JP2007045025A - Polyester film for electronic paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive polyester film having good processing suitability in manufacture of electronic paper and meeting functional characteristics required as a substrate for electronic paper. <P>SOLUTION: The polyester film for electronic paper has an easy-to-adhere layer or a hard coat layer on at least one side. The film has a haze value of ≤1.5%, an average of the Ra value in the front and back surfaces of 0.004-0.015 μm and an absolute value of the heat shrinkage rate of the film after one-hour treatment at 150°C of ≤0.7% in the longitudinal and the transverse direction. <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 base material for electronic paper.

  One of the electronic display applications is an electronic paper display. In this case, a glass substrate is used as a base material as a support, but in recent years, various applications have been made in order to provide flexibility or reduce the total thickness. Attempts have been made to use plastic films.

  In one configuration of the electronic paper, a transparent electrode layer and further a microencapsulated electronic ink coating layer are provided on the 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), etc., but in terms of workability, functionality and cost. From a viewpoint, a more suitable film base material is desired.

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 in the progress of practical use of electronic paper, is inexpensive, has excellent processability in electronic paper manufacture, and has the functional characteristics required as an electronic paper substrate. An object of the present invention is to provide a satisfactory polyester film substrate.

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

  That is, the gist of the present invention is that at least one surface has an easy-adhesion layer or a hard coat layer, a haze value is 1.5% or less, and an average value of Ra values on the front and back surfaces is 0.004 to 0.015 μm. In the polyester film for electronic paper, the absolute value of the heat shrinkage in the machine direction and the transverse direction after treatment at 150 ° C. for 1 hour is 0.7% or less.

Hereinafter, the present invention will be described in more detail.
The base material used in the present invention relates to a polyester film that is inexpensive and widely used for industrial purposes, and the polyester here is, for example, an aromatic dicarboxylic acid and an aliphatic glycol. It is obtained by polycondensation. 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. A typical example of the most inexpensive polyester is polyethylene terephthalate (PET).

  The polyester may be a homopolyester or a copolyester. In the case of a copolyester, it is a copolymer containing usually 30 mol% or less of the third component.

  The polyester used in the present invention may be obtained by a melt polymerization reaction, or may be obtained by solid-phase polymerization of a chip-formed polyester after melt polymerization.

  In the present invention, it may be a single layer structure film or a film having a structure in which different types of polyesters are coextruded and laminated, and any polyester layer is within the range that does not impair the gist of the present invention. If present, an antistatic agent or the like may be blended.

  In general, polyester film is used to properly roll up the formed film without causing scratches or distortion, and to ensure that continuous processing is properly performed without any trouble in various processing. Appropriate slipperiness needs to be imparted. In this case, inert inorganic or organic fine particles are added to the polyester. Examples of the particles to be blended include silicon oxide, alumina, calcium carbonate, calcium phosphate, and kaolin. , Talc, crosslinked polymer fine powder, and the like. These particles may be used alone or in combination of two or more components.

  In this case, the arithmetic average roughness (referred to as Ra value) and haze value (cloudiness) of the film vary depending on the type, particle size, or addition amount of the added particles.

  The smaller the added particle size and the smaller the added amount, the lower the Ra value and haze value of the film, and a more transparent film having a flatter film surface can be obtained. If the film thickness is increased too much, the slipperiness of the film is deteriorated, and not only a normal roll as a film roll cannot be obtained, but also various troubles are liable to occur during post-processing. Therefore, it is necessary to adjust the particle or amount to be added according to the application used.

  As a result, when the haze value after processing into a film having an easy-adhesion layer or a hard coat layer exceeds 1.5%, or when the average Ra value exceeds 0.015 μm, the transparency and clearness of the film If the average Ra value is less than 0.004 μm, the slipperiness of the film becomes too bad, and troubles due to slipperiness tend to be caused in the processing process of the electronic paper.

  In this Ra value, even if one side is too small, the trouble can be solved if the back side is large. Therefore, when the front and back Ra values are different, the average value is the target.

  In the use of electronic paper, in the case of a single-layer film (in the case of a multilayer film, in the target surface layer), the amount of particles to be added varies depending on the particle size (precipitation method), but particles of 1 to 2 μm In the case of, it is the range of 10-500 ppm.

