JP2011224856A - Laminate polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate polyester film suitably usable in an application requiring having excellent visibility and adhesion for a hard coat layer or the like, for instance, a member or the like of a liquid crystal display.SOLUTION: This laminate polyester film includes, at least on one surface of a polyester film, a coating layer containing a compound having condensed polycyclic aromatic series, an isocyanate-based compound and particles having an average particle diameter ≤0.15 μm, wherein absolute reflectivity of the coating layer has one minimum value in a range of wavelength of 400-800 nm, and the absolute reflectivity at the minimum value is ≥4.0%.

Description

  The present invention relates to a laminated polyester film, for example, a laminated polyester film that needs to reduce interference unevenness due to reflection of external light, such as a liquid crystal display, a plasma display panel, and organic electroluminescence.

  In recent years, polyester films are frequently used for various optical films, and are used for applications such as touch panels, antireflection films, prism sheets, light diffusion sheets, and electromagnetic wave shielding films, which are members of liquid crystals and plasma displays. The base film used for these members is required to have excellent transparency and visibility.

  These films are often hard-coated in order to improve performance such as curling prevention, damage prevention, and surface hardness. Moreover, as a base material, the polyester film excellent in transparency and mechanical characteristics is generally used. In order to improve the adhesion between the polyester film and the hard coat layer, an easily adhesive coating layer is generally provided as an intermediate layer. For this reason, interference unevenness occurs unless the refractive index of the three layers of the polyester film, the easily adhesive coating layer, and the hard coat layer is taken into consideration.

  When a film with interference unevenness is used for a display such as a touch panel, the visibility becomes poor and it is difficult to use. Therefore, it is required to take measures against interference unevenness. In general, the refractive index of the coating layer for reducing interference unevenness is considered to be around the geometric mean of the refractive index of the polyester film of the substrate and the refractive index of the hard coat layer, and is adjusted to the refractive index around this. Ideally. Since the refractive index of the polyester film is high, it is generally necessary to design the coating layer with a high refractive index.

  As an example of improving interference unevenness by increasing the refractive index of the coating layer, for example, there is a method of increasing the refractive index in the coating layer by including a metal oxide having a high refractive index in the coating layer. In this case, the transparency of the film is lowered, and there are cases where sufficient performance for various optical applications cannot be exhibited (Patent Document 1). As another example, there is a method of combining a metal chelate compound and a resin. In this case, the stability of the coating solution may not be sufficient depending on the combination due to the instability of the metal chelate in the aqueous solution, which may lead to an increase in the liquid exchange work when producing for a long time. (Patent Document 2). Moreover, the high refractive index material used normally is inferior to adhesiveness with surface functional layers, such as a hard-coat layer. Therefore, a coating layer that can effectively improve adhesion even when combined with a high refractive index material is required.

JP 2004-54161 A JP 2005-97571 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a laminated polyester film with reduced interference unevenness due to external light reflection and excellent adhesion to various surface functional layers such as hard coats. It is to provide.

  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 that at least one surface of a polyester film has a coating layer containing a compound having a condensed polycyclic aromatic, an isocyanate compound, and particles having an average particle size of 0.15 μm or less. The absolute reflectance of the layer has one minimum value in the wavelength range of 400 to 800 nm, and the absolute reflectance at the minimum value is 4.0% or more.

  According to the laminated polyester film of the present invention, when various surface functional layers such as a hard coat are laminated, there is little interference unevenness due to reflection of external light, and a film excellent in adhesiveness with various surface functional layers is provided. And its industrial value is high.

Hereinafter, the present invention will be described in more detail.
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.

  Moreover, you may contain a ultraviolet absorber in a polyester film in order to improve the weather resistance of a film, and to prevent deterioration of the pigment | dye used for a color filter etc. 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 cyclic imino ester type, a benzotriazole type, a benzophenone type etc. are mentioned. From the viewpoint of durability, a cyclic imino ester type and a benzotriazole type are more preferable. It is also possible to use two or more ultraviolet absorbers in combination.

  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 of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. 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 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 0.01-3 micrometers normally, Preferably it is the range of 0.01-2 micrometers. When the average particle size is less than 0.01 μm, the slipperiness may not be sufficiently imparted, or the particles may be aggregated, the dispersibility becomes insufficient, and the transparency of the film may be lowered. On the other hand, when the thickness exceeds 3 μm, the surface roughness of the film becomes too rough, and a problem may occur when various surface functional layers are applied 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.

