JPH1039288A - Liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color display with high contrast and excellent angle of visibility characteristics by forming a protective film on a color filter in such a manner that the protective film has a specified refractive index and film thickness. SOLUTION: This liquid crystal element consists of a pair of substrate 2a, 2b having transparent electrodes 8a, 8b, respectively, and a liquid crystal 7 showing a chiral smectic phase interposed between the substrates. At least a color filter 3 and a protective film 4 on the color filter 3 are formed between the one substrate 2a and the transparent electrode 8a. As for the protective film 4, various kinds of resins such as polysiloxane, acryl resin and polyamide resin can be used. The protective film is formed to have <0.40 refractive index and <4.0μm film thickness. By controlling the refractive index and film thickness of the protective film 4 for the color filter 3, decrease in the contrast can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color display liquid crystal element used for a terminal display of a computer, a television receiver, and the like.

[0002]

2. Description of the Related Art As one of the conventional liquid crystal devices, there is a liquid crystal display device of a type that controls transmitted light in combination with a polarizing element by utilizing the refractive index anisotropy of ferroelectric liquid crystal molecules. And Lagerwal
1) (JP-A-56-107216).
No. 4,367,924). This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range.
^* ) And takes either the first optical stable state or the second optical stable state in response to the electric field applied in this state, and in a thin cell when no electric field is applied Has the property of maintaining that state, that is, has bistability,
Further, the response to a change in the electric field is quick, and wide use as a high-speed and storage-type display element is expected.

[0003]

The characteristics of a liquid crystal device using a liquid crystal exhibiting a chiral smectic phase as described above include a wide viewing angle characteristic in addition to bistability and high-speed response. However, in order to perform color display, in a color display element having a color dot pattern and a protective film for protecting the color dot pattern, the provision of the protective film lowers the display characteristics, that is, the viewing angle characteristics due to the lowering of the contrast. There was a problem of a decline.

An object of the present invention is to solve the above problems and realize a color display having high contrast and excellent viewing angle characteristics in a chiral smectic liquid crystal element.

[0005]

A first aspect of the present invention is a liquid crystal device having a liquid crystal exhibiting a chiral smectic phase sandwiched between a pair of substrates each having a transparent electrode,
At least a color filter and a protective film laminated on the color filter are provided between one of the substrates and the transparent electrode. The protective film has a birefringence of 0.40 or less and a thickness of 4.0.
a liquid crystal element having a diameter of less than μm.

A second aspect of the present invention is a liquid crystal device in which a liquid crystal exhibiting a chiral smectic phase is sandwiched between a pair of substrates each having a transparent electrode, wherein at least a color filter is provided between one of the substrates and the transparent electrode. And a protective film laminated on the color filter, wherein the protective film has a birefringence of 0.50 or less and a film thickness of less than 2.0 μm.

The present inventor has found that by controlling the birefringence and the film thickness of the protective film of the color filter described above, it is possible to prevent a decrease in contrast, thereby achieving the present invention.

[0008]

FIG. 1 is a sectional view showing an example of the liquid crystal device of the present invention. In the figure, 1a and 1b are polarizing plates, 2a and 2b
Is a glass substrate, 3 is a color filter, 4 is a protective film of the color filter 3, 5a and 5b are insulating films, 6a and 6b are alignment control films, 7 is a chiral smectic liquid crystal, 8a,
8b is a transparent electrode, 9 is a spacer bead.

In the present invention, the protective film 4 having a birefringence of less than 0.5 is used, and the thickness is less than 2.0 μm, preferably 1.0 μm or less. Further, in the present invention, when a material having a small birefringence of less than 0.4 is used, the film thickness is less than 4.0 μm, preferably 3.0.
It may be formed to a thickness of μm or less.

As the material of the protective film 4 used in the present invention, various resins are used. For example, polysiloxane, acrylic resin and polyamide resin can be used.

In the present invention, the thickness of the protective film 4 is defined as
The thickness of the protective film in the area on the color filter is defined.

[0012]

【Example】

Examples 1 and 2 Comparative Examples 1 and 2 A liquid crystal device having the cross section shown in FIG. 1 was manufactured, and the difference in viewing angle characteristics due to the difference in the material of the protective film was confirmed. For the color filter, use a finely dispersed pigment of each color based on polyamide resin,
Organic phenyl siloxane (PSB)
-K31, manufactured by Toray Industries, Inc., polyamide (PA-1000)
C, Ube Industries, Ltd.), polyimide (PI-300, Ube Industries), and acrylic resin (LC-2040, Sanyo Chemical Co., Ltd.). . Table 1 shows the results. In the table, “reversal of display” is “present” when there is a reversal portion in 30% or more of the observed area, and “slightly present” when the reversal portion is recognized in less than 30%. . The “contrast ratio” is the average value of the 360 ° omnidirectional contrast when the visual field is tilted by 60 ° from the direction of the normal to the display surface. Means

[0013]

[Table 1]

As is evident from Table 1, it was found that a cell using polysiloxane or acrylic resin having a small birefringence Δn at the same film thickness did not invert the display and was excellent in viewing angle characteristics.

However, when an acrylic resin is used for the protective film, the temperature of the heat treatment in the post-process is high in the chiral smectic liquid crystal element, and the high temperature of the heat treatment causes the protective film to be colored and the spectral transmittance to be reduced. Small is not practical. Therefore, when using an acrylic resin for the protective film, it is necessary to design so that there is no high-temperature heat treatment step in the post-process.

Examples 3 to 6 and Comparative Examples 3 to 8 Next, in the same manner as in Example 1, the viewing angle characteristics were examined by adjusting the film thickness of each of the polysiloxane and the polyamide. Table 2 shows the results.

[0017]

[Table 2]

As is clear from Table 2, when the film thickness increases, the contrast of any of the protective films decreases, and the viewing angle characteristics decrease. Thus, a sufficient contrast ratio was obtained without inversion of the display. Is 3 for polysiloxane.
The film thickness was 0 μm or less, and the film thickness of polyamide was 1.0 μm.

When polysiloxane and polyamide are compared, polysiloxane is superior in performance of flattening irregularities on the surface of the color filter,
When the thickness is from 3.0 to 3.0 μm, sufficient flattening performance can be obtained, which is preferable.

Reference Example The effect of the material of the color filter on each characteristic of the visual field was examined. Pigment of each color is dispersed and mixed in various base resins, formed into a paint to form a dot matrix of each color, and in order to avoid the influence of the protective film, a transparent electrode is formed directly on the color filter, and the viewing angle characteristics are examined. Was. Table 3 shows the results.

[0021]

[Table 3]

As is apparent from Table 3, in the system in which the pigment is dispersed, the viewing angle characteristics are not necessarily lowered, but the birefringence of the base resin affects the contrast, and the birefringence is small. It is preferable to obtain a higher contrast ratio.

As a matter of course, the absence of the protective film itself is excellent in the viewing angle characteristics, but is indispensable at the present time in view of the panel manufacturing process.
It can be seen that the use of a material having a small birefringence as the material of the color filter is more effective in view angle characteristics.

[0024]

As described above, according to the present invention, a chiral smectic liquid crystal element having a high contrast ratio, no display inversion, and excellent viewing angle characteristics is provided, and a high-definition display with high definition and a large screen are provided. Is realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a liquid crystal element of the present invention.

[Explanation of symbols]

 1a, 1b Polarizing plate 2a, 2b Glass substrate 3 Color filter 4 Protective film 5a, 5b Insulating film 6a, 6b Alignment control film 7 Liquid crystal 8a, 8b Transparent electrode 9 Spacer beads

Claims (7)

[Claims] 1. A liquid crystal element comprising a pair of substrates each having a transparent electrode and a liquid crystal exhibiting a chiral smectic phase sandwiched therebetween, wherein at least a color filter is provided between one of the substrates and the transparent electrode. Having a birefringence of 0.40.
A liquid crystal element having a thickness of less than 4.0 μm below. 2. The protective film has a thickness of 1.0 to 3.0 μm.
The liquid crystal device according to claim 1, wherein 3. The liquid crystal device according to claim 1, wherein the protective film is formed of polysiloxane. 4. A liquid crystal element having a liquid crystal exhibiting a chiral smectic phase sandwiched between a pair of substrates each having a transparent electrode, wherein at least a color filter is provided between one of the substrates and the transparent electrode. Having a birefringence of 0.50.
A liquid crystal element having a thickness of less than 2.0 μm. 5. The liquid crystal device according to claim 4, wherein said protective film has a thickness of 1.0 μm or less. 6. The liquid crystal device according to claim 4, wherein the protective film is made of a polyamide resin. 7. The liquid crystal device according to claim 1, wherein the base resin forming the color filter is either polysiloxane or acrylic resin.