JP2007183423A - Polyester film for electronic paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for electronic paper excellent in workability in production of electronic paper, having high durability even to ultraviolet radiation and excellent in visibility. <P>SOLUTION: The polyester film for electronic paper has a coating layer on at least one surface of a polyester film support containing an ultraviolet absorber, and has a film haze of ≤2.0% and a light transmittance at 380 nm wavelength of ≤5.0%. When the polyester film is heat-treated at 150°C for 1 h, the absolute values of heat shrinkage ratios in lengthwise and crosswise directions of the film are ≤0.7% each. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polyester film suitable as a substrate for electronic paper.

  Polyester films represented by polyethylene terephthalate are excellent in mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc., and cost performance, so they are used as base films in various applications. Has been. An example of the application is a substrate for electronic display.

  There is an electronic paper display as one of electronic display applications. Electronic paper displays are superior in terms of ease of viewing, operability, shape changeability, ease of rewriting, and very low power consumption compared to conventional electronic displays typified by LCD and PDP. It is expected to be used as an electronic bulletin board, an advertising signboard, an electronic information board, an office, a home information display board, an information display board display device in an emergency disaster, or an electronic book display device.

  Conventionally, glass substrates have been used for substrates as supports for electronic paper displays, but in recent years, various plastic films have been tried to provide flexibility or reduce total thickness. It has been.

  As one configuration example of the electronic paper, a transparent electrode layer and further a microencapsulated electronic ink coating layer are provided on a substrate. In this microencapsulated electronic ink, internal particles are charged by applying voltage, and are divided into white and black to display characters and images. Electronic paper is a laminate structure in which the electronic ink coating layer and the back electrode substrate are bonded together, and further, a hard coat for preventing scratches on the exposed surface side.

  For this electronic paper, an example of a support for a conductive layer (Patent Document 1) comprising various resin sheets / moisture-proof layers / adhesive layers / resin sheets, a hard coat layer on the surface, and the surface layer There are examples of a base material using a polyester film imparted with antistatic properties (Patent Document 2), an example using a polybutylene terephthalate film base material (Patent Document 3), and the like. From a viewpoint, a more suitable film base material is desired.

  In addition, as the use of electronic paper displays expands, the opportunity to use outdoors increases, and the time for direct exposure to sunlight increases. Sun rays contain ultraviolet rays that degrade the thermoplastic resin film. When exposed to sunlight for a long time, the film will deteriorate, causing problems with visibility and laminate adhesion, The problem of yellowing occurs.

Japanese Patent Laid-Open No. 2003-175656 Japanese Patent Laid-Open No. 2003-182009 JP 2005-162768 A

  The present invention has been made in view of the above circumstances as electronic paper has been put into practical use, and has excellent processability in the manufacture of electronic paper, has high durability against ultraviolet rays, and has excellent visibility. An object of the present invention is to provide a polyester film for electronic paper.

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

  That is, the gist of the present invention is that a polyester film support containing an ultraviolet absorber has a coating layer on at least one surface, the film haze is 2.0% or less, and the light transmittance at a wavelength of 380 nm is 5.0%. In the polyester film for electronic paper, the absolute value of the heat shrinkage in the vertical and horizontal directions of the film in the heat treatment at 150 ° C. for 1 hour is 0.7% or less, respectively.

Hereinafter, the present invention will be described in detail.
The film constituting the polyester film of the present invention may be a single layer structure or a laminated structure, and may be a multilayer having four or more layers as long as the gist of the present invention is not exceeded other than the two-layer or three-layer structure. There is no particular limitation.

  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 dimethanol, neopentyl glycol, are mentioned.

  The film haze of the film of the present invention is 2.0% or less, preferably 1.5% or less, more preferably 1.0% or less. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 2.0%, it becomes inappropriate for electronic paper.