  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 can be formed into a film as a film, Usually, 10-300 micrometers, Preferably it is the range of 50-250 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 and / 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 times, preferably 3.0 to 6 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 times, preferably 3.5 to 6 times. is there. 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. As for the coating layer, it may be provided by in-line coating, which treats the film surface during the stretching process of the polyester film, or may be applied off-system on the film once manufactured, and may employ both offline coating. You may use together. In-line coating is preferably used in that it can be applied at the same time as film formation, and thus can be manufactured at low cost, and the thickness of the coating layer can be changed by the draw ratio.

  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 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 processed at a high temperature, and a film suitable as a polyester film can be produced.

  In the present invention, at least one surface of the polyester film has a coating layer containing a compound having a condensed polycyclic aromatic, an isocyanate compound, and particles having an average particle size of 0.15 μm or less. It is an essential requirement to have a coating layer having one minimum value in the wavelength range of 400 to 800 nm and having an absolute reflectance of 4.0% or more at the minimum value.

  Specific examples of the condensed polycyclic aromatic in the present invention are compounds having a structure represented by the following formula.

  In consideration of applicability on the polyester film, the compound having a condensed polycyclic aromatic is preferably a polymer compound such as a polyester resin, an acrylic resin, or a urethane resin. In particular, polyester resins are more preferable because more condensed polycyclic aromatics can be introduced.

  As a method of incorporating the condensed polycyclic aromatic into the polyester resin, for example, two or more hydroxyl groups are introduced into the condensed polycyclic aromatic as a substituent to form a diol component or a polyvalent hydroxyl component, or There is a method in which two or more acid groups are introduced to prepare a dicarboxylic acid component or a polyvalent carboxylic acid component.

  In the laminated polyester film production process, the condensed polycyclic aromatic contained in the coating layer is preferably a compound having a naphthalene skeleton in that it is difficult to be colored. In addition, a resin in which a naphthalene skeleton is incorporated as a polyester component is suitably used in terms of good adhesion to various surface functional layers formed on the coating layer and transparency. Representative examples of the naphthalene skeleton include 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid.

  In addition to the hydroxyl group and the carboxylic acid group, the condensed polycyclic aromatic has a refractive index of a refractive index by introducing a substituent containing a sulfur element, an aromatic substituent such as a phenyl group, a halogen element group, and the like. Improvements can be expected, and substituents such as alkyl groups, ester groups, and amide groups may be introduced from the viewpoints of coatability and adhesion.

An isocyanate compound is a compound derived from an isocyanate derivative typified by isocyanate or blocked isocyanate. Examples of the isocyanate 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.

Examples of the blocking agent for the blocked isocyanate in the present invention include phenol compounds such as bisulfites, phenol, cresol and ethyl phenol, alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol and ethanol, and malonic acid. Active methylene compounds such as dimethyl, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, mercaptan compounds such as butyl mercaptan, dodecyl mercaptan, lactam compounds such as ε-caprolactam, δ-valerolactam, diphenylaniline, Amine compounds such as aniline and ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, formaldehyde, acetoaldoxime, Examples include oxime compounds such as 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 may be used 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 urethane resin or a polyester resin.

  In the laminated polyester film of the present invention, the coated surface is improved, interference unevenness is reduced when various surface functional layers such as a hard coat layer are laminated on the coated surface, transparency and adhesion are improved, and the coated surface is formed. It is also possible to use various binder polymers in combination for improving the quality.

  The “binder polymer” used in the present invention is a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (hosted by the Chemical Substance Council in November 1985). ) Is a polymer compound having a molecular weight of 1000 or more and having a film-forming property.

  Specific examples of the binder polymer include polyester resin, acrylic resin, urethane resin, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkylene imine, methyl cellulose, hydroxy cellulose, and starch. And the like.

  Furthermore, in the coating layer, a crosslinking agent other than the isocyanate compound can be used in combination as long as the gist of the present invention is not impaired. As the crosslinking agent other than the isocyanate compound, various known resins can be used, and examples thereof include an oxazoline compound, a melamine compound, and an epoxy compound.

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.

  A 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.

  As an epoxy compound, the compound containing an epoxy group in a molecule | numerator, its prepolymer, and hardened | cured material are mentioned, for example. 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 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.

  In the present invention, the coating layer contains particles for the purpose of improving adhesion and slipperiness of the coating layer, and the average particle diameter is in the range of 0.15 μm or less from the viewpoint of the transparency of the film. Preferably, it is the range of 0.12 μm or less. Further, from the viewpoints of adhesion and slipperiness, the average particle size is preferably in the range of 0.03 μm or more, 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.

  Furthermore, as long as it does not impair the gist of the present invention, the coating layer has an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, an antioxidant, foaming as necessary. Agents, dyes, pigments and the like may be contained.

