JPH0335201A - Phase difference plate and production thereof - Google Patents

Abstract

PURPOSE:To obtain the optically active phase difference plate which is thin and has excellent light transmittance by providing vapor-deposited layers consisting of a double refractive material on a light transparent substrate and forming the vapor-deposited layers with the superposed layers of the layers which vary in orientation direction. CONSTITUTION:The light transparent substrate 2 is disposed diagonally with a vapor deposition source having the double refractive material 1 and a vacuum vapor deposition is executed under the continuous or intermittent rotation of the light transparent substrate 2 to form the superposed layers 11 to 14 of the vapor-deposited layers which vary in the orientation direction on the light transparent substrate 2. The orientation direction can be controlled by rotating the light transparent substrate 2 at this time and the superposed layers 11 to 14 of the vapor-deposited layers which are different in the orientation direction are formed. The superposed layers 11 to 14 of the vapor-deposited layers formed in such a manner vary in the orientation direction and, therefore, exhibit the optical rotatory power and since these layers are the vapor-deposited layers, the layers are excellent in small thickness and light transmittability.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a retardation plate having a superimposed layer of vapor deposited layers with different alignment directions, exhibiting optical rotation, and suitable for STN liquid crystal display devices, etc., and a method for manufacturing the same. .

Background of the invention STN (Super Twisted Ne5at)
ic) Liquid crystal display devices that use liquid crystals and have improved time-division drive characteristics are used in large displays in office automation equipment and the like.

Due to birefringence of STN liquid crystals, there is a problem in that the display (background area or display area) is colored through the polarizing plate.In order to prevent this coloration and achieve black and white display, there is a means to compensate for the phase difference due to birefringence. It is being taught.

BACKGROUND OF THE INVENTION Conventionally, as the above-mentioned means, the D-
A 3TN system has been proposed. However, since a plurality of liquid crystal cells are used, it is unavoidably bulky and heavy, and it is difficult to form a combination of liquid crystal cells that satisfy a complementary relationship, resulting in poor mass productivity.

To overcome these problems, a BFTN method has been proposed in which a retardation plate is interposed between the liquid crystal cell and the polarizing plate, which achieves a single-layer liquid crystal cell and solves the problems of bulkiness, high weight, and mass production. are doing.

Problems to be Solved by the Invention However, the BFTN system has a disadvantage in that it is inferior to the D-8TN system in terms of contrast ratio in black and white display.

The inventors of the present invention have conducted extensive research to overcome these difficulties, and have discovered that the above object can be achieved by imparting optical rotation to the retardation plate.

Therefore, attempts were made to form a laminate by adhering multiple retardation plates with an adhesive with their optical axes shifted, but the contrast ratio was not satisfactory due to the problem of increased bulk and a decrease in light transmittance. It was found that there was no improvement in

In view of the above, an object of the present invention is to develop a optically active retardation plate that is thin and has excellent light transmittance.

Means for Solving the Problems The present invention overcomes the above problems by imparting optical rotation using a superimposed layer of vapor deposited layers having different orientation directions.

That is, the present invention provides a retardation plate characterized in that a vapor-deposited layer of a birefringent substance is provided on a light-transmitting substrate, and the vapor-deposited layer is formed of a superimposed layer of layers with different orientation directions, and has optical rotation. A transparent substrate is placed obliquely to a deposition source equipped with a birefringent material, and vacuum deposition is performed while the transparent substrate is rotated continuously or intermittently. The present invention provides a method for manufacturing the above-mentioned retardation plate, characterized in that a superimposed layer of vapor deposited layers having different orientation directions is formed thereon.

It is possible to form a vapor deposited layer with good orientation using the action oblique vapor deposition method, and at this time, the orientation direction can be controlled by rotating the translucent substrate, forming a superimposed layer of vapor deposited layers with different alignment directions. be able to.

The formed superimposed layer of vapor deposited layers exhibits optical rotation due to the different orientation directions, and is excellent in thinness and translucency based on the fact that it is a vapor deposited layer.

Example As illustrated in FIG. 1, the retardation plate of the present invention has optical rotation by superimposing vapor deposited layers 11 to 14 made of birefringent substances on a transparent substrate 2 so that their orientation directions (arrows) are different. is given.

For example, as shown in FIG. 2, the light-transmitting substrate 2 is disposed obliquely with respect to a vapor deposition source equipped with a birefringent substance 1, and the light-transmitting substrate 2 is rotated continuously or intermittently. This can be done by performing a vacuum evaporation process to form a superimposed layer (11 to 14) of evaporated layers with different orientation directions on the transparent substrate 2.

Note that 3 in the figure is a vacuum chamber.

In the present invention, as the light-transmitting substrate, any suitable material that transmits light may be used. Generally, for example, a transparent plastic film or a glass plate is used. Moreover, a polarizing plate etc. can also be used. When a polarizing plate is used, an elliptically polarizing plate can be formed. An inorganic film made of silica, alumina, titania, etc. may be provided on the transparent substrate in advance to facilitate formation of the vapor deposition layer. The plastic film or glass plate used is usually isotropic, but anisotropic ones such as those exhibiting birefringence may also be used. The thickness of the light-transmitting substrate is usually less than 5 mm, but may be determined as appropriate depending on the light transmittance and the like.

