JPH11223727A - Manufacturing method of retardation plate - Google Patents

Abstract

(57) [Problem] To provide a phase difference plate which does not cause any color unevenness of a display screen when incorporated in a liquid crystal display device. A thermoplastic resin is kneaded by an extruder and discharged from a mold. The molten thermoplastic resin film, which has a certain degree of variation in the film thickness accuracy immediately after the discharge, is taken up by the pinch rolls 2 and 3 while being cooled by the cooling device 5 such as air. At the time of drawing from the mold lip to the pinch rolls 2 and 3, the film is stretched while being cooled to (glass transition temperature of thermoplastic resin film −30 ° C.) to (glass transition temperature of thermoplastic resin film + 40 ° C.). Let it.

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 plate, and more particularly to a method for producing a uniform retardation plate in a melt extrusion method.

[0002]

2. Description of the Related Art Conventionally, twisted nematic liquid crystal and super twisted nematic liquid crystal display devices have been used for various OA equipment and display devices. However, in these liquid crystal display devices, since the liquid crystal display element generates a phase difference, there is a problem that coloring and shading occur on the black and white liquid crystal display screen.In order to obtain a normal display screen, the liquid crystal display screen has a phase difference. Board is attached.

[0003] If such a phase difference plate has unevenness in thickness or refractive index, a uniform phase difference cannot be obtained over the entire surface of the phase difference plate, causing color unevenness and contrast unevenness on a display screen.

[0004] The performance of the phase difference plate to make the phase difference uniform is evaluated by the variation of the retardation value of the phase difference plate, and the retardation value is determined by the product of the thickness d of the phase difference plate and the refractive index difference Δn. Therefore, the retardation plate is required to have high uniformity in thickness and uniformity in refractive index difference.

Hitherto, as a method for producing a retardation plate, a method of uniaxially stretching a thermoplastic resin film has been mentioned. As a stretching method, longitudinal uniaxial stretching (Japanese Patent Application Laid-Open No. 2-191904) and horizontal uniaxial stretching (Japanese Patent Application Laid-Open No. 42406). Further, as a method for producing a retardation plate having an extremely uniform retardation value, there is a casting film forming method in which a solvent is contained in a resin, a film is formed, and the solvent is volatilized (Japanese Patent Application Laid-Open No. Hei 8-
122526).

[0006]

However, in order to manufacture a retardation plate by the method described in Japanese Patent Application Laid-Open No. 8-122526, it is required to maintain and control high film thickness accuracy. When a film having a large thickness unevenness is used, a retardation value varies in proportion to the thickness unevenness in the retardation plate when the film is stretched. That is, when the retardation plate is incorporated in the liquid crystal display device, there is color unevenness that can be visually discriminated.

Further, Japanese Patent Application Laid-Open No. 2-191904,
Also in the method for manufacturing a retardation plate described in Japanese Patent Application Laid-Open No. 2-42406, the retardation value varies because stretching unevenness occurs in proportion to the thickness unevenness for the same reason as described above.
As described above, the conventional method for manufacturing a retardation plate requires highly accurate film forming equipment and complicated equipment management.

In view of these problems, an object of the present invention is to produce a retardation plate having a uniform retardation value over the entire liquid crystal display screen even if the film before stretching has uneven thickness. .

[0009]

According to the first aspect of the present invention,
In a melt extrusion method, a molten thermoplastic resin film extruded from a mold is cooled by cooling means arranged between the mold and a pinch roll arranged downstream of the mold in the extrusion direction. The thermoplastic resin is (Tg−30 ° C.) to (Tg +
A method of producing a retardation plate, wherein the film is stretched with the pinch roll while cooling to a temperature range of 40 ° C.).

The thermoplastic resin used in the first aspect of the present invention has a birefringent property by stretching.
An appropriate thermoplastic resin can be used, and examples thereof include a cellulose resin, a polystyrene resin, a vinyl chloride resin, an acrylonitrile resin, an olefin resin, a polymethyl methacrylate resin, and a polyarylate resin.

Among these thermoplastic resins, the polysulfone resin and the polycarbonate resin have characteristics in which the wavelength dispersion of light is close to that of liquid crystal, and can satisfactorily compensate for elliptically polarized light different at each wavelength, thereby improving the contrast of liquid crystal display. It is preferred.

