JPH09304621A - Production of phase difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase difference film having less defect caused by contamination with foreign matters. SOLUTION: A carrier film 5 unwound from a carrier film unwinding part 1 is brought into contact with an adhesive roll 3, thereby foreign matters on a casting surface are removed by cleaning (adhesion). Then, foreign matters on a reverse side surface of the casting surface are removed by cleaning (adhesion) by coming into contact with an adhesive roll 4. Thereafter, solvent solution 6 of a transparent plastic is applied on the casting surface of the carrier film at an applying part 2 according to a conventional method, the film is introduced in a coater furnace 7 and the solvent is evaporated to form a film. Then, the carrier film 5 is stripped off to obtain a casting film and further the film is stretched to obtain a phase difference film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a retardation film having improved defects, and more particularly to a method for producing a retardation film in which "color loss" due to foreign matter is prevented. Is.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have attracted attention due to their low power consumption and excellent image quality, and have been widely put into practical use as display devices for notebook personal computers. In these liquid crystal display devices, polymer films are used for polarizing plates, protective layers, retardation plates and the like. Among them, the retardation film is used for improving the visibility of images in STN type liquid crystal display elements and TN type liquid crystal display elements, and plays a role of converting elliptically polarized light passing through the liquid crystal device into linearly polarized light. There is.

As a material for these retardation films, a raw material film of transparent plastic such as polycarbonate, polyarylate, polysulfone, etc. is mainly uniaxially stretched and used. The appearance of
Solution casting, which is superior to the melt extrusion method in terms of surface smoothness, transparency and thickness accuracy, is the mainstream, and a method of forming a film on a carrier film such as polyethylene terephthalate is industrially known. There is.

As seen in recent notebook computers, the required images are VGA to SVGA and even XG.
As the fineness is increased to A, the demand for the retardation film has become stricter. As one of them, there is a demand for a retardation film having fewer defects. The defect referred to here is what is called "color loss", and when sandwiching two retarder films with two crossed polarizers, they may become different from the surroundings in spots, or the color may be lost. Is.

Examination of this "color loss" defect revealed that most of it was caused by foreign matter. These transparent plastics have a high polarizability because they contain an aromatic group in the molecule, and the refractive index anisotropy is easily exhibited by molecularly orienting the film by uniaxial stretching. Therefore, it is advantageous in that the retardation required for the retardation film can be obtained by a slight stretching, but on the other hand, even if a small foreign substance is mixed, the resin around it is distorted, which easily causes an optical defect. . Furthermore, upon closely examining the mixing paths of these foreign substances into the film, it was found that most of the foreign substances adhering to the carrier film were taken into the casting film.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a method for producing a retardation film with few defects.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies in view of the above-mentioned circumstances, the present inventors have found that the above object can be achieved by washing the carrier film and removing foreign matters before the coating step, The present invention has been completed. That is, the present invention, when a casting film obtained by applying a solvent solution of a transparent plastic on a carrier film and then drying and film-forming the carrier film is stretched to produce a retardation film, A method for producing a retardation film, which comprises washing the carrier film before applying the solvent solution onto the carrier film.

As the transparent plastic of the present invention, a resin having a positive birefringence characteristic is generally used, and examples thereof include polycarbonate, polyvinyl alcohol, polyarylate, polyester, polysulfone, etc., but a negative birefringence characteristic is shown. Resin can be used. The resin exhibiting a positive birefringence property is one in which the refractive index in the stretching direction increases (a slow axis appears in the orientation direction of molecules), and the resin exhibiting a negative birefringence property is a stretch A decrease in the refractive index in the direction (in which the fast axis appears in the molecular orientation direction).

In the production method of the present invention, a washing section is provided between the unwinding section and the coating section of the carrier film, and the carrier film is washed in advance before the solvent solution of the transparent plastic is applied onto the carrier film. Thus, the foreign matter mixed in the casting film is removed. By stretching the film obtained by this method, a retardation film in which the number of defects is significantly reduced can be obtained. The washing method is not particularly limited, and for example, the foreign matter may be adhesively removed by using an adhesive roll or may be washed and removed by washing with water, but the former is preferable because the apparatus and operation are simple. . Cleaning is required only on the casting surface of the carrier film, but it is more effective if the opposite surface is also cleaned.

