//liquid crystal//protective film C/rear side polarizing film/protection. It becomes film D.

As a 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 has a drawback that it is inferior in dimensional stability and resistance to moist heat, and that the surface must be saponified with an alkaline solution in advance in order to adhere it to the polarizing film. As the size and quality of liquid crystal displays have increased in recent years, it has been required to improve mechanical strength and stability under high temperature and high humidity environment. Also, due to alkali treatment, bleed-out and haze increase of low molecular weight materials may occur. There is a need to avoid quality deterioration. Furthermore, since the above-mentioned alkali treatment uses a high-concentration alkali 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-based film, have been studied (Patent Documents 1 and 2). However, since films made of other materials do not use general-purpose resins, there is a problem of high cost. Therefore, there has been proposed a method of using a polyester film which is a general-purpose resin, which can secure dimensional stability, does not require an alkali treatment step having various problems, and has no cost problem.

However, the polyester film alone has poor adhesiveness with the adhesive used for adhering the polarizing film and the protective film, and has a lower total light transmittance as compared with the TAC film, so that it is used as a polarizing plate. There is a drawback that the brightness sometimes decreases. In order to improve the adhesiveness of the polyester film, a structure in which an anchor layer is provided is also proposed, but there is no specific disclosure, and it is difficult to secure sufficient adhesiveness depending on the adhesive. (Patent Documents 3 to 5).

JP, 6-511117, A JP, 2006-227090, A JP, 2002-116320, A Japanese Unexamined Patent Publication No. 8-271733 Japanese Patent Laid-Open No. 8-271734

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

The present inventors have conducted intensive studies in view of the above circumstances, and as a result, have found that the above problems can be easily solved by using a laminated polyester film having a specific structure, and have completed the present invention.

That is, the gist of the present invention lies in a polarizing plate characterized by having a coating layer containing polyvinyl alcohol and an isocyanate compound on one surface of a polyester film, and having a polarizing film on the coating layer side.

According to the present invention, for example, when used as a protective film of a polarizing plate, particularly as a protective film on the rear surface side of a rear surface side polarizing plate, the adhesive force with an adhesive for adhering a polarizing film is good, and the polarizing plate. It is possible to provide a polarizing plate using a laminated polyester film which is excellent in the total light transmittance after forming the film, and its industrial value is high.

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

The polyester used in the present invention may be a homopolyester or a copolyester. When it is made of homopolyester, it is preferably obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol. 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. Polyethylene terephthalate etc. are illustrated as a typical polyester. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, p-oxybenzoic acid). One kind or two or more kinds may be mentioned, and the glycol component may be one kind or two or more kinds such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, neopentyl glycol.

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 an 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, and the organic ultraviolet absorber is preferable from the viewpoint of transparency. The organic ultraviolet absorber is not particularly limited, and examples thereof include benzotriazole type, cyclic iminoester type, and benzophenone type. From the viewpoint of durability, benzotriazole type and cyclic iminoester type are more preferable. It is also possible to use two or more kinds of ultraviolet absorbers in combination.

The benzotriazole-based ultraviolet absorber is not limited to the following, but for example, 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'-(methacryloyloxyethyl)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'-(methacryloyloxy Ethyl)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 can be mentioned.

The cyclic iminoester-based ultraviolet absorber is not limited to the following, and examples thereof include 2-methyl-3,1-benzoxazin-4-one and 2-butyl-3,1-benzoxazine-4. -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, 2 -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-on-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'-decamethylene bis(3,1-benzoxazin-4-one, 2,2'-p-phenylene bis(3,1-benzoxazin-4-one), 2,2'-m-phenylene bis( 3,1-benzoxazin-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-benzoxazine-4 -On), 2,2'-(1,4-cyclohexylene)bis(3,1-benzoo Xazin-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-benzoxazin-4-one), 6,6'-bis(2 -Phenyl-4H,3,1-benzoxazin-4-one), 6,6'-methylenebis(2-methyl-4H,3,1-benzoxazin-4-one), 6,6'-methylenebis(2 -Phenyl-4H,3,1-benzoxazin-4-one), 6,6'-ethylenebis(2-methyl-4H,3,1-benzoxazin-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 '-Carbonylbis(2-phenyl-4H,3,1-benzoxazin-4-one), 7,7'-methylenebis(2-methyl-4H,3,1-benzoxazin-4-one), 7, 7'-methylenebis(2-phenyl-4) H,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′-methylenebis(2-phenyl-4H,3,1-benzoxazin-4-one) and the like.

