JP2009202356A - Polyester film for optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film good in optical performances which, materializes high brightness and can give high-quality images without distortions and irregularities when used as a substrate and the like for a diffusion sheet, a prism sheet or a composite sheet. <P>SOLUTION: The polyester film for optical use is a biaxially oriented polyester film having resin layers stacked on both surfaces of a polyester resin layer, the above resin layer consisting of a polyester composition that contains 1-20 wt.% of a copolyester in which 70-90 mol% of the dicarboxylic acid component is terephthalic acid and 10-30 mol% is 2,6-naphthalene dicarboxylic acid and in which 20-60 mol% of the glycol component is 1,4-butanediol and 40-80 mol% is ethylene glycol. The polyester film has a haze of ≤2.5% and an all-light transmittance of ≥89.0%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical polyester film, and more particularly to an optical polyester film that can contribute to improving the quality of optical products because it has excellent optical properties and can achieve high brightness.

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Magnetic tape, ferromagnetic thin film tape, photographic film, packaging It is widely used as a material for films, films for electronic parts, electrical insulation films, metal laminate films, films to be attached to glass surfaces such as glass displays, and protective films for various members.

  Polyester films have been used in recent years, especially for various optical films. Base films such as prism sheets for LCD members, light diffusion sheets, composite sheets, reflectors, and touch panels, antireflection base films, and explosion-proof bases for displays It is used for various applications such as films and PDP filter films. In these optical products, in order to obtain a bright and clear image, the base film used as an optical film has good transparency from its usage pattern and does not have defects such as foreign matter and scratches that affect the image. Is required.

  As these optical films, a relatively thick polyester film having a thickness of about 50 to 350 μm is used, but as the thickness increases, it becomes difficult to uniformly heat or cool the film, so the film forming process In particular, in the step of cooling and solidifying a melted polyester resin to produce an amorphous sheet, a crystallized product is generated in the polyester sheet and causes optical defects, so that a solution is desired.

JP 2001-261856 A JP 2003-49011 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that when it is used as a member for optical products, particularly as a base material for backlight diffusion sheets, prism sheets, and composite sheets for LCDs. It is an object of the present invention to provide a polyester film excellent in optical performance capable of realizing high brightness and giving a high-quality image free from optical defects due to crystallized products.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is that, on both sides of the polyester resin layer, 70 to 90 mol% of the dicarboxylic acid component is terephthalic acid, 10 to 30 mol% is 2,6-naphthalenedicarboxylic acid, and 20 to 60 of the glycol component. A biaxially oriented polyester film in which a resin layer made of a polyester composition containing 1 to 20% by weight of a copolyester in which mol% is 1,4-butanediol and 40 to 80 mol% is ethylene glycol is laminated. An optical polyester film having a haze of 2.5% or less and a total light transmittance of 89.0% or more.

Hereinafter, the present invention will be described in more detail.
The polyester film of the present invention is a laminated film consisting of at least three layers, and all layers are co-melt extruded from a die of an extruder, extruded by a so-called co-extrusion method, and stretched and heat-treated. As obtained. Hereinafter, the coextruded three-layer film will be described. However, the present invention is not limited to the three-layer film as long as the gist of the present invention is not exceeded, and may be a multilayer of four layers or more.

  In the present invention, a polyester resin constituting the central layer (hereinafter sometimes abbreviated as A layer) and a copolymer constituting a layer laminated on both sides thereof (hereinafter sometimes abbreviated as B layer) Polyester resins other than polyester (hereinafter sometimes abbreviated as C) are obtained by a polycondensation reaction by a conventional method of polyvalent carboxylic acid and polyhydric alcohol. Further, two or more kinds of polyester resins obtained in the same manner and having different melting points can be mixed to form a composition. Examples of the dicarboxylic acid component used include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecadicarboxylic acid, and cyclohexanedicarboxylic acid. . As the diol component, ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, neopentyl glycol, polyethylene glycol, polytetramethylene ether glycol and the like aliphatic Examples thereof include alicyclic diols such as diol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanediol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like.

