JP2007086562A - Optical polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film with excellent optical performance, which has no unevenness and no defect, attains a high degree of luminance, and can give a high-quality image without any defect, when used as the member of an optical product, in particular as a substrate for a diffusion plate of a backlight for an LCD, or for a prism sheet. <P>SOLUTION: The polyester film is characterized in that haze lies in the range of 0-5.0% and R expressed with equation (1) lies in the range of 1.0-10.0, R=(T÷Δn)÷1,000...(1), here in the equation, T is the film thickness (μm) and Δn is birefringence. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical polyester film, and more specifically, various optical members used for liquid crystal displays (hereinafter sometimes abbreviated as LCD), plasma displays (hereinafter sometimes abbreviated as PDP), and the like. , A polyester film used in protective films, release films, etc. used in the manufacturing process of products in the optical field, with excellent optical properties, and can contribute to improving the quality of optical products and reducing energy consumption It relates to a polyester film.

  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. In addition to this, it is necessary to obtain an image having no unevenness even when polarized light is used, so that there is no retardation unevenness due to uneven orientation of the polymer and uneven thickness.

  A polyester film is usually obtained by subjecting an amorphous sheet obtained by melt extrusion to a sheet and quenching and solidifying it in the longitudinal and transverse directions, followed by heat treatment. If the uniformity of cooling and stretching is not sufficient in these steps, the above-mentioned retardation unevenness remains, and there is a problem that the image is deteriorated when used for optics.

One of the important characteristics in a display is luminance. It is known that the luminance of a polyester film used as a member affects the luminance. 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 optical product, particularly as a base material for a diffusion plate of an LCD backlight or a prism sheet, unevenness and defects are present. It is another object of the present invention to provide a polyester film with good optical performance, capable of realizing high brightness and providing a high-quality image without defects.

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

That is, the gist of the present invention is that the haze is in the range of 0 to 5.0% and R represented by the following formula (1) is in the range of 1.0 to 10.0. Axial-oriented polyester film.
R = (T ÷ Δn) ÷ 1000 (1)
(In the above formula, T is the film thickness (μm), and Δn is the birefringence)

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 2.0-10.0 mol% of 3rd components other than a main structural component, More preferably, it is 2.5-10 mol%, Most preferably, it is 3.0-8.0. Mol%.

  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, 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.

  The polyester film of the present invention preferably contains both a titanium compound and a phosphorus compound. The content of titanium element in at least one layer of the film of the present invention is preferably 20 ppm or less, more preferably 10 ppm or less, and the lower limit is usually 1 ppm, preferably 2 ppm. When there is too much content of a titanium compound, an oligomer byproduces in the process of melt-extruding polyester, and it may be impossible to obtain a film having low transparency and high transparency. Further, when no titanium element is contained, the productivity at the time of producing the polyester raw material tends to be inferior, and the polyester raw material reaching the target degree of polymerization may not 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 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. 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. 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.

  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 wt% 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.

  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 more preferably 0.40 to 0.90 dl / g.

  In the polyester layer which comprises the polyester film of this invention, you may mix | blend particle | grains for the main purpose of providing lubricity. 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 500 μm, preferably 20 to 350 μm, more preferably 50 to 250 μm.

  The film of the present invention has a film haze of 0 to 5.0%, preferably 0 to 3.5%, more preferably 0 to 3.0%. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 5.0%, it is unsuitable for optical use.

  In the film of the present invention, it is essential that R represented by the following formula (1) is 1.0 to 10.0, preferably 2.0 to 8.0, more preferably 2.0 to 6.0. Range.

R = (T ÷ Δn) ÷ 1000 (1)
(In the above formula, T is the film thickness (μm), and Δn is the birefringence)

  When R is larger than 10.0 or smaller than 1.0, when the film of the present invention is sandwiched between polarizing plates and light is passed through, strong red coloration may be conspicuous depending on the angle of the polarizing plate. Therefore, the color tone of the liquid crystal screen may be remarkably deteriorated.