  In the compound having a condensed polycyclic aromatic used in the coating layer constituting the laminated polyester film in the present invention, the proportion of the condensed polycyclic aromatic in the compound is preferably in the range of 5 to 80% by weight. Yes, more preferably in the range of 10 to 60% by weight. The proportion of the compound having a condensed polycyclic aromatic in the entire coating layer is usually in the range of 10 to 99% by weight, preferably in the range of 40 to 95% by weight, more preferably in the range of 50 to 92% by weight. is there. If it falls outside these ranges, the visibility may deteriorate due to interference unevenness after the surface functional layer such as a hard coat layer is formed. The ratio of the condensed polycyclic aromatic can be determined by, for example, dissolving and extracting the coating layer with an appropriate solvent or warm water, separating by chromatography, analyzing the structure by NMR or IR, and further pyrolyzing GC-MS (gas It can be determined by analyzing with chromatography mass spectrometry.

  The ratio of the isocyanate compound in the coating layer constituting the laminated polyester film in the present invention is usually in the range of 1 to 80% by weight, preferably in the range of 3 to 50% by weight, more preferably in the range of 5 to 30% by weight. is there. When it is out of these ranges, there is a possibility that the adhesion with the surface functional layer such as the hard coat layer may be lowered, or the coated surface state may be deteriorated.

The proportion of particles having an average particle size of 0.15 μm or less in the coating layer constituting the laminated polyester film in the present invention is usually in the range of 1 to 30% by weight, more preferably in the range of 1 to 15% by weight, and further preferably 3 It is in the range of -10% by weight. When it is outside these ranges, there is a concern that the transparency and adhesion of the coating layer may be lowered.

  In the polyester film of the present invention, a coating layer can also be provided on the surface opposite to the surface on which the coating layer is provided. For example, when a functional layer such as a microlens layer, a prism layer, a sticking prevention layer, a light diffusion layer, or a hard coat is formed on the opposite side of the surface functional layer such as a hard coat layer, the adhesion to the functional layer It is possible to improve. A conventionally well-known thing can be used as a component of the coating layer formed in the surface on the opposite side. Examples thereof include binder polymers such as polyester resins, acrylic resins and urethane resins, cross-linking agents such as isocyanate compounds, oxazoline compounds, melamine compounds and epoxy compounds. These materials may be used alone or in combination. May be used in combination. Further, it may be a coating layer (coating layer having the same surface on both sides of a polyester film) containing a compound having a condensed polycyclic aromatic and an isocyanate compound as described above.

  Analysis of the 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.

  Regarding the laminated polyester film in the present invention, the thickness of the coating layer provided on the polyester film is usually in the range of 0.04 to 0.20 μm, preferably 0.07 to 0.15 μm. When the film thickness is out of the above range, visibility may deteriorate due to interference unevenness after the surface functional layer is laminated.

  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.

  The coating layer in the present invention has a refractive index adjusted to suppress the occurrence of interference unevenness, and the refractive index is in the vicinity of the geometric mean of the surface functional layer such as the base material polyester film and the hard coat layer. Designed. The refractive index of the coating layer and the reflectance of the coating layer are closely related. For the absolute reflectance of the present invention, a graph showing the wavelength on the horizontal axis and the reflectance on the vertical axis is drawn, and the minimum value of the reflectance needs to be one in the wavelength range of 400 to 800 nm, and the minimum value is 4 0.0% or more. In the range of the absolute reflectance of the present invention, if the minimum value appears at the same wavelength, the reflectance of the minimum value is a high value when the refractive index is high, and a low value when the refractive index is low.

The absolute reflectance in the present invention has one minimum value in the wavelength range of 400 to 800 nm, more preferably one minimum value in the wavelength range of 500 to 700 nm. The minimum value is preferably in the range of 4.0 to 6.5%, more preferably 4.5 to 6.2%. If the minimum value in the wavelength range of 400 to 800 nm is not one, and if the absolute reflectance of the minimum value deviates from the above value, interference unevenness occurs after the surface functional layer such as a hard coat layer is formed. The visibility of the film may be reduced.
In the present invention, the absolute reflectance in the above range can be obtained, for example, by appropriately selecting the type and amount of the compound having a condensed polycyclic aromatic to be used, the type and amount of the isocyanate compound to be used, and the like.

  In the present invention, a film having high transparency is more preferred for use in applications where transparency is required, such as for displays. For example, haze is mentioned as one index of transparency, and the value is preferably in the range of 1.5% or less, more preferably in the range of 1.2% or less, and further preferably in the range of 1.0% or less. is there. When the haze is high, the visibility of the film may be lowered.

