JP5174606B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film, and more particularly to a laminated polyester film that is suitably used as a member for a prism sheet used in a backlight unit of a liquid crystal display and has good adhesion to various functional layers. It is.

  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 prism sheet used in this configuration is for improving luminance by improving the optical efficiency of the backlight. As the transparent base film, a polyester film is generally used in consideration of transparency and mechanical properties. In order to improve the adhesion between the base polyester film and the prism layer, these intermediate layers are easily bonded. In general, a conductive coating layer is provided. As an easily adhesive coating layer, for example, polyester resin, acrylic resin, and urethane resin are known (Patent Documents 1 to 3).

  As a method for forming the prism layer, for example, an active energy ray-curable coating material is introduced into a prism type, irradiated with active energy rays while being sandwiched between polyester films, the resin is cured, and the prism type is removed to remove polyester. The method of forming on a film is mentioned. In the case of such a method, it is necessary to use a solventless active energy ray-curable coating material in order to form the prism type with precision. However, solventless paints are less permeable and swellable to the easy-adhesion layer laminated on the polyester film than solvent-based paints, and tend to have insufficient adhesion. A coating layer made of a specific urethane resin has been proposed to improve the adhesion, but even with such a coating layer, the adhesion is not necessarily sufficient for solvent-free paints. (Patent Document 4).

  In addition, a prism sheet and a light diffusion sheet are formed by forming a light diffusion layer on the surface opposite to the prism layer with respect to the polyester film in order to cope with the recent thinning and cost reduction of various displays. A method of creating a single sheet has been proposed. Also, a binder and a small amount of beads are contained on the surface opposite to the prism layer or the light diffusion layer in order to prevent sticking (partial adhesion) with the light diffusion sheet, liquid crystal panel, light guide plate, etc. It can also be proposed to form an anti-sticking layer (Patent Documents 5 to 7).

  In order to improve the adhesion between the polyester film of the substrate and the light diffusing layer or the anti-sticking layer, an easily adhesive coating layer is generally provided as an intermediate layer thereof.

  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. In the case of the light diffusing layer, light is diffused to a high degree and interference unevenness is unlikely to occur. However, in the case of the anti-sticking layer, the light diffusibility is not high, so interference unevenness occurs compared to the light diffusing layer. It is easy to do. For this reason, particularly in the case of forming an anti-sticking layer, 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 base and the refractive index of the resin used for the anti-sticking layer or the light diffusion 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 the interference unevenness of the light diffusion layer, 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) Reference 8). 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.

It is also known to use a melamine compound as another method for increasing the refractive index of the coating layer (Patent Documents 9 and 10). However, in recent years, the hard coat layer and the antireflection layer formed on the coating layer for the antireflection film are generally compared with the antisticking layer and the light diffusion layer formed for the prism and the light diffusion film. The refractive index is high. Therefore, the refractive index of the coating layer preferably used for the antireflection film is very high, and for prisms and light diffusing sheets, on the contrary, the refractive index is too high, which may cause interference unevenness. is there. Furthermore, the hard coat layer and antireflection layer formed for the antireflection film and the antisticking layer and light diffusion layer formed for the prism and the light diffusion film have different components. For this reason, even if a coating layer showing good adhesion is used for an antireflection film, it does not necessarily show perfect adhesion for a prism or a light diffusion film.
JP-A-8-281890 Japanese Patent Laid-Open No. 11-286092 JP 2000-229395 A JP-A-2-158633 JP-A-10-160914 JP 2004-4598 A JP 2007-286166 A JP 2006-20993 A JP 2008-208223 A JP 2008-209681 A

  The present invention has been made in view of the above circumstances, and the solution to the problem is good visibility when a functional layer is formed, and good adhesion that can flexibly cope with various layer configurations. For example, it is providing the laminated polyester film which can be utilized suitably as a member for prism sheets used for the backlight unit etc. of a liquid crystal display.

