JPH0212272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal composition which has a large negative dielectric anisotropy and whose alignment can be controlled at low voltage. More specifically, the present invention relates to a liquid crystal composition with a low driving voltage, in which an additive having a polar group is added to an ester-based liquid crystal with a low polarity, and a large amount of a poorly soluble component with a large negative dielectric anisotropy is dissolved. Conventionally, ester compounds shown in the following formula are typical as liquid crystalline substances with negative dielectric anisotropy Δε. (However, R ₁ to _{R 4} represent an alkyl group.) These themselves have a dielectric anisotropy of about −1, and the voltage required for switching the orientation is as high as about 6 to 8 V. Therefore, including non-liquid crystal substances,
By adding a large amount of a compound with a large negative Δε, it is possible to lower the voltage. Table 1 shows the main additives. Among these, the ones with large |△ε| It is a type of compound. However, ester-based liquid crystals with low polarity have
These only melt by a few percent even at room temperature, so
It was very impractical. A feature of the present invention is that an additive having a polarity intermediate between that of the solute and the solvent is added in order to improve the solubility of a compound having excellent dielectric properties. The present invention will be explained below based on Examples. Table 2 is

[Formula] shows the effect of additives on the solubility of type compounds. However, the composition of the base liquid crystal is shown in Table 3.

【table】

【table】

【table】

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【table】

[Table] As is clear from Table 2, most of the compounds Nos. 5 to 10 in Table 3 precipitate in the systems with low polarity No. 1 and No. 2, but As shown in .4, although it is not a liquid crystal by itself and |Δε| is small, by adding a compound having a polar group in the molecule, a remarkable improvement in solubility can be seen. As a result, it has a large negative △ε, and the switching voltage when used in display elements is 3 to 3, which is comparable to that of normally used positive liquid crystals.
A 4.5V drive version was obtained. In addition, such effects are not inhibited by the presence of other substances, as shown in Table 2.
From the comparison between No. 2 and No. 4, it is possible to add a large amount of a material with small polarity and low viscosity, such as PCH-negative, and as a result, a high-speed response is possible. This is the most promising application for negative liquid crystals.
It consists of a rod-like structure as shown in Table 4, and a dichroic dye with different absorption spectra in the long axis direction and short axis direction of the molecule is dissolved, sandwiched between opposing electrodes, and displayed by applying and removing voltage. There is a guest/host (G/H) effect. FIG. 1 shows a sectional view of the structure of the display cell. The inner surfaces of the glass supports 3 and 4 having opposite transparent electrodes 1 and 2 are covered with vertical alignment films 5 and 6 such as organic chromium complexes. Therefore, in the peripheral area 9 where no voltage is applied, the liquid crystal molecules are aligned perpendicular to the substrate surface, and in the voltage application area 10, because Δε<0, they are subjected to torque by the electric field and take an alignment structure parallel to the substrate surface. Display is performed using the difference in light absorption between these two states.

[Table] FIG. 2 shows the relationship between the applied voltage (horizontal axis) and transmittance (vertical axis) of such a display cell. When the voltage is increased from state 11 with high transmittance, it passes through a clear threshold value Vth and transitions to colored state 12. 12
saturation is slow and is not complete even if the voltage is increased considerably. The drive voltage required for display is expected to be at least twice Vth. Table 5 shows the voltage and response characteristics of compositions according to the invention. In actual use, optically active substances or cholesteric liquid crystals are added to these liquid crystals to prevent domains from appearing when voltage is applied. Addition of an optically active substance or the like has a substantial effect of lowering the voltage, and as shown by the broken line 13 in FIG. 2, the fall of Vth when it begins to fall becomes more rapid. Figure 3 shows the change in Vth when optically active substances are added to these liquid crystals. The horizontal axis shows the amount added. In this state, the critical concentration of Co is a critical value at which the cholesteric twisting force is so strong that the molecules cannot maintain vertical orientation from the beginning. Therefore, sufficient 3V drive is possible by adding an appropriate amount of optical activity. Table 6 illustrates representative optically active species. (however,
L and R indicate that when added to a nematic liquid crystal, it takes a levorotatory or dextrorotatory helical structure. )

【table】 As explained above, according to the present invention, The general formula is

A compound having a predetermined alkyl group represented by [Formula] and a compound whose general formula is

A predetermined compound represented by [Formula] is used as a base liquid crystal composition; or By adding these, it is possible to provide a liquid crystal composition that has excellent solubility of the liquid crystal compound and is capable of high-speed response and low-voltage driving. The positive type display, which can be driven in bright colors against a bright background, can be widely used in watches, clocks, and other small information devices.

【table】 [Brief explanation of drawings]

FIG. 1 shows the configuration of a display cell using the G.H effect. 1, 2...Transparent electrode, 3, 4...Glass plate,
5, 6... Vertical alignment film, 7, 8... Spacer,
9...Peripheral area, 10...Lighting area. FIG. 2 shows the voltage dependence of the light transmittance of a positive GH cell. 11...Non-lit state, 12...Lighted state, 13
...A state in which an optically active substance is added. FIG. 3 shows the dependence of the threshold voltage Vth on the amount of optically active additive.

Claims (1)

[Claims] 1. The general formula or chemical formula is A liquid crystal composition consisting of a compound represented by the general formula A compound represented by or whose chemical formula is and A liquid crystal composition comprising a compound represented by: (However, R ₁ is a straight chain alkyl group having 3 to 5 carbon atoms,
R ₂ is an alkyl group with 1 or 2 carbon atoms or a linear alkyl group with 4 carbon atoms, R ₃ and R ₄ are linear alkyl groups with 4, 5, or 7 carbon atoms, and R ₅ and R ₆ are linear alkyl groups with 4 or 5 carbon atoms. It represents a straight chain alkyl group, and X and Y represent Cl or CN. )