JP2013001045A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film excellent in optical characteristics such as transparency, low haze, optical uniformity or the like, capable of contributing to the enhancement of quality preventing the generation of an image defect as an optical product and suitable as various optical members such as LCD, PDP or the like.SOLUTION: The laminated polyester film is composed of at least three layers and characterized in that a reflection method y value corresponding to the 1,000 μm thickness of the film surface is 0.3240-0.3440 and the reflectivity R of 460 nm corresponding to the 1,000 μm thickness of the film surface is 87% or above.

Description

  The present invention relates to a laminated polyester film suitable for optical use.

  Polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance, so magnetic tape, ferromagnetic thin film tape, photographic film, and 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 and scratches that affect the image. Necessary.

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

  Polyester film is usually obtained by melt-extrusion into a sheet form, and by stretching and heat-treating an amorphous sheet obtained by rapid cooling and solidification. In these steps, cooling and stretching are uniform. If it is not sufficient, the above-mentioned retardation unevenness remains, and there is a problem that the image is deteriorated when used for optics.

  An important characteristic in a display is optical characteristics (brightness), but it is known that a polyester film used as a member is affected. In particular, in order to obtain a high quality image, high optical properties have been required. For this purpose, it is necessary that the polyester film serving as the base of the member has advantageous characteristics in terms of luminance.

Japanese Patent Laid-Open No. 2003-237006 Japanese Patent Application No. 2010-36486

  The present invention has been made in view of the above-described circumstances, and its solution is excellent in optical properties such as transparency, low haze, and optical uniformity, and prevents the occurrence of image defects when used as an optical product. The present invention provides a film suitable for various optical members such as LCD and PDP.

  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 laminated polyester film composed of at least three layers, the reflection method y value corresponding to 1000 μm thickness of the film surface is 0.3240 to 0.3440, and corresponds to 1000 μm thickness of the film surface. In the laminated polyester film, the reflectance R at 460 nm is 87% or more.

  According to the present invention, it has excellent optical properties such as brightness, low haze, and optical uniformity, and can contribute to quality improvement such as prevention of image defects when it is used as an optical product. Films suitable as various optical members such as PDP can be provided, and the industrial value of the present invention is high.

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

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

You may mix | blend particle | grains in the polyester layer in this invention with the main objective of providing lubricity. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples thereof include particles of magnesium silicon oxide, kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.
On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.
Further, the average particle size of the particles used is usually preferably 0.01 to 5 μm. If the average particle size is less than 0.01 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, if the average particle size exceeds 5 μm, the surface roughness of the film becomes too rough and transparent. It will become inferior.

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

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, fluorescent brighteners, dyes, pigments, and the like are added to the polyester film in the present invention as necessary. be able to. Depending on the application, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber, may be contained.

  The thickness of the polyester film of this invention is 150-500 micrometers normally, Preferably it is the range of 150-350 micrometers. Outside the above range, it may be unsuitable for optical use.

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

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

  The polyester film of the present invention has a reflection method y value of 0.3240 to 0.3440 corresponding to a thickness of 1000 μm. When the color tone y value exceeds 0.3340, the film has a strong yellowish tint, and when used for a display, the color tone of the image becomes inferior or the luminance becomes low. When the color tone y value is less than 0.3240, it cannot be used as an optical film.

  The reflectance R of 460 nm corresponding to a thickness of 1000 μm on the surface of the film of the present invention is 87% or more. If the reflectance R is less than 87%, it cannot be used for optical purposes.

  In order to make such a film, a catalyst for producing the raw material polyester, an auxiliary agent is selected, the amount of the catalyst is reduced as much as possible, the polyester becomes a temperature higher than necessary during polymerization and film formation, Methods such as preventing the melting time from becoming longer, and reducing the blending amount of the regenerated raw material can be employed.

  In particular, in the present invention, the film preferably contains a compound that absorbs a specific wavelength. That is, a compound that absorbs light of 300 to 500 nm is particularly preferable. Specific examples include azo dyes and pigments, and UV absorbers. Among these, dispersibility in a film and bleed out resistance Therefore, an azo pigment is particularly preferable.

  The film of the present invention can be formed into a laminated structure using a coextrusion method. In this case, it is preferable that the outermost layer thickness is usually 2 μm or more and ¼ or less of the total thickness on one side only. . When the thickness is less than 2 μm, oligomers (cyclic trimers) contained in the inner layer are deposited on the film surface due to heat history during processing, etc., and production line contamination and an increase in the amount of foreign matter on the film surface are observed. On the other hand, if it is thicker than 1/4 of the total thickness, the amount of particles blended in the outermost layer may increase and the transparency may be impaired.

  On the other hand, when the present invention is carried out with a single-layer film, it is also preferable that the film should not contain particles as much as possible, and that the front and back coating layers contain particles.

