JPH0539430A - Dichroic dye for addition to liquid crystal - Google Patents

Abstract

PURPOSE:To obtain a new compound having low dyeability to a resin film, exhibiting purple or blue color, having large dichroic ratio and high durability, and suitable for high polymer dispersible liquid crystal display, etc. CONSTITUTION:A compound expressed by formula I [R<1> is (substituted)alkyl, (substituted)alkoxy, halogen or H; R<2> and R<3> are H, halogen, methyl, ethyl, methoxy or ethoxy] e.g. a compound expressed by formula II. Furthermore, the compound expressed by formula I is obtained by reacting a halogen- substituted 1, 4-diaminoanthraquinone compound expressed by formula III (X is Cl, Br or I) with a 4-hydroxyazobenzene compound expressed by formula IV in a polar organic solvent such as DMF in the presence of a base such as potassium carbonate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel purple dichroic dye to be added to liquid crystals. In particular, the present invention provides a dichroic dye exhibiting high performance in a polymer dispersed liquid crystal display (hereinafter abbreviated as PDLC).

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used from the viewpoint of energy saving and miniaturization.

Most of the liquid crystal display elements currently in use utilize the electro-optical effect of twisted nematic type liquid crystal, and display is made as an essential condition when combined with two polarizing plates. The reality is that they are restricted by. As an alternative liquid crystal display method, a so-called guest-host liquid crystal display utilizing the electro-optical effect of a colored liquid crystal composition in which a dichroic dye is dissolved in a nematic liquid crystal has been studied, and some of them have already been used for watches and home appliances. , Is used as a display element in industrial instruments and the like.

The principle of this guest-host type liquid crystal display system is that the dichroic dye molecules which are guests are oriented and arranged according to the arrangement of the liquid crystal molecules which are hosts. That is, when an external stimulus, which is usually an electric field, is applied, 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 the alignment direction. Based on the principle that the degree of light absorption by the dye molecules in both states changes, and display is performed.

Recently, an element in which this liquid crystal display system is applied to PDLC, that is, a system in which a liquid crystal layer is enclosed in a polymer matrix and sandwiched between plastic sheets with electrodes for display, has been put into practical use. The method of adding and using a dichroic dye in the liquid crystal composition used here is
It has proved to be a very advantageous method for the purpose of increasing the contrast.

[0006] PDLC is a display method which has received a great deal of attention because it has excellent characteristics such as a large area and a light weight as compared with the conventional device using a glass cell.

[0007]

The dichroic dye used here has sufficient coloring ability with a small amount, exhibits a large contrast, has sufficient compatibility with liquid crystals, and has durability. It is excellent, stable, and does not deteriorate the performance of the device even if it is used for a long period of time, as in the conventional guest-host dichroic dye. The condition that the resin layer, which is the polymer matrix, is not dyed and colored is added.

[0008] The dyed and colored portion remains uncolored because the orientation direction cannot be changed even when a voltage is applied, which causes a decrease in contrast and is a decisive defect in display. In particular, among the compounds developed so far as purple dichroic dyes,
These improvements have been strongly desired because there is no dye capable of satisfying the performance of all of the above conditions.

[0009]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of such a situation, and as a result, satisfy the conditions (1) to (4) required for a guest-host dichroic dye in PDLC, and improve the durability. We have found a new dichroic dye which is excellent, has a large dichroic ratio, and does not dye the matrix resin layer. That is, the present invention provides a liquid crystal dye of the general formula
(1) (Chemical formula 2)

[0010]

[Chemical 2]

[Wherein R ¹ is an alkyl group which may have a substituent, an alkoxy group which may have a substituent,
A halogen atom or a hydrogen atom, R ² and R ³ are
It represents a hydrogen atom, a halogen atom, a methyl group, an ethyl group, a methoxy group or an ethoxy group, which may be the same or different. ] A dichroic dye for liquid crystal addition represented by

The feature of the dichroic dye of the present invention is that P-substituted azobenzene is introduced into the 2- and 3-positions of the anthraquinone skeleton, which makes the dichroic dye more dichroic than the similar known anthraquinone dichroic dye. The properties, durability and colorability of the resin are remarkably improved.

The dye for liquid crystal according to the present invention is represented by the general formula (1). Specific examples of R ¹ in the general formula (1) include an alkyl group such as a methyl group, an ethyl group and a propyl group. , Butyl group, pentyl group, hexyl group,
As a heptyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, an isopropyl group, an isobutyl group, a tert-butyl group, a cyclohexyl group, a 3,5-dimethylhexyl group, and an alkoxy group, a methoxy group, an ethoxy group,
Examples of the propyloxy group, butyloxy group, hexyloxy group, cyclohexyloxy group, isobutyloxy group, heptyloxy group, dodecyloxy group and halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

Specific examples of R ² and R ³ include hydrogen atom, fluorine atom, chlorine atom, bromine atom, iodine atom, methyl group, ethyl group, methoxy group and ethoxy group.

