JPS6337186A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal composition capable of providing a ferroelectric liquid crystal material capable of rapidly responding, showing a liquid crystal phase readily in a wide temperature range including room temperature and containing a novel phenylpyrimidine liquid crystal compound showing nonchiral smectic C phase. CONSTITUTION:The aimed composition containing one or more phenylpyrimidine liquid crystal compounds shown by the formula I [R and R' are alkyl or alkoxy (e.g. C9H19O etc.)]. The aimed liquid crystal material is obtained by adding the composition to a ferroelectric liquid crystal composition comprising a compound shown by formula II, etc., having an extended spiral pitch.

Description

[Detailed description of the invention] It particularly relates to ferroelectric liquid crystal materials.

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 have also begun to appear on the market. Currently, the mainstream color display liquid crystal panels are those using nematic liquid crystals. but,
The characteristics of the nematic liquid crystal are far from ideal and include many problems. Ferroelectric liquid crystals have characteristics that are not found in nematic liquid crystals, such as fast response speeds and memory properties, and are being researched from various angles for potential applications in display devices (Optronics, 1983, Toru 9).
), ferroelectric liquid crystal will be explained below with reference to the drawings. FIG. 6 is a schematic diagram of ferroelectric liquid crystal molecules. A ferroelectric liquid crystal is a liquid crystal having a layered structure, which is usually called a smectic liquid crystal, and the liquid crystal molecules have a structure tilted by θ with respect to the normal direction of the layers. Furthermore, ferroelectric liquid crystal molecules are usually composed of optically active liquid crystal molecules that are not racemic.

In FIG. 6, 7 is a liquid crystal molecule, 8 is spontaneous polarization, 9 is a C director 110 is a cone, 11 is a layer structure, 12 is a layer normal direction, and 13 is a tilt angle θ.

As shown in Figure 6, ferroelectric liquid crystal molecules have spontaneous polarization, and in the chiral smectic C phase, the 6th
It can move freely outside the cone 10 (cone) shown. The direction of the long axis of the molecules deviates slightly from layer to layer, resulting in a twisted structure as a whole. Next, we will discuss the display principle of ferroelectric liquid crystal. FIG. 7 is a diagram showing the operating principle of a ferroelectric liquid crystal. Figure 7 (al is the state with no voltage applied,
(Fig.
Figure tc) is a diagram showing the principle of operation when voltage is applied in the opposite direction. 14 is a liquid crystal molecule whose long axis is tilted by +0 degrees with respect to the layer normal, 15 is a liquid crystal molecule tilted by 1 θ degree, 16 is a dipole moment pointing toward the front of the page, and 17 is a dipole moment facing toward the back of the page. The dipole moment 18 is the direction of the two polarizing plates.If a ferroelectric liquid crystal is sandwiched between glass substrates with transparent electrodes and the thickness of the panel is less than the helical pitch, it will form a spiral as shown in Figure 7 fat. It is divided into a region where the molecules are tilted by +θ degrees and a region where the molecules are tilted by 1θ degrees with respect to the unraveled layer. By applying a voltage from the back side of the paper surface to the front side between the upper and lower electrodes, the
The entire cell becomes a monodomain tilted by +θ degrees as shown in l. Furthermore, when a reverse voltage is applied, the entire cell becomes a monodomain tilted by 1θ degree as shown in FIG. 7 (C1).

Therefore, by using birefringence or dichroism due to the electro-optic effect, brightness and darkness can be represented by two states tilted by +θ degrees.

When applying ferroelectric liquid crystal to display devices,
The following conditions are required for liquid crystal materials.

(2) Exhibits a ferroelectric liquid crystal phase (for example, chiral smectic C phase) over a wide temperature range including room temperature.

■ The response speed τ of ferroelectric liquid crystal to electric field is τ−η
/Ps-B where η; viscosity PS; spontaneous polarization E; given by applied electric field. Therefore, in order to achieve a high-speed response on the order of several microseconds, it is necessary to have a large spontaneous polarization.

(2) As mentioned above, the optical response of a ferroelectric liquid crystal is first realized in two stable states (bistable 5 states). According to C1erk et al., in order to achieve this state, it is necessary to make the cell gap d less than the helical pitch and unwind the helix. N.

