JP2018062151A - Laminated polyester film for transparent conductive film substrates - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for transparent conductive film substrates that can prevent the yellowing of a transmission color when transparent conductive layers are laminated.SOLUTION: A laminated polyester film for transparent conductive film substrates has a laminate structure consisting of three or more layers. The film contains a fluorescent brightener at least in an intermediate layer. In the film the content of the fluorescent brightener is 0.005-0.09 wt.%. The film has chromaticity bvalue of -5.0-0.5 and a haze of 1.5% or less.SELECTED DRAWING: None

Description

  The present invention relates to a laminated polyester film used for a transparent conductive film substrate, and relates to a laminated polyester film suitable for a transparent conductive film substrate in which a transparent conductive layer such as indium tin oxide (ITO) is laminated.

  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

  As a transparent electrode substrate used for a capacitive touch panel, a transparent electrode layer made of a metal oxide such as ITO or zinc oxide on a polyester film is generally used. Since the transparent conductive film obtained in this way has a yellow color due to the influence of the transparent conductive layer, the transmitted light is yellowish. For this reason, there is a problem that the color of the display device arranged under the touch panel cannot be accurately expressed. Therefore, solutions such as laminating a hard coat layer, a first color tone correction layer, and a second color tone correction layer as in Patent Document 1 have been taken, but the present situation is not always sufficient.

Japanese Patent Laying-Open No. 2015-107557

  An object of the present invention is to provide a polyester film for a transparent conductive film substrate capable of suppressing the yellowness of a transmitted color when a transparent conductive layer is laminated.

  As a result of intensive studies in view of the above problems, the present inventors have found that a film having a specific configuration is suitable, and have completed the present invention.

That is, the gist of the present invention is a laminated polyester film having a laminated structure of three or more layers, which contains a fluorescent brightening agent in at least an intermediate layer, and the content of the fluorescent brightening agent in the film is 0.005 to 0.005. A laminated polyester film for a transparent conductive film substrate, characterized in that it is 0.09% by weight, the chromaticity b ^* value is -5.0 to 0.5, and the haze is 1.5% or less. .

  The film of the present invention can contribute to the production of a transparent conductive film with little yellowishness, and when used as a substrate of a transparent conductive film used for a touch panel or the like, its advanced characteristics are exhibited, Industrial value is extremely high.

Hereinafter, the present invention will be described in more detail.
The laminated polyester film for transparent conductive film substrate of the present invention is a laminated film having at least 3 layers. The polyester film for transparent conductive film base 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 if necessary, biaxially in the vertical direction and the horizontal direction. It is a film oriented in the direction.

  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 one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, and sebacic acid, and the glycol component includes ethylene. One type or two or more types such as glycol, diethylene glycol, propylene glycol, and butanediol can be used.

  In the present invention, the polyester used for the outermost layer of the laminated polyester film preferably contains 80% by weight or more of polyester having an ester cyclic trimer content of 0.5% by weight or less. When a polyester having an ester cyclic trimer content of more than 0.5% by weight is used, or when the content is less than 80% by weight, the resulting laminated polyester is kept at 150 ° C. for a long time. When used in severe processing conditions such as heat treatment, sputtering under high tension conditions, durability testing under high-temperature and high-humidity conditions, the film haze is greatly increased. As a result, the optical properties and visibility may be reduced.

  In the laminated polyester film of the present invention, the thickness of the outermost layer is preferably 4 μm or more, more preferably 5 μm or more, and further preferably 6 μm or more. When the thickness of the outermost layer is less than 4 μm, the ester cyclic trimer precipitation sealing effect and the fluorescent whitening agent precipitation preventing effect of the outermost layer may be weakened.

  The thickness of the laminated polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 10 to 300 μm, preferably 20 to 250 μm, more preferably 25 to 200 μm. . When the total film thickness is less than 10 μm, when forming an ITO film by a sputtering method in order to form a transparent conductive film, the film strength is lost to the processing tension, and wrinkles are generated and the transparent conductive film cannot be formed properly. There is a fear.