  The polyester film of the present invention contains an ultraviolet absorber, and the content thereof is usually 0.20 to 10.0% by weight, preferably 0.30 to 1.8% by weight. When the ultraviolet absorber is less than 0.10% by weight, the polyester film may be deteriorated by ultraviolet rays. When the ultraviolet absorber is contained in an amount exceeding 10.0% by weight, the ultraviolet absorber is bleeded on the surface. May cause deterioration of surface functionality such as adhesion loss.

  The polyester film for electronic paper of the present invention has a light transmittance at a wavelength of 380 nm of 5.0% or less, preferably 2.0% or less, more preferably 1.0% or less. When the light transmittance at a wavelength of 380 nm is larger than 5.0%, it is sufficient to prevent the adhesive layer that bonds the electronic ink layer and each functional sheet from being deteriorated by the ultraviolet rays transmitted through the polyester film. I can not say.

  Examples of ultraviolet absorbers that can be used in the present invention include benzophenone compounds, 1,3,5-triazine compounds, benzoxazinone compounds, and the like, and one or more of these are used in combination. However, when the color tone is taken into consideration, a benzoxazinone-based compound that is less likely to have a yellow tint is preferably used.

  An example of a benzoxazine-based compound used as an ultraviolet absorber is 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one].

  In the use of electronic paper, a heating step is performed in processing steps such as processing of the transparent conductive layer and application processing of electronic ink. At this time, if the heat shrinkage rate of the base film is high, dimensional deviation or damage occurs in the interval between the attached electrodes, causing trouble. In addition, curling may occur when the sandwich structure is laminated. Even in the finished product, it is a requirement that the heat expansion and contraction is small.

  Therefore, for the film of the present invention, the absolute values of the heat shrinkage in the vertical and horizontal directions of the film after heat treatment at 150 ° C. for 1 hour are each 0.7% or less. The polyester film formed under normal conditions is about 1.0 to 3.0% in the vertical direction and about 0.0 to 0.5% in the horizontal direction. As a method for reducing the longitudinal heat shrinkage of the film in an industrial state, that is, in the state of a continuous long film, it is possible to reduce the tension, temperature, and processing by heating and relaxing through a heating furnace with a low tension and abnormal temperature. Depending on the time, it can be reduced. From trial experience, it is effective to reduce the heat shrinkage rate at 150 ° C. for electronic paper applications, and when the length and width are 0.7% or less, particularly large effects are exhibited.

The film according to the present invention preferably has a total sum of front and back surfaces of oligomer (cyclic trimer) deposition on the film surface of 15.0 mg / m ² or less, more preferably when heat-treated at 180 ° C. for 10 minutes. Is 10.0 mg / m ² or less, particularly preferably 8.0 mg / m ² or less. When the oligomer precipitation amount on the film surface exceeds 15.0 mg / m ² , the film haze tends to deteriorate due to the heat history during processing. Moreover, it is preferable that the oligomer precipitation amount to a film surface is 15.0 mg / m < ² > or less also for the durable adhesive improvement with a hard-coat layer or an adhesive layer.

  In order to suppress the oligomer precipitation amount on the film surface by heat treatment, a method using polyester with a low oligomer content can be mentioned. Moreover, in the case of the laminated film by coextrusion, the oligomer precipitation amount on the film surface after heat processing can be suppressed to said range by using polyester with little oligomer content for outermost layer. Specifically, by setting the amount of oligomer contained in the polyester film to 5000 ppm or less, further 4000 ppm, particularly 3000 ppm or less, oligomers that deposit on the film surface when heated can be prevented.

  It is known that the oligomer in the polymer increases due to the melting step in film formation, and the increase is strongly influenced by the water content in the polymer, the temperature at the time of melting, the residence time, etc. It is considered to increase by about ˜5000 ppm.

  In order to obtain the amount of oligomer contained in the film, the amount of oligomer in the polyester raw material is preferably 4000 ppm or less, more preferably 3000 ppm or less, and particularly preferably 2500 ppm or less in consideration of an increase in the melting step.

