JPH0313916A - Phase difference plate and liquid crystal electro-optical device using this plate - Google Patents

Abstract

PURPOSE:To allow the more perfect optical compensation of the phase difference plate consisting of two sheets of oriented films of a high polymer by laminating two sheets of the above-mentioned films in such a manner that the orienting directions thereof intersect orthogonally with each other. CONSTITUTION:The phase difference plate is formed by laminating the uniaxially oriented film 30 consisting of polycarbonate PC of 580mum thickness and the uniaxially oriented film 31 consisting of polypropylene PP of 850mum thickness, which films vary in the dependency of the double refractive index DELTAn on wavelength from each other, in such a manner that the orienting directions thereof intersect orthogonally with each other. The nu values to indicate the dependency, on wavelength, of the double refractive indices DELTAn of the PC and PP having the large dependency of DELTAn on wavelength and the larger retardation are respectively 1.12 and 1.05, but the phase difference plate of the high dispersion as high as nu=1.34 is obtd. by superposing both in such a manner that the axes of orientation intersect orthogonally with each other. Namely, the phase difference plate which can make the more perfect optical compensation is obtd. according to such constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a retardation plate and a liquid crystal electro-optical element using the same.

[Prior Art] A retardation plate is a film or sheet having birefringence, and is now widely used as an optical compensation plate for liquid crystal electro-optic elements.

For example, in the conventional super twisted nematic mode, there was a characteristic coloration in the display, but it was proposed in Japanese Patent Publication No. 519/1986 that this coloration could be reduced by providing one or more retardation plates. Proposed. Such a liquid crystal display mode will hereinafter be referred to as FTN mode.

FIG. 2 shows a cross-sectional view of a conventional liquid crystal electro-optical device using the FTN mode. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is a retardation plate, and 4 is a lower polarizing plate. The liquid crystal 8 of the liquid crystal cell is a nematic liquid crystal ZLI-4 manufactured by Merck & Co.
336 was used. The birefringence Δn of this liquid crystal for light with a wavelength of 590 nm is 0.142. The cell gap d is 6.3 μm, and the retardation Δnd is 0.89 μm. On the other hand, the retardation plate is made of polycarbonate (hereinafter referred to as PC).
A uniaxially stretched film of a polyurethane resin was used. That Δn
(590nm) is 0.0039, d is 145μm, Δ
nd is 0.57 μm.

40 in FIG. 3 shows the wavelength dependence of the retardation of the PC film. Here, the parameter y indicating the wavelength dependence of Δn is Δn for light with a wavelength of 450 nm,
It is defined as the ratio of Δn to light with a wavelength of 650 nm.

y=Δn (150nm)/Δn (650nm)pc
The y value of is approximately 1.12.

FIG. 4 shows a relationship diagram of each axis of a conventional liquid crystal electro-optical element. The angle 20 between the polarization axis (absorption axis) direction 10 of the upper polarizing plate and the rubbing direction 11 of the upper substrate of the liquid crystal cell is 4 to the left.
5° Turn the twist angle 21 of the liquid crystal of the liquid crystal cell to the left 230″′
The angle 22 between the axial direction 13 where the retardation plate has the largest refractive index (the stretching direction of the -axis stretched film) and the rubbing direction 12 of the lower substrate of the liquid crystal cell is 90°. The polarizing axis (absorption axis) of the lower polarizing plate The angle 23 that the direction 14 makes with 13 is defined as 45 to the left.

FIG. 7 shows the on-state and off-state spectral characteristics of a conventional liquid crystal electro-optic device manufactured under the above conditions. Its display contrast is about 1:25.

[Problems to be Solved by the Invention] However, in conventional retardation plates and liquid crystal electro-optical devices using the same, optical compensation by the retardation plate is insufficient.
There was a problem in that the liquid crystal electro-optical element had a large amount of coloration when it was off.

The present invention is intended to solve these problems, and its purpose is to provide a retardation plate that enables more complete optical compensation, and a liquid crystal electro-optical element that uses the retardation plate and exhibits less coloring in display. It's about doing.

[Means for Solving the Problems] The retardation plate of the present invention includes: a) a retardation plate composed of two stretched polymeric films, b) the stretching directions of the two films are orthogonal to each other; C) The wavelength dependence of the birefringence Δn of the films is different from each other.

Furthermore, among the two stretched films constituting the retardation plate, the film with greater wavelength dependence of Δn is characterized in that it has greater retardation.

On the other hand, a liquid crystal electro-optical device using the retardation plate of the present invention is characterized by comprising the retardation plate, a liquid crystal cell, and two polarizing plates disposed on both sides of the retardation plate.

[Effect] The coloring of the FTN mode depends on the V value of the retardation plate.

FIG. 6 shows the colored changes in the off state when only the y value of the η retardation plate is changed from 1.0 to 1.7 under the conditions of the prior art described above using CIEI931 (x, y) It is shown on the coordinates. The * mark in the center of the figure is the white point,
Hail, the closer you are to this point, the less colored it will be. In this case, the coloring becomes minimal when the y phrase is 1°5. The optimal value of y varies slightly depending on the cell conditions, but it is generally the conventional value of 1.12.
It can be said that the coloring becomes smaller when the value is made larger than .

However, the y value of ordinary polymers is in the range of 1.00 to 1.15 degrees, and even if the molecular structure of the polymer is devised, it is extremely difficult to obtain a value of 1.2 or more.

