JP2008195806A - Optical polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which little deposits oligomers, realizes high grade brightness, can give high quality images, and is good in optical performance, when used as an optical member for LCD, PDP, organic EL, or projection displays. <P>SOLUTION: This optical biaxially oriented polyester film comprising a polyester film is characterized by having a haze (H0) in a range of 1.0 to 3.0% and having a difference (ΔH) of ≤1.0% between a haze (H1) after heated at 150°C for 30 min. and a haze (H0) before heated. <P>COPYRIGHT: (C)2008,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 for use in a protective film, a release film or the like used in the process, which is excellent in optical properties 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. However, as the uses diversify, the processing conditions and use conditions of the film diversify, and when the polyester film is heat-treated, there is a problem that the oligomer exuding from the inside is deposited on the film surface. . When oligomer deposition on the film surface is severe, various problems occur, such as when the film is processed, the oligomer adheres to the process and becomes contaminated, or cannot be used for applications requiring high transparency.

Brightness is an important characteristic in displays, and it is known that the polyester film used as a member affects the brightness. In particular, when a high-quality image is obtained, a high brightness is required. Therefore, the polyester film has been required to have a characteristic for realizing a 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.
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 realize a very high luminance and high-quality image by using an extremely small amount of oligomer precipitation when used as an optical member. Another object of the present invention is to provide a polyester film having good 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 film made of polyester, the haze (H0) is in the range of 1.0 to 3.0%, the haze (H1) after heating at 150 ° C. for 30 minutes, and before the heat treatment. It exists in the biaxially-oriented polyester film for optics characterized by the difference ((DELTA) H) of haze (H0) being 1.0% or less.

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.

  The polyester film of the present invention preferably contains both a titanium compound and a phosphorus compound. The titanium element content in at least one layer of the film of the present invention needs to be 20 ppm or less, preferably 10 ppm or less, and the lower limit is usually 1 ppm, but preferably 2 ppm. 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 needs to be 1 ppm or more, preferably 5 ppm or more, and the upper limit is 300 ppm, preferably 200 ppm, and 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. In the present invention, when the titanium compound and the phosphorus compound are contained in the above-described range, the by-product of the oligomer can be prevented, and the effect of the present invention is highly obtained.

  Further, the layer containing the titanium compound and the phosphorus compound preferably contains no antimony element, usually 100 ppm or less, preferably 60 ppm or less, and most preferably substantially free, ie 10 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 film of the present invention satisfies the above problems to a high degree and exhibits particularly excellent effects for optical use. That is, by using a titanium compound as a catalyst, darkening as in the case of using antimony can be prevented, and a film having excellent transparency can be obtained, and by adding a phosphorus compound at the same time, the color tone of the film can be improved. Demonstrate the effect of not worsening. Specifically, when the b * value of the film is high, that is, when the film is used for optical purposes, the brightness may decrease and the image may be deteriorated when used for optics. It exhibits excellent properties in terms of transparency and color tone.

  In the present invention, by mixing a polyester produced by using titanium as a catalyst and a polyester containing a predetermined amount of a phosphorus compound, it is possible to obtain a film having the above-described amounts of titanium and phosphorus, thereby obtaining an excellent film. Can exert the effect. That is, when a polyester is produced by polymerization using titanium as a catalyst, if a phosphorus compound is added in the polymerization step, the polymerization rate is slowed down, resulting in deterioration of productivity, or the polymerization time is prolonged and the yellowish color becomes stronger. Problems can occur. On the other hand, when the polyester of the titanium catalyst is subjected to a melt extrusion process in which a film is produced in the absence of a phosphorus compound, a problem that yellowness increases due to thermal deterioration tends to occur. In the present invention, in order to prevent the occurrence of such a problem, a method in which a polyester containing a predetermined amount of a phosphorus compound is prepared as a master batch and mixed with a polyester using a titanium catalyst is preferable. Examples of the method for producing a master batch of a phosphorus compound include a method of polymerizing with a germanium catalyst, a method of polymerizing with a minimum amount of an antimony catalyst, and a method of adding in a step of melt extrusion to a polyester with a titanium catalyst. It is particularly preferable to employ a catalyst.

  In the polyester film of the present invention, as the polyester constituting the layer containing the titanium compound and the phosphorus compound within the aforementioned range, if a raw material obtained by solid-phase polymerization of the polyester formed into a chip after melt polymerization is used, This is preferable because the amount of oligomer contained in can be reduced.

  In the polyester film of the present invention, the amount of the oligomer contained in the layer containing the titanium compound and the phosphorus compound within the aforementioned range is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, particularly preferably 0. .3% by weight or less. When the amount of oligomer in the polyester layer is small, the amount of oligomer contained in the polyester film of the present invention is reduced and the effect of preventing oligomer precipitation on the film surface is particularly high.

