JPS5940864B2 - Mixed cholesteric liquid crystal and its device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mixed cholesteric liquid crystal and its device, and more particularly to a mixed cholesteric liquid crystal that has a clear threshold value, has a fast response speed, and is suitable for an X-Y matrix display device, and its device. It is related to the device.

There has been a desire to develop liquid crystal materials with display characteristics superior to those of the past, and at present several nematic liquid crystals that can be used in display devices are known and are being manufactured and sold.

However, these conventional liquid crystals have the drawback of not having a clear threshold value.

In order to improve this problem, there is a nematic liquid crystal mixed with a cholesterin derivative to give it a clear threshold value, but this mixed liquid crystal has the disadvantage of extremely slow response speed.

These conventional liquid crystals cannot be used for XY matrix display which is advantageous for multi-pixel display, and even if they could be used, the display performance would be significantly degraded.

This can be easily understood from the fact that each of the conventional liquid crystals described above does not have both a clear threshold value and a good response speed. The X-Y matrix display refers to mn ( Here, m represents the number of X electrodes, and n represents the number of Y electrodes, respectively. The advantage of such an XY matrix display is that mn picture elements can be controlled with an extremely small number of lead wires and driver circuits.

That is, the number of lead wires necessary for the above picture element control may be m+n, and the driver circuit may be m+n circuits. However, in the above-mentioned X-Y matrix display, a pixel at the intersection is selected by one X electrode in the X electrode group and one Y electrode in the Y electrode group, and the voltage between these X and Y electrodes is When V is applied, a voltage of V2 is applied to each picture element arranged in a cross shape with this intersection as the center, and there is a drawback that undesired picture elements become half-selected, that is, crosstalk occurs.

In order to prevent crosstalk in the X-Y matrix display, the liquid crystal sandwiched between the X electrode group and the Y electrode group must be a liquid crystal that does not cause any visual change, such as light scattering, up to a voltage of Y2. A liquid crystal with a threshold is required.

Furthermore, in the X-Y matrix display, since a scanning means is used to sequentially address each picture element, a liquid crystal with a fast response speed is required.

However, the conventional liquid crystal described above cannot have both a clear threshold value and a good response speed, and therefore is of no use in XY matrix display.

Therefore, the object of the invention is to have a clear threshold;
Moreover, it is an object of the present invention to provide a mixed cholesteric liquid crystal that has a fast response speed and is suitable for an XY matrix display device, and a device thereof.

According to the present invention, various liquid crystal substrates such as P-nematic liquid crystals and n-nematic liquid crystals can be coated with optically active materials.
0.1% to 70% by weight of -p-alkoxyphenyl-φ-(2-methylbutyl)benzoate is mixed.

0.1% to 70% by weight of optically active (t)-P-alkoxyphenyl-P-(2-methylbutyl)benzoate (hereinafter, for convenience of explanation, this compound will be referred to as AP(2MB)B) is mixed into the liquid crystal matrix. The present inventors have revealed that the mixed cholesteric liquid crystal obtained by the present invention has a clear threshold value and a fast response speed.

The reason for limiting the mixing ratio of AP(2MB)B in the present invention is as follows.

The threshold value of a mixed cholesteric liquid crystal containing 0.1% by weight or more of AP(2MB)B is much clearer than that of a liquid crystal containing no AP(2MB)B.

Furthermore, if the AP(2MB)B content is 70% by weight or more, the threshold voltage will be about 70V or more, and dielectric breakdown will easily occur, making it difficult to use. As AP(2MB)B used in the present invention, for example, (t)-P-hexyloxyfurenyl-P-(2-methylbutyl)benzoate (cholesteric liquid crystal temperature range 2
All mixed cholesteric liquid crystals containing 4-3'C' exhibit a cholesteric phase and have a threshold value.

In the following, cases where the parent liquid crystal is a P-nematic liquid crystal and an n-nematic liquid crystal will be explained.