  The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low-polymerization degree polyester by reaction of a dicarboxylic acid and a diol, or a lower alkyl ester of a dicarboxylic acid and a diol reacted with a conventionally known transesterification catalyst. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony compound, a germanium compound, or a titanium compound may be used. Preferably, the amount of antimony compound is zero or 100% or less as antimony to reduce film dullness. .

  The polyester may be converted into chips after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  In the present invention, the copolymer polyester (C) means that 70 to 90 mol% of the acid component is terephthalic acid, 10 to 30 mol% is 2,6-naphthalenedicarboxylic acid, and 20 to 60 mol% of the glycol component is 1, 4-Butanediol, refers to a copolyester in which 40 to 80 mol% is ethylene glycol.

  As a method for obtaining the B layer in the present invention, a method of blending the copolymerized polyester (C) with another polyester and melt-kneading is preferably used. The content of the copolyester (C) in the present invention is 1 to 20% by weight, preferably 1 to 15% by weight. If it is less than 1% by weight, an optical defect due to a crystallized product occurs in the polyester sheet, and a high-quality image cannot be obtained. On the other hand, if it exceeds 20% by weight, the heat resistance is impaired, breakage occurs frequently during the production of the film, the stretchability is remarkably deteriorated, and the productivity is lowered.

  The copolymer polyester (C) constituting the B layer of the present invention is such that 70 to 90 mol% of the acid component is a terephthalic acid component, 10 to 30 mol% is a 2,6-naphthalenedicarboxylic acid component, preferably 75 to 90 mol. % Is terephthalic acid, and 10 to 25 mol% is composed of a 2,6-naphthalenedicarboxylic acid component. Outside this range, the dimensional stability of the film deteriorates, and when used as a member of a display product, distortion and unevenness occur in the image, and a clear and high-definition image cannot be obtained.

  Moreover, 20-60 mol% of the glycol component of the copolyester (C) constituting the B layer is a 1,4-butanediol component, 40-80 mol% is an ethylene glycol component, preferably 20-50 mol% is 1 , 4-butanediol component, preferably 50 to 80 mol% is composed of an ethylene glycol component. Outside this range, in the process of producing an amorphous sheet, an island-like non-uniform portion that is thought to be caused by partial crystallization occurs in the polyester sheet, which is not preferable.

  You may mix | blend particle | grains in the polyester layer in this invention with the main objective of providing lubricity. 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 thereof include particles of magnesium silicon oxide, kaolin, aluminum oxide, titanium oxide and the like. 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.

  Further, the average particle size of the particles used is usually preferably 0.01 to 5 μm. If the average particle size is less than 0.01 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, if the average particle size exceeds 5 μm, the surface roughness of the film becomes too rough and transparent. It will become inferior.

  Furthermore, the particle content in the polyester is usually in the range of 0.0003 to 1.0% by weight, preferably 0.0005 to 0.5% by weight, based on the total polyester constituting the film. When the particle content is less than 0.0003 wt%, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 1.0 wt%, the transparency of the film is insufficient. There are cases.

  The method for adding particles to the polyester 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, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. 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, heat stabilizers, lubricants, antistatic agents, fluorescent brighteners, dyes, pigments, and the like are added to the polyester film in the present invention as necessary. be able to. Depending on the application, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber, may be contained.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 50 to 350 μm, preferably 75 to 250 μm.

  The film of the present invention has a total light transmittance of 89.0% or more, preferably 89.5% or more, more preferably 90.0% or more. The film of the present invention is widely used in optical applications because of its excellent light transmittance. However, when the total light transmittance is less than 89.0%, it is unsuitable for optical use.

  The film haze of the film of the present invention is 2.5% or less, preferably 0.5 to 2.0%, more preferably 0.5 to 1.8%. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 2.5%, it is unsuitable for optical use.

