JP2008255236A - Polyester film for optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film that has no unevenness and no defect, provides a high-quality image realizing a high brightness and has excellent processing characteristics and optical performance when used as members for LCD, PDP, organic EL, projection display etc. <P>SOLUTION: The biaxially oriented polyester film for optical use is a polyester film having a coated layer on at least one side and has a film haze of 1.0-3.0%, a SRa of both film sides of 0.005-0.020 μm and a P-V of 0.5-2.0 μm, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an optical polyester film, and more specifically, various optical members used for liquid crystal displays (hereinafter abbreviated as LCD), plasma displays (hereinafter abbreviated as PDP), and the manufacture of products in the optical field. The present invention relates to a polyester film used for a protective film, a release film, and the like used in the process, which is excellent in optical characteristics and can contribute to improving the quality of optical products and reducing energy consumption.

  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.

  In recent years, polyester films have been frequently used for various optical films. Base films such as prism sheets, lens sheets, diffusers, reflectors, and touch panels for LCD components, antireflection base films, and explosion-proof base films for displays It is used for various applications such as 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, and there are no defects such as foreign matter and scratches that affect the image. Necessary.

  Image color tone and brightness are important characteristics in displays, and it is known that the polyester film used as a member affects the image color tone and brightness. In particular, when obtaining high quality images, high color reproducibility and brightness are required. Therefore, polyester films have been required to have characteristics for realizing color reproducibility and high brightness. . For this purpose, it goes without saying that the polyester film has a high degree of transparency, but in addition to this, it is necessary to have further optically advantageous properties.

In addition, the processing characteristics at the time of processing are important as the display becomes larger and mass-produced. For example, it is important to design a surface that can prevent scratches and improve processing speed by improving slipperiness. That is, film characteristics that maintain good workability while maintaining the above optical characteristics and at the same time conflict with each other have become important.
JP 2005-263853 A JP 2005-179486 A

  The present invention has been made in view of the above circumstances, and its solution is to achieve high brightness with no unevenness and defects when used as a member of LCD, PDP, organic EL, projection display and the like. An object of the present invention is to provide a polyester film that can give a quality image and has excellent processing characteristics and excellent optical performance.

  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 a polyester film having a coating layer on at least one side, the film haze is in the range of 1.0 to 3.0%, the SRa on both sides of the film is 0.005 to 0.020 μm, P -V exists in the range of 0.5-2.0 micrometers, respectively exists in the biaxially-oriented polyester film for optics.

Hereinafter, the present invention will be described in more detail.
The polyester used for the polyester film in the present invention refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. 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. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. In this invention, it is preferable to contain 2-10 mol% of 3rd components other than a main structural component.

  As a method for containing the third component, a copolymer polyester containing a predetermined amount of a copolymer component as a raw material for producing a film may be used, or a copolymer polyester containing a copolymer component larger than a predetermined amount. Further, a raw material obtained by blending a copolymer polyester or homopolyester having a small content of copolymer components may be used. Examples of the third component herein include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like as the dicarboxylic acid component, and P-oxybenzoic acid as the oxycarboxylic acid. Examples of the glycol component include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like. Among these, when diethylene glycol, triethylene glycol, or 1,4-cyclohexanedimethanol is used, it is preferable in that the optical unevenness of the film due to polymer orientation and thickness unevenness can be efficiently reduced. Here, as a third component contained in the polyester, diethylene glycol by-produced from ethylene glycol during polymerization is also included.

  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. However, the film of the present invention is preferably an antimony compound or a titanium compound catalyst.

  In the case of using an antimony compound catalyst, the amount is preferably set to zero or 100 ppm or less as antimony so that dullness of the film can be reduced and the light transmittance can be improved.