P-nematic liquid crystal is a nematic liquid crystal in which the dielectric constant in the long axis direction of liquid crystal molecules is larger than the dielectric constant in the perpendicular direction, and the dielectric constant direction is positive. As a P-nematic liquid crystal with such characteristics, for example, P-nematic liquid crystal
-Alkoxybenzylidene-P-cyanoaniline, P
-Cyanobenzylidene-P-alkoxyaniline, P-alkylbenzylidene-P-cyanoaniline, P-cyanobenzylidene-P-alkylaniline, P-acyloxybenzylidene-P-cyanoaniline, P-cyanoben! Zylidene-P-acyloxyaniline, P-cyano! phenyl-P-alkylbenzoate, P-cyanophenyl-P-alkoxybenzoate, p-alkylphenyl-P-cyanobenzoft, P-alkoxyphenyl-P-cyanobenzoate, P-alkoxybenzylidene-P-amino Benzene, n-alkyl-P-cyanobendi'lidene-P-aminocynamate,
P-n-alkyral-P-n-alkylazobenzene,
P-Aruki! Examples include P-cyanobiphenyl, P-alkoxy-P-cyanobiphenyl, and the like.

A mixture of several of these P-nematic liquid crystals is also a P-nematic liquid crystal.

Further, as a P-nematic liquid crystal, there is a mixture of the above-mentioned P-nematic liquid crystal and an n-nematic liquid crystal described later. Here, the fact that this mixed liquid crystal is a P-nematic liquid crystal means that the average value of the dielectric constant in the orientation direction of the liquid crystal (the long axis direction of the molecules) is greater than the average value of the dielectric constant in the direction perpendicular to the orientation direction. It is determined by the fact that the value is also large. Therefore, it is necessary to adjust the amount of n-nematic liquid crystal mixed. For example, P- which belongs to P-nematic liquid crystal
Butoxybenzylidene-P-cyanoaniline and n-P-methoxybetenzylidene, which belongs to nematic liquid crystals, p-
In the mixed liquid crystal mixed with butylaniline, P-
It is known that if the content of butoxybenzylidene P-cyanoaniline is 5 mol % or more, a P nematic liquid crystal is formed.

Figure 2 shows the electro-optical characteristics of a P-cholesteric mixed liquid crystal obtained by mixing the above-mentioned P-nematic liquid crystal with the above-mentioned AP(2MB)B between two transparent electrodes, using the above-mentioned P-nematic liquid crystal as the parent liquid crystal. show. The low value voltage Vth is AP(2
MB) Varies depending on the mixing ratio of B.

That is, the threshold voltage Vth increases as the mixture ratio of AP(2MB)B increases. An abrupt change in the curve represents a phase transition from a cholesteric phase to a nematic phase; below the threshold voltage Vth, the phase is cholesteric, and above the saturation voltage Vsat, the phase is nematic. As is clear from the characteristic curve in the same figure, by mixing P-nematic liquid crystal and AP(2MB)B in a desired mixing ratio range, a P-cholesteric mixed liquid crystal having a clear threshold value can be obtained. was completed.

(See Examples 1 and 2) Next, an n-nematic liquid crystal and an n-cholesteric mixed liquid crystal obtained by mixing the n-nematic liquid crystal and AP (2 MB) B will be described.
The n-nematic liquid crystal is a nematic liquid crystal in which the dielectric constant in the long axis direction of liquid crystal molecules is smaller than the dielectric constant in the direction perpendicular thereto, and the dielectric constant anisotropy is negative.

As an n-nematic liquid crystal with such characteristics,
For example, P-alkoxy-P-n-altkylazoxybenzene, P-n-alkyl-P-alkoxyazoxybenzene, P-alkoxy-P-alkoxyazoxybenzene, P-n-alkyl-P-alkoxyazoxybenzene, P-alkoxy-P-alkylazobenzene, P
-Alkoxy-P-alkoxyazobenzene, P-alkoxybenzylidene-P-acyloxyaniline, Pn-
Alkylbenzylidene-P-acyloxyaniline, P-
n-alkylbenzylidene-P-alkoxyaniline,
P-alkoxybenzylidene! Examples include P-n-alkylaniline and P-n-alkyl-P-acyloxyazoxybenzene.