  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 a polyester film has a coating layer containing a urethane resin having a polycarbonate structure on one surface, a melamine compound on the other surface, and has an absolute reflectance of a wavelength of 350 nm. When the minimum value exists in the range of 550 nm or more and less than 550 nm, the value of the minimum value is 3.4 to 3.9%, and when the minimum value exists in the wavelength range of 550 nm or more and 750 nm or less, the value of the minimum value is 3 It exists in the laminated polyester film characterized by having a coating layer which is 0.1-3.8% .

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.

  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 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 functional layer such as a prism layer or a light diffusion layer is formed in a later step.

  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, one surface of the polyester film has a coating layer containing a urethane resin having a polycarbonate structure (hereinafter sometimes abbreviated as a first coating layer), and the melamine compound is disposed on the opposite surface. It is an essential requirement to have a coating layer (hereinafter sometimes abbreviated as “second coating layer”) containing bismuth.

  Although the 1st application layer of the film of this invention is not limited, it is provided especially in order to improve adhesiveness with a solventless type active energy ray hardening layer, and on the 1st application layer For example, a prism layer or a microlens layer can be formed.

  The urethane resin having a polycarbonate structure contained in the first coating layer of the film of the present invention uses a polycarbonate resin as one of the main constituent polyols of the urethane resin. Polycarbonate-based polyols are obtained from a polyhydric alcohol and a carbonate compound by a dealcoholization reaction. Examples of the polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane. Diol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decane Diol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like can be mentioned. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate. Examples of polycarbonate polyols obtained from these reactions include poly (1,6-hexylene) carbonate, poly (3- And methyl-1,5-pentylene) carbonate.

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

  In addition, polyols other than polycarbonate polyols can be used as long as the gist of the present invention is not impaired, and examples thereof include polyether polyols, polyester polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

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

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

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

  In particular, the urethane resin used in the present invention is preferably a resin comprising a polycarbonate polyol, a polyisocyanate, a chain extender having a reactive hydrogen atom, a group that reacts with an isocyanate group, and a compound having at least one anionic group. The amount of the anionic group in the urethane resin is preferably 0.05% by weight to 8% by weight. When the amount of anionic groups is small, the water-soluble or water-dispersible properties of the urethane resin are poor, and when the amount of anionic groups is large, the water resistance of the coating layer after coating is poor, or the film tends to stick to each other due to moisture absorption. Because.

  The content of the polycarbonate component in the urethane resin is usually 10 to 90% by weight, preferably 20 to 70% by weight. If the content is less than 10% by weight, the effect of improving the adhesiveness of the urethane resin is poor, and if it exceeds 90% by weight, the coating property is deteriorated.

  The urethane resin in the present invention preferably has a glass transition point (hereinafter sometimes referred to as Tg) of 10 ° C. or less. When Tg is higher than 10 ° C., easy adhesion may be insufficient. The measurement of Tg mentioned here refers to a temperature at which E ″ is maximized by preparing a dry film of urethane resin and performing dynamic viscoelasticity measurement.

  Furthermore, it is also possible to use a compound having a double bond for the urethane resin having a polycarbonate structure contained in the first coating layer of the film of the present invention. The double bond is for improving the adhesion with the layer formed on the first coating layer. When the layer formed on the first coating layer is a curable resin by radical reaction of a double bond, it can also react with the double bond in the first coating layer, and has stronger adhesion. It becomes possible to put out. In this case, since the first coating layer and the layer formed thereon are connected by a strong carbon-carbon bond, even if the glass transition point of the urethane resin having the polycarbonate structure described above is not low. Adhesion can be effectively obtained.

  When a double bond is introduced into a urethane resin having a polycarbonate structure, a vinyl group is preferred in consideration of reactivity due to radicals. The vinyl group can be introduced by various methods in each stage of preparing the urethane resin. For example, there are a method of using a resin having a vinyl group as a copolymerization component during prepolymer synthesis, and a method of using a diol, diamine, amino alcohol, or the like having a vinyl group as needed at each stage of polymerization. Specifically, for example, vinyl ether compounds such as 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether can be copolymerized in advance with some of the components.