  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, in the present invention, the absolute value of the heat shrinkage rate in the vertical and horizontal directions of the film after heat treatment at 150 ° C. for 1 hour is 0.7% or less. Although the polyester film formed under normal conditions depends on the film forming conditions, in the case of a general sequential longitudinal-lateral stretching / heat setting method, the heat shrinkage ratio is 1.0-3. 0% and the horizontal direction is about 0.0 to 0.5%. As a method of reducing the heat shrinkage in the longitudinal direction of the film industrially, that is, in the state of a continuous long film, the tension and temperature are reduced by heating and relaxing through a heating furnace at a predetermined temperature or higher under a low tension. Depending on the processing time, it can be reduced.

  From trial experience, it is effective to reduce the heat shrinkage at 150 ° C. for electronic paper use. In particular, when the length and width are both 0.7% or less, a large effect is exhibited.

  Next, an example of a polyethylene terephthalate film is shown as an example of the method for producing a polyester film of the present invention, but the production conditions differ depending on the polyester used or additive particles, and the present invention is not necessarily limited thereto. The addition of particles can be carried out at any stage from the polyester polymerization stage to the polyester resin feed stage.

  First, bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterification from terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol according to a conventional method. Next, this BHT is heated to 280 ° C. under reduced pressure to proceed the polymerization reaction to obtain a polyester raw material.

  This polyester raw material is extruded as a molten sheet from a die using an extruder, and cooled and solidified with a cooling roll to obtain an unstretched sheet. The unstretched sheet is stretched in the first stage by a roll or 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, stretching is performed in a direction orthogonal to the first-stage stretching direction. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 115 ° C., and the stretching ratio is usually 3.0 to 6 times, preferably 3.5 to 5 times. Subsequently, heat treatment is performed at a temperature in the range of 130 ° C. to 250 ° C. under a relaxation of 30% or less to obtain a biaxially stretched polyester film.

  The thickness of the polyester film as the substrate of the present invention can be selected from various thicknesses depending on the application, but for electronic paper application, the thickness is suitably in the range of 100 to 260 μm.

  In the present invention, in order to impart easy adhesion to the polyester film of the substrate, an easy adhesion imparting coating is applied by an in-line coating method or an offline coating method.

  Inline coating refers to the case where paint is applied during the film formation process, and offline coating refers to the case where the biaxially stretched polyester film obtained in film formation is applied to a coater, and the paint is applied and dried. is there. In the present invention, in-line coating is preferred. That is, in the electronic paper application, functional resin is coated on at least one side, and an easy-adhesion layer is required to improve the adhesion of the coating layer. In order to accomplish this at a low cost, it is preferable to apply an easy-adhesion layer in-line when forming a polyester film.

  Examples of paint application methods include roll coating, gravure coating, micro gravure coating, reverse coating, reverse gravure coating, bar coating, roll brushing, air knife coating, curtain coating, and die coating. Any coating method may be applied singly or in combination as appropriate.

  Examples of the component of the easy-adhesive coating material include a combination of a polyester resin, an acrylic resin and a melamine resin as a crosslinking agent component as described in JP-A-11-198329.

The range of 0.05 to 0.3 g / m ² is appropriate for the coating amount after drying of the easy adhesion layer.

  The polyester film of the present invention is suitably used as a base film for electronic paper and has high industrial value.

  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 addition, the evaluation method of the various characteristics in this invention is as follows.

(1) Haze Based on JIS K-7136, the haze value of the film was obtained as the ratio of the diffuse transmittance (τd) to the total light transmittance (τt) of the sample film.
Haze (%) = (τd / τt) × 100

(2) Arithmetic mean roughness (Ra)
The film surface was measured and calculated based on JIS B0601 with a cut-off value of 0.08 mm.

