JPH09138307A - Phase difference plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a phase difference plate with which the retardation value is made uniform with high accuracy and the execution of high-grade display uniform approximately over the entire area is possible by stretching a thermoplastic resin film dividely in two stages in directions orthogonal with each other. SOLUTION: The phase difference plate is obtd. by clamping a thermoplastic film P by a jig 2 and stretching this film in two stages. Namely, the film is subjected to transverse uniaxial stretching, then to longitudinal uniaxial stretching while the film is shrunk in a transverse direction. The film is otherwise subjected to longitudinal uniaxial stretching, then to transverse uniaxial stretching while the film is shrunk in the longitudinal direction. The orientation state obtainable finally in the film P is uniaxial orientation. As a result, the difference in the retardation values between arbitrary two points apart 1cm within the film plane is made as small as <=0.5% of the average value of the retardation value over the entire part of the film.

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 thermoplastic resin film, and more specifically, a retardation plate suitable for compensating the retardation in a liquid crystal display device. Regarding

[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 d.

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, the retardation plate is also required to have a uniform retardation value over the entire surface.

In order to satisfy the above requirements, when a thickness change is continuously measured in the length direction, a sinusoidal thickness variation with a pitch of 50 mm or less and an amplitude of the thickness of 0.5 μm or more. Thermoplastic polymer film, which does not exist
And an optical film which is formed by uniaxially or biaxially stretching the film in a direction perpendicular to the extrusion direction, has a retardation value of 1200 nm or less, and has a deflection width of 10% or less. A film has been proposed (JP-A-2-256003).

Further, a substantially non-oriented film is uniaxially stretched at a uniform temperature selected from the temperature range of glass transition temperature Tg to Tg + 30 ° C., and the variation in retardation value is 1. A retardation film having a ratio of 0% or less has been proposed (JP-A-2-89007).

Further, when the thermoplastic resin film is uniaxially stretched, the thermoplastic resin film is contracted in a direction perpendicular to the stretching axis, and a method for producing a retardation plate having an improved viewing angle by the method is disclosed in JP-A-2-191904. It is disclosed in the official gazette.

[0010]

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, the retardation value was difficult to be uniformized to a level that was sufficiently satisfactory for practical use, and when the retardation plate was incorporated into the liquid crystal display device, there was color unevenness with a fine pitch that could be visually discriminated. .

This is because when a retardation plate is incorporated in a liquid crystal display device for evaluation, it is easy to determine the difference in retardation value between two adjacent points. Therefore, in the retardation plate, the retardation value is retarded. Will be more strongly required.

In view of the above-mentioned problems of the prior art, an object of the present invention is that the retardation value is made uniform with high accuracy, and a phase difference that enables uniform and high-quality display over substantially the entire area. To provide a plate.

[0013]

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 stretching a thermoplastic resin film, after laterally uniaxially stretching the thermoplastic resin film. , Longitudinally uniaxially stretched while contracting in the width direction, or longitudinally uniaxially stretched, and then laterally uniaxially stretched while contracting in the longitudinal direction, the difference in retardation value between any two points separated by 1 cm in the film plane, 0.5% of the average retardation value of the entire film
It becomes much smaller than the following, and by using the retardation plate obtained in this way, when applied to a liquid crystal display device, it is possible to perform uniform and high-quality display over almost the entire display area of the display device. The present invention has been found out and the present invention has been completed.

That is, the retardation plate of the present invention is a retardation plate obtained by uniaxially stretching a thermoplastic resin film. After the thermoplastic resin film is uniaxially stretched in the transverse direction, it is longitudinally uniaxially stretched while being contracted in the width direction. Or longitudinally uniaxially stretched and then laterally uniaxially stretched while contracting in the longitudinal direction, and the difference in retardation value between any two points separated by 1 cm in the film plane is the average of the retardation values of the entire film. The retardation plate is characterized by being 0.5% or less with respect to the value.

The details of the present invention will be described below. 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 thermoplastic resin film, any method such as a solvent casting method, a calendar method or a melt extrusion method can be adopted.