As the birefringent substance, one that forms a birefringent deposited layer by vacuum deposition treatment is used. Generally, organic polymers,
A birefringent substance is used that is made of an inorganic material such as metal or ceramic and forms a vapor deposited layer with excellent transparency. Among these, oxide-based inorganic compounds such as Ta205, TiOz, A1203, and Fe2O3 are preferably used from the viewpoint of durability, transparency, birefringence, and the like.

The angle of the oblique arrangement of the light-transmitting substrate with respect to the vapor deposition source during the vacuum vapor deposition process may be appropriately determined depending on the orientation of the vapor deposited layer and the like. Generally, the angle is 20 to 80 degrees with respect to the vertical direction.

Furthermore, the rotation angle of the light-transmitting substrate during the vacuum deposition process is typically 100 to 300 degrees, but is not limited thereto. The general method for rotating the light-transmitting substrate is to continuously or intermittently rotate the axis in a fixed direction. In that case, by using a continuous rotation method according to the formation speed of the vapor deposited layer,
It is possible to form a superimposed layer of vapor deposited layers in which the orientation direction is continuously twisted. Further, by using the intermittent rotation method, it is possible to form a superimposed layer of vapor deposited layers whose orientation directions are shifted by a predetermined angle. As for the retardation plate used in the STN liquid crystal display device, it is preferable in terms of contrast ratio that its optical rotation is closer to that of the liquid crystal layer.

As the vacuum deposition method, an appropriate method such as a resistance heating method, an electron beam heating method, a sputtering method, an ion beam method, etc. may be adopted. In particular, from the viewpoint of the orientation of the vapor deposited layer, a resistance heating method or an electron beam heating method is preferred, which is performed in a high vacuum where the vapor deposited material can move in a straight line.

The thickness of the superimposed layer of vapor deposited layers may be appropriately determined depending on the magnitude of the retardation to be provided. A retardation plate used in an STN liquid crystal display device preferably has a thickness that forms a retardation of 100 to 700 ni. Note that prevention of coloring in the STN liquid crystal display device, and therefore black and white display, is achieved by using a retardation plate that compensates for the phase difference in the STN liquid crystal cell, but color display can be achieved by adding a color filter, etc. It is also possible.

By the way, a non-oriented polycarbonate film with a thickness of 10,017 m or a polarizing plate (manufactured by Nichizuka Denko Co., Ltd.: NPF;
G5225 type> or a transparent substrate made of a glass plate with a thickness of 1 day, Ta205 was vacuum-deposited using an oblique evaporation method using an electron beam heating method. The process begins with evaporation under a vacuum on the order of % 1O-6 Torr.
The vapor deposition was completed while maintaining the degree of vacuum on the order of 10''5 Torr. Furthermore, the light-transmitting substrate was placed at an angle of inclination of 70 degrees with respect to the vertical direction with respect to the evaporation source equipped with Ta205, and the substrate was rotated 180 degrees at a constant speed while maintaining this angle. The total thickness of the deposited layer is 54 mm.

Next, the three types of retardation plates thus formed were adhered to one side of the STN liquid crystal cell via an acrylic adhesive to produce a black and white liquid crystal display device. The contrast ratio of the obtained liquid crystal display device in the driving state and in the non-driving state was as high as 25:l in both cases.

For comparison, a black-and-white STN liquid crystal display device was fabricated using a retardation plate made of a polycarbonate film with a birefringent light phase difference of 27On+++ according to the above-mentioned example, and the driving state and non-driving state of the liquid crystal display device were compared. When the contrast ratio in this state was examined, it was 8:1.

Effects of the Invention The retardation plate of the present invention has a superimposed layer of vapor deposited layers with different orientation directions, has optical rotation, is thin, and has excellent light transmittance. As a result, when this is applied to an STN liquid crystal display device, a black and white display with an excellent contrast ratio can be achieved.

Further, the manufacturing method of the present invention is excellent in manufacturing efficiency of the above-mentioned retardation plate.

[Brief explanation of drawings]

FIG. 1 is a partially sectional perspective view illustrating a retardation plate, and FIG. 2 is an explanatory diagram illustrating a method of manufacturing the same. 11.12.13,14 Vapor deposited layer 2 with different orientation directions (arrows): Transparent substrate

Claims (1)

[Claims] 1. A vapor-deposited layer of a birefringent substance is provided on a transparent substrate,
A retardation plate characterized in that the vapor deposited layer is formed of a superimposed layer of layers with different orientation directions and has optical rotation. 2. The retardation plate according to claim 1, wherein the transparent substrate is a polarizing plate. 3. A transparent substrate is placed obliquely to a deposition source equipped with a birefringent substance, and vacuum evaporation is performed while the transparent substrate is rotated continuously or intermittently. 2. The method of manufacturing a retardation plate according to claim 1, further comprising forming a superimposed layer of vapor deposited layers having different orientation directions thereon.