JPH0990127A - Phase difference plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase difference plate capable of making display uniform over the entire area of a display section when this plate is applied to a liquid crystal display cell for the purpose of phase difference compensation. SOLUTION: The phase difference plate formed by uniaxially or biaxially stretching a thermoplastic resin film has such a distribution in the retardation value within the film plane that the retardation value increases from the central part toward the first direction where the max. refractive index is exhibited. The difference in the retardation value between the central part and the end part in this direction is >=2 to <20% and/or the film has such a distribution that the retardation value decreases from the central part toward the end part in the second direction orthogonal with the first direction. The difference in the retardation value between the central part and the end part in the second direction is >=2 to <20%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate formed by using a uniaxially stretched or biaxially stretched thermoplastic resin film, and more specifically, it is used for compensating a retardation in a liquid crystal display device. The present invention relates to a retardation plate suitable for.

[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 widely used in various OA equipment and display devices.

The liquid crystal display device has a problem that the display image is colored due to the phase difference generated in the liquid crystal. For example, the STN liquid crystal display device, which has better characteristics than the TN liquid crystal display device, has a fatal problem that the display image is colored blue or yellow. Therefore, it has been attempted to solve the above coloring problem by bonding a retardation plate made of a thermoplastic resin film to the surface of the liquid crystal display cell to compensate for the retardation.

By the way, the retardation plate made of the thermoplastic resin film functions to eliminate the retardation caused by the liquid crystal by utilizing the birefringence of the stretched thermoplastic resin film. . As the retardation plate as described above, conventionally, those made of various materials have been proposed. For example, a cellulosic resin (JP-A-63-16)
7363), vinyl chloride resin (Japanese Patent Publication No. 45-3)
4477, JP-A-56-125702),
Polycarbonate resin (Japanese Patent Publication No. 41-12190, Japanese Patent Publication No. 56-130703), acrylonitrile resin (Japanese Patent Publication No. 56-130702), styrene resin (Japanese Patent Publication No. 56-125703), It is proposed to use a film made of a synthetic resin such as an olefin resin (Japanese Patent Laid-Open No. 60-24502). Conventionally, a retardation plate has been constructed by uniaxially stretching each thermoplastic resin film as described above. In this case, as a stretching method, a method of longitudinal uniaxial stretching (Japanese Patent Laid-Open No. 2-191904), a method of lateral uniaxial stretching (Japanese Patent Laid-Open No. 2-42406) and the like have been reported.

[0005] The retardation compensation performance of the retardation plate is represented by a so-called retardation value. The retardation value is Δn, where Δn is the anisotropy of the refractive index of the resin film (that is, birefringence) and d is the thickness of the film.
It is represented by xd.

On the other hand, in a liquid crystal display device, it is strongly required that color unevenness and contrast unevenness hardly occur over the entire surface of the display. In order to provide a liquid crystal display device capable of such a uniform display, even in the above retardation film, the retardation value is uniform over the entire surface, and not only when observed from the front, but also when observed from an oblique direction. Even if the change in retardation value is small,
That is, a retardation plate having a small viewing angle dependency is required.

For example, Japanese Patent Laid-Open No. 2-191904 discloses that, in the uniaxial stretching method, the ratio between the dimension in the direction orthogonal to the stretching axis and the dimension in the same direction before stretching is specified in the uniaxial stretching method. A method for manufacturing a retardation plate in which the variation in display quality due to the viewing angle is improved by controlling the range, and the retardation value when a monochromatic light beam is vertically incident on the retardation plate and the incident angle is 40 °. A retardation plate having a ratio with a retardation value in a specific range within a specific range has been proposed.

Further, in JP-A-5-346507, after stretching a synthetic resin film having a positive intrinsic birefringence, it is swollen in a poor solvent, or conversely, after it is swollen in a poor solvent, There has been proposed a method for producing a birefringent film in which a retardation value changes little even when a viewing angle changes by stretching a synthetic resin film.