Among the above compounds, in consideration of the color tone, a benzoxazinone-based compound that does not easily give a yellow tint is preferably used, and as an example thereof, a compound represented by the following general formula (1) is more preferably used. To be

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 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 the ultraviolet absorber is contained in an amount of more than 10.0% by weight, the ultraviolet absorber may bleed out on the surface, which may lead to deterioration of surface functionality such as decrease in adhesiveness.

In addition, in the case of a film having a multi-layer structure, a film having at least a three-layer structure is preferable, and the ultraviolet absorber is preferably blended in the intermediate layer. By blending the ultraviolet absorber in the intermediate layer, it is possible to prevent the compound from bleeding out to the film surface, and as a result, it is possible to maintain characteristics such as adhesiveness of the film.

When used as a protective film for a polarizing film, if the laminated polyester film of the present invention prevents deterioration of liquid crystal due to ultraviolet rays, as a guide, 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-mentioned ultraviolet absorber.

In the polyester layer of the film of the present invention, particles are preferably blended mainly for the purpose of imparting slipperiness and preventing scratches in each step. The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting lubricity, and specific examples include, for example, silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, phosphoric acid. Examples thereof 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, during the polyester production process, precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed can be used.

On the other hand, the shape of the particles to be used is not particularly limited, and may be spherical, lumpy, rod-shaped, flattened, or the like. Further, the hardness, specific gravity, color, etc. are not particularly limited. Two or more kinds of these series of particles may be used in combination, if necessary.

The average particle size of the particles used is usually 0.01 to 5 μm, preferably 0.1 to 3 μm. If the average particle size is less than 0.01 μm, slipperiness may not be sufficiently imparted, or particles may aggregate to cause insufficient dispersibility, resulting in deterioration of transparency of the film. On the other hand, when it exceeds 5 μm, the surface roughness of the film becomes too rough, which may cause a problem in a post process.

Further, the content of particles in the polyester layer is usually 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, while when added in excess of 5% by weight, the transparency of the film is insufficient. There are cases.

The method of 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 of producing the polyester constituting each layer, but it is preferably added after the completion of the esterification or transesterification reaction.

Further, a method of blending a slurry of particles dispersed in ethylene glycol or water with a polyester raw material using a kneading extruder with a vent, or a method of blending dried particles and a polyester raw material using a kneading extruder. It is performed by the method.

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

The thickness of the polyester film in the present invention is not particularly limited as long as it can be formed into a film, but is usually 10 to 200 μm, preferably 25 to 50 μm.

Next, production examples of the polyester film in the present invention will be specifically described, but the production examples are not limited to the following production examples. That is, it is preferable to use the above-mentioned polyester raw material and obtain a non-stretched sheet by cooling and solidifying a molten sheet extruded from a die with a cooling roll. In this case, in order to improve the flatness of the sheet, it is preferable to enhance the adhesion between the sheet and the rotary cooling drum, and the electrostatic application adhesion method or the liquid application adhesion method is preferably adopted. Next, the unstretched sheet obtained is stretched biaxially. In that case, first, the unstretched sheet is stretched in one direction by a roll or 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. Then, it is stretched in a direction orthogonal to the stretching direction of the first stage, in which 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. Then, 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 stretching, it is possible to employ a method in which stretching in one direction is performed in two or more stages. In that case, it is preferable that the stretching ratios in the two directions finally fall within the above ranges.

Further, in the present invention, the simultaneous biaxial stretching method may be adopted for producing the polyester film constituting the laminated polyester film. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120° C., preferably 80 to 110° C. in a temperature controlled state at the same time. Is an area magnification of 4 to 50 times, preferably 7 to 35 times, more preferably 10 to 25 times. Then, subsequently, heat treatment is performed at a temperature of 170 to 250° C. under tension or under relaxation within 30% to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device that employs the above-described stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be adopted.

