JP2000206332A - Manufacture of phase difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing stably a wide phase difference film having excellent optical uniformity and a small dispersion of a retardation value in the film face, suitable for a large-sized STN-LCD panel. SOLUTION: This manufacturing method of a phase difference film, for giving double refractivity by executing uniaxial drawing of a polycarbonate film produced by a solvent-cast method, has such a characteristic that a residual solvent quantity in the polycarbonate film before drawing is 0.5 wt.% or less, and that the drawing is executed as much as 1.1-1.5 times in the longitudinal direction in a temperature zone over Tg of the polycarbonate resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a retardation film. More specifically, the present invention relates to a method for producing a retardation film having a small fluctuation of a retardation value in a film plane and excellent in optical uniformity.

[0002]

2. Description of the Related Art Conventionally, a retardation film for an STN-LCD panel is a uniaxial polycarbonate film formed by a solution casting method because of its excellent optical uniformity and viewing angle characteristics. A birefringent film which has been stretched in particular is used. In particular, as a technique for improving optical uniformity and viewing angle characteristics, a technique for stretching a polycarbonate-based film containing a relatively large amount of residual solvent is disclosed.

[0003] For example, Japanese Patent No. 2632242, Japanese Patent No. 2670925, Japanese Patent Application Laid-Open No. 10-239522.
However, according to the methods disclosed therein, the apparent Tg of the film is reduced by the residual solvent present in the film, and stretching at a relatively low temperature becomes possible. . However, since the apparent viscosity of the film rapidly decreases due to the presence of the residual solvent, the retardation expression efficiency is deteriorated. If the stretching ratio is not increased, a desired retardation value cannot be obtained, and as a result, the neck-in increases. There is a problem of doing.
Generally, the polycarbonate-based film used for this purpose is obtained by a solution casting method, and it is difficult to obtain a wide-area film for reasons of an apparatus.
Width is the mainstream. Therefore, when it is necessary to produce a retardation film having a width of 1 m or more, an increase in neck-in is a serious problem.

[0004] Even when the amount of the residual solvent is controlled to a predetermined value at the time of casting, it changes with time,
In the stretching step, since the stretching is performed in the heating furnace while evaporating the residual solvent, the amount of the residual solvent in the film surface varies, making it difficult to perform uniform stretching.
As a result, there are problems such as the occurrence of stretching unevenness and large fluctuation of the retardation value.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a method for producing a retardation film excellent in optical uniformity with small fluctuation of retardation value in a film plane. It is in.

[0006]

Means for Solving the Problems The present inventor has conducted technical studies to solve the above-mentioned problems. As a result, the polycarbonate film contains substantially no polycarbonate resin containing components such as a solvent and a plasticizer. It was found that an optically uniform retardation film could be obtained by stretching in a form close to the single component of the present invention, and the present invention was reached. That is, the present invention relates to a method for producing a retardation film that imparts birefringence by uniaxially stretching a polycarbonate film formed by a solution casting method, wherein the amount of residual solvent in the polycarbonate film before stretching is 0.1%. A method for producing a retardation film, characterized in that the film is stretched 1.1 to 1.5 times in the longitudinal direction in a temperature range of 5% by weight or less and at least Tg of the polycarbonate resin.

In the present invention, the amount of the residual solvent in the polycarbonate film formed by the solution casting method is set to 0.5% by weight or less substantially close to a single component of the polycarbonate resin. If the amount of the residual solvent exceeds 0.5% by weight, it becomes a two-component system, and the apparent Tg decreases by 5 ° C. or more.
In the stretching step, the residual solvent evaporates, and the amount of the residual solvent in the film surface varies. As a result, stretching unevenness occurs, and an optically uniform retardation film cannot be obtained.

The stretching method in the present invention is preferably a longitudinal uniaxial stretching method in which the film is stretched in the longitudinal direction. In particular, since a wide product excellent in optical uniformity can be obtained, it is heated and stretched in an air floating type furnace. Is preferred.

The heating and stretching temperature at this time must be equal to or higher than the glass transition temperature Tg of the polycarbonate resin alone. When the stretching temperature is equal to or lower than the Tg of the polycarbonate resin, the film does not soften uniformly, so that stretching unevenness occurs and a retardation film having optical uniformity cannot be obtained.

In order to obtain a product having a wide stretching ratio and excellent optical uniformity, a low ratio is adopted.
And more preferably 1.1 to 1.3 times. If the stretching ratio is less than 1.1 times, only a low retardation retardation film can be obtained, which is not preferable. Conversely, if the stretching ratio exceeds 1.5 times, a wide retardation film cannot be obtained due to an increase in neck-in, which is not preferable.

The retardation film of the present invention obtained in this manner is a film having a width of 1 m or more, a film having a small fluctuation of the retardation value in the film plane and excellent in optical uniformity, and a large STN-LCD. It can be suitably used for panels and the like.

[0012]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples. The residual solvent amount, the retardation value, and the neck-in rate described in the present invention and Examples were measured by the following methods.