[0009]

However, even if the above-mentioned conventional method for manufacturing a retardation plate is used, it is still impossible to obtain a retardation plate which is sufficiently satisfactory in practical use. That is, when the retardation plate described in the above prior art is incorporated in a liquid crystal display device and the liquid crystal display cell surface is viewed from the front, coloring of the peripheral portion of the liquid crystal display cell surface cannot be completely avoided, and therefore the entire surface is covered. It was difficult to obtain a uniform display.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to suppress coloring in the peripheral portion when applied to a liquid crystal display device, and therefore to perform uniform and high-quality display over substantially the entire area. It is to provide a retardation plate that enables the above.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, in a retardation plate formed by uniaxially or biaxially stretching a thermoplastic resin film, a retardation value in the film plane. If it is configured so as to have a specific distribution, it is possible to reduce the coloring in the peripheral portion when applied to a liquid crystal display device, and thus to perform uniform and high-quality display over substantially the entire display cell surface. The inventors have found that it is possible to accomplish the present invention.

That is, in the retardation plate of the present invention, the retardation value distribution in the film plane has such a distribution that the retardation value increases from the central portion toward the first direction showing the maximum refractive index. However, the difference in retardation value between the central portion and the end portion in the first direction is 2% or more 20
% And / or has a distribution such that the retardation value decreases from the central portion toward the end portion in the second direction orthogonal to the first direction, and In this direction, the difference in retardation value between the central portion and the end portion is 2% or more and less than 20%.

Hereinafter, the present invention will be described in detail. As the thermoplastic resin film used in the present invention, it is possible to use a film made of an appropriate resin exhibiting birefringence by stretching, for example, cellulose resin, vinyl chloride resin, polycarbonate resin, acrylonitrile resin, olefin. Examples thereof include resin, polystyrene resin, polymethylmethacrylate resin, polysulfone resin, polyarylate resin, and polyethersulfone resin. Further, as a method for producing the resin film, any method such as a solvent casting method, a calender method or a melt extrusion method can be adopted.

The method of stretching the thermoplastic resin film in the present invention includes longitudinal uniaxial stretching with a roll, lateral uniaxial stretching with a denter, biaxial stretching with a combination of these, and gripping the peripheral portions of a plurality of films. A known appropriate stretching method such as a uniaxial or biaxial stretching method can be adopted.

The temperature during stretching is preferably in the range of glass transition point (Tg) -10 ° C or higher and Tg + 30 ° C or lower. When the stretching temperature is lower than Tg-10 ° C, the resin film does not have sufficient flexibility, so that the resin film easily breaks during stretching. On the other hand, when the stretching temperature exceeds Tg + 30 ° C., the increase in stretching stress due to deformation becomes small, so that only the portion that has once been stretched is preferentially stretched, and uneven stretching tends to occur.

Further, in the present invention, the thermoplastic resin film has the above-mentioned specific retardation value distribution.
As a method of controlling the retardation value distribution in the film plane, a temperature distribution is formed in the film plane by forming a temperature distribution in a heating furnace or a heating roll used at the time of stretching, and the retardation of the low temperature part is obtained. Higher value, lower retardation value in high temperature area, thickness distribution in original film, higher retardation value in thick area, lower retardation value in thin area, or film surface A method of forming a Tg distribution by adding a plasticizer or a solvent so that a content distribution is formed in the inside, and lowering the retardation value in the low Tg portion and increasing the retardation value in the high Tg portion An appropriate method such as the above can be used.

As a method of forming the content distribution of the plasticizer and the solvent in the film surface, for example, when the film is formed by the solvent casting method, the plasticizer is partially dispersed after coating. Alternatively, a method of forming a temperature distribution during drying after coating can be adopted.

