JPH0745660B2 - 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 carried out in various fields. (Opttronics, 1983, No.9)
The ferroelectric liquid crystal will be described below with reference to the drawings. FIG. 6 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. 6, 10 is a liquid crystal molecule, 11 is a spontaneous polarization, and 12 is C.
A director, 13 is a cone, 14 is a layered structure, 15 is a layer normal direction, and 16 is a tilt angle θ.

As shown in FIG. 6, 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. 6 is a diagram showing the principle of operation of the ferroelectric liquid crystal. FIG. 6 (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 a 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 tilted by + θ degrees with respect to the unwinding layer as shown in FIG. It is divided into regions that are inclined by θ degrees. 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. 7 (b). When a reverse voltage is applied, the entire cell is -θ as shown in Fig. 7 (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 τ = η / Ps · E where η; viscosity Ps; spontaneous polarization E; applied electric field. Therefore, it is necessary to have a large spontaneous polarization in order to realize a high-speed response of 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., In order to realize this state, it is necessary to set the cell gap d to a spiral pitch p or less and unwind the spiral. N. A. Clark, S. tea. Ragaval; Apple. Fizz. Let. , 36 899 (1980) (N.
A. Clerk ST Lagerwall; Apll.Phys.Lett., 36 899 (198
Therefore, in order to use a cell with a large cell gap, which is easy to make in cell preparation, it is necessary to lengthen the spiral 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 the 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 * However, Iso; isotropic liquid Ch; cholesteric phase SmA; smectic A phase SmC *; chiral smectic C phase is desirable.

Furthermore, among the liquid crystal materials with the above-mentioned phase series, Ch
It is believed that the longer the phase pitch, the better the orientation.

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-methylbutyl cinnamate (+ 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 liquid crystal materials that satisfy all of the above four conditions and can be immediately applied to display devices. 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.

Action Generally, in order to extend the temperature range of the 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 that when the magnitudes of spontaneous polarization are almost equal,
FIG. 6B shows changes in spontaneous polarization when the magnitudes of spontaneous polarization are significantly 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, but 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. 5B, when one of the spontaneous polarizations is larger than the other, the decrease of the spontaneous polarization is suppressed and is relatively large. A liquid crystal compound having 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, Wai. 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 is S and the number of atoms from the benzene ring to the chiral center is an even number, the twist direction is right, and if it is an odd number. On the left. Also, if the absolute configuration of the chiral center is the R configuration, the opposite will occur. Generally, two methods can be considered for extending the pitch. One is a method in which a ferroelectric liquid crystal material is mixed with a liquid crystal material having no chiral, and a method in which a liquid crystal material having a reverse twist direction is mixed. 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, a liquid crystal material having the same polarity of the spontaneous polarization and the opposite twist direction of the pitch is mixed, or one of the spontaneous polarization has the opposite polarity even if the polarities of the spontaneous polarization are opposite. By using a liquid crystal material containing a liquid crystal material that is very large and has twisting directions opposite to each other, a ferroelectric liquid crystal display device having a good alignment state and capable of high-speed response can be obtained.

Example An example of the present invention will be described with reference to the drawings. First, in this example, the structure of a liquid crystal cell in which the response characteristics of the ferroelectric liquid crystal material was measured is shown in FIG. 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.

For the phase transition temperature, see the textur
e Observation and DSC were performed, and the Sc * phase pitch was 10 cells thick.
A cell having an alignment treatment of 0 micron was used, and a compound having no Ch phase was used as a Ch phase by mixing with a nematic liquid crystal for a Ch phase pitch. The measurement was performed by a usual method using a wedge cell.

Example 1 In the compound (I) described in claim (1), the configuration of the chiral moiety is S-configuration, R is a nonyl group, and 1 is 0.
And the configuration of the chiral moiety below is 2
Since the compound (VII) which is S, 3C has a right-handed helix, the compound (IV) has a chiral configuration of S-form and R'is an octanoicoxy group The transition temperature and the pitch length of the ternary system using the compound (VIII) in which 1 is 2 and m and n are 1 were measured.

The composition of the compound measured was 40 wt% of compound (VI).
%, Compound (VII) 10 wt%, compound (VIII) 50 wt%
Met. The results are shown below.

Phase transition temperature Helical pitch of Ch phase; infinity Example 2 The configuration of the chiral moiety of compound (I) described in claim (1) is 2S, R is an octyl group, and l is 0.
Compound (VI), which has a right-handed helix direction, has a compound (III)
Of the chiral configuration of S-form, R is a desiloxy group, and l, m, and n are 1 respectively (2)
The transition temperature and pitch length of the component system were measured. FIG. 1 shows a phase diagram of this two-component mixed system.
The composition of the compound measured was 70 wt% of compound (VI).
%, And compound (IX) was 30 wt%. The results are shown below.

Phase transition temperature Helical pitch of Ch phase; infinity Example 3 The configuration of the chiral moiety of compound (I) described in claim (1) is S-configuration, R is nonyl group, and l is 0.
The compound (VI) is a compound having a helical twist direction on the right, and therefore, as a compound having a reverse twist, the compound (V) having a left twist direction has an R configuration in the chiral moiety and R ′ is a decyloxy group. The phase transition temperature and pitch length of the two-component system using (X) were measured. In addition, the composition of the measured compound is the compound (VI)
Was 50 wt% and the compound (IX) was 50 wt%. In addition, the alignment state of the liquid crystal cell formed using the above liquid crystal was good. The results are shown below.

Phase transition temperature Ch phase pitch; infinity Effect of the invention As described above, the present invention can be used in 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,
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 phase diagram of a two-component mixed system in Example 1 of the present invention, FIG. 2 is a schematic diagram showing polarities of spontaneous polarization, and FIG. 3 is spontaneous when compounds having the same polarities of spontaneous polarization are mixed. FIG. 4 is a concentration-dependent characteristic diagram of polarization, and FIG. 4 is a concentration-dependent characteristic diagram of spontaneous polarization when compounds having different polarities of spontaneous polarization are mixed.
FIG. 6 is a configuration diagram of a ferroelectric liquid crystal cell, FIG. 6 is a schematic diagram of the ferroelectric liquid crystal, and FIG. 7 is a schematic diagram showing the 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. In a smectic liquid crystal exhibiting ferroelectricity, a 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 moiety 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. In a smectic liquid crystal exhibiting ferroelectricity, a general formula (In the formula, 1 is an integer of 0 or 1, and R is an alkyl group) The liquid crystal compound in which the chiral portion does not form a racemate and the helical twist direction of the compound are opposite to each other, and the spontaneous polarization The liquid crystal display device according to claim 1, wherein a liquid crystal composition containing one or more kinds of compounds 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). The liquid crystal display device according to any one of items (1) and (2). 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), wherein 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), wherein 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), wherein the liquid crystal display device according to any one of claims 1, 2 and 3 .