Next, the formation of the coating layer constituting the laminated polyester film in the present invention will be described. The coating layer may be provided by in-line coating, which is a treatment of the film surface during the film forming process of the polyester film, or may be off-line coating, which is applied to the once-produced film outside the system. In-line coating is preferably used because it can be applied at the same time as film formation and can be manufactured at low cost.

Although the in-line coating is not limited to the following, for example, in the sequential biaxial stretching, the coating treatment can be performed before the transverse stretching after the longitudinal stretching is completed. When a coating layer is provided on a polyester film by in-line coating, coating can be performed simultaneously with film formation, and the coating layer can be treated at a high temperature in the heat treatment step of the stretched polyester film. Performance such as adhesion to various surface functional layers that can be formed on the layer and resistance to moist heat can be improved. When coating is performed before stretching, the thickness of the coating layer can be changed by the stretching ratio, and thin film coating can be performed more easily than offline coating. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

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

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

The present inventors have studied a polyester resin for improving the adhesion with the polyester film, and polyvinyl alcohol for improving the adhesion with the adhesive layer, but in the coating layer formed by each of them, There was no adhesiveness. Further, a coating layer was examined by combining a polyester resin and polyvinyl alcohol, but no significant improvement in adhesiveness was observed. Furthermore, when a combination of various materials was examined, a coating layer having adhesiveness for protecting a polarizing film can be improved by combining polyvinyl alcohol and an isocyanate compound and devising the composition ratio thereof. Was successfully formed. Further, they have also found that the adhesiveness can be significantly improved by combining a polyester resin.

The polyvinyl alcohol contained in the first coating layer of the film of the present invention is one having a polyvinyl alcohol moiety, and for example, a modified compound which is partially acetalized or butyralized with respect to polyvinyl alcohol is conventionally used. Known polyvinyl alcohol can be used. The degree of polymerization of polyvinyl alcohol is not particularly limited, but is generally 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. Further, the saponification degree of polyvinyl alcohol is not particularly limited, but saponified polyvinyl acetate having 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 or an isocyanate derivative represented by a blocked isocyanate. As the isocyanate, for example, an aromatic isocyanate such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, or an aromatic ring such as α,α,α′,α′-tetramethylxylylene diisocyanate. Aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), isopropylidene dicyclohexyl diisocyanate, etc. And the alicyclic isocyanate of Further, polymers and derivatives of these isocyanates such as burettes, isocyanurates, uretdiones, and carbodiimide modified products are also included. These may be used alone or in combination of two or more. 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 a blocked isocyanate state, examples of the blocking agent include bisulfites, phenolic compounds such as phenol, cresol and ethylphenol, propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, alcohols such as methanol and ethanol. Compounds, dimethyl malonate, diethyl malonate, active methylene compounds such as 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, and ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, oxime compounds such as formaldehyde, acetoaldoxime, acetone oxime, methylethylketone oxime, and cyclohexanone oxime. These can be used alone. Two or more kinds may be used in combination.

Further, the isocyanate compound in the present invention may be used alone, or may be used as a mixture or a combined product with various polymers. From the standpoint of improving the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or combination of a polyester resin and a urethane resin.

A polyester resin is preferably used in combination with the first coating layer of the present invention in order to improve the adhesiveness.

The polyester resin that can be contained in the first coating layer in the present invention is composed of, 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 their ester-forming derivatives can be used, and the polyhydric hydroxy compound is ethylene glycol. 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, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, potassium dimethylolpropionate and the like can be used. One or more may be appropriately selected from these compounds, and the polyester resin may be synthesized by an ordinary polycondensation reaction.

