JPH09202881A - Dichroic dye for liquid crystal, liquid crystal composition and liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dichroic pigment for liquid crystal which is prepared by purifying a dichroic pigment for liquid crystal through contact of the pigment with a basic alumina, thus has high electric resistance and is useful as a liquid crystal element of high voltage retention for a high-contrast display element of an active matrix driving type. SOLUTION: (A) A dichroic pigment such as an azo pigment of formula I (R, R' and R" are each an alkyl, an alkoxy, cyano, a halogen) or an anthraquinone pigment of formula II is brought into contact with (B) a basic alumina (for example, of ph>=9 and 100-300 mesh particle size to purify the pigment. The component B is used preferably in an mount of 0.01-50 pts.wt., particularly 0.1-10 pts.wt. per 1 pt.wt. of the component A. In an embodiment, the component A is dissolved in a solvent, the solution is passed through a column filled with the alumina of component B, the eluate is evaporated to remove the solvent and crystallized out or by other purification process to isolate the purified component A.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dichroic dye for liquid crystals having high electric resistance, a liquid crystal composition containing the same, and a liquid crystal device using the liquid crystal composition.

[0002]

2. Description of the Related Art At present, as a liquid crystal display, a twist nematic (TN) type display mode and a super twist (ST) are used.
N) In addition to the modes, various display modes have been proposed. A guest-host (GH) type display system (hereinafter, abbreviated as "GH mode") in which a dichroic dye is dissolved in liquid crystal has a wide viewing angle and the like, and is therefore a display panel of an automobile or the like. Is widely used as. Conventionally, a simple matrix driving method has been mainly used as a driving method for these liquid crystal displays, but in recent years, an active matrix driving method using a thin film transistor (TFT) or the like that can obtain high image quality is widely used. Is starting to appear.

As the dichroic dyes used in the GH mode, many dyes such as anthraquinone dyes, azo dyes, quinophthalone dyes, and perylene dyes are known. These dichroic dyes are known. Usually, it is used by sufficiently purifying it before it is used in a liquid crystal composition. As a method for purifying this dichroic dye, a method by recrystallization or silica gel (Japanese Unexamined Patent Publication (Kokai) No. Sho 6-96) is used.
No. 2-138584) or a method by chromatography using an adsorbent such as neutral alumina (see Japanese Patent Publication No. 63-503073).

[0004]

When a voltage is applied to a liquid crystal element, a liquid crystal material or liquid crystal composition for liquid crystal display will generate a large amount of current if the liquid crystal material or liquid crystal composition has a low electric resistance, and heat or Since an unfavorable phenomenon such as electrolysis of the liquid crystal substance or the liquid crystal composition occurs, high electric resistance is required.

Particularly, in the active matrix driving method, it is necessary to hold the voltage holding ratio of the liquid crystal element at a high rate of generally 95% or more until the voltage is applied again after the voltage is applied to the scanning electrodes. The electric resistivity of the liquid crystal substance or the liquid crystal composition required in the conventional simple matrix driving method was in the range of 1E10 to 1E12 Ω · cm, whereas recently, the higher electric resistance of 1E12 to 1E14 Ω · cm was obtained. Are becoming required.

As described above, the liquid crystal substance or liquid crystal composition is
Since the liquid crystal composition is required to have a high electric resistance, when the liquid crystal composition is in the GH mode, the dichroic dye to be used is also required to have a high electric resistance. Most of the organic dyes have a low electric resistance, and the liquid crystal composition using such a dichroic dye has a drawback that the electric resistance is lower than that of a liquid crystal substance alone.
(See Coloring Material, 61, p. 229, (1988)) This has been a major limitation in using a GH mode liquid crystal composition in an active matrix driving method which requires particularly high electric resistance. .

