JP2017062272A - Optical polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusibility (shielding property) to a biaxially stretched polyester film itself, especially in combination with a lens sheet or a prism sheet, has low luminance and excellent luminance characteristics, is excellent in processing suitability, and Provided is a polyester film in which oligomer precipitation due to heat and humidity changes is suppressed.
A polyester film having a multilayer structure comprising at least two or more polyester layers, the haze of the film is in the range of 4 to 50%, the total light transmittance is in the range of 87% or more, and An optical polyester film having a difference (ΔH) in haze value before and after heat treatment of the polyester film at 80 ° C. for 100 hours is 3 or less.
[Selection figure] None

Description

  TECHNICAL FIELD The present invention relates to an optical polyester film, and more particularly to an optical polyester film that can contribute to improving the quality of optical products because it has excellent optical properties and can achieve high brightness.

  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. Base films such as prism sheets, light diffusion sheets, composite sheets, reflectors, and touch panels for LCD members, antireflection base films, PDP filter films, etc. It is used for various applications. In these optical products, in order to obtain a bright and clear image, the base film used as an optical film needs to have good transparency due to its usage, but in recent years, in particular, with higher image definition, As a backlight unit, it has become possible to achieve high brightness and to reduce power consumption.

  The backlight unit is provided with a light diffusion film that diffuses and scatters the light emitted from the light guide plate and uniformly illuminates the illumination surface. Furthermore, in order to improve the front luminance, a prism sheet or a sheet having a light collecting function called a lens sheet may be used so that light transmitted through the light diffusing film is collected in the front direction as much as possible. The surface of the sheet has a large number of minute irregularities such as a prism shape, a wave shape, and a pyramid shape, and the emitted light that has passed through the light diffusing film is refracted and collected in the front to improve the luminance of the illumination surface. Such a prism sheet is used by being arranged one or two on the surface side of the light diffusing film.

  Furthermore, a light diffusing film is also provided on the surface side of the prism sheet in order to make the brightness unevenness, the prism sheet defects, scratches and the like caused by the arrangement of the prism sheet inconspicuous (improve concealment). There is a case.

  As the light diffusing film used in the backlight unit as described above, a film in which a light diffusing layer made of a transparent resin containing fine particles is coated on the surface of a biaxially stretched polyester film is mainly used.

  However, in this method, since it is necessary to provide a light diffusion layer on the base film by coating, curling due to heating is likely to occur due to the high processing cost and the difference in linear expansion coefficient between the light diffusion layer and the base film. There is a problem. In particular, liquid crystal displays that employ direct-type backlight units, such as recent large-sized liquid crystal TVs, are becoming an important problem, and curling becomes prominent when the liquid crystal TVs have a large area.

  In recent years, many studies have been made to integrate a light diffusing film with another optical functional film for the purpose of reducing the number of backlight unit parts, simplifying the manufacturing process, and reducing the cost.

  For example, a prism row is formed on the first surface side of a translucent substrate having two main surfaces, the first surface and the second surface, and a light diffusion layer including a number of glass beads is formed on the second surface side. A formed prism sheet (see Patent Document 3) is disclosed.

  Furthermore, a light-scattering biaxially stretched polyester film for a prism sheet (see Patent Document 4) in which light diffusibility is imparted by a light-scattering agent added inside the film and voids generated around the light-scattering agent is disclosed.

  However, the method disclosed in Patent Document 3 has a problem in that a light diffusion layer containing glass beads must be provided, leading to a reduction in processing cost and film yield.

  On the other hand, although the method disclosed in Patent Document 4 does not incur processing costs, the light scattering polyester film for a prism sheet provided with light diffusibility by bubbles generated after stretching around the inert particles of the polyester layer. Although it is an invention, there is a problem that light is absorbed by inert particles and the total light transmittance is lowered.

The above-mentioned backlight unit prism, lens, and diffusion layer are provided with a thermosetting type or UV curable resin layer. Depending on the heat history in the processing process, heat received from the light source of the display, and changes in the usage environment, etc. Depending on the humidity change, the oligomer tends to precipitate on the surface, and problems such as the generation of bright spots and a decrease in luminance due to the oligomer are caused.

