JPH03185422A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display device which has excellent water resistance and a high contrast ratio by forming a medium of a high-polymer compd. having a hydroxyl group and crosslinking the high-polymer compd. CONSTITUTION:A mixture composed of a liquid crystal added with a dichromatic dye and a crosslinking agent is added to an aq. soln. of the high-polymer compd. having the hydroxyl group. After the soln. is mixed and emulsified, the soln. is applied on one substrate provided with transparent electrodes. The water is evaporated and the high-polymer compd. is crosslinked to impart the water resistance to the coating. Another substrate having the transparent electrodes is then stuck to the above- mentioned substrate to form the liquid crystal display device. The liquid crystal or the liquid crystal and the dichromatic dye are mixed with the crosslinking agent and thereafter, the mixture is mixed with the high-polymer compd. having the hydroxyl group and is emulsified with the resulted polymer dispersion type liquid crystal layer and, therefore, the dispersion and incorporation of the liquid crystal or the liquid crystal and the dichromatic dye in the form of microdroplets into the high-polymer compd. are lessened and particularly the dichromatic dye is mainly incorporated into the liquid crystal. The liquid crystal display device produced by the polymer dispersion type liquid crystal obtd. by the crosslinking is, therefore, excellent in the water resistance and is high in the contrast ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polymer-dispersed liquid crystal display device with excellent water resistance.

The liquid crystal display device of the present invention can be used for various displays, optical shutters, control devices, etc., and can sometimes be suitably used as a large screen liquid crystal display device.

[Prior art and its problems]

In recent years, a new liquid crystal film technology called polymer-dispersed liquid crystal has been developed, and its use is progressing in film-like large-area optical shutters and large-area display members.

When a polymer-dispersed liquid crystal layer made using a liquid crystal with positive dielectric anisotropy and a normal refractive index almost equal to the refractive index of the polymer is sandwiched between two electrode substrates, light will be scattered when the electric field is off. However, when the electric field is ON, light can be transmitted.

As a polymer-dispersed liquid crystal, NCAP (Ne+mati
c Curvilinear Aligned Pha
se: Nematic curve type aligned phase) liquid crystal (Special Publication 1987-
501631), latex-incorporated liquid crystal (Japanese Unexamined Patent Publication No. 60-252687), a material in which liquid crystal microdroplets are dispersed in epoxy resin (Japanese Unexamined Patent Publication No. 61-502128), or a network structure prepared by a solvent casting method. Liquid crystal composite film (Polymer Preprints)
+Japan vol, 37+No, 8+2450 (1
98B)) etc. are known.

NCAP liquid crystal obtained using a water-soluble polymer as described in the above-mentioned Japanese Patent Publication No. 58-501631 has good contrast, but because the polymer is hygroscopic,
There are problems with long-term stability of electrical characteristics.

On the other hand, in the method described in JP-A-60-252687, a solution in which a polymer and a liquid crystal are dissolved in an organic solvent is spread on a substrate, and the solvent is removed by evaporation. There is a problem that the components evaporate and the composition of the liquid crystal changes.

In addition, epoxy resin monomers described in Japanese Patent Publication No. 61-502128, or mixtures of ultraviolet curable resin monomers and liquid crystals are sandwiched between substrates, polymerized and cured, and liquid crystals are phase-separated and dispersed in the polymer. In polymer-dispersed liquid crystals or liquid crystal composite films prepared by solvent casting, part of the liquid crystal is dispersed in the polymer in the form of very small droplets (diameter of 0.5 μm or less), and this liquid crystal is Since it does not respond to an electric field, the ratio when the electric field is ON compared to when the electric field is OFF (hereinafter abbreviated as contrast ratio) is insufficient, and not only does the light transmission and absorption function not fully demonstrate, but also the amount of transmitted light when the electric field is ON is small. There was a problem. Furthermore, for example, when ultraviolet light is used, there are problems such as deterioration of the liquid crystal and dichroic dye added to improve the contrast ratio.

Furthermore, when a dichroic dye is used together with a liquid crystal, in any of the methods described above, a portion of the liquid crystal in which the dichroic dye is dissolved is dispersed in the polymer in the form of very small droplets.
These liquid crystals and dichroic dyes do not respond to a normal electric field, resulting in the same problems as described above.

[Means for solving problems]

The present invention relates to a liquid crystal display device that solves the above problems.

The present invention consists of two substrates on which transparent electrodes are disposed, and a medium layer in which liquid crystal is dispersed in the medium, and the medium layer is
The present invention relates to a liquid crystal display device in which the medium is a polymer compound having a hydroxyl group, and the polymer compound is crosslinked, in a liquid crystal display device having a structure in which transparent electrode surfaces are sandwiched between two substrates so as to face each other.

Polymer compounds having hydroxyl groups used in the present invention include polyvinyl alcohol, cellulose derivatives,
and polyalkylene glycols such as polypropylene glycol can be preferably mentioned.

Specific examples of the crosslinking agent used to crosslink the polymer compound include polyisocyanates, typical examples of which include diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate;
Examples include triisocyanates such as (OCN (GHz)i) and N. Polymer compounds having hydroxyl groups 10
The ratio of the crosslinking agent to 0 parts by weight is usually preferably 5 to 50 parts by weight, because if it is too large, the contrast ratio will be lowered, and if it is too small, sufficient water resistance will not be obtained.