  The polyester film for optical use of the present invention, particularly for display, has a color tone y value as measured by a single transmission method of preferably 0.3180 or less, more preferably 0.3178 or less. When the color tone y value exceeds 0.3180, the film has a strong yellowish tint and when used for a display, the color tone of the image becomes inferior or the luminance becomes low. There are many. In order to obtain a film having such a color tone, the catalyst and auxiliary agent for producing the raw material polyester are selected, the amount of the catalyst is reduced as much as possible, and the temperature of the polyester becomes higher than necessary during polymerization and film formation. In addition, it is possible to adopt a method such as preventing the melting time from becoming longer or reducing the amount of the recycled raw material.

In the film of the present invention, the sum of the front and back surfaces of the amount of oligomer (cyclic trimer) deposited on the film surface after heat treatment at 180 ° C. for 10 minutes is preferably 15 mg / m 2 or less, more preferably 10 .0mg / ^{m 2,} particularly preferably not more than 8.0 mg / ^{m 2.} When the amount of oligomer deposition on the film surface exceeds 15 mg / m ² , the oligomer crystallizes on the surface and lowers the transparency of the film, or dissolves in the functional layer provided on the film and affects the properties. It is easy to cause problems such as. The method of setting the oligomer precipitation amount on the film surface by heat treatment in the above range is not particularly limited, but the method using a raw material in which the oligomer is reduced in advance by a solid layer polymerization method to the polyester resin to be used, catalyst deactivation method, oligomer A method of coating the precipitation preventing layer is preferably used.

  The film of the present invention can be obtained by stretching and heat-treating the one extruded by the co-extrusion method. At that time, the thickness of the outermost layer (B layer) is usually 3 μm or more and the total thickness of only one side. It is preferable that it is 1/4 or less of thickness. If the thickness is less than 3 μm, the oligomer (cyclic trimer) contained in the inner layer is deposited on the film surface due to heat history during processing, etc., and contamination of the production line and an increase in the amount of foreign matter on the film surface are observed. On the other hand, if it is thicker than 1/4 of the total thickness, the amount of particles to be blended in the outermost layer may increase and the transparency may be impaired.

  Moreover, when adding additives, such as the said ultraviolet absorber and dye, it is preferable to mix | blend with the intermediate | middle layer (A layer) of a laminated | multilayer film.

In the film of the present invention, the number of crystallized substances having a diameter of 20 μm or more is usually 50 pieces / m ² or less, preferably 30 pieces / m ² or less. When deviating from the above conditions, when used as a member of an LCD or PDP, a defect due to a crystallized product may occur in the image, thereby impairing transparency and causing a significant deterioration in quality.

  Hereinafter, although the manufacturing method of the polyester film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  First, a dried or undried polyester chip by a known method is supplied to a melt-extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented 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. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 5 times in the longitudinal direction at 70 to 145 ° C. to form a longitudinal uniaxially stretched film, and then in the transverse direction at 90 to 160 ° C. It is preferable to perform 2 to 5 times stretching and heat treatment at 150 to 240 ° C. for 10 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, as described above, the polyester melt extruder is a plurality of extruders, a multi-layer multi-manifold die or a feed block, each polyester is laminated, and a multi-layer melt sheet is extruded from the die, and a cooling roll To obtain a substantially amorphous unstretched sheet. As a structure of a layer, it can be set as the D / E / D structure using D raw material and E raw material, and also it can be set as the D / E / F structure or other structure using F raw material. For example, the surface shape of the D layer can be designed using specific particles as the D raw material, and a film having no D / E / D structure can be obtained using a raw material not containing particles as the E raw material. In this case, since the raw material for the E layer can be freely selected, the cost advantage is great. Further, even if the recycled material of the film is blended with the E layer, the surface roughness can be designed by the D layer as the surface layer, so that the cost advantage is further increased.

  In particular, since the film of the present invention is used for optical applications, a hard coat layer, an antireflection layer, an antiglare layer, or the like is provided, or a vapor deposition layer or the like is provided. A coating layer as an undercoat layer can be provided for the purpose of improving adhesion or preventing charging in order to keep the surface clean. In forming such a coating layer, the method of forming a film, in particular, after stretching in the longitudinal direction and before stretching in the lateral direction can form a very thin coating layer, and the coating solution drying and curing reaction Is preferable in that it can be carried out in the film forming process. The coating layer is preferably a combination of a crosslinking agent and various binder resins, and as the binder resin, a polymer selected from polyester, acrylic polymer and polyurethane is usually employed from the viewpoint of adhesiveness. Each of the above polymers shall also include derivatives thereof. The derivative here refers to a polymer obtained by reacting a reactive compound with a copolymer or a functional group with another polymer.

  In addition, you may coat by an offline coat after manufacture of a film as needed. Moreover, it does not matter on one side or both sides. The coating material may be either water-based and / or solvent-based for offline coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, since the film of the present invention is used for optics, it is also preferable to form a functional multilayer thin film for the purpose of preventing dust reflection due to reflection of external light and static electricity, as well as electromagnetic shielding, in addition to improving adhesiveness. .

  Among the polyesters, acrylic polymers, and polyurethanes that are used as coating agents in the present invention, particularly preferred polymers have a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher. It is a polyurethane having a carboxylic acid residue, at least a part of which is made water-based using an amine or ammonia.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin may be either a monomer, a condensate composed of a dimer or higher multimer, or a mixture thereof.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipperiness, adhesion and the like. The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the transparency of the film is hindered and the sharpness of the image tends to be lowered. Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes. On the other hand, examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound containing two or more carbon-carbon double bonds in one molecule (for example, divinylbenzene).

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. The content of the particles in the coating layer is preferably 10% by weight or less, more preferably 5% by weight or less as an appropriate addition amount that does not impair the transparency.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.

  The coating layer may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually 0.01 to 0.5 μm, preferably 0.015 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  When such a coating film is applied to an optical application, the coating layer surface coating is problematic when an antireflection layer or the like is provided on the coating layer. The reason for the occurrence of coating leakage is not clear, but foreign matter in the film creates coarse protrusions on the film surface, which acts as a core and the coating agent repels, and it is stretched to generate coating leakage or the film surface. There may be a case where the oligomer or dust attached to the core becomes a nucleus and the coating agent repels and disappears from the nucleus. Therefore, it is necessary to form a film under such a condition that dust and foreign matters that can become nuclei are removed as much as possible. Such foreign substances include oligomers adhered or deposited on the film, so that reducing the amount of oligomers contained in the film has the effect of reducing the amount of coating.

When the film of the present invention thus obtained has a coating layer, the number of coating spots (N) is usually 50 or less per 10 m ^{2 of} film, more preferably 30 or less, and particularly preferably 10 or less. In any case, in an optical film that will become more and more severe in the future, it is necessary to make coating coating as zero as possible.

  The film of the present invention exhibits particularly excellent effects when used for optical purposes, and specific members thereof include diffusion sheets and prisms used as backlights for liquid crystal displays, plasma displays and the like. It is effectively used as a base material that requires a high degree of transparency, such as a sheet, a composite sheet having the functions of diffusion and prism, a lens sheet, and a brightness enhancement film.

  The film of the present invention has excellent optical properties such as transparency, low haze, and optical uniformity, and also improves quality such as preventing the occurrence of image defects of crystallized products that are optical defects when used as an optical product. A polyester film having good optical properties can be provided when used as various optical members used in LCDs, PDPs, etc., and the industrial value is extremely 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 measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was accurately weighed and dissolved by adding 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), 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) Total light transmittance, haze Total light transmittance is JIS-K-7361, haze is based on JIS-K-7136 by Nippon Denshoku Industries Co., Ltd. integrating sphere turbidimeter “NDH2000”. The rate and haze were measured.

(4) Color tone y value The color tone y value was measured with a Minolta spectrocolorimeter “CM-3700d” according to JIS-Z-5722.

(5) Number of crystallized materials on the film surface Light is irradiated with a halogen lamp to the film surface having a width of 1000 mm and a length of 20 m (area 20 m ² ) in a dark room, and the film surface is visually observed to crystallize a diameter of 20 μm or more. The number of objects was counted, and the number of crystallized substances per 1 m ^{2 of} film was calculated.

(6) Suitability for optical members (brightness)
As a representative optical member, characteristics when used as a prism sheet were evaluated. That is, an acrylic binder was applied to one side of the film to form a prism layer. The obtained prism sheet was incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints.
Luminance level (evaluated using a luminance meter and compared with the case of using the film of Comparative Example 1)
A: Brightness improved and improved B: Decrease in luminance could not be confirmed C: Reduced luminance

Examples and Comparative Examples are shown below, and the method for producing the polyester used in the Examples and Comparative Examples is as follows.
<Manufacture of polyester>
<Method for producing polyester (1)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (1) was 0.68.

<Method for producing polyester (2)>
In the production method of polyester (1), after adding 0.04 part of ethyl acid phosphate, 0.3 part of silica particles having an average particle diameter of 2.2 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide are added. In addition, polyester (1) was obtained using the same method as the production method of polyester (1) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.66. The obtained polyester (2) had an intrinsic viscosity of 0.66.

<Method for producing polyester (3)>
In the production method of polyester (1), the starting materials are 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, and the production method of polyester (1) except that germanium oxide is used as a polymerization catalyst. A polyester (3) was obtained using the same method as described above. In addition, the addition method of germanium oxide employ | adopted the well-known method, The addition amount was 100 ppm with respect to the raw material weight as germanium. The intrinsic viscosity of the obtained polyester (3) was 0.68.

<Method for producing copolymerized polyester (C)>
75 mol% of dimethyl terephthalate, 25 mol% of dimethyl 2,6-naphthalenedicarboxylate, 50 mol% of 1,4-butanediol, 50 mol% of ethylene glycol, and 0.005 part of tetrabutyl titanate are added to the reactor, and the reaction start temperature The reaction temperature was gradually raised along with distillation of methanol, and the temperature was raised to 225 ° C. after 3 hours. Furthermore, a polycondensation reaction was performed by a conventional method. In this reaction, the temperature was gradually increased and the pressure was gradually decreased from the normal pressure. After 2 hours, the temperature was 280 ° C. and the pressure was 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained copolyester (C) was 0.76.

Example 1:
A mixed raw material in which the polyesters (2), (3) and the copolyester (C) are mixed at a ratio of 10%, 82% and 8%, respectively, is used as a raw material for the B layer, and a raw material of 100% polyester (2) is used. As a raw material for the A layer, each is supplied to two vent type twin screw extruders and melted at 285 ° C., respectively, and the B layer is the outermost layer (surface layer) and the A layer is an intermediate layer of two types and three layers (B / A / B) was co-extruded and extruded from the die, and cooled and solidified on a cooling roll set at a surface temperature of 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, the film was stretched 3.2 times in the machine direction at a film temperature of 81 ° C. by utilizing the difference in peripheral speed of the roll, and after applying a coating agent having the composition shown below, it was led to a tenter, and 3. The film was stretched 7 times, heat-treated at 229 ° C., and then relaxed 5% in the transverse direction to obtain a laminated polyester film having a thickness of 250 μm. The thickness of each layer of the obtained film was 9/232/9 μm. The thickness of the coating layer was 0.10 μm.

(Coating agent composition: weight ratio)
a / b / c / d = 47/20/30/3
Here, a is a polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio); b is Methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) emulsion polymer (emulsifier: anionic surfactant); c is hexamethoxymethylmelamine (melamine type) D) is an aqueous dispersion (inorganic particles) of silicon oxide having a particle size of 0.06 μm.

Example 2:
In Example 1, except that the copolymerized polyester (C) is dimethyl terephthalate 85 mol%, 2,6-naphthalenedicarboxylate 15 mol%, 1,4-butanediol 40 mol%, ethylene glycol 60 mol%. In the same manner as in Example 1, a laminated polyester film having a layer configuration of 2 types and 3 layers (B / A / B) and a thickness of 250 μm was obtained. The thickness of each layer of the obtained film was 12/226/12.

Example 3:
A layer similar to Example 1 except that a mixed raw material obtained by mixing polyester (2), (3) and copolymer polyester (C) at a ratio of 12%, 73% and 15%, respectively, is used as the raw material of the B layer. A laminated polyester film having a structure of two types and three layers (B / A / B) and a thickness of 250 μm was obtained. The thickness of each layer of the obtained film was 9/232/9.

Comparative Example 1:
A mixed raw material obtained by mixing polyester (2), (3), and copolymerized polyester (C) at a ratio of 10%, 89.7%, and 0.3%, respectively, was used as a raw material for layer B, and 100% of polyester (2) Except that the raw material was used as the raw material of the A layer, a polyester film having a layer configuration of 2 types and 3 layers (B / A / B) and a thickness of 250 μm was obtained in the same manner as in Example 1. The thickness of each layer of the obtained film was 10/230/10 μm.

Comparative Example 2:
A mixed raw material obtained by mixing polyester (2), (1), and copolymerized polyester (C) at a ratio of 10%, 89.7%, and 5%, respectively, is used as a raw material for the B layer, and a raw material of 100% polyester (1) A polyester film having a layer structure of 2 types and 3 layers (B / A / B) and a thickness of 250 μm was obtained in the same manner as in Example 1 except that the raw material of layer A was used. The thickness of each layer of the obtained film was 11/228/11 μm.

Comparative Example 3:
In Example 1, the copolymer polyester (C) had dimethyl terephthalate 90 mol%, dimethyl 2,6-naphthalenedicarboxylate 10 mol%, 1,4-butanediol 5 mol%, and ethylene glycol 95 mol%. Except for the above, in the same manner as Example 1, the layer structure was 2 types / 3 layers (B / A / B), and a polyester film having a thickness of 250 μm was obtained. The thickness of each layer of the obtained film was 10/230/10 μm.

Comparative Example 4:
The polyester (2) and polyester production of Example 1 were prepared by using a mixed raw material obtained by mixing polyester (2), (3), and copolymerized polyester (C) at a ratio of 13%, 77%, and 10%, respectively, as the raw material for layer B. The film formation conditions were the same as in Example 1 except that the mixed material obtained by mixing the regenerated products from the ears and the film ends that were sometimes generated in proportions of 25 and 75% was used as the material for the A layer. A polyester film having a thickness of 188 μm of two types and three layers (B / A / B) was obtained. The thickness of each layer of the obtained film was 11/166/11 μm.

Comparative Example 5:
The same method as in Example 1 except that a mixed raw material obtained by mixing polyester (2), (3) and copolymerized polyester (C) in proportions of 10%, 10% and 80%, respectively, was used as the raw material for the B layer. However, it was impossible to obtain a satisfactory film because the stretchability was extremely poor and the film was frequently broken.

  The physical property values and optical member suitability of the obtained film are summarized in Table 1 below. It can be seen that a film satisfying the requirements of the present invention is highly suitable for optical use.

  The film of the present invention can be suitably used as a base material for, for example, a diffusion sheet, a prism sheet, or a composite sheet.

Claims (1)

On both sides of the polyester resin layer, 70 to 90 mol% of the dicarboxylic acid component is terephthalic acid, 10 to 30 mol% is 2,6-naphthalenedicarboxylic acid, and 20 to 60 mol% of the glycol component is 1,4-butane. Diol, a biaxially oriented polyester film in which a resin layer made of a polyester composition containing 1 to 20% by weight of a copolymer polyester whose ethylene glycol is 40 to 80 mol% is laminated, and the film haze is 2.5% or less, An optical polyester film having a total light transmittance of 89.0% or more.