JPH0323405A - Production of phase difference plate - Google Patents

Abstract

PURPOSE:To lessen the dependency of an optical path difference on angles by adopting a method for narrowing the direction perpendicular to a stretching direction. CONSTITUTION:A sheet-like material is stretched in one direction at n-fold stretching magnification. The material is stretched while the material is fed in such a manner that the sheet width (w) after the stretching attains a w0>w>=w0/ sq. rt. n range with respect to the film or sheet width w0 before the stretching. The film or sheet formed by this method has the excellent depen dency on angles as compared to a biaxially oriented material and a uniaxially stretched material having a specified width. While the ratio of the change in the optical path difference when an incident ray is inclined in the stretching direction and the plane direction perpendicular to the stretching direction is largest when the incident ray is inclined, the change to the lower optical path difference side arises with the film or sheet formed by this method. The depen dency of the optical path difference on angles is lessened in this way by the method of narrowing the perpendicular direction while stretching the material in one direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a resin retardation plate in which the optical path difference has little dependence on the angle of incidence.

[Prior art] Retardation plates have become increasingly important with the recent development of optical technology.For example, in black and white liquid crystal display devices, which have been made colorless by compensating for the birefringence inherent in liquid crystals, the retardation plate has become increasingly important. , and is expected to be used as a compensating retardation plate. Conventionally, an anisotropic polycarbonate film has been used as such a retardation plate. however,
These anisotropic films produced by the conventional biaxial stretching method or constant width uniaxial stretching method have a drawback that the optical path difference varies greatly depending on the incident angle of light. As a result, in the liquid crystal display, when viewed from an oblique angle, compensation for distortion and refraction is inadequate, resulting in incomplete colorlessness.

[The problem that the invention tries to solve! Il1 An object of the present invention is to solve the problems of the prior art described above, that is, to develop a method for manufacturing a retardation plate with less angular dependence of the optical path difference.

[Means for Solving the Problems] An object of the present invention is to provide a method for manufacturing a retardation plate by stretching an unstretched film or a sheet-like material of transparent resin in one direction at a stretching ratio of n times. The film or sheet width W after stretching in a direction perpendicular to the film or sheet width W0 before stretching satisfies w O>w≧wO/. This is achieved by manufacturing a retardation plate with a small dependence of the optical path difference on the 14-angle, which is characterized in that the optical path difference is extended while being fed to a range of H.

The resin used in the present invention is a transparent resin, and preferable examples include polycarbonate resin, polyvinyl alcohol resin, polyethylene terephthalate resin, cellulose diacetate resin, polystyrene resin, and acrylic resin.

The method for manufacturing a retardation plate of the present invention is characterized in that an unstretched film or sheet is stretched in the - direction, and at that time, the width is narrowed in that direction by feeding in a direction perpendicular to the stretching direction.

In the conventional manufacturing of retardation plates, the stretching ratio in one direction is larger than the other, so-called unbalanced biaxial stretching.
Alternatively, a constant uniaxial stretching method that does not change the dimension in the perpendicular direction has been adopted. That is, the width in the direction perpendicular to the stretching direction is kept constant or the width is slightly stretched. However, what about the retardation plate manufactured by this method? However, even if the stretching conditions such as the stretching temperature and stretching ratio were changed, the optical path difference varied greatly depending on the angle of incidence of the light beam.

The present inventors discovered that a retardation plate with small angular dependence of the optical path difference can be obtained by adopting a method of narrowing the direction perpendicular to the stretching direction, contrary to the conventional method, and developed the present invention. It happened.

FIG. 1 shows that the retardation plate produced by the method of the present invention has excellent angle dependence compared to a retardation plate made of a biaxially stretched product and a constant width uniaxially stretched sheet. The resin is polycarbonate resin, and (a) has a stretching ratio of 2.5.
0.8 times narrower in the direction perpendicular to the stretching direction,
(b) is a constant width uniaxially stretched product with a stretching ratio of 2.5ff4,
(c) is a biaxially stretched intermediary with a magnification of 2.5 times in one direction and 1.1 times in the other direction, and the optical path difference is 1 5 2 ns and 1 5 5 n, respectively.
m. 1 1 1. It is nm. Here, the change in optical path difference due to the incident angle is calculated as follows: %).

When the incident light beam is tilted in these directions, the change in optical path difference becomes the largest, and in the former case the optical path difference changes to a low optical path difference of 4, and in the latter case it changes to a high optical path difference side.

film or sheath in the direction perpendicular to the stretching direction]・The extent to which the width is narrowed is determined by the film or sheath after stretching 1・width W
is the film or sheet width WO before stretching, w O
＞W≧wO/F1. If it is narrowed too much, wrinkles will appear and the unevenness of the optical path difference will increase, which is not preferable.

