JPH0745661B2 - Liquid crystal display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal composition containing a novel liquid crystal substance, and more particularly to a ferroelectric liquid crystal display device.

2. Description of the Related Art In recent years, liquid crystal displays have come to be widely used not only in wristwatches, calculators, etc. but also in video equipment, and liquid crystal color televisions are also on the market. At present, the mainstream of liquid crystal panels for color display are those using nematic liquid crystals. But,
The properties of the nematic liquid crystal are not ideal and include many problems. Ferroelectric liquid crystals have various characteristics that nematic liquid crystals do not have, such as fast response speed and memory property, and are expected to be applied to display devices, and research is being conducted from various fields (Opttronics, 1983, No.
9). The ferroelectric liquid crystal will be described below with reference to the drawings. FIG. 7 is a schematic diagram of a ferroelectric liquid crystal molecule. Ferroelectric liquid crystal is a liquid crystal having a layer structure usually called smectic liquid crystal, and liquid crystal molecules have a structure inclined by θ with respect to the layer normal direction. Further, the ferroelectric liquid crystal molecules are usually composed of optically active liquid crystal molecules which are not racemic.

In FIG. 7, 10 is a liquid crystal molecule, 11 is a spontaneous polarization, 12 is a C director, 13 is a cone, 14 is a layer structure, 15 is a layer normal direction, and 16 is a tilt angle θ.

As shown in FIG. 7, the ferroelectric liquid crystal molecules have spontaneous polarization, and in the chiral smectic C phase,
It can move freely outside the cone 13 (cone) in the figure. The direction of the molecular long axis is slightly deviated for each layer, and the structure has a twisted structure as a whole. Next, the display principle of the ferroelectric liquid crystal will be described. FIG. 8 is a diagram showing the principle of operation of the ferroelectric liquid crystal. FIG. 8 (a) shows a state in which no voltage is applied, and FIG.
FIG. 6C is a principle diagram of the operation when a voltage is applied in the opposite direction. 17 is a liquid crystal molecule whose molecular long axis is tilted by + θ degrees with respect to the layer normal, 18 is a liquid crystal molecule whose −θ degree is tilted, 19 is a dipole moment facing the front of the paper, and 20 is facing the back of the paper. The dipole moment, 21 is the direction of the two polarizing plates.
When the ferroelectric liquid crystal is sandwiched between glass substrates having transparent electrodes and the thickness of the panel is set to a spiral pitch or less, a region where molecules are inclined by + θ degrees with respect to the unwinding layer and −θ as shown in FIG. 8 (a). Divided into a tilted area. By applying a voltage in the front direction from the back surface of the space between the upper and lower electrodes, the entire cell becomes a monodomain tilted by + θ degrees as shown in FIG. When a reverse voltage is applied, the entire cell is -θ as shown in Fig. 8 (c).
It becomes a mono-domain tilted. Therefore, if birefringence or dichroism due to the electro-optic effect is used, it is possible to represent light and dark by two states tilted by + θ degrees.

When applying a ferroelectric liquid crystal to a display device,
The conditions required for liquid crystal materials are as follows.

It exhibits a ferroelectric liquid crystal phase (for example, a chiral smectic C phase) in a wide temperature range including room temperature.

The response speed τ of the ferroelectric liquid crystal to the electric field is given by τ = η / Ps · Ε, where η; viscosity Ps; spontaneous polarization Ε; applied electric field. Therefore, it is necessary to have a large spontaneous polarization in order to realize a high-speed response on the order of several μsec.

As described above, the optical response of the ferroelectric liquid crystal is realized only by the stable bi-state. According to Clerk et al.
It is necessary to make the cell gap d equal to or smaller than the spiral pitch p and unwind the spiral. N. A. Clark, S. Tei. Ragaval; Apple. Fizz. Let. , 36 899 (1980)
(NAClerk, STLagerwall; Apll.Phys.Lett., 36 899
(1980)) Therefore, in order to use a cell with a thick cell gap that is easy to create, it is necessary to lengthen the helical pitch of the ferroelectric liquid crystal.

The alignment state of the ferroelectric liquid crystal depends on the phase sequence of the liquid crystal material. Especially, the liquid crystal material having the smectic A phase (SmA) and cholesteric phase (Ch) on the high temperature side of the ferroelectric liquid crystal phase can obtain a good alignment state. It is believed that
That is, when the phase sequence of the ferroelectric liquid crystal material is, for example, a chiral smectic C phase * Iso → Ch → SmA → SmC * where Iso; isotropic liquid Ch; cholesteric phase SmA; smectic A phase SmC *; chiral It is preferably a smectic C phase.

