JP2010066301A - Laminated polyester film for light-diffusing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polyester film for a light-diffusing sheet, suitably used for such applications that require reduction in generation of interference irregularity due to reflection of light and good adhesiveness to a light-diffusing layer or an antisticking layer, for example, for a backlight unit of a liquid crystal display. <P>SOLUTION: The laminated polyester film for a light-diffusing sheet has a coating layer containing a melamine compound and an acrylic resin on both surfaces of a polyester film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laminated polyester film for a light diffusing sheet. For example, it has reduced interference unevenness due to reflection of light, such as a backlight unit of a liquid crystal display, and good adhesion to a light diffusing layer and an anti-sticking layer. The present invention relates to various optical laminated polyester films.

  In recent years, liquid crystal displays have been widely used as display devices for televisions, personal computers, digital cameras, mobile phones and the like. Since these liquid crystal displays do not have a light emitting function by a liquid crystal display unit alone, a method of displaying by irradiating light using a backlight from the back side is widespread.

  The backlight system has a structure called an edge light type or a direct type. Recently, there is a tendency to reduce the thickness of liquid crystal displays, and an edge light type is increasingly used. The edge light type is generally configured in the order of a reflection sheet, a light guide plate, a light diffusion sheet, and a prism sheet. As the flow of light, the light incident on the light guide plate from the backlight is reflected by the reflection sheet and emitted from the surface of the light guide plate. The light beam emitted from the light guide plate enters the light diffusion sheet, is diffused and emitted by the light diffusion sheet, and then enters the next existing prism sheet. The light beam is condensed in the normal direction by the prism sheet and emitted toward the liquid crystal layer.

  The light diffusion sheet used in this configuration is used for uniformly diffusing transmitted light in multiple directions, and needs to have high light diffusibility and high light transmittance. As the light diffusing sheet, the surface of the sheet is roughened by heating and pressing during finishing, so-called embossing, or a light diffusing layer made of a transparent resin containing particles on a transparent base film The one made by coating is known. In the light diffusion sheet, a binder and a small amount of beads are used to prevent sticking (partial adhesion) between the light diffusion sheet and the light guide plate on the surface of the transparent base film opposite to the light diffusion layer. It has also been proposed to form a sticking-preventing layer containing Pt (Patent Documents 1 to 3).

  A polyester film is generally used as the transparent base film for forming the light diffusion sheet in consideration of transparency and mechanical properties, and improves the adhesion between the base polyester film and the light diffusion layer or anti-sticking layer. In order to make this happen, an easily adhesive coating layer is generally provided as the intermediate layer.

  In recent years, in the field of liquid crystal displays, there has been a demand for larger screens and higher image quality. Along with this, the level of demand for suppression of iris-like colors (interference unevenness) particularly under fluorescent lamps is increasing. In addition, fluorescent lamps have become a three-wavelength type for daylight color reproducibility, and interference unevenness is more likely to occur. Because light is diffused to the light diffusion layer side, interference unevenness is unlikely to occur.However, because the sticking prevention layer side is not highly diffusible, interference unevenness is likely to occur compared to the light diffusion layer. is there. Therefore, especially on the anti-sticking layer side, the optical design of the coating layer laminated on the polyester film has become important. Specifically, a coating layer having a higher refractive index adjusted to be between the refractive index of the polyester substrate and the refractive index of the resin used for the light diffusion layer or the anti-sticking layer is required.

  If the refractive index of the coating layer is not adjusted, the occurrence of uneven interference may not be sufficiently suppressed. When a film in which interference unevenness is conspicuously generated is used as a liquid crystal display, various problems due to deterioration in visibility may become apparent. In addition, various problems caused by the deterioration of visibility caused by interference unevenness may cause eye fatigue and health problems.