<Amount of residual solvent> 50 mm × 2 from the film
The strips of 50mm were taken three points, were weighed weight on an analytical balance and the measured value W _0. Then take the strip 1
It is dried for 1 hour in a dryer at 50 ° C., weighed again after cooling,
That the measured values and W _1. And the residual solvent amount was calculated by the following formula. Residual solvent amount = (W ₀ −W ₁ ) / W ₀ × 100

<Retardation value> The retardation value was measured using an instantaneous multi-photometry system MCPD-1000 manufactured by Otsuka Electronics Co., Ltd. <Neck-in rate> The width L ₀ of the polycarbonate film before uniaxial stretching and the width L ₁ of the polycarbonate film after uniaxial stretching were measured, and were measured by the following formula. Neck-in rate = (L ₀ −L ₁ ) / L ₀ × 100

Example 1 A polycarbonate film formed by a solution casting method (Pure Ace (trade name) manufactured by Teijin Limited, Tg of polymer: 158 ° C., thickness: 70 μm)
m, width: 1200 mm, residual solvent amount: 3.0% by weight) was introduced into a continuous drying furnace maintained at 130 ° C., and dried so that the residence time in the furnace was about 5 minutes. When the residual solvent amount of the obtained polycarbonate film was measured, it was 0.5
% By weight. Next, this film was introduced into a vertical stretching machine having a heating furnace of a floating type, and was stretched in the longitudinal direction by 1 mm.
The film was stretched 1.2 times at 60 ° C. The product width of the obtained retardation film was 1050 mm, and the in-plane (1050 mm
130 in width × 500mm length plane at 20mm intervals
The fluctuation of the retardation value of (0 point) is 450 nm ± 4.
At 5 nm, the film was excellent in optical uniformity.

[Example 2] The polycarbonate film (residual solvent amount: 3.0% by weight) used in Example 1 was
It was introduced into a continuous drying oven maintained at 0 ° C. and dried so that the residence time in the oven was about 7 minutes. When the amount of residual solvent in the obtained polycarbonate film was measured, it was 0.4% by weight. Next, this film was introduced into a longitudinal stretching machine as in Example 1, and stretched 1.15 times at 162 ° C. in the longitudinal direction. The product width of the obtained retardation film is 1100 m
m, the fluctuation of the retardation value in the film plane (1375 mm width × 500 mm length in the plane of 1375 points at intervals of 20 mm in length and width) was 435 nm ± 4.0 nm, and the film was excellent in optical uniformity.

Example 3 A polycarbonate film formed by a solution casting method (Pocalon (trademark) manufactured by Lonza, polymer Tg: 165 ° C., thickness: 75 μm,
Width: 1250 mm, residual solvent amount: 1.0% by weight)
It was introduced into a continuous drying oven maintained at 0 ° C and the residence time in the oven was 5
And dried. When the residual solvent amount of the obtained polycarbonate film was measured, it was 0.2% by weight.
Met. Next, this film was introduced into a longitudinal stretching machine as in Example 1, and stretched 1.5 times at 170 ° C. in the longitudinal direction. The product width of the obtained retardation film was 1000 mm, and the fluctuation of the retardation value in the film plane (1250 points in a plane of 1000 mm width × 500 mm length at intervals of 20 mm in length and width) was 560 nm ± 5.0 nm, and was optically uniform. The film had excellent properties.

Comparative Example 1 The polycarbonate film (residual solvent amount: 3% by weight) used in Example 1 was heated to 130 ° C.
And dried so that the residence time in the furnace was 1 minute. When the amount of residual solvent in the obtained polycarbonate film was measured, it was 2.0% by weight. Next, this film was introduced into a longitudinal stretching machine in the same manner as in Example 1, and stretched 1.5 times at 145 ° C. in the longitudinal direction.
The product width of the obtained retardation film is 900 mm, and is within the film plane (900 mm width × 500 mm length within the horizontal and vertical directions.
The runout of the retardation value (at 1125 points at 0 mm intervals) was 420 nm ± 7.0 nm, and the film had stretch unevenness.

Comparative Example 2 The polycarbonate film used in Example 1 (residual solvent amount: 3% by weight) was used in Example 1.
And introduced at 160 ° C. in the longitudinal direction.
It was stretched twice. The product width of the obtained retardation film is 1
000 mm, but stretch unevenness occurs and 2
Only a low retardation value of 00 nm or less was exhibited, and the desired retardation value of the order of 400 nm was not exhibited.

Table 1 shows the fluctuation of the retardation value and the neck-in ratio of the retardation films obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0021]

[Table 1]

As is clear from Table 1, a retardation film obtained by uniaxially stretching a polycarbonate film having a residual solvent content of 0.5% or less under predetermined conditions has a small fluctuation in retardation value and is excellent in optical uniformity. It is clear that When compared at the same stretching ratio (Example 1 and Comparative Example 2 and Example 3 and Comparative Example 1), it is clear that the neck-in is improved.

[0023]

As shown in the examples, the method for producing a retardation film of the present invention provides a retardation film having a wide width, a small fluctuation of the retardation value in the film plane, and excellent optical uniformity. Can be done.

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Claims (1)

[Claims] In a method for producing a retardation film for imparting birefringence by uniaxially stretching a polycarbonate film formed by a solution casting method, the amount of residual solvent in the polycarbonate film before stretching is reduced to 0.1%. 5% by weight
A method for producing a retardation film, characterized in that the film is stretched 1.1 to 1.5 times in a longitudinal direction in a temperature range not lower than Tg of the polycarbonate resin.