JPS6272781A - Dichromatic coloring matter for liquid crystal - Google Patents

Abstract

PURPOSE:To provide the titled novel anthraquione-based coloring matter having specific structure, of large dichromatic ratio, high in durability, highly compatible with liquid crystal, giving adequate color-developing ability even with small amount, suitable for liquid crystal display in watches, etc. CONSTITUTION:For example, a coloring matter of formula I is allowed to react with dimethyl sulfoxide, etc. at 95 deg.C for 6hr followed by discharge into water. The resultant system is subjected to ammonium persulfate followed by filtration, washing with water, drying, etc., thus obtaining the objective coloring matter of formula II (R<1>, R<2> are each 1-20C alkyl) having absorption at wavelength between 700 and 800nm.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dichroic dye used in liquid crystals having absorption in the range of 700 to 800 nm, a liquid crystal composition containing the dye, and furthermore, a method for using this composition. This invention relates to display devices.

Background Art and Problems to be Solved by the Invention In recent years, liquid crystal display devices have become widely used6 from the viewpoint of energy saving and miniaturization. Most of the liquid crystal display elements currently in use utilize the electro-optic effect of twisted nematic liquid crystals, and are required to be combined with two polarizing plates for display. The reality is that there are many restrictions. As an alternative liquid crystal display method, a so-called guest-host type liquid crystal display, which utilizes the electro-optic effect of a colored liquid crystal composition in which a dichroic dye is dissolved in a nematic liquid crystal, has been studied.
Some of them have already begun to be used as display elements in watches, home appliances, industrial meters, etc.

The principle of this guest-host type liquid crystal display system is that dichroic dye molecules, which are guests, are aligned and arranged according to the arrangement of liquid crystal molecules, which are hosts. That is, by applying an external stimulus, usually an electric field, the liquid crystal molecules change their alignment direction from the 'off' state to the 'on' state, but at the same time, the dichroic dye molecules also change their alignment direction. This is based on the principle that as a result of the change, the degree of light absorption by the dye molecules in both states changes, resulting in a display.

The dichroic dye used here (1) has sufficient coloring ability in a small amount, (2) has a large dichroic ratio and shows a large contrast between voltage application and no voltage application.
3) It must have sufficient compatibility with liquid crystals, and (4) It must have basic conditions such as being highly durable and stable, and not deteriorating the performance of the device even when used for a long time. Minimum required.

In the case of black dichroic dyes, two or more types of dichroic dyes are mixed and the composition is used as a black liquid crystal. The color of the display and its brightness are mostly determined by the pigment in the composition.

A pure black dye is particularly preferable in terms of the color tone displayed by a dichroic dye mixture composition, but since it is not possible to obtain a pure black color as a single dye, Unfortunately, the display is configured to produce a black display by mixing and combining yellow, red, blue pigments, etc. However, in the liquid crystal material for black display using the above-mentioned mixed combination, it is difficult to display pure black, and the display contains other visible light, which often lacks sharpness.

Means for Solving the Problems In light of the above circumstances, the inventors of the present invention have made extensive studies and have found a new dichroic dye that has a large dichroic ratio and is highly durable. It's arrived.

That is, the present invention provides a liquid crystal dye represented by the general formula (I> [In formula (1), R'' and R' each independently represent a branched or chained alkyl group having 1 to 20 carbon atoms.] It has been found that the anthraquinone dye has absorption near 750 nm, has good dichroism, and has good compatibility with liquid crystals.

Furthermore, when the dye of formula (I) is used in combination with yellow, red, and blue dichroic dyes, a black liquid crystal dye that absorbs light in the visible region (400 to 7200 m) can be obtained. It was discovered that when used in a liquid crystal display device, clear black display can be achieved.

Specific representative examples of the dichroic dye of the present invention are shown in Table-1.

