JPH03109523A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element having a wide visual field angle by inserting at least one sheet of oriented film or sheet consisting of a resin having a negative intrinsic double refractive value between a liquid crystal cell and a polarizing plate. CONSTITUTION:At least one sheet of the oriented film or sheet 3 consisting of the resin having the negative intrinsic double refractive value is inserted between the liquid crystal cell and the polarizing plate. Transparent substrates made of glass or resin are used for the substrates 4A, 4B of the liquid crystal cell and ITO films, etc., are used for transparent electrodes 5A, 5B. The films which consist of resins, such as polyimide or polyamide, or inorg. matter, such as silicon oxide and titanium oxide, and are subjected to rubbing or vapor deposition are used for the oriented films 6A, 6B. The liquid crystal display element improved in the visual angle characteristics is obtd. in this way and is adequately used for black and white liquid crystal displays, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element with an improved viewing angle.

[Conventional technology] The applications of liquid crystal display panels are expanding more and more, and recently monochrome S
T N (Super Twisted Nemat
IC) type liquid crystal display panels have been developed. In this display panel, achromatic coloring is achieved by compensating for the inherent birefringence of the liquid crystal, which causes coloration, with an optical retardation element inserted between the liquid crystal cell and the polarizing plate.

One of these methods is to use the same STN type liquid crystal cell as the driving liquid crystal cell as an optical retardation element, and this method has been commercialized. In addition, there is a liquid crystal display panel (FTN type liquid crystal display panel) whose optical retardation element is an anisotropic oriented film or sheet of polycarbonate resin or polyvinyl alcohol resin whose intrinsic birefringence value is the same sign as that of the STN type liquid crystal cell, that is, positive. It is being considered. This reduces the weight of the display panel and improves the light transmittance (NIKKEI
MICRODEVICES 10. PP, 54-57
(1988)), and furthermore, two or more anisotropically oriented films or sheets of polycarbonate resin or polyvinyl alcohol resin having positive intrinsic birefringence values are arranged so that the major axes of the in-plane refractive index ellipses intersect with each other. Liquid crystal display panels using stacked optical retardation elements have been proposed. However, conventional liquid crystal display elements have the disadvantage that the optical path difference changes greatly depending on the incident angle of light, and in particular, in monochrome liquid crystal display panels, compensation in the oblique direction is not performed properly, resulting in coloring and narrow viewing angles. There is a problem.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problems of the prior art described above, that is, to provide a liquid crystal display element with a wide viewing angle.

[Means to solve the problem] The purpose of the present invention is to:

A liquid crystal cell in which twisted oriented nematic liquid crystal is sandwiched between a pair of transparent electrodes placed opposite each other.

In a liquid crystal display element consisting of a pair of polarizing plates arranged on both sides of a liquid crystal cell, at least one oriented film or sheet of resin having a negative intrinsic birefringence value is inserted between the liquid crystal cell and the polarizing plate. This is achieved using a characteristic liquid crystal display element.

The present invention will be explained using the drawings.

FIG. 1 shows a sectional view of a liquid crystal display element for a monochrome STN liquid crystal display panel, which is a preferred example of the liquid crystal display element of the present invention.

In FIG. 1, numeral 1 is a twist-aligned nematic liquid crystal cell equipped with transparent electrodes and an alignment film, 2A and 2B are polarizing plates, and 3 is an anisotropic alignment film of resin with a negative intrinsic birefringence value or It is a sheet. The anisotropically oriented film or sheet of resin having a negative intrinsic birefringence value of 3 is selected to have an appropriate optical path difference so as to compensate for the birefringence inherent in liquid crystals, which causes coloring.

The structure of the liquid crystal display element of the present invention is similar to a conventional FTN type liquid crystal display element, but the conventional element has a positive sign of the intrinsic birefringence value as an anisotropic alignment film or sheet for retardation compensation. While an anisotropically oriented film or sheet made of polycarbonate resin or polyvinyl alcohol resin is used, the element of the present invention uses an anisotropically oriented film or sheet whose intrinsic birefringence value has a negative sign, which has not been used in the past. This method is characterized by the use of a liquid crystal display element with excellent viewing angle characteristics.

Examples of resins having a negative intrinsic birefringence value include poly(meth)acrylic acid ester resins, resins of unsaturated aromatic compounds such as polystyrene, and the like. Films or sheets of these transparent homopolymers, copolymers, blends, polymer alloys, etc. mainly composed of these can be used.

Additives such as a lubricant and an ultraviolet absorber may be added to the resin for the film or sheet as required.

