JP2013154557A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film suitable for optics capable of suppressing the increase of film haze even after passing steps under severe condition such as heat treatment for a long time under a temperature of 150°C or lower, a spattering step under high tension, and a durability test under high temperature and high humidity atmosphere for example, and has superior optical characteristics and visibility even after machining the same as products for optical parts.SOLUTION: A laminated polyester film is the laminated film having at least three layers having both surface layers of a polyester containing 1,200 to 4,800 ppm of polycarbodiimide.

Description

  The present invention relates to a laminated polyester film, for example, severe conditions such as a long-time heat treatment at 150 ° C., a sputtering process at a high tension, and a durability test in a high-temperature and high-humidity atmosphere. The present invention relates to an optical laminated polyester film that is characterized in that the increase in film haze is as small as possible even after undergoing the following steps, and that is excellent in optical properties and visibility even after being processed as a product for optical members. In particular, the present invention relates to a laminated polyester film that is suitable for optical applications requiring high transparency, such as a touch panel, that places importance on so-called visibility when transmitting light.

  Conventionally, in touch panel applications, various methods such as a resistive film method and a capacitance method have been adopted depending on the position detection method. Among them, there is a tendency to increase the spread of a capacitance method characterized by multipoint detection, high light transmittance, high resolution, and high response speed. There are two types of capacitive touch panels: surface type and projection type. The surface type consists of three layers: a cover, a transparent conductive layer, and a glass substrate. The projection type consists of a glass or plastic film, a transparent electrode layer, and a substrate layer equipped with an IC that performs arithmetic processing. The

  In the manufacturing process of the transparent conductive laminate, it is generally heat-processed. For example, in order to form a transparent conductive film, an ITO film is formed by a sputtering method, and then heat treatment is performed at 150 ° C. for crystallization (Patent Document 1), or in the production of a conductive laminated film. When it is allowed to stand at 150 ° C. for 1 hour for low heat shrinkage treatment (Patent Document 2), or when processing a transparent conductive film, heat treatment at about 150 ° C. may be required to print a silver paste or the like. Yes (Patent Document 3). In the transparent conductive thin film manufacturing process, with heat treatment in a high temperature atmosphere, low molecular weight substances called oligomers contained in the polyester film (especially cyclic trimers) precipitate and crystallize on the film surface, resulting in coating defects, etc. Occurrence of this may make it difficult to obtain a highly accurate transparent conductive thin film.

  In addition, in the touch panel application, in recent years, the frequency of mounting on communication information devices such as mobile phones and PDAs (Personal Digital Assistance), game machines, etc. has been increasing. High visibility tends to be preferred. As a result, in the polyester film used in this field, the visibility degradation accompanying the increase in film haze due to oligomer precipitation after processing has been increasingly regarded as a problem.

  A technique for suppressing oligomer precipitation by applying a coating layer on a polyester film substrate has also been proposed (Patent Document 4). However, the coating layer may be peeled off due to contact or rubbing between the conveying guide roll and the polyester film surface in the processing step. In such a case, the precipitation of the oligomer in the part cannot be suppressed. When the amount of oligomer precipitation on the base material itself decreases, the technique for suppressing oligomer precipitation on the polyester film base material itself is stronger because the amount of oligomer precipitation can be further reduced in combination with a coating layer having a function of suppressing oligomer precipitation. There was also a demanded situation.

JP 2007-200823 A JP 2007-42473 A JP 2007-320144 A JP 2003-237005 A

  The present invention has been made in view of the above circumstances, and the present invention relates to a laminated polyester film, for example, a long-time heat treatment under 150 ° C. conditions, a sputtering step with high tension, Even after going through harsh conditions such as a durability test in a high-temperature, high-humidity atmosphere, the increase in film haze is kept small, and even after processing as a product for optical components, optical characteristics and visual recognition It is providing the laminated polyester film for optics excellent in the property.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above-described 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 resides in a laminated polyester film characterized by being a laminated film having a laminated structure of at least three layers, in which polyester containing 1200 to 4800 ppm of polycarbodiimide is used as both surface layers.