A mixture of several of these n-nematic liquid crystals is also an n-nematic liquid crystal. n mentioned above
- Using a nematic liquid crystal as a matrix liquid crystal, an n-cholesteric mixed liquid crystal obtained by mixing this liquid crystal matrix and the above-mentioned AP(2MB)B is sandwiched between two transparent electrodes, and its electro-optical characteristics are shown in Figure 3. show.

As is clear from the characteristic curve in the same figure, the n-cholesteric mixed liquid crystal has a memory effect, and when no voltage is applied, the light transmittance is high and it is in a transparent state.

When a direct current or an alternating current voltage below a certain limit frequency Fc is applied between the two electrodes, the state changes from the transparent state shown at 1 in the figure to the opaque state shown at 2, and even if the applied voltage is lowered in this state, it changes as shown at 3. remain in an opaque state. Under this opaque state shown in 3, the limit frequency F
When an AC voltage of c or more is applied, the transparent state shown by 1 is restored.

This limit frequency Fc changes depending on the temperature of the liquid crystal and the properties of the n-nematic liquid crystal, such as viscosity, conductivity, and dielectric constant.

The above-mentioned limit frequency Fc is usually several tens of Hz to several Hz.
The memory effect of the above-mentioned n-cholesteric mixed liquid crystal is AP.
(2MB) When the B content is 10% by weight or less, the content decreases and dynamic scattering is exhibited. However, as long as 0.1% by weight or more of AP(2MB)B is contained, the threshold value of the liquid crystal is extremely sharp and clear compared to the case where AP(2MB)B is not contained. In this way, by mixing n-nematic liquid crystal and AP(2MB)B in a desired mixing ratio range, n-nematic liquid crystal with a clear threshold value can be obtained.
- A cholesteric mixed liquid crystal could be obtained.

(Refer to Example 3) In the above explanation, P-cholesteric mixed liquid crystal and n-cholesteric mixed liquid crystal were described, but electro-optical liquid crystals in which cholesteric liquid crystal made of a cholesterin derivative is added to each of these mixed liquid crystals can also be used. When cholesteric nonanoate was added as a cholesterin derivative, it was possible to have a low threshold voltage.

(See Example 4) Cholesteric liquid crystals made of cholesterin derivatives include, for example, cholesterol chloride,
These include cholesterol bromide, cholesterin carboxylic acid esters such as cholesteronanoate, and cholesterin carbonate esters such as cholesteryl oleyl carbonate.

As is clear from the above description and the description of the following embodiments, according to the first aspect of the present invention, the present invention has a clear threshold value, has a fast response speed, and is suitable for an X-Y matrix display device. It has the advantage of being able to provide mixed cholesteric liquid crystals.

Further, according to the second invention, it is possible to provide an electro-optical liquid crystal display device that has a clear threshold value, has a fast response speed, and is suitable for an X-Y matrix display device. There is.

Example 1 As a P-nematic liquid crystal, 70% by weight of P-n-hexyl benzylidene-p-cyanoaniline,
As AP (2MB) B, (t)-P-hexyloxydiphenyl-P-(2-methylbutyno(ha)benzoate (cholesteric liquid crystal temperature range 24-3'C)
The mixed cholesteric liquid crystal obtained by mixing % by weight has a temperature of 2
When applying a square wave 250Hz alternating current at 0°C with a distance of 6μ between electrodes, there is a clear threshold, and the threshold voltage is 1
It was 2 volts.

Also, when a voltage of 20 volts is applied, the rise time is 30 m.
It showed a fast response speed with a sec1 decay time of 15 msec.

Here, if AP(2MB)B is 2% by weight or less, there is no clear threshold value, and conversely, if the mixture ratio of AP(2MB)B is 70% by weight or more, the threshold voltage is about 70V.
If this happens, dielectric breakdown is likely to occur, making it difficult to use.