When the polyester resin is dispersed in water and used, a hydrophilic functional group is generally contained in the polyester resin. Examples of the hydrophilic functional group include a carboxylic acid group, a sulfonic acid group, and the like, but a dispersion having a carboxylic acid group is preferable from the viewpoint 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, more preferably 20 to 50% by weight. If it is less than 10% by weight, the polyvinyl alcohol component may be insufficient, so that the adhesiveness to the adhesive layer may not be sufficient, and if it exceeds 80% by weight, the amount of other components may be small, resulting in poor adhesion to the polyester film. The sex 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, more preferably 20 to 40% by weight. If it is less than 10% by weight, the coating layer may be brittle and the moist-heat resistance may be deteriorated due to the small amount of the cross-linking component, and if it exceeds 80% by weight, the adhesion to the polyester film may be poor due to the small amount of other components. And the 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: The range is 1.0 to 4.0, and more preferably 1.0 to 2.5:1.0 to 2.5.

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

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

Further, a crosslinking agent other than the isocyanate compound may be used in combination in the first coating layer as long as the gist of the present invention is not impaired. Various known compounds can be used as the cross-linking agent, and examples thereof include an oxazoline-based compound, a melamine-based compound, an epoxy-based compound, and a carbodiimide-based compound.

The oxazoline-based compound is a compound having an oxazoline group in the molecule. Particularly, 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. The addition-polymerizable oxazoline group-containing monomer includes 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 kind or a mixture of two or more kinds thereof can be used. Among these, 2-isopropenyl-2-oxazoline is industrially easily available and suitable. The other monomer is not limited as long as it is a monomer copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include alkyl (meth)acrylate (wherein the alkyl group is 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, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group Groups, cyclohexyl groups, etc.), unsaturated amides; vinyl acetates, such as vinyl acetate and vinyl propionate; vinyl ethers, such as methyl vinyl ether and ethyl vinyl ether; α-olefins, such as ethylene and propylene; vinyl chloride, vinylidene chloride And halogen-containing α,β-unsaturated monomers such as vinyl fluoride; α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and one or more of these. Can be used.

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

Examples of epoxy compounds include compounds containing an epoxy group in the molecule, prepolymers and cured products thereof. Examples thereof include condensation products of epichlorohydrin and a hydroxyl group or an amino group such as ethylene glycol, polyethylene glycol, glycerin, polyglycerin, and bisphenol A, and polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, 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. Examples of ethers, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl amine compounds of N, N, N′, Examples thereof include N′,-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

Further, these crosslinking agents preferably have water solubility or water dispersibility in consideration of application to in-line coating.

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

The second coating layer of the film of the present invention has a low reflectance design, and when used as a protective film on the rear surface side of a rear surface side polarizing plate, it improves the total light transmittance when used as a polarizing plate. It is a coating layer that can 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 characteristics do not significantly 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 for the total light transmittance of the laminated polyester film, it cannot be discussed exactly because of the influence of the first coating layer, but generally 90.0% or more, preferably 90.5% or more, more preferably It is 91.0% or more.

As a result of various studies, in order to grasp the optical characteristics of only the second coating layer more accurately and to consider the total light transmittance when used as a polarizing plate, consider the absolute reflectance of only the second coating layer. Turned out to be important. Focusing on the fact that reflectance and transmittance are mutually related properties, and in a polyester film having low light absorption and high transparency, generally, high transmittance indicates low reflectance.

In the present invention, in order to increase the total light transmittance when it is used as a polarizing plate, the second coating layer has one minimum value in the absolute reflectance range of wavelength 300 to 800 nm, and the minimum value is It is essential that the content is 3.5% or less. More preferable conditions for the minimum wavelength are in the range of 400 to 700 nm, and further preferably in the range of 450 to 650 nm. The minimum value is preferably 3.0% or less, 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 of the polarizing plate becomes low, which leads to a decrease in the brightness of the polarizing plate and a liquid crystal display. The screen becomes dark.

