JPH03245122A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To minimize the difference in the transmittance of light by a difference in colors and to prevent coloring at the time of a black display by forming >=2 kinds of parts which vary in gap thickness in one display picture element of a liquid crystal cell. CONSTITUTION:Polarizing plates 1, glass substrates 2, transparent electrodes 4, a protective film 7, oriented films 5, color filters red 31, green 32, blue 33 are disposed and a nematic type liquid crystal is injected into the space therebetween. The protective film 7 is formed with steps. The one display picture element is divided to the parts of the two gap thicknesses; d1 and d2. If the ratio of the area of the part of the large gap thickness to one picture element is designated as alpha, the alpha is changed by each color to alphaR with the picture element of the color filter red, alphaG with the green picture element and alphaB to the blue picture element to the relation alphaR>alphaG>alphaB. The gap thicknesses are provided by >=2 kinds and the ratio of the area of the parts where the gap thickness varies to the area over the entire part of the picture element is adjusted by each color of the picture elements to minimize the difference in the transmittance per color of the picture elements, by which the coloring at the time of the black display is suppressed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention sets the optimum transmittance for each pixel when controlling light with a unique wavelength for each pixel in controlling transmitted light in a liquid crystal. The present invention relates to a liquid crystal display device that can be used.

[Conventional technology]

As described in JP-A-60-159830, in the conventional device, the gap thickness is changed in the order of red, green, and blue, and the transmittance when no voltage is applied is determined for each color. is kept to a minimum. Also, JP-A-63-2910
In the example described in Publication No. 31.

By forming steps in the protective film within one display pixel and providing three different gap thicknesses, differences in transmittance due to different colors are reduced.

[Problem to be solved by the invention]

The above-mentioned example is effective in reducing the difference in light transmittance of the liquid crystal cell due to the difference in color, and in eliminating coloration when displaying black. The present inventors developed this method as a method for reducing the difference in light transmittance due to differences in color.

Provides a simpler method than the previously described method.

An object of the present invention is to minimize coloring during black display in color display of a liquid crystal cell.

[Means to solve the problem]

The above object can be achieved by forming two or more types of portions with different gap thicknesses in one display pixel of a liquid crystal cell. Further aspects of the present invention are as follows.

(1) The gap thickness of the portion occupied by the liquid crystal in the liquid crystal cell is varied in two or more types for each display pixel, and the ratio of the areas of the portions with different gap thicknesses in each display pixel is
A liquid crystal display element that changes the color of each display pixel.

(2) When the colors of the display pixels of the liquid crystal cell are the three primary colors of red, green, and blue, two types of gap thickness were set, and the area ratio of the portion with the largest gap thickness was set in the order of red>green>blue. Liquid crystal display element.

Furthermore, in the present invention, the gap thickness refers to the length of the portion of the liquid crystal through which the passing light passes; however, if there is a spacer that fixes the thickness of the liquid crystal layer, it also includes the distance passing through the spacer.

In addition, the area of a portion with a certain gap thickness refers to the area within a certain display pixel where light that passes through the liquid crystal or spacer with a specified gap thickness and is actually displayed passes through the protective film. .

[Effect]

Transmittance T of liquid crystal is expressed by the following formula.

λ Here, Δn is the refractive index anisotropy of the liquid crystal, d is the gap thickness of the liquid crystal cell, and λ is the wavelength of transmitted light.

Since Δn has almost no wavelength dependence, the transmittance T is determined by λ and d
determined by the value of Here, a plurality of types (n types) of gap thickness in one display pixel are provided, and each d+(i=
1p n), and the ratio of each area to the entire area of one pixel is αt (i=1+n), then the average transmittance of one pixel can be expressed by the following equation.

λ If λ differs in the above equation, the value of T will also change, but an appropriate α1
By selecting the set of , it is possible to select the optimum transmittance.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a liquid crystal display element of a twisted nematic liquid crystal color display device. Polarizing plate 1゜Glass substrate 2
．． Transparent electrode 4. Protective film7. Alignment film 5° color filter (
Red) 31. (Green) 32. (Blue) 33 are arranged as shown in Figure 1, and nematic liquid crystal is injected into the space between them.The protective film has a step formed, and one display pixel is
It is divided into two gap thickness parts, di and d2.

If the ratio of the area of the thick gap part to one pixel is α, then for the pixel of the color filter (red), α
B1 green is αG, blue is αB, and α is changed for each color, and the relationship is αR>αG>αB. The polarizing plates are arranged in the same direction, and the upper and lower orientation films 5 are set so that the orientation direction is at an angle of 90° or more.