  When using a titanium compound, it is preferable to contain both a titanium compound and a phosphorus compound. When a titanium compound and a phosphorus compound are used, the titanium element content in one layer needs to be 20 ppm or less, preferably 10 ppm or less, and the lower limit is usually 1 ppm, preferably 2 ppm. It is. When there is too much content of a titanium compound, an oligomer is by-produced in the process of melt-extruding polyester, and a film having high transparency with a low oligomer cannot be obtained. Further, when no titanium element is contained, the productivity at the time of production of the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization cannot be obtained. On the other hand, the amount of phosphorus element is preferably 1 ppm or more, more preferably 5 ppm or more, and the upper limit is usually 300 ppm, preferably 200 ppm, more preferably 100 ppm. By containing a specific amount of the above-described titanium compound and containing a phosphorus compound, it is possible to exert a remarkable effect on the reduction of the contained oligomer. When there is too much content of a phosphorus compound, gelatinization will occur and it may become a foreign material and cause the quality of a film to fall. When a titanium compound and a phosphorus compound are contained in the above-described range, oligomer by-products can be prevented. The layer containing the titanium compound and the phosphorus compound preferably contains no antimony element, and is usually 100 ppm or less, preferably 60 ppm or less. If the amount of the antimony element is too large, it may be reduced by the phosphorus compound during melt extrusion and aggregate to cause foreign matters, or the film may become dark and the transparency may be impaired.

  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 polyester layer in the present invention, it is necessary to blend particles for the main purpose of imparting slipperiness. 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. Among the above particles, silica and organic particles are preferable for the film of the present invention in order to increase transparency.

  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.

  The average particle diameter of the particles used is usually 0.01 to 5 μm, more preferably 0.1 to 4.0 μm, and particularly preferably 0.5 to 3.0 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 may become inferior.

  Further, 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. By appropriately selecting the particle type, particle size, and blending amount, the values of light transmittance, haze, light transmittance, and surface roughness, which are matters of the present invention, can be satisfied.

  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 this invention is 100-300 micrometers normally, More preferably, it is 150-250 micrometers, Most preferably, it is the range of 170-250 micrometers. When the thickness of the film is less than 100 μm, there is a concern that the film will be worn or deteriorated in workability when mounted on a large screen. In addition, when the thickness exceeds 300 μm, there is a concern that the film-forming property of the film is deteriorated or the workability is deteriorated due to the strength of the waist of the film.

  The film haze of the film of the present invention is 1.0 to 3.0%, preferably 1.0 to 2.5%. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 3.0%, it is unsuitable for optical use. The light transmittance is preferably 90% or more. If the light transmittance is less than 90%, it may be inappropriate for optical use due to a decrease in light transmittance.

  The birefringence (hereinafter referred to as Δn) of the film of the present invention is usually in the range of 0.02 to 0.10, preferably 0.02 to 0.08, and more preferably 0.03 to 0.07. When Δn is 0.02 or less, when the film of the present invention is sandwiched between polarizing plates and light passes through, strong red color is likely to be developed depending on the angle of the polarizing plates, and the color tone of the liquid crystal screen may be remarkably deteriorated. . On the other hand, film forming conditions where Δn exceeds 0.10 may be inappropriate for optical use due to problems such as increased heat shrinkage.

  Regarding the surface roughness of both surfaces of the polyester film of the present invention, SRa (average roughness) is in the range of 0.005 to 0.020 μm, preferably 0.007 to 0.018 μm, more preferably 0.010 to 0.017 μm. The PV (maximum height) is in the range of 0.5 to 2.0 μm, preferably 0.5 to 1.8 μm, and more preferably 0.7 to 1.7 μm. When SRa or PV is lower than the above lower limit, the film surface is too smooth, resulting in poor film slipperiness, film handling properties, winding properties, and film runnability during processing. Scratches and the like are mixed when passing the roll. On the other hand, when SRa or PV exceeds the above upper limit value, the film surface has a large roughness, the light scattering on the surface is large and the light transmittance is reduced, and also because of large protrusions existing on the film surface. There is a concern that the unevenness of the coating becomes a starting point during processing, or a problem due to the dropping of the protrusion. Furthermore, for example, after assembling a liquid crystal backlight that uses the films in lamination, there is a concern that large protrusions on the film surface may damage the films before and after that.