In the present invention, the thermoplastic resin film is stretched by the following two stages of stretching. That is, it is a method of uniaxially stretching in the transverse direction and then uniaxially stretching in the longitudinal direction while contracting in the width direction, or a method of uniaxially stretching in the longitudinal direction and then uniaxially stretching in the transverse direction while contracting in the longitudinal direction.

In the above-mentioned or stretching method, the stretching is performed in two stages in directions orthogonal to each other, but in the second stage stretching, the stretching is performed while contracting in the direction stretched in the first stage. Therefore, the orientation state of the finally obtained thermoplastic resin film is uniaxial orientation.

In the present invention, the stretching in the first stage is carried out in order to equalize the orientation in the stretching direction of the first stage by equalizing the stress in the stretching direction. As a result, not only the stress in the stretching direction in the second stage is made uniform during the stretching in the second stage, but also the stress in the stretching direction in the first stage is made uniform. The contraction in the direction also progresses uniformly. As a result, any two 1 cm apart
The difference in retardation value between points is 0.5% or less,
It is possible to obtain a retardation plate in which the retardation value in the film plane is made uniform with high accuracy.

The stretching ratio in the above stretching is 1.05 times or more and 2.0% or more for the first stage stretching ratio.
It is preferably at most twice. If it is less than 1.05 times, the effect of uniformizing the orientation in the stretching direction may be reduced, and if it exceeds 2.0 times, the shrinkage amount during the second stage stretching becomes too large, and rather the retardation. The values may be uneven. The stretching ratio in the second stage is appropriately determined according to the stretching temperature and the required retardation value.

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 thermoplastic resin film does not have sufficient flexibility, and thus the thermoplastic 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.

[0021] In effect the present invention, by stretching the first stage, the stress in the stretching direction is made uniform, when the second-stage stretching, only the extending direction of the stress of the second stage is uniform Not only that, the shrinkage in the stretching direction of the first step also progresses uniformly. Therefore, as described above, when the difference in retardation value between any two points 1 cm apart is 0.5% or less, the retardation value in the film plane can be made uniform with high accuracy.

[0022]

The present invention will be clarified by giving concrete examples of the present invention. Example 1 A polysulfone resin (Tg = 190 ° C.) obtained by cocondensation of 4,4-dichlorophenylsulfone and a sodium salt of bisphenol A and having a styrene-equivalent weight average molecular weight of 7 × 10 ⁴ was dissolved in methylene chloride. Then, a 20 wt% methylene chloride solution of the polysulfone resin was obtained.

The above solution was cast on a chrome-plated steel belt, dried in a hot air oven to remove the solvent, and then peeled from the steel belt to give a width of 800 m.
m, and an average thickness of 75 μm, a polysulfone unstretched original fabric was produced.

The polysulphone unstretched raw fabric was transversely uniaxially stretched at a stretching temperature of 190 ° C. and a stretching ratio of 1.2 times using a tenter stretching machine, and then both ends of the raw fabric were slit to have a width of 85.
A film having a thickness of 0 mm and an average thickness of 65 μm was obtained.

Subsequently, this film was longitudinally uniaxially stretched by a roll stretching machine. The roll stretching machine used has different peripheral speeds.
Stretching is performed between a pair of nip rolls, and the length between the nip rolls is 2.5 m. The film is stretched at 190 ° C. by the roll stretching machine,
A film having a width of 610 mm and an average thickness of 65 μm was obtained by longitudinally uniaxially stretching at a draw ratio of 1.4 times while contracting in the width direction.

A retardation plate sample having a width of 500 mm and a length of 1000 mm was cut out from the center of the film obtained as described above. The retardation value of the obtained sample at 590 nm was 1c in both the width direction and the length direction.
When measured at m intervals, the average value was 436 nm. Further, the difference in retardation value between two points separated by 1 cm was 1.0 nm at maximum (0.23% of the above average value) in the number of measurements = 146.

Example 2 Polycarbonate resin (Tg = 155 ° C.) was melt extruded from a T die to prepare an unstretched raw fabric having a width of 500 mm and an average thickness of 70 μm.

