JP5730927B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film, for example, a backlight unit of a liquid crystal display, etc., reduction of interference unevenness due to light reflection, and good adhesion to a surface functional layer such as a light diffusion layer or a sticking prevention layer. The present invention relates to a laminated polyester film for various optics that requires

  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 transmission. 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.

  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.

  It is also known to use a compound having a condensed polycyclic aromatic as another technique for increasing the refractive index of the coating layer (Patent Documents 5 and 6). In recent years, however, hard coat layers and antireflection layers formed on coating layers for antireflection films are generally refracted compared to light diffusion layers and antisticking layers formed for light diffusion films. The rate is high. Therefore, the refractive index of the coating layer suitably used for the antireflection film is very high. On the contrary, for the light diffusing sheet, the refractive index is too high, thereby causing interference unevenness. Further, the hard coat layer or antireflection layer formed for the antireflection film and the light diffusion layer or antisticking layer formed for the light diffusion film have different components. Therefore, even if an application layer showing good adhesion is used for an antireflection film, it does not always show perfect adhesion for a light diffusing film.

JP 2000-89007 A JP 2004-4598 A JP 2007-286166 A JP 2006-20993 A JP 2006-175628 A JP 2007-181994 A

  The present invention has been made in view of the above circumstances, and its solution is to reduce the occurrence of interference unevenness due to reflection of light and to provide good adhesion to surface functional layers such as a light diffusion layer and an anti-sticking layer. It is an object of the present invention to provide a laminated polyester film that can be suitably used in, for example, a backlight unit 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, on at least one surface of the polyester film, the condensed polycyclic aromatic compound having a urethane resin, and have a coating layer formed from a coating solution containing a carbodiimide compound, the coating layer In the absolute reflectance of the surface, when a minimum value exists in the wavelength range of 400 nm or more and less than 550 nm, the minimum value is in the range of 3.4 to 3.9%, and the minimum value is in the range of the wavelength of 550 nm or more and 750 nm or less. Is present in the laminated polyester film characterized by having a minimum value of 3.1 to 3.8% .

  According to the polyester film of the present invention, when various surface functional layers such as a light diffusion layer and an anti-sticking layer are formed, there is little interference unevenness due to reflection of external light, and excellent adhesion to various surface functional layers. A base film can be provided, and its industrial value is high.

  The polyester film constituting the laminated polyester film in the present invention may have a single layer structure or a 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, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, p-oxybenzoic acid). 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.

  There is no restriction | limiting in particular as a polymerization catalyst of polyester, A conventionally well-known compound can be used, For example, an antimony compound, a titanium compound, a germanium compound, a manganese compound, an aluminum compound, a magnesium compound, a calcium compound etc. are mentioned. Among these, titanium compounds and germanium compounds are preferable because they have high catalytic activity, can be polymerized in a small amount, and the amount of metal remaining in the film is small, so that the brightness of the film becomes high. Furthermore, since a germanium compound is expensive, it is more preferable to use a titanium compound.

  Moreover, you may contain a ultraviolet absorber in a polyester film in order to improve the weather resistance of a film, and to prevent deterioration of the pigment | dye used for a color filter etc. The ultraviolet absorber is not particularly limited as long as it is a compound having ultraviolet absorbing ability and can withstand the heat applied in the production process of the polyester film.

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

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

  Moreover, the average particle diameter of particle | grains is 5 micrometers or less normally, Preferably it is 0.01-3 micrometers, More preferably, it is the range of 0.05-2 micrometers. When the average particle diameter exceeds 5 μm, the surface roughness of the film becomes too rough, and a problem may occur when various surface functional layers are formed in the subsequent process.

  Furthermore, the particle content in the polyester layer is usually 5% by weight or less, preferably 0.0003 to 3% by weight, when there are no or few particles, the transparency of the film becomes high and a good film. However, since the slipperiness may be insufficient, it may be necessary to devise measures such as improving the slipperiness by putting particles in the coating layer. Further, when the particle content exceeds 5% by weight, the transparency of the film may be insufficient.

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.

  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.

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

  Although the thickness of the polyester film in this invention will not be specifically limited if it can be formed into a film as a film, Usually, 10-300 micrometers, Preferably it is the range of 50-250 micrometers.