  The polyester film of the present invention is generally provided with a surface functional layer such as a hard coat layer on the coating layer. Although it does not specifically limit as a material used for a hard-coat layer, For example, hardened | cured materials, such as reactive silicon compounds, such as monofunctional (meth) acrylate, polyfunctional (meth) acrylate, and tetraethoxysilane, are mentioned. Among these, from the viewpoint of achieving both productivity and hardness, a polymerization cured product of a composition containing an ultraviolet curable polyfunctional (meth) acrylate is particularly preferable.

  It does not specifically limit as a composition containing a ultraviolet curable polyfunctional (meth) acrylate. For example, a mixture of one or more known ultraviolet curable polyfunctional (meth) acrylates, those commercially available as ultraviolet curable hard coat materials, or the range that does not impair the purpose of this embodiment other than these, What added the other component further can be used.

  The UV-curable polyfunctional (meth) acrylate is not particularly limited. For example, dipentaerythritol hexa (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, tetramethylolmethanetri (meth) acrylate, (Meth) acryl derivatives of polyfunctional alcohols such as trimethylolpropane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,6-bis (3-acryloyloxy-2-hydroxypropyloxy) hexane And polyethylene glycol di (meth) acrylate and polyurethane (meth) acrylate.

  Other components contained in the composition containing an ultraviolet curable polyfunctional (meth) acrylate are not particularly limited. Examples thereof include inorganic or organic fine particles, polymerization initiators, polymerization inhibitors, antioxidants, antistatic agents, dispersants, surfactants, light stabilizers, and leveling agents. In addition, when the film is dried after film formation in the wet coating method, an arbitrary amount of solvent can be added.

  As a method for forming the hard coat layer, when an organic material is used, a general wet coat method such as a roll coat method or a die coat method is employed. The formed hard coat layer can be subjected to a curing reaction by heating, irradiation with active energy rays such as ultraviolet rays and electron beams as necessary.

  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 diameter The surface of the coating layer was observed using an electron microscope (S-4500 manufactured by HITACHI), and the average value of the particle diameters of 10 particles was defined as the average particle diameter.

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

(5) Measuring method of haze It measured by JISK7136 using Murakami Color Research Laboratory make haze meter HM-150.

(6) Interference unevenness evaluation method On the polyester film coating layer side, 72 parts by weight of dipentaerythritol hexaacrylate, 18 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, 10 parts by weight of antimony pentoxide, a photopolymerization initiator ( (Product name: Irgacure 184, manufactured by Ciba Specialty Chemical) 1 part by weight and 200 parts by weight of methyl ethyl ketone were applied so that the dry film thickness was 5 μm and cured by irradiating with ultraviolet rays to form a hard coat layer. The obtained film is visually observed under a three-wavelength fluorescent lamp, and interference unevenness is observed. If the interference unevenness is not confirmed, ◎, thin sparse interference unevenness is confirmed, thin, linear The case where the interference unevenness was confirmed was indicated by Δ, and the case where clear interference unevenness was confirmed was indicated by ×.

(7) Adhesive evaluation method In order to evaluate the tighter adhesiveness, it examined by the material remove | excluding antimony pentoxide from the hard-coat liquid used by the evaluation of said (5). That is, 80 parts by weight of dipentaerythritol hexaacrylate, 20 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, 5 parts by weight of a photopolymerization initiator (trade name: Irgacure 184, manufactured by Ciba Specialty Chemical), and 200 parts by weight of methyl ethyl ketone The coating liquid was applied so as to have a dry film thickness of 5 μm and cured by irradiating with ultraviolet rays to form a hard coat layer. The obtained film was initially (adhesiveness 1), and after 50 hours (adhesiveness 2) in an environment of 80 ° C. and 85% RH (adhesiveness 2), 10 × 10 cross-cut, and 18 mm wide on it. (A Nichiban Co., Ltd. cello tape (registered trademark) CT-18) was applied and the peeled surface was observed after abrupt peeling at a 180 degree peel angle. % If less than 20% and less than 20%, Δ if more than 20% and less than 50%, and x if more than 50%.

(8) Evaluation method of slipperiness When the surface of the first coating layer is rubbed with a nail, there is no catching feeling and there is a slipping feeling, ○, there is no catching feeling and there is no slipping feeling, and there is a catching feeling. The case was marked with x.

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 1.6 μm and 0.04 part of antimony trioxide are added. A polyester (B) was obtained using the same method as the production method of the polyester (A) except that the polycondensation reaction was stopped at a time corresponding to the intrinsic viscosity of 0.65 by adding parts by weight. The obtained polyester (B) had an intrinsic viscosity of 0.65.