  According to the laminated polyester film of the present invention, for example, under severe conditions such as long-time heat treatment at 150 ° C., sputtering process with high tension, durability test under high temperature and high humidity atmosphere, etc. Even after passing through the process, the increase in film haze is suppressed to a small level, and even after processing as a product for optical members, it is possible to provide an optical laminated polyester film excellent in optical properties and visibility. Industrial value is high.

  The optical laminated polyester film of the present invention is required to be a multilayer film having at least 3 layers. The laminated polyester film for optics referred to in the present invention is a polyester film extruded by a so-called extrusion method that is melt-extruded from an extrusion die, and is oriented in the biaxial direction of the vertical direction and the horizontal direction as necessary. Film.

  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 used in the present invention may be a homopolyester or a copolyester. In the case of a copolyester, it is a copolymer containing 30 mol% or less of the third component. Examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acids (for example, P-oxybenzoic acid). Or 2 or more types are mentioned, As a glycol component, 1 type, or 2 or more types, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanone neopentyl glycol, is mentioned.

  The polyester constituting both outermost layers of the film of the present invention needs to contain 1200 to 4800 ppm of carbodiimide, and when it is less than 1200 ppm or more than 4800 ppm, the laminated polyester is heat-treated for a long time under conditions of 150 ° C. or high When used in harsh conditions such as sputtering in tension and durability testing in high-temperature and high-humidity atmospheres, the film haze increases greatly, and after processing as a product, optical characteristics and visual recognition It is not suitable for an optical member in terms of properties.

  The film of the present invention preferably has a haze of 1.5% or less. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the haze exceeds 1.5%, the transparency as an optical display member is impaired due to poor transparency. End up.

  The total film thickness of the film of the present invention is preferably in the range of 50 μm or more and 188 μm or less. When the total film thickness is less than 50 μm, after forming a transparent conductive film on the film, when forming a transparent conductive film sheet (laminated transparent conductive film) formed by laminating the film and film, wrinkles occur in the film Thus, a transparent conductive film sheet may not be formed properly. When the thickness exceeds 188 μm, the sheet flexibility of the sheet for forming the transparent conductive film sheet (laminated transparent conductive film) formed by laminating the film and film after forming the transparent conductive film on the film is It may be damaged.

  In the polyester layer of the film of the present invention, particles may be blended mainly for the purpose of imparting slipperiness and preventing scratches in each step. 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 of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. 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.

  Although it does not specifically limit as an average particle diameter of the particle | grains mix | blended in a polyester film, Usually, 0.02-3 micrometers, Preferably it is 0.02-2.5 micrometers, More preferably, it is the range of 0.02-2 micrometers. It is. When particles having an average particle size of less than 0.02 μm are used, sufficient slipperiness cannot be imparted, so that the winding characteristics in the film production process tend to be inferior. On the other hand, when the average particle diameter exceeds 3 μm, the degree of roughening of the film surface becomes too large and the film may become hazy.

  Furthermore, the particle content in the polyester layer is usually in the range of 0.0005 to 0.5% by weight, preferably 0.001 to 0.3% by weight. When the particle content is less than 0.0005% by weight, the slipperiness of the film may be insufficient, resulting in poor appearance such as scratches during film processing. On the other hand, when adding over 0.5 weight%, the transparency of a film may be inadequate.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage of producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction, The polycondensation reaction may proceed. 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.

  Hereinafter, although the manufacturing method of the 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.

  Polyester chips dried by a known method are supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to melt. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the laminated polyester film for optics of the present invention, a coating layer may be provided for the purpose of improving the adhesion with the layer processed on it, improving the slipperiness during processing, and the like. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. Since the coating can be performed simultaneously with the film formation, the production can be handled at a low cost, and therefore in-line coating is preferably used.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed particularly before the lateral stretching after the longitudinal stretching is finished. When the coating layer is provided on the polyester film by in-line coating, it is possible to apply at the same time as the film formation, and the coating layer can be processed at a high temperature in the heat treatment process of the polyester film after stretching. Performances such as adhesion to various surface functional layers that can be formed on the layer and heat and humidity resistance can be improved. Moreover, when coating before extending | stretching, the thickness of an application layer can also be changed with a draw ratio, and compared with off-line coating, uniform coating can be performed with a thin film. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

  Moreover, the coating layer of the film of the present invention comprises a surfactant, an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, organic particles, inorganic particles, an antioxidant, an ultraviolet absorber, a foaming agent, It may contain additives such as dyes and pigments. These additives may be used alone or in combination of two or more as necessary.