  As a film forming method of the film of the present invention, a generally known film forming method can be adopted, and there is no particular limitation. For example, when producing a biaxially stretched polyester film, the polyester raw material described above is first melt extruded from a die using an extruder, and the molten sheet is cooled and solidified with a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in 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-stage stretching direction at usually 70 to 170 ° C. and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, a method of obtaining a biaxially oriented film by performing heat treatment at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% can be mentioned. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

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

  Next, formation of the coating layer which comprises the laminated polyester film in this invention is demonstrated. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. More preferably, it is formed by in-line coating.

  In-line coating is a method of coating within the process of manufacturing a polyester film, and specifically, a method of coating at any stage from melt extrusion of a polyester to heat setting after stretching and winding up. Usually, it is coated on any of an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, and a film after heat setting and before winding. Although not limited to the following, for example, in sequential biaxial stretching, a method of stretching in the transverse direction after coating a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction) is particularly excellent. According to such a method, film formation and coating layer formation can be performed at the same time, so there is an advantage in manufacturing cost. In addition, in order to perform stretching after coating, the thickness of the coating layer can be changed by the stretching ratio. Compared to offline coating, thin film coating can be performed more easily. Further, by providing the coating layer on the film before stretching, the coating layer can be stretched together with the base film, whereby the coating layer can be firmly adhered to the base film. Furthermore, in the production of a biaxially stretched polyester film, the film can be restrained in the longitudinal and lateral directions by stretching while gripping the film end with a clip, etc. High temperature can be applied while maintaining the properties. Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the film forming property of the coating layer can be improved, and the coating layer and the base film can be more firmly adhered to each other. Furthermore, it can be set as a firm coating layer, and performances such as adhesion to various functional layers that can be formed on the coating layer and wet heat resistance can be improved.

  In the present invention, it is an essential requirement to have a coating layer formed from a coating solution containing a compound having a condensed polycyclic aromatic, a urethane resin and a carbodiimide compound on at least one surface of the polyester film. is there.

  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 be designed to be close to the geometric mean of the refractive index of the polyester film and the refractive index of the surface functional layer such as 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 urethane resin as the coating layer component used for imparting easy adhesion. Therefore, it is necessary to prepare a higher refractive index, and by using a condensed polycyclic aromatic capable of designing a compound that can prevent a decrease in adhesion, there is no interference unevenness and adhesion is good. A technique for forming the coating layer is effective.

  Specific examples of the condensed polycyclic aromatic include, for example, compounds having naphthalene, anthracene, phenanthrene, naphthacene, benzo [a] anthracene, benzo [a] phenanthrene, pyrene, benzo [c] phenanthrene, and perylene. .

  As a method of incorporating the condensed polycyclic aromatic into the polyester resin, for example, two or more hydroxyl groups are introduced into the condensed polycyclic aromatic as a substituent to form a diol component or a polyvalent hydroxyl component, or There is a method in which two or more acid groups are introduced to prepare a dicarboxylic acid component or a polyvalent carboxylic acid component. From the viewpoint of the stability of the polyester resin, it is preferable to introduce a carboxylic acid group into the condensed polycyclic aromatic to form an acid component. Moreover, in the laminated polyester film manufacturing process, it is preferable that the condensed polycyclic aromatic has a naphthalene structure in that it is difficult to be colored.

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

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

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

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

  In the present invention, in order to supplementarily adjust the refractive index of the coating layer, it is possible to use a high refractive index material other than the compound having a condensed polycyclic aromatic. Examples thereof include metal oxide fine particles, compounds containing many aromatic structures such as bisphenol A structures, compounds containing sulfur elements and halogen elements, and the like.

  The urethane resin is a polymer compound having a urethane bond in the molecule. 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 carboxylic acid group or a sulfonic acid group is preferable from the viewpoint of coating film properties and adhesion.

  One method for preparing a urethane resin, which is a constituent component of the coating layer used in the present invention, is a reaction between a hydroxyl group and an isocyanate. As the hydroxyl group used as a raw material, a polyol is preferably used, and examples thereof include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

  Examples of polycarbonate polyols include polycarbonate diols obtained by dealcoholization reaction from polyhydric alcohols and dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, and the like, such as poly (1,6-hexylene) carbonate, poly ( And 3-methyl-1,5-pentylene) carbonate.

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

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

  Among the above polyols, polycarbonate polyols and polyester polyols are more preferably used in order to improve adhesion to various surface functional layers.

  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.

  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-Bisaminomethylcyclohexane And alicyclic diamines.