  The content of the vinyl group in the urethane resin is not particularly limited. For example, 1 mol or more can be used for 100 mol of the urethane bond, and 5 mol or more can be used for improving adhesion. Is possible. The upper limit is not limited, but even if it is contained in excess, it is difficult to see further effects, and since the mechanical properties of the urethane resin are inferior, it is preferably 50 mol or less, more preferably 25 mol or less. It is.

  In the first coating layer in the present invention, it is preferable to contain a crosslinking agent in order to strengthen the coating film of the coating layer and improve the heat and heat resistance after forming the prism layer and the like. As the crosslinking agent, an oxazoline compound, a melamine compound, an epoxy compound, an isocyanate compound, a carbodiimide compound, or the like, or a so-called polymer-type crosslinking agent in which a crosslinking reactive functional group as described above is copolymerized in another polymer skeleton. Etc. are also exemplified. In the present invention, the most preferred embodiment is to use an oxazoline compound for a urethane resin containing a carboxyl group.

  Moreover, when the coating layer containing a urethane resin having a low Tg as described above is made into a laminated polyester film and then wound into a roll, the front and back of the film stick, so-called blocking is likely to occur. In order to prevent blocking, it is preferable to contain particles as a constituent component of the coating layer. The content of the particles is preferably in the range of 3 to 25%, more preferably in the range of 5 to 15%, and in the range of 5 to 10% in terms of the weight ratio of the entire coating layer. Further preferred. If it is less than 3%, the effect of preventing blocking may be insufficient. On the other hand, if it exceeds 25%, the blocking prevention effect is high, but there is a concern that the transparency of the coating layer is lowered, the coating film strength is lowered due to the loss of the continuity of the coating layer, or the easy adhesion property is lowered. By using particles in the above range, it is possible to achieve both easy adhesion performance and anti-blocking performance.

  As the particles, for example, inorganic particles such as silica, alumina, and metal oxide, or organic particles such as crosslinked polymer particles can be used. In particular, silica particles are preferred from the viewpoint of dispersibility in the coating layer and transparency of the resulting coating film.

  If the particle size is too small, the effect of preventing blocking is difficult to obtain, and if it is too large, dropping off from the coating film tends to occur. The average particle size is preferably about 1/2 to 10 times the thickness of the coating layer. Furthermore, if the particle size is too large, the transparency of the coating layer may be inferior, so the average particle size is preferably 300 nm or less, and more preferably 150 nm or less. The average particle diameter of the particles described here can be obtained by measuring the 50% average diameter of the number average of the particle dispersion with Microtrac UPA (Nikkiso Co., Ltd.).

  In the first coating layer in the present invention, the above-mentioned polycarbonate is used for improving the coating surface, improving the visibility when various prism layers, microlens layers, etc. are formed on the coating surface, and improving the transparency. It is also possible to use a binder polymer other than the urethane resin having a structure in combination.

  In the present invention, the “binder polymer” 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). It is defined as a polymer compound 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.

  Content of the said urethane resin which occupies in the 1st application layer in this invention is not limited. This may constitute the coating layer with the urethane resin as a main component, but the adhesiveness can be improved by simply mixing the urethane resin with a coating layer mainly composed of other easily adhesive resin. For this reason, it can be appropriately selected within the range where the desired characteristics appear. However, if the amount is too small, it is difficult to obtain the effect, so the lower limit is usually in the range of 20% or more, preferably in the range of 40% or more, and more preferably in the range of 50% or more in terms of the weight ratio of the entire coating layer.

  Although the 2nd application layer in this invention is not limited, it was provided in order to improve adhesiveness with the layer formed especially by apply | coating solvent containing resin, and on 2nd application layer For example, formation of a sticking prevention layer etc. can be mentioned.