The liquid crystal used in the present invention is not particularly limited, but preferably has a large dielectric anisotropy and a large refractive index anisotropy, such as a cyanobiphenyl-based, cyanophenyl biridine-based, or cyanophenylpyrazine-based liquid crystal. Preferred examples include nematic liquid crystals. In particular, a liquid crystal mixture in which cyanophenylpyrimidine liquid crystal and/or cyanophenylpyrazine liquid crystal having large refractive index anisotropy and dielectric anisotropy is added to the cyanobiphenyl liquid crystal in an amount of about several percent by weight, preferably 5 percent by weight or more. When using dichroic dyes to create liquid crystal display devices, the contrast ratio is good, and when dichroic dyes are used, their solubility is high, so there is no dye precipitation even at low temperatures, and an excellent contrast ratio is maintained. can do.

Further, in the present invention, it is preferable to use dichroic dyes in order to increase the contrast, and a specific example thereof is a dye obtained by mixing a plurality of dichroic dyes such as azo dyes and anthraquinone dyes in an appropriate ratio. Examples include black dichroic dyes.

The liquid crystal display device of the present invention can be manufactured, for example, by the following method.

A mixture of a liquid crystal and a crosslinking agent, to which a dichroic dye is optionally added, is added to an aqueous solution of a polymer compound having a hydroxyl group, mixed and emulsified, and then applied to one substrate on which a transparent electrode is disposed. After evaporating and crosslinking the polymer compound to impart water resistance, the other substrate having the transparent electrode was bonded together to manufacture a liquid crystal display device.

The polymer-dispersed liquid crystal layer obtained by the method described above is produced by mixing liquid crystal or liquid crystal, a dichroic dye, and a crosslinking agent, and then mixing and emulsifying it with a polymeric compound having a hydroxyl group. Dichroic dyes are rarely dispersed and contained in the form of microdroplets in polymer compounds, and in particular, dichroic dyes are mainly contained in liquid crystals. Therefore, a liquid crystal display device manufactured using a polymer-dispersed liquid crystal obtained by crosslinking has excellent water resistance and a high contrast ratio.

〔Example〕

The present invention will be described in further detail below with reference to manufacturing examples and drawings.

Production Example 1 1.5 g of nematic liquid crystal (E-31LV, manufactured by BDH) containing 0.04 g of 3% dichroic dye (S-344; manufactured by Mitsui Toatsu Dye Co., Ltd. and isophorone diisocyaner)
was added onto 4.0 g of a 10% polyvinyl alcohol aqueous solution (KM-11; manufactured by Nippon Taisoko Kagaku) and stirred and dispersed to form a 0/W type emulsion.

The emulsion thus formed was placed on one substrate 2a having a transparent electrode 3a using a doctor blade.
Coated with a coating thickness of 00μm and heated at 100℃ using a hot air dryer.
This was dried for 1 hour to produce a polymer-dispersed liquid crystal layer 4 imparted with water resistance.

A liquid crystal display device 1 was fabricated by bonding the other substrate 2b having the transparent electrode 3b to the polymer dispersed liquid crystal layer 4 fabricated in this way.

FIG. 1 shows a longitudinal cross-sectional view of the liquid crystal display device 1. As shown in FIG. An alternating current voltage was applied between the upper and lower electrodes to examine changes in the amount of transmitted light. 10
The contrast ratio when 0V voltage was applied was 36. Further, this liquid crystal display device was immersed in stirring water at room temperature to examine its water resistance. Even when immersed for 10 minutes, almost no change was observed at the interface of the polymer-dispersed liquid crystal layer.

Production Example 2 A liquid crystal display device was produced in the same manner as Production Example 1 except that the amount of isophorone diisocyanate added was changed to 0.16 g.

An AC voltage was applied between the upper and lower electrodes of this liquid crystal display device, and changes in the amount of transmitted light were examined. The contrast ratio when a voltage of 100 V was applied was 24. Further, this liquid crystal display device was immersed in stirring water at room temperature to examine its water resistance. Even when immersed for 10 minutes, almost no change was observed at the interface of the polymer-dispersed liquid crystal layer.

Production Example 3 A liquid crystal display device was produced in the same manner as Production Example 1 except that isophorone diisocyaner 1 was not added to the liquid crystal in Production Example 1.

When water resistance was examined in the same manner as in Production Example 1, the interface of this polymer-dispersed liquid crystal layer began to dissolve immediately.

〔Effect of the invention〕

The liquid crystal display device obtained by the present invention has excellent water resistance and high contrast ratio.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a liquid crystal display device of the present invention. 1: Liquid crystal display device, 2a, 2b: Substrate, 3a.

Claims (1)

[Claims] (1) Consisting of two substrates on which transparent electrodes were arranged and a medium layer in which liquid crystal was dispersed in the medium, the medium layer was sandwiched between the two substrates so that the transparent electrode surfaces faced each other. 1. A liquid crystal display device according to the above configuration, wherein the medium is a polymer compound having a hydroxyl group, and the polymer compound is crosslinked.