  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 5 times in the longitudinal direction at 70 to 145 ° C. to form a longitudinal uniaxially stretched film, and then in the transverse direction at 90 to 160 ° C. It is preferable to perform 2 to 5 times stretching and to perform heat treatment at 200 to 240 ° C. for 10 to 600 seconds. Further, at this time, it is preferable to relax 5 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. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, as described above, two 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 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 thereof include ketones such as ethyl cellosolve, methyl cellostel, methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. 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. 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 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 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 reduce the coating amount to 0 as much as possible.

  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) Reflection method Y, y value Using a Minolta spectrophotometer CM-3700d, the films are overlapped so that the thickness is close to 1000 μm (5 if 188 μm, 4 if 250 μm). The film surface was measured. A C light source and a 2 ° field of view were used, and the color system was XYZ (CIE 1931).
y = Y / (X + Y + Z)

(3) Reflectance measurement (% R)
Using the Minolta spectrocolorimeter CM-3700d, the film surface was measured by superimposing the films so that the thickness was about 1000 μm (5 for 188 μm, 4 for 250 μm). Using a C light source and a 2 ° visual field, the reflectance of each wavelength of the film was calculated by comparison with the reflectance of a standard white plate.

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, 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 gradually distilled off. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.68.

<Method for producing polyester (B)>
In the production method of polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.3 part of silica particles having an average particle diameter of 2.2 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide 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.

<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 intrinsic viscosity of the obtained polyester (C) was 0.68.

<Method for producing polyester (D)>
In the production method of polyester (B), after adding 0.04 part of ethyl acid phosphate, 5 parts of azo pigment PR-48: 1 manufactured by Dainippon Chemical Co., Ltd. dispersed in ethylene glycol, 0.03 part of antimony trioxide And polyester (D) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.66. The obtained polyester (D) had an intrinsic viscosity of 0.63.

Example 1:
The mixed raw materials obtained by mixing the above polyesters (A) and (B) at a ratio of 94% and 6%, respectively, are used as the raw material for the A layer, and polyesters (C) and (D) are respectively 99.89% and 0.11%. Using the mixed raw materials mixed at the ratio of B as the raw material of the B layer, each is supplied to two vent type twin screw extruders and melted at 285 ° C., the A layer is the outermost layer (surface layer), and the B layer is the intermediate layer Coextruded in a layer configuration of 2 types and 3 layers (A / B / A), extruded from the die, cooled and solidified on a cooling roll set at a surface temperature of 40 ° C. using an electrostatic application adhesion method, and unstretched sheet Got. Next, the film was stretched 3.0 times in the longitudinal direction at a film temperature of 81 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 3.9 times at 120 ° C. in the transverse direction, and heat-treated at 225 ° C. Thereafter, the film was relaxed 10% in the lateral direction to obtain a laminated polyester film having a thickness of 100 μm. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Example 2:
In Example 1, polyester (C) and (D) were mixed in the proportions of 99.77%, 0, and 23%, respectively, except that a mixed raw material was used as the raw material for the B layer. A 100 μm polyester film was obtained. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Example 3:
In Example 1, the thickness was changed in the same manner as in Example 1 except that a mixed raw material in which polyesters (C) and (D) were mixed at a ratio of 99.73%, 0, and 27%, respectively, was used as the raw material for the B layer A 100 μm polyester film was obtained. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Example 4:
In Example 1, the thickness is the same as in Example 1 except that a mixed raw material obtained by mixing polyesters (C) and (D) in proportions of 99.68%, 0, and 32%, respectively, was used as the raw material for the B layer. A 100 μm polyester film was obtained. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Comparative Example 1:
In Example 1, a polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that only polyester (C) was used as the raw material for the B layer. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Comparative Example 2:
In Example 1, the thickness was changed in the same manner as in Example 1 except that a mixed raw material in which polyesters (C) and (D) were mixed at a ratio of 99.99%, 0, and 01%, respectively, was used as the raw material for the B layer. A 100 μm polyester film was obtained. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

Comparative Example 3:
In Example 1, the thickness was changed in the same manner as in Example 1 except that a mixed raw material in which polyesters (C) and (D) were mixed in proportions of 98.95% and 1.05%, respectively, was used as the raw material for the B layer. A 100 μm polyester film was obtained. The thickness of each layer of the obtained film was 2.5 / 95 / 2.5 μm.

  The physical properties and dimensional stability (appropriateness of optical members) of the obtained film are shown in Table 1 below and FIGS. It can be seen that the film satisfying the requirements of the present invention has an increased luminance Y.

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

Claims (1)

It is a laminated polyester film composed of at least three layers, the reflection method y value corresponding to 1000 μm thickness of the film surface is 0.3240 to 0.3440, and the reflectance R of 460 nm corresponding to 1000 μm thickness of the film surface is A laminated polyester film characterized by being 87% or more.