JP2007077220A - Polyester film for optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which precipitates a very little amount of an oligomer when used as an LCD member, realizes a high-degree luminance, can give a high-quality image, and has a good optical capability. <P>SOLUTION: A biaxially oriented polyester film for optical use is provided, of which the contents of a titanium compound and a phosphor compound satisfy the below-described formulas (1) and (2) and which contains 2.0-10.0 mol% polyester constituent other than the main polyester constituent and has a total light transmittance of 91.0% or more. Formula (1) is 0<W<SB>Ti</SB>≤20 (wherein W<SB>Ti</SB>is the titanium element content (ppm) in the polyester film). Formula (2) is 1≤W<SB>P</SB>≤300 (wherein W<SB>P</SB>is the phosphor element content (ppm) in the polyester film). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical polyester film, and more particularly to a polyester film suitably used as a base material for a diffusion plate and a prism sheet used in a liquid crystal display (hereinafter sometimes abbreviated as LCD). The present invention relates to an optical polyester film that has excellent 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 widely used for various optical films, in particular, prism films for LCD members, light diffusion sheets, reflectors, touch panels, and other base films, antireflection base films, display explosion-proof base films, and PDPs. It is used for various applications such as 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 or scratches that affect the image. Necessary. However, as the application diversifies, 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 2003-201357 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that, when used as a member of an LCD, the amount of oligomer precipitation is extremely small, high brightness can be realized, and a high-quality image can be provided. An 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 inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a polyester film in which the contents of the titanium compound and the phosphorus compound simultaneously satisfy the following formulas (1) and (2), and the polyester film is composed of 2 polyester constituents other than the main polyester constituent. The present invention resides in a biaxially oriented polyester film for optics characterized by containing 0.0 to 10.0 mol% and having a total light transmittance of 91.0% or more.
0 <W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} titanium element content in the polyester film (ppm), _{W P} denotes phosphorus element content in the polyester film (ppm))

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 needs to contain 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 film preferably contains no antimony element, usually 100 ppm or less, preferably 60 ppm or less, 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. In other words, when a polyester is produced by polymerizing using titanium as a catalyst, adding a phosphorus compound in the polymerization process slows down the polymerization rate, leading to a decrease in productivity, or a longer polymerization time, resulting in a stronger yellow color. Problems may 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, there is a problem that yellowness increases due to thermal deterioration. 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.

  The amount of oligomer contained in the polyester film of the present invention is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, and 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 film of this invention, it is required to contain 2.0-10.0 mol% of polyester components other than the main polyester component, Preferably it is 2.5-10 mol%, More preferably, it is 3.0- 8.0 mol%.

  As a method for containing the third constituent 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 containing more than a predetermined amount of a copolymer component may be used. You may use the raw material obtained by blending polymeric polyester and copolymer polyester or homopolyester of content with little copolymerization component.

  Examples of the third component here include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like as dicarboxylic acid component, and P-oxy as oxycarboxylic acid. Benzoic acid and the like can be mentioned, and 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, the optical unevenness of the film due to the orientation and thickness unevenness of the polymer 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. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst.

  In addition, after melt-polymerizing polyester, this may be chipped, and solid-state polymerization may be further performed 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 film in this invention with the main objective of providing slipperiness. The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness, and specific examples thereof include, for example, silica, calcium carbonate, magnesium carbonate, barium carbonate, 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 if necessary.

  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 use, 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 film of the present invention has a total light transmittance of 91.0% or more, preferably 91.5%, 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 91.0%, it is unsuitable for optical use.

  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 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 It is 10.0 mg / m ² or less, and particularly preferably 8.0 mg / m ² or less. When 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 in 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, The amount of oligomer deposition on the film surface after heat treatment can be controlled within the above range by suppressing the oligomer deposition on the film surface by providing a coating layer inline / offline.

  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 of only one side, Usually, it is 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 carrying out by a single layer, it is also preferable to make a film not contain particle | grains as much as possible, and to make a coating layer of front and back contain particle | grains.

  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, is related to the transmitted light of the film, and is not limited to the film surface or the inside, but is related 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 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 2-6 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.

  If necessary, the film may be coated with an off-line coat after production. 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-mentioned 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 optical applications, the coating layer surface is not coated. This is a problem when an antireflection layer or the like is further provided on the surface of the substrate. The reason for the occurrence of coating leakage is not clear, but foreign matter in the film creates coarse protrusions on the surface of the film, which acts as a core and the coating agent repels and stretches to cause coating leakage or the film surface. It is conceivable that the oligomer or dust adhering 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 (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 necessary to make coating coating as zero 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 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.), 1 H-NMR was measured to assign each peak, and the content of the copolymer component was calculated from the integrated value of the peak.

(3) Measurement of average particle size (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.

(4) 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.

(5) Applicability of optical member—luminance As a representative of the optical member, characteristics when used as a diffusion plate were evaluated. That is, an acrylic binder containing particles was applied to one side of the film to form a light diffusion layer. 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 was improved and improvement was observed. B: Decrease in luminance could not be confirmed. C: Decrease in luminance was observed.

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, tetrabutoxy titanate is taken as a catalyst in the reactor, the reaction start temperature is 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 0.63 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.

<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 (B) was 0.65.

<Method for producing polyester (C)>
In the production of the polyester (A), a polyester (E) 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 (E), 0.15 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 <Production of Polyester Film>
Raw materials in which polyester (A), (B), and (G) chips are blended at a ratio of 90%, 5%, and 5%, respectively, are 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 having a surface temperature 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. A heat treatment was performed at 220 ° C. to obtain a polyester film having a thickness of 50 μm. 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 200 μm in the same manner as in Example 1 except that the polyester (A), (B), and (E) chips were used as raw materials of 94%, 1%, and 5%, respectively. Got.

Example 3
A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the polyesters (A), (B), and (E) were 90%, 5%, and 5%, 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
In Example 1, each of the polyesters (D) and (E) was 95%. A polyester film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that the content was 5%.

Comparative Example 4
A polyester film having a thickness of 200 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 properties 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.

  In the above table, DEG means diethylene glycol, and 1,4-CHDM means 1,4-cyclohexanedimethanol. Moreover, the amount of DEG is also included in the third component content of Example 4 and Comparative Example 3.

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

Claims (2)

It is a polyester film in which the content of the titanium compound and the phosphorus compound satisfies the following formulas (1) and (2) at the same time, and the polyester film contains 2.0 to 10.0 mol% of polyester constituents other than the main polyester constituent. An optically biaxially oriented polyester film comprising: a total light transmittance of 91.0% or more.
0 <W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} titanium element content in the polyester film (ppm), _{W P} denotes phosphorus element content in the polyester film (ppm)) A biaxially oriented polyester film for a diffusing plate and a prism sheet, comprising a coating layer on at least one side of the film according to claim 1.