(3) Heat shrinkage rate A strip-shaped test piece is cut out from the vertical and horizontal directions of the film, and 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, It measured with the stainless steel scale, and calculated | required by following Formula.
Heat shrinkage (%) = | [(original length−length after heating) / (original length)] | × 100

(4) Transparency clarity The sample film was piled up on the newspaper, and the visibility of the characters was relatively compared from above and obliquely, and judged according to the following criteria.
When characters are clearly visible from any angle: ○ When characters are slightly difficult to see depending on the angle: ×

(5) Winding property At the time of film formation and hard coat resin coating processing, the state of the winding film roll was visually determined according to the following criteria.
The wound film roll has no traces of damage such as irregularities and distortion: 〇 The wound film roll is distorted and cannot be wound smoothly: ×

(6) Dimensional distortion A grid of 5 mm intervals is put on the sample film, placed in a hot air circulation 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. The appearance distortion was observed and evaluated according to the following criteria.
Dimensional distortion occurs in the grid, and there is a deviation in the dimension interval: ×
There is almost no dimensional distortion in the grid: 〇

(7) Curling after heating Apply the following hard coat paint on the easy-adhesion layer of the sample polyester film at a running speed of 30 m / min with a coater with a drying furnace of about 8 m and UV irradiation equipment, and dry at 100 ° C. Thereafter, UV curing was 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 was 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 The film was heated at 150 ° C. for 3 minutes in a hot-air circulating thermostat, taken out, observed for the degree of curling of the film, and evaluated according to the following criteria.
Obviously the film curls: ×
Curling is inconspicuous: 〇 ・ Creation of easily adhesive paint

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 B of terephthalic acid / isophthalic acid / 5-sodiumsulfoisophthalic acid / ethylene glycol / neopentyl glycol = 24/25/1/25/25 molar ratio:
Methyl acrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 molar ratio emulsion polymer emulsifier: anionic surfactant C:
Melamine cross-linking agent: hexamethoxymethylmelamine D: aqueous dispersion of silicon oxide having a particle size of 0.06 μm

  Pellets of polyethylene terephthalate (added 15PPM of silica particles with an average particle size of about 1.5μm) are crystallized by hot air drying at 180 ° C, then fed to an extruder, and melt extruded from a T die into a sheet at a temperature of 280-300 ° C. The film was cast and quenched on a mirror-cooled drum in combination with an electrostatic adhesion method to form an unstretched film having a thickness of about 1925 μm. Subsequently, this film was 3.2 in the longitudinal (longitudinal) direction at 85 to 95 ° C. Double-stretched to make a uniaxially stretched film, and then using the above water-based paint, an easy-adhesive paint was applied and stretched in the transverse direction at 110 to 150 ° C. in the transverse direction at a rate of 3.2 times, at 230 ° C. Heat treatment and fixing were performed to obtain a single-sided easy-adhesive polyester film-H1 having a thickness of 188 μm and a dry-adhesive layer coating thickness of about 0.1 μm.

  This single-side easy-adhesive polyester film-H1 is passed through a heat treatment machine having a heat treatment zone adjusted to an atmospheric temperature of 170 ° C., and heat relaxation treatment is performed 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 shrinkable single-sided easily-adhesive polyester film-T1 was wound up.

(Examples 2-3)
In the same manner as in Example 1, low shrinkable single-sided easily-adhesive polyester films -T2 and -T3 were obtained by changing the heat treatment zone passing speed.

(Comparative Example 1)
The single-sided easy-adhesive polyester film-H1 having no shrinkage-reducing treatment in Example 1 was defined as Comparative Example 1.

(Comparative Example 2)
The polyethylene terephthalate pellets used in Example 1 were changed to those obtained by adding 600 PPM of silica particles having an average particle size of about 2.3 μm to obtain a single-sided easily-adhesive polyester film-H2 having no low shrinkage treatment.

(Comparative Example 3)
The polyethylene terephthalate pellets used in Example 1 were changed to those obtained by adding 2 PPM of silica particles having an average particle diameter of about 1.5 μm to obtain a single-sided easily-adhesive polyester film-H3 having no low shrinkage treatment.

(Comparative Example 4)
In the same manner as in Example 1, a low-shrinkage single-sided easily-adhesive polyester film-H4 was obtained by changing the passing speed of the heat treatment zone.

  The properties and evaluation results of the obtained films are as shown in Table 1 below. Examples 1 to 3 can be satisfied in all properties, while Comparative Examples 1 to 4 satisfy all of these properties. Not what you want.

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

Claims (1)

It has an easy-adhesion layer or a hard coat layer on at least one surface, has a haze value of 1.5% or less, an average value of Ra values on the front and back surfaces is 0.004 to 0.015 μm, and is at 150 ° C. for 1 hour A polyester film for electronic paper, characterized in that the absolute value of the heat shrinkage in the machine and transverse directions after treatment is 0.7% or less.