Action In the present invention, the distribution of retardation values in the plane of the film has such a distribution that the retardation values gradually increase from the center of the film toward the first direction showing the maximum refractive index, And / or the retardation plate is configured to have a distribution in which the retardation value decreases from the central portion toward the end portion in the direction orthogonal to the first direction, and in any case, The difference in retardation value at each end is 2% or more and less than 20%, which makes it possible to reliably suppress coloring of the peripheral portion when applied to a liquid crystal display cell, for example.
A uniform and high-quality display can be obtained over substantially the entire display cell surface. As described above, when the retardation plate having the above-mentioned specific retardation value distribution is used, the problem of coloring in the peripheral portion can be solved because the viewing angle dependency of the retardation value is in the first direction. The retardation value tends to decrease as the viewing angle increases, and the retardation value tends to increase as the viewing angle increases in the second direction. Therefore, a retardation value distribution is formed to cancel this. This is because the retardation value when viewed from the front of the center of the display is made uniform.

[0019]

The present invention will be clarified by giving concrete examples of the present invention. Example 1 Polycarbonate resin (Tg = 150 ° C.) was melt extruded from a T die to prepare an unstretched original fabric having a width of 300 mm.
When manufacturing the above-mentioned original fabric, the thickness of the central portion in the width direction is 85
The thickness of the T-die was adjusted so that the thickness was gradually decreased toward both ends in the width direction and the thickness of both ends became 75 μm.

[0020] The original fabric obtained as described above was cut into a length of 200
Cut to a size of mm, length 200 mm x width 300 mm
To obtain a polycarbonate resin film. Using a high temperature biaxial stretching tester manufactured by Toyo Seiki Seisaku-sho, the polycarbonate resin film was stretched 1.4 times in the length direction while restraining it in the width direction. At the time of this stretching, hot air of 160 ° C. is circulated horizontally in a thermostatic chamber, and hot air of 163 ° C. is blown from below to the center of the film so that the temperature of the center of the film becomes higher than that of the peripheral part. It was stretched while being fed. Next, the retardation plate of Example 1 made of a polycarbonate resin film was obtained by cutting into a length of 200 mm and a width of 250 mm so that the stretching direction was the longitudinal direction.

The retardation value of the above retardation film at 590 nm was measured at 1 cm intervals along the horizontal and vertical directions so as to pass through the center of the retardation plate. The measurement results are shown in FIGS. 1 and 2. FIG. 1 shows the distribution of retardation values along the horizontal direction, and FIG. 2 shows the distribution of retardation values along the vertical direction.

The difference in retardation value between the central portion and the end portion of the retardation plate is 8% in the horizontal direction and 10 in the vertical direction.
%Met. Further, when the above-mentioned retardation plate was incorporated into an STN type liquid crystal display device and the liquid crystal display cell surface was observed from the front, uniform black and white display was made over the entire screen,
It was confirmed that the contrast was also good.

Example 2 A polysulfone resin having a styrene-equivalent weight average molecular weight of 7 × 10 ⁴ obtained by co-condensation of 4,4′-dichlorophenylsulfone and a sodium salt of bisphenol A was dissolved in methylene chloride to give 20 A weight% methylene chloride solution was used.

The above polysulfone resin (Tg = 190 ° C.)
Of 20 wt% methylene chloride solution was cast on a chrome-plated steel belt, dried in a hot air oven to remove the solvent and peeled off to produce a polysulfone unstretched raw fabric having a width of 400 mm and an average thickness of 75 μm. During the drying of the above-mentioned raw fabric, the hot air stove is divided into three in the width direction so that the temperature of the center of the film in the width direction becomes higher than that of the end in the width direction, and the temperature of the center becomes higher than that of the end in the width direction. It dried while forming such a temperature distribution. In addition, the set temperature of the final zone is 183 ° C. at the center in the width direction and 1 at both ends in the width direction.
It was 73 ° C. The residual solvent amount of the raw fabric obtained as described above was 0.5% by weight at the center portion in the width direction and 0.7% by weight at both ends in the width direction.

All the heating rolls were composed of dielectric heating rolls, and the section (including a pair of nip rolls) in which the film was stretched was kept as it was in a hot air oven using a stretching machine as described above. The obtained raw fabric was longitudinally and uniaxially stretched at a stretching temperature of 190 ° C. and a stretching ratio of 1.4 times to obtain a film having a width of 350 mm and an average thickness of 65 μm. This film,
200 mm in length x 25 in width so that the stretching direction is the longitudinal direction
The retardation plate of Example 2 was obtained by cutting to a size of 0 mm.