  As a method for reducing the amount of oligomer in the polyester, conventionally known solid phase polymerization can be used.

  In the case of a film having a laminated structure, the outermost layer thickness is a thickness on one side only, usually 3 μm or more, and preferably ¼ or less of the total thickness. If the thickness is less than 3 μm, the oligomer (cyclic trimer) contained in the inner layer may be deposited on the film surface due to heat history during processing, etc., and production line contamination and film haze may deteriorate. If the thickness is more than 1/4 of the thickness, the haze value (particularly the internal haze value) due to the lubricant particles blended in the outermost layer film is increased to improve the roll-up property of the film, and the transparency of the film is deteriorated. Tend.

  The total film thickness of the film of the present invention is usually 50 to 300 μm or more, preferably 75 to 250 μm. If the total film thickness is less than 50 μm, the film is weak, so after punching into a single sheet, the workability at the time of final inspection performed for each sheet or sticking to a display tends to be worse, from 300 μm If it is thick, workability may deteriorate due to its rigidity.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all. That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in a direction orthogonal to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. is there. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In the present invention, the simultaneous biaxial stretching method can be adopted for the production of the polyester film constituting the laminated polyester film. The simultaneous biaxial stretching method is a method in which the above-mentioned unstretched sheet is usually stretched and oriented in the machine direction and the width direction at a temperature controlled normally at 70 to 120 ° C., preferably 80 to 110 ° C. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be employed.

  Furthermore, what is called an in-line coating which processes the film surface during the extending | stretching process of the above-mentioned polyester film can be given. When a coating layer is provided on a polyester film by in-line coating, coating can be performed simultaneously with stretching, and the thickness of the coating layer can be changed by the stretching ratio, so that a film suitable as a polyester film can be produced. .

  In the present invention, in order to obtain desired surface characteristics, a coating layer is formed on at least one surface of a polyester film support, which will be described in detail below. As for the coating layer, it may be provided on the polyester film by the above-mentioned in-line coating, a so-called off-line coating applied outside the system on the film once manufactured may be employed, or both may be used in combination. In-line coating is preferably used because it can be manufactured at low cost.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed before the transverse stretching in which the longitudinal stretching is finished. When a coating layer is provided on a polyester film by in-line coating, coating can be performed simultaneously with film formation, and the coating layer can be processed at a high temperature, and a film suitable as a polyester film can be produced.

  As the coating layer, a binder polymer is used to improve antireflection performance and transparency when various surface functional layers are laminated on the coating layer, and to improve adhesion to various surface functional layers. Is preferred.

  The “binder polymer” used in the present invention is a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (sponsored by the Chemical Substance Council in November 1985). ) Is a polymer compound having a molecular weight of 1000 or more and having a film-forming property.

  Specific examples of the binder polymer include polyester resin, acrylic resin, urethane resin, polyvinyl, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches. A polyester resin, an acrylic resin, and a urethane resin are more preferable in terms of improving adhesion with the surface functional layer.

  Furthermore, in the coating layer, a crosslinking agent may be used in combination as long as the gist of the present invention is not impaired, and various known resins can be used, but at least one selected from melamine compounds, epoxy compounds, oxazoline compounds, and isocyanate compounds. Preferably it is a seed. A melamine compound is more preferable in that it can be designed with a high absolute reflectance.

  Examples of the melamine compound in the present invention include methoxymethylated melamine and butoxymethylated melamine which are alkylol or alkoxyalkylolated melamine compounds, and those obtained by co-condensing urea or the like with a part of melamine can also be used. .

  Further, for the purpose of improving the adhesion and slipperiness of the coating layer, inert particles may be contained, and specific examples include silica, alumina, kaolin, calcium carbonate, titanium oxide, organic particles, and the like.