Therefore, it is desired to improve interference unevenness by increasing the refractive index of the coating layer. For example, as a method of reducing interference unevenness on the light diffusion layer side, a method of increasing the refractive index of the coating layer by combining an aqueous polyester resin and a metal chelate compound such as a water-soluble titanium chelate compound has been proposed ( Patent Document 4). However, due to the instability of the metal chelate compound in an aqueous solution, depending on the combination, the stability of the coating solution may not be sufficient, and when performing production for a long time, there is a possibility of increasing the liquid exchange work. Moreover, in the said coating layer structure, adhesiveness may not be enough depending on resin used for a light-diffusion layer, or the conditions of an endurance test.
JP 2000-89007 A JP 2004-4598 A JP 2007-286166 A JP 2006-20993 A

  The present invention has been made in view of the above-described circumstances, and the problem to be solved is to reduce the occurrence of interference unevenness due to light reflection and to have good adhesion to the light diffusion layer and the anti-sticking layer. Therefore, it is an object of the present invention to provide a laminated polyester film for a light diffusing sheet that can be suitably used in, for example, a liquid crystal display backlight unit.

  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 resides in a laminated polyester film for a light diffusing sheet, which has a coating layer containing a melamine compound and an acrylic resin on both sides of a polyester film.

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, it is preferable that the polyester film of this invention has a layer containing both a titanium compound and a phosphorus compound as a main component of the whole film. In the layer, the titanium element content is preferably 20 ppm or less, more preferably 10 ppm or less, and the lower limit is usually 1 ppm, but preferably 2 ppm. On the other hand, phosphorus element content is 1 ppm or more normally, Preferably it is 5 ppm or more, and an upper limit becomes like this. Preferably it is 300 ppm or less, More preferably, it is 200 ppm or less. That is, it is preferable that the main component of the polyester film contains an amount of a titanium compound and a phosphorus compound that simultaneously satisfy the following formulas (1) and (2).
1 ≦ W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} titanium element content in the polyester film (ppm), _{W P} denotes phosphorus element content in the polyester film (ppm))

  In the layer containing both the titanium compound and the phosphorus compound, if the content of the titanium compound is too large, the polyester is decomposed and oligomers are produced as a by-product due to the high activity of the titanium compound in the melt extrusion process. May occur. Moreover, the activity of a titanium compound can be moderately prepared by using a phosphorus compound in said range. If the content of the phosphorus compound is too large, gelation may occur, resulting in a foreign matter and causing the quality of the film to deteriorate. If the content is too small, the activity of the titanium compound cannot be sufficiently suppressed, In some cases, the generation of by-product or yellow coloring cannot be sufficiently controlled.

  The layer containing the titanium compound and phosphorus compound preferably contains no antimony element, and is usually 100 ppm or less, preferably 60 ppm or less, and more preferably 10 ppm or less. If the amount of the antimony element is too large, there is a risk that the melt will cause agglomeration and cause foreign matters, or the film will become dark and the transparency may be impaired.

  By using a titanium compound as a catalyst, it is possible to prevent darkening as when antimony is used, and to make the film extremely excellent in transparency, and by blending a phosphorus compound at the same time, the color tone of the film is deteriorated. Demonstrate the effect of not letting. Specifically, the brightness is improved as compared with using antimony as a catalyst, and a more preferable state is obtained as a laminated polyester for a light diffusion sheet (Japanese Patent Laid-Open No. 2007-86562). Particularly in recent years, in backlight units of liquid crystal displays, there is a tendency to reduce power consumption by reducing the number of lamps, etc., so improvement in luminance has become a necessary technique to compensate for this.

  In addition, due to thermal history during film processing, oligomers contained in the film may be deposited on the surface of the film, which may lead to deterioration of the visibility of the film due to contamination of the production line or deterioration of film haze, etc. It is also possible to use a material having a reduced amount of oligomer contained as a polyester forming the outermost layer of the multilayer structure film. As a method for reducing the amount of oligomer in the polyester, solid phase polymerization or the like can be used.

  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 may be used.

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

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.1-2 micrometers. If the average particle size is less than 0.01 μm, the slipperiness may not be sufficiently imparted, or the particles may be aggregated to make the dispersibility insufficient, thereby reducing the transparency of the film. On the other hand, when the thickness exceeds 3 μm, the surface roughness of the film becomes too rough, and a problem may occur when a light diffusion layer, a sticking prevention layer, or the like is formed in a subsequent process.