Further, among the liquid crystal materials having the above-mentioned phase series, it is considered that the one having a longer Ch phase pitch has a better alignment state.

In addition to the conditions described above, there are various requirements for the tilt angle θ of liquid crystal molecules.

There are few practical materials for conventional ferroelectric liquid crystal materials even if only the temperature range is taken up, and there is no ferroelectric liquid crystal display device with excellent display quality using materials that meet all of the above conditions and can withstand practical use. The current situation was equal to.

An example of a conventional ferroelectric liquid crystal material is shown below. (+) P
-Decyloxybenzylidene p'amino 2-methylbutylcinnamate (+ DOBAMBC) However, SmG *; chiral smectic G phase Ps = 4 to 5 nC τ = several hundred μsec to several msec In a liquid crystal display cell using such a liquid crystal compound, a good alignment state cannot be obtained, and as shown in the above results. The temperature range showing the chiral smectic C phase was narrow and the display characteristics were poor.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, conventional ferroelectric liquid crystal materials are not practical even if only the temperature range is taken into consideration, and all of the above four conditions are satisfied, and the liquid crystal material can be immediately applied to a display device. The present situation is that nothing is equal to nothing. Therefore, in the present invention, by using a liquid crystal composition containing a liquid crystal material having large spontaneous polarization and opposite twist directions,
The present invention provides a ferroelectric liquid crystal display device which operates in a wide temperature range, easily obtains good orientation, and is capable of high-speed response on the order of several tens of microseconds and has excellent display quality.

Means for Solving the Problems In order to solve the above problems, a ferroelectric liquid crystal display device of the present invention comprises a liquid crystal composition containing a liquid crystal material having large spontaneous polarization and opposite twist directions. When used, it operates in a wide temperature range, easily obtains good orientation, and exhibits excellent display quality capable of high-speed response on the order of several tens of μsec.

Operation Generally, in order to extend the temperature range of liquid crystal, it is necessary to mix two or more kinds of liquid crystal compounds having different molecular shapes. However, when mixing a ferroelectric liquid crystal material, it is necessary to consider the material constants such as the polarity of spontaneous polarization of the compound, the twisting direction of the ferroelectric liquid crystal phase, and the twisting direction of the cholesteric phase. . Spontaneous polarization is + as shown in FIG. 3 (a) and − as shown in FIG. 3 (b). The polarity is determined by the configuration of the chiral center and the dipole moment direction. It FIG. 4 shows changes in spontaneous polarization when liquid crystal compounds having the same polarities of spontaneous polarization were mixed, and FIG. 5 shows changes in spontaneous polarization when liquid crystal compounds having different polarities of spontaneous polarization were mixed. Further, FIG. 5 (a) shows changes in the spontaneous polarization when the magnitudes of the spontaneous polarization are almost equal, and FIG. 5 (b) shows changes in the spontaneous polarization when the magnitudes of the spontaneous polarization are largely different. As is clear from this figure, when liquid crystal compounds having different polarities of spontaneous polarization are mixed, the value of spontaneous polarization becomes small. However, by mixing liquid crystal compounds having the same polarities of spontaneous polarization, liquid crystal compounds having large spontaneous polarization are mixed. Can be easily obtained. Even when liquid crystal compounds having different polarities of spontaneous polarization are mixed, as shown in FIG. 5 (b),
When the magnitude of one spontaneous polarization is larger than that of the other, a decrease in spontaneous polarization is suppressed and a liquid crystal compound having a relatively large spontaneous polarization can be obtained.