  Furthermore, as long as it does not impair the gist of the present invention, an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, an antistatic agent, an antioxidant, a foaming agent, a dye, and the like are contained as necessary. Also good.

  Furthermore, in the case of in-line coating, the above-described series of compounds is used as an aqueous solution or water dispersion, and the coating solution adjusted with a solid content concentration of about 0.1 to 50% by weight as a guide is laminated on the polyester film. It is preferred to produce a polyester film. In addition, a small amount of an organic solvent may be contained in the coating solution for the purpose of improving the dispersibility in water, improving the film forming property, and the like within the range not impairing the gist of the present invention. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

Although there is no restriction | limiting in the application quantity (after drying) of the coating layer provided on a polyester film regarding the lamination | stacking polyester film in this invention, Usually 0.005-1g / m < ² >, Preferably 0.005-0.5g / m ² range. When the coating amount is less than 0.005 g / m ² , the uniformity of the coating thickness may be insufficient. On the other hand, when the coating is applied in excess of 1 g / m ² , problems such as a decrease in slipperiness may occur.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 3 to 40 at 80 to 200 ° C. The heat treatment may be performed for 2 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds. On the other hand, when the coating layer is provided by in-line coating, heat treatment is usually performed at 70 to 280 ° C. for 3 to 200 seconds as a guide.

  Further, irrespective of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as required. 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.

  The average particle size of the particles to be blended in the polyester film is not particularly limited, but is usually in the range of 0.02 μm to 3 μm, preferably 0.02 μm to 2.5 μm, more preferably 0.02 μm to 2 μm. It is. When particles having an average particle size of less than 0.02 μm are used, the film surface is flattened and the winding properties 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.

  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.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film for electronic paper which is excellent in the processability in electronic paper manufacture, has high durability with respect to an ultraviolet-ray, and was excellent in visibility can be provided, The industrial value is high. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. 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) Content of oligomer (cyclic trimer) in polyester After a predetermined amount of polyester raw material or polyester film was dissolved in o-chlorophenol, it was reprecipitated with tetrahydrofuran and filtered to remove linear polyethylene terephthalate. After that, the filtrate obtained was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer (cyclic trimer) contained in the polyester, and this value was divided by the amount of polyester used for the measurement. The amount of oligomer contained in the polyester (cyclic trimer). The amount of oligomer (cyclic trimer) determined by liquid chromatography 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 (dimethylformamide). The conditions of 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

(4) Heat treatment of film A4 size Kent paper and polyester film to be heat treated are combined. At that time, clip the four corners with a gem clip or the like so that the measurement surface is on the outside, and stop the Kent paper and the polyester film. Under a nitrogen atmosphere, the polyester film is left in an oven at 180 ° C. for 10 minutes to perform heat treatment.

(5) Film surface oligomer amount By the method shown below, the film surface oligomer amount of front and back was measured, and the sum total of the film surface oligomer amount of the surface and back surface was made into the film surface oligomer amount. That is, the polyester film after heat treatment is folded so that the upper part is opened and the area of the bottom side is 250 cm ² to create a square box. Next, 10 ml of DMF is put into the box prepared by the above method, and the DMF is recovered after being left for 3 minutes. The recovered DMF is supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value is divided by the film area in contact with DMF to obtain the amount of oligomer on the film surface (mg / m ² ). To do. 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 DMF accurately weighed. The concentration of the standard sample is preferably in the range of 0.001 mg / ml to 0.01 mg / ml. The liquid chromatograph measurement conditions 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) Film haze Film haze was measured with an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K7105.

(7) Light transmittance With a spectrophotometer UV3100 manufactured by Shimadzu Corporation, the light transmittance is measured continuously at a low scanning speed, a sampling pitch of 2 nm, and a wavelength range of 300 to 700 nm, and the light transmittance at a wavelength of 380 nm is obtained. Detected.