In the film of the present invention, the sum of the front and back surfaces of the 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.} If the amount of oligomer deposition on the film surface exceeds 15 mg / m ² , the oligomer may crystallize on the surface to reduce the transparency of the film, or it may dissolve into the functional layer provided on the film and affect the properties. It is easy to cause problems such as.

  In order to make the oligomer precipitation amount on the film surface by heat treatment within the above range, it is particularly a laminated film composed of at least three layers by coextrusion, and a polyester having a low oligomer content is used as the outermost layer constituting the surface layer, By providing the coating layer inline or offline, the oligomer deposition amount on the film surface after the heat treatment can be controlled within the above range by suppressing oligomer precipitation on the film surface.

  The film of the present invention can be formed into a laminated structure using a coextrusion method. In this case, the thickness of the outermost layer is preferably 3 μm or more, more preferably 5 μm or more in terms of the thickness on only one side, and the total thickness. Is usually 1/4 or less, more preferably 1/5 or less, and particularly preferably 1/10 or less. When the thickness is less than 3 μm, oligomers (cyclic trimers) contained in the inner layer are 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 blended in the outermost layer may increase and the transparency may be impaired.

  On the other hand, when the present invention is carried out with a single layer, it is also preferable that the film is made to contain no particles as much as possible and the coating layers on the front and back sides contain particles.

  When it manufactures as this laminated | multilayer film, it is preferable that content of the 3rd component in this invention sets the amount of 3rd component contained in the whole film with respect to polyester of the whole film as the above-mentioned range. This is because the prevention of optical unevenness, which is a problem to be improved in the present invention, relates to the transmitted light of the film and relates not only to the film surface and the inside but to the entire characteristics. Moreover, when adding additives, such as the said ultraviolet absorber and dye, it is preferable to mix | blend with the intermediate | middle layer of a laminated | multilayer film.

  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 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then at 90 to 160 ° C. in the lateral direction. It is preferable to perform 2-6 times stretching and to heat-process at 150-240 degreeC for 1 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, two or three or more polyester melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. As the layer structure, an A / B structure using an A raw material and a B raw material, or an A / B / A structure, and further using a C raw material to form an A / B / C structure or other film. Can do. For example, the surface shape of the A layer can be designed using specific particles as the A raw material, and a film having an A / B or A / B / A structure can be formed using a raw material not containing particles as the B raw material. In this case, since the raw material of B layer can be selected freely, a cost advantage etc. are large. Further, even if the recycled material of the film is blended with the B layer, the surface roughness can be designed by the surface A 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 with an offline coat after manufacture of a film as needed. Further, the coat may be 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, 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, 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 it is formed only on one side, an application layer different from the above-mentioned application layer can be formed on the opposite side as necessary to give other characteristics. 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. Moreover, 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 are cases where oligomers and dust adhering to the core serve as nuclei, and the coating agent repels and disappears from the nuclei. 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 (N) of coating spots having a major axis of 2 mm or more is 50 or less, further 30 or less, particularly 10 or less per 10 m ^{2 of} film. preferable. 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 exerts particularly excellent effects when used for optics, and as its specific members, a reflector for LCD, a diffuser, a prism sheet, a lens for LCD Sheets, brightness enhancement films, protective films for liquid crystal panels, release films for panel manufacturing processes, and so-called PDP filters for PDPs, electromagnetic shielding, near infrared shielding, color correction, ultraviolet shielding, reflection Effectively used as a substrate that requires a high degree of transparency, such as film substrates having various functions such as prevention, and processes for panel manufacturing, and projection televisions for image forming screens. . In particular, it is suitably used for LCDs as a base material for diffusion plates, prism sheets, and lens sheets because of its high brightness, workability, and durability.