In the first aspect of the present invention, the thermoplastic resin is formed into a film in a film forming step. In addition, the "film" here does not refer to a film in a strict sense defined by a thickness, but may be a so-called sheet, from a rollable flat material to a plate-like material. including.

In the step of forming a thermoplastic resin film, a known melt extrusion method in which a thermoplastic resin is melt-kneaded by an extruder and discharged into a film by a mold is used. Here, the ejection direction may be horizontal to the ground or vertical.

The molten thermoplastic resin film extruded from the mold is cooled by a cooling means arranged between the mold and a pinch roll arranged downstream in the extrusion direction. Hereinafter, Tg means the glass transition temperature of the thermoplastic resin film.

The cooling means is not particularly limited as long as it can cool the molten thermoplastic resin film to the range of (Tg−30 ° C.) to (Tg + 40 ° C.). For example, a cooling device using a refrigerant such as cold air In addition, an apparatus using a heat medium having excellent heat transfer with the film may be used. For example, desired cooling is possible even with a hot air device in which hot air having a temperature corresponding to Tg of a thermoplastic resin flows at a speed of 20 m / sec or more to the film surface. The thermoplastic resin cooled by the cooling means is cooled from (Tg−30 ° C.) to (Tg + 40).
(° C.) and stretched with a pinch roll while cooling to within the temperature range of (° C.).

When the temperature of the thermoplastic resin film is (Tg-3)
If the temperature is lower than 0 ° C.), the film does not have sufficient flexibility to be stretched, so that the film is easily broken. Further, the temperature of the thermoplastic resin film is (Tg +
When the temperature is higher than 40 ° C.), the retardation value of the stretched thermoplastic resin film becomes small, and a retardation plate having a desired retardation value cannot be obtained.

The stretching ratio in the cooling stretching step is not particularly limited, but it is preferable that the stretching is performed 3 to 30 times. If the stretching ratio is less than 3, the desired retardation may not be developed, or the thermoplastic resin film may hang due to insufficient pulling. Further, if the stretching ratio is 30 times or more, film breakage occurs, neck-in becomes large,
This is because the length of the width of the thermoplastic resin film is reduced, and the productivity may be deteriorated.

Here, the stretching ratio means "(thickness of the thermoplastic resin film at the exit of the pinch roll) / (thickness of the thermoplastic resin film immediately after being discharged from the mold)".

In the cooling and stretching step, it is preferable to perform cooling and stretching in a room where the temperature can be controlled in order to offset the influence of the change in the ambient temperature on the thermoplastic resin film.

In the thermoplastic resin film, the retardation value of the retardation plate also changes in accordance with the change in the ambient temperature of the surroundings. Therefore, the temperature of the ambient temperature in contact with the molten thermoplastic resin between the mold and the pinch roll is changed. The smaller the variation, the better. As the variation amount of the ambient temperature, the error range from the set temperature is preferably within ± 0.5 ° C., and more preferably within ± 0.25 ° C.

According to a second aspect of the present invention, there is provided the method for producing a retardation plate according to the first aspect, wherein the thermoplastic resin film is made of a polysulfone resin. Among the thermoplastic resins, polysulfone resins are particularly preferable because they have characteristics in which the wavelength dispersibility of light is close to that of liquid crystals, can satisfactorily compensate for different elliptically polarized light at each wavelength, and improve the contrast of liquid crystal display.

(Function) According to the first aspect of the present invention, the retardation value of the thermoplastic resin film can be made extremely uniform in the cooling and stretching step.

When a thermoplastic resin film having a uniform in-plane film temperature is cooled in the cooling and stretching step, a difference in heat capacity occurs due to unevenness in film thickness. Therefore, a portion having a large film thickness is hardly cooled, and a portion having a small film thickness is easily cooled. Therefore, the film temperature of the thicker portion is higher than that of the thinner portion. In general, it is known that the refractive index difference Δn when a film having a high film temperature is stretched is smaller than when a film having a low film temperature is stretched. Retardation value is thickness and refractive index difference Δn
Therefore, the retardation value of the thick part and the retardation value of the thin part are substantially equal.