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

The acrylic resin is a polymer composed of a polymerizable monomer having a carbon-carbon double bond, as represented by acrylic and methacrylic monomers. These may be either homopolymers or copolymers. Moreover, the copolymer of these polymers and other polymers (for example, polyester, polyurethane, etc.) is also included. For example, it is a block copolymer or a graft copolymer. Alternatively, a polymer (polymer mixture in some cases) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyester solution or polyester dispersion is also included. Similarly, a polymer (polymer mixture in some cases) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyurethane solution or a polyurethane dispersion is also included. Similarly, a polymer (polymer mixture in some cases) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in another polymer solution or dispersion is also included. Further, in order to more efficiently improve the total light transmittance, it is possible to use a compound containing a fluorine atom 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, monobutylhydroxyfumarate, Various hydroxyl group-containing monomers such as monobutyl hydroxy itaconate; various (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; styrene, α-methylstyrene, divinylbenzene, vinyltoluene, etc. Various styrene derivatives, various vinyl esters such as vinyl acetate and vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers Various vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, trifluorochloroethylene, tetrafluoroethylene, chlorotrifluoroethylene and hexafluoropropylene; various conjugated dienes such as butadiene The kind is mentioned.

The urethane resin is a polymer compound having a urethane resin in its molecule. Urethane resins are usually made by the reaction of polyols and isocyanates. Examples of the polyol include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols, and these compounds may be used alone or in combination of two or more.

Polycarbonate polyols are obtained from a polyhydric alcohol and a carbonate compound by dealcoholization reaction. 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 Examples thereof include diol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylolheptane and the like. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, and the like. Examples of the polycarbonate-based polyols obtained from these reactions include poly(1,6-hexylene) carbonate and poly(3- Methyl-1,5-pentylene) carbonate and the like can be mentioned.

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. And polyhydric alcohols (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, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyl dialkanolamine, lactone diol, etc.).

Examples of the 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 having an aromatic ring such as tetramethylxylylene diisocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, aliphatic diisocyanates such as hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl Examples thereof include alicyclic diisocyanates such as methane diisocyanate and isopropylidene dicyclohexyl diisocyanate. These may be used alone or in combination of two or more.

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 capable of reacting 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, xylylene glycol, aromatic glycols such as bishydroxyethoxybenzene, and esters such as neopentyl glycol hydroxypivalate. Mention may be made of 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 decanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isoprobilitin cyclohexyl-4,4'-diamine, 1,4-diaminocyclohexane, 1 And alicyclic diamines such as 3-bisaminomethylcyclohexane.

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

In the film of the present invention, the content of the acrylic resin or urethane resin in the second coating layer cannot be unconditionally discussed because it also depends on the refractive index of the acrylic resin or urethane resin, but preferably 40% by weight or more. Range, more preferably 50% by weight or more, still more preferably 60% by 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 coated surface state and transparency. Considering the influence on the total light transmittance, it is preferable not to use many polymers having a high refractive index as the polymers to be used in combination.

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

Further, a cross-linking agent may be used in the second coating layer as long as the gist of the present invention is not impaired. The use of the cross-linking agent strengthens the coating layer, which may further improve the wet heat resistance and the scratch resistance. 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. Further, in consideration of 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.

Further, within the range not impairing the gist of the present invention, the first coating layer and the second coating layer may optionally contain an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorbing agent. Agents, antioxidants, foaming agents, dyes, pigments and the like may be contained.

The various components in the coating layer can be analyzed by surface analysis such as TOF-SIMS.

When the coating layer is provided by in-line coating, the above-mentioned series of compounds is used as an aqueous solution or water dispersion, and a coating solution whose solid content concentration is adjusted to about 0.1 to 50% by weight is coated on a polyester film. It is preferable to produce a laminated polyester film in. In addition, a small amount of an organic solvent may be contained in the coating liquid for the purpose of improving the dispersibility in water, improving the film-forming property, etc., within the range not impairing the gist of the present invention. Only one type of organic solvent may be used, or two or more types may be appropriately used.

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 further preferably 0.04 to 0.2 μm. .. When the film thickness is less than 0.002 μm, sufficient adhesiveness may not be obtained, and when it exceeds 1.0 μm, the appearance, transparency, and blocking property of the film may be deteriorated.

The 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, and 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 generally stated. However, when the film thickness is out of this range, a high total light transmittance may not be obtained when it is used as a polarizing plate.