(8) Heat shrinkage rate A strip-shaped test piece is cut out from the vertical and horizontal directions of the film, the test piece is placed in a hot-air circulating thermostat and heated at 150 ° C. for 1 hour, taken out, immediately cooled with water, Measure with a stainless steel scale and use the following formula.
Heat shrinkage = | [(original length−length after heating) / (original length)] | × 100

(9) Weather resistance Ultraviolet long life fade meter (FAL-3 type) manufactured by Suga Test Instruments Co., Ltd. was used and irradiated with ultraviolet rays at 63 ± 3 ° C. for 1000 hours. The appearance of the film after the test was observed and evaluated according to the following criteria.
○: No deterioration △: Slightly yellow ×: Yellowing deterioration is conspicuous

(10) Transparency sharpness A sample film is placed on newspaper, and the relative visibility of character visibility is determined from above and obliquely.
○: Characters are clearly visible from any angle ×: Characters are slightly difficult to see depending on the angle

(11) Dimensional distortion A grid of 5 mm intervals is put on the sample film, placed in a hot air circulating thermostat, heated at 130 ° C. for 3 minutes, taken out, and the vertical and horizontal intervals of the grid of the processed film are set as electrode wiring intervals. Look at the amount of distortion.
○: There is almost no dimensional distortion in the cross board. ×: Dimensional distortion occurs in the cross board, and there is a deviation in the dimensional spacing.

(12) Hard coat adhesion The following hard coat paint was applied onto the easy adhesion layer of the sample polyester film at a running speed of 30 m / min with a coater having a drying furnace of about 8 m and UV irradiation equipment, and dried at 100 ° C. Thereafter, UV curing is performed with two high-pressure mercury lamps with an irradiation distance of 100 mm and 120 W / cm, and after drying, a single-side hard-coated polyester film having a hard-coating layer with a coating thickness of 3 μm is produced.
Nippon Synthetic Chemical Co., Ltd. UV7600B: 100 parts by weight (oligomer component)
Nippon Synthetic Chemical Co., Ltd. D-1173: 3 parts by weight (photoinitiator)
Diluting solvent MEK: 100 parts by weight

Immediately after the hard coat layer is formed, a cross-cut is made in the hard coat layer so that there are 100 grids in a 1-inch width, and a cellotape (registered trademark) rapid peel test is carried out three times at the same location. evaluated. The judgment criteria are as follows.
A: Number of cross-cuts = 0
○: 1 ≦ Number of cross cuts ≦ 10
Δ: 11 ≦ number of cross-cuts ≦ 20
×: 21 <Number of cross-cuts peeled

(13) Curling after heating The film test piece is heated at 150 ° C. for 3 minutes in a hot air circulating thermostat and taken out to check the degree of curling of the film.
○: Curling is inconspicuous ×: The film is clearly curled

(14) Film haze after heat treatment A polyester film that has been heat-treated by being left in an oven at 180 ° C. for 10 minutes in a nitrogen atmosphere is subjected to an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K7105. The turbidity of the film after heat treatment was measured.

(15) 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 almost in parallel with the film surface, and the interface is observed by contrast. 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.

The manufacturing method of the polyester raw material used in the following examples and comparative examples 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 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 intrinsic viscosity of the obtained polyester (A) was 0.63, and the content of the oligomer (cyclic trimer) was 0.83% by weight.

<Method for producing polyester (B)>
Polyester (A) is pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C., and has an intrinsic viscosity of 0.75 and an oligomer (cyclic trimer) content of 0.24% by weight. Polyester (B) was obtained.

<Method for producing polyester (C)>
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.

<Method for producing polyester (D)>
Polyester (A) is subjected to a vented twin-screw extruder and 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] (CYTECOR manufactured by CYTEC Co., Ltd.) as an ultraviolet absorber. UV-3638 (Molecular weight 369 benzoxazine) was supplied to a concentration of 10% by weight, melt-kneaded to form chips, and an ultraviolet absorbent master batch polyester (D) was prepared. The intrinsic viscosity of the obtained polyester (D) was 0.59.