If cooling is not performed in the stretching step, the thermoplastic resin film is stretched at an isothermal temperature, and the difference between the retardation value of the thick portion and the retardation value of the thin portion is It becomes larger in proportion to the thickness unevenness ratio. Therefore, by performing cooling in the stretching step, a state is created in which the temperature of a thick part is higher than that of a thin part, so that a retardation plate having no variation in retardation value can be obtained.

Next, the thermoplastic resin film is stretched by a pinch roll to give a difference in refractive index. In this step, when the molten thermoplastic resin film discharged from the mold is stretched by a pinch roll while being cooled by a cooling device, a region closer to the mold in the extrusion direction of the film is pinched. Greater strain is imparted than the area near the roll.

This is because, when tension is applied to the film between the mold discharge port and the pinch roll, a greater strain is applied to a region closer to the mold because the resin temperature is higher and the viscosity is lower. However, in the region near the mold, the viscosity is small, so that the strain of the molecule is immediately relaxed, and the orientation is not formed, so that the difference in the refractive index is not sufficiently provided. On the other hand, even in a region where the resin temperature is low near the pinch roll, distortion is applied to the resin region, although it is smaller than that in the region close to the mold. In a region where the resin temperature is low and the viscosity is large, the distortion remains without relaxing while giving the orientation to the thermoplastic resin film, and thus gives a difference in refractive index to the film.

For this reason, a difference in the refractive index can be imparted to the molten film immediately after discharging the mold. For example,
The stretching ratio is 5 times, and the temperature of the molten thermoplastic resin film (Tg = 190 ° C.) discharged from the mold is 300 ° C.
When the film temperature at the time of biting into the pinch roll is 220 ° C., in a region close to the mold where the film temperature is in the range of 260 ° C. to 300 ° C., the film is stretched about 4 times and the film temperature is 2
In the region close to the pinch roll at 20 ° C. to 260 ° C., the film is stretched about 1.25 times.

Here, the film temperature is from 260 ° C. to 300 ° C.
In the range of ° C., even if the film is stretched four times, the stress is greatly relaxed and no orientation is formed. However, if the film temperature is 2
In the range of 20 ° C. to 260 ° C., when the film is stretched 1.25 times, the orientation is formed and the refractive index difference Δn can be expressed.
Thus, according to the first aspect of the present invention, a retardation plate can be manufactured without using an additional stretching machine.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the examples and comparative examples, the manufacturing apparatus shown in FIG. 1 was used. The manufacturing apparatus shown in FIG. 1 includes an extruder (not shown), a T-die mold 1, pinch rolls 2 and 3, and an air cooling device 5. The air cooling device 5 is installed inside the stretching cooling chamber 6. By providing the stretching cooling chamber 6, the influence of the fluctuation of the ambient temperature can be offset.

After the thermoplastic resin film 4 is discharged from the T-die mold 1 using this manufacturing apparatus, cold air is blown from the air cooling device 5 while the film is being taken up by the pinch rolls 2 and 3, and then the film is allowed to cool. Room temperature (25
C.) and then wound up with a roll (not shown) to produce a retardation plate with an extremely uniform retardation value.

(Example 1) Polycarbonate resin (trade name "PANLITE" manufactured by Teijin Chemicals Ltd.) Glass transition temperature:
(150 ° C.) into a hopper of a single-screw extruder, kneaded the molten resin at a temperature of 260 ° C. in the extruder, and discharged from a T-die mold 1 set to a mold temperature of 260 ° C. Then, while cooling the thermoplastic resin film 4 made of polycarbonate discharged from the T-die mold 1 with the cool air generated by the air cooling plasticizer 5, the film temperature is reduced to 155 ° C.
It is stretched 4 times by pinch rolls 2 and 3 and average thickness 6
A 7 μm ± 5 μm stretched polycarbonate film was produced.

The obtained stretched polycarbonate film had a width of 100 mm and a length of 1000 mm from the center.
A sample of the retardation plate of mm was cut out. This sample was taken at 633 nm in the width direction and the length direction at 1 c
When the retardation values were measured at m intervals, the average value of the retardation values was 380 nm. The value obtained by subtracting the minimum value of the retardation value from the maximum value of the retardation value in the film plane, that is, the maximum value of the variation of the retardation value was 2.3 nm. Furthermore, the difference between the retardation values of adjacent measurement points is a maximum of 0.
It was 9 nm.