The twist direction of the helical axis is considered to be determined by the absolute configuration of the chiral part and whether the number of molecules from the benzene ring to the chiral center is even or odd. M. Tsukamoto, Tay. Otsuka, Kei. Morimoto, Yi. Murakami; Japan. Jay. Apple. Fizz. , 14 1307 (1975)
(M.Tukamoto, T.Otsuka, K.Morimoto, Y.Murakami, Japan.
J.APPL.Phys., 14 1307 (1975)) That is, if the absolute configuration of the chiral center or the S configuration and the number of atoms from the benzene ring to the chiral center is even, the direction of twist is right, and if the number is odd, On the left. In addition, if the absolute configuration of the chiral center is the R configuration, the opposite is true. Generally, two methods can be considered for extending the pitch. One is a method of mixing a liquid crystal material having no chiral with a ferroelectric liquid phase material and a method of mixing a liquid crystal material having a twist direction opposite to that of the liquid crystal material. According to the former method, in order to extend the pitch, it is necessary to mix a liquid crystal material having no chiral in a large proportion, and the spontaneous polarization decreases with an increase in the non-chiral component, so that it becomes extremely small. On the other hand, according to the latter method, as described above,
Mixing liquid crystal materials with the same polarity of spontaneous polarization and opposite pitch twisting directions, or even if the polarities of spontaneous polarization are opposite, one spontaneous polarization is very large and the pitch twisting directions are opposite to each other. By mixing a liquid crystal material, a ferroelectric liquid crystal material having large spontaneous polarization and diverging pitch can be easily obtained.

Example An example of the present invention will be described with reference to the drawings. First, FIG. 6 shows the structure of a liquid crystal cell in which the response characteristics of the ferroelectric liquid crystal material were measured in this example. Here, 4 is a polarizing plate,
Reference numeral 5 is a glass substrate, 6 is a transparent electrode, 7 is an organic polymer film which has been oriented by rubbing, 8 is a ferroelectric liquid crystal layer, and 9 is a ferroelectric liquid crystal layer.
Indicates a spacer for keeping the cell thickness constant.
A ferroelectric liquid crystal material was enclosed in a cell having such a structure, and its response characteristics and spontaneous polarization were measured. The spontaneous polarization was measured using the triangular wave method.

Also, regarding the phase transition temperature, texture with a polarization microscope
Observation and DSC were used. The pitch of the Sc * phase was 100 μm and the orientation of the cell was 100 μm.
The compound which does not show the Ch phase was measured by a usual method using a wedge-shaped cell using a glass substrate which was mixed with a nematic liquid phase to give the Ch phase an orientation treatment with a thickness of 5 mm.

Example 1 The configuration of the chiral moiety of compound (I) according to claim 1 is 2S, 3S, R is an octyl group, and 1 is 1.
Compound (VI) has a right-handed helical twisting direction. Therefore, as a compound with a reverse twist, the left-handed twisting direction of Compound (II) has an S configuration of the chiral moiety and R'is a desiloxy group. Using the compound (VII) in which m and n are 1 respectively, the phase transition temperature, spontaneous polarization, pitch length and response speed were measured for these binary mixture systems. The composition of the mixture measured was 70 wt% of compound (VI), compound (VII)
Is 30 wt%. FIG. 1 shows the measurement results of the response speed at 25 ° C. of the liquid crystal cell prepared by using the compound having the above composition, and FIG. 2 shows the phase diagram of this binary mixture system. The results are shown below.

Phase transition temperature Spontaneous polarization; 60 nC Ch phase pitch; infinite response speed; 80 μsec (25 ° C.) Example 2 The configuration of the chiral part of compound (I) according to claim 1 is 2S, 3S and R is nonyl. The group compound (V
III) and the compound (I) according to claim 1.
The compound (VI) in which the configuration of the chiral part of 2 is 2S, 3S and R is an octyl group has the right twist direction of the helix, so as a compound of the reverse twist, the chiral part of the compound (II) with the left twist direction is (VII) in which the configuration of is the S configuration, R'is a desiloxy group, and l, m, and n are each 1
The phase transition temperature and pitch length of the three-component system using was measured. The composition of the compound measured was 21 wt% of compound (VIII) and 49 wt% of compound (VI).
%, And compound (VII) was 30 wt%. The results are shown below.

Phase transition temperature Helical pitch of Ch phase; infinite response speed; 90 μsec. Example 3 The configuration of the chiral moiety of compound (I) according to claim 6 is 2S, 3S, R is a nonyl group, and l is 0. A helical twist of a compound (VIII) and a compound (VI) according to claim 1, wherein the configuration of the chiral moiety is 2S, 3S, R is an octyl group, and l is 1. Since the direction is to the right, a three-component system using a compound (IX) in which the chiral configuration of compound (IV) is the S-form and R'is an octanoicoxy group as a compound of a left-handed twist with a reverse twist The transition temperature and the pitch length were measured. The composition of the compound measured was 40 wt% of compound (VIII) and 10 wt% of compound (VI).
%, And compound (IX) was 50 wt%. The results are shown below.