(Adjustment of aqueous coating agent)
Water-based paints were prepared by mixing the following paint stock solutions A to D at a weight ratio A / B / C / D = 20/45/30/5.
A: Polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / neopentyl glycol = 24/25/1/25/25 molar ratio B: methyl acrylate / ethyl acrylate / acrylonitrile / N- Methylol methacrylamide = 45/45/5/5 molar emulsion polymer (emulsifier is an anionic surfactant)
C: Melamine cross-linking agent: hexamethoxymethylmelamine D: aqueous dispersion of silicon oxide having a particle size of 0.06 μm

Example 1:
The mixed raw materials obtained by mixing the polyesters (B) and (C) at a ratio of 90% and 10%, respectively, were used as the raw material for the A layer, and the polyesters (A) and (D) were mixed at a ratio of 94% and 6%, respectively. Casting with mixed raw material as raw material of B layer, each supplied to two extruders, melted at 285 ° C each, then cooled to 40 ° C with A layer as outermost layer (surface layer) and B layer as intermediate layer A non-oriented sheet was obtained by co-extrusion on a drum in a layer configuration of two types and three layers (ABA) and cooling and solidifying. Next, the film was stretched 3.4 times in the machine direction at a film temperature of 82 ° C. using the difference in peripheral speed of the roll, and then the aqueous coating agent was applied to one side of the machined film, guided to a tenter, and 120 in the transverse direction. After stretching at 3.6 ° C. and heat treatment at 225 ° C., the film is relaxed by 2% in the lateral direction, the film is wound up into a roll at a production rate of 30 m / min, and has a coating layer with a thickness of 0.1 μm A laminated polyester film-H1 having a thickness of 188 μm and an intrinsic viscosity of 0.61 was obtained. This laminated polyester film-H1 is passed through a heat treatment machine having a heat treatment zone adjusted to an atmosphere of 170 ° C., and subjected to heat relaxation treatment with a film tension of 5 kg / 1000 mm width when passing through the heat treatment zone and a heat treatment zone passage time of 20 seconds, The low-shrinkage laminated polyester film-T1 was wound up.

Examples 2 and 3:
In the same manner as in Example 1, low shrinkage laminated polyester films -T2 and T-3 were obtained by changing the heat treatment zone passing speed.

Comparative Example 1:
The laminated polyester film-H1 without the low shrinkage treatment in Example 1 was used as Comparative Example 1.

Comparative Example 2:
In Example 1, except that the polyester raw material used in the A layer and the blending ratio thereof were changed as shown in Table 1 below, a laminated polyester film-H2 having no low shrinkage treatment was obtained in the same manner as in Example 1. .

Comparative Example 3:
In the same manner as in Example 1, a low-shrinkage laminated polyester film-H3 was obtained by changing the heat treatment zone passing speed.

Comparative Example 4:
In Example 1, a low-shrinkage laminated polyester film-H-4 was obtained in the same manner as in Example 1 except that the aqueous coating agent was not applied.

Comparative Examples 5-6:
In Example 1, except that the polyester raw materials used in the A layer and the B layer and the blending ratio thereof were changed as shown in Table 1 below, the low shrinkage polyester film-H5, H6, H7 was obtained.

  The evaluation results of the films obtained in each example and comparative example are summarized in Table 2 below.

The film of the present invention can be suitably used as a base material for electronic paper, for example.

Claims (1)

It has a coating layer on at least one surface of a polyester film support containing an ultraviolet absorber, has a film haze of 2.0% or less, a light transmittance of 380 nm at a wavelength of 5.0% or less, and 1 at 150 ° C. A polyester film for electronic paper, wherein the absolute value of the heat shrinkage in the vertical and horizontal directions of the film in the time heat treatment is 0.7% or less, respectively. sz