  In the present invention, the third component other than the main constituent component is 2.0 to 10.0 mol%, preferably 2.5 to 10 mol%, more preferably 3.0 to 8.0 mol%. Is preferred. 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, optical unevenness of the film due to polymer orientation and thickness unevenness can be efficiently reduced, and the flatness of the film and This is preferable in that heat resistance and dimensional stability can be maintained at a high level. 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. Thereafter, it can be obtained by a method of performing a polymerization reaction in the presence of a polymerization catalyst.

  The polyester used in the present invention may be obtained by forming a chip after melt polymerization and subjecting it to further 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.

  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.

  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.

  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 9 to 300 μm, preferably 20 to 250 μm, and more preferably 25 to 250 μm.

  The total light transmittance of the film of the present invention is usually 90.0% or more, preferably 91.0%, more preferably 92.0% or more. The film of the present invention is widely used in optical applications because of its excellent transparency. However, when the total light transmittance is less than 90.0%, it may be inappropriate for optical use.

  The film of the present invention has a film haze of 1.0 to 3.0%, preferably 1.0 to 2.7%, more preferably 1.2 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 5%, it is unsuitable for optical use. On the other hand, when the content is lower than 1.0%, the film surface becomes smooth, and there is a concern that a scratch may be mixed during processing or a defect such that the mixed scratch is easily visible.

  In the film of the present invention, the difference between haze (H1) after heat treatment at 150 ° C. for 30 minutes and before heat treatment (H0) is 1.0% or less, preferably 0.8% or less. When the difference is 1.0% or more, there is a possibility that optical characteristics over time, particularly deterioration of light transmittance, etc. may occur after completion as a product. Furthermore, if it is bad, there is a possibility that the yield of the product may be deteriorated due to the contamination of the secondary process and the tertiary process due to the precipitation of the oligomer which is one of the causes of haze-up.

  The polyester film for optical use of the present invention, particularly for display, has a color tone b * value measured by a single transmission method of preferably -5 to +3, more preferably -4 to +2, particularly preferably -3. The range is 5 to +1. When the b * value exceeds +3, it is often unsuitable in that the yellow tone is strong and the color tone of the image becomes inferior or the luminance is low when used for a display. On the other hand, in the film lower than -5, there is a problem of color tone, but in the case of a polyester film, since the b * value is not lower than -5, a method such as using an additive is used. This is not preferable because it may cause problems such as bleeding out of additives and reliability during long-term use. 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 polyester is heated to an unnecessarily high temperature during polymerization and film formation. Further, it is possible to adopt methods such as preventing the melting time from becoming longer and 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 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. It is 0 mg / m 2 or less, particularly preferably 8.0 mg / m 2 or less. If the amount of oligomer deposition on the film surface exceeds 15 mg / m2, the oligomer may crystallize on the surface and decrease the transparency of the film, or it may affect the characteristics by dissolving in the functional layer provided on the film. Prone to causing problems.

  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 / offline, the oligomer deposition amount on the film surface after the heat treatment can be controlled within the above range by suppressing the oligomer deposition on the film surface.

  The film of the present invention can be formed into a laminated structure using a co-extrusion 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 of only one side, and the total thickness is 1/4 or less is preferable, 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 to be 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, content of the 3rd component in this invention needs to make the amount of 3rd component contained in the whole film with respect to polyester of the whole film into 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 also 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, as needed, you may coat with an offline coat after manufacture of a film. 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, in addition to improving adhesiveness, it is also possible to prevent external light reflection and dust adhesion due to static electricity, and to form a functional multilayer thin film for the purpose of electromagnetic wave shielding. preferable.

  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 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 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 3 mm or more is preferably 50 or less, more preferably 30 or less, particularly preferably 10 m ^{2 of the} film. 10 or less. In any case, in an optical film that will become more and more severe in the future, it is preferable to reduce coating coating to zero as much as possible.

  The film of the present invention exerts particularly excellent effects when used for optical purposes, and its specific members include advanced diffusers and prism sheets for backlights for liquid crystal displays. It is effectively used as a substrate that requires transparency.

  The film of the present invention is excellent in optical properties such as transparency, low haze, and optical uniformity, and can contribute to improving the quality of optical products and reducing energy consumption. When used as various optical members, the advanced characteristics are exhibited 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) Quantification of amount of metal element and phosphorus element in film Using a fluorescent X-ray analyzer (model “XRF-1500” manufactured by Shimadzu Corporation), the film FP method was used. The amount of elements in the film was determined by sheet measurement, and the detection limit in this method is usually about 1 ppm.

(4) Film haze (H)
In a nitrogen atmosphere, the polyester film was left to stand in an oven at 150 ° C. for 30 minutes and subjected to heat treatment according to JIS-K7105, using an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. ) Was measured. The difference in film haze before and after the heat treatment (ΔH) was determined by subtracting the turbidity (H0) of the polyester film before the heat treatment from (H1).