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.

  Moreover, you may use together heat treatment and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of offline coating or in-line coating as needed. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, when the polyester film of the present invention is used for optics, a colorant, a conductive material, etc. may be added, and further, reflection of external light, electric shock due to static electricity, prevention of dust adhesion, and further electromagnetic wave shielding. An intended functional multilayer thin film may be formed.

  The coating liquid used in the present invention is preferably an aqueous solution or an aqueous dispersion in terms of handling and working environment, but contains water as the main medium and contains an organic solvent as long as it does not exceed the gist of the present invention. You may do it.

  Although there is no restriction | limiting in particular in the solid content density | concentration of a coating liquid, Usually, 0.3 to 65 weight%, Preferably it is 0.5 to 30 weight%, More preferably, it is 1 to 20 weight%. When the concentration is too high or too low than these ranges, it may be difficult to provide a coating layer having a thickness necessary for fully expressing the function.

  The thickness of a coating layer is dry thickness, and is 0.003-1.5 micrometers normally, Preferably it is 0.01-0.5 micrometer, More preferably, it is 0.01-0.3 micrometer. If the thickness of the coating layer is less than 0.003 μm, sufficient performance may not be obtained, and if it exceeds 1.5 μm, blocking between the films tends to occur.

  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.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipping property, the fixing property 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.

  Examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound (for example, divinylbenzene) containing two or more carbon-carbon double bonds in one molecule.

  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.

  The coating layer may contain 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.

  For the laminated polyester film in the present invention, for example, for a touch panel or the like, high transparency may be required even after being exposed to a high temperature atmosphere for a long time.

The oligomer (cyclic trimer) amount (OL) extracted with dimethylformamide from the coating layer surface before and after heat treatment (150 ° C., 90 minutes) of the laminated polyester film in the present invention is usually 6.0 mg / m ² or less. Yes, preferably 5.0 mg / m ² or less, more preferably 4.0 mg / m ² or less. When OL exceeds 6.0 mg / m ² , in post-processing, for example, 180 ° C., 90 minutes, etc., the amount of oligomer precipitation increases with heat treatment for a long time in a high temperature atmosphere, and the transparency of the film decreases. There is a case.

  As a use for which the film of the present invention is used, for example, it is most suitable for a capacitive touch panel application in which a transparent conductive film-film is bonded.

  In addition, when the polyester film of the present invention is used for optics, a colorant, a conductive material, etc. may be added, and further, reflection of external light, electric shock due to static electricity, prevention of dust adhesion, and further electromagnetic wave shielding. An intended functional multilayer thin film may be formed.

  The polyester film of the present invention can be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Moreover, you may mix | blend coloring agents, such as a ultraviolet absorber, antioxidant, surfactant, a fluorescent whitening agent, a lubricant agent, a light-shielding agent, a matting agent, and a dye, a pigment. In addition, for the purpose of improving the slipperiness and abrasion resistance of the film, inert inorganic or organic fine particles can be blended with the polyester as necessary.

  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. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Average particle diameter (d50)
The particle size was measured by a sedimentation method based on Stokes' resistance law using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation.

(3) 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.

(4) Method for measuring oligomer amount (OL) extracted from the surface of the laminated polyester film In advance, an untreated laminated polyester film is heated in air at 150 ° C. for 90 minutes. Thereafter, the heat-treated film is brought into close contact with the inner surface of a box having an upper portion of 10 cm in length and width of 3 cm and a height of 3 cm to form a box shape. When the coating layer is provided, the coating layer surface is set to the inside. Next, 4 ml of DMF (dimethylformamide) is placed in the box prepared by the above method and left for 3 minutes, and then DMF is recovered. The recovered DMF was supplied to liquid chromatography (manufactured by Shimadzu Corporation: LC-7A) to determine the amount of oligomer in DMF, and this value was divided by the film area in contact with DMF to obtain the amount of film surface oligomer (mg / M ² ). The amount of oligomer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method).

  The standard sample was prepared by accurately weighing an oligomer (cyclic trimer) collected in advance and dissolving it in accurately measured DMF. The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml.