Phase transition temperature Helical pitch of Ch phase; infinity Effect of the invention As described above, the present invention has a wide temperature range including room temperature by mixing ferroelectric liquid crystal materials having large spontaneous polarization and having opposite pitch twist directions. Shows a liquid crystal phase in the range,
A ferroelectric liquid crystal display device having excellent display quality is provided by using a ferroelectric liquid crystal material having a good orientation state and large spontaneous polarization and capable of high-speed response.

[Brief description of drawings]

FIG. 1 is a characteristic diagram of the response of a ferroelectric liquid crystal cell in Example 1 of the present invention, FIG. 2 is a phase diagram of a two-component mixed system in Example 1 of the present invention, and FIG. 3 is a polarity of spontaneous polarization. Fig. 4 is a schematic diagram, Fig. 4 is a concentration-dependent characteristic diagram of spontaneous polarization when compounds having the same spontaneous polarization polarity are mixed, and Fig. 5 is a concentration dependence of spontaneous polarization when compounds having different polarities of spontaneous polarization are mixed. FIG. 6 is a characteristic diagram, FIG. 6 is a configuration diagram of a ferroelectric liquid crystal cell, FIG. 7 is a schematic diagram of a ferroelectric liquid crystal, and FIG. 8 is a schematic diagram showing an operation principle of the ferroelectric liquid crystal. 1 ... Layer normal direction, 2 ... Molecular long axis direction, 3 ... Spontaneous polarization direction, 4 ... Polarizing plate, 5 ... Upper and lower glass substrates, 6
...... Transparent electrodes, 7 ...... Alignment-treated organic alignment film, 8
…… Ferroelectric liquid crystal phase, 9 …… Spacer for keeping the cell thickness constant, 10 …… Ferroelectric liquid crystal molecule, 11 …… Spontaneous polarization, 12 …… C director, 13 …… Cone, 14… …layer,
15 …… Layer normal, 16 …… Inclination angle θ of molecule with respect to layer normal,
17 …… Liquid crystal molecules whose major axis is tilted + θ with respect to the layer normal, 18 …… Liquid crystal molecules whose major axis is tilted with −θ with respect to the layer normal, 19 …… Face direction The dipole moment that exists, 20 ... the dipole moment that faces the back of the paper,
21 …… Direction of two polarizing plates.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Sakurai 1-1 1-1 Suzuki-cho, Kawasaki-ku, Kanagawa Prefecture No. 1 in Ajinomoto Co., Inc. Central Research Laboratory

Claims (6)

[Claims] 1. A smectic liquid crystal exhibiting ferroelectricity,
General formula (Wherein l represents an integer of 0 or 1 and R represents an alkyl group) and a liquid crystal compound in which the chiral portion does not form a racemate and a compound in which the twist direction of the helix is opposite to that of the compound. A liquid crystal display device comprising a liquid crystal composition containing one or more of the above. 2. A smectic liquid crystal exhibiting ferroelectricity,
General formula (Wherein l represents an integer of 0 or 1 and R represents an alkyl group) and the liquid crystal compound in which the chiral portion does not form a racemate and the compound and the helix have opposite twist directions and spontaneous polarization. The liquid crystal display device according to claim 1, wherein a liquid crystal composition containing one or more kinds of compounds each having the same polarity is used. 3. A compound represented by the general formula (I), wherein the helical twist direction is opposite to that of the compound represented by the general formula: (Wherein R'represents an alkanoyl group or an alkoxy group, l and m are integers of 1 or 2 and n is an integer of 0 or 1) 3. The liquid crystal display device according to either the first or second range. 4. A compound represented by the general formula (I) having a helical twist direction opposite to that of the compound represented by the general formula: (Wherein R ′ represents an alkanoyl group or an alkoxy group), The liquid crystal display device according to any one of claims 1, 2 and 3. . 5. A compound represented by the general formula (I) wherein the helical twist direction is opposite to that of the compound represented by the general formula: (Wherein R ′ represents an alkanoyl group or an alkoxy group), The liquid crystal display device according to any one of claims 1, 2 and 3. . 6. A compound represented by the general formula (I), wherein the twist direction of the helix is opposite to that of the compound represented by the general formula: (Wherein R ′ represents an alkanoyl group or an alkoxy group), The liquid crystal display device according to any one of claims 1, 2 and 3. .