  Further, the content of particles in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% 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, 10-350 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, it is an essential requirement to have a coating layer containing a melamine compound and an acrylic resin on both sides of the polyester film.

  In the present invention, it is necessary to adjust the refractive index of the coating layer. It is preferable that the optimum refractive index of the coating layer in which interference unevenness hardly occurs is designed to be in the vicinity of the geometric mean of the refractive index of the polyester film and the refractive index of the light diffusion layer or the anti-sticking layer. For example, considering the case where the refractive index of the polyester film is about 1.65 and the refractive index of the resin used for the light diffusion layer or the anti-sticking layer is about 1.50, the polyester film is positioned between these layers. The ideal refractive index of the coating layer is about 1.57, which is usually a high refractive index that is difficult to achieve with only the acrylic resin as the coating layer component used for imparting easy adhesion. Therefore, it is necessary to use a melamine compound that requires a higher refractive index adjustment and can be designed to improve the adhesion after heat and humidity resistance, thereby eliminating interference unevenness and providing good adhesion. A method of forming a layer is effective.

  In the present invention, the coating layers laminated on both surfaces may be formed with the same coating layer or different coating layers as long as the gist of the present invention is not impaired. The coating layers are preferably the same in consideration of manufacturing convenience. When different coating layers are required, for example, the refractive index of the light diffusion layer formed on one surface and the refractive index of the anti-sticking layer formed on the other surface are significantly different, and interference unevenness does not occur in both. When the conditions cannot be adjusted with the same coating layer, or because different resins are used for both the light diffusion layer and the anti-sticking layer, the same coating layer provides good adhesion. There are cases where this is not possible. However, it is usually advantageous to use the same or similar compound as the resin for forming the light diffusion layer and the anti-sticking layer in consideration of the convenience of production. For this reason, it is possible to cope with the same coating layer, and in the coating layer, the same one in manufacturing is preferable because convenience is improved.

  The necessity of the melamine compound in this invention exists in the place where a melamine compound has a high-density aromatic ring, and is useful as a high refractive index material of an application layer. Moreover, since it has a crosslinking function at the same time, the coating film of the coating layer can be strengthened, and the heat and moisture resistance and the solvent resistance after forming the light diffusion layer and the anti-sticking layer can be improved. That is, it is a compound that can bring out two characteristics of high refractive index and durability with one compound and is useful.

  The melamine compound in the present invention 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.

  The acrylic resin in the present invention is a polymer composed of a polymerizable monomer having a carbon-carbon double bond, as typified by acrylic and methacrylic monomers. These may be either a homopolymer or a copolymer. Moreover, the copolymer of these polymers and other polymers (for example, polyester, polyurethane, etc.) is also included. For example, a block copolymer or a graft copolymer. Alternatively, a polymer (possibly a mixture of polymers) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyester solution or a polyester dispersion is also included. Similarly, a polymer (in some cases, a mixture of polymers) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyurethane solution or polyurethane dispersion is also included. Similarly, a polymer obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in another polymer solution or dispersion (in some cases, a polymer mixture) is also included.

  The polymerizable monomer having a carbon-carbon double bond is not particularly limited, but particularly representative compounds include, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, citracone. Various carboxyl group-containing monomers such as acids, and salts thereof; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutyl hydroxyl fumarate, Various hydroxyl group-containing monomers such as monobutylhydroxy itaconate; various monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate ( (Meth) acrylic acid esters; Various nitrogen-containing vinyl monomers such as (meth) acrylimide, diacetone acrylamide, N-methylol acrylamide or (meth) acrylonitrile; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, Various vinyl esters such as vinyl acetate and vinyl propionate; γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, “Silaplane FM-07” (methacryloyl silicon macromer) manufactured by Chisso Corporation Various silicon-containing polymerizable monomers; phosphorus-containing vinyl monomers; vinyl chloride, biliden chloride, vinyl fluoride, vinylidene fluoride, trifluorochloroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafur Various vinyl halides such as Russia propylene; various conjugated dienes such as butadiene and the like.