  In order to increase the refractive index of the coating layer, the urethane resin may contain an aromatic compound as long as the adhesive properties are not impaired. In the polyester film manufacturing process, the aromatic compound includes a benzene skeleton or a naphthalene skeleton in that it is difficult to be colored.

  In the laminated polyester film in the present invention, in order to improve the appearance and transparency when various surface functional layers such as a light diffusing layer and an anti-sticking layer are formed on the coated surface, the coating appearance is improved. It is also possible to use a polymer other than the urethane resin in combination. As a polymer, for example, when a coating layer is formed only with a polyester resin or a carbodiimide compound without using a urethane resin, adhesion with a surface functional layer such as a light diffusion layer or an anti-sticking layer may not be sufficient. Therefore, it is necessary to use in combination as long as the gist of the present invention is not impaired.

  The carbodiimide compound used in the present invention is a compound having a carbodiimide structure, and improves the adhesion between the light diffusion layer that can be formed on the coating layer and the surface functional layer such as an anti-sticking layer, and the coating layer. It is used to improve the heat and moisture resistance of the. The carbodiimide compound is a compound having one or more carbodiimide or carbodiimide derivative structures in the molecule, but a polycarbodiimide compound having two or more in the molecule is more preferable for better adhesion and the like.

  The carbodiimide compound can be synthesized by a conventionally known technique, and generally a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and any of aromatic and aliphatic compounds can be used. Specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexa Examples include methylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

  Furthermore, in order not to lose the effect of the present invention, in order to improve the water solubility and water dispersibility of the polycarbodiimide compound, adding a surfactant, polyalkylene oxide, quaternary ammonium salt of dialkylamino alcohol, You may add and use hydrophilic monomers, such as a hydroxyalkyl sulfonate.

  The content of the carbodiimide group contained in the carbodiimide-based compound is a carbodiimide equivalent (weight of the carbodiimide compound to give 1 mol of carbodiimide group [g]) and is usually 100 to 1000, preferably 250 to 800, more preferably 300. It is -700, More preferably, it is the range of 350-650. Use within the above range is preferable because adhesion to the functional layer is improved.

  In the laminated polyester film of the present invention, when surface functional layers such as a light diffusing layer and an anti-sticking layer are laminated on the coated surface, adhesion is improved, interference unevenness is reduced, transparency is improved, and coating appearance is improved. For example, various polymers can be used in combination.

  Specific examples of the polymer include polyester resin, acrylic resin, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches and the like. It is done. Among these, polyester resins and acrylic resins are more preferably used from the viewpoint of improving the adhesion between the light diffusion layer and the surface functional layer such as a sticking prevention layer.

  Furthermore, in the formation of the coating layer, a crosslinking agent other than the carbodiimide compound can be used in combination as long as the gist of the present invention is not impaired. As the crosslinking agent other than the carbodiimide compound, various known crosslinking agents can be used, and examples thereof include an oxazoline compound, a melamine compound, an epoxy compound, an isocyanate compound, and a silane coupling compound. Among these, in particular, an oxazoline compound, a melamine compound, an epoxy compound, and an isocyanate compound may be used in combination with a carbodiimide compound to improve adhesion, and may be a more preferable form. Further, the melamine compound has a high refractive index and is a useful compound for adjusting the refractive index of the coating layer.

  These cross-linking agents are used in a design that improves the performance of the coating layer by reacting in the drying process or film forming process. It can be inferred that unreacted products of these crosslinking agents, compounds after the reaction, or mixtures thereof exist in the finished coating layer.

  In addition, in the formation of the coating layer, particles can be used in combination for the purpose of blocking and improving slipperiness. The average particle diameter is in the range of 1 μm or less, preferably 0.7 μm or less, more preferably 0.2 μm or less from the viewpoint of the transparency of the film. Further, from the viewpoint of adhesion and slipperiness, the average particle size is preferably in the range of 0.01 μm or more, more preferably 0.03 μm or more, and further preferably 0.05 μm or more. Specific examples of the particles include silica, alumina, kaolin, calcium carbonate, titanium oxide, and organic particles. Among them, silica is particularly preferable.

  Further, in the range not impairing the gist of the present invention, an antifoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant are formed as necessary for forming the coating layer. , Foaming agents, dyes, pigments and the like may be used in combination.