The dichroic ratio shown in Table 1 is the characteristic value that most characterizes the usefulness of the novel dichroic dye of the present invention. The dichroic ratio shown in Table 1 is calculated by dissolving 1.0% by weight of each dye in Merck liquid crystal (product number E-8), which is a typical nematic liquid crystal, and using a 10 μm thick liquid crystal that has been previously treated to homogeneously align. After encapsulating it in a liquid crystal cell, it is placed in the optical path of a spectrophotometer.
Absorbance (A) measured by applying linearly polarized light parallel to the liquid crystal alignment
11) and the absorbance (above A) measured by applying linearly polarized light perpendicular to the liquid crystal alignment, and calculated from the following formula. All of the dichroic dyes of the present invention exhibit extremely high dichroic ratios.

The dichroic dye of the present invention can be incorporated into a liquid crystal and used as a liquid crystal composition for color display in commonly used display devices.

Table-1 1CH(C1,)2 C)((CH,), 75
0 12.92 C5Hu(”) CsH,
y(n) 752 12.43 C,,H2
s(n) C,,H,(n) 751 12.
04 C−H,,ω>C,. H,,(n)
751 11.85 CH, CH, 752
'13.06 C(CH,), C(CH
), 754 12.88 CH,CH(C
H,)2CH2,CH(CH,), 752 12.8
9 CH, C, H, 75011, 810C, H
,,(n) C,H,,(n) 752
12.7 (Note): Measurement by dissolving in liquid crystal ZL11840 (product of Merck & Co.) The dyes according to the present invention may be used alone or in combination of two or more. The concentration of the dye to be used may be within a range where the dye can be dissolved in the liquid crystal, and within a range where the dye molecules can be aligned with the liquid crystal molecules (thus, the alignment can be sufficiently controlled); 01-1
It is preferred to use a concentration of 0% by weight, preferably 0.01-5% by weight.

It is also possible to mix such dichroic dyes of the present invention with other dichroic dyes or non-dichroic dyes to obtain a desired hue. For example, as described above, a vivid black dye can be obtained. be able to.

Dissolving a dichroic dye into a liquid crystal is done by mixing a predetermined amount of the dye with the liquid crystal and stirring for a long time, or by heating and stirring above the temperature at which the liquid crystal becomes an isotropic liquid.
A desired color display liquid crystal composition can be obtained.

[Example-1] 5 parts of the dye of formula (A) were reacted with 7 parts of sodium cyanide and 4 parts of ammonium bicarbonate in 100 parts of dimethyl sulfoxide at 95°C for 6 hours. After discharging into 500 parts of water and reacting with 4 parts of ammonium persulfate, it was filtered, washed with water, and dried.
) were obtained.

The dye of formula (B) below was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel.

Next, add 100 parts of liquid crystal ZLI 1840 (product of Merck & Co., Ltd.) and 05 parts of the above purified dye to a beaker, and add about 80 parts of the purified dye.
00 to give a completely clear solution. Next, after the contents were left to cool, this colored liquid crystal solution was sealed inside a liquid crystal display element.

This display device showed a blue-green color when no voltage was applied, and only the electrode portions became colorless when a voltage was applied, showing good contrast. □Also, the dichroic ratio has a maximum absorption wavelength of 750 nm.
It was 12.9.

[Example-2] 3.5 parts of a yellow dye of the known formula (C), 3.5 parts of a known yellow dye of the formula (D)
), 3.0 parts of a red dye of formula (E), and 2 of a known blue dye of formula (E).
．． 5 parts and 2 parts of the dye of formula (F) below to liquid crystal ZLI-184.
0 (product of Merck & Co., Ltd.) and the dichroic ratio was measured in the same manner as in Example 1, a display board with good contrast was obtained, and the absorption of light in the visible region was good. It was black in color.

0H

Claims (1)

[Claims] General formula (I) ▲Mathematical formulas, chemical formulas, tables, etc.▼(I) [In the general formula (I), R^1 and R^2 each independently represent a branched or straight chain carbon It represents an alkyl group having numbers 1 to 20. ] Anthraquinone-based dichroic dye for liquid crystals