JP-A-6-59108 Japanese Patent No. 3698978 JP-A-9-281310 JP 2005-181648 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that the biaxially stretched polyester film itself has light diffusibility (shielding property), particularly in combination with a lens sheet or a prism sheet, at low cost, And it is providing the polyester film which has the outstanding brightness | luminance characteristic, is excellent in process appropriateness, and can suppress precipitation of the oligomer by a heat | fever / humidity change.

  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 polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a polyester film having a multilayer structure composed of at least two or more polyester layers, the haze of the film is in the range of 4 to 50%, and the total light transmittance is in the range of 87% or more. And the difference in the haze value before and after heat treatment of the polyester film at 80 ° C. for 100 hours (ΔH) is 3 or less.

  According to the present invention, the biaxially stretched polyester film itself has light diffusibility (shielding property), particularly in combination with a lens sheet or a prism sheet, and has low luminance and excellent luminance characteristics, and is suitable for processing. It is possible to provide a polyester film that is excellent and suppresses oligomer precipitation due to changes in heat and humidity, and the industrial value of the present invention is high.

  In the present invention, the polyester is 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. Typical 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. Examples of the polymerization catalyst include known catalysts such as antimony compounds, germanium compounds, and titanium compounds.

  The polyester used in the present invention may be obtained by a melt polymerization reaction, but is included in the raw material if a raw material obtained by solid-phase polymerization of the polyester formed into chips after the melt polymerization is used. Since the amount of oligomer can be reduced, it is preferably used. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  In this invention, in order to suppress the precipitation amount after the heat processing of the oligomer contained in a polyester raw material, manufacturing a film using polyester with a small oligomer content as a raw material is mentioned. Various known methods can be used as a method for producing a polyester having a low oligomer content, and examples thereof include a method of solid-phase polymerization after polyester production.

  In the present invention, it may be a film having a structure obtained by coextrusion laminating a polyester having a low oligomer content on the surface of at least one side of a layer composed of a polyester having a normal oligomer content. The effect of suppressing oligomer precipitation obtained in the present invention can be exhibited to a high degree.

  In the present invention, the difference (ΔH) in haze value between before and after heat treatment of the polyester film at 80 ° C. for 100 hours is 3 or less, preferably 2 or less. When the difference (ΔH) in haze values before and after the heat treatment exceeds 3, it is used as an optical film, and when incorporated into a panel, a problem that a bright spot due to oligomer precipitation is detected as a foreign matter occurs.

  The thickness of the layer containing polyester with a low oligomer content is usually 1 to 20 μm, preferably 3 to 15 μm. When the layer thickness is 1 μm or less, oligomers from adjacent layers pass through the layer having a low oligomer content and are deposited on the film surface, and the bright spot is detected as a foreign substance, or the luminance is reduced. This can be a problem. Moreover, when this layer thickness is 20 micrometers or more, the ratio of the usage-amount of polyester with few oligomer content and polyester containing particle | grains increases, and it becomes high cost.

  The polyester film of the present invention needs to be a laminated polyester film composed of at least two polyester layers. In particular, it is preferable to add particles to the outermost layer on one side of the three-layer structure to impart light diffusibility (shielding property).

  The polyester film of the present invention preferably contains particles having an average particle diameter of 2 to 15 μm mainly for the purpose of imparting easy slipping, preventing the occurrence of scratches in each step, and light diffusibility (shielding property). The average particle size is preferably in the range of 3 to 10 μm. When the average particle size is less than 2 μm, the desired diffusion effect may not be obtained. On the other hand, when the thickness exceeds 15 μm, the film surface becomes prominent and the application to optical applications may be difficult.

  The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. For example, as inorganic particles, calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, Examples thereof include lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, and lithium fluoride. On the other hand, examples of the organic salt particles include calcium oxalate, terephthalate such as calcium, barium, zinc, manganese, and magnesium. Examples of the crosslinked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, acrylic acid or a methacrylic acid vinyl monomer homopolymer or copolymer. In addition, organic particles such as polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin may be used.

The shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc.
These series of particles may be used in combination of two or more as required.

  The 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 included.

  The film thickness in the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually in the range of 38 to 300 μm from the viewpoint of mechanical strength, handling properties, productivity, and the like. preferable.

  The haze value of the film of the present invention needs to be in the range of 4 to 50%. Preferably it is 7 to 30% of range. If it is less than 4%, the diffusibility is insufficient and a film suitable for this application cannot be obtained. On the other hand, if it exceeds 50%, the total light transmittance is lowered, and the luminance in the display becomes insufficient, which is not suitable for optical use.