The conditions for the liquid chromatograph were as follows.
Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: “MCI GEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(5) Measuring method of film haze Film haze was measured for the sample film according to JIS-K-7136 with a haze meter “HM-150” manufactured by Murakami Color Research Laboratory.

(6) Method for evaluating film visibility after lamination of transparent conductive film (practical property substitution evaluation)
In the laminated polyester film, a sintered body of 95% indium oxide and 5% by weight tin oxide on the surface opposite to the coating layer in an atmosphere of 0.4 Pa composed of 95% argon gas and 5% oxygen gas. An ITO film (transparent conductive thin film) having a thickness of 25 nm was formed by a reactive sputtering method using the material. The ITO film was crystallized by heat treatment at 150 ° C. for 1 hour.
The transparency and visibility of the obtained film were determined according to the following criteria.
<Criteria>
○: Transparency / Visibility is good (practically acceptable level)
×: Transparency / visibility poor (practical problem level)

(7) Film-film bonding property evaluation method (practical property substitution evaluation)
A coreless double-sided adhesive was applied to a film heated at 150 ° C. for 2 hours, and the film was attached to the opposite surface for determination. In addition, the roller was used at the time of bonding.
<Criteria>
○: Wrinkle-free and particularly good (practical problem-free level)
×: Wrinkled and defective (practically problematic level)

(8) Film-film sheet flexibility evaluation method (practical property substitution evaluation)
The A4 cut size film sample was bent into a loop shape, and the strength of the stiffness was evaluated by loading when the diameter direction of the loop was crushed.
○: Film stiffness is weak and sheet flexibility is good (practically satisfactory level)
×: Strong film stiffness and poor sheet flexibility (practical problem level)

<Manufacture of polyester>
[Method for producing ester (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 adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 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 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.65 and an oligomer (cyclic trimer) content of 0.97% by weight.

[Production method of polyester (B)]
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.2 part of silica particles dispersed in ethylene glycol having an average particle diameter of 1.6 μm and 0.04 part of antimony trioxide are added. In addition, polyester (C) 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 0.65. The obtained polyester (C) had an intrinsic viscosity of 0.65 and an oligomer (cyclic trimer) content of 0.82% by weight.

Example 1:
The above-mentioned polyesters (A) and (B) are 81% and 16%, respectively, and a mixed raw material in which a polyester having a polycarbodiimide content of 10% is mixed at a ratio of 3% is used as a raw material for the A layer. Casting drums with the raw material as the raw material for layer B, each supplied to two extruders, melted at 285 ° C., and then cooled to 40 ° C. with layer A as the outermost layer (surface layer) and layer B as the intermediate layer On top, two types and three layers (ABA) were coextruded and cooled and solidified to obtain a non-oriented sheet. Next, the film was stretched in the longitudinal direction by utilizing the difference in peripheral speed of the roll, then led to a tenter, stretched in the transverse direction, and heat treated, and then the film was wound on a roll to obtain a laminated polyester film. The characteristics of the obtained film are shown in Tables 1 and 2 below.

Comparative Example 1:
Example 1 is the same as Example 1 except that the coextrusion in which polyesters (A) and (B) are mixed at a ratio of 83% and 16% respectively and a polyester having a polycarbodiimide content of 10% is changed to 1%. In the same manner as above, a polyester film was obtained. The characteristics of the obtained laminated polyester film are shown in Tables 1 and 2 below.

Comparative Example 2:
Example 1 is the same as Example 1 except that the coextrusion in which polyesters (A) and (B) are mixed at a ratio of 79%, 16%, and polyester having a polycarbodiimide content of 10% is changed to 5%. In the same manner as above, a polyester film was obtained. The characteristics of the obtained laminated polyester film are shown in Tables 1 and 2 below.

Comparative Example 3:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the coextrusion in which polyesters (A) and (B) were mixed in proportions of 84% and 16%, respectively, was changed. The characteristics of the obtained laminated polyester film are shown in Tables 1 and 2 below.

  The film of the present invention can be suitably used as an optical film, for example.

Claims (1)

A laminated polyester film, characterized in that it is a laminated film having a laminated structure of at least 3 layers, wherein both layers are polyesters containing 1200 to 4800 ppm of polycarbodiimide.