  In order to increase the refractive index of the coating layer, the acrylic resin can contain a sulfur compound, an aromatic compound, or the like as long as the adhesive properties are not impaired. In order to improve the adhesion with the light diffusion layer or the anti-sticking layer, it is preferable to use an acrylic resin containing a functional group such as a hydroxyl group, an amino group, or an amide group.

  In the laminated polyester film for light diffusing sheet in the present invention, acrylic is used to improve the coated surface, improve the visibility when various light diffusing layers and anti-sticking layers are formed on the coated surface, and improve the transparency. It is also possible to use a binder polymer other than the resin in combination. If the coating layer is formed only with a polyester resin without using an acrylic resin as a binder, the adhesiveness with the light diffusion layer or the anti-sticking layer may not be sufficient. There is a need to.

  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 (sponsored 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, urethane resin, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches, and the like. Can be mentioned.

  Furthermore, a crosslinking agent other than the melamine compound can be used in combination in the coating layer as long as the gist of the present invention is not impaired. As the crosslinking agent other than the melamine compound, various known resins can be used, and examples thereof include an epoxy compound, an oxazoline compound, and an isocyanate 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. A typical example is a condensate of epichlorohydrin and bisphenol A. In particular, a reaction product of a low molecular polyol with epichlorohydrin gives an epoxy resin having excellent water solubility.

  The oxazoline compound in the present invention is a compound having an oxazoline ring in the molecule, and includes a monomer having an oxazoline ring and a polymer synthesized using the oxazoline compound as one of raw material monomers.

  The isocyanate compound in the present invention refers to a compound having an isocyanate group in the molecule, specifically, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, tolylene diisocyanate. And polymers and derivatives thereof.

  These cross-linking agents may be used alone or in combination of two or more. Furthermore, when consideration is given to application to in-line coating, it is preferable to have water solubility or water dispersibility.

  Further, for the purpose of improving the adhesion and slipperiness of the coating layer, inert particles may be contained, and specific examples include silica, alumina, kaolin, calcium carbonate, titanium oxide, organic particles, and the like.

  Furthermore, as long as it does not impair the gist of the present invention, an antifoaming agent, a coatability improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, etc. May be contained.

  Regarding the content of the melamine compound in the coating layer constituting the laminated polyester film in the present invention, the weight ratio of the entire coating layer is usually in the range of 5 to 80%, more preferably in the range of 10 to 60%, still more preferably. It is 10 to 30% of range. If it is less than 5%, interference unevenness and adhesion may be reduced after the formation of the light diffusion layer and the anti-sticking layer. Especially in the adhesion after the wet heat resistance test, especially when the amount of acrylic resin contained in the coating layer is small, the coating layer containing even a small amount of melamine compound is compared with the coating layer not containing Adhesion may be improved. It is presumed that the crosslink density of the coating layer is increased by the melamine compound, and further, the durability against wet heat of the coating layer is improved by effectively crosslinking the melamine compound and the acrylic resin. However, on the other hand, the coating layer containing a large amount of melamine compound may work to inhibit the adhesion between the acrylic resin and the light diffusion layer or the anti-sticking layer. It is speculated that the crosslink density is too high and the melamine compound is the main component, which inhibits the movement of the acrylic resin and weakens the binding force with the resin component in the light diffusion layer and anti-sticking layer. The Therefore, when content of a melamine compound exceeds 80%, there exists a concern about the fall of adhesiveness.

  Regarding the content of the acrylic resin in the coating layer constituting the laminated polyester film in the present invention, the weight ratio of the entire coating layer is usually in the range of 5 to 80%, more preferably in the range of 10 to 70%, still more preferably. It is in the range of 20 to 50%. If it is less than 5%, the adhesion to the light diffusing layer or the anti-sticking layer may be poor. If it exceeds 80%, the refractive index of the coating layer cannot be increased. Visibility may not be good due to uneven interference.

  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 a coating solution prepared by adjusting the solid content concentration to about 0.1 to 50% by weight as a guide is applied to 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.