  The total light transmittance of the present invention needs to be in the range of 87% or more, preferably 88% or more. If the total light transmittance is less than 87%, the luminance is reduced and it is not suitable for optical use.

  In this application, surface irregularities are formed in order to impart light diffusibility (shielding property) by blending particles in the outermost layer on one side of the laminated polyester film. However, since the other outermost layer is subjected to prism processing, microlens processing, etc., it is preferable that the processed surface has less surface irregularities in consideration of their processing suitability.

  In the film of the present invention, coating layers such as an antistatic layer, an adhesive layer, and an oligomer precipitation preventing layer may be provided as long as the gist of the present invention is not impaired.

  When providing a coating layer, it is preferable to provide by an in-line coating. In-line coating is a method of coating within the process of producing a polyester film. Specifically, it is a method of coating at any stage from melt-extrusion of polyester to biaxial stretching, heat setting and winding. is there. Usually applied to either a substantially amorphous unstretched sheet obtained by melting and quenching, a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction), or a biaxially stretched film before heat setting. To do. In these, the method of extending | stretching to a horizontal direction after apply | coating to a uniaxially stretched film is excellent. According to such a method, since film formation and coating / drying can be performed simultaneously, there is a merit in manufacturing cost, thin film coating is easy to perform stretching after coating, and heat treatment performed after coating is not limited. Since the high temperature is not achieved by this method, the coating film and the polyester film are firmly adhered.

  The polyester film coating layer used in the present invention is made of polyurethane resin, acrylic resin / vinyl resin, polyether resin, cellulose resin, epoxy resin, nylon resin, gelatin, carbodiimide resin, melamine. -What contains at least 1 sort (s) of resin chosen from the group which consists of a urea type crosslinking agent, an oxazoline crosslinking agent, etc. is preferable.

  The molecular weight of the resin forming the coating layer of the polyester film provided with the coating layer is preferably in the range where the number average molecular weight is shown below. When the number average molecular weight is within this range, the adhesion between the coating layer and the polyester film and the toughness of the coating layer are excellent.

  The polyurethane resin is a polymer or copolymer obtained from a polyfunctional isocyanate and a compound having a polyhydroxy group, and preferably has a number average molecular weight of 5,000 to 25,000. As the polyurethane resin, for example, diisocyanate, polyether, polyester, glycol, diamine, dimethylolpropionate and the like can be used, and an emulsion or aqueous solution is preferable.

  Examples of the acrylic resin include ethyl acrylate, methyl acrylate, acrylic acid, butyl acrylate, sodium acrylate, ammonium acrylate, ethyl methacrylate, methyl methacrylate, methacrylic acid, butyl methacrylate, glycidyl methacrylate, 2-hydroxy A polymer or copolymer mainly composed of an acrylic monomer represented by ethyl acrylate, acrylamide, methacrylamide, N-methoxymethyl acrylamide, N-methylol acrylamide, etc., and has a number average molecular weight of 5,000 to 250 1,000 is preferred.

  Vinyl resin has a styrene, α-methyl styrene, sodium styrene sulfonate, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl ether, sodium vinyl sulfonate, sodium methallylate, polyvinyl alcohol, polyvinyl butyral, etc. A polymer or copolymer obtained from a monomer having an unsaturated double bond, preferably having a number average molecular weight of 5,000 to 250,000.

  Examples of the polyether resin include polyethylene oxide, polypropylene oxide, phenoxy resin, and the like, and those having a number average molecular weight of 800 to 400,000 are preferable.

  Cellulosic resins are resins having a cellulose structure in the molecule, such as methylcellulose and nitrocellulose.

  The epoxy resin is a polymer or copolymer obtained from a compound having a bifunctional or higher functional glycidyl group in the molecule, and preferably has a number average molecular weight of 150 to 30,000. Examples of the compound include bisphenol glycidyl ether, glycerin polyglycidyl ether, and aminoglycidyl ether.

  Examples of the nylon resin include 6 nylon, 6 and 6 nylon, methoxymethylated resins, and copolymers such as acrylic acid.

  Gelatin is a high-molecular-weight polypeptide, and those obtained from protein raw materials such as collagen can be used.

  As the carbodiimide-based crosslinking agent, a polyfunctional carbodiimide-containing resin is preferably used as a compound having a carbodiimide group having two or more functional groups in the molecule.

  Examples of melamine include hexamethoxymethyl melamine and methoxy urea melamine as compounds having two or more thermoreactive cross-linking groups such as methoxymethyl group and methylol group in the molecule.

  As the oxazoline-based crosslinking agent, a polyfunctional oxazoline-containing resin obtained by copolymerizing isopropenyl oxazoline with a compound having a bifunctional or higher functional oxazoline group in the molecule is preferably used.

  These resins can be used alone or in combination.

  The thickness of a coating layer is 0.001-10 micrometers normally as thickness after drying, Preferably it is 0.010-5 micrometers, More preferably, it is 0.015-2 micrometers. When the thickness of the coating layer is less than 0.001 μm, the antistatic effect may not be sufficiently improved. When the thickness of the coating layer exceeds 10 μm, so-called blocking may occur in which the coating layer acts like an adhesive and the films wound up on the roll adhere to each other.

  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.

(1) Measurement of intrinsic viscosity (dl / g) of polyester Weigh out 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed, and mix phenol / tetrachloroethane = 50/50 (weight ratio) 100 ml of solvent was added and dissolved, and measurement was performed at 30 ° C.

(2) Thickness of Laminated Polyester Layer After fixing a small piece of film with an epoxy resin, it was cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed in parallel with the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the laminated thickness.

(3) Measurement of haze and total light transmittance of polyester film A polyester film and a product that has been prism-processed into a polyester film in a hot-air circulating oven at 80 ° C. are treated for 100 hours, and manufactured by Nippon Denshoku Industries Co., Ltd. The haze of the film before and after the heat treatment was measured with an integrating sphere turbidimeter NDH-20D. From these, the haze difference (ΔH) and the total light transmittance difference (ΔT) before and after the heat treatment were calculated using the following formula.
ΔH = Ho−H _, ΔT = To−T
(In the above formula, Ho is haze after heating, H is haze, To is total light transmittance after heating, and T is total light transmittance)

(4) Luminance evaluation of polyester film (practical property substitution evaluation)
As a representative optical member, characteristics when used as a prism sheet were evaluated. That is, an acrylic binder was applied to one side of the film to form a prism layer. The obtained prism sheet was incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints. For luminance measurement, CS-200 manufactured by Konica Minolta Sensing Co., Ltd. was used, and the luminance value (cd / m ² ) was measured with a measurement angle of 1 °, the distance between the sample and the luminance meter being 500 mm, and compared with a reference sample. As a reference sample, a sample obtained by processing a light diffusion layer having a haze of 10% on the film of Comparative Example 1 was used.
・ Luminance level ○: Brightness is equal to or higher than the standard △: Brightness is slightly decreased compared to the standard (difference is less than 1%)
X: The brightness was greatly reduced compared to the standard (difference was 1% or more).

(5) Diffusion evaluation of polyester film (practical property substitution evaluation)
The obtained sample film was placed on a flat illuminator HF-SL-A48LCF manufactured by Dentsu Sangyo Co., Ltd. so that the coating layer surface was the upper surface, and the determination was made according to the following criteria.
(Criteria)
○: No light source unevenness is visible Δ: Light source unevenness is slightly visible ×: Light source unevenness can be easily observed

The content of the polyester raw material used in the following examples will be described.
<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 intrinsic viscosity of the obtained polyester (a) was 0.63.

<Method for producing polyester (b)>
Polyester (a) is used as a starting material, and is continuously fed into a stirred crystallizer maintained at about 160 ° C. in a nitrogen atmosphere so that the residence time is about 60 minutes. Continuously supplied to a solid phase polycondensation apparatus, and at 215 ° C. in a nitrogen atmosphere, the residence time was adjusted so that the intrinsic viscosity of the obtained polyethylene terephthalate resin was 0.82, and solid phase polycondensation was performed. ) The intrinsic viscosity of the obtained polyester (b) was 0.82.

<Method for producing polyester (c)>
In the production method of polyester (a), a polyester having an intrinsic viscosity of 0.65 is produced in the same manner except that silica particles having an average particle diameter of 2.1 μm are added so that the content thereof is 0.3% by weight based on the polyester. (C) was obtained.