  It is necessary to adjust the refractive index of the second coating layer in the present invention. The optimum refractive index of the coating layer in which interference unevenness is unlikely to occur is preferably designed to be close to the geometric mean of the refractive index of the polyester film and the refractive index of the anti-sticking layer or the light diffusion 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 anti-sticking layer or the light diffusing layer is about 1.50, it is located in the middle of these layers. The ideal refractive index of the coating layer to be applied is about 1.57, and it is usually difficult to achieve with an acrylic resin or urethane resin alone as the coating layer component used for imparting easy adhesion. Rate. Therefore, by using a melamine compound that requires a high refractive index adjustment and that can be designed to prevent adhesion deterioration, it is possible to form a coating layer with good interference and no interference unevenness. This method is effective.

  The second coating layer is a coating layer having good adhesion to the anti-sticking layer and the light diffusion layer. In the case of a normal light diffusion layer, since the light diffusibility is high, 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 generally 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. It is. For this reason, the light diffusibility is low and interference unevenness is easily observed. Therefore, it is very important to adjust the refractive index of the coating layer.

  The necessity of the melamine compound in the 2nd application layer of the film of this invention exists in the place useful as a high refractive index increasing material of a 2nd application layer, since a melamine compound has a high-density aromatic ring. 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 solvent resistance after formation of the anti-sticking layer, the light diffusion layer and the like 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 second coating layer of the film of 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.

  In the second coating layer of the film of the present invention, it is preferable to use a binder polymer in combination in order to improve the coating surface shape and improve transparency when various anti-sticking layers are formed on the coating surface. 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. A urethane resin having a polycarbonate structure used in the first coating layer can also be used. Among these binder polymers, polyester resins, acrylic resins, and urethane resins are preferably used in terms of good coating surface and adhesion. However, if the second coating layer is formed only of the polyester resin as the binder polymer, the adhesiveness with the anti-sticking layer or the like may not be sufficient, so it is preferable to use an acrylic resin or a urethane resin in combination as appropriate.

  The polyester resin contained in the second coating layer of the film of the present invention includes, for example, the following polyvalent carboxylic acid and polyvalent hydroxy compound as main components. That is, examples of the polyvalent carboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4′-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6- Naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid , Succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt and ester-forming derivatives thereof can be used, Examples of polyvalent hydroxy compounds include ethylene glycol 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol , Neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol Polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, and the like can be used. One or more compounds may be appropriately selected from these compounds, and a polyester resin may be synthesized by a conventional polycondensation reaction.

  The acrylic resin contained in the second coating layer of the film of 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; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers; vinyl chloride , Vinylidene chloride, vinyl fluoride, vinylidene fluoride, trifluorochloroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and other vinyl halides; butadiene and other conjugated dienes 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 to the anti-sticking layer and the light diffusion 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.

  The urethane resin contained in the second coating layer of the film of the present invention is a polymer compound having a urethane resin in the molecule, and includes various urethane resins having a polycarbonate structure contained in the first coating layer. Urethane resin can be used. Examples of the polyol include polyether polyols, polyester polyols, polyolefin polyols, and acrylic polyols in addition to the polycarbonates. These compounds may be used alone or in combination.

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

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

  In order to obtain the urethane resin contained in the second coating layer, these polyols and isocyanate compounds and chain extenders used for obtaining the urethane resin having the polycarbonate structure described above can be used. In consideration of appropriateness of in-line coating, a water-dispersible or water-soluble urethane resin is preferable. In order to impart water dispersibility or water solubility, it is important to introduce a hydrophilic group such as a hydroxyl group, a carboxyl group, a sulfonic acid group, a sulfonyl group, a phosphoric acid group, or an ether group into the urethane resin. Among the hydrophilic groups, a carboxyl group is preferable from the viewpoint of coating film properties and adhesion.

  Further, in order to increase the refractive index of the second coating layer, the urethane resin may contain a sulfur compound, an aromatic compound, or the like as long as the adhesive properties are not impaired. A benzene skeleton etc. are mentioned as an aromatic compound at the point that it is hard to color in a polyester film manufacturing process.