Respect laminated polyester film of the present invention, the thickness of the coating layer provided on the polyester film is usually 0.02~0.3g / ^{m 2,} more preferably 0.05~0.25g / ^{m 2,} more preferably in the range of 0.07~0.20g / ^{m 2.} In the adjustment of the refractive index of the coating layer in the present invention, when the coating amount is out of the above range, interference unevenness may occur after the formation of the light diffusion layer or the anti-sticking layer, and the visibility may be lowered.

  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. Regarding the coating method, there is a description example in “Coating Method” (published by Yoji Harasaki in 1979).

  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 designed in the vicinity of the geometric mean of the polyester film of the substrate and the diffusion layer or anti-sticking layer. Is. The refractive index of the coating layer and the reflectance of the coating layer are closely related. In the film thickness within the range of the present invention, it is preferable that a graph showing the wavelength on the horizontal axis and the reflectance on the vertical axis is drawn, and one minimum value of the reflectance appears in the wavelength range of 350 to 800 nm. If they appear at the same wavelength, the minimum reflectivity is high when the refractive index is high, and low when the refractive index is low. In the present invention, the reflectance of the minimum value varies depending on the wavelength range of the minimum value even if the material design of the coating layer is exactly the same. Specifically, comparing the case where the wavelength range of the minimum value exists in the short wavelength region and the case where it exists in the long wavelength region, the reflectance is lower in the case where it exists in the long wavelength region.

  In the present invention, the favorable reflectance means that, in the absolute reflectance, when a minimum value exists in the range of the wavelength of 350 nm or more and less than 550 nm, the value of the minimum value is preferably 3.0 to 4.5%, more preferably. Is in the range of 3.3 to 4.0%, more preferably 3.4 to 3.9%. When a minimum value exists in the wavelength range of 550 nm to 750 nm, the value of the minimum value is preferably Is in the range of 2.8 to 4.3%, more preferably 3.1 to 3.8%, and still more preferably 3.2 to 3.7%. When there is no minimum value between wavelengths of 350 nm and 750 nm, or when the absolute reflectance of the minimum value is outside the above value, interference unevenness occurs after forming the light diffusion layer and the anti-sticking layer, and the film is visually recognized. May decrease.

  The laminated polyester film of the present invention is generally provided with a light diffusing layer, an anti-sticking layer and the like on the coating layer. The light diffusing layer contains particles and a binder.

  The particles to be included in the light diffusion layer may be any particles having a property of diffusing light, such as organic particles such as acrylic resin, acrylic urethane resin, urethane resin, polyester resin, and polyvinyl resin, silica, and metal oxide. And inorganic particles such as barium sulfate can be used. Of these, acrylic resins and acrylic urethane resins having good transparency are preferably used. Moreover, the particle size of these particles is not particularly limited, but the average particle size is 1 to 50 μm, more preferably 5 to 15 μm.

  The binder contained in the light diffusing layer is used to fix particles and develop light diffusibility. For example, polyester resin, acrylic resin, polyurethane resin, fluororesin, silicone resin, epoxy resin, UV curable type Examples thereof include resins. In consideration of processability, a polyol compound is preferably used, and examples thereof include acrylic polyol and polyester polyol.

  When a polyol compound is used as a binder, it is preferable to contain isocyanate as a curing agent. By containing isocyanate, a stronger cross-linked structure can be formed, and physical properties as a light diffusion layer are improved. Further, when an ultraviolet curable resin is used as the binder, an acrylate resin is preferable, which can be used for improving the hardness of the light diffusion layer.

  The light diffusion layer may contain a surfactant, a fine inorganic filler, a plasticizer, a curing agent, an antioxidant, an ultraviolet absorber, a rust preventive agent, etc. within a range not impairing the light diffusion performance. .

  The mixing ratio of the binder and the particles in the light diffusion layer can be appropriately set depending on the light diffusibility to be obtained, and is not particularly limited. For example, the binder / particles are in the range of 0.1 to 50 by weight ratio, More preferably, it is the range of 0.5-20.

