JP2000009934A - Production of phase difference plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method of a phase difference plate by which even a film having poor thickness accuracy can be stretched into a plate having little irregularity in the phase difference. SOLUTION: A thermosetting resin film consisting of an inner layer resin having <=45000 weight average mol.wt., and outer resin layers having >=60000 weight average mol.wt. laminated on both surfaces of the inner layer is preheated in a temp. range from Tg-30 deg.C to Tg+100 deg.C, wherein Tg is the glass transition temp. of the thermoplastic resin. Further, the film is stretched while cooled to a lower temp. than the preheating temp. The thermoplastic resin for the film is not limited as far as 100 to 1000 nm phase difference required as a phase difference plate can be obtd. after the film is stretched. For example, a cellulose resin, styrene resin, vinyl chloride resin, polycarbonate resin, polysulfone resin and acrylonitrile resin can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a retardation plate made of a uniaxially or biaxially stretched thermoplastic resin film, and more particularly to a method for producing a retardation plate suitable for compensating a retardation in a liquid crystal display device. The present invention relates to a method for manufacturing a plate.

[0002]

2. Description of the Related Art Conventionally, TN (twisted nematic) liquid crystal display devices and STN (super twisted nematic) liquid crystal display devices have been used for various OA devices and display devices. However, the above liquid crystal display device has a problem that a display screen is colored by a phase difference generated in a liquid crystal cell. Therefore, a method of compensating for a phase difference using a phase difference plate and eliminating the above-mentioned coloring has been performed.

In a liquid crystal display device or the like, it is strongly required that color unevenness and contrast unevenness be small over the entire display portion. Therefore, in order to enable such a uniform display, it is necessary that the retardation of the retardation plate attached to the liquid crystal display cell is uniform over the entire surface.

[0004] When the above-mentioned color unevenness and contrast unevenness are incorporated in a liquid crystal display device, the image quality is poor due to the phase difference variation of the phase difference plate, and it is necessary to suppress the phase difference variation. Incidentally, the phase difference compensation performance of the phase difference plate is represented by a phase difference. The retardation is represented by Δn × d, where Δn is the refractive index difference (that is, birefringence) of the resin film, and d is the thickness of the resin film.

As a method for producing a retardation plate having a uniform retardation, Japanese Patent Application Laid-Open No. 8-122526 discloses a method in which a solvent content of a raw film before stretching is set to 0.5 to 7 parts by weight on a solid basis. Stretching is disclosed. However, in the retardation plate obtained by this method, for example, even if the refractive index difference Δn is made uniform in the width direction, if the thickness d of the film varies, the retardation will vary, and color unevenness will not necessarily occur. And uneven contrast could not always be eliminated.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is intended to provide a retardation plate capable of sufficiently reducing retardation unevenness after stretching even in a film having poor thickness accuracy. It is intended to provide a manufacturing method.

[0007]

According to the method for producing a retardation plate of the present invention, an outer layer resin having a weight average molecular weight of 60,000 or more is laminated on both surfaces of an inner layer resin having a weight average molecular weight of 45,000 or less. After preheating the thermoplastic resin film obtained in a temperature range of Tg-30 ° C. to Tg + 100 ° C. of the thermoplastic resin, the film is stretched while being cooled to a temperature lower than the preheating temperature.

In the present invention, the thermoplastic resin, which is a film, is stretched to a thickness of 100 to 1 which is required as a retardation plate after stretching.
There is no limitation as long as a phase difference of 000 nm can be obtained. For example, a cellulose resin, a styrene resin, a vinyl chloride resin, a polycarbonate resin, a polysulfone resin, an acrylonitrile resin, a polyolefin resin, a polyether sulfone resin Resins, polyarylate resins and the like.

Of the above, polycarbonate resins and polysulfone resins, which are particularly excellent in transparency and wavelength dispersibility of light, are preferable, and polysulfone resins are particularly preferable because the wavelength dispersibility of light is close to that of liquid crystal. Good wavelength dispersion of light means that light having different elliptically polarized light at each wavelength due to liquid crystal can be favorably compensated, and the contrast of the liquid crystal display is improved.

[0010] The glass transition temperature of the above thermoplastic resin is Tg
Then, in the present invention, the thermoplastic resin film is made of Tg
Preheat in a temperature range of -30 ° C to Tg + 100 ° C. When the preheating temperature is lower than Tg-30 ° C., the flexibility of the film is insufficient, and the film is easily broken during stretching. Also, Tg + 1
When the temperature is higher than 00 ° C., the shape retention of the thermoplastic resin film is reduced, and the film may sag or be deformed during transportation.

The means for preheating is not particularly limited, and a heater using hot air, microwaves or far-infrared rays, or a known heating means using a roll or metal belt heated by adjusting the temperature can be employed. .

The thermoplastic resin film preheated as described above is stretched while being cooled to a temperature lower than the preheating temperature. Stretching may be performed continuously to the film extrusion molding step, or may be performed as a separate step in which the film is once wound up after extrusion molding and then stretched. The stretching mode may be any of longitudinal uniaxial stretching, horizontal uniaxial stretching, simultaneous vertical and horizontal biaxial stretching, and sequential biaxial stretching. However, stretching by vertical uniaxial stretching is preferable because of excellent viewing angle characteristics. The stretch ratio is not particularly limited, but is usually about 1.2 to 2 times when used for a liquid crystal display device.

In the present invention, the stretching while cooling the thermoplastic resin film to a temperature lower than the preheating temperature depends on the difference in cooling rate caused by the difference in heat capacity between the thick and small portions of the thermoplastic resin film. This is to take advantage of the fact that the refractive index difference Δn differs depending on the originally generated temperature difference. At the same time, by utilizing the temperature difference between the outer layer resin and the inner layer resin and making the outer layer resin having a lower temperature than the inner layer resin more highly oriented, the phase difference between the thick portion and the small portion is reduced.

The cooling temperature is not particularly limited as long as the thermoplastic resin film is not broken by stretching. However, if the stretching is performed at a temperature lower than Tg-30 ° C., the thermoplastic resin film is likely to break. Therefore, the preheating temperature is in the range from around Tg to Tg + 100 ° C., and the temperature at the time of stretching is lower than Tg-30 ° C. It is preferable not to do so.

In the present invention, a thermoplastic resin whose outer layer resin has a larger weight average molecular weight than the inner layer resin is used as the retardation plate. The reason for this is to make the phase difference more uniform. Under the same stretching conditions, the outer layer resin having a larger weight average molecular weight has a higher degree of orientation and a larger refractive index difference, so that the refractive index between the outer layer resin and the inner layer resin is large. The difference is larger.

In the above, if the weight average molecular weight of the surface layer resin is smaller than 60,000, even if it is stretched, the orientation is easily relaxed and sufficient orientation cannot be provided, and it is difficult to obtain a desired retardation. If the thickness is increased, it is possible to obtain a desired phase difference, but there are problems such as high cost, heavy weight and poor handling. On the other hand, if the weight average molecular weight of the inner layer resin exceeds 45,000, the difference in the degree of orientation from the outer layer resin is not sufficient, and the uniformity of the phase difference is insufficient.

The T-die coextrusion molding method is suitable for the method of forming the thermoplastic resin film used as the retardation plate of the present invention because of the possibility of multilayering, good thickness accuracy and low distortion due to molding. However, a method of forming a multilayer by a solution casting method can also be adopted.

(Function) The film is made of Tg-
After preheating in a temperature range of 30 ° C. to Tg + 100 ° C., the film is stretched while being cooled to a temperature lower than the preheating temperature. Therefore, even if the film has uneven thickness in the plane direction, cooling is performed in a portion having a large thickness during stretching. The temperature is higher than that of the portion having a small thickness. Since the refractive index difference Δn decreases as the film temperature increases, Δn
And the phase difference can be made closer to a portion having a small thickness.

On the other hand, looking at the temperature distribution in the thickness direction of the film, the temperature of the film which has been cooled from the outside is not uniform over the entire thickness direction but has a temperature gradient that increases from the surface toward the center. Thus, the degree of orientation due to stretching, that is, the difference in refractive index, is smaller in the inner layer resin. When the film is stretched in this state, the thickness unevenness is offset over the entire film, the refractive index difference becomes uniform, and the phase difference unevenness can be reduced.

Further, in the present invention, since the outer layer resin is a thermoplastic resin having a larger weight average molecular weight than the inner layer resin, the degree of orientation in the outer layer resin is larger than that in the inner layer resin, and as described above, from the surface. This has the effect of increasing the effect when a temperature gradient is generated in the thickness direction that increases in temperature toward the center.

[0021]

Embodiments of the present invention will be described below. (Example 1) Polysulfone resin (manufactured by Teijin Amoko Engineering Plastics Co., Ltd., trade name "P-3500", weight average molecular weight 65000) pellets and polysulfone resin (manufactured by Teijin Amoko Engineering Plastics Co., trade name "P-1700", weight average) (Molecular weight 44000) The pellets were each 30
After kneading at 0 ° C, the mold temperature is 300 with a T die for coextrusion.
℃, mold tip temperature (lip temperature) set to 330 ℃ 3
Layer extrusion was performed. The thickness of each layer is 30 μm, 20 μm
m and 30 μm. Set the cooling roll temperature to 150 ° C, cool the nip with a metal roll and rubber roll,
An unstretched polysulfone film of 1 ± 2 μm was produced.

The unstretched film is preheated to 220 ° C. in an oven having transport rolls, and a stretching ratio of 1. is applied by a roll stretching machine (roll temperature: 190 ° C.) in an oven at 190 ° C.
The film was longitudinally and uniaxially stretched three times to obtain a stretched film having an average thickness of 69 ± 2.5 μm.

A width of 50 from the center of the obtained stretched film
A phase difference film sample having a length of 0 mm and a length of 1000 mm was cut out. The phase difference (retardation value) of this sample was 5
When measured at 90 nm at 1 cm intervals in both the width direction and the length direction, the average value was 502 nm, and the maximum value of the variation of the retardation value (the maximum value of the retardation value in the sheet surface minus the minimum value) was 2.8 nm. Was.

(Example 2) Pellets of polycarbonate resin (trade name "Panlite K-1300" manufactured by Teijin Chemicals Ltd., weight average molecular weight: 65,000) and polycarbonate resin (trade name "Panlite K-1200" manufactured by Teijin Chemicals Ltd.) ,
Weight average molecular weight 43000) The pellets were kneaded at 250 ° C. using different twin screw extruders, respectively.
Three-layer extrusion molding was performed by setting the mold temperature to 260 ° C. and the mold tip temperature (lip temperature) to 270 ° C. using a co-extrusion T-die. The thickness of each layer was set to 30 μm, 20 μm, and 30 μm. The temperature of the cooling roll was set to 120 ° C., the nip was cooled by a metal roll and a rubber roll, and an unstretched polycarbonate film having a thickness of 80 ± 2 μm was produced.

The unstretched film was rolled in the same roll stretching machine (roll temperature 190 ° C.) as used in Example 1 in a preheating zone 170 ° C. and a stretching zone 145 ° C. (roll temperature 14 ° C.).
5 ° C.), and stretched longitudinally and uniaxially to a draw ratio of 1.4 to obtain a stretched film having an average thickness of 66 ± 2.5 μm.

When the retardation was measured using the obtained stretched film in the same manner as in Example 1, the average value was 680 n.
m, the maximum value of the variation of the retardation value is 3.2n.
m.

(Comparative Example 1) Polysulfone resin (trade name "P-3" manufactured by Teijin Amoko Engineering Plastics Co., Ltd.)
500 ", weight-average molecular weight 65000) The pellets were kneaded at 290 ° C using a twin-screw extruder, and the mold temperature was 290 ° C.
Extrusion molding was performed at a temperature of ℃ and a mold tip temperature (lip temperature) of 330 ° C. Set the cooling roll temperature to 150 ° C, cool the nip with a metal roll and rubber roll, and make the thickness 80 ± 2μ.
m of polysulfone unstretched film.

The unstretched film was set in a preheating zone of 200 ° C. and a stretching zone of 195 ° C. (roll temperature: 195 ° C.) using the same roll stretching machine as used in Example 1, and was stretched vertically at a stretching ratio of 1.4. Uniaxially stretched, average thickness 71 ± 2.5μ
m of the stretched film was obtained.

When the retardation was measured using the obtained stretched film in the same manner as in Example 1, the average value was 615 n.
m, maximum value of variation in retardation value is 25 nm
Met.

[0030]

In general, a film formed by a melt extrusion method is inferior in thickness accuracy to a film formed by a casting method, but even a melt extruded film having a poor thickness accuracy has a uniform retardation after stretching. Can provide board.
Therefore, the equipment is less expensive than the casting method,
Since a solvent is not used, a retardation plate having high uniformity can be obtained by using an extruded film which can be manufactured safely. Further, a retardation plate having a high retardation (500 nm or more) can be obtained. Can also be applied.

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Claims (1)

[Claims] 1. A thermoplastic resin film in which an outer layer resin having a weight average molecular weight of 60,000 or more is laminated on both sides of an inner layer resin having a weight average molecular weight of 450,000 or less, a Tg- A method for producing a retardation plate, comprising preheating in a temperature range of 30 ° C. to Tg + 100 ° C., and then stretching while cooling to a temperature lower than the preheating temperature.