  Further, a crosslinking agent other than the melamine compound can be used in combination in the second 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, an isocyanate compound, and a carbodiimide 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. For example, there is a condensate of epichlorohydrin and a polyhydric alcohol. Examples of the polyhydric alcohol include ethylene glycol, polyethylene glycol, glycerin, polyglycerin, 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 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.

  Isocyanate compound 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 the like. 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, the second coating layer may contain particles for the purpose of improving the blocking property and slipperiness of the coating layer, and inorganic particles such as silica, alumina and metal oxide, or organic particles such as crosslinked polymer particles. Etc.

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

  Regarding the content of the melamine compound in the second 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%. 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 moist heat resistance test, especially when the amount of the binder polymer contained in the coating layer is small, the coating layer containing even a small amount of the 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 binder polymer. However, on the other hand, the coating layer containing a large amount of melamine compound may work to inhibit the adhesion between the binder polymer and the anti-sticking layer or the light diffusion layer. It is speculated that the crosslink density is too high and the melamine compound is the main component, which hinders the movement of the binder polymer and weakens the bonding force with the resin component in the anti-sticking layer and light diffusion layer. The Therefore, when content of a melamine compound exceeds 80%, there exists a concern about the fall of adhesiveness.

  In the present invention, it is preferable to contain an acrylic resin or a urethane resin as a binder polymer in the second coating layer in order to improve adhesion. Regarding the total content of the acrylic resin and the urethane resin in the second coating layer, the weight ratio of the entire second coating layer is preferably in the range of 5 to 90%, more preferably in the range of 15 to 80%, and even more preferably. Is in the range of 25-70%. When the content is small, the adhesion to the anti-sticking layer or the light diffusion layer may not be good. On the other hand, when the content is too large, the refractive index of the second coating layer cannot be increased. In some cases, the visibility is not good due to uneven interference after formation of the light diffusion layer or the like.

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

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

Respect laminated polyester film of the present invention, the thickness of the first coating layer provided on the polyester film is usually 0.002~1.0g / ^{m 2,} more preferably 0.005 to 0.5 / ^{m 2,} further Preferably it is the range of 0.01-0.2 g / m < ² >. If the film thickness is less than 0.002 g / m ^2, sufficient adhesion may not be obtained, and if it exceeds 1.0 g / m ² , the appearance, transparency, and film blocking properties may be deteriorated. There is sex. On the other hand, the thickness of the second coating layer is usually 0.02~0.3g / ^{m 2,} more preferably 0.05~0.25g / ^{m 2,} more preferably 0.07~0.20g / ^{m 2} Range. 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, after forming the anti-sticking layer or the light diffusing layer, interference unevenness may occur and 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 Yasuharu 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.

  In the present invention, the second coating layer has a refractive index adjusted in order to suppress the occurrence of interference unevenness, and the refractive index is a geometric mean of the base material polyester film and the anti-sticking layer or the light diffusion layer. It is designed in the vicinity. 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, even if the material design of the second coating layer is exactly the same, the reflectance of the minimum value varies depending on the wavelength range of the minimum value. 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 of the second coating layer means that, in the absolute reflectance, when there is a minimum value in the range of a 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 3.3 to 4.0%, and even more preferably 3.4 to 3.9%. When a minimum value exists in the wavelength range of 550 nm to 750 nm, the minimum value is present. Is preferably in the range of 2.8 to 4.3%, more preferably 3.1 to 3.8%, and even more preferably 3.2 to 3.7%. When there is no minimum value between wavelengths of 350 nm and 750 nm or less, and when the absolute reflectance of the minimum value deviates from the above value, interference unevenness occurs after forming a sticking prevention layer or a light diffusion layer, etc. Visibility may be reduced.