  In the laminated polyester film of the present invention, particles may be blended mainly for the purpose of imparting slipperiness and preventing the occurrence of 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 with a polyester film, Usually, 0.02 micrometer-3 micrometers, Preferably it is 0.02 micrometer-2.5 micrometers, More preferably, it is in the range of 0.02 micrometer-2 micrometers. is there. 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 size exceeds 3 μm, the degree of roughening of the film surface becomes too large and the film haze may increase.

  Furthermore, the particle content of the polyester film 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 and appearance defects such as scratches may occur during film processing. On the other hand, when the particle content exceeds 0.5% by weight, the transparency of the film may be insufficient.

  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, the particles can be added at any stage for producing the polyester, but 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. Then, 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.

  In the present invention, it is important that a fluorescent whitening agent is contained in the film in order to reduce yellowishness when used as a transparent conductive film substrate. The content of the optical brightener is 0.005 to 0.09% by weight with respect to the entire film. When the content of the optical brightener is less than 0.005% by weight, the effect of reducing yellowness is insufficient and the object of the present invention cannot be achieved. On the other hand, if the content of the fluorescent brightening agent exceeds 0.09% by weight, the bluish color becomes too strong and the color of the display device cannot be accurately expressed. Since the fluorescent whitening agent may bleed out and cause problems such as adverse effects during use, it is not preferable.

  Furthermore, in order to prevent bleeding out of the optical brightener, it is important in the present invention that at least one of the intermediate layers contains the optical brightener. For example, in the case of a polyester film having an A / B / A structure or an A / B / C structure, it is essential that the layer B contains a fluorescent brightening agent. A layer other than the B layer (A layer or C layer) can contain the optical brightener, but the content of the optical brightener contained in the A layer or the C layer is preferably lower than that of the B layer. . Even in this case, the content of the optical brightener needs to have a predetermined content with respect to the entire film.

  In the present invention, the fluorescent whitening agent absorbs ultraviolet rays in sunlight or artificial light, retains the function of radiating the ultraviolet rays into violet to blue visible rays, and the lightness of the polymer substance by the fluorescence action. It is a compound that promotes whiteness without lowering. Examples of fluorescent brighteners that can be suitably used in the present invention include a product “Ubitec” manufactured by Ciba Specialty Chemicals, a product “OB-1” manufactured by Eastman, and the like. The method of adding the optical brightener may be added during the production process of the polyester, or may be a method in which the polyester raw material is made into a chip shape and then applied, or may be added during the melt extrusion process of the polyester. A method of adding a polyester raw material to which a fluorescent whitening agent is added at a high concentration by such a method as a master batch in a melt extrusion process at the time of film formation can also be adopted. In any case, the effect of the present invention will be exhibited if the obtained film contains a predetermined amount of fluorescent brightening agent.

  In the laminated polyester film of the present invention, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, dyes, pigments and the like are added as necessary in addition to the above-described particles and fluorescent brightening agent. can do. Further, depending on the use, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber may be contained.

  Hereinafter, although the manufacturing method of the laminated 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 the polymer to be 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 2.7 to 5 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 90 to 160 in the lateral direction. It is preferable that the film is stretched 3 to 5 times at ° C and heat-treated at 210 to 240 ° C for 10 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, as described above, two or more polyester melt extruders can be used to form a laminated film of three or more layers by a so-called coextrusion method. As the layer structure, a film having an A / B / A structure or B / A / B structure using the A raw material and the B raw material, and an A / B / C structure or other structure using the C raw material. be able to. For example, the surface shape of the A layer is designed using specific particles as the A raw material, and the raw material not containing particles is used as the B raw material to form a film having an A / B / A configuration or a B / A / B configuration. it can. In this case, since the raw material of B layer can be selected freely, a cost advantage is large. Further, even if the recycled raw material of the film is blended with the B layer, the surface roughness can be designed by the A layer which is the outermost layer, so that the cost advantage is further increased.