(5) Suitability of optical members-brightness (1)
As a representative optical member, the characteristics when used as a diffusion plate were evaluated. That is, a light diffusion layer was formed by applying an acrylic binder containing particles on one side of the film. 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.
Luminance level (evaluated using a luminance meter, compared with the case of using a conventional PET film, ie, Comparative Example 3 film in the present invention)
A: Brightness improved and improved B: Decrease in luminance could not be confirmed C: Decrease in luminance was observed

(6) Suitability for optical members-luminance after heating (2)
In the suitability evaluation described above, the obtained diffusion sheet was left in an oven at 150 ° C. for 30 minutes in a nitrogen atmosphere, and then incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints.
A: Level that can be used without any change in brightness before and after heating B: Level that can be used before and after heating, but level C that can be used C: Level that cannot be used due to large fluctuations in brightness before and after heating

(7) Optical member suitability—workability suitability In the above (5), the degree of contamination of the roll of the processing machine during diffusion sheet processing was confirmed visually and evaluated from the following viewpoints.
A: Level at which oligomer adhesion can hardly be confirmed on the roll after processing, and it seems that long run processing is possible B: Level at which oligomer can be confirmed on the roll after processing but can be used
C: Oligomer is clearly attached to the roll after processing, long run processing is not possible, and there is a risk of affecting productivity

  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 and 60 parts by weight of ethylene glycol are used as starting materials, tetrabutoxytitanate is taken as a catalyst in the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off for 3 hours. Later, the temperature was set to 230 ° C. 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 0.55 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester chip. The intrinsic viscosity was 0.55. The obtained polyester chip was subjected to solid phase polymerization at 220 ° C. under vacuum to obtain a polyester (A) having an intrinsic viscosity of 0.65.

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

<Method for producing polyester (C)>
In the production of polyester (A), a polyester (C) chip having an intrinsic viscosity of 0.62 was obtained in the same manner as in the general production method, except that the amount of tetrabutoxy titanate was changed. The intrinsic viscosity of the obtained polyester (C) was 0.62.

<Method for producing polyester (D)>
In the production of polyester (A), polyester (D) was obtained using the same method as the production method of polyester (A), except that antimony trioxide was used as a polymerization catalyst. The intrinsic viscosity of the obtained polyester (D) was 0.65.

<Method for producing polyester (E)>
In the method for producing polyester (A), 0.6 part of silica particles having an average particle diameter of 2.0 μm dispersed in ethylene glycol was added and the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.66. Obtained polyester (E) using the method similar to the manufacturing method of polyester (A). The obtained polyester (E) had an intrinsic viscosity of 0.66.

Example 1:
Polyester (A), (B), and (E) chips were blended at a rate of 92%, 5%, and 3%, respectively, and melt-extruded at 290 ° C by a twin screw extruder with a vent, and electrostatically applied. By using this method, it was cooled and solidified on a cooling roll whose surface temperature was set to 40 ° C. to obtain an unstretched sheet. Next, the film was stretched 3.7 times in the longitudinal direction at 83 ° C., and then a coating agent having the composition shown below was applied to both sides of the film and then led to a tenter, and stretched 3.9 times in the lateral direction at 110 ° C. Heat treatment was performed at 220 ° C. to obtain a 160 μm thick polyester film. The contents of antimony, titanium, and phosphorus in the obtained film were 0 ppm (below the lower limit of detection), 5 ppm, and 50 ppm, respectively. The thickness of the coating layer was 0.08 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.

  The antimony, titanium, and phosphorus element contents in the films obtained in each Example and Comparative Example are shown in Table 1 below.

Example 2:
A polyester film having a thickness of 230 μm in the same manner as in Example 1 except that the polyester (A), (B), and (E) chips were used as raw materials of 98%, 1%, and 1%, respectively. Got.

Example 3:
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the polyesters (A), (B), and (E) were 93%, 5%, and 4%, respectively.

Comparative Example 1:
A polyester film having a thickness of 150 μm was obtained in the same manner as in Example 1, except that the polyesters (B), (C), and (E) were changed to 5%, 90%, and 5%, respectively.

Comparative Example 2:
The film forming conditions were the same as in Example 1 except that the polyesters (A), (B), and (E) were 80%, 5%, and 15%, respectively, and the film thickness was 200 μm. 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 3:
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1, except that the polyesters (D) and (E) were 97% and 3%, respectively.

Comparative Example 4:
A polyester film having a thickness of 175 μm was obtained in the same manner as in Example 1, except that the polyesters (A), (B), and (E) were changed to 60%, 35%, and 5%, respectively.

  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 has high suitability for optical use.

  The film of the present invention can be suitably used for, for example, various optical members used for LCDs, PDPs, and the like, and protective films and release films used in the manufacturing process of products in the optical field.

Claims (1)

A film made of polyester, having a haze (H0) in the range of 1.0 to 3.0%, and a difference between haze (H1) after heating at 150 ° C. for 30 minutes and haze (H0) before heat treatment (Δ A biaxially oriented polyester film for optics, wherein H) is 1.0% or less.