  In general, a prism layer, a microlens layer, or the like is provided on the first coating layer of the laminated polyester film of the present invention in order to improve luminance. In recent years, various shapes have been proposed for the prism layer in order to improve the luminance efficiently. Generally, prism layers are formed by arranging prism rows having a triangular cross section in parallel. Similarly, various shapes of the microlens layer have been proposed, but in general, a large number of hemispherical convex lenses are provided on the film. Any layer can have a conventionally known shape.

  Examples of the shape of the prism layer include a triangular cross section having a thickness of 10 to 500 μm, a pitch of prism rows of 10 to 500 μm, and an apex angle of 40 ° to 100 °. As the material used for the prism layer, conventionally known materials can be used, for example, those made of an active energy ray-curable resin, such as polyester resin, epoxy resin, polyester (meth) acrylate, epoxy Examples include (meth) acrylate resins such as (meth) acrylate and urethane (meth) acrylate.

  Examples of the shape of the microlens layer include a hemispherical shape having a thickness of 10 to 500 μm and a diameter of 10 to 500 μm, but may have a shape such as a cone or a polygonal pyramid. As the material used for the microlens layer, conventionally known materials can be used as in the prism layer, and examples thereof include an active energy ray curable resin.

  It is common to provide a sticking prevention layer etc. on the 2nd application layer of the lamination polyester film of the present invention. The anti-sticking layer is used for preventing sticking with a light diffusing sheet, a liquid crystal panel or the like, and contains a binder and a small amount of beads.

  The particles to be included in the anti-sticking layer may be anything that can produce performance that does not cause sticking, such as acrylic resin, acrylic urethane resin, urethane resin, polyester resin, polyvinyl resin, silica, Inorganic particles such as metal oxide and 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 30 μm, more preferably 3 to 15 μm.

  The binder contained in the anti-sticking layer is used for fixing particles, and examples thereof include polyester resins, acrylic resins, polyurethane resins, fluororesins, silicone resins, epoxy resins, and UV curable 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 crosslinked structure can be formed, and the physical properties as an anti-sticking layer are improved. In addition, when an ultraviolet curable resin is used as the binder, an acrylate resin is preferable, which can be used to improve the hardness of the anti-sticking layer.

  Examples of the method for forming the anti-sticking layer include a method in which a coating liquid containing a binder and particles is prepared, and coated 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. The thickness of the anti-sticking layer is not particularly limited, but is in the range of 1 to 10 μm in consideration of transparency, film strength and the like.

  In addition to the anti-sticking layer, a light diffusion layer can be formed on the second coating layer in the present invention. The light diffusion layer is used for uniformly diffusing transmitted light in multiple directions, and is required to have high light diffusibility and high light transmittance. The light diffusing layer contains the same binder and particles as the anti-sticking layer, and it is preferable that the light diffusing layer contains larger and larger amount of particles than the anti-sticking layer, depending on the light diffusibility level.

  The particles to be contained in the light diffusion layer may be any particles having a property of diffusing light, and the same particles as those contained in the above-mentioned sticking prevention layer can be 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 for fixing particles and developing light diffusibility, and the same resin as the anti-sticking layer can be used.

  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.

  As a method for forming the light diffusion layer, the same method as the formation of the anti-sticking layer can be used, and the thickness of the light diffusion layer is not particularly limited, but the light diffusion property, film strength, etc. Is considered to be in the range of 1 to 100 μm, more preferably in the range of 3 to 30 μm.

  In addition, the anti-sticking layer or light diffusion layer contains surfactants, fine inorganic fillers, plasticizers, curing agents, antioxidants, UV absorbers, rust inhibitors, etc., as long as the performance is not impaired. May be.

  According to the laminated polyester film of the present invention, when a prism layer or the like is formed on one side, a sticking prevention layer or the like is formed on the opposite side, a laminated polyester film excellent in adhesion and visibility can be provided. 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) Glass transition point (Tg)
The urethane resin solution or aqueous dispersion is dried in a petri dish made of Teflon (registered trademark) so that the film thickness after drying is 500 μm to obtain a film. As drying conditions, after drying at room temperature for one week, further drying at 120 ° C. for 10 minutes. The obtained film was cut into a width of 5 mm, and set in a measuring device so that the distance between chucks was 20 mm in a dynamic viscoelasticity measuring device (DVA-200 type) manufactured by IT Measurement Control Co., Ltd. Until the temperature is increased at a rate of 10 ° C./min, measurement is performed at a frequency of 10 Hz. The point where E ″ was the maximum was taken as Tg.

