JPH0629423B2 - Liquid crystal composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal composition, and more particularly to a liquid crystal composition suitable for use in a liquid crystal device controlled by a dual frequency driving method.

[Conventional technology]

Liquid crystal devices are being applied to televisions, computer terminals, office equipment and the like. A liquid crystal device used in this type of equipment is of a type in which a large number of pixels are arranged in a matrix and the pixels are driven in a time division manner. However, in this type of liquid crystal device, as the number of pixels increases, the number of scanning lines increases, and the number of time divisions increases. Therefore, due to a cross-effect phenomenon or the like, it is possible to sufficiently increase the contrast between illuminated and non-illuminated pixels. Can not. Further, this type of liquid crystal device has a problem that its operation speed is slow when it is applied to a computer terminal, office equipment and the like.

In order to solve such a problem, there is known a two-frequency driving method utilizing a dielectric dispersion phenomenon in which the dielectric anisotropy Δε of liquid crystal depends on the frequency of an applied electric field. In this driving method, a liquid crystal molecular axis is oriented perpendicular to an electric field by applying a high frequency signal voltage to the liquid crystal, and a liquid crystal molecular axis is applied to the electric field by applying a low frequency signal voltage. It is controlled so as to be aligned in parallel. According to this dual frequency drive system, the liquid crystal device can respond at high speed and can be applied to the above-mentioned office equipment.

As a liquid crystal used in a liquid crystal device of this dual frequency driving system, for example, Japanese Patent Application Laid-Open No. 57-83577 discloses a liquid crystal composition containing various liquid crystal compounds.

[Problems to be solved by the invention]

The conventional two-frequency driving liquid crystal material including the liquid crystal composition disclosed in the above-mentioned publication has a still higher driving voltage (for example, 30 V), and the tolerance for the withstand voltage of the semiconductor integrated device forming the driving circuit. There is a problem that
There is a demand for liquid crystal materials that can be driven at lower voltages.
Further, this liquid crystal material has a low response speed (for example, 1 millisecond) and is still unsuitable for a device operating at a high speed such as a computer terminal and office equipment. Furthermore, since the conventional liquid crystal material has a high frequency (crossover frequency fc) when Δε of the liquid crystal becomes 0, it is necessary to particularly increase the frequency of the applied signal on the high frequency side. Since a high frequency signal having a particularly high frequency is applied to a liquid crystal material having a complicated and large dielectric constant, the current flowing between the electrodes of the liquid crystal element increases and there is a problem that heat is generated on the electrode surface.

Therefore, an object of the present invention is to provide a liquid crystal composition which has a low frequency and can be driven by a low voltage signal and has a high response speed.

[Means for solving problems]

To achieve the above object, the liquid crystal composition must have a large Δε or have a low viscosity in order to make a high-speed response at a low voltage. Further, in order to lower the crossover frequency fc, it is necessary to mix liquid crystals having a low crossover frequency fc and being substantially equal to each other, and having a large change width with respect to a low applied electric field, so that the crossover frequency fc does not become high when mixing various liquid crystal materials. There is.

That is, in the present invention, a liquid crystal compound having a low viscosity itself and a good compatibility with other liquid crystal compositions is used as a base, and various liquid crystal compounds are added thereto. The liquid crystal compound as the base has a large dielectric anisotropy,
(Δε is approximately 0 to −1.5), and the dielectric dispersibility may not be exhibited. The liquid crystal compound as the base has the general formula (R ¹ is an alkyl group having 1 to 8 carbon atoms, R ² is an alkyl group or alkoxy group having 1 to 8 carbon atoms), and in the present invention, among these types of liquid crystal compounds, At least one selected liquid crystal compound is used, and this is referred to as a first liquid crystal material. As the first liquid crystal material, it is preferable to select a liquid crystal compound represented by the formula (I) in which R ² is an alkoxy group.

The first liquid crystal material has dielectric dispersibility and cross frequency fc
A liquid crystal compound in which Δε in the lower frequency region fL is positively large and Δε in the high frequency region fH is relatively smaller than the crossover frequency fc (about −1.5) is compounded. This liquid crystal compound imparts dielectric dispersibility to the final liquid crystal composition. (In each formula, R is each independently an alkyl group having 1 to 8 carbon atoms).
In the present invention, among the group consisting of these liquid crystal compounds,
At least one liquid crystal compound is used, and these liquid crystal compounds are referred to as a second liquid crystal material.

Among the liquid crystal compounds used for the second liquid crystal material, the liquid crystal compound shown in (II) has a large variation width of Δε with respect to the frequency change of the applied electric field, so that | Δε | is increased as the liquid crystal composition. It is possible to give the final liquid crystal composition a high-speed response. Further, since this liquid crystal compound has a cross frequency fc substantially equal to that of the other liquid crystal compounds mixed as the second liquid crystal material, and is low, the cross frequency fc of the final liquid crystal composition is also obtained by mixing these liquid crystal compounds.
Never raise.