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to a liquid crystal dichroic dye having a high electric resistance, which is obtained by bringing a dichroic dye for liquid crystal into contact with basic alumina, and a liquid crystal substance to contact with basic alumina. The present invention provides a liquid crystal composition containing the thus-purified dichroic dye for liquid crystal, and a liquid crystal element using the liquid crystal composition between a pair of substrates with electrodes, at least one of which is transparent.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The dichroic dye for liquid crystal of the present invention is a dye having a high solubility in a liquid crystal substance and having a high dichroic property, preferably a dye having an order parameter (S) value of 0.7 or more. It is not particularly limited as long as it is, for example, its structure is azo, anthraquinone, quinophthalone, perylene, indigo,
Examples include dyes selected from thioindigo-based, merocyanine-based, styryl-based, azomethine-based, and tetrazine-based dyes, preferably azo-based and anthraquinone-based dyes, and specific examples thereof include dyes shown in Table 1 below. The dichroic dye for liquid crystal of the present invention is obtained by bringing such a dye into contact with basic alumina for purification. Although the above dyes are usually used as a single product for purification, a mixture of a plurality of dyes may be processed.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

In these formulas, R, R ′ and R ″ represent an alkyl group, an alkoxy group, a cyano group and a halogen atom. Examples of the alkyl group include a methyl group, an ethyl group,
1 carbon atom such as propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc.
And 10 to 10 linear or branched alkyl groups. This alkyl group is, for example, an alkoxy group, a hydroxy group, an aryl group such as benzene, a cyclopentyl group, an alicyclic group such as a cyclohexyl group, a halogen atom,
It may be substituted with a cyano group or the like.

Examples of the alkoxy group include those having 1 to 10 carbon atoms such as methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, and busyloxy groups. A linear or branched alkoxy group is exemplified. The alkoxy group may be substituted with, for example, an alkyl group, a hydroxy group, an aryl group such as benzene, an alicyclic group such as a cyclopentyl group or a cyclohexyl group, a halogen atom, a cyano group, or the like.

The basic alumina used in the present invention has a p
It means that H is 8 or more, and preferably pH is 9 or more. Also, purification such as washing with water may be carried out, but the pH
Must not be less than 8. In the present invention, neutral alumina is usually used for chemical reaction and the like from the viewpoint of stability, whereas purification using basic alumina is particularly effective for obtaining a dichroic dye having high electric resistance. It was made by finding suitable.

Further, the basic alumina used in the present invention may have its activity adjusted if necessary.
This activity may be adjusted by a known method, for example, a method described in “Experimental Chemistry Lecture (continued) 2 (Separation and Purification); Chemical Society of Japan (1967); p296” and the like. In addition, this activity represents what was measured by the method of Blockmann. (See, for example, "Introduction Chromatography, Second Edition", Tokyo Doujinsha, issued April 5, 1988. In addition, the basic alumina is usually 100 to 300 mesh particle size in view of operability and contact area. To be

If the amount of basic alumina used is too small, the effect is not sufficient, and conversely, if it is too large, it is not preferable in terms of cost. It is 50 parts by weight, preferably 0.1 to 10 parts by weight. As a specific purification method, any method may be used as long as it can effectively contact the dichroic dye and the basic alumina, but usually, the dichroic dye is dissolved in a suitable solvent, and the base is added thereto. Basic alumina added, stirred and filtered, or a column packed with basic alumina,
It is achieved by passing the solution of the dichroic dye through a filter having a basic alumina layer in which basic alumina is spread on a filter cloth. Of these, column usage is particularly preferable. Separation of the dichroic dye from the solution in contact with the basic alumina is usually simple by means of solvent distillation, crystallization by addition of a poor solvent, cooling crystallization, or the like.