<Method for producing polyester (d)>
In the production method of polyester (c), a polyester having an intrinsic viscosity of 0.65 was produced in the same manner except that silica particles having an average particle size of 8.0 μm were added so that the content with respect to the polyester was 0.3% by weight. (D) was obtained.

<Method for producing polyester (e)>
The polyester (c) was produced in the same manner except that 10% by weight of organic particles of an alkyl methacrylate-styrene copolymer having an average particle size of 1.1 μm were contained in place of the silica particles. A polyester (e) of 0.65 was obtained.

<Method for producing polyester (f)>
In the production method of the polyester (e), the polyester (e) was produced in the same manner except that 10% by weight of organic particles of an alkyl methacrylate-styrene copolymer having an average particle size of 4.0 μm were contained. f) was obtained.

<Method for producing polyester (g)>
In the production method of the polyester (e), a polyester (e) having an intrinsic viscosity of 0.65 was produced in the same manner except that 10% by weight of organic particles of an alkyl methacrylate-styrene copolymer having an average particle size of 8.0 μm were contained. g) was obtained.

<Method for producing polyester (h)>
In the production method of the polyester (e), the polyester (e) was produced in the same manner except that 10% by weight of organic particles of an alkyl methacrylate-styrene copolymer having an average particle size of 12.0 μm were contained. h).

-Coating layer composition The example of a compound which comprises a coating layer is as follows.
(Compound example) It is a mixture in which the following compounds (a), (b), (c) and (d) are mixed at a weight ratio of 47/20/30/3.

Acrylic resin: (a) Aqueous dispersion of acrylic resin polymerized with the following composition: ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylol acrylamide / acrylic acid = 65/21/10/2/2 (% by weight) Emulsion polymer (emulsifier: anionic surfactant)

Polyester resin: (b) Water dispersion of polyester resin copolymerized with the following composition: Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid /// (diol component) ethylene glycol / 1 4-butanediol / diethylene glycol = 56/40/4 // 70/20/10 (mol%)

・ Oxazoline compounds: (c)
Acrylic polymer Epocros WS-500 having an oxazoline group and a polyalkylene oxide chain (manufactured by Nippon Shokubai, containing about 38% by weight of 1-methoxy-2-propanol solvent)

-Particles: (d) Silica sol with an average particle size of 65 nm

Example 1:
Polyesters (b) and (g) mixed at a ratio of 95% and 5%, respectively, are used as the raw material for the A layer, 100% polyester (a) is used as the raw material for the B layer, and the polyesters (a) and (c) Were mixed at a ratio of 95% and 5%, respectively, and each of them was supplied to three extruders and melted at 285 ° C., and then the A layer and the C layer were the outermost layers ( Surface layer) and B layer as an intermediate layer, co-extruded on a casting drum cooled to 40 ° C. with 3 types and 3 layers (ABC) so that the thickness composition ratio is A: B: C = 10: 230: 10 A non-oriented sheet was obtained by cooling and solidifying. Next, the film was stretched 3.1 times in the machine direction at a film temperature of 95 ° C. using the difference in roll peripheral speed, and then the coating layer (after drying) composed of the following coating solution was applied to a coating thickness of 0.03 g / m ² . After being coated on the surface of layer C, this longitudinally stretched film was guided to a tenter, stretched 4.1 times at 120 ° C. in the transverse direction, heat treated at 220 ° C. for 10 seconds, and then 10% in the width direction. After relaxation, the film was rolled up to obtain a 250 μm thick polyester film provided with a coating layer.

Examples 2-6:
In Example 1, it manufactured similarly to Example 1 except the raw material mixing | blending and thickness structure differing, and obtained the polyester film.

Comparative Examples 1-6;
In Example 1, it manufactured similarly to Example 1 except the raw material mixing | blending and thickness structure differing, and obtained the polyester film.

  The characteristic of each film obtained by the said Example and the comparative example is put together in the following Tables 1-3, and is shown.

  The film of the present invention can be suitably used for, for example, a prism sheet, a light diffusing sheet, a composite sheet, a reflecting plate, etc. for LCD components.

Claims (1)

It is a polyester film having a multilayer structure comprising at least two or more polyester layers, the haze of the film is in the range of 4 to 50%, the total light transmittance is in the range of 87% or more, and the polyester film is 80%. An optical polyester film, wherein a difference (ΔH) in haze value before and after heat treatment at 100 ° C. for 100 hours is 3 or less.