(4) Adhesion evaluation method As a coating solution for the anti-sticking layer, on the second coated surface, 60 parts of acrylic polyol (Acridic A-801 manufactured by Dainippon Ink and Chemicals), polyisocyanate (Mitsui Chemical Polyurethane, Takenate) D110N) 15 parts, 7 parts of acrylic resin particles having an average particle diameter of 5 μm (MBX-5 manufactured by Sekisui Plastics Industry), 100 parts of toluene, 100 parts of methyl ethyl ketone, and 3 g / m in thickness by coating and heat curing ^Two anti-sticking layers were formed. Furthermore, in order to form a prism layer, 50 parts by weight of phenoxyethyl acrylate, 50 parts by weight of bisphenol A-diepoxy-acrylate, 2-hydroxy- is added to a mold member in which a large number of prism rows having a pitch of 50 μm and an apex angle of 65 ° are arranged in parallel. An active energy ray-curable composition composed of 1.5 parts by weight of 2-methyl-1-phenyl-propan-1-one is disposed, and the first coating layer contacts the active energy ray-curable resin from above. The laminated polyester film was laminated in the direction, the active energy ray-curable composition was uniformly stretched by a roller, and ultraviolet rays were irradiated from an ultraviolet irradiation device to cure the active energy ray-curable composition. Subsequently, the film was peeled off from the mold member to obtain a film on which a prism layer was formed. The layer structure of the film is prism layer / first coating layer / polyester film / second coating layer / sticking prevention layer. Then, after leaving in a constant temperature and humidity chamber at 60 ° C. and 90% RH for 500 hours, 10 × for each of the prism layer (first coating layer) and the anti-sticking layer (second coating layer). 10 crosscuts are put, 18mm wide tape (Cellotape (registered trademark) CT-18 manufactured by Nichiban Co., Ltd.) is pasted on it, and it is peeled off rapidly at a peeling angle of 180 degrees. When the peeled area was 0%, ◎, when it exceeded 0% and 5% or less, ◯, when it exceeded 5% and 20% or less, Δ, and when it exceeded 20%, ×.

(5) Method for measuring absolute reflectance minimum value from second coating layer surface in polyester film In advance, a black tape (vinyl tape VT-50 manufactured by Nichiban Co., Ltd.) is pasted on the first coating layer side of the polyester film, and the spectrophotometer Meter (Nippon Bunko UV-Vis spectrophotometer V-570 and automatic absolute reflectometer AM-500N) using synchronous mode, incident angle 5 °, N-polarized light, response Fast, data collection interval The absolute reflectance in the wavelength range of 300 to 800 nm was measured on the surface of the second coating layer at 0 nm, the bandwidth was 10 nm, and the scanning speed was 1000 m / min, and the wavelength (bottom wavelength) and absolute reflectance at the minimum value were evaluated.

(6) Interference unevenness evaluation method (4) For prism layer / first coating layer / polyester film / second coating layer / sticking prevention layer, which is a double-sided processed product created by the adhesion evaluation method, prism A black tape (vinyl tape VT-50 manufactured by Nichiban Co., Ltd.) is attached to the layer side, and the interference unevenness is visually observed under the three-wavelength fluorescent lamp from the sticking prevention layer side, and the interference unevenness cannot be confirmed. ◎, where interference unevenness with unclear color is confirmed, ○ when interference unevenness with which color can be identified is confirmed, with strong interference unevenness with which color can be identified, and interference even under white fluorescent lamps What was confirmed as unevenness was evaluated as 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, 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. Obtained polyester (C) having an intrinsic viscosity of 0.66 using a method similar to the method for producing polyester (A).