Examples of compounds constituting the coating layer are as follows.
(Example compounds)
・ Compounds having condensed polycyclic aromatics: (I)
Water dispersion of polyester resin copolymerized with the following composition: Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / diethylene glycol = 92/8 // 80/20 (mol%)

・ Polyester resin: (II)
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%)

・ Urethane resin (III)
Hydran AP-40 (manufactured by Dainippon Ink & Chemicals, Inc.), a carboxylic acid water-dispersed polyester polyurethane resin

・ Isocyanate compounds: (IVA)
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. Then, the temperature of the system was once lowered to 50 ° C., 73 parts by weight of a 30% aqueous sodium bisulfite solution was added, the mixture was stirred at 45 ° C. for 60 minutes, and then diluted with 718 parts by weight of water.
・ Isocyanate compounds: (IVB)
158 parts by weight of hexamethylene diisocyanate trimer, 26 parts by weight of methoxypolyethylene glycol (OH value = 81 mg KOH / g), 27.8 parts by weight of diethyl diethylene glycol and 0.001 part by weight of dioctyltin laurate were reacted at 85 ° C. Thereafter, the mixture was allowed to cool, and 66 parts by weight of methyl ethyl ketone oxime was added dropwise to react. Subsequently, 115 parts by weight of 1,6-hexamethylenediol-based polycarbonate diol (OH value = 56 mgKOH / g), 1.2 parts by weight of trimethylolpropane (OH value = 1254 mgKOH / g), dimethylolpropionic acid (OH value = 837 mgKOH) / G) 7.6 parts by weight and 50 parts by weight of dimethyldipropylene glycol were added, and after stirring, 40.3 parts by weight of isophorone diisocyanate was added and reacted. After allowing to cool, 8.2 parts by weight of hexamethylene diisocyanate trimer was added, and after stirring, 5.8 parts by weight of triethylamine was added and stirred. A block isocyanate compound obtained by dropping 450 parts by weight of water into this mixed solution and dropping and stirring 21 parts by weight of a 15% aqueous diethylenetriamine solution.

・ Hexamethoxymethylmelamine (V)

・ Particles: (VIA) Silica sol with an average particle size of 0.07 μm ・ Particles: (VIB) Silica sol with an average particle size of 0.12 μm ・ Particles: (VIC) Silica sol with an average particle size of 0.30 μm

Example 1:
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 each of two extruders. Are melted at 285 ° C. and then coextruded and cooled on a cooling roll set at 40 ° C. in a layer configuration of two types and three layers (surface layer / intermediate layer / surface layer = 1: 18: 1 discharge amount). Solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the difference in peripheral speed of the roll, and then the coating liquid 1 shown in Table 1 below was applied to both sides of the longitudinally stretched film, and led to a tenter. Polyester with a thickness of 100 μm having a coating layer with a film thickness (after drying) of 0.10 μm after stretching 3.9 times at 120 ° C. in the transverse direction and heat treatment at 225 ° C. A film was obtained.

  When the absolute reflectance of the obtained polyester film was measured, the minimum value was 610 nm, and the reflectance was 5.1%. Interference unevenness could not be confirmed in the film after laminating the hard coat layer, adhesion was good, haze was low, and transparency was good. The properties of this film are shown in Table 2 below.

Examples 2-14:
In Example 1, it manufactured similarly to Example 1 except having changed the coating agent composition into the coating agent composition shown in Table 1, and obtained the polyester film. As shown in Table 2, the finished polyester film had high reflectivity, good interference unevenness level, and good adhesion.

Comparative Examples 1-5:
In Example 1, it manufactured similarly to Example 1 except having changed the coating agent composition into the coating agent composition shown in Table 1, and obtained the polyester film. When the finished laminated polyester film was evaluated, as shown in Table 2, when clear interference unevenness could be observed, adhesion was not good, haze was high, or slipperiness was poor.

Comparative Example 6:
In Example 1, it manufactured like Example 1 except not providing an application layer, and obtained the polyester film. When the completed film was evaluated, as shown in Table 2, the adhesion was poor.

  The film of the present invention can be suitably used for, for example, various optical films that are members of liquid crystal, plasma displays, etc., for applications that place importance on adhesion and visibility with a hard coat layer or the like.

Claims (1)

At least one surface of the polyester film has a coating layer containing a compound having a condensed polycyclic aromatic, an isocyanate compound, and particles having an average particle diameter of 0.15 μm or less, and the absolute reflectance of the coating layer is a wavelength of 400 A laminated polyester film having one minimum value in a range of ˜800 nm and an absolute reflectance at the minimum value of 4.0% or more.