  In particular, the laminated polyester film of the present invention is used for optical applications, so that a light diffusion layer, a hard coat layer, an antireflection layer, an antiglare layer, etc. are provided, or a vapor deposition layer is provided. A coating layer as an undercoat layer can be provided for the purpose of improving the coating property and adhesiveness during the treatment, or preventing charging in order to keep the surface clean. The formation of such a coating layer is a method in which a very thin coating layer can be formed in the process of producing a film, particularly after stretching in the longitudinal direction and before stretching in the transverse direction, and the coating agent is dried and cured. This is preferable in that it can be performed 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, the laminated polyester film of the present invention, when used for optical applications, for example, forms a functional laminated thin film for the purpose of preventing dust reflection due to reflection of external light and static electricity as well as improving adhesion, and also for electromagnetic wave shielding. It is also preferable that

As the binder resin used in the coating layer, a polymer having a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher is more preferable among the above polyesters, acrylic polymers, and polyurethanes.
Among the polyurethanes, polyester polyurethane is more preferable, and a polymer having a carboxylic acid residue and at least a part of which is made aqueous with amine or ammonia is more preferable.

  Melamine-based, epoxy-based, and oxazoline-based resins are generally used as the crosslinking agent used in the coating layer, but melamine-based resins are particularly preferable from the viewpoints of coating properties 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, stickiness and the like. The compounding amount of the particles in the coating layer 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 (for example, divinylbenzene) containing two or more carbon-carbon double bonds in one molecule.
The 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.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol and methyl alcohol, glycols such as propylene glycol, ethylene glycol and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or any other coating as shown in “Coating system” (Yuji Harasaki, Tsuji Shoten, published in 1979). The device 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. Among these, in order to further improve the surface characteristics, it is more preferable to perform a discharge treatment after forming the coating layer.

  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 are likely to adhere to each other, and particularly when the coated film is re-stretched to increase the strength of the film, the film tends to stick to the roll. Tend to. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  Analysis of various components in the coating layer formed on the laminated polyester film in the present invention can be performed by surface analysis such as TOF-SIMS, ESCA, and fluorescent X-ray.

  The laminated polyester film of the present invention has an essential requirement that the haze is 1.5% or less, and preferably 1.0% or less. When the haze is higher than 1.5%, the visibility of the film is lowered and it is not suitable as a transparent conductive film substrate.

The laminated polyester film of the present invention has an essential requirement that the chromaticity b ^* value measured with one film by a transmission method is −5.0 to 0.5, and preferably −1.5 to 0. . When the chromaticity b ^* value is higher than 0.5, the yellowness of the transmitted color when the transparent conductive layer is laminated is clearly recognized. On the other hand, when the chromaticity b ^* value is lower than −5.0, the blue color of the transmitted color when the transparent conductive layer is laminated is recognized.

In the laminated polyester film of the present invention, the amount of ester cyclic trimer extracted from the film surface by dimethylformamide before and after heat treatment (150 ° C., 90 minutes) is preferably 10 mg / m ² or less, more preferably 6 mg / m ^2. m ² or less, particularly preferably 4 mg / m ² or less. When the amount of the ester cyclic trimer exceeds 10 mg / m ² , the amount of the ester cyclic trimer increases in post-processing, for example, with a long-time heat treatment in a high temperature atmosphere such as 150 ° C. for 90 minutes. The transparency of the film may be reduced.
Although the structure of the transparent conductive film using the lamination | stacking polyester film of this invention is not limited, The structure which laminated | stacked metal oxides, such as transparent conductive layers, such as indium tin oxide (ITO), and zinc oxide, is mentioned.

  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) Intrinsic viscosity of polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measured at 30 ° C.

(2) Average particle diameter (d50: μm)
The value of 50% of integration (weight basis) in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer “SA-CP3 type” (manufactured by Shimadzu Corporation) was defined as the average particle size.