Examples of compounds constituting the coating layer are as follows.
(Example compounds)

・ Polyurethane resin with polycarbonate structure: (IA)
400 parts of polycarbonate polyol composed of 1,6-hexanediol and diethyl carbonate having a number average molecular weight of 2000, 10.4 parts of neopentyl glycol, 58.4 parts of isophorone diisocyanate, and 74.3 parts of dimethylolbutanoic acid. An aqueous dispersion of urethane resin having a Tg of −30 ° C., obtained by neutralizing a prepolymer with triethylamine and extending the chain with isophoronediamine.

・ Polyurethane resin with polycarbonate structure: (IB)
RU-40-350 (manufactured by Stahl), which is a water-dispersed polycarbonate polyurethane resin having a carboxyl group and Tg of −20 ° C.

・ Urethane resin with polycarbonate structure: (IC)
SPX-039 (manufactured by ADEKA), which is a vinyl group-containing polycarbonate polyurethane resin having a Tg of 3 ° C. in a carboxylic acid water dispersion type

Melamine compound: (II) Hexamethoxymethylmelamine Acrylic resin: (IIIA) 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 (wt%) emulsion polymer (emulsifier: anionic surfactant)

-Acrylic resin: (IIIB) 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)

-Urethane resin: (IVA)
Neoresin R-960 (DSM NeoResins), an aliphatic polyester polyurethane resin
-Urethane resin: (IVB)
Hydran AP-40 (manufactured by DIC ), which is a carboxylic acid water-dispersed polyester polyurethane resin.
・ Polyester resin: (V)
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%)

Oxazoline compound: (VIA) Epocros WS-500 (manufactured by Nippon Shokubai Co., Ltd.), which is a polymer type cross-linking agent in which an oxazoline group is branched to an acrylic resin
Epoxy compound: (VIB) Denacol EX-521 (manufactured by Nagase ChemteX), which is polyglycerol polyglycidyl ether
-Particles: (VII) Silica sol with an average particle diameter of 65 nm-Metal chelate compounds: (VIII) 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 roll peripheral speed difference, and then the coating liquid A1 shown in Table 1 below was applied to one side of the longitudinally stretched film, and the surface on the opposite side Coating solution B1 was applied to the film, guided to a tenter, stretched 4.0 times at 120 ° C in the transverse direction, heat treated at 225 ° C, and relaxed by 2% in the transverse direction, indicating the coating amount (after drying). A polyester film having a coating layer as shown in 2 and a thickness of 188 μm (surface layer 9 μm, intermediate layer 170 μm) was obtained.

  When the adhesiveness of the obtained polyester film was evaluated, both the first coating layer side and the second coating layer side were good. Further, there was no interference unevenness on the sticking prevention layer side, and the visibility was good. The properties of this film are shown in Table 2 below.

Examples 2 to 15 :
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 finished polyester film was as shown in Table 2.

Comparative Examples 1 to 7 :
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, as shown in Table 2, there were cases where the adhesion was weak or the level of interference unevenness was not good.

The concentration of the coating solution was a 3 wt% aqueous solution when the coating amount was 0.03 g / m ² , and a 10 wt% aqueous solution when the coating amount was 0.10 g / m ² or more.

  The film of the present invention can be suitably used for applications that require good adhesion and visibility with various functional layers such as a backlight unit of a liquid crystal display.

Claims (2)

One side of the polyester film has a coating layer containing a urethane resin having a polycarbonate structure, the other side contains a melamine compound, and the absolute reflectance has a minimum value in the range of wavelengths from 350 nm to less than 550 nm. Is present, the minimum value is 3.4 to 3.9%, and when the minimum value is in the wavelength range of 550 nm to 750 nm, the minimum value is 3.1 to 3.8%. A laminated polyester film comprising a coating layer. The laminated polyester film according to claim 1, further comprising a crosslinking agent in the coating layer containing a urethane resin having a polycarbonate structure.