In the present invention, by combining two films, it is possible to obtain a retardation plate having a large y value.

41 and 42 in Fig. 3 are PCs with a thickness of 580 μm, respectively.
Uniaxially stretched film and 850 μm thick polypropylene (
The wavelength dependence of the retardation of a uniaxially stretched resin film (hereinafter referred to as PP) was shown. The V values of PC and pp are 1.12 and 1°05, respectively, but by overlapping them so that their stretching axes are orthogonal, a retardation plate with a high dispersion of y = 1.34 can be obtained as shown in Figure 43. is obtained. This is because the wavelength dependence of retardation has simple additivity.

Hereinafter, the details of the present invention will be shown by examples.

[Example] FIG. 1 shows the structure of the retardation plate of the present invention. In the figure, the arrow drawn on the film indicates the stretching direction. The retardation plate of the present invention has a thickness of 580 μm. A PC uniaxially stretched film 30 and a PP uniaxially stretched film 31 having a thickness of 850 μm are laminated so that their stretching directions are perpendicular to each other. 41 and 42 in FIG. 3 show the wavelength dependence of the retardation of the -axis stretched films 30 and 31. The y values of PC and PP are 1.12 and 1°05, respectively, but by overlapping them so that their stretching axes are orthogonal, a retardation film with a high dispersion of y = 1.34 can be obtained as shown in Figure 43. I got it.

FIG. 2 shows a cross-sectional view of the liquid crystal electro-optical element of the present invention.

In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is a retardation plate,
4 is a lower polarizing plate. The liquid crystal 8 of the liquid crystal cell is a nematic liquid crystal for STN manufactured by Merck ZLI-43 as before.
36 was used. The cell gap d is 6.3 μm, and the retardation Δnd is 0.89 μm.

FIG. 4 shows a relationship diagram of each axis of the liquid crystal electro-optical element of the present invention. The angle 20 that the polarization axis (absorption axis) direction 10 of the upper polarizing plate makes with the rubbing direction 11 of the upper substrate of the liquid crystal cell is 45 degrees to the left. The twist angle 21 of the liquid crystal of the liquid crystal cell is 230 degrees to the left.
The angle 22 between the axial direction 13 where the combined refractive index of the retardation plate is the largest (the stretching direction of the PC film with large retardation) and the rubbing direction 12 of the lower substrate of the liquid crystal cell is 9.
The angle 23 formed by the polarization axis (absorption axis) direction 14 of the 0 lower polarizing plate with 13 was set to 45° to the left.

FIG. 5 shows the on-state and off-state spectral characteristics of the liquid crystal electro-optical device of the present invention produced under the above conditions. Its display contrast is 1:28. The main feature of this device is that it has improved coloring when turned off compared to conventional liquid crystal electro-optical devices.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a retardation plate that enables more complete optical compensation and a liquid crystal electro-optical element that uses the retardation plate and exhibits less coloring in display. can.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a retardation plate of the present invention. FIG. 2 is a cross-sectional view of the present invention and a conventional liquid crystal electro-optical element. FIG. 3 is a diagram showing the wavelength dependence of retardation of a retardation plate. FIG. 4 is a diagram showing the relationship between the axes of the present invention and a conventional liquid crystal electro-optical element. FIG. 5 is a diagram showing the spectral characteristics of the liquid crystal electro-optical element of the present invention when it is on and when it is off. FIG. 6 is a diagram showing the influence of the y value of the retardation plate on coloring when off. FIG. 7 is a diagram showing the spectral characteristics of a conventional liquid crystal electro-optical element when it is on and off. 1. Upper polarizing plate 2, liquid crystal cell 3, retardation plate 4, lower polarizing plate 5, upper substrate 6 of liquid crystal cell, lower substrate 7 of liquid crystal cell, transparent electrode 8, twisted oriented nematic liquid crystal 0, upper polarized light A direction 1 of the polarization axis (absorption axis) of the plate 1, a rubbing direction 2 of the upper substrate 5 of the liquid crystal cell, a rubbing direction 3 of the lower substrate 6 of the liquid crystal cell, and an axial direction 4 in which the retardation plate 3 has the maximum refractive index. , the direction of the polarization axis (absorption axis) of the lower polarizing plate 4 is 0.1
The angle 1 that 0 makes with 11, the angle 3 that the torsion angle of the liquid crystal of the liquid crystal cell makes with 2.12 and the angle 13 makes with 13, the angle o that 14 makes with 13, PC uniaxially stretched film 1, PP uniaxially stretched film 0 to 43 ．． Wavelength dependence of retardation of the following retardation plate 40, -axis stretched film of PC (115 μm thickness) 4
1. -axially stretched film 42 of PC (480 μm thick),
-axis stretched film of PP (850 μm thickness) 43.4
1 and 42 stacked as shown in Figure 1. Spectral characteristics when turned on Spectral characteristics when turned off 0° 1° or more

Claims (3)

[Claims] (1) a) In a retardation plate made of two stretched polymer films, b) the two films are laminated so that their stretching directions are perpendicular to each other, and c) the birefringence Δn of the film is A retardation plate characterized by having mutually different wavelength dependencies. (2) The retardation plate according to claim 1, wherein of the two stretched films constituting the retardation plate, the film with greater wavelength dependence of Δn has larger retardation. . (3) A liquid crystal electro-optical element using a retardation plate, characterized in that it consists of the retardation plate, a liquid crystal cell, and two polarizing plates disposed on both sides of the retardation plate.