In addition, the liquid crystal composition of the present invention has a high viscosity (that is, a low crossover frequency fc and a high nematic-isotropic phase transition point (N-I point), so that the temperature exhibiting a liquid crystal phase is pushed to the high temperature side. ), A liquid crystal compound having a large negative Δε, that is, lowering the overall dielectric anisotropy of the final liquid crystal composition to the negative side,
In addition, a liquid crystal compound for lowering the crossover frequency fc is mixed. This type of liquid crystal compound has the general formula (R ¹ and R ³ each independently have 1 to 8 carbon atoms.
And an at least one liquid crystal compound selected from the group consisting of this kind of liquid crystal compound, and is referred to as a third liquid crystal material in the present invention. .

Now, the liquid crystal composition of the present invention may be composed of only the above-mentioned three kinds of liquid crystal materials. Another aspect of the invention is to use the above-mentioned liquid crystal composition for fine adjustment when the viscosity of the liquid crystal composition is too high with only the first to third liquid crystal materials or when the dielectric characteristics are poor. General formula At least one liquid crystal compound selected from the group consisting of liquid crystal compounds of the type represented by (R is an alkyl group having 1 to 8 carbon atoms) is compounded as a fourth liquid crystal material. It is a thing. The fourth liquid crystal material in the present invention does not exhibit dielectric dispersibility, and the liquid crystal compound of the formula (VII) has low viscosity and Δε is about +3. The liquid crystal compound used in the present invention is known per se.

The general mixing ratio of the above four kinds of liquid crystal materials is 30 to 70% of the first liquid crystal material, based on the total weight of the liquid crystal composition.
The second liquid crystal material is 17 to 60%, the third liquid crystal material is 2 to 15%, and the fourth liquid crystal material is 0 to 15%.
Is desirable.

After satisfying the above general blending ratio, the blending ratio of the liquid crystal compound of the formula (I) in the first liquid crystal material is 30 to 7
It is preferably within the range of 0%. The compounding ratio of the liquid crystal compound represented by the formula (VI) of the third liquid crystal material is 2
It is preferably from 15 to 15%.

In the most preferred embodiment of the present invention, the liquid crystal compound represented by the formula (I) has a ratio of 40 to 65%.
The liquid crystal compounds represented by the formula (I), the formula (III), the formula (IV) and the formula (V) are contained in the formula (VI) in a proportion of 17 to 40% in total.
It is desirable that the liquid crystal compound represented by the formula (2) is blended in a proportion of 2 to 15%, and the liquid crystal compound represented by the formula (VII) is blended in a proportion of 0 to 15%.

In this case, the second liquid crystal material contains 2 to 20% of the liquid crystal compound represented by the formula (II), 10 to 20% of the liquid crystal compound represented by the formula (III), and is represented by the (IV). It is optimum that the liquid crystal compound is blended in a proportion of 5 to 20% and the liquid crystal compound represented by the formula (V) is blended in a proportion of 0 to 10%.

The liquid crystal compound represented by the above (I) to formula (VII) is
It is particularly preferable to mix within the following quantitative ranges, provided that the above-mentioned general mixing ratio is satisfied. That is,
Within the range of 20 to 70% of the liquid crystal compound represented by the formula (I), 2 to 20% of the liquid crystal compound represented by the formula (II) is contained.
%, The liquid crystal compound represented by the formula (III) is 10
In the range of 5 to 20%, the liquid crystal compound of the formula (IV) is in the range of 5 to 20%, the liquid crystal compound of the formula (V) is in the range of 0 to 20%, and the liquid crystal compound of the formula (VI) is Within the range of 2 to 15%, the liquid crystal compound represented by the formula (VII)
The liquid crystal compound represented by is within the range of 0 to 15%.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the most preferred embodiments.

The liquid crystal compounds shown in Table 1 were mixed in the proportions shown in the table to prepare four kinds of liquid crystal compositions. Using this liquid crystal composition, a liquid crystal cell was prepared, and a voltage of 25 V was applied at 200 Hz and 10
It was driven at two frequencies of 0 kHz. Table 2 shows Δε and the crossover frequency fc (measurement temperature 25 ° C.) of the liquid crystal composition at this time. The viscosity of each liquid crystal composition (measurement temperature 25 ° C.),
And the NI points are also shown in Table 2. The rise and fall times of each liquid crystal compound are 0.5 milliseconds or less,
None of the liquid crystal compositions were frozen even after standing in a freezer at 0 ° C for 4 days (C-N point 0 ° C or lower).

As shown in Table 2, the liquid crystal composition of this example has a low viscosity, Δε in the low frequency region fL shows a positively large value (that is, Δε in 200 Hz is +4 or more), and the high frequency region fH. Δε at 100 kHz is −1 or less, and the NI point is 110 ° C. or more.

〔The invention's effect〕

The liquid crystal composition of the present invention described above contains at least the liquid crystal compound represented by the formula (II) in the second liquid crystal material, and this liquid crystal compound has a large variation width of Δε with respect to the frequency variation of the applied electric field. , Low viscosity, and crossover frequency fc
Is almost equal to and lower than the crossover frequency fc of other liquid crystal compounds, so that a low voltage of about 20 to 25 V is operated, and a high-speed response with a rise / fall time of 1.5 milliseconds or less is exhibited. Further, the crossover frequency fc is low and the temperature range in which the liquid crystal phase is exhibited is wide.