Example 2 As a P-nematic liquid crystal, 30% by weight of P-butoxybenzylidene-p-cyanoaniline, as an n-nematic liquid crystal, 50% by weight of P-methoxybenzylidene-p-butylaniline, and as AP(2MB)B. ,(stomach)
The mixed cholesteric liquid crystal obtained by mixing 20% by weight of -P-methoxyphenyl P-(2-methylbutyl)benzoate was prepared at a temperature of 20°C, an electrode spacing of 6μ, and a square wave of 250H.
When an alternating current of z was applied, it had a well-defined threshold, and the threshold voltage was 16 volts.

Also, when a voltage of 25 volts is applied, the rise time is 25 ms.
It showed a fast response speed with an ec1 decay time of 10 msec.

Example 3 As an n-nematic liquid crystal, 70% by weight of P-methoxybenzylidene-Pn-butylaniline and AP (2M
B) As B, 30% by weight of (t)-P-hexyloxyphenyl-P-(2-methylbutyl)benzoate;
The mixed cholesteric liquid crystal obtained by mixing is heated at a temperature of 20°C,
When an alternating current voltage of 300 Hz square wave with an electrode spacing of 12 μm was applied, a clear threshold voltage was obtained, and the threshold voltage was 10 volts.

Also, when a voltage of 20 volts is applied, the standing time is 4 m.
The sec1 limit frequency Fc was 700Hz.

Furthermore, when an alternating current voltage of 2KIIz30V with a rectangular wave was applied, the erasing time was 800 msec.

Small clear threshold and fast response speed as above.
Example 4 As a P-nematic liquid crystal, 60% by weight of P-hexylbenxylidene-P-cyanoaniline, AP (2MB)
As B, (t)-P-hexyloxyphenyl-P-
A mixed cholesteric liquid crystal obtained by mixing 10% by weight of cholesteric nonanoate with 30% by weight of (2-methylbutyl)benzoate and a cholesterin derivative exhibits the electro-optical characteristics shown in Figure 2, and exhibits the electro-optical properties shown in Figure 2. When a square wave alternating current of 250 Hz was applied at 20° C. with an electrode spacing of 6 μm, a clear threshold voltage was obtained, and the threshold voltage was 8 volts.

Also, when the voltage is 20 volts, the rise time is 1
00 msec, and a decay time of 80 msec, showing a fast response speed.

As is clear from the description of each example above, AP(2
By adding MB)B to various liquid crystal matrixes, it was possible to obtain mixed cholesteric liquid crystals having clear threshold values, fast response speeds, and various other properties.

Furthermore, to improve the performance of mixed cholesteric liquid crystals,
It is also possible to add compounds other than liquid crystal to such an extent that the liquid crystal state is not destroyed.

For example, by adding an appropriate amount of P-n-alkylbenzylidene-Pn-alkylaniline, the transition temperature from solid to liquid crystal can be lowered and high-speed response characteristics can be obtained.

Further, a trace amount of an organic electrolyte may be added in order to obtain appropriate conductivity.

As this organic electrolyte, trimethylammonium halide or the like is used. Although a transmissive display device has been described as an electro-optical liquid crystal display device according to the present invention, it is also possible to make one of the two electrodes sandwiching the mixed cholesteric liquid crystal a reflective surface such as a mirror surface. Needless to say, a reflective display device may also be used. As is clear from the above description, the present invention has a clear threshold value, a fast response speed, and an X-
It realizes a Y-matrix display device, and has the remarkable effect of exhibiting excellent performance even when used in other display devices.

[Brief explanation of the drawing]

Figure 1 shows the optical activity...-P-hexyloxyphenyl-P
The chemical structural formula of -(2-methylbutyl)benzoate, FIG. 2 is an electro-optical characteristic diagram of a P-cholesteric mixed liquid crystal, and FIG. 3 is an electro-optical characteristic diagram of an n-cholesteric mixed liquid crystal.

Claims (1)

[Claims] 1 Optically active (+)-P-alkoxyphenyl-■-(
0.1% to 7% by weight of 2-methylbutyl)benzoate
A mixed cholesteric liquid crystal characterized by containing 0% by weight. 2. An electro-optical liquid crystal display device, characterized in that the mixed cholesteric liquid crystal described in the preceding paragraph is sandwiched between two electrodes, and at least one of these electrodes is a transparent electrode.