(3) Chromaticity b ^* value Using a spectrocolorimeter “CM-3700d” (manufactured by Minolta Co., Ltd.), the chromaticity b ^* value of one film was measured according to JIS Z8781-4 by the transmission method.

(4) Haze (transparency evaluation)
Haze was measured with an integrating sphere turbidimeter “NDH2000” (manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K7136. Using the obtained haze value, transparency was determined according to the following criteria.
(Criteria)
A: Good transparency (haze is 1.5% or less)
B: Transparency failure (haze greater than 1.5%)

(5) Amount of ester cyclic trimer contained in polyester raw material About 200 mg of polyester raw material was weighed and dissolved in 2 ml of a mixed solvent having a ratio of chloroform / HFIP (hexafluoro-2-isopropanol) of 3: 2. After dissolution, 20 ml of chloroform was added, and 10 ml of methanol was added little by little. The precipitate was removed by filtration, and the precipitate was further washed with a mixed solvent having a chloroform / methanol ratio of 2: 1. The filtrate / washing solution was collected, concentrated by an evaporator, and then dried. After the dried product was dissolved in 25 ml of DMF (dimethylformamide), this solution was supplied to liquid chromatography “LC-7A” (manufactured by Shimadzu Corporation) to determine the amount of ester cyclic trimer in DMF. Is divided by the amount of the polyester raw material dissolved in the chloroform / HFIP mixed solvent to obtain the amount of ester cyclic trimer (weight%). The amount of ester cyclic trimer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area. (Absolute calibration method)
The standard sample was prepared by accurately weighing the amount of the ester cyclic trimer collected in advance and dissolving it in DMF that was accurately weighed. 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

(6) Amount of ester cyclic trimer extracted from the surface of the laminated polyester film (amount of oligomer precipitation)
In advance, the untreated laminated polyester film was heated in air at 150 ° C. for 90 minutes. Thereafter, the heat-treated film was 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. Next, 4 ml of DMF 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 a liquid chromatography “LC-7A” (manufactured by Shimadzu Corporation) to determine the amount of ester cyclic trimer in DMF, and this value was divided by the film area contacted with DMF, It was set as the amount of ester cyclic trimers (mg / m ² ) on the film surface. The amount of ester cyclic trimer in DMF was calculated according to the absolute calibration curve method described in (5) Method for measuring amount of ester cyclic trimer contained in polyester raw material.

(7) Formation of transparent conductive thin film (evaluation of yellowness reduction effect)
Reactive sputtering method using a sintered body material of 95% by weight of indium oxide and 5% by weight of tin oxide in an atmosphere of 0.4 Pa composed of 95% by volume of argon gas and 5% by volume of oxygen gas on the surface of the sample film Thus, an ITO film (transparent conductive thin film) having a thickness of 25 nm was formed.
The obtained film with a transparent conductive thin film was visually observed, and the yellowness reduction effect was determined according to the following criteria.
(Criteria)
A: There is an effect of reducing yellowness B: There is no effect of reducing yellowness

  Examples and Comparative Examples are shown below, and the production method of the polyester used for this is as follows.

<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 adding 0.04 part by weight of ethyl acid phosphate to this reaction mixture, 0.03 part by weight 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 when the intrinsic viscosity was 0.67 dL / g 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 0.67 dL / g and an ester cyclic trimer amount of 0.97% by weight.

<Method for producing polyester (b)>
In the method for producing polyester (a), after adding 0.04 part of ethyl acid phosphate, 0.4 part by weight of silica particles having an average particle size of 2.2 μm dispersed in ethylene glycol and 0.03 part by weight of antimony trioxide A polyester (b) was obtained using the same method as the production method of the polyester (a) except that the polycondensation reaction was stopped when the intrinsic viscosity was 0.66 dL / g. The obtained polyester (b) had an intrinsic viscosity of 0.67 dL / g and an ester cyclic trimer amount of 0.85% by weight.