[0010]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto. FIG. 1 shows an example of a manufacturing apparatus used in the present invention, in which a cleaning section, that is, adhesive rolls 3 and 4 are provided between a carrier film unwinding section 1 and a coating section 2. As the adhesive roll, for example, a tacky roll manufactured by Odaka Rubber Industry Co., Ltd. is preferably used. As shown in the drawing, the adhesive rolls 3 and 4 are arranged so as to contact one surface and the other surface of the carrier film 5, respectively, and to contact both surfaces of the carrier film 5.

When the carrier film 5 unwound from the carrier film unwinding section 1 is brought into contact with the adhesive roll 3, foreign matter on the casting surface is washed (adhered) and removed, and then brought into contact with the adhesive roll 4. The foreign matter on the surface opposite to the casting surface is cleaned (adhesion) removed. Then, according to a conventional method, in the coating section 2,
A transparent plastic solvent solution 6 is applied to the casting surface of the carrier film, and then introduced into a coater furnace 7 which is a drying zone to evaporate the solvent to form a film, and then the carrier film 5 is peeled off to obtain a casting film. It is further stretched to obtain a retardation film.

Example 1 and Comparative Example 1 A polyarylate film having a thickness of 66 μm was obtained by using the apparatus shown in FIG. 1 using polyarylate (Ermec: registered trademark of Kanefuchi Chemical Industry Co., Ltd.). The obtained unstretched film was stretched at a ratio of 120% to obtain a retardation film having a retardation of 570 nm. A polyethylene terephthalate film was used as the carrier film. For comparison, a retardation film was obtained by similarly stretching an original film prepared in the same manner except that the carrier film was not passed through the washing section (Comparative Example 1). The number of defects in the obtained retardation film was observed and compared. The defects were observed by visually slicing a 1 m square sample from the obtained retardation film. In Example 1, the number was only 3, whereas in Comparative Example 1, it was 17
Individual defects were observed.

Example 2, Comparative Example 2 Using polycarbonate (glass transition temperature: 150 ° C., Panlite C-1400: a registered trademark of Teijin Chemicals Ltd.), a raw film was obtained and stretched in the same manner as in Example 1. To obtain a retardation film. As Comparative Example 2, a retardation film was obtained from an original film prepared in the same manner as in Comparative Example 1 without passing through the washing section. When the numbers of defects of both were observed, there was only one defect in Example 2 and eight defects in Comparative Example 1.

Example 3, Comparative Example 3 Polysulfone (glass transition temperature: 170 ° C., P-35
00: manufactured by Teijin Amoco Co., Ltd.) to obtain a raw film in the same manner as in Example 1 and stretched to obtain a retardation film. As Comparative Example 3, a retardation film was obtained from an original film prepared without passing through the washing section as in Comparative Example 1.
Observing the number of defects of both, it was only 2 in Example 2.
There were 14 defects in Comparative Example 1 and Comparative Example 1.

[0015]

As described above, according to the manufacturing method of the present invention, a high-quality retardation film with few defects can be obtained by a simple method.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a manufacturing apparatus used in the present invention.

[Explanation of symbols]

 1 Carrier Film Unwinding Part 2 Coating Part 3 Adhesive Roll 4 Adhesive Roll 5 Carrier Film 6 Solvent Solution of Transparent Plastic 7 Coater Furnace

Claims (5)

[Claims] 1. A transparent plastic solvent is used for producing a retardation film by stretching a casting film obtained by applying a solvent solution of transparent plastic on a carrier film, drying the film, and then peeling off the carrier film. A method for producing a retardation film, which comprises washing the carrier film before applying the solution onto the carrier film. 2. A method of cleaning both sides of a carrier film.
The manufacturing method as described. 3. The method according to claim 1, wherein the carrier film is polyethylene terephthalate. 4. The method according to claim 1, 2 or 3, wherein the carrier film is washed with an adhesive roll. 5. The production method according to claim 1, 2 or 3, wherein the carrier film is washed by washing with water.