JP2670925B2 - Method for manufacturing retardation film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical film, in particular,
The present invention relates to a method for manufacturing a retardation film. Furthermore, the present invention relates to a method of manufacturing a retardation film having excellent viewing angle characteristics.

[0002]

2. Description of the Related Art As a conventional method for producing a retardation film, a tenter stretching method (Japanese Patent Laid-Open No. 12205/1990) is used.
(See Japanese Patent Application Laid-Open No. Hei 2) A method in which a film is necked in by longitudinal uniaxial stretching, a heat relaxation region is provided after stretching, and stretching is performed with two pairs of rolls (Japanese Patent Application No. Hei.
-32264) As a method for eliminating the optical unevenness that occurs during stretching, a method of defining the amount of solvent in the film during stretching (Japanese Patent Application No. 2-
330772) Method for manufacturing retardation film having optical characteristics in one step (Japanese Patent Application No. 3-69438) A method of combining two kinds of films having positive and negative intrinsic birefringence values to improve viewing angle characteristics No. 24502), etc. are disclosed or applied for.

[0003]

However, the above-mentioned method is described as a method of stretching a retardation plate, which is a method in which tenter stretching is less likely to cause optical unevenness. It is known that when used as a compensator for liquid crystals, it is inferior in terms of quality. Further, heat treatment and residual heat are required, and the stretching temperature is as high as around 170 ° C. The film is necked-in by longitudinal uniaxial stretching, a heat relaxation area is provided after stretching, and stretching is performed between two pairs of rolls to improve stretching unevenness and viewing angle characteristics. Pretreatment at 150 ℃ -160 ℃ and 160-180
A stretching region of C and a heat relaxation region of 135 to 155 C are required, and a high temperature region is required. As a method of eliminating optical unevenness that occurs during stretching,
It defines the amount of solvent in the film before stretching. However, there is no mention of viewing angle here. Here again, a method of providing a retardation film having optical properties in one step is described. However, here, only the process tension and the temperature are specified, and the viewing angle characteristics are not mentioned. A method of combining two kinds of films having positive and negative intrinsic birefringence values for improving the viewing angle characteristics is described, but using different kinds of films leaves problems in cost and manufacturing. Of course, it is important for the retardation film to have uniform optical properties for making the liquid crystal display black and white. Make a film and set the solvent content to 2 to 10 on a solids basis.
%, It is uniformly stretched, and a retardation film having a retardation that matches the liquid crystal can be obtained, but another important item as a liquid crystal display device is the viewing angle characteristic. In general, in an anisotropic film, the optical path difference changes depending on the incident angle of light, which causes a phenomenon in which compensation is not properly performed and coloring occurs when viewed obliquely. This can be dealt with by changing the refractive index in the vertical direction, but for this purpose, it is necessary to combine different kinds of films as described in, for example, Japanese Patent Laid-Open No. 3-24502. However, this method requires time and effort in the manufacturing process.

An object of the present invention is to solve the problems of the prior art and to provide a retardation film having little optical color unevenness and good viewing angle characteristics. As a method, there is provided a method in which casting uniaxial stretching is performed consistently, and which has excellent viewing angle characteristics, does not require a pretreatment step, and can be performed at a relatively low stretching temperature. .

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide a method for producing a retardation film having a birefringence by stretching after casting a methylene chloride solution of polycarbonate. When the solvent content of the formed film is in the range of 3 to 10% on the basis of solid content, the film is stretched in the traveling direction of the film in an atmosphere of 155 ° C. or more and 175 ° C. or less, a method for producing a retardation film. Achieved by

In the present invention, the latter half of the casting film forming process, that is, the region where the residual volatile matter in the film is 10% by weight or less, preferably 8% by weight or less and 3% by weight based on the solid content.
When in the above range, the membrane is passed under an atmosphere in which the stretching zone temperature is 155 ° C. or higher and 175 ° C. or lower, preferably 160 ° C. or higher and 170 ° C. or lower. The time of exposure to this temperature range is not particularly limited, but naturally limited due to the length of the process. That is, 10 minutes or less is sufficient as an appropriate condition. On the other hand, it is desirable that the same condition be maintained for at least 10 seconds after the appearance of the phase difference. Under that condition, the film is stretched in the traveling direction. In this case, except for the stretching zone, heat treatment at a high temperature exceeding 150 ° C. and a residual heat zone are not particularly required, and the temperature as a drying zone may be secured. In addition, the residual volatile content is 10% to 3% by weight.
After being wound up in the above manner, it may be passed through a chamber having a temperature of 155 ° C. to 175 ° C. again and stretched in the traveling direction in the chamber.

[0007]

【Example】

(Example-1) As a polymer solution, a polycarbonate methylene chloride solution was prepared at 18% by weight, and a film formed on a support was cast and dried until the residual solvent became about 25% or less. It was stripped off, and this was put in a dry zone after being provided with a stretching zone in the latter half and dried. The residual volatile content in the film when entering the stretching zone is 7%, and the temperature is 165 ° C.
16.6% in the film advancing direction under the atmosphere of
A retardation film showing retardation of 70 nm was obtained.

(Comparative Example-1) The temperature in the stretching zone was set to 150.
The same as the above example except that the temperature was set to ° C. However, since the temperatures are different, there are some differences in the stretching ratio. When the viewing angle characteristics of the two retardation films are compared, the results are as shown in Table 1, and the effect of the present invention can be seen.

[0009]

[Table 1]

(Comparative Example-2) The polycarbonate film produced by the casting film forming apparatus had a residual volatile content of 4%. This film was stretched uniaxially by about 20% in a residual heat zone of 160 ° C. and a stretching zone of 168 ° C. in a separate step using a tenter to obtain a retardation of 580 nm. The change in retardation at this time was 25%.

(Example-2) The temperature was adjusted in the drying step of the casting machine, and the polycarbonate film adjusted to have a volatile content of 8% by winding was stretched by a stretching machine in another step. In the preheating zone 152 ° C., the stretching zone 162 ° C. and the relaxation zone 145 ° C., the retardation change was 9.1%. From these results, it can be seen that even when the film is offline, when the volatile content in the film is high, a retardation film with good viewing angle characteristics can be obtained by stretching at a relatively low temperature.

[0012]

In the production process of a retardation film using a polycarbonate, a production method having a vertical uniaxial stretching process in a casting / drying process, wherein the film is passed through a zone of 155 ° C. to 175 ° C. in the stretching process; Since the volatile content in the film passing through the zone is 3 to 10%, the stretching temperature can be made relatively low, and a retardation film having good viewing angle characteristics can be provided. As a result, an excellent film for liquid crystal display can be obtained.

Claims (1)

(57) [Claims] 1. A method for producing a retardation film in which a methylene chloride solution of a polycarbonate is cast and then birefringent by stretching, wherein the solvent content of the cast film is 3% on a solid basis. 1 when in the range of 10%
A method for producing a retardation film, which comprises stretching the film in an advancing direction in an atmosphere of 55 ° C. or higher and 175 ° C. or lower.