In FIG. 1, the substrates 4A and 4B of the liquid crystal cell are transparent substrates made of glass or wood.
L5A, 5B are alignment films 6A, in which ITO films or the like are used;
6B is a film of a resin such as polyimide or polyamide, or an inorganic film such as cane oxide or titanium oxide, which is rubbed or vapor-deposited to align the liquid crystal. 7 is a nematic liquid crystal.

The polarizing plate used is one in which iodine is adsorbed to a uniaxially stretched polyvinyl alcohol resin.

FIG. 2 is another example of a preferred liquid crystal display element for a monochrome STN liquid crystal display panel of the present invention. 8A in this element
, 8B is an anisotropically oriented resin film or sheet with a negative intrinsic birefringence value, and two sheets are used, and the long axis directions of the refractive index ellipses in the plane of the film or sheet intersect each other at a specific angle. They are superimposed to look like this. This liquid crystal display element has an excellent contrast ratio compared to the one shown in FIG.

The optical path difference of the oriented film or sheet of a resin with a negative intrinsic birefringence value used in the liquid crystal display element of the present invention, and the overlapping angle of the polarizing plate, liquid crystal cell, oriented film or sheet, etc. are based on the characteristics of the liquid crystal cell. For example, it can be found by optimization calculations known in this field (
Television Society Technical Report ITEJ Technic
Al Report Vol, 12. No.32. PP,
29-34. ID '888-75 (Au, 1988)
).

In the liquid crystal display element of the present invention, various oriented films or sheets of resins having negative intrinsic birefringence values can be used, but in particular, oriented films or sheets whose absolute value of variation in optical path difference depending on the incident angle is close to that of the liquid crystal cell. is preferable because the dependence on the incident angle is particularly small.

The liquid crystal display device of the present invention can take various forms other than the device shown in FIGS. 1 and 2 for monochrome STN liquid crystal display panels.

Three or more anisotropic oriented films or sheets whose intrinsic birefringence value has a negative sign may be used, or in black-and-white STN liquid crystal display panels, the sign of the intrinsic birefringence value is used to compensate for the birefringence inherent in the liquid crystal. It is also possible to use an anisotropically oriented film or sheet of polycarbonate resin or polyvinyl alcohol resin with a positive birefringence, and improve the viewing angle characteristics with a balanced oriented film or sheet whose intrinsic birefringence value has a negative sign.

Further, in liquid crystal display elements other than those for black-and-white STN liquid crystal display panels that do not require compensation for birefringence of a liquid crystal cell, a balanced orientation film or sheet in which the sign of the intrinsic birefringence value is negative is preferably used.

Further, an oriented film or sheet whose intrinsic birefringence value has a negative sign can also serve as a part of another element, for example, a protective film or sheet for a polarizing plate. In this case, there is an advantage that the total amount of constituent material is reduced.

The oriented film or sheet used in the present invention is formed by extrusion molding a raw material resin into a film or sheet shape, and then
It can be obtained by uniaxial stretching or biaxial stretching at a temperature up to 40°C higher.

The thickness of the oriented film or sheet whose intrinsic birefringence value has a negative sign is not directly related to the effects of the present invention, but it does affect productivity,
From the viewpoint of handleability, the thickness is preferably 10 to 1000μ.

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, methods for measuring physical property values used in the description of the invention will be shown.

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

・Incidence angle dependence of raw material film or sheet: Calculate the absolute amount of change in optical path difference as a percentage when the incident light beam is tilted in the long axis and short axis directions, based on the case where the light beam is incident perpendicularly to the sample surface. The average value of both was evaluated. The angle of incidence indicates the angle of inclination.

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

Example 1 From an unstretched sheet of acrylic resin (Parapet SH, manufactured by Kyowa Gas Chemical Industry Co., Ltd.) with a negative intrinsic birefringence value, 13
Uniaxially stretched at a stretching temperature of 5°C and a stretching ratio of 2.5 times, an anisotropically oriented sheet with an optical path difference of 268 nm, an incident angle dependence of the optical path difference at an angle of 45° of 15%, and a thickness of 262 μm was obtained. .

A polarizing plate, an STN liquid crystal cell with an optical path difference of 800 nm and a twist angle of 240°, an acrylic resin orientation sheet, and finally an analyzer plate with crossed nicols are assembled to create a liquid crystal display element for a black and white STN liquid crystal display panel that becomes dark in the off state. Created. The viewing angle characteristics were evaluated by observing changes in the darkness of the liquid crystal display element in the off state depending on the viewing angle at 2.5° intervals. 27.5
Viewing angle characteristics were good, with no change in darkness observed up to 30°.