  In the compound having a condensed polycyclic aromatic that can be used for forming the coating layer constituting the laminated polyester film in the present invention, the proportion of the condensed polycyclic aromatic in the compound is preferably 5 to 80% by weight. More preferably, it is the range of 10 to 60% by weight. Further, the content of the compound having a condensed polycyclic aromatic is preferably in the range of 1 to 80% by weight, more preferably 3 to 70% by weight, as a ratio to the total nonvolatile components in the coating liquid forming the coating layer. More preferably, it is the range of 5 to 60 weight%. By using in these ranges, the refractive index of the coating layer can be easily adjusted, and interference unevenness after forming a surface functional layer such as a light diffusion layer or an anti-sticking layer can be easily reduced. The ratio of the condensed polycyclic aromatic can be determined by, for example, dissolving and extracting the coating layer with an appropriate solvent or warm water, separating by chromatography, analyzing the structure by NMR or IR, and further pyrolyzing GC-MS (gas It can be determined by analyzing by chromatography mass spectrometry) or optical analysis.

  As a ratio with respect to all the non-volatile components in the coating liquid forming the coating layer constituting the laminated polyester film in the present invention, the urethane resin is usually in the range of 5 to 80% by weight, preferably in the range of 10 to 70% by weight, and more preferably. Is in the range of 20-60% by weight. If it is out of the above range, if there is a possibility that the adhesion with the surface functional layer such as the light diffusion layer or the anti-sticking layer may decrease, the interference after the surface functional layer such as the light diffusion layer or the anti-sticking layer is formed. The visibility may not be good due to unevenness.

  As a ratio with respect to all the non-volatile components in the coating liquid which forms the coating layer which comprises the laminated polyester film in this invention, a carbodiimide type compound is the range of 1 to 80 weight% normally, Preferably it is the range of 5 to 70 weight%, and more. Preferably it is the range of 10 to 60 weight%. If it is out of these ranges, there is a possibility that the adhesion with the surface functional layer such as the hard coat layer may be lowered, or the coating appearance may be deteriorated.

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

  The analysis of the components in the coating layer can be performed by surface analysis such as TOF-SIMS, ESCA, and fluorescent X-ray.

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

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

  Examples of the method for forming the coating layer of the present invention include gravure coating, reverse roll coating, die coating, air doctor coating, blade coating, rod coating, bar coating, curtain coating, knife coating, transfer roll coating, squeeze coating, and impregnation. Conventionally known coating methods such as coat, kiss coat, spray coat, calendar coat, and extrusion coat can be used.

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

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

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

  The coating layer in the present invention has a refractive index adjusted in order to suppress the occurrence of interference unevenness, and the refractive index is a synergistic effect of the base polyester film and a surface functional layer such as a diffusion layer or an anti-sticking layer. It is designed around the average. 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 400 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 400 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 400 nm and 750 nm, or when the absolute reflectance of the minimum value is outside the above value, interference unevenness occurs after the formation of a surface functional layer such as a light diffusion layer or anti-sticking layer And the visibility of a film may fall.

  The laminated polyester film of the present invention is generally provided with a surface functional layer such as a light diffusion layer or an anti-sticking layer 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, an ultraviolet curable resin, or the like is preferably used, and examples thereof include acrylic polyol, polyester polyol, and various (meth) acrylates. In particular, from the viewpoint of increasing the hardness, an ultraviolet curable resin is preferable to a thermosetting resin. In addition, the description of (meth) acrylate in this specification represents an acrylate and a methacrylate.

  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, a (meth) acrylate resin is preferable, which can be used for improving the hardness of the light diffusion layer.

  The ultraviolet curable (meth) acrylate is not particularly limited. For example, a known active energy ray-curable monofunctional (meth) acrylate, bifunctional (meth) acrylate, or a mixture of one or more types of polyfunctional (meth) acrylate, or a resin material for ultraviolet curable hard coats. In addition to these, in addition to these, other additives may be used as long as the object of the present embodiment is not impaired.

  The UV-curable monofunctional (meth) acrylate is not particularly limited, but for example, methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate , Alkyl (meth) acrylates such as stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and other hydroxyalkyl ( Alkoxy alcohols such as meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, methoxypropyl (meth) acrylate, ethoxypropyl (meth) acrylate, etc. Amino group-containing (meth) acrylates such as aromatic (meth) acrylates such as ru (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, diaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, Methoxyethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, ethylene oxide modified (meth) acrylate such as phenylphenol ethylene oxide modified (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, Examples include (meth) acrylic acid.