  Examples of the method for forming the light diffusion layer include a method in which a coating liquid containing a binder and particles is prepared, applied and dried. As a coating method, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, spray coating, spin coating or the like can be used. Although the thickness of a light-diffusion layer is not specifically limited, Considering light diffusibility, film | membrane intensity | strength, etc., it is the range of 1-100 micrometers, More preferably, it is the range of 3-30 micrometers.

  It is preferable that an anti-sticking layer is formed on the surface opposite to the light diffusion layer. The anti-sticking layer contains the same binder and particles as the light diffusion layer, and the content of the particles is not intended to be light diffusive. Therefore, a method of containing a smaller amount with a smaller particle size is generally used. It is. The formation method can also be formed by coating similarly to the light diffusion layer, and the thickness is not particularly limited, but is preferably in the range of 1 to 10 μm.

  According to the laminated polyester film for light diffusing sheet of the present invention, when the light diffusing layer or the anti-sticking layer is formed, it is possible to provide a laminated polyester film having no adhesion unevenness and excellent adhesion, Industrial value is high.

  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) Measurement 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. It was dissolved and measured at 30 ° C.

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

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

(4) Evaluation method of interference unevenness As a coating solution for the light diffusion layer, 60 parts of acrylic polyol (Acrydic A-801 manufactured by Dainippon Ink and Chemicals), 15 parts of polyisocyanate (manufactured by Mitsui Chemicals Polyurethane, Takenate D110N), average particle A 15 g / m ² light diffusion layer was formed by preparing 25 parts of acrylic resin particles having a diameter of 15 μm (MBX-15 manufactured by Sekisui Plastics Industries Co., Ltd.), 100 parts of toluene, and 100 parts of methyl ethyl ketone, and applying and heat curing. . Further, acrylic resin particles having an average particle size of 15 μm used in the coating solution for the light diffusion layer as an anti-sticking layer on the side opposite to the light diffusion layer were replaced with acrylic resin particles having an average particle size of 5 μm (manufactured by Sekisui Plastics Co., Ltd.). MBX-5) A double-sided product was prepared in the same manner except that a layer having a thickness of 3 g / m ² was formed instead of 7 parts. A black tape (vinyl tape VT-50 manufactured by Nichiban Co., Ltd.) is attached to the light diffusion layer side of the obtained film, and interference unevenness is visually observed under a three-wavelength fluorescent lamp from the sticking prevention layer side. ◎ if the interference unevenness can not be confirmed, ◯ if the interference unevenness of the color is confirmed, △ if the interference unevenness that can distinguish the color is △, strong interference unevenness that can distinguish the color Those which were confirmed and confirmed to have interference unevenness even under a white fluorescent lamp were evaluated as x. In the case of a normal light diffusing layer, since the light diffusibility is high like the above light diffusing layer, interference unevenness is hardly observed. However, in the case of a light diffusion layer with low light diffusibility, interference unevenness may be observed, so that the refractive index adjustment of the coating layer is more important. On the other hand, the anti-sticking layer is formed of particles and a binder in the same manner as the light diffusion layer, but generally has a smaller amount of particles and a smaller film thickness than the light diffusion layer. For this reason, the light diffusibility is lowered, and interference unevenness may be observed. Therefore, it is very important to adjust the refractive index of the coating layer.

(5) Adhesion evaluation method By the same method as the interference unevenness evaluation method, a light diffusion layer was formed on one side of the laminated polyester film, and a sticking prevention layer was formed on the other side. Then, after leaving in a constant temperature and humidity chamber for 50 hours in an environment of 80 ° C. and 85% RH, each of the light diffusion layer and the anti-sticking layer has a 18 mm width tape (cello tape (registered by Nichiban Co., Ltd.)) (Trademark) CT-18) was affixed and peeled off rapidly at a peeling angle of 180 degrees, and then the peeled surface was observed. For the larger peeled area, if the peeled area was 0%, ◎, 0% Exceeding 5% or less, ◯, exceeding 5% and 20% or less, Δ, exceeding 20%, ×. In general, the anti-sticking layer has less surface irregularities, and therefore has better adhesion to the tape to be peeled, and therefore the peel area tends to be larger than the light diffusion layer.

