JPS60386B2 - Nematic liquid crystal composition exhibiting positive dielectric anisotropy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nematic liquid crystal composition having positive dielectric anisotropy.

It is known that a liquid crystal exhibiting a nematic liquid crystal phase exhibits a phenomenon in which light transmittance (or reflectance) changes when an electric field is applied to the liquid crystal.

In particular, those using liquid crystals that exhibit positive dielectric anisotropy have a twisted nematic effect, that is, sandwich cells with transparent electrodes, in which the long axes of liquid crystal molecules are parallel to the electrode planes and oriented in a fixed direction, and near each electrode. The liquid crystal molecules are arranged so that they are separated from each other by 9 degrees, and when no voltage is applied to the electrodes, the plane of linear polarization is rotated 900 degrees, and when an electric field is applied, the molecules are rotated perpendicular to the electrode plane. The linear deflection oriented perpendicularly to the electrode surface has the effect of appearing as it is, and various displays have been proposed that utilize this effect. Such display systems can operate at low voltages, have extremely low power consumption, and have good contrast. However, liquid crystal materials exhibiting positive dielectric anisotropy used in such systems include mixed liquid crystals containing liquid crystals with nitrile groups in their side chains, but the temperature range in which these liquid crystals exhibit liquid crystallinity is generally much higher than room temperature. Therefore, in order to extend the liquid crystal range to room temperature or below room temperature, it was necessary to use a mixture of several types of liquid crystals.

A specific example of a mixed liquid crystal with a wide liquid crystal temperature range is a 1:2 mixture of 1:2 and 2, which exhibits a nematic liquid crystal range of -30 to 620.

However, this mixed liquid crystal is susceptible to hydrolysis and is very unstable, making it difficult to handle and having other drawbacks that make it impractical.

In addition, there are several types of mixed liquid crystals (wherein R is an alkyl group or an alkoxy group).

Although this liquid crystal is chemically stable, it has the disadvantage that it is difficult to obtain uniform homogeneous alignment with respect to the electrode surface and the glass surface. Furthermore, the biggest problem is that these known liquid crystals have slow response speeds due to their electro-optical characteristics.

The relationship between response speed and liquid crystal viscosity is generally known, and the most effective way to improve response speed is to use a liquid crystal composition with a low viscosity, and the appearance of such a liquid crystal has been strongly desired. The inventors have conducted extensive research and testing on nematic liquid crystal compositions, and have discovered a liquid crystal composition that can cover the low temperature range, has improved chemical stability, and has particularly significantly improved response speed. That is, this invention relates to azoxybenzene derivatives represented by the general formula (where x is n-propyl group, n-butyl group, n-bentyl group, n-hexyl group), in which X is n-propyl group. p′-n-propylazoxybenzene (EPAB) alone or a mixture of this EPAB and other azoxybenzene derivatives, and the general formula [
B}, (wherein Y is n-bentyloxy group, n-hexyloxy group, n-heptyloxy group), and the general formula {C}
, n-butyl group, n-pentyl group, n-hexyl group,
A nematic liquid crystal composition comprising at least one benzoic acid phenyl ester derivative represented by n-heptyl group, n-octyl group, in a weight ratio of 50 to 80%, 5 to 35%, and 5 to 45%, respectively. It is.

In this invention, the azoxybenzene derivatives represented by the above formula include p-ethyl-p-n-propylazoxybenzene, p-ethyl-p'-butylazoxybenzene, p-ethylPn-bentyl Examples include azoxybenzene and p-ethyl-pn-hexylazoxybenzene.

This azoxybenzene derivative does not exhibit a nematic phase when the substituent is a methyl group or an ethyl group. It is also clear from the drawings that the viscosity of the liquid crystal increases as the length of the substituent group increases, but when the substituent group is longer than the n-heptyl group, the characteristic low viscosity of the present liquid crystal is lost. Therefore, it needs to be an n-propyl group, n-butyl group, n-bentyl group, or n-hexyl group. The azoxybenzene derivative has isomers of and, and a mixture thereof was used.

In addition, piphenyl derivatives represented by the above formula {B- include p-n-bentyloxy-p'-cyanobiphenyl, P
-n-hexyloxy-p'-cyanobifunyl, p-
Examples include n-heptyloxy-p'-cyanobiphenyl.

The biphenyl derivative has the role of increasing the NI point (transition temperature at which nematic liquid crystal changes to liquid when temperature rises) of the liquid crystal, and it is necessary that the biphenyl derivative has a high NI point and does not have a smectic phase. That is, as mentioned above, the substituents must be n-bentyloxy, n-hexyloxy, or n-heptyloxy.

Furthermore, p'-cyanophenyl p-n-butyl benzoate, p'-cyanophenyl p-n-bentyl benzoate, etc. are used as the benzoic acid phenyl ester derivatives represented by the above.

