JPH0323406A - Production of phase difference plate - Google Patents

Abstract

PURPOSE:To lessen the dependency of an optical path difference on angles and to improve the uniformity of the optical path difference by adopting a method for narrowing the direction perpendicular to a stretching direction and further executing by a tenter method. CONSTITUTION:A material is stretched by the tenter method in a range of 1.2 to 3.5 range in stretching magnification (n) in such a manner that the sheet width w after the stretching in the direction perpendicular to the stretching direction attains a w0>w>=w0/ sq. rt. n range with respect to the sheet width w0 before the stretching. The phase difference plate formed by this method has the excellent dependency on angles as compared to a biaxially oriented material and a uniaxially stretched material having a specified width. The uniformity of the narrowing direction is preferably within the prescribed value indicating the width of the fluctuation from an average value by percent. Such uniformity is attained by the tenter system. The sheet having the excellent dependency of the optical path difference on angles and the excellent uniformity is obtd. in this way.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides an industrially preferable continuous manufacturing method for a resin retardation plate having a small dependence of the optical path difference on the angle of incidence and excellent uniformity of the optical path difference. Regarding. [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 refraction, the coloring caused by the birefringence inherent in liquid crystals has been made colorless. , 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 a liquid crystal display, when viewed from an oblique angle, compensation for birefringence is inadequate and colorlessness is incomplete.

[Problems to be Solved by the Invention MJ The purpose of the present invention is to solve the problems of the prior art described above, namely, to industrially manufacture a retardation plate with small angular dependence of optical path difference and excellent uniformity of optical path difference. This is the development of a method.

[Means for solving rag] An object of the present invention is to provide a method for differentially manufacturing a retardation plate by stretching an unstretched film or a sheet-like material of transparent resin in one direction. The film or sheet width W before stretching is within the range of 2 to 3.5 times and the film or sheet width W in the direction perpendicular to the stretching direction
This is achieved by a method for producing a retardation plate, which is characterized in that stretching is carried out by a tenter method while feeding the film so that w O>w≧wo/F■ is satisfied.

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 producing a retardation plate of the present invention is characterized in that an unstretched sheet is stretched in one direction, and the sheet is fed in a direction perpendicular to the stretching direction to uniformly narrow the width in that direction.

In the conventional industrial production of retardation plates, the so-called unbalanced biaxial stretching method, in which the stretching ratio in one direction is larger than the other, or the constant width uniaxial stretching method, in which the dimension in the perpendicular direction is not changed, are continuously carried out. He had been hired. That is,
In the direction perpendicular to the stretching direction, the width was kept constant or the width was slightly stretched. However, in the retardation plate manufactured by such a method, the stretching temperature,
Even if the stretching conditions such as the stretching ratio were changed, only the one in which the optical path difference changed greatly depending on the incident angle of the light beam could be obtained.

Contrary to the conventional method, the present inventors adopted a method of narrowing the direction perpendicular to the stretching direction, and by performing this with a tenter method at a specific stretching ratio, the angular dependence of the optical path difference was improved. It was discovered that a retardation film having a small optical path difference and excellent uniformity of optical path difference can be obtained, leading to the present invention.

FIG. 1 shows that the retardation plate produced by the method of the present invention has excellent angle dependence compared to retardation plates made of biaxially stretched products and constant width uniaxially stretched products. The resin is polycarbonate resin, and (a) has a stretching ratio of 1.8.
0.8 times narrower in the direction perpendicular to the stretching direction,
(b) is a uniaxially stretched product with a constant width of 1.8 times the length of the stretched roller,
) are biaxially stretched products of 2.2 times in one direction and 1.1 times in the other direction, and the optical path differences are 182 nm, 182 nll, and 159 nm, respectively.
It is l. Here, the change in optical path difference due to the incident angle is defined as the ratio of change in optical path difference when the incident ray is tilted in a plane direction perpendicular to the stretching direction and the extending direction, compared to when the ray is incident on the retardation plate at right angles. 1! Shown in (%). 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 the low optical path difference side, and in the case of the optical path difference, it changes to the high optical path difference side.

The stretching ratio "4n" is 1.2 to 3.5, preferably 1.3 to
3.0 is good. If the stretching ratio is small, it is difficult to provide the desired optical path difference of 1, and depending on the resin and stretching conditions, for example, the uniformity of the optical path difference may be poor at high drawing temperatures. l! If the intermediate magnification is too large, the tenter clip will easily break in the tenter method. Moreover, the optical path difference unevenness also increases.

The degree to which the width of the film or sheet in the direction perpendicular to the stretching direction is narrowed is determined by the following formula: WO>W≧
It is preferable to set it within the range of W/π. If it is too narrow, wrinkles will occur and the unevenness of the optical path difference will increase, which is not preferable.

Further, in the method of the present invention, it is necessary to use a tenter method. As a result, a retardation plate with a uniform optical path difference can be obtained. The roll stretching method is known as a continuous stretching method other than the tenter method, but in this method, the center and edge of the stretched film or sheet are narrowed differently, with the former being smaller and the narrower being larger. Therefore, the optical path difference becomes different. As for the uniformity of the narrowing, it is preferable that the fluctuation range with respect to the average value is within ±5% expressed as a percentage, and this can be achieved by the tenter method.

Specifically, this manufacturing method uses a mechanism similar to, for example, a device for simultaneous two-axis offshore stretching, in which the width in the horizontal direction narrows rather than just widening as it advances, while stretching in the vertical direction. This can be carried out by a method of narrowing the length, or by a method of narrowing the length in the length direction while opening the width direction and stretching with a device that narrows the length in the length direction as it progresses.

As for the stretching conditions, normal biaxial stretching conditions can be used. For example, the stretching temperature for non-grade resin is 10 to 10% higher than the glass transition temperature of the resin.
A temperature 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 is obtained by extruding and shaping a raw material resin. The thickness of the unstretched film or sheet is not essentially limited, but from the viewpoint of productivity and handling, it is 25μ to 5III1
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 method dual polarization microscope (manufactured by Nippon Kogaku Kogyo Co., Ltd.,
LABOP}IOT-POL) was used for measurement according to Joyo. The angle dependence was measured by tilting the sample at a predetermined angle and fixing it on a sample stand.

・Evaluation of angle dependence 1i+ffi: Absolute amount of change in optical path difference when the incident light ray is tilted in the stretching direction and in the plane direction perpendicular to the stretching direction, based on the case where the ray is incident on the retardation plate at right angles. was calculated using the Q fraction, and evaluated using the average value of both. The angle of incidence indicates the angle of inclination.

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

Execution Ml Bo1 carbonate resin molded with a 50φ extruder (
Made by Idemitsu Petrochemical Co., Ltd., A-2500) thickness is 180
An unstretched film of μ was stretched to 1.8 in one direction at a stretching temperature of 180'C using a tenter-type continuous stretching tester installed in an oven that circulated uniformly heated air.
Continuous stretching was carried out under the condition that one width was stretched twice while the other width was narrowed to 0.8 times. The continuous stretching test machine has a width of 81 mm, which is the same as the simultaneous biaxial stretching device, but it has been modified so that stretching is performed in the longitudinal direction and the width is narrower.The tenter length in the stretching section is 4 m, and the The line speed was 3 m/min.

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

In front of the stretching machine, equally spaced lines were drawn parallel to the longitudinal direction on the unstretched film, and after stretching, the uniformity of narrowing in the lateral direction within the effective range excluding the vicinity of the clip portion was determined. The variation range with respect to the average value was ±3%.

Note that the vertical direction is abbreviated as MD, and the horizontal direction as TD.

Example 2 In Example 1, the thickness of the unstretched material was changed to 320 μm, and the stretching was continued under conditions such that one direction was stretched 1.8 times while the other direction was stretched 0.9 times.

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

Comparative Example 1 In Example 1, the thickness of the unstretched product was set to 360μ, the stretching method was modified to allow constant width uniaxial stretching, and constant width uniaxial stretching was performed at a stretching ratio of 1.8 times. .

As shown in Table 1, the stretched product had a large angle dependence.

Comparative Example 2 A 700 μm unstretched sheet produced in the same manner as in Example 1 was stretched using a simultaneous biaxial stretching machine at a stretching temperature of 180° C. and at a stretching ratio of 2 times in the direction and 1.1 times in the direction.

The tenter length of the stretching section of the simultaneous biaxial stretching machine was 4 m, and the line speed of the low speed section was 3 m/min.

As shown in Table 1, the stretched product had a large angle dependence.

Example 3 The thickness of acrylic resin (manufactured by Wakiwa Gas Kagaku Kogyo Co., Ltd., Barapet S H) was extruded using a 50φ extruder.
An unstretched sheet of .mu. was stretched at a stretching temperature of 130.degree. C. in one direction using the tenter-type continuous stretching tester used in Example 1.
The line was stretched continuously by 8 times while the width of the other side was narrowed to 0.85 times, and the line speed in the low speed section was set to 3 m/min.

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

Further, the fluctuation range of the optical path difference within the effective range excluding the vicinity of the clip portion was ±4%.

Comparative Example 3 In Example 3, the width was narrowed by 0.85 times to 0.7
It was stretched to double the original size. It was a retardation plate with a large fluctuation range of optical path difference of ±12%.

Comparative Example 4 In Example 3, the stretching ratio was increased to 4 times, but the film was easily broken at the clip portion, and continuous operation was not possible.

Comparison 1'f15 An unstretched sheet produced in the same manner as in Example 3 was stretched 2.0 times in the machine direction at a stretching temperature of 130'C using a roll type stretching machine. Preheat with a preheat roll at 120°C, heat to stretching temperature with an infrared heater, and roll at a low speed of 5 m/min.
The speed of the high speed roll was 10 m/min, and the distance between the low speed roll and the high speed roll was 30 c-.

The width of the stretched product in the lateral direction was 0.85 times narrower than the width before stretching.

The optical path difference of this stretched product was 127 na at the center and 172 n2 at the ends, and the optical path difference was different between the center and the ends.

Practical Examples 4-5 Practical IIf. Similar to Example 1, # shown in Table 1! A retardation plate was produced using No. 1 resin under the conditions shown in Table 1. The angular dependence of the retardation plate was small.

Comparative Examples 6 to 7 Retardation plates were produced in the same manner as in Comparative Example 1 using the resins shown in Table 1 under the conditions shown in Table 1. The angle dependence of the retardation plate was large.

[Effects of the Invention] A retardation plate with excellent angular dependence and uniformity of optical path difference can be manufactured by a continuous manufacturing method using a tenter method, in which stretching is performed in one direction at a specific stretching ratio while narrowing the direction perpendicular to the stretching direction. Ta. The material produced by this method has a wide viewing angle in black-and-white liquid crystal displays and is useful as a retardation plate for birefringence compensation.

[Brief explanation of drawings]

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

Claims (1)

[Claims] (1) In a method of continuously manufacturing a retardation plate by stretching an unstretched film or sheet-like material of transparent resin in one direction,
Film or sheet width w after stretching in a direction perpendicular to the stretching direction with a stretching ratio n in the range of 1.2 to 3.5 times
is the film or sheet width w0 before stretching, w0>
A method for manufacturing a retardation plate, which comprises stretching by a tenter method while feeding the film so that w≧w0/√n.