Comparative Example 1 Instead of the acrylic resin sheet, a polycarbonate resin with a positive intrinsic birefringence value was used, and the optical path difference was 272 nm, 45''
A liquid crystal display element was produced in the same manner as in Example 1 using an anisotropic oriented film having an incident angle dependence of the optical path difference of 14% and a thickness of 96 μm, and the viewing angle characteristics were evaluated. 20
A change in darkness was observed at 30°, and the viewing angle characteristics were poor.

Example 2 MS resin (manufactured by Nippon Steel Chemical Co., Ltd., estyrene MS-60
0) has an optical path difference of 226 nm, an incident angle dependence of the optical path difference at an angle of 45'' is 16%, and an anisotropic alignment film with a thickness of 103 μ; An anisotropically oriented film with a dependence of 17% and a thickness of 74μ is arranged so that the long axis direction of the refractive index ellipse in the plane of the latter film is to the right with respect to the long axis direction of the refractive index ellipse in the plane of the former film. An optical retardation element was produced by attaching the two layers so that they were shifted by 26 degrees. A polarizing plate, a liquid crystal cell with an optical path difference of 800 nm and a twist angle of 240° with the twist of a line connecting the long sleeve direction of the refractive index ellipse of the optical retardation element, and a film with an optical path difference of 158 nm. An optical retardation element was placed facing the cell, and finally an analyzer plate was assembled as a cross niffle to create a liquid crystal display element that became dark in the off state. The viewing angle characteristics were evaluated by observing the change in darkness of the liquid crystal display element in the off state depending on the viewing angle at 2.5' intervals.

No change in darkness was observed up to 32.5'', and the viewing angle characteristics were good.

Comparative Example 2 Instead of using an MS resin film, the optical path difference was 225 nm, 4
The incident angle dependence of the optical path difference at an angle of 5° is 21% and the thickness is 212μ, and the optical path difference is 158 nm, and the incident angle dependence of the optical path difference at an angle of 45° is 22% and the thickness is 14
An optical retardation element and a liquid crystal display element were produced in the same manner as in Example 2 using an anisotropic oriented film of a 7μ polycarbonate resin, and the viewing angle characteristics were evaluated. At 20'', a change in darkness was observed and the viewing angle characteristics were poor.

Example 3 Polystyrene resin (Dialex HF-77 manufactured by Mitsubishi Monsando Co., Ltd.) was placed between the anisotropically oriented polycarbonate resin film of the liquid crystal display element of Comparative Example 1 and the analyzer plate.
A liquid crystal display device was prepared by inserting a balanced orientation film, and the viewing angle characteristics were evaluated. No change in darkness was observed up to 30", and the viewing angle characteristics were good. The polystyrene resin film showed no birefringence in the direction perpendicular to the surface.
The average absolute value of the optical path difference in the major axis direction and the minor axis direction at an angle of 45'' was 73 nm, and the thickness was 182 μm.

[Effects of the Invention] A liquid crystal display element with improved viewing angle characteristics is obtained by using an anisotropic oriented film or sheet having a negative intrinsic birefringence value as a component.The present invention can be used for monochrome liquid crystal displays, etc. It is suitably used for.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are cross-sectional views each showing a configuration example of a liquid crystal display element of the present invention. 1...Liquid crystal cell 2A, 2B...Polarizing plate 3.8A, 8B...Anisotropic alignment film or sheet

Claims (4)

[Claims] (1) In a liquid crystal display element consisting of a liquid crystal cell in which nematic liquid crystal is twisted and oriented between a pair of transparent electrodes placed opposite each other, and a pair of polarizing plates placed on both sides of the liquid crystal cell, the gap between the liquid crystal cell and the polarizing plate is 1. A liquid crystal display element, wherein at least one oriented film or sheet of resin having a negative intrinsic birefringence value is inserted into the wafer. (2) The liquid crystal display element according to claim 1, wherein the oriented film or sheet is an anisotropic oriented film or sheet produced by uniaxial stretching or unbalanced biaxial stretching. (3) The liquid crystal display element according to claim 1, wherein the oriented film or sheet is a balanced oriented film or sheet produced by balanced biaxial stretching. (4) The liquid crystal display element according to any one of claims 1 to 3, wherein the resin having a negative intrinsic birefringence value is a film or sheet of acrylic resin or styrene resin.