<Method for producing polyester (c)>
In the method for producing polyester (a), the starting material is 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, and the method for producing polyester (a) is used except that germanium oxide is used as a polymerization catalyst. A polyester (c) was obtained using the same method as described above. In addition, the addition method of germanium oxide employ | adopted the well-known method, The addition amount was 100 ppm with respect to the raw material weight as germanium. The obtained polyester (c) had an intrinsic viscosity of 0.66 dL / g and an ester cyclic trimer amount of 0.89% by weight.

<Method for producing polyester (d)>
98.5 parts by weight of polyester (c) and 1.5 parts by weight of optical brightener “OB-1” (manufactured by Eastman) are blended and melt-kneaded using a twin screw extruder, and the optical brightener is A containing masterbatch was created.

<Method for producing polyester (e)>
The polyester (a) is preliminarily crystallized at 160 ° C. and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C., the intrinsic viscosity is 0.75 dL / g, and the ester cyclic trimer content is 0.46. A weight percent of polyester (e) was obtained.

Example 1
<Manufacture of polyester film>
A mixed raw material obtained by mixing the above polyesters (b) and (e) at a ratio of 8% by weight and 92% by weight, respectively, is used as a raw material for the A layer, and polyesters (c) and (d) are respectively 98.5% by weight, The raw materials mixed at a ratio of 5% by weight are supplied to the two vent type twin-screw extruders as the raw materials for the B layer and melted at 285 ° C., respectively, and the A layer is the outermost 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 3.3 times in the machine direction at a film temperature of 81 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 3.6 times in the transverse direction at 120 ° C., and heat-treated at 225 ° C. Thereafter, it was relaxed by 2% 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 6 μm / 88 μm / 6 μm.

Example 2
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the mixed raw material in which the polyesters (b) and (e) were mixed at a ratio of 15% by weight and 85% by weight was used as the raw material for the A layer. .

Example 3
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the thickness of each layer of the film was 4 μm / 92 μm / 4 μm.

Example 4
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the thickness of each layer of the film was 2 μm / 96 μm / 2 μm.

Example 5
A polyester film having a thickness of 100 μm was prepared in the same manner as in Example 1 except that the mixed raw material in which the polyesters (c) and (d) were mixed at 94.7% by weight and 5.3% by weight was used as the raw material for the B layer. Obtained.

Example 6
A polyester film having a thickness of 100 μm was prepared in the same manner as in Example 1 except that a mixed raw material in which polyesters (c) and (d) were mixed at 99.5% by weight and 0.5% by weight, respectively, was used as the raw material for the B layer. Obtained.

Comparative Example 1
A polyester film was obtained in the same manner as in Example 1 except that 100% by weight of the polyester (c) was used as the raw material for the B layer.

Comparative Example 2
A polyester film having a thickness of 100 μm was prepared in the same manner as in Example 1 except that a mixed raw material in which polyesters (c) and (d) were mixed at 92.4% by weight and 7.6% by weight, respectively, was used as the raw material for the B layer. Obtained.

Comparative Example 3
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the mixed raw material in which the polyesters (b) and (e) were mixed in proportions of 25% by weight and 75% by weight was used as the raw material for the A layer. .

  Table 1 below summarizes the physical properties of the films obtained in Examples and Comparative Examples and the characteristics when the films are used as the base material of the diffusion plate. It can be seen that a film satisfying the requirements of the present invention is highly suitable for this application.

  The laminated polyester film of the present invention can be suitably used as a base material for transparent conductive films used for touch panels and the like.

Claims (2)

A laminated polyester film having a laminate structure of three or more layers, containing a fluorescent brightening agent in at least the intermediate layer, and the content of the fluorescent brightening agent in the film is 0.005 to 0.09% by weight,
A laminated polyester film for a transparent conductive film substrate, having a chromaticity b ^* value of −5.0 to 0.5 and a haze of 1.5% or less.   A transparent conductive film using the laminated polyester film according to claim 1.