JPS63256688A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To prepare a ferroelectric liq. crystal material which easily exhibits a liq. crystal phase over a wide temp. range including room temp. and enables a high speed response, by adding a liq. crystal material exhibiting nonchiral smectic C phase to a ferroelectric liq. crystal material in particular proportions. CONSTITUTION:A liq. crystal compsn. prepd. by adding at least one liq. crystal material exhibiting nonchiral smectic C phase in an amt. of at least 30-70wt.% to a ferroelectric liq. crystal material. Examples of the liq. crystal material include a compd. of formula 1 (wherein R and R' are each an alkyl, alkoxy, or acyloxy group).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to liquid crystal compositions containing novel liquid crystal materials, and in particular 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 nematic liquid crystals are far from ideal and include many problems. Ferroelectric liquid crystals have various properties that are not found in nematic liquid crystals, such as fast response speed and memory properties, and are being studied in a variety of fields for potential applications in display devices. (e.g. Optronics, 198
3.9) The 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 usually a liquid crystal having a layered structure 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. In addition, ferroelectric liquid crystal molecules are usually composed of optically active liquid crystal molecules that are not lace bodies.

In Figure 6, 7 indicates liquid crystal molecules, 8 indicates spontaneous polarization, 9 indicates C director, 1) 0 indicates cone, 1) indicates layer structure, 12 indicates layer normal method, and 13 indicates 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 on the outside of the conical shape 10 (cone) shown in the figure. 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. Fig. 7(a) shows the state when no voltage is applied, and Fig. 7(b) shows the case when the voltage is applied from the surface of the paper toward the front side.
FIG. 7(C) 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 +θ degrees with respect to the layer normal, 15 is a liquid crystal molecule tilted by 10 degrees, 16 is a dipole moment facing 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. When a ferroelectric liquid crystal is sandwiched between glass substrates with transparent electrodes and the thickness of the panel is made equal to or less than the helical pitch, the helix unwinds as shown in Figure 7 (al), and the molecules are +θ with respect to the layer.
It is divided into a region tilted by 10 degrees and a region tilted by 10 degrees. By applying a voltage between the upper and lower electrodes from the back of the paper toward the front, the entire cell becomes a monodomain tilted by +θ degrees as shown in FIG.

Furthermore, when a reverse voltage is applied, the entire cell becomes a monodomain tilted by -θ degrees as shown in FIG. 7(C). 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-E 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, Fizz, Left, 36
899 (1980) (N, A, C1er
k.

S, T, Lagerwall; APH, Phy
(S, Lett, 36899 (1980)) Therefore, in order to utilize a cell with a thick cell gap that is easy to fabricate, it is necessary to lengthen the helical pitch of the ferroelectric liquid crystal.

Φ The orientation state of the ferroelectric liquid crystal varies depending on the phase series of the liquid crystal material, and especially the smectic A phase (Sa+A) and cholesteric phase (ch) on the high temperature side of the ferroelectric liquid crystal phase.
It is believed that a liquid crystal material having a good alignment state can be obtained. That is, when the phase series of the ferroelectric liquid crystal material is, for example, chiral smectic C phase, water Iso -*Ch-+SmA-4SmC*However, I
so: Isotropic liquid Ch: Cholesteric phase SmA: Smectic A phase SmC: Chiral smectic C phase is desirable.

Furthermore, among liquid crystal materials with 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 above four conditions, we must take into consideration the left and right direction of pitch, the size, the polarity of spontaneous polarization, etc. in the cholesteric phase and chiral smectic C phase of many ferroelectric liquid crystal material units. However, there is a problem in that it is difficult to obtain a practical ferroelectric liquid crystal composition, and a method of mixing a compound exhibiting a non-chiral smectic C phase has been adopted.

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. Practical ferroelectric liquid crystal compositions have the disadvantage that they must be mixed while adjusting many material constants, such as polarity, the direction of helix twist in the chiral smectic C phase, and the direction of helix twist in the cholesteric phase. Therefore, the ferroelectric liquid crystal composition of the present invention contains a liquid crystal compound exhibiting a non-chiral smectic C phase in an amount of 30 to 30%.
By mixing 70-t%, it is possible to provide a ferroelectric liquid crystal material that exhibits a ferroelectric liquid crystal phase over a wide temperature range, can easily obtain good alignment, and can respond at high speed.

Means for Solving the Problems In order to solve the above problems, the liquid crystal composition of the present invention has a ferroelectric liquid crystal material that is non-chiral (i.e. has a twisted structure,
By mixing 30 to 70-t% of a liquid crystal material exhibiting a smectic C phase (which has no spontaneous polarization at all), a ferroelectric liquid crystal material capable of expanding the temperature range of the ferroelectric liquid crystal phase, achieving good alignment, and high-speed response. It has the characteristic that it can be easily obtained.

