JPH07116440B2 - Liquid crystal composition and liquid crystal display device - Google Patents

Description

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

2. Description of the Related Art In recent years, liquid crystal displays have come to be widely used not only for wristwatches, calculators, etc. but also for 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. However, the characteristics 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 properties, and they are expected to be applied to display devices, and are being researched in various fields (eg Optronics, 1983, No. .9).

The ferroelectric liquid crystal will be described below with reference to the drawings. FIG. 3 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. 3, 11 is a ferroelectric liquid crystal molecule, 12 is a spontaneous polarization, 13 is a C director, 14 is a cone, 15 is a layered structure, 16
Indicates the layer normal direction, and 17 indicates the inclination angle θ with respect to the layer normal direction 16. As shown in FIG. 3, the ferroelectric liquid crystal molecule 11 has a spontaneous polarization 12, and in the chiral smectic C phase, it can move freely outside the conical cone 8 in FIG. The direction of the major axis of the molecule is slightly deviated from layer to layer, and the layer has a twisted structure as a whole.

Next, the display principle of the ferroelectric liquid crystal will be described. FIG. 4 is a diagram showing the principle of operation of the ferroelectric liquid crystal. FIG. 4 (a) shows a state when no voltage is applied, FIG. 4 (b) shows a state when voltage is applied from the back side of the paper to the front direction, and FIG. 4 (c) shows application of voltage in the opposite direction. It is a figure which respectively shows the state when doing. 18 is a liquid crystal molecule whose molecular long axis is tilted by + θ degrees with respect to the layer normal, 19 is a liquid crystal molecule tilted by −θ degrees, 20 is a dipole moment facing the front of the paper, and 21 is the back of the paper. The dipole moment, 22 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, the spiral is unwound as shown in FIG. It is divided into regions that are inclined by θ degrees. By applying a voltage between the upper and lower electrodes in the front direction from the back side of the paper, the entire cell becomes a monodomain tilted by + θ degrees as shown in FIG. 4 (b).
When a reverse voltage is applied, the entire cell becomes a monodomain tilted by −θ degrees as shown in FIG. 4 (c). Therefore,
If birefringence or dichroism due to electro-optic effect is used,
Brightness can be represented by two states inclined by + θ degrees.

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

To exhibit a ferroelectric liquid crystal phase (eg, chiral smectic C phase) in a wide temperature range including room temperature.

The response speed τ to the electric field of the ferroelectric liquid crystal is τ = η / (P _S · E) where η: viscosity P _S : spontaneous polarization E: applied electric field. In order to realize it, it has a large spontaneous polarization and a low viscosity.

As described above, the optical response of the ferroelectric liquid crystal is realized for the first time by a stable two-state (bistable static), but according to Clark et al.
It is necessary to set the cell gap d to be equal to or smaller than the spiral pitch p and unwind the spiral [N. A. Clark, S. Tee.
Ragaval; Apple. Fizz. Let. , 36 899 (198
0) (NAClark, STLagerwa 11; Apll.Phys.Lett., 36
899 (1980))]. Therefore, it is necessary to lengthen the spiral pitch of the ferroelectric liquid crystal in order to use a cell with a thick cell gap that is easy to create.

The alignment state of the ferroelectric liquid crystal depends on the phase sequence of the liquid crystal material, and particularly 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. Therefore, 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 *: A chiral smectic C phase is desirable, and a wide temperature range of SmC * 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.

Since the conventional ferroelectric liquid crystal materials used an ester-based ferroelectric liquid crystal compound, the response speed is slow at about 100 μsec, and all the above conditions are satisfied and practically no material is available at present. there were.

An example of a conventional ferroelectric liquid crystal material is shown below. here,
The wt% of the chiral components (1) to (4) and the non-chiral components (5) to (6) of the mixed system is 50%.

Transition temperature Iso → Ch → SmA → SmC * 74 ℃ 63 ℃ 57 ℃ Melting point -6 ℃ Spontaneous polarization 13nC / cm ² (C: Coulomb) Response speed 150μsec (when 24Vpp is applied) Liquid crystal display using such liquid crystal composition The panel had a slow response speed and was not satisfactory in terms of display quality.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, conventional ferroelectric liquid crystal materials are represented by the compounds (1) and (2) having large spontaneous polarization as described above and the compound (3). In order to expand such a temperature range or extend the spiral pitch, an ester-based ferroelectric liquid crystal compound has been used. Ester-based compounds have high viscosity, and even when used with a ferroelectric liquid crystal compound with large spontaneous polarization, the response speed becomes as slow as about 150 μsec, making it difficult to obtain a ferroelectric liquid crystal display device with excellent display quality. Had.

The present invention solves the above problems, and an object of the present invention is to provide a liquid crystal composition which exhibits a liquid crystal phase in a wide temperature range including room temperature and can respond at high speed, and a liquid crystal display device using the liquid crystal composition. To do.

Means for Solving the Problems In order to solve the above problems, the present invention is a mixture of a phenylpyrimidine-based liquid crystal material having large spontaneous polarization and low viscosity. (Wherein, X is any one of R-, RO-, RCOO-, and ROCOO-, and R represents an alkyl group),
General formula (Wherein m represents an integer and R ′ represents any of an alkyl group, an alkoxy group, and an acyloxy group) and at least a phenylpyrimidine-based liquid crystal compound in which the chiral portion does not form a racemate. A liquid crystal composition containing one type and a liquid crystal display device using this liquid crystal composition.