The benzoic acid phenyl ester derivative exhibits a nematic phase and is preferably one that mixes well with the azoxybenzene derivative and the biphenyl derivative, and has the effect of lowering the solid-to-nematic liquid crystal transition temperature to a low temperature by this mixing. Butyl group, n-pentyl group, n-hexyl group,
n-hebutyl group and n-octyl group are effective. In this invention, these azoxybenzene mysterious conductors, piphenyl derivatives, and benzoic acid phenyl ester derivatives are contained in a weight ratio of 50 to 80%, 5 to 35%, and 5 to 45%, respectively.
The reason for this is that it is difficult to obtain the effects of the present invention, which will be described later, outside this weight range.

Furthermore, in the present invention, two or more of these derivatives can be selected and used within the above-mentioned ranges.
In general, in order to increase the response speed mentioned above, it is necessary to lower the viscosity of the liquid crystal as mentioned above, and in order to operate at low voltage, it is necessary to mix nematic liquid crystals that exhibit large positive dielectric anisotropy. Furthermore, the mixed liquid crystal must have a nematic region with a wide temperature range. In the present invention, an azoxybenzene derivative is used as a main component because it has a low viscosity, and specifically, it is contained in an amount of 50% or more.

Since EPAB has a particularly low viscosity among the azoxybenzene derivatives, high-speed response of electro-optic properties can be appropriately obtained.

Other azoxybenzene derivatives other than the above-mentioned EPAB also have lower viscosity than general liquid crystals, and also have a different nematic liquid crystal temperature range from EPAB, so by mixing them with EPAB, the nematic liquid crystal temperature range can be expanded. become.

In addition, since the azoxybenzene transferor used in the present invention has a relatively small positive yield anisotropy, if the component ratio is too large, the driving voltage will become high, and from a practical point of view, the component ratio will be lower. The limit is about 80%.

(For the above-mentioned azoxybenzene derivatives, refer to the electro-optical properties of low-temperature P-type liquid crystals (1) in the 35th Japan Society of Applied Physics, Academic Lecture Proceedings AI, 197 RIMO Autumn, by the present inventors). Next, cyanobiphenyl conductors with alkoxy groups in their side chains have large positive dielectric anisotropy, and
Because of its high NI point, when mixed with the azoxybenzene derivatives mentioned above, the positive dielectric anisotropy can be increased, and the upper limit of the temperature range in which the nematic liquid crystal phase is exhibited can be increased depending on the weight of each component. This will be higher than the upper limit of .

Furthermore, in the case of a mixed liquid crystal in which a biphenyl derivative is added to an azoxybenzene derivative, the lower limit of the nematic liquid crystal temperature range is lowered than in the case of each component alone. In this invention, the benzoic acid phenyl ester derivative is mixed with the EPAB (or a mixture of EPAB and other azoxybenzene derivatives) and the biphenyl derivative at the CN point in the mixed liquid crystal (from solid to nematic as the temperature rises). This allows the CN point to be lowered even further than the dislocation temperature at which the liquid crystal is dislocated.

Specifically, by containing 5% or more of each of these biphenyl derivatives and benzoic acid phenyl ester derivatives, the CN point can be lowered to 0° C. or lower. In the end, by mixing the three derivatives detailed above in the above proportions, it is possible to obtain a highly stable mixed liquid crystal that maintains low viscosity as described above, has large positive dielectric anisotropy, and has a wide nematic liquid crystal temperature range. This means that the above problems can be almost completely eliminated. The figure particularly shows the viscosity of these azoxy compounds in comparison with that of p-methoxybenzylidene-P-n-phthylaniline, which is a typical nematic liquid crystal. The present invention will be explained in more detail with reference to Examples below.

Example 1 Azoxybenzene derivative, (nematic liquid crystal temperature range: 16 to 34 o'clock C) 70% by weight, biphenyl transferor, (nematic liquid crystal temperature range: 53 pm)
~75°C) 2% by weight and phenylester benzoate conductor (monotropic liquid crystal m.p. 670, IN point (transition temperature at which it transitions from liquid to nematic liquid crystal upon temperature drop) 41°C) 1% by weight The mixed liquid crystal exhibited a nematic liquid crystal phase at −11 to 53 qo (temperature rise: 2° C. for 1 minute).

Next, the characteristics of the above nematic liquid crystal composition were investigated.

The measurement method was to rub the electrode surface in a certain direction, fill the cell with a liquid crystal composition so that the rubbing direction of the two electrodes was perpendicular, and measure between crossed nicols.