Effect of the present invention By using the above-mentioned liquid crystal compound exhibiting the non-chiral smectic C phase, it is possible to easily obtain a liquid crystal composition having a wide temperature range without considering material constants such as the direction of twist and the polarity of spontaneous polarization. Can be done. 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 4. It becomes extremely small and τ=η/P
From s-E (where τ is the response speed, η is the viscosity, Ps is the spontaneous polarization 1, and E is the applied electric field), the response speed τ becomes slower as the non-chiral component increases. In the case of the present invention, since 30 to 70-t% of a non-chiral liquid crystal compound is mixed, the spontaneous polarization Ps decreases, but the non-chiral component increases due to the correlation with the viscosity η, as shown in FIG. In this case, the response speed τ has not become slower, but tends to become faster.

Example An embodiment of the present invention will be described below with reference to the drawings.

First, in this example, the structure of the liquid crystal cell in which the response characteristics of the ferroelectric liquid crystal material were measured is shown in FIG. 5, where 1.1' is a polarizing plate 2.2' is a glass substrate, 3. 3' is a transparent electrode, 4.4' is an organic polymer film subjected to alignment treatment by rubbing, 5 is a ferroelectric liquid crystal layer, and 6 is 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.

Further, the phase transition temperature was measured by texture observation using a polarizing microscope and using a DSC (differential scanning calorimeter).

Example 1 Regarding a mixed system in which the compound (I) represented by the formula (or acyloxy group) is a compound represented by the formula (III) and the chiral component exhibiting ferroelectricity is represented by the formula (IV) The phase transition temperature, spontaneous polarization, pitch length, and response speed were measured. 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 V pI) is applied. A shows the concentration dependence of spontaneous polarization, and B shows the concentration dependence of response speed. From Figure 2, the value of spontaneous polarization decreases almost linearly as the non-chiral component increases, and when the content of compound (IV) is less than 20-t%, the spontaneous polarization increases in viscosity and affects the response speed.
24 at 25°C when compound (IV) is 20-t%
The response speed when a voltage of Vpp was applied was as slow as 140 μsec. On the other hand, when compound (IV) is 80 wt% or less, the spontaneous polarization shows a high value, but the viscosity also increases accordingly.
The response speed when applying a voltage of 24 V pp at ℃ is 1
It showed a slow value of 20 μsec. Also, in this area,
The temperature range is also narrower than in Figure 1. However, compound (IV)
When a voltage of 24 V pp was applied at 25 DEG C. when 50-t%, the response speed was as fast as 62 .mu.sec, and a liquid crystal phase with a wide temperature range was obtained. Further, in this composition, the pitch was considerably long and the orientation state was good. As described above, the response speed is determined by the correlation between spontaneous polarization and viscosity, and liquid crystal materials are required to exhibit high-speed response and a wide temperature range.

By mixing 30 to 70-t% of a non-chiral component, a liquid crystal material with a fast response and a wide temperature range can be obtained (in the formula, R, R', R', and R- represent an alkyl group, an alkoxy group, or an acyloxy group). A mixture in which the compound (1) and (II) are the compounds represented by the (V) and (VI) formulas, and the chiral component exhibiting ferroelectricity is represented by the (■) formula. The phase transition temperature was measured for the system. Figure 3 shows the phase diagram of this mixed system. From FIG. 3, a liquid crystal phase was exhibited over a wide temperature range as the wt% of the chiral component decreased.

H3 C@H+? O effect■X(C←C00CHzCHCzHs
... (■) Effects of the present invention As described above, the present invention can easily handle a wide range of temperatures including room temperature by mixing 30 to 70 wt% of a liquid crystal material exhibiting a non-chiral smectic C phase to a ferroelectric liquid crystal material. The object of the present invention is to provide a ferroelectric liquid crystal material that exhibits a liquid crystal phase within a range of 100 to 100 nm and is capable of high-speed response.

[Brief explanation of the drawing]

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 graph showing the concentration dependence characteristics of the response speed and spontaneous polarization of the ferroelectric liquid crystal cell in Example 1 of the present invention, Figure 3 is the phase diagram of the mixed system in Example 2 of the present invention, and Figure 4 is A graph showing 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 the ferroelectric liquid crystal. 7 are schematic diagrams showing the operating principle of a ferroelectric liquid crystal. A, A'・・・Concentration dependence of spontaneous polarization, B, B'・
...1.1'...indicating concentration dependence of response speed
...Polarizing plate, 2.2'... Upper and lower glass substrates, 3.3