The retardation value of the above retardation film at 590 nm was measured at 1 cm intervals along the horizontal and vertical directions so as to pass through the center of the retardation plate. The measurement results are shown in FIGS. 3 and 4. FIG. 3 shows the distribution of retardation values along the lateral direction of the retardation plate of Example 2, and FIG. 4 shows the distribution of retardation values along the longitudinal direction. The difference in retardation value between the central portion and the end portion of this retardation plate was 5% in the horizontal direction and 1% in the vertical direction.

Further, the retardation plate of Example 2 was used and incorporated in a liquid crystal display device as in Example 1, and observed. As a result, a uniform black-and-white display was made over the entire area in the horizontal direction of the screen, and the contrast was good.

Comparative Example 1 The same T-die as in Example 1 was used, and the thickness in the width direction was 75 μm.
An unstretched polycarbonate raw fabric having a width of 300 mm was produced in the same manner as in Example 1 except that the lip gap of the T-die was adjusted to be substantially uniform.

[0029] The above-mentioned original fabric is processed into a width of 300 mm and a length of 200.
Cut to mm and stretch at 16
A retardation plate of Comparative Example 1 was obtained in the same manner as in Example 1, except that the temperature was set to 0 ° C.

The retardation value distribution of the retardation film of Comparative Example 1 at 590 nm was measured at 1 cm intervals along the horizontal and vertical directions so as to pass through the center of the retardation plate. The measurement results are shown in FIGS. FIG. 5 shows the distribution of retardation values along the horizontal direction in the retardation plate of Comparative Example 1, and FIG. 6 shows the distribution of retardation values along the vertical direction.

Further, the difference in retardation value between the central portion and the end portion of the retardation plate of Comparative Example 1 was 1% in both the horizontal and vertical directions. Further, when the retardation plate of Comparative Example 1 was incorporated in a liquid crystal display device and observed in the same manner as in Example 1, black and white display was achieved in the central portion of the screen.
The periphery of the screen was colored blue, making it very difficult to see.

[0032]

As described above, in the retardation plate of the present invention,
In the uniaxially or biaxially stretched thermoplastic resin film, the retardation value is configured to have the above specific distribution, and the difference in the retardation value between the central portion and the end portion is within the above specific range. Has been done. Therefore,
For example, when incorporated in a liquid crystal display device, coloring in the peripheral portion of the screen can be effectively suppressed, and uniform and high-quality display can be achieved over substantially the entire liquid crystal display cell surface.

[Brief description of drawings]

FIG. 1 is a diagram showing a distribution of retardation values along a lateral direction of a retardation plate of Example 1.

FIG. 2 is a diagram showing a distribution of retardation values along the longitudinal direction of the retardation plate of Example 1.

FIG. 3 is a diagram showing the distribution of retardation values along the lateral direction of the retardation plate of Example 2.

FIG. 4 is a diagram showing the distribution of retardation values along the longitudinal direction of the retardation plate of Example 2.

5 is a diagram showing the distribution of retardation values along the lateral direction of the retardation plate of Comparative Example 1. FIG.

FIG. 6 is a diagram showing a distribution of retardation values along the longitudinal direction of the retardation plate of Comparative Example 1.

Claims (1)

[Claims] 1. A retardation plate obtained by uniaxially or biaxially stretching a thermoplastic resin film, wherein the distribution of retardation values in the plane of the film is from the central part toward the first direction showing the maximum refractive index. Has a distribution such that the retardation value becomes high, and the difference in the retardation value between the central portion and the end portion in the first direction is 2% or more and less than 20%, and / or the first Has a distribution in which the retardation value decreases from the central portion to the end portion in the second direction orthogonal to the direction, and the difference in the retardation value between the central portion and the end portion in the second direction is 2% or more and less than 20%, The phase difference plate characterized by the above-mentioned.