Knee, Clark, Nis, Tee, Raghaval; Able;
Huiz, Lett 9, 2 899 (1980) (N,
A, C1erk, S, T, -Lagerw
(all; APH, Phys, Lett, 1989 (1980)) Therefore, in order to utilize 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 ferroelectric liquid crystal varies depending on the phase series of the liquid crystal material, and in particular, liquid crystal materials with smectic A phase (SmA) and cholesteric phase (Ch) on the high temperature side of the ferroelectric liquid crystal phase have a good alignment state. It is believed that it can be obtained. That is, when the phase series of the ferroelectric liquid crystal material is, for example, chiral smectic C phase, water Iso-4Ch-4SmA-4SmC*However, lso;
Isotropic liquid Ch; cholesteric phase SmA; smectic A phase SmC*H chiral smectic C phase is desirable.

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

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

In order to expand the temperature range, it is necessary to mix many ferroelectric liquid crystal materials.At this time, in order to satisfy the four conditions mentioned above, many ferroelectric liquid crystal materials must be mixed in the cholesteric phase and Mixing must be done while taking into account the left and right pitch directions, sizes, polarities of spontaneous polarization, etc. in each of the chiral smectic C phases, and a practical ferroelectric liquid crystal composition is particularly difficult to prepare. Due to these problems, a method of mixing compounds exhibiting a non-chiral smectic C phase was used. Figure 3 shows the spontaneous polarization of a mixed system using a conventional ester-based non-chiral compound and its effect at 25°C. 24
It shows the response speed when a voltage of VPp is applied.

Problems to be Solved by the Invention Conventional ferroelectric liquid crystal materials cannot be used to expand the temperature range.
A method of mixing compounds exhibiting a non-chiral smectic C phase has been used. However, by mixing non-chiral compounds, the spontaneous polarization becomes smaller, and as the non-chiral component increases, the response speed becomes slower. There was a problem that it was difficult to obtain a practical ferroelectric liquid crystal composition because it was necessary to adjust many material constants such as polarity, direction of twist of the helix in the chiral smectic C phase, and direction of twist of the helix in the cholesteric phase. . Therefore, the ferroelectric liquid crystal composition of the present invention is a liquid crystal compound exhibiting a non-chiral smectic C phase (
1) By using a phenylpyrimidine-based liquid crystal compound as shown in the formula, we provide a ferroelectric liquid crystal material that exhibits a ferroelectric liquid crystal phase over a wide temperature range, can easily change its orientation, and can respond at high speed. It is something to do.

Means for Solving the Problems In order to solve the above problems, the present invention provides a ferroelectric liquid crystal material having a phenylpyrimidine non-chiral structure (i.e., a twisted structure, By mixing a liquid crystal material that exhibits a smectic C phase (which has no spontaneous polarization at all), the amount of non-chiral components added can be increased, exhibiting a ferroelectric liquid crystal phase over a wide temperature range, and achieving good alignment. , a ferroelectric liquid crystal material capable of high-speed response on the order of several tens of microseconds can be easily obtained.

Function Generally, in order to expand the temperature range of liquid crystals, it is necessary to mix two or more types of liquid crystal compounds with different molecular shapes. However, when mixing ferroelectric liquid crystal materials, material constants such as the polarity of the spontaneous polarization of the compound, the direction of twist of the ferroelectric liquid crystal phase, and the direction of tearing of the cholesteric phase must be taken into consideration. should not. Therefore, if the non-chiral smectic C phase, which has no twisted structure or spontaneous polarization, is used to expand the temperature range, the temperature range can be expanded without considering material constants such as the direction of twist and the polarity of spontaneous polarization. A wide range of liquid crystal compositions can be easily obtained. When a liquid crystal compound exhibiting a non-chiral smectic C phase is mixed with a ferroelectric liquid crystal compound, the spontaneous polarization of the mixture decreases linearly as the non-chiral component increases, as shown in Figure 3, so the spontaneous polarization of the mixture becomes extreme. As a result, the response speed becomes slower as the non-chiral component increases. In the case of the present invention, since a phenylpyrimidine-based non-chiral liquid crystal compound with extremely low friction viscosity is mixed, its spontaneous polarization decreases, but as shown in Figure 4, even if the non-chiral component increases, the response speed increases. is not slowing down, it is trending faster. In this way, by using a phenylpyrimidine-based liquid crystal compound that exhibits a non-chiral smectic C phase, even if the amount added does not result in faster response characteristics, the non-chiral component is added to the liquid crystal compound that exhibits ferroelectricity. If a phenylpyrimidine-based liquid crystal material as shown in formula N) is mixed, a large amount of non-chiral component can be added, so that a ferroelectric liquid crystal composition with a long pitch and high-speed response characteristics over a wide temperature range can be obtained. easily obtained.