(6) Measurement of thickness of polyester layer After fixing a small piece of film with an epoxy resin, it was cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed in parallel with the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the layer thickness.

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, adding tetrabutoxy titanate as a catalyst to the reactor, setting the reaction start temperature to 150 ° C., and gradually increasing the reaction temperature as methanol is distilled off. It was 230 degreeC after 3 hours. After 4 hours, the transesterification reaction was substantially completed, and then a polycondensation reaction was performed 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 vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (A) having an intrinsic viscosity of 0.63.

<Method for producing polyester (B)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate / tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. Was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, orthophosphoric acid was added, and germanium dioxide was added to carry out a polycondensation reaction 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 0.65 due to a change in stirring power in the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (B) having an intrinsic viscosity of 0.65.

<Method for producing polyester (C)>
In the production method of polyester (A), 0.2 part of silica particles having an average particle diameter of 2.0 μm dispersed in ethylene glycol was added, and the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.66. A polyester (C) having an intrinsic viscosity of 0.66 was obtained using a method similar to the method for producing polyester (A).

Examples of compounds constituting the coating layer are as follows.
(Compound example)
Melamine compound: (I) Hexamethoxymethylmelamine acrylic resin: (IIA) 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)
Acrylic resin: (IIB) Aqueous dispersion of acrylic resin polymerized with the following composition: ethyl acrylate / methyl methacrylate / 2-hydroxyethyl methacrylate / N-methylol acrylamide / acrylic acid = 65/28/3/2/2 (% by weight) Emulsion polymer (emulsifier: anionic surfactant)
Polyester resin: (III)
Aqueous 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%)
Particle: (IV) Silica sol metal chelate compound having an average particle diameter of 65 nm: (V) Titanium triethanolamate

Example 1:
A mixed raw material obtained by mixing polyesters (A), (B), and (C) at a ratio of 85%, 5%, and 10%, respectively, is used as a raw material of the outermost layer (surface layer), and polyesters (A) and (B) are each 95 %, 5% mixed raw materials were used as intermediate layer raw materials, each was supplied to two extruders, melted at 290 ° C, and then on a cooling roll set at 40 ° C. It was coextruded with a layer structure of a layer (surface layer / intermediate layer / surface layer) and cooled and 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. Thickness having a coating layer in which the film is stretched 4.0 times at 120 ° C. in the transverse direction and heat-treated at 225 ° C. and then relaxed by 2% in the transverse direction and the coating amount (after drying) is 0.10 g / m ^2. A polyester film having a thickness of 188 μm (surface layer: 9 μm, intermediate layer: 170 μm) was obtained.

  When the absolute reflectance of the obtained polyester film was measured in the wavelength range of 300 to 800 nm, the wavelength at the minimum value (bottom wavelength) was 440 nm and the absolute reflectance was 3.8%. There was no interference unevenness of the anti-sticking layer, and the visibility was good. Also, the adhesion was good. The properties of this film are shown in Table 2 below.

Examples 2-6:
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. The completed polyester film is as shown in Table 2. When the interference unevenness after forming the anti-sticking layer was evaluated, the visibility was good and the adhesion was also good.

Comparative Examples 1-3:
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 completed laminated polyester film was evaluated, it was as shown in Table 2.

  The concentration of the coating solution was a 10% by weight aqueous solution.

  The film of the present invention can be suitably used for applications that need to reduce interference unevenness due to light reflection, such as a backlight unit of a liquid crystal display.

Claims (2)

A laminated polyester film for a light diffusing sheet, comprising a coating layer containing a melamine compound and an acrylic resin on both sides of a polyester film. The laminate for a light diffusion sheet according to claim 1, wherein the main component constituting the polyester film is a polyester containing an amount of a titanium compound and a phosphorus compound that simultaneously satisfy the following formulas (1) and (2). Polyester film.
1 ≦ W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} titanium element content in the polyester film (ppm), _{W P} denotes phosphorus element content in the polyester film (ppm))