  Although it does not specifically limit as ultraviolet curable bifunctional (meth) acrylate, For example, 1, 4- butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 6-hexanediol Di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, alkanediol di (meth) acrylate such as tricyclodecane dimethylol di (meth) acrylate, bisphenol A ethylene oxide modified di (meth) acrylate, bisphenol F Bisphenol-modified di (meth) acrylate such as ethylene oxide-modified di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, urethane di (meth) acrylate, epoxy Sidi (meth) acrylate etc. are mentioned.

  The UV curable polyfunctional (meth) acrylate is not particularly limited, but for example, dipentaerythritol hexa (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, penta Isocyanuric acid modified tri (meth) acrylates such as erythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, isocyanuric acid ethylene oxide modified tri (meth) acrylate, ε-caprolactone modified tris (acryloxyethyl) isocyanurate, Pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer Mer, urethane acrylates such as dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, and the like.

  Among these (meth) acrylates, a surface functional layer having a highly cross-linked structure can be formed, and therefore there is a merit such as high hardness and resistance to scratches, so a material having a larger number of functional groups is used. Ideally, a bifunctional or higher (meth) acrylate is preferable, and a tetrafunctional or higher (meth) acrylate is more preferable.

  In addition, the above-mentioned compound may be used independently and may be used together 2 or more types.

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

  The light diffusing 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 compound and particles as the light diffusing layer, and the content of the particles is not intended to be light diffusive, so a method of incorporating a smaller amount with a smaller particle size is common. 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.

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

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

(2) Measuring method of average particle diameter The coating layer was observed using TEM (H-7650 made by Hitachi, acceleration voltage 100V), and the average value of the particle diameters of 10 particles was defined as the average particle diameter.

(3) Method for measuring film thickness of coating layer The surface of the coating layer was dyed with RuO4 and embedded in an epoxy resin. Then, the section | slice produced by the ultrathin section method was dye | stained by RuO4, and the coating layer cross section was measured using TEM (H-7650 made from Hitachi, acceleration voltage 100V).

(4) Evaluation method of absolute reflectance from the coating layer surface in the polyester film In order to measure the absolute reflectance on one side of the polyester film, in order to suppress the reflection from the back surface, black tape is applied to the measurement back surface of the polyester film in advance. (Nichiban Co., Ltd. vinyl tape VT-50) is applied, synchronized mode and incidence using a spectrophotometer (UV-spectrophotometer V-570 and automatic absolute reflectance measuring device ARM-500N manufactured by JASCO Corporation) The absolute reflectance of the coating layer surface with a wavelength range of 400 to 800 nm was measured at an angle of 5 °, N polarization, response Fast, data collection interval of 1.0 nm, bandwidth of 10 nm, and scanning speed of 1000 m / min. Bottom wavelength) and reflectance were evaluated.

(5) Interference unevenness evaluation method As a light diffusion layer coating solution, 60 parts by weight of dipentaerythritol hexaacrylate, 20 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, a photopolymerization initiator (trade names: Irgacure 184, Ciba 5 parts by weight of specialty chemicals), 20 parts by weight of acrylic resin particles having an average particle size of 15 μm (MBX-15 manufactured by Sekisui Plastics Industry) and 200 parts by weight of methyl ethyl ketone were applied so that the dry film thickness was 5 μm. A light diffusing layer was formed by curing by irradiating with ultraviolet rays. 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.

(6) Adhesive 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. After being left for 100 hours (adhesion 2) in an environment of 80 ° C. and 85% RH in an initial temperature (adhesion 1) and a constant temperature and humidity chamber for the obtained film (adhesion 2), the light diffusion layer and the anti-sticking layer respectively After applying a 10 × 10 cross cut to the tape and applying an 18 mm wide tape (Cello Tape (registered trademark) CT-18 manufactured by Nichiban Co., Ltd.) on the tape, the tape was peeled off rapidly at a peeling angle of 180 degrees. When the peeled area is 0%, the peeled surface is observed, ◎ if the peeled area is 0%, ◯ if it exceeds 0% and 5% or less, ◯ if it exceeds 5% and 20% or less, △ and 20%. When it exceeded, it was set as x. 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.