Embodiment An embodiment of the present invention will be described with reference to the drawings. First, FIG. 5 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, 1 is a polarizing plate, 2 is a glass substrate, 3 is a transparent electrode,
4 is an organic polymer film subjected to alignment treatment by rubbing, 5
6 represents a ferroelectric liquid crystal layer, and 6 represents a spacer for keeping the cell thickness constant. A ferroelectric liquid crystal material was sealed in a cell with such a structure, and its response characteristics and spontaneous polarization were measured. Spontaneous polarization was measured using the triangular wave method.

In addition, regarding the phase transition temperature, the text
Measurements were performed by ure observation and DSC (differential scanning calorimeter).

Example 1 Compound (I) according to claim 1 has the formula (II)
The phase transition temperature, spontaneous polarization, pitch length, and response speed were measured for a mixed system in which the chiral component exhibiting ferroelectricity is represented by the formula (I[[). FIG. 1 shows the phase diagram of this mixed system, and FIG. 2 shows the spontaneous polarization at 25° C. and the concentration dependence of the response speed when 20 Vpl) is applied.

From Figure 2, the value of spontaneous polarization decreases almost linearly as the non-chiral component increases;
Even at t%, the response speed when a voltage of 24 Vl)p is applied at 25°C is as fast as 110 μsec.
When the non-chiral component is 5 Qwt%, it exhibits a high-speed response of 62 μsec. Further, in this composition, the pitch was considerably long and the orientation state was good. Good orientation was also obtained with compounds having compositions other than those mentioned above.

Effects of the Invention As described above, the present invention can easily be used over a wide range of temperatures including room temperature by mixing a phenylpyrimidine liquid crystal material shown by the formula (1) which exhibits a non-chiral smectic C phase with a ferroelectric liquid crystal material. The present invention provides a ferroelectric liquid crystal material that exhibits a liquid crystal phase in a temperature range and is capable of high-speed response.

[Brief explanation of drawings]

Figure 1 is the phase diagram of the mixed system in Example 1 of the present invention, and Figure 2 is the phase diagram of the mixed system in Example 1 of the present invention.
The figure is a characteristic diagram of the concentration dependence of the response speed and spontaneous polarization of the ferroelectric liquid crystal cell in Example 1 of the present invention, and FIG. 3 is the concentration dependence of the chiral component of the spontaneous polarization and response speed of the conventional ferroelectric liquid crystal composition. FIG. 4 is a characteristic diagram of the concentration dependence of the chiral component of the spontaneous polarization and response speed of the ferroelectric liquid crystal composition of the present invention, FIG. 5 is a diagram of the configuration of the ferroelectric liquid crystal cell, and FIG. 6 is a schematic diagram of a ferroelectric liquid crystal, and FIG. 7 is a schematic diagram showing the operating principle of a ferroelectric liquid crystal. 1... Polarizing plate, 2... Upper and lower glass substrates, 3... Transparent electrode, 4... Organic alignment film subjected to alignment treatment, 5... ...ferroelectric liquid crystal phase,
6...Spacer to keep cell thickness constant,
7... Ferroelectric liquid crystal molecules, 8... Spontaneous polarization, 9... C director-110...
- Cone, 11... layer, 12... layer normal, 13... tilt angle θ of the molecule with respect to the layer normal,
14...Liquid crystal molecules whose long axis of the molecule is tilted by 10 degrees with respect to the layer normal, 15...Liquid crystal molecules whose long axis of the molecule is tilted by 10 degrees with respect to the layer normal, 16...Dipole moment facing toward the front of the page, 17...Dipole moment pointing toward the back of the page, 18...
・Direction of the two polarizing plates. Name of agent Patent attorney Toshio Nakao 1 person Fig. 1 06θ lθθ Compound CI [) no W-t7A Fig. 2 WtZ of compound (I) Fig. 3 Opi 100 Chiral 8th W Ch No. Figure 4 wt% of chiral A Figure 5 Figure 6 Figure 7

Claims (2)

[Claims] (1) Liquid crystal exhibiting a non-chiral smectic C phase represented by the general formula ▲ Numerical formulas, chemical formulas, tables, etc. A liquid crystal composition characterized by adding at least one type of compound. (2) Liquid crystal exhibiting a non-chiral smectic C phase represented by the general formula ▲ Numerical formulas, chemical formulas, tables, etc. 2. The liquid crystal composition according to claim 1, wherein at least one compound is added to the ferroelectric liquid crystal composition having an extended helical pitch.