In the present invention, as a method for providing a coating layer, conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating and 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 about 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, it is usually good to perform heat treatment at 70 to 280° C. for 3 to 200 seconds as a guide.

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

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

For example, polyvinyl alcohol that is uniaxially stretched and dyed with iodine or the like is attached as a polarizing film on the created adhesive layer. A protective film, a retardation film, or the like may be attached 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 structure exemplified above is protective film/polarizing film/adhesive/first coating layer/polyester film/second coating layer.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. The measuring method and the evaluating method used in the present invention are as follows.

(1) Method for measuring intrinsic viscosity of polyester 1 g of polyester in which other polymer components incompatible with polyester and pigment are removed is precisely weighed, and 100 ml of a mixed solvent of phenol/tetrachloroethane=50/50 (weight ratio) is added. Dissolved and measured at 30°C.

(2) Method of measuring average particle size (d50: μm) Accumulation (weight basis) 50% in equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was used 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. After that, the section prepared by the ultrathin section method was stained with RuO ₄ , and the cross section of the coating layer was measured using TEM (H-7650 manufactured by Hitachi, accelerating voltage 100V).

(4) Evaluation method of adhesiveness A 5% by weight polyvinyl alcohol aqueous solution having a polymerization degree of 1000 and a saponification degree of 98.5 mol% was applied as an adhesive to the surface of the first coating layer of the laminated polyester film so that the dry film thickness was 2 μm. It was dried to form an adhesive layer. An 18 mm wide tape (Cellotape (registered trademark), L-Pack (registered trademark) LP-18 manufactured by Nichiban Co., Ltd.) was attached on the adhesive layer, and was rapidly peeled off at a peeling angle of 180 degrees, and then peeled off. The surface was observed, and when the peeled area was 5% or less, it was marked with ⊚, when it was more than 5% and less than 20%, it was marked with ◯, when it was more than 20% and less than 50%, it was marked with Δ, and when it exceeded 50%, it was marked with x.

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

(6) Method of measuring total light transmittance It was measured according to JIS K7361 using a haze meter HM-150 manufactured by Murakami Color Research Laboratory.

(7) Method of evaluating total light transmittance when used as a polarizing plate A 5% by weight aqueous solution of polyvinyl alcohol having a degree of polymerization of 1000 and a degree of saponification of 98.5 mol% was applied to the first coating layer side of the laminated polyester film, A polyvinyl alcohol-iodine polarizing film was laminated 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 by the same method for a triacetyl cellulose film (TAC film). In the created polarizing plate, the total light transmittance was measured according to JIS K7361 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, in comparison with the total light transmittance of the polarizing plate formed from the TAC film, if the reduction amount is 1% or less, it is ◯, and if the reduction amount is more than 1% and there is a concern that the luminance may be reduced. And

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

The polyesters used in the examples and comparative examples were 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 was placed in a reactor, the reaction start temperature was set to 150° C., and methanol was gradually distilled off. 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 atmospheric pressure, and finally set to 0.3 mmHg. After the reaction was started, the reaction was stopped at a time point 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.

<Production method of 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 size of 2 μm and 0.04 part by weight of antimony trioxide are added. Was added, and polyester (B) was obtained by the same method as the method for producing polyester (A) except that the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65. The obtained polyester (B) had an intrinsic viscosity of 0.65.

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

Examples of the compound that constitutes the coating layer are as follows.
(Compound example)
・Polyvinyl alcohol: (I)
Polyvinyl alcohol with a saponification degree of 88 mol% and a polymerization degree of 500

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

・Polyester resin: (IIIA)
Carboxylic acid-based water 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-based water 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)
Sulfonic acid-based water dispersion of polyester resin copolymerized with the following composition 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) Aqueous dispersion of acrylic resin 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 carboxylic acid water-dispersed polyester polyurethane resin

-Melamine compound: (VIA) hexamethoxymethyl melamine-Epoxy compound: (VIB) Polyglycerol polyglycidyl ether, Denacol EX-521 (manufactured by Nagase Chemtex).
Particles: (VII) Silica sol having an average particle size of 65 nm