The dichroic dye of the general formula (1) of the present invention can be easily synthesized by a conventional method. That is, for example, halogen-substituted 1,4 represented by the general formula (2) (chemical formula 3)
A diaminoanthraquinone compound and a 4-hydroxyazobenzene compound represented by the general formula (3)
The compound of the general formula (1) can be obtained by reacting in a polar organic solvent such as dimethylformamide, dimethylsulfoxide or sulfolane in the presence of a base such as potassium carbonate or potassium hydroxide.

[0016]

[Chemical 3]

[0017]

[Chemical 4] Wherein, R ^1, R ² and R ³ have the general formula (1) of R ^1, R
^The same substituents as ² and R ³ are shown. ]

The crude dye of the general formula (1) thus obtained can be purified by recrystallization, column chromatography or the like to obtain a highly pure dye.

The dichroic dye of the present invention can be contained in a liquid crystal and used in a display device which is usually used as a liquid crystal composition for color display.

The liquid crystal used is, for example, 4-cyano-4'-n-pentylbiphenyl, 4-cyano-4'-.
Cyano-biphenyl liquid crystal such as n-propoxybiphenyl, 4-cyano-4'-n-pentoxybiphenyl, 4-cyano-4'-n-octoxybiphenyl, 4-cyano-4'-n-pentylterphenyl Mixture (for example, Merck company code E-8) or trans-4
-N-propyl- (4-cyanophenyl) -cyclohexane, trans-4-n-pentyl- (4-cyanophenyl) -cyclohexane, trans-4-n-heptyl- (4-cyanophenyl) -cyclohexane, trans- A cyclohexane-based liquid crystal mixture such as 4-n-pentyl- (4′-cyanobiphenyl) -cyclohexane (for example, product code ZLI-1132, ZLI-18 manufactured by Merck & Co., Inc.).
40) and the like.

Further, in a state in which no electric field is applied, in which an optically active substance such as cholesteryl nonanoate or optically active 4-cyano-4'-isopentylbiphenyl is added to the liquid crystal mixture, it is in a cholesteric phase state and in an electric field applied state. It is also possible to use so-called chiral nematic liquid crystal mixtures which undergo a phase transition to the nematic phase state.

The liquid crystal is not limited to the above examples, but other biphenyl liquid crystals, phenylcyclohexane liquid crystals, Schiff base liquid crystals, ester liquid crystals,
Pyrimidine-based liquid crystals, tetrazine-based liquid crystals, and other liquid crystals can be used alone or as a mixture.

The dye according to the present invention may be used alone or in combination of two or more. The dye concentration used is within the limit that the dye dissolves in the liquid crystal,
Moreover, the dye molecules may be within the range in which the alignment can be sufficiently controlled by the alignment of the liquid crystal molecules, but in general, 0.
It may be used in a concentration of 1 to 10% by weight, preferably 0.1 to 5% by weight.

It is also possible to mix the dichroic dye according to the present invention with another dichroic dye or a dye having no dichroism and use it as a desired hue, without any limitation. The dichroic dye is dissolved in the liquid crystal by mixing a predetermined amount of the dye with the liquid crystal and stirring the mixture for a long time, or by heating the liquid crystal to a temperature at which the liquid crystal becomes an isotropic liquid or more and stirring the mixture to obtain a desired color. It can be a liquid crystal composition for display.

[0025]

Although various dichroic dyes used in conventional PDLC have been proposed, they are dyed with a resin film layer as a base to cause a decrease in contrast or have a low dichroic ratio. It has drawbacks such as not being able to display a clear image practically and lacking in durability. However, the dichroic dye of the present invention represented by the general formula (1) has a low dyeing property with respect to a resin film, has a large dichroic ratio, and has high durability, and thus the dye is extremely valuable in practical use. It is a pigment.

[0026]

EXAMPLES Hereinafter, synthesis examples of the dichroic dye of the present invention are shown,
Next, Table 1 shows the structures of typical dyes, liquid crystal E- manufactured by Merck & Co., Inc.
The dichroic ratio and maximum absorption wavelength in 44 are shown.