(Example 2) Polysulfone resin pellet (trade name "UDEL P3500" manufactured by Teijin Amoko Engineering Plastics Co., Ltd.) Glass transition temperature: 19
0 ° C.) into the hopper of the single screw extruder, and the temperature in the extruder is set to 3
The molten resin was kneaded at 40 ° C. and discharged from the T-die mold 1 set at a mold temperature of 340 ° C. And T-die mold 1
The thermoplastic resin film 4 made of polysulfone discharged from the
While cooling the film temperature to 190 ° C., the film is stretched 5 times by pinch rolls 2 and 3 to obtain an average thickness of 65 μm ±
A 5 μm stretched polysulfone film was prepared.

From the central part of the stretched polysulfone film thus obtained, a width of 100 mm and a length of 1000 mm
Was cut out. This sample is 63
At 3 nm, when the retardation values were measured at intervals of 1 cm in the width direction and the length direction, the average value of the retardation values was 426 nm. The value obtained by subtracting the minimum value of the retardation value from the maximum value of the retardation value in the film plane, that is, the maximum value of the variation of the retardation value was 3.0 nm. Furthermore, the difference between the retardation values of adjacent measurement points is 0.8 nm at the maximum.
Met.

(Comparative Example 1) Polysulfone resin pellet (trade name "UDEL P3500" manufactured by Teijin Amoko Engineering Plastics Co., Ltd.) Glass transition temperature: 19
0 ° C.) into the hopper of the single screw extruder, and the temperature in the extruder is set to 3
The molten resin was kneaded at 40 ° C. and discharged from the T-die mold 1 set at a mold temperature of 340 ° C. And T-die mold 1
The thermoplastic resin film 4 made of polysulfone discharged from the container is allowed to cool (at room temperature 25 ° C.) without using an air-cooled plasticizer.
C), the polysulfone film was stretched 5 times while being cooled to 270 to prepare a polysulfone film having a thickness of 60 ± 7 μm.

From the central portion of the polysulfone stretched film thus obtained, a width of 100 mm and a length of 1000 mm
Was cut out. This sample is 63
At 3 nm, when the retardation values were measured at intervals of 1 cm in the width direction and the length direction, the average value of the retardation values was 50 nm. The value obtained by subtracting the minimum value of the retardation value from the maximum value of the retardation value in the film plane, that is, the maximum value of the variation of the retardation value was 8 nm. Further, the difference between the retardation values of adjacent measurement points was 3 nm at maximum.

The production conditions of the examples and comparative examples are summarized in Table 1, and the performance evaluation of the produced retardation plates is summarized in Table 2.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

According to the first and second aspects of the present invention, even if the thickness of the thermoplastic resin film is not uniform before the stretching step, the retardation having a uniform retardation value over substantially the entire area of the stretched film. Can provide board. Therefore, when incorporated in a liquid crystal display device, it is possible to prevent color unevenness of the display screen from occurring at all. In addition, since the thermoplastic resin film may have uneven thickness before the stretching step is performed, complicated equipment management is not required.

Furthermore, since the film forming step and the stretching step of the thermoplastic resin film are directly connected, and the film can be stretched by a simple apparatus which does not require a special stretching machine, it can be easily introduced, and A phase difference plate can be manufactured with inexpensive equipment.

According to the second aspect of the present invention, the contrast of the liquid crystal display device using the retardation plate can be effectively increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of a manufacturing apparatus used in carrying out the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 T-die mold 2 Pinch roll 3 Pinch roll 4 Thermoplastic resin film 5 Air-cooled plastic machine 6 Cooling drawing room

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 81:00 B29L 7:00 11:00

Claims (2)

[Claims] 1. A molten thermoplastic resin film extruded from a mold by a melt extrusion method is disposed between the mold and a pinch roll disposed downstream of the mold in the extrusion direction. The thermoplastic resin by (Tg-30)
(C) to (Tg + 40 ° C) while stretching the film with the pinch roll while cooling to a temperature range of (Tg + 40 ° C). 2. The method according to claim 1, wherein the thermoplastic resin film is made of a polysulfone resin.