Further, the method of narrowing must be uniform in the effective range excluding the ears, etc., and if it is not done uniformly, optical path difference unevenness will occur. As for this uniformity, it is preferable that the fluctuation range with respect to the average value is within ±5% expressed as a percentage.

Specifically, such a manufacturing method can be carried out by stretching in one direction and contracting in a direction perpendicular to the stretching direction using a pantograph type stretching machine, for example.

For the stretching properties, normal biaxial stretching conditions can be used, and the stretching temperature for non-grade resins is generally 10 to 10% higher than the glass transition temperature of the resin.
A degree 40°C higher is chosen. The magnitude of the optical path difference is influenced by the type of resin and the stretching conditions, and the lower the stretching temperature and the higher the stretching ratio, the larger the optical path difference.

The unstretched film or sheet used in the method of the present invention can be obtained, for example, by extrusion molding a raw resin. The thickness of the unstretched film or sheet 1 is not essentially limited, but from the viewpoint of productivity and handling, it is 25μ to 5μ.
mm is preferred.

It should be noted that a layer of 254 μm or more was classified as a sheet, and a layer of 254 μm or more was classified as a film.

Below, a method for measuring the optical path difference and a method for evaluating the angular dependence of the optical path difference in Examples will be shown.

- Optical path difference measurement: Measurement was performed using a polarizing microscope (LABOPHOT-POL, manufactured by Nippon Kogaku Kogyo Co., Ltd.) according to a conventional method. The angle dependence was measured by tilting the sample at a predetermined angle and fixing it on a sample stand.

・Angle dependence evaluation method: Based on the case where the light beam is incident on the retardation plate at right angles, the absolute change in optical path difference when the incident light beam is tilted in the stretching direction and in the plane direction perpendicular to the stretching direction. The amount was calculated as a percentage and evaluated based on the average f value of both. The angle of incidence indicates the angle of inclination.

[Example] The present invention will be specifically explained with reference to Examples.

Example 1 Polycarbonate resin (manufactured by Idemitsu Petrochemical Co., Ltd., A-2
5001 is molded using a 50φ extruder to a thickness of 400μ.
An unstretched sheet was prepared. This was printed with an equally spaced checkerboard pattern, and then stretched 2.5 times in one direction at a stretching temperature of 185°C using a pantograph-type stretching machine that can stretch one direction and contract the other. ! The width on both sides was narrowed by 0.8 times. It takes 20 seconds from the start of stretching to the end of the process.

The dimensions of the grid were measured within the effective range excluding the vicinity of the clip portion, and the uniformity of the narrowing was determined.

The variation range with respect to the average value was ±3%.

The angle dependence of this stretched product was small as shown in Table 1.

Note that the stretching direction is MD, and the direction perpendicular to the stretching direction is T.
Abbreviated as D.

Example 2 In Example 1, stretching was carried out continuously under the conditions that the width in one direction was stretched 2.5 times and the width in the other direction was narrowed to 0.9 times.

The angle dependence of this stretched product was small as shown in Table 1.

Comparisons 1 and 2 In Example 1, a retardation plate was produced by changing the thickness of the unstretched sheet to 580 μm and changing the stretching method to constant width uniaxial stretching and biaxial stretching. The stretching ratio is 2.5 fg. in constant width uniaxial stretching.
By biaxial stretching, the film was stretched 2.5 times in one direction and 1.1 times in the direction.

As shown in Table 1, angle dependence was large.

Comparative Example 3 In Actual IM Example 1, the other width was changed from 0.8 times to 0.6 times and stretched. The retardation plate had wrinkles parallel to the stretching direction ('Er), and the uniformity of narrowing was ±12% with respect to the average value, and the optical path difference was uneven.

Examples 3 to 5, Ratio V Examples 4 to 6 Retardation plates were produced using the resins shown in Table 1 under the conditions shown in Table 1. The angular dependence of the retardation plate produced by the method of the present invention was small, but the angular dependence of the retardation plate produced by constant radius uniaxial stretching was large.

〔Effect of the invention〕

By stretching in one direction and narrowing the direction perpendicular to the stretching direction, a retardation plate with small angular dependence of optical path difference could be manufactured. The material produced by this method has a wide viewing angle in a black-and-white liquid Desbray, and is useful as a retardation plate for birefringence capture.

[Brief explanation of drawings]

FIG. 1 shows the angular dependence of the optical path difference between a retardation plate according to the method of the present invention and a retardation plate using a conventional method.

Claims (1)

[Claims] (1) In a method for manufacturing a retardation plate by stretching an unstretched film or sheet-like material of transparent resin in one direction at a stretching ratio of n times, the width of the film or sheet after stretching in the direction perpendicular to the stretching direction. A phase difference in which the optical path difference has a small dependence on the incident angle, which is characterized by stretching while performing feeding so that w is in the range of w0>w≧w0/√n with respect to the film or sheet width w0 before stretching. Method of manufacturing boards.