Example 1:
A mixed raw material obtained by mixing polyesters (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) at a ratio of 85% and 15%, respectively. Each of the mixed raw materials was fed to two extruders as a raw material for the intermediate layer, melted at 285° C. and then melted at 285° C., and then two kinds of three layers (surface layer/intermediate layer/ An unstretched sheet was obtained by coextrusion with the layer constitution of (surface layer) and cooling and solidification. Then, 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 solution A1 shown in Table 1 below was applied to one side of the film (first coating layer). Coating solution B1 shown in Table 2 below (formation of the second coating layer), guided to a tenter, laterally stretched 4.3 times at 120°C, and heat-treated at 225°C. Polyester having a thickness of 38 μm (surface layer 4 μm, intermediate layer 30 μm) having a first coating layer having a thickness (after drying) of 0.05 μm and a second coating layer having a thickness of 0.05 μm after being relaxed in the lateral direction. I got a film. 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 suppressed to 2.5%, and the transmittance at 380 nm was 4%. It was confirmed that it was absorbing ultraviolet rays. The characteristics of this film are shown in Table 3 below.

Examples 2-17:
A polyester film was obtained in the same manner as in Example 1, except that the coating composition was changed to the coating composition shown in Tables 1 and 2. The completed polyester film was as shown in Table 3.

Example 18:
A mixed raw material obtained by mixing polyesters (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) 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 the raw material for the intermediate layer. The completed polyester film is as shown in Table 3, and the transmittance at 380 nm was 1%, and it was confirmed that it absorbs ultraviolet rays.

Example 19:
A mixed raw material prepared by mixing polyesters (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) at a ratio of 90% and 10%, respectively. A polyester film was obtained in the same manner as in Example 1 except that the mixed raw material was used as the raw material for the intermediate layer. The completed polyester film is as shown in Table 3, and the transmittance at 380 nm was 9%, and it was confirmed that the film absorbs ultraviolet rays.

Example 20:
Example 1 except that a mixed raw material obtained by mixing polyesters (A) and (B) in a proportion of 90% and 10%, respectively, was used as a raw material for the outermost layer (surface layer) and polyester (A) was used as a raw material for the intermediate layer. A polyester film was obtained in the same manner. The completed polyester film was as shown in Table 3.

Comparative Examples 1-10:
A polyester film was obtained in the same manner as in Example 1, except that the coating composition was changed to the coating composition shown in Tables 1 and 2. When the completed laminated polyester film was evaluated, it was as shown in Table 4, and it was found that the adhesiveness was weak, the minimum reflectance was not observed, and the minimum reflectance was high.

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

Claims (8)

A coating layer formed from a coating liquid containing polyvinyl alcohol and an isocyanate compound is provided on one surface of a polyester film, and a polarizing film is provided on the coating layer side of the polyester film. 10 wt% or more the content of the isocyanate compound in the component state, and are 45 wt% or less, a polarizing plate, characterized in Rukoto that having a adhesive layer between the coating layer and the polarizing film. The polarizing plate according to claim 1 , wherein the polarizing film is a polyvinyl alcohol-iodine polarizing film. The polarizing plate according to claim 1 or 2 , which has a coating layer on the surface of the polyester film opposite to the coating layer formed from a coating liquid containing polyvinyl alcohol and an isocyanate compound. The coating layer formed on the polyester film side opposite to the coating layer formed from the coating liquid containing polyvinyl alcohol and an isocyanate compound has an absolute reflectance having one minimum value in the wavelength range of 300 to 800 nm, The polarizing plate according to claim 3 , wherein the minimum value is 3.5% or less. The polarizing plate according to any one of claims 1-4 saponification degree of the polyvinyl alcohol is not less than 70 mol%. The weight ratio of polyvinyl alcohol and an isocyanate compound in the total non-volatile components accounted for coating solution from 1.0 to 8.0: polarization according to any one of the which claims 1-5 range 1.0 to 8.0 Board. The polarizing plate according to any one of claims 1 to 6, the coating liquid containing a polyester resin. The polarizing plate according to claim 7 , wherein the polyester resin in the coating liquid contains a hydrophilic functional group.