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 30 ppm of ethyl acid phosphate with respect to the resulting polyester, and 100 ppm of magnesium acetate tetrahydrate with respect to the resulting polyester as the catalyst at 260 ° C. in a nitrogen atmosphere at 260 ° C. The reaction was allowed to proceed. Subsequently, 50 ppm of tetrabutyl titanate was added to the produced polyester, the temperature was raised to 280 ° C. over 2 hours and 30 minutes, the pressure was reduced to 0.3 kPa in absolute pressure, and melt polycondensation was further performed for 80 minutes to obtain the intrinsic viscosity. 0.63 polyester (A) was obtained.

<Method for producing polyester (B)>
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, and magnesium acetate tetrahydrate as a catalyst were subjected to an esterification reaction at 225 ° C. in a nitrogen atmosphere at 900 ppm with respect to the produced polyester. Subsequently, 3500 ppm of orthophosphoric acid was added to the produced polyester, and 70 ppm of germanium dioxide was added to the produced polyester. The temperature was raised to 280 ° C. over 2 hours and 30 minutes, and the pressure was reduced to an absolute pressure of 0.4 kPa. After 85 minutes of melt polycondensation, polyester (B) having an intrinsic viscosity of 0.64 was obtained.

<Method for producing polyester (C)>
In the production method of polyester (A), polyester (C) is obtained using the same method as the production method of polyester (A), except that 0.3 part by weight of silica particles having an average particle diameter of 2 μm is added before melt polymerization. It was.

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

-Urethane resin: (IIA)
Water of polyester polyurethane resin formed from isophorone diisocyanate unit: terephthalic acid unit: isophthalic acid unit: ethylene glycol unit: diethylene glycol unit: dimethylolpropanoic acid unit = 12: 19: 18: 21: 25: 5 (mol%) Dispersion.

-Urethane resin: (IIB)
An aqueous dispersion of a polycarbonate-based polyurethane resin formed from isophorone diisocyanate unit: polyhexamethylene carbonate unit: polyoxytetramethylene glycol unit: pentaethylene glycol unit = 12: 74: 5: 9 (mol%).

・ Carbodiimide compounds: (IIIA)
Polycarbodiimide compound Carbodilite (carbodiimide equivalent = 400, manufactured by Nisshinbo Co., Ltd.)

・ Carbodilite compounds: (IIIB)
Polycarbodiimide compound Carbodilite (carbodiimide equivalent = 430, manufactured by Nisshinbo Co., Ltd.)

・ Carbodilite compounds: (IIIC)
Polycarbodiimide compound Carbodilite (carbodiimide equivalent = 600, manufactured by Nisshinbo Co., Ltd.)

・ Polyglycerol polyglycidyl ether (IVA)

・ Hexamethoxymethylolmelamine (IVB)

-Particles: Silica particles (V) with an average particle size of 0.07 μm
Example 1:
A mixed raw material in which polyesters (A), (B), and (C) were mixed in proportions of 91%, 3%, and 6%, respectively, was used as a raw material for the outermost layer (surface layer), and polyesters (A) and (B) were each 97 %, 3% of the mixed raw material is used as an intermediate layer raw material, each is supplied to two extruders, melted at 285 ° C., and then on a cooling roll set at 40 ° C. Coextruded with a layer structure of layers (surface layer / intermediate layer / surface layer = 1: 18: 1 discharge amount) 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 layer thickness (after drying) is 0.08 μm. A 125 μm polyester film was obtained.

  When the obtained polyester film was evaluated, the bottom wavelength at the minimum value of the absolute reflectance of the coating layer was 540 nm, the reflectance was 3.8%, and the surface functional layers such as the light diffusion layer and the anti-sticking layer The film after forming the film had no interference unevenness and good adhesion. The properties of this film are shown in Table 2 below.

Examples 2-15:
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. As shown in Table 2, the finished polyester film had good interference unevenness level and good adhesion.

Comparative Examples 1-6:
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. When the finished laminated polyester film was evaluated, as shown in Table 2, there were cases where clear interference unevenness could be observed and adhesion was not good.

  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 (1)

On at least one surface of a polyester film, a compound having a condensed polycyclic aromatic, urethane resins, and have a coating layer formed from a coating solution containing a carbodiimide compound, in absolute reflectance of the coating layer surface, wavelength When the minimum value exists in the range of 400 nm or more and less than 550 nm, the minimum value is in the range of 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 minimum value exists. A laminated polyester film having a value of 3.1 to 3.8% .