The solvent may be any solvent which dissolves the dichroic dye and is stable with respect to the basic alumina used,
For example, aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and octane,
Halogenated hydrocarbons such as methylene chloride, chloroform, dichloroethane, chlorobenzene and dichlorobenzene, ethers such as diethyl ether and dibutyl ether.
Esters such as tellers, ethyl acetate, butyl acetate,
Alcohols such as butanol and amyl alcohol,
Examples include ketones such as methyl propyl ketone and methyl butyl ketone. Of these, toluene,
Xylene, methylene chloride, chloroform and the like. These solvents may be used alone or in combination. The amount of the solvent used is not particularly limited as long as it can dissolve the dichroic dye, but if the amount is too small, the dye may precipitate during the operation, which is not preferable. Further, if it is too large, it is disadvantageous in terms of cost. Therefore, it is usually used in an amount such that the solubility of the dye is in the range of 95 to 5%, preferably 90 to 20% of the saturated solubility.

The purification of the present invention may be carried out in combination with other purification methods such as recrystallization or chromatography with another adsorbent. The liquid crystal composition of the present invention is obtained by purifying a high-electric-resistance dichroic dye for liquid crystal obtained by the above-mentioned method, in "Liquid Crystal Device Handbook; Japan Society for the Promotion of Science, 142nd Ed. (1989); p154-192. , P7
15-722 ”and various liquid crystal compounds (liquid crystal substances) such as biphenyl, phenylcyclohexane, phenylpyrimidine, cyclohexylcyclohexane, etc. exhibiting a nematic or smectic phase or a liquid crystal composition are mixed by a known method. , Can be easily prepared by dissolving. Preferred liquid crystal compounds used in the present invention are shown in Table 2 below.

[0019]

[Table 4]

(Wherein V and W are respectively an alkyl group, an alkoxy group, an alkoxyalkyl group, an alkylphenyl group, an alkoxyalkylphenyl group, an alkoxyphenyl group, an alkylcyclohexyl group, an alkoxyalkylcyclohexyl group, an alkylcyclohexylphenyl group, Cyanophenyl group, cyano group, halogen atom,
Represents a fluoromethyl group, a fluoromethoxy group, an alkylphenylalkyl group, an alkoxyphenylalkyl group, an alkylcyclohexylalkyl group, an alkoxyalkoxycyclohexylalkyl group, an alkoxyphenylalkyl group, or an alkylcyclohexylphenylalkyl group; It may have an optically active center. Y represents a hydrogen atom, a halogen atom or a cyano group, and the phenyl group or phenoxy group in V and W may be further substituted with a halogen atom such as a cyano group, a fluorine atom and a chlorine atom. Further, the phenyl group in each of the above structural formulas is 1 to 4
It may be further substituted with a halogen atom such as a fluorine atom and a chlorine atom, and a cyano group. )

Recently, instead of the conventional liquid crystal compound containing a cyano group, a so-called fluorine-based liquid crystal compound having a substituent such as a fluorine atom or a fluorine atom-containing group such as —F, —CF ₃ , and —OCF _{3 has been} developed. , Especially TFT / LCD
It is suitable for (thin film transistor type liquid crystal display) and the like, and these fluorine-based liquid crystal compounds are also preferably used for the liquid crystal composition of the present invention.

The liquid crystal composition of the present invention is mixed with an optically active compound such as cholesteryl nonanoate and a liquid crystal phase, or almost no liquid crystal phase. It may contain a substance capable of changing the temperature range shown), or may contain various additives such as an ultraviolet absorber and an antioxidant.

By sandwiching the liquid crystal composition thus obtained between a pair of substrates having electrodes, at least one of which is transparent, an element applying the guest-host effect (Shouichi Matsumoto, Ichio Kakuda, “ "Latest LCD technology" published by Industrial Research Council,
34 (1983), and J. L. Fergason,
SID 85 Digest, 68 (1985), etc.) and the like.

Examples of the electrode substrate used in the present invention include glass plates and various synthetic resin plates such as acrylic resin, polycarbonate resin, and epoxy resin. At least one of the pair of substrates is transparent. is required. An electrode layer is formed on the substrate, and as the electrode layer, one made of a metal oxide such as indium oxide, indium tin oxide (ITO), tin oxide is usually used.

