JP2000086590A - Ester compound and liquid crystal composition containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ester compound capable of raising a nematic isotropic phase transition temperature (hereafter referred to as N-I point) of a liquid crystal composition and lowering a threshold voltage Vth. SOLUTION: This ester compound is shown by formula I (R is an alkyl) such as a compound of formula II. The compound of formula I can be obtained, for example, by treating a carboxylic acid of formula III with a halogenating agent such as thionyl chloride, phosphorus pentoxide, etc., to give an acid chloride, then reacting the acid chloride with a substituted phenol of formula IV in an inert organic solvent such as pyridine, etc., washing the reaction mixture with water, drying and recrystallizing the mixture. At least one kind of the compound of formula I is mixed with a liquid crystal composition to raise the N-I point of the liquid crystal composition and to lower a threshold voltage Vth. Consequently a liquid crystal display apparatus having excellent characteristics as a liquid crystal material, a wide temperature range and a wide angle of visibility can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ester compound useful as a liquid crystal material, and more particularly to a liquid crystal composition containing the ester compound and a liquid crystal display device using the liquid crystal composition containing the ester compound. .

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used in clocks, calculators, word processors, televisions, and the like. Among these liquid crystal display devices, a liquid crystal display device that utilizes the optical anisotropy and the dielectric anisotropy of a liquid crystal material is particularly frequently used.

The characteristics required of a liquid crystal material used in a liquid crystal display device include a wide liquid crystal temperature range, a small viscosity for obtaining a high response speed electro-optically, a wide viewing angle range, and a high contrast. It is necessary to have an appropriate birefringence (△ n) for obtaining the same, to have a large dielectric anisotropy (△ ε) for obtaining a low driving voltage, and to be chemically and optically stable.

Conventionally, liquid crystal compositions that are practically used are usually prepared by mixing a compound having a liquid crystal phase near room temperature and a compound having a liquid crystal phase in a temperature range higher than room temperature. -40 ° C for liquid crystal display to be usable outdoors
It must exist stably in the temperature range of up to 90 ° C., and considering the temperature dependence of the dielectric anisotropy and the refractive index anisotropy, near the NI point (nematic-isotropic phase transition temperature). Since a rapid change occurs, a liquid crystal material having a high NI point is required.

The drive voltage depends on the value of the threshold voltage Vth, and the threshold voltage Vth is inversely proportional to the square root of the dielectric anisotropy Δε. Therefore, when a liquid crystal material having a positive dielectric anisotropy Δ △ is used, the threshold voltage Vth can be suppressed to a low value.

Until now, various liquid crystal compounds have been developed,
Although used, a single liquid crystal compound that satisfies all the above characteristics has not been found yet. For this reason, at present, several kinds of liquid crystal compounds having various characteristics are mixed or non-liquid crystal compounds are mixed and put to practical use, but it is still not satisfactory.

Among the ester compounds used in such a mixture, 4- (4-alkylcyclohexyl) benzoic acid- (4-fluorophenol) -ester is disclosed in Japanese Patent Application Nos. 38652,
4- (4-alkylcyclohexyl) benzoic acid- (3-
Fluoro-4-cyanophenol) -ester was disclosed in Japanese Patent Application No. 57-191963, Japanese Patent Application No. 58-44329, or Japanese Patent Application No. 58-44330, as 4- (4-alkylcyclohexyl) benzoic acid- (3,4, 5-trifluorophenol) -esters are described in Japanese Patent Application No. 01-54150, but none of them is sufficient to satisfy the characteristics.

[0008]

As described above, various studies have been made on liquid crystal compositions, but none of them has been found to be perfect. In addition, the compounds used in the liquid crystal composition each have advantages and disadvantages in characteristics, and further, depending on the liquid crystal display device, the degree of the required characteristics is different, so that a new liquid crystal compound that provides characteristics according to the purpose, The emergence of liquid crystal additives has been awaited.

Accordingly, an object of the present invention is to provide a novel ester compound capable of increasing the NI point of the liquid crystal composition and lowering the threshold voltage Vth by mixing with the liquid crystal composition. That is.

[0010]

Means for Solving the Problems The ester compound of the present invention is represented by the following general formula (I).

[0011]

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(Where R represents an alkyl group)

The liquid crystal composition of the present invention has the general formula (I)
At least one ester compound represented by the formula:

The liquid crystal display of the present invention comprises at least one ester compound represented by the general formula (I):
A liquid crystal display device comprising a liquid crystal composition containing the same.

The amount of the ester compound of the present invention in the liquid crystal composition of the present invention is not determined unconditionally by the type and the mixing ratio of the other liquid crystal compounds. To 50% by weight, more preferably 3 to 20% by weight.