  The film of the present invention is excellent in optical properties such as transparency, low haze, and optical uniformity, can contribute to improving the quality of optical products and reducing energy consumption, and is used for various types of LCDs, PDPs, etc. When used as an optical member, its advanced characteristics are exhibited and its 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 third component (copolymerization component) content About a solution in which a resin sample was dissolved in a deuterated chloroform / hexafluoroisopropanol (weight ratio 7/3) mixed solvent to a concentration of 3% by weight, Using a nuclear magnetic resonance apparatus (“JNM-EX270 type” manufactured by JEOL Ltd.), 1H-NMR was measured, each peak was assigned, and the content of the copolymer component was calculated from the integrated value of the peak.
(3) Quantitative determination of the amount of metal element and phosphorus element Using a fluorescent X-ray analyzer (model “XRF-1500” manufactured by Shimadzu Corporation), single-sheet measurement by the film FP method under the conditions shown in Table 1 below The detection limit in this method is usually about 1 ppm.

(4) 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.

(5) Film haze and light transmittance Film haze and light transmittance were measured with an integrating sphere turbidimeter “NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7105.

(6) Film thickness The film thickness was measured using a micrometer.

(6) Film surface roughness (SRa, PV)
SRa (average surface roughness) and PV (maximum height) were measured using a non-contact surface shape system (micromap 512) using a direct phase detection interference method, so-called two-beam interference method, manufactured by Micromap. . The measurement wavelength was 554 nm, the objective lens was 20 times, 20 fields were measured, and the average value was obtained.

(7) Workability As a representative of the optical member, the characteristics when used as a diffusion plate were evaluated. For the base material evaluation, the required characteristics of the diffusion sheet, the prism sheet, and the base sheet of the lens sheet are the same. That is, an acrylic binder containing particles containing particles was applied to one side of the film to form a light diffusion layer. The workability during the processing was evaluated from the following viewpoints.
A: Level that can be used without confirming appearance defects such as scratches on the obtained diffuser plate B: Level that can be used although some scratches etc. can be confirmed on the obtained diffuser plate C: Scratches etc. on the obtained diffuser plate Level that can be clearly confirmed and cannot be used D: Level that cannot be used because there is a protrusion on the surface of the resulting diffuser plate that may cause damage to the front and rear members when used as a product.

(8) Optical member suitability A-luminance In (7), the obtained diffusion sheet was incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints.
A: Brightness is high and usable level B: Brightness is comparable to conventional products and usable level C: Brightness is inferior to conventional products and cannot be used

(9) Suitability of optical member-workability The workability when the sheet obtained in (7) above was incorporated into a backlight unit was observed from the following viewpoints.
A: Level with no wrinkles and good workability when assembled. B: Slight wrinkles can be confirmed when assembled, but there is no problem with workability. C: Applicable screen when used due to wrinkles. Level that seems to be limited in size etc.

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 (A)>
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, and 2 parts by weight of diethylene glycol are used as starting materials, tetrabutoxy titanate as a catalyst, and a reactor with a Ti (titanium) content of 5 ppm. The reaction temperature was gradually increased as methanol was distilled off, and the temperature was increased to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed, and then a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.63. The diethylene glycol content was 4.0 mol%.

<Method for producing polyester (B)>
In the production method of polyester (A), antimony trioxide (200 ppm as antimony content) is used as a polymerization catalyst, 0.3 part of silica particles having an average particle diameter of 2.4 μm dispersed in ethylene glycol, and an intrinsic viscosity of 0.66. The polyester (B) was obtained using the same method as the production method of the polyester (A) except that the polycondensation reaction was stopped at the time corresponding to. The obtained polyester (B) had an intrinsic viscosity of 0.66.

<Method for producing polyester (C)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate / tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. Was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, and orthophosphoric acid was added to a P (phosphorus) content of 1000 ppm, and then germanium dioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the polyester (C) was 0.65. The diethylene glycol content was 1.5 mol%.

<Method for producing polyester (D)>
In the production method of the polyester (A), the polyester (D) is prepared using the same method as the production method of the polyester (A) except that the starting dicarboxylic acid is 80 parts by weight of dimethyl terephthalate and 20 parts of isophthalic acid. Obtained. The obtained polyester (D) had an intrinsic viscosity of 0.67, and the content of isophthalic acid and diethylene glycol as the third component was 21.0 mol%.