Therefore, by using the liquid crystal composition of the present invention, it is possible to obtain a liquid crystal element having a wide operating temperature range, a high speed response even by dual frequency driving by a simple driving circuit using a low voltage and a relatively low frequency.

Claims (13)

[Claims] 1. A general formula (R ¹ is an alkyl group having 1 to 8 carbon atoms, and R ² is an alkyl group or alkoxy group having 1 to 8 carbon atoms), a first liquid crystal material comprising at least one liquid crystal compound, and a general formula: (In each formula, R is an alkyl group having 1 to 8 carbon atoms), a second liquid crystal material containing at least three kinds of liquid crystal compounds selected from the group consisting of liquid crystal compounds, and a general formula (R ¹ and R ³ each independently have 1 to 8 carbon atoms.
And a third liquid crystal material comprising at least one kind of liquid crystal compound represented by (alkyl group). 2. The first liquid crystal material is 30 to 70% and the second liquid crystal material is 17 to 6 with respect to the total weight of the liquid crystal composition.
The liquid crystal composition according to claim 1, wherein 0% and the third liquid crystal material are mixed in a ratio of 2 to 15%. 3. The liquid crystal composition according to claim 1, wherein the second liquid crystal material contains a liquid crystal compound represented by the formula (V). 4. The first liquid crystal material is 40 to 65%, and the second liquid crystal material is 17 to 4 with respect to the total weight of the liquid crystal composition.
The liquid crystal composition according to claim 1, wherein the liquid crystal composition is blended at a ratio of 0%. 5. The liquid crystal composition according to claim 4, wherein the second liquid crystal material contains the liquid crystal compound represented by the formula (II) in the range of 2 to 20%. 6. The second liquid crystal material contains the liquid crystal compound represented by the formula (III) within the range of 10 to 20% and the liquid crystal compound represented by the formula (IV) within the range of 5 to 20%. The liquid crystal composition according to claim 5. 7. A liquid crystal compound represented by formula (I) within the range of 30 to 70% and a liquid crystal compound represented by formula (II) within the range of 2 to 20%, represented by formula (III). Within the range of 10 to 20% of the liquid crystal compound and within the range of 5 to 20% of the liquid crystal compound of the formula (IV), the liquid crystal compound of the formula (V)
A liquid crystal compound represented by formula (IV) is compounded within the range of 0 to 20%, and a liquid crystal compound represented by formula (IV) is compounded within the range of 2% to 15%.
Item 6. A liquid crystal composition according to item. 8. General formula (R ¹ is an alkyl group having 1 to 8 carbon atoms, and R ² is an alkyl group or alkoxy group having 1 to 8 carbon atoms), a first liquid crystal material comprising at least one liquid crystal compound, and a general formula: (In each formula, R is an alkyl group having 1 to 8 carbon atoms), a second liquid crystal material containing at least three kinds of liquid crystal compounds selected from the group consisting of liquid crystal compounds, and a general formula (R ¹ and R ³ each independently have 1 to 8 carbon atoms.
A third liquid crystal material comprising at least one kind of liquid crystal compound represented by A liquid crystal composition comprising a fourth liquid crystal material containing at least one kind of liquid crystal compound represented by the formula (R is an alkyl group having 1 to 8 carbon atoms). 9. The first liquid crystal material is 30 to 70% and the second liquid crystal material is 17 to 6 with respect to the total weight of the liquid crystal composition.
9. The liquid crystal composition according to claim 8, wherein 0%, 3 to 15% of the third liquid crystal material, and 15% or less of the fourth liquid crystal material are mixed. 10. A liquid crystal composition, wherein the first liquid crystal material is blended in a proportion of 40 to 65% and the second liquid crystal material is blended in a proportion of 17 to 40% with respect to the total weight of the liquid crystal composition. A liquid crystal composition according to item 9. 11. The liquid crystal composition according to claim 10, wherein the second liquid crystal material contains the liquid crystal compound represented by the formula (II) in the range of 2 to 20%. 12. The second liquid crystal material contains the liquid crystal compound represented by the formula (III) within the range of 10 to 20% and the liquid crystal compound represented by the formula (IV) within the range of 5 to 20%. The liquid crystal composition according to claim 11, wherein 13. A liquid crystal compound represented by formula (I) within the range of 20 to 70%, and a liquid crystal compound represented by formula (II) within the range of 2 to 20%, represented by formula (III). Within the range of 10 to 20% of the liquid crystal compound, within the range of 5 to 20% of the liquid crystal compound represented by the formula (IV), and within the range of 0 to 20% of the liquid crystal compound of the formula (V), A liquid crystal compound represented by the formula (VI) is compounded within a range of 2 to 15%, and a liquid crystal compound represented by the formula (VII) is compounded within a range of 30% or less. Item 9. The liquid crystal composition according to item 9.