The dichroic ratio shown in Table 1 is 2.0% by weight for each dye.
Was dissolved in a liquid crystal (product number E-44) manufactured by Merck Ltd., which is a typical nematic liquid crystal, and sealed in a liquid crystal cell having a thickness of 10 μm that had been previously treated for homogeneous alignment, and then placed in the optical path of a spectrophotometer. The absorbance (A‖) measured by applying a linearly polarized light parallel to the array and the absorbance (A⊥) measured by applying a linearly polarized light orthogonal to the liquid crystal array,
It is calculated from the following equation (Equation 1).

[0028]

[Equation 1]

Each of the dichroic dyes of the present invention showed an extremely high dichroic ratio and was a compound having no matrix resin dyeing property in PDLC. In addition, "part" in an Example shows a weight part.

Example 1 4-Hydroxy-4'-octylazobenzene 8.3
Parts, 1,4-diamino-2,3-dichloroanthraquinone (3.1 parts) and potassium carbonate (3.6 parts) were placed in 50 parts of DMF, and reacted at 120 ° C. for 10 hours under a nitrogen atmosphere. After cooling, it was discharged into 30 parts of water, filtered, washed with water and dried.
5 parts of crude product are obtained. This was purified by silica gel column chromatography (developed with toluene) to obtain 3.0 parts (yield 35%) of a dye of the following formula (4) (formula 5) (dye number 2 in Table 1).

[0031]

[Chemical 5]

Next, in a small beaker, a liquid crystal (E-
44) To 100 parts of the above, 1.5 parts of the above dye was added, and the mixture was heated with stirring at about 80 ° C. to obtain a completely clear solution. Then, after the contents were left to cool, the colored liquid crystal was sealed in the liquid crystal display element under reduced pressure. This display device exhibited a red color when no voltage was applied, and became colorless only when the voltage was applied, showing good contrast.

The dichroic ratio of this purified dye was 12.3 at the maximum absorption wavelength of 584 nm. In a 200-hour light resistance test using a sunshine weather meter, changes in absorption spectrum and dichroic ratio were within 1%, which was a good result.

A liquid crystal (E-
44) 40 parts, water 16 parts, PVA 20/30 (trade name manufactured by Airco) 3.7 parts, GANTRES 169 (polymethyl vinyl ether / maleic anhydride copolymer manufactured by GAF)
0.2 parts and 0.1 part of glycerin were mixed and vigorously stirred with a homogenizer to form an emulsion.

The produced emulsion was previously indium
It was coated to a thickness of 0.5 mm on a Mylar film on which tin oxide (ITO) had been vapor deposited. The film thus obtained was placed on another Mylar film coated with ITO, and 10
It was left in a dryer at 0 ° C. for 1 hour. Furthermore, after cooling to room temperature, activation with a DC voltage of 100 V gave an opaque blue liquid crystal film.

When an AC voltage of 60 Hz and 100 V was applied to this liquid crystal film, it changed from purple to colorless and good contrast was obtained. Furthermore, after leaving this film display panel at room temperature for 2 weeks, it was put in acetone, the liquid crystal layer was extracted, and only the matrix resin film was examined, and when the dyeability of the resin with the dye was examined, no coloring was observed at all, It showed good results.

Example 2 4-hydroxy-4'-octylazobenzene was used in place of 4-hydroxy-4'-octylazobenzene used in Example 1, and the reaction was carried out in exactly the same manner.
By purification, a dye of the following formula (5) (Chemical Formula 6) (Dye No. 14 in Table 2) was obtained. The dichroic ratio of this dye has a maximum absorption wavelength of 586 nm.
Shows a good value of 12.4, and PDLC also obtained a good result as described above.

[0038]

[Chemical 6]

Examples 3 to 43 The structures of the dyes (compounds of dye numbers 3 to 23 in Tables 1 and 2) obtained in the same manner as above and the dichroic ratios are summarized in Tables 1 to 1.
2 shows.

Tables 1 and 2 also show the results of observing the matrix resin dyeability in PDLC in the same manner as in Example 1. The positions of the substituents in the table are shown according to the following general formula (6) (Chemical formula 7).

[0041]

[Chemical 7]

[0042]

[Table 1]

[0043]

[Table 2]

Claims (1)

[Claims] 1. General formula (1) (Chemical formula 1) [In the formula, R ¹ is an alkyl group which may have a substituent,
An alkoxy group which may have a substituent, a halogen atom or a hydrogen atom, R ² and R ³ represent a hydrogen atom, a halogen atom, a methyl group, an ethyl group, a methoxy group or an ethoxy group, which are the same or different from each other; May be different. ] The dichroic dye for liquid crystal addition represented by.