<Method for producing polyester (E)>
In the production of polyester (A), the starting materials were polyester (A) except that 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol and antimony trioxide as a polymerization catalyst were added so as to have an antimony content of 300 ppm. The polyester (E) was obtained using the same method as the production method. The intrinsic viscosity of the obtained polyester (E) was 0.65. The content of diethylene glycol was 1.0 mol%.

Example 1:
The above-mentioned polyesters (A), (B), and (C) were mixed at a ratio of 87%, 8%, and 5%, respectively, to prepare a raw material for the A layer, and polyesters (A) and (C) were each 95 %, 5% of the raw material as the raw material for the B layer, each supplied to two vent type twin screw extruders and melted at 285 ° C., the A layer as the outermost layer (surface layer), and the B layer as the intermediate layer Co-extruded in a layer configuration of 2 types, 3 layers (A / B / A), extruded from the die, cooled and solidified on a cooling roll set at a surface temperature of 40 ° C. using an electrostatic application adhesion method, and an unstretched sheet Obtained. Next, the film was stretched 3.3 times in the machine direction at a film temperature of 85 ° 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 6 times, heat treated at 230 ° C., and then relaxed 2% in the transverse direction to obtain a laminated polyester film having a thickness of 100 μm. The thickness of each layer of the obtained film was 15/70/15 μm. The thickness of the coating layer was 0.08 μm.

(Coating agent composition: weight ratio)
a / b / c / d = 50/20/30/3
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, the raw material of layer B is a raw material in which polyesters (A), (C), and (D) are mixed at a ratio of 90%, 5%, and 5%, respectively, and the thickness of each layer is 15/95/15 μm. The film forming conditions were a draw ratio of 3.0 times in the vertical direction and 3.6 times in the horizontal direction, and a polyester film having a thickness of 125 μm was obtained in the same manner as in Example 1.

Example 3;
In Example 1, the raw material of the A layer is 3% and 99% of (C) and (E), respectively, and the raw material of the B layer is polyester (C), (E), 1% and 99%. A polyester film having a thickness of 180 μm was obtained in the same manner as in Example 1 except that the thickness was changed to 10/160/10.

Example 4;
In Example 1, the raw material of the A layer is a raw material in which polyesters (A), (B), and (C) are mixed in proportions of 88%, 7%, and 5%, respectively, and the thickness of each layer is 12/236 / Except for the above, a polyester film having a thickness of 260 μm was obtained in the same manner as in Example 1.

Example 5;
A single layer polyester film using one extruder was prepared using raw materials in which polyesters (E) and (C) were mixed in proportions of 5% and 95%, respectively. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the film thickness was 75 μm.

Comparative Example 1;
Polyester having a thickness of 180 μm in the same manner as in Example 1 except that a mixed raw material in which polyesters (A), (B), and (C) are mixed in proportions of 75%, 20%, and 5%, respectively, was used as the raw material for the A layer A film was obtained.

Comparative Example 2;
A single layer polyester film using one extruder was prepared using raw materials in which polyesters (A) and (B) were mixed at a ratio of 95% and 5%, respectively. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the film thickness was 200 μm.

Comparative Example 3;
A layer is polyester (A), (B) is 95%, 5%, B layer is polyester (A), (B), (D) is 45%, 5%, except 50%, In the same manner as in Example 1, a 250 μm polyester film was obtained. The resulting film has too much content of the third component, so when used for optics, its properties deteriorate, heat resistance is insufficient, and the flatness of the film during actual use is insufficient. It was seen.

Comparative Example 4;
A single layer polyester film using one extruder was prepared using raw materials in which polyesters (E) and (C) were mixed at a ratio of 10% and 90%, respectively. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the thickness of the film was 50 μm.

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, for example, as a member for LCD or PDP.

Claims (1)

It is a polyester film having a coating layer on at least one side, the film haze is in the range of 1.0 to 3.0%, SRa on both sides of the film is 0.005 to 0.020 μm, and PV is 0.5 to 2 An optically biaxially oriented polyester film characterized by being in the range of 0.0 μm.