When a voltage is applied between the transparent electrodes, the transmittance is maximum, and when no voltage is applied, the transmittance is minimum. However, as shown in equations (1) and (2), the transmittance is
Depends on wavelength. Figure 2 shows the transmittance T and Δncl (Δn:
The relationship between the refractive index anisotropy of the liquid crystal (d: gap thickness of the liquid crystal cell) is shown. It can be seen that if λ differs, Δnd at which T becomes zero also differs. Since Δn is a constant, it can be seen that the transmittance T of light of wavelength λ depends on the gap thickness d. Table 1 shows the transmittance for each wavelength when one type of gap thickness is used without providing a step in the gap thickness.

As shown in Table 1, when there is only one gap thickness, the transmittance varies depending on the wavelength, and a coloring phenomenon occurs depending on the wavelength with a large transmittance.

On the other hand, dl and dz in Fig. 1 are Δndt: 0.4
40. Set so that Δndz=0.502,
If the values shown in Table 2 are selected for αR9αG and αB shown in Figure 1, the transmittance of each pixel is 0.826% for red as shown in Table 2.
, green is 0.803%, blue is 0.814%, and the difference between the maximum and minimum values is 0.022%. This value is -100% lower than that in the case of one type of gap thickness, and the coloring phenomenon during black display can be suppressed to a very small level.

Table 2 Δnd1. Δndz, αR, aa, (!B are determined by the method described below.
As shown in the figure. First, the upper limit value of the transmittance T determined by Δnd is determined. If the upper limit is 1%, the portion below the broken line ■ shown in FIG. 3 becomes the permissible range.

In this case, for blue, 0.374≦Δnd≦0.444
, 0.438≦Δnd≦0.519 for green, and 0.486≦Δnd≦0.576 for red. In this range,
The two gap thicknesses dl and da are determined by Δ in the overlapping range of Ha and Ha and the overlapping range of Ha and HFI shown in Figure 3.
It is necessary to correspond to nd. Why, in order for the average value of transmittance for each red, green, and blue pixel to be less than 1%,
This is because either dz or da needs to have a transmittance of 1% or less for red, green, and blue wavelengths. Upper limit value 1%
As mentioned above, the range of Δndx+ Δndz is 0.486≦Δndx≦0.519, 0.438≦
Δndz≦0.444. The upper limit of transmittance is set to 0.8
When it is set to 4%, as shown by the broken line ■ in Figure 3.

The range where Ha and Ha overlap is only one point, Δnd = 0.4406, and the upper limit value cannot be lowered any further, so Δndz = 0.44 is decided, and the upper limit value of the range of Δnd is 0.84%. Assuming the overlapping range of Ha and HR when
It became 5. Since Δndz and λ in equation (3) are determined, the average transmittance T of one pixel can be considered as a function of α and dl.

In the following equation.

=f(α, d1)
...(5) In the case of blue, Ts=f(αB, dl) is
In the range of Δndt, when αB=O, the minimum value is 0.814%
Therefore, it is determined that αB=0. In order to eliminate the coloring phenomenon during black display, the closer the other TR and TO are to Ta, the better, so TFI: f (αR, dx) = 0.814 Ta = f
(αc, dx)=0.814. αRI aa,
Find dz (0,489≦Δndx≦0.51.5). In this case, as a convenient method, a value at the intersection of the green and red graphs shown in FIG. 3 was selected as the value of Δndl. Table 2 shows the values determined in this way.

FIG. 4 shows another example of the shape of the protective film. The example shown in Fig. 1 has one step, but even if one step is increased as shown in Fig. 4, the ratio of the area of the thick part to the thin part of the gap will be the same as shown in the drawing. As long as the situation is the same, you can get the same effect. The intervals between the steps within one pixel do not necessarily have to be regular as shown in FIG.

〔Effect of the invention〕

According to the present invention, two or more types of gap thickness are provided in one pixel of a liquid crystal cell for color display, and the ratio of the area of the portion with different gap thickness to the area of the entire one pixel is adjusted for each pixel color. Minimize the difference in transmittance between colors,
Coloring phenomenon during black display can be suppressed.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of the smallest unit of a liquid crystal color display device that is an embodiment of the present invention, and Figure 2 shows the relationship between transmittance T and Δnd for three wavelengths (red, green, and blue). FIG. 3 is a partially enlarged explanatory diagram of FIG. 1, and FIG. 4 is a vertical sectional view of the smallest unit of a liquid crystal color display device according to another embodiment of the present invention. l... Polarizing plate, 2... Glass substrate, 4... Transparent electrode, 5... Alignment film, 6... Liquid crystal, 7... Protective film, 3
1... Color filter (red), 32... Color filter (green). 33...Color filter (blue). Figure V, 3 Rent zI21 41ft ρ576

Claims (1)

[Claims] 1. The gap thickness of the portion occupied by the liquid crystal in the liquid crystal cell is varied in two or more types for each display pixel, and the ratio of the areas of the portions with different gap thicknesses in each display pixel is
A liquid crystal display device characterized by changing the color tone of each display pixel.