The above original fabric was longitudinally and uniaxially stretched at a stretching temperature of 160 ° C. and a stretching ratio of 1.1 times by using a roll stretching machine to obtain a width of 4
A film having a thickness of 75 mm and an average thickness of 67 μm was obtained. next,
Using the stretching device shown in FIGS. 1 and 2, the film was uniaxially stretched in the transverse direction while shrinking in the longitudinal direction. In the apparatus shown in FIG. 1 and FIG. 2, the film p is configured to be transported by the transport roll 3, and a plurality of jigs 2 are arranged along the guide rail 1. Each jig 2 is provided with a film gripping means 10 for gripping the end portion of the film. Reference numeral 4 denotes an oven, which is provided to heat the film p. It should be noted that 11 is an upper linear guide portion, 12 is a lower linear guide portion, and 13 and 14 are curved guide portions. As is apparent from FIG. 2, the film p is a film grip provided on the jig 2. The edge is gripped by the means, and the film p is gripped on both sides of the film p. The distance between the jigs 2 is expanded, and the film p is laterally uniaxially stretched while being conveyed.

In this embodiment, the film gripping means 10 sequentially grips the lateral ends of the film p in the curved guide portion 13 of the guide rail, and in the upper linear guide portion 11 at the temperature of 160 ° C. The film p is stretched 1.3 times in the transverse direction while contracting in the longitudinal direction, whereby a width of 600 mm and an average thickness of 60 μm.
Was obtained.

From the center of the obtained film, a width of 500
A retardation plate sample having a length of mm and a length of 1000 mm was cut out. The retardation value of this sample at 590 nm was measured at 1 cm intervals in both the width direction and the length direction. As a result, the average retardation value was 539 nm, and the difference in retardation value between two points separated by 1 cm was 1.3 at the maximum when the number of measurements was 146.
nm (0.24% of the average value).

Comparative Example 1 An unstretched polysulfone raw material having a width of 800 mm and an average thickness of 75 μm obtained in the same manner as in Example 1 was stretched at a stretching temperature of 190 ° C. and a stretching ratio of 1.4 times by using a roll stretching machine. Was longitudinally uniaxially stretched to obtain a film having a width of 670 mm and an average thickness of 65 μm.

A retardation sample having a width of 500 mm and a length of 1000 mm was cut out from the center of the film obtained as described above, and the retardation value was measured in the same manner as in Example 1. As a result, the average retardation value of the entire film was 452 nm, and the difference in retardation value between two points separated by 1 cm was 3.5 nm at the maximum (0.
77%).

[0033]

As described above, in the retardation plate of the present invention,
Since the thermoplastic resin film is stretched in two steps as described above, it is possible to use any 2
The difference in retardation value between the points is 0.5% or less with respect to the average value of the retardation values. Therefore,
In the retardation plate of the present invention, since the uniformity of the retardation value is enhanced over substantially the entire area of the film, when used in, for example, a liquid crystal display device, color unevenness does not occur,
It can exhibit excellent phase difference compensation performance. Therefore, it is possible to provide a liquid crystal display device capable of performing uniform and excellent display over substantially the entire area of the screen without coloring of the peripheral portion of the screen.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for explaining a stretching device used for laterally uniaxially stretching in Example 2.

2 is a partially cutaway enlarged plan view for explaining a step of laterally uniaxially stretching a film in the stretching apparatus shown in FIG.

[Explanation of symbols]

 p ... Film 1 ... Guide rail 2 ... Jig 3 ... Conveying roll 4 ... Oven 10 ... Film gripping means 11 ... Upper linear guide portion 12 ... Lower linear guide portion 13, 14 ... Curved guide portion

Claims (1)

[Claims] 1. A retardation plate obtained by uniaxially stretching a thermoplastic resin film, wherein the thermoplastic resin film is uniaxially stretched in the transverse direction, and then uniaxially stretched in the longitudinal direction while shrinking in the width direction, or after uniaxially stretched in the longitudinal direction. The film is stretched laterally uniaxially while contracting in the machine direction, and the difference in retardation value between any two points 1 cm apart in the plane of the film is 0.5% with respect to the average value of the retardation values of the entire film. A retardation plate characterized by being: