JPH06258620A - Display element - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the viewing angle dependence of visibility in a reflective display element in which a liquid crystal and a polymer are oriented and dispersed with each other, which is used for a display of information equipment. [Structure] The birefringence of the liquid crystal used and the thickness of the liquid crystal / polymer layer are controlled. [Effect] The display is not inverted even when the display element is viewed obliquely, and it is possible to realize a reflective display element that is bright and has good visibility regardless of where it is viewed. Therefore, it can be applied not only to information devices but also to outdoor advertising boards.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of a display element used in a computer, an information equipment terminal such as a television, or an outdoor display device.

[0002]

2. Description of the Related Art Conventionally, a cathode ray tube has been used as an information equipment terminal, but technological innovations in downsizing and weight reduction have progressed,
As a portable type, a display using liquid crystal has come into wide use. Further, in recent years, a polymer dispersion type liquid crystal display device has been developed as a bright reflection type display which does not use a polarizing plate (Japanese Patent Publication No. 58-501631, Mol.
electrical Crystal and Liquid
Crystal, 1991, vol. 198, pp.
357-370).

[0003]

However, in the conventional reflective polymer-dispersed liquid crystal display device, when the display device is viewed obliquely from the front, the scattering layer composed of the liquid crystal and the polymer is too strong. The scattering layer creates a shadow on the reflection surface, and as a result, the reflection is weakened and the display becomes dark. Therefore, the present invention solves such a problem, and an object thereof is to control the birefringence of liquid crystal or the thickness of liquid crystal / polymer layer in a display device in which liquid crystal and polymer are aligned and dispersed. By doing so, a bright display element with a wide viewing angle is provided.

[0004]

In a display device having a reflective layer and in which a liquid crystal and a polymer are aligned and dispersed, the product of the birefringence of the liquid crystal and the thickness of the liquid crystal / polymer layer is 1.4.
It is characterized by being less than or equal to μm. Further, the birefringence of the liquid crystal is 0.2 or less. Alternatively, the thickness of the liquid crystal and the polymer layer is between 3 μm and 7 μm.

The present invention will be described in detail below with reference to examples.

[0006]

【Example】

(Example 1) In this example, a case where the birefringence of the liquid crystal is 0.2 or less will be described. A simple cross-sectional view of the display element in this example is shown in FIG. First, a method for manufacturing the display element will be described. Two substrates with electrodes (one with a reflective electrode) were subjected to an alignment treatment, and the electrode surfaces were fixed facing each other with a gap of 5 μm facing inward. Liquid crystals (ML1009: manufactured by Merck, S-1011: manufactured by Merck, S-344 manufactured by Mitsui Toatsu Dye Co., Ltd., 96:
A mixture of a polymer precursor (biphenyl methacrylate) at 90:10 was encapsulated. Next, ultraviolet rays were irradiated in the liquid crystal phase to polymerize the polymer precursor, and the liquid crystal and the polymer were phase-separated to produce a display element. Further, as liquid crystals having different birefringence, SS9059RZ (manufactured by Chisso), ZLI4792 (manufactured by Merck), RDP0053
6 and RDP80616 (both manufactured by Rodic Corporation) were similarly manufactured as display elements.

With respect to the display element thus manufactured, if the birefringence is 0.2 or less, the display state is not reversed even when viewed from a direction inclined by 70 degrees from the normal line of the display element surface. Incidentally, when a liquid crystal having a birefringence anisotropy of about 0.25 is used, the display appears to be reversed in this state. The results are shown in Table 1.

[0008]

[Table 1]

The reflectance on the front is 100 times that of white paper.
It is the relative reflectance when it is defined as%. When the birefringence of the liquid crystal used in this way is 0.1 or less, the scattering becomes weak and the liquid crystal becomes unbright. Further, when the birefringence is 0.2 or more, the display is likely to be inverted and the brightness is reduced.

Although the chiral component is used here, it may not be used. For use, R10
11, S801, R801, CB15 (manufactured by Merck Ltd.), CM19, CM20 (manufactured by Chisso Corp.), etc. can be used as long as they can twist the alignment of the liquid crystal.

Although the dichroic dye is used here, it can be displayed without using it. However, it is hard to see because white letters will appear in the mirror. When using a dichroic dye, dyes of various colors can be used depending on the application.

As the polymer precursor, not only a methacrylate type but also an acrylate type, an epoxy type, or the like which is polymerized by an external stimulus can be used. The polymer precursor preferably has a skeleton similar to that of liquid crystal molecules. For example, it is desirable to have a structure in which benzene rings are connected, such as a phenyl, biphenyl, or terphenyl skeleton. At this time, if the birefringence of the polymer becomes too large, the scattering intensity increases and the viewing angle characteristics deteriorate, so it is necessary to select a polymer precursor in order to optimize the display characteristics. At this time, it is easy to obtain good properties by mixing and using different polymer precursors.

The ratio of the liquid crystal, the chiral component, the dichroic dye, and the polymer precursor in the case of mixing is not limited to the ratio shown here, but is determined to optimize the characteristics according to the application.

As the substrate to be used, a glass substrate with a transparent electrode and a substrate with a reflective electrode were used here, but the substrate is not limited to glass and may be plastic or metal. A soft substrate can also be used. Without using a reflective electrode,
You may combine two transparent substrates with a transparent electrode, and may provide a reflective layer outside. Regarding the alignment treatment performed on the substrate, the alignment film may or may not be provided. Alignment treatment such as rubbing may be performed. Vertical alignment treatment may be performed (at this time, a liquid crystal having a negative dielectric anisotropy is used). In short, the surface of the substrate may be treated so that the liquid crystal is aligned.
Large capacity display can be performed by using a substrate with a two-terminal element or a three-terminal element, and a reflective color display element can be obtained by disposing a color filter. If the surface of the display element is subjected to non-glare treatment or further anti-reflection treatment, the display can be easily viewed.

(Embodiment 2) This embodiment shows an example in which the thickness of the liquid crystal / polymer layer (cell thickness) of the display element is changed. The substrates and materials used here are the same as in Example 1. The liquid crystal used was fixed to RDP00536.
Cell thickness is 3μm, 4μm, 5μm, 6μm, 7
μm and 8 μm. The viewing angle dependence of the display was examined for the above six levels.

[0016]

[Table 2]

When the cell thickness is increased in this way, the display state is reversed when viewed obliquely, and the display becomes extremely difficult to see. The brightness is also reduced. If the cell thickness is 3 μm or less, the scattering layer becomes too thin and scattering is less likely to occur, resulting in a dark display. Therefore, it is considered that the cell thickness is preferably about 3 μm to 7 μm.

The conditions for other materials and substrates are the same as those in the first embodiment. As the liquid crystal, it is possible to use the liquid crystal shown in Example 1 instead of the liquid crystal shown here.

(Embodiment 3) In this embodiment, when the product of the birefringence of the liquid crystal and the thickness of the liquid crystal / polymer layer is 1.4 μm or less, the birefringence of the liquid crystal is larger than 0.2. Then, an example is shown in which the thickness of the liquid crystal / polymer layer (cell thickness) is changed. The substrates and materials used here are the same as in Example 1. The liquid crystal used was fixed to BL007 (manufactured by Merck & Co., Inc., birefringence 0.286). Cell thickness is 3μ
m, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm.
The viewing angle dependence of the display was examined for the above six levels.

[0020]

[Table 3]

When a liquid crystal having a large birefringence is used, even if the cell thickness is thin to some extent, the display state is reversed when viewed obliquely, and the display becomes extremely difficult to see. The brightness is also reduced. If the cell thickness is 3 μm or less, the scattering layer becomes too thin and scattering is less likely to occur, resulting in a dark display. Therefore, when the birefringence of the liquid crystal is as large as about 0.28, it is considered that the cell thickness should be about 3 μm to 4 μm.

The conditions for other materials and substrates are the same as those in the first embodiment. As the liquid crystal, it is possible to use the liquid crystal shown in Example 1 instead of the liquid crystal shown here.

(Embodiment 4) In this embodiment, when the product of the birefringence of the liquid crystal and the thickness of the liquid crystal / polymer layer is 1.4 μm or less, the birefringence of the liquid crystal is set to about 0.1. In addition, an example in which the thickness of the liquid crystal / polymer layer (cell thickness) is changed is shown. The substrates and materials used here are the same as in Example 1. The liquid crystal used was fixed to ZLI4792 (manufactured by Merck & Co., Inc., birefringence 0.09). Cell thickness is 5μ
m, 7 μm, 10 μm, 13 μm, 15 μm, 17 μm
And The viewing angle dependence of the display was examined for the above six levels.

[0024]

[Table 4]

When a liquid crystal having a small birefringence is used, even if the cell thickness is large to some extent, the display state is not easily inverted when viewed obliquely, and the display is very easy to see. However, as the cell thickness increases, the driving voltage increases, which is not practical.

The conditions for other materials and substrates are the same as those in the first embodiment. As the liquid crystal, it is possible to use the liquid crystal shown in Example 1 instead of the liquid crystal shown here.

[0027]

As described above, according to the present invention, in a display device in which a liquid crystal and a polymer are aligned and dispersed, the birefringence of the liquid crystal used and the thickness of the liquid crystal / polymer layer can be controlled to provide a bright viewing angle. It has become possible to easily manufacture a display element. By using the present invention, it is possible to produce a bright and large-capacity color display having good visibility.

[Brief description of drawings]

FIG. 1 is a simple cross-sectional view of a display device of the present invention.

[Explanation of symbols]

 1 Substrate 2 Electrode 3 Alignment Film 4 Polymer 5 Liquid Crystal 6 Dye 7 Alignment Film 8 Electrode 9 Substrate

Front Page Continuation (72) Inventor Hidehito Iizaka 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (3)

[Claims] 1. A display device comprising a reflective layer and comprising a liquid crystal and a polymer aligned and dispersed with each other, wherein the product of the birefringence of the liquid crystal and the thickness of the liquid crystal / polymer layer is 1.4 μm or less. Characteristic display element. 2. The display element according to claim 1, wherein the birefringence of the liquid crystal is 0.2 or less. 3. The display device according to claim 1, wherein the thickness of the liquid crystal and the polymer layer is between 3 μm and 7 μm.