The temperature in the measurement chamber was 23 qo, and the applied voltage was 3.0V. As a result, the threshold voltage is 1.2V, and the saturation voltage (the minimum voltage where the light transmittance decreases when a voltage is applied, but the transmittance does not change even if a voltage is applied) is a low value of 2.0V. showed that. Furthermore, the transient response characteristics to voltage changes are shown in Table 4 below, and are several times faster than conventional products.
．． Table 4 The thickness between the electrodes is 16.8 rm, and the rise time (yr) indicates the time from when voltage is applied until the light transmittance To reaches 30% of when no voltage is applied, and the fall time (d) indicates the time required to recover to 70% of To after cutting off the applied voltage.

Example 2 Table 1 A mixed liquid crystal having the composition shown in Table 1 exhibits a nematic liquid crystal phase at -4 to 46°C (temperature rise: 2°C for 1 minute) and has r(m.sec) and d(m.sec) according to the above measurement method. sec) is 1 each
It was 10,180.

Note that the applied voltage was 3.0V. Example 3 Table 2 A mixed liquid crystal having the composition shown in Table 2 exhibits a nematic liquid crystal phase at -20 to 42°C (temperature rise: 2°C for 1 minute), and has r(m.sec) and d(m.sec) according to the above measurement method. sec) were 100 and 180, respectively.

Note that the applied voltage was 3.0V. As shown in Examples 1 to 3 above, it is clear that the mixed liquid crystal of the present invention has a fast response speed. This is thought to be due to the low viscosity of the azoquidibenzene derivatives such as the above-mentioned EPAB. Examples 4 to 6, Comparative Example Mixed liquid crystals were obtained according to Example 1 with the compositions shown in Table 3 below.

The response speed was measured in the same manner as in Examples 1 to 3, and the applied voltage was 3V. In Table 3 above, ``A biphenyl derivative was used as the cyano compound, ``A benzoic acid phenyl ester derivative was used, and the weight percent ratio was fixed at 2:1, and EPAB and p-ethyl p'-n-1,000 syl The response speed was investigated by varying the content of azoxybenzene (abbreviated as EPAB).

According to the results in the table above, the above 7r (m・sec), d(m
・It is considered that the response speed is fast if the sec) is within 20 hsec, but EPAB and EHAB that satisfy this are 50~
8% by weight, and EGAB alone may be used, but Comparative Example 3
As shown in the figure, sufficient response speed could not be obtained with EHAB alone.

In this invention, the azoxybenzene derivative, biphenyl derivative and benzoic acid phenyl ester derivative mentioned above are 50 to 80%, 5 to 35% and 5 to 4% by weight, respectively.
It is necessary to contain it within a range of 5%.

As is clear from the above examples, the nematic liquid crystal composition of the present invention has a low threshold voltage, a high response speed, and sufficiently covers the low overflow region. It significantly improves the above-mentioned conventional drawbacks such as excellent chemical stability.

Therefore, displays using this liquid crystal composition can be operated at low voltages, and if the thickness between the electrodes is 10 m or less, the response time (i.e. rise time + fall time) can be reduced to 10 blood·sec. It is possible to manufacture the following electro-optical device with extremely high response speed.

Furthermore, in conventional displays with large screens, the gap between the electrodes is uneven, and the response is slow in areas where the gap is large, making it difficult to achieve this. However, by using the liquid crystal composition of the present invention, it is possible to Since the response speed is high, it is possible to display a large screen. Since the above azoxybenzene derivative, biphenyl derivative, and benzoic acid phenyl ester derivative are all chemically stable, a chemically extremely stable liquid crystal composition having a practical nematic liquid crystal temperature range can be provided. It is.

[Brief explanation of the drawing]

The drawing shows the viscosity curves of azoxybenzene derivatives and P-methoxybenzylidene p'-n-butylaniline.
2 and 3 represent the change in viscosity of p-ethyl-p'-n-propylazoxybenzene, p-ethyl-p'-n-hexylazoxybenzene, and p-methoxybenzylidene-p'-butylaniline, respectively, as the reciprocal of the absolute temperature. This is the curve shown for .

Claims (1)

[Claims] General formula (A), ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (wherein X is n-propyl group, n-butyl group, n-pentyl group, n-hexyl group) Among azoxybenzene derivatives, p-ethyl p' where X is n-propyl group
-n-propylazoxybenzene (EPAB) alone,
Or, there is a mixture of this EPAB and other azoxybenzene derivatives, general formula (B), ▲mathematical formula, chemical formula, table, etc.▼ (In the formula, Y is n-pentyloxy group, n-hexyloxy group , n-heptyloxy group), and general formula (C), ▲ mathematical formula, chemical formula, table, etc. ▼ (where Z is n-butyl group, n-pentyl group, and at least one type of benzoic acid phenyl ester derivative represented by n-hexyl group, n-heptyl group, n-octyl group) in a weight ratio of 50 to 80%, 5 to 35%, and 5 to 45%, respectively. A nematic liquid crystal composition exhibiting positive dielectric anisotropy.