The surface of the electrode layer which is in contact with the liquid crystal is preferably subjected to an alignment treatment if necessary. Examples of the orientation treatment method include a method of applying octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, hexadecyltrimethylammonium bromide and the like for vertical orientation, a method of applying polyimide for parallel orientation, and a cotton cloth. A method of rubbing with absorbent cotton or the like for parallel alignment, a method of vapor-depositing SiO _x from an oblique angle for parallel alignment, and the like are appropriately used. Specifically, transparent electrodes of an arbitrary pattern are provided on a pair of glass substrates, one of which is transparent, by the above-mentioned method, respectively, and an appropriate spacer is interposed so that the electrode surfaces face each other. Then, a device in which an element (cell) is configured such that a pair of glass substrates are parallel to each other is used. In this case, the spacer determines the gap (space) of the device. This element gap is 1 to 50
[mu] m, particularly 1 to 20 [mu] m is preferable from a practical viewpoint. Then, the liquid crystal composition is enclosed in this space to form the liquid crystal element of the present invention.

[0026]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited by the following examples unless it exceeds the gist. The measurement of the specific resistance and the voltage holding ratio of the liquid crystal composition in this example and the comparative example was performed as follows.

The specific resistance was measured by adding 1 ml of the liquid crystal composition to a liquid electrode (trade name: LE-21) manufactured by Ando Electric Co., Ltd., and using an electrometer 6 manufactured by KEITHLEY.
The current value when DC 10 V was applied was measured at 25 ° C. with a No. 17 type, and the specific resistance was calculated. The voltage holding ratio is measured by a cell having a gap of 9 μm, which is formed by aligning two liquid crystal composition-coated glass substrates with a transparent electrode, which are coated with a polyimide resin, cured, and rubbed so that the liquid crystals are aligned in parallel. And then apply a pulse of DC5V, 60μs,
The voltage after 7.6 ms was measured at 70 ° C., and the voltage holding ratio was calculated.

The basic alumina used is the same as the basic activated alumina manufactured by Wako Pure Chemical Industries, Ltd., which has an activity I.
Alternatively, the alumina can be treated as “New Experimental Chemistry Course 1 (Basic Operation I);
According to the method described in "The Chemical Society of Japan (1975); p343", water was added to adjust the activity to II and used. [Example 1] Anthraquinone-based dichroic dye represented by the following structural formula

[0029]

Embedded image

3.00 g of basic alumina 1 having activity I
After performing column chromatography using 0 g as a carrier and toluene as a separation solvent, the eluted toluene solution was distilled off under reduced pressure until the volume became 20 ml. 70 g of methanol was added to this solution, and the precipitated crystals were filtered, washed with methanol and dried to obtain 2.41 g of a purified product. This purified product was dissolved in a fluorine-based liquid crystal mixture marketed under the trade name ZLI-4792 (manufactured by E. MERCK) at a concentration of 3% by weight to prepare a guest-host liquid crystal composition, and its specific resistance was measured. As a result, 7.5E12Ω · cm (25 ° C, DC
10 V was applied).

The voltage holding ratio of this guest-host liquid crystal composition was measured and found to be 97.9% (70 ° C., DC5
The retention rate was 17.6 ms after application of V and 60 μs. In the same manner, this purified product was traded under the trade name ZLI-1840.
A guest-host liquid crystal composition was prepared by dissolving it in a cyano liquid crystal mixture commercially available as E. MERCK at a concentration of 3% by weight, and the specific resistance and voltage holding ratio were measured. It was 2E11 Ω · cm and the voltage holding ratio was 50%.

Example 2 The same procedure as in Example 1 was carried out except that the basic alumina used had an activity of II, to obtain 2.49 g of a purified product. The purified product obtained was dissolved in a fluorine-based liquid crystal mixture ZLI-4792 at a concentration of 3% by weight to prepare a guest-host liquid crystal composition, and the specific resistance and voltage holding ratio were measured in the same manner as in Example 1, The specific resistance was 8.3E12 Ω · cm and the voltage holding ratio was 98.0%. [Example 3] Azo dichroic dye represented by the following structural formula

[0033]

Embedded image

3.00 g of basic alumina 1 having activity I
After performing column chromatography using 0 g of the carrier as the separating solvent and chloroform, the eluted chloroform solution was distilled off under reduced pressure to 7 ml. To this solution, 20 g of methanol was added, and the precipitated crystals were filtered to remove methanol.
After washing and drying, 2.51 g of a purified product was obtained. The obtained purified product was added to a fluorine-based liquid crystal mixture ZLI-4792 at 3% by weight.
To prepare a guest-host liquid crystal composition by dissolving at a concentration of
The specific resistance and the voltage holding ratio were measured in the same manner as in Example 1. As a result, the specific resistance was 6.6E12 Ω · cm and the voltage holding ratio was 97.1.
%Met.

[Comparative Example 1] The same procedure as in Example 1 was carried out except that neutral alumina (Activity I manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the basic alumina.
I got The obtained purified product is used as a fluorine-based liquid crystal mixture ZLI-
A guest-host liquid crystal composition was prepared by dissolving it in 4792 at a concentration of 3% by weight, and the specific resistance and the voltage holding ratio were measured in the same manner as in Example 1. As a result, the specific resistance was 1.1E12 Ω · cm.
The voltage holding ratio was 95.0%. Similarly, this purified product was dissolved in a cyano liquid crystal mixture ZLI-1840 at a concentration of 3% by weight to prepare a guest-host liquid crystal composition, and the specific resistance and voltage holding ratio were measured. As a result, the specific resistance was 6.9E10Ω.
-Cm, voltage holding ratio was 31%.

Comparative Example 2 2.53 g of a purified product was obtained by the same procedure as in Example 1 except that acidic alumina (Activity I manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of basic alumina.
I got The obtained purified product is used as a fluorine-based liquid crystal mixture ZLI-
A guest-host liquid crystal composition was prepared by dissolving it in 4792 at a concentration of 3% by weight, and the specific resistance and the voltage holding ratio were measured in the same manner as in Example 1. As a result, the specific resistance was 8.5E11 Ω · cm.
The voltage holding ratio was 93.8%.

[Comparative Example 3] The same operation as in Example 1 was carried out except that silica gel (Wakogel C-200; manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the basic alumina to obtain 2.40 g of a purified product. It was The purified product obtained was dissolved in a fluorine-based liquid crystal mixture ZLI-4792 at a concentration of 3% by weight to prepare a guest-host liquid crystal composition, and the specific resistance and voltage holding ratio were measured in the same manner as in Example 1, Specific resistance 8.
It was 2E11 Ω · cm and the voltage holding ratio was 92.5%.

[Comparative Example 4] The same procedure as in Example 3 was carried out except that neutral alumina (Activity I manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the basic alumina.
I got The obtained purified product is used as a fluorine-based liquid crystal mixture ZLI-
A guest-host liquid crystal composition was prepared by dissolving it in 4792 at a concentration of 3% by weight, and the specific resistance and voltage holding ratio were measured in the same manner as in Example 1. As a result, the specific resistance was 6.5E11 Ω · cm.
The voltage holding ratio was 93.0%.

[0039]

The dichroic dye having a high electric resistance of the present invention and the liquid crystal composition containing the dichroic dye are used for a display element or the like driven by an active matrix excellent in contrast.
A liquid crystal element having a high voltage holding ratio can be obtained.

Claims (3)

[Claims] 1. A dichroic dye for liquid crystals, which is purified by bringing the dichroic dye for liquid crystals into contact with basic alumina. 2. A liquid crystal composition containing a liquid crystal substance and a dichroic dye for liquid crystals purified by contacting with basic alumina. 3. A liquid crystal device comprising a pair of substrates with electrodes, at least one of which is transparent, and a liquid crystal composition containing a liquid crystal substance and a dichroic dye for liquid crystals purified by contacting with basic alumina. .