The ester compound of the present invention is an excellent compound capable of increasing the NI point of the liquid crystal composition and lowering the threshold voltage Vth by being mixed with the liquid crystal composition.

Further, the ester compound of the present invention can be mixed with many liquid crystal compounds to produce a liquid crystal composition. Examples of the liquid crystal compound that can be mixed with the ester compound of the present invention include ester compounds, cyclohexylphenyl compounds, biphenyl compounds, pyrimidine compounds, dioxane compounds, and tolan compounds. Further, the ester compound of the present invention can be used by mixing a plurality of these liquid crystal compounds.

As described above, the liquid crystal composition containing the ester compound of the present invention has excellent characteristics as a liquid crystal material, and the liquid crystal display device equipped with this liquid crystal composition has a wide temperature range and a wide visual field. Can have horns.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the ester compound of the present invention is represented by the general formula (I) in Chemical formula 2.

In the general formula (I), R represents an alkyl group.

Further, the liquid crystal composition of the present invention is a liquid crystal composition containing at least one ester compound represented by the aforementioned general formula (I).

Further, the liquid crystal display device of the present invention is a liquid crystal display device equipped with a liquid crystal composition containing at least one kind of the ester compound represented by the above general formula (I).

Next, the method for producing the ester compound of the present invention will be described with reference to Chemical Formula 3 as an example. Note that R in the formula has the meaning described in the general formula (I).

First, thionyl chloride is added to the carboxylic acid (a),
An acid chloride (b) is prepared by the action of a halogenating agent such as phosphorus pentoxide. Next, the acid chloride (b) and the substituted phenol (c) are reacted in an inert organic solvent such as pyridine, and then the reaction mixture is washed with water, dried and recrystallized to obtain a compound represented by the general formula (I). Can be obtained.

[0025]

Embedded image

[0026]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The threshold voltage Vth in this example is a value measured by mounting the liquid crystal composition on a TN type liquid crystal display device having a cell thickness of 9 μm.

Example 1 To 24.6 g of 4-propylcyclohexylbenzoic acid was added 24 g of thionyl chloride, and the mixture was reacted under reflux for 2 hours. After the completion of the reaction, thionyl chloride was distilled off. 19 g of -propylcyclohexyl benzoate were obtained. This was dissolved in 80 ml of toluene, 9.1 g of 3,5-difluorophenol and 8 g of pyridine were added, and the mixture was reacted under reflux for 3 hours. After completion of the reaction, 100 ml of water was added to separate an organic layer, and the mixture was washed with diluted hydrochloric acid and then with a diluted alkali aqueous solution,
After further washing with a saturated saline solution, anhydrous sodium sulfate was added and dried. Next, this organic layer was filtered, and the solvent was distilled off from the filtrate under reduced pressure. The obtained reaction product was recrystallized from toluene to obtain 18 g of a compound described in Chemical Formula 4. This compound had a melting point of 106 ° C. FIG. 1 shows the infrared absorption spectrum of this compound.

[0028]

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Example 2 A liquid crystal composition was prepared by adding 5 parts by weight of the ester compound of the present invention prepared in Example 1 to 95 parts by weight of a commercially available nematic liquid crystal composition ZLI-1132 (manufactured by Merck). .

The liquid crystal composition of Example 2 and ZLI-1
Using a liquid crystal composition consisting of only 132 as a comparative example, the NI point, Δn, viscosity and Vth were measured. The results are shown in the following table.

[0031]

[Table 1]

As is evident from the results, the ester compound of the present invention was able to increase the NI point of the liquid crystal composition containing the same and to lower the threshold voltage Vth.

[0033]

By mixing the ester compound of the present invention with a liquid crystal composition, the NI point of the liquid crystal composition can be raised and the threshold voltage Vth can be lowered. Therefore, the liquid crystal composition containing the ester compound of the present invention has excellent characteristics as a liquid crystal material, and a liquid crystal display device equipped with the liquid crystal composition has a wide temperature range and a wide viewing angle. Furthermore, the ester compound of the present invention has sufficient mutual solubility with various compounds, can be used in combination with many liquid crystal materials as a constituent material of a liquid crystal composition, and is useful for improving characteristics of a liquid crystal composition. It is something.

[Brief description of the drawings]

FIG. 1 is a diagram showing an infrared absorption spectrum of an ester compound of the present invention.

Claims (3)

[Claims] 1. An ester compound represented by the general formula (I). Embedded image (However, R represents an alkyl group.) 2. A liquid crystal composition comprising at least one ester compound according to claim 1. 3. A liquid crystal display device comprising a liquid crystal composition containing at least one ester compound according to claim 1.