Effect With the above configuration, when a phenylpyrimidine-based ferroelectric liquid crystal compound with low viscosity is mixed with a ferroelectric liquid crystal compound with large spontaneous polarization, the magnitude of spontaneous polarization decreases with an increase in the phenylpyrimidine component, but the viscosity also decreases. Therefore, the response speed does not become slower but rather becomes faster than the relationship of τ = η / (P _S · E), and high-speed response of the order of several tens of μsec is possible.

In addition, since the phenylpyrimidine-based ferroelectric liquid crystal compound exhibits the SmC * phase in a wide temperature range, it is easy to expand the temperature range. Further, by using a phenylpyrimidine compound having a twisting direction opposite to that of a biphenyl compound such as the conventional compound (1), a ferroelectric liquid crystal compound having a spiral pitch and capable of high-speed response can be easily obtained. To be By using this liquid crystal composition, a liquid crystal display device having a good alignment state, operating in a wide temperature range and capable of high-speed response and exhibiting excellent display quality can be easily obtained.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the structure of a liquid crystal cell using a ferroelectric liquid crystal material according to an embodiment of the present invention. In FIG. 2, 1 is a polarizing plate arranged at both ends, 2 is a glass substrate arranged inside thereof, 3 is a transparent electrode attached to the opposite surface of the glass substrate 2, and 4 is an alignment treatment by rubbing. An organic polymer film attached to the opposite surface of the transparent electrode 3, 5 is a space for keeping the cell thickness constant, and 6 is a ferroelectric liquid crystal material enclosed in the cell having such a structure. This ferroelectric material has the general formula (Wherein, X is any one of R-, RO-, RCOO-, and ROCOO-, and R represents an alkyl group),
The general formula is (Wherein m represents an integer and R ′ represents any of an alkyl group, an alkoxy group, and an acyloxy group) and at least one compound having a non-racemic chiral moiety is contained. It was done.

Next, a specific example will be described. Table 1 shows the composition. The compounds (1) and (2) are used as the liquid crystal material having a negative spontaneous polarization polarity and the pitch twist direction to the right, and the following compounds are used as the liquid crystal materials having a negative spontaneous polarization polarity and the pitch twist direction to the left. Using (7) and (8), and for expanding the temperature range of the mixture, a non-chiral
Using compound (5) and compound (6) as the SmC component, wt% of the chiral component and the non-chiral component of this mixed system
Made a 50% composition. FIG. 1 shows a phase diagram of the chiral component and the non-chiral component of this mixed system. Here, it can be seen that the ferroelectric liquid crystal phase is exhibited in a wide temperature range including room temperature over almost the entire composition range.

Next, the above composition was enclosed in a cell having a structure as shown in FIG. 2, and the response and spontaneous polarization were measured. The spontaneous polarization was measured using the triangular wave method. The phase transition temperature was measured by texture observation with a polarization microscope, and the pitch was measured with a wedge-shaped cell using a glass substrate having a thickness of 5 mm.

Transition temperature Iso → Ch → SmA → SmC * → Cryst 70 ℃ 61 ℃ 56 ℃ −28 ℃ Melting point −10.6 ℃ Response speed 55μsec (25 ℃) Spontaneous polarization 13nC / cm ² Ch Phase spiral pitch Almost infinite The ferroelectric liquid crystal display device produced by using the dielectric liquid crystal composition showed a good alignment state and good display characteristics.

As described above, according to the present invention, by mixing a liquid crystal compound having a large spontaneous polarization with a low-viscosity phenylpyrimidine-based liquid crystal compound, a liquid crystal phase is exhibited in a wide temperature range including room temperature, and an alignment state A good ferroelectric liquid crystal composition capable of responding at high speed can be obtained, and a liquid crystal display device using this ferroelectric liquid crystal composition as a liquid crystal material shows excellent display quality.

[Brief description of drawings]

FIG. 1 is a phase diagram of a mixed system in one embodiment of the present invention, and FIG.
FIG. 3 is a configuration diagram of a ferroelectric liquid crystal cell, FIG. 3 is a schematic diagram of ferroelectric liquid crystal molecules, and FIG. 4 is an operation principle diagram of ferroelectric liquid crystal. 1 ... Polarizing plate, 2 ... Glass substrate, 3 ... Transparent electrode, 4
...... Organic polymer film, 5 …… Spacer, 6 …… Ferroelectric liquid crystal material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuyoshi Uemura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Central Research Institute Co., Ltd. (72) Inventor Kouichi Higuchi 1-1, Suzuki-cho, Kawasaki-ku, Kanagawa Prefecture No. 1 Ajinomoto Co., Inc. Central Research Laboratory

Claims (4)

[Claims] 1. A general formula (Wherein, X is any one of R-, RO-, RCOO-, and ROCOO-, and R represents an alkyl group),
General formula (Wherein m represents an integer and R ′ represents any one of an alkyl group, an alkoxy group, and an acyloxy group), and a liquid crystal compound containing at least one kind of liquid crystal compound in which the chiral moiety is not racemic. Composition. 2. The liquid crystal composition according to claim 1, wherein m is an odd number. 3. General formula (Wherein, X is any one of R-, RO-, RCOO-, and ROCOO-, and R represents an alkyl group),
General formula (Wherein m represents an integer and R ′ represents any one of an alkyl group, an alkoxy group, and an acyloxy group) and a liquid crystal composition containing at least one kind of liquid crystal compound in which the chiral portion does not form a racemate. Liquid crystal display device using objects. 4. The liquid crystal display device according to claim 3, wherein m is an odd number.