  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 color tone of the image becomes inferior or the luminance becomes low when used for a display because of its strong yellowishness. On the other hand, although there is a problem of color tone in a film lower than -5, since a b * value is not lower than -5 in the case of a normal polyester film, a method such as using an additive is used. However, it is not preferable because it may cause problems such as bleeding out of the additive 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 .0mg / ^{m 2,} particularly preferably not more than 8.0 mg / ^{m 2.} When the amount of oligomer deposition on the film surface exceeds 15 mg / m ² , the oligomer 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 co-extrusion method. In this case, the thickness of the outermost layer is preferably 3 μm or more, more preferably 5 μm or more and only 1 / of the total thickness. It is 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, 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, 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.

  In addition, you may coat by an offline coat after manufacture of a film as needed. Moreover, it does not ask one side and both sides to coat. 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 necessary to form a functional multilayer thin film for the purpose of preventing dust reflection due to reflection of external light and static electricity, and further electromagnetic shielding. Is also 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, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. These organic solvents may be used in combination of two or more as required.

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

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

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

  When such a coating film is applied to an optical application, the coating layer surface coating is problematic when an antireflection layer or the like is provided on the coating layer. The reason for the occurrence of coating leakage is not clear, but foreign matter in the film creates coarse protrusions on the film surface, which acts as a core and the coating agent repels, and it is stretched to generate coating leakage or the film surface. There 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 also has the effect of reducing the amount of coating waste.

When the film of the present invention thus obtained has a coating layer, the number (N) of coating spots is preferably 50 or less per 10 m ^{2 of} film, more preferably 30 or less, particularly preferably 10 or less. It is. 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 specific members thereof, a reflector for a backlight for a liquid crystal display, a diffuser, a prism sheet, Lens sheets, brightness enhancement films, protective films for liquid crystal panels, release films for processes during panel manufacturing, and so-called PDP filters for plasma displays, electromagnetic shielding, near infrared shielding, color correction, ultraviolet shielding Effectively used as a substrate that requires a high degree of transparency, such as a film substrate having various functions such as antireflection, and a process for manufacturing a panel, and an image forming screen for a projection television. Is done.

  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.), 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.

(4) Measurement of R It calculated based on the following formula.
R = (T ÷ Δn) ÷ 1000
(In the above formula, T is the film thickness (μm), and Δn is the birefringence)

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

(6) Measurement of birefringence (Δn) Using an Abbe refractometer manufactured by Atago Co., Ltd., using a sodium lamp as the light source, the refractive index of the film is measured, and the birefringence (Δn) is calculated by the following equation. did.
n = nγ−nβ
(In the above formula, nγ and nβ respectively represent the maximum refractive index in the plane of the film and the refractive index in the plane of the film orthogonal thereto)

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

(8) Optical member suitability-1
As a representative optical member, the 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 and compared with the case of using a conventional PET film, that is, the film of Comparative Example 2 in the present invention)
A: Brightness improved and improved B: No reduction in luminance was confirmed and usable level C: Luminance decreased

(9) Optical member suitability—color unevenness A film was sandwiched between polarizing plates, and the quality and color tone were observed on the backlight unit from the following viewpoints. The angle between the polarizing plates was such that the film color tone was most clear.
A: A strong red part cannot be confirmed, and color tone unevenness is hardly observed. B: A strong red part can be confirmed partially, or a color unevenness is somewhat observed, but a practical level C; Can be confirmed, or the color tone is very uneven, affecting the image on the LCD screen

Examples / Comparative Examples are shown below, and the production method of the polyester used therein is as follows.
<Manufacture of polyester>
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.68 and a diethylene glycol content of 1.0 mol%.

<Method for producing polyester (B)>
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.3 part of silica particles having an average particle diameter of 1.9 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide were added. In addition, polyester (B) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.66. The obtained polyester (B) had an intrinsic viscosity of 0.66 and a diethylene glycol content of 1.0 mol%.

<Method for producing polyester (C)>
In the method for producing polyester (A), the starting material is 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, and the method for producing polyester (A) is used except that germanium oxide is used as a polymerization catalyst. A polyester (C) was obtained using the same method as described above. In addition, the addition method of germanium oxide employ | adopted the well-known method, The addition amount was 100 ppm with respect to the raw material weight as germanium. The obtained polyester (C) had an intrinsic viscosity of 0.68, and the diethylene glycol content in the polymer was 4.0 mol%.

<Method for producing polyester (D)>
The starting material is 100 parts by weight of dimethyl terephthalate, 54 parts by weight of ethylene glycol and 25 parts by weight of 1,4-cyclohexanedimethanol, 0.011 part by weight of tetrabutoxy titanate is used as a catalyst, and the reaction start temperature is 150 ° C. The reaction temperature was gradually increased with the distillation of methanol, and the temperature was raised to 230 ° C. after 3 hours, and the reaction was continued for another hour. Thereafter, the temperature of the reaction product was gradually raised from 230 ° C., and the pressure was gradually reduced from the normal pressure, and finally the temperature was 280 ° C. and the pressure was 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.70 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (D) was 0.70, the content of 1,4-cyclohexanedimethanol was 33 mol%, and the content of diethylene glycol was 1.0 mol%.

<Method for producing polyester (E)>
In the production method of the polyester (A), the polyester (E) is produced 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 (E) had an intrinsic viscosity of 0.67 and a content of diethylene glycol of 1.0 mol%.

Example 1 <Production of Polyester Film>
Polyester (C) and (B) chips were blended at a ratio of 96% and 4%, respectively, and melt-extruded at 290 ° C. with a vented twin-screw extruder, and the surface temperature was adjusted using an electrostatic application adhesion method. It cooled and solidified on the cooling roll set to 40 degreeC, and the unstretched sheet was obtained. Next, the film was stretched 3.4 times in the longitudinal direction at 85 ° C., then led to a tenter, stretched 4.0 times in the transverse direction at 120 ° C., and further heat treated at 220 ° C. to obtain a polyester film having a thickness of 188 μm. . The diethylene glycol content was 3.8 mol%.

Example 2
In Example 1, polyester (A), (B), and (D) chips were used as raw materials with 75%, 5%, and 20%, respectively, stretched 3.6 times in the longitudinal direction, and 3.9 in the lateral direction. A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that it was heat-treated at double stretching and 240 ° C.

Example 3
In Example 1, the polyester (A), (B), and (E) chips were 80%, 5%, and 10%, respectively, stretched 3.0 times in the longitudinal direction, and stretched 4.2 times in the transverse direction, 240 A polyester film having a thickness of 150 μm was obtained in the same manner as in Example 1 except that heat treatment was performed at 0 ° C.

Comparative Example 1
In Example 1, the polyester (A) and (B) chips were 95% and 5%, respectively, except that they were stretched 3.4 times in the longitudinal direction, 3.5 times in the transverse direction, and heat-treated at 230 ° C. A polyester film having a thickness of 250 μm was obtained in the same manner as in Example 1.

Comparative Example 2
In Example 1, the polyester (B) and (A) chips were 5% and 95%, respectively, except that they were stretched 3.0 times in the longitudinal direction and 4.5 times in the transverse direction. Thus, a polyester film having a thickness of 188 μm was obtained.

Comparative Example 3
The polyester (A), (B), (D) chips were made into 50%, 15%, and 35%, respectively, except that they were stretched 3.4 times in the longitudinal direction and 3.9 times in the transverse direction. The conditions were the same as in Example 1, and the film thickness was 150 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.

  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.

  In Table 1 above, DEG means diethylene glycol, 1,4-CHDM means 1,4-cyclohexanedimethanol, IPA means isophthalic acid, and contains the third component of Example 2, Example 3, and Comparative Example 3. The amount includes DEG.

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

Claims (1)

A biaxially oriented polyester film for optics, wherein haze is in the range of 0 to 5.0%, and R represented by the following formula (1) is in the range of 1.0 to 10.0.
R = (T ÷ Δn) ÷ 1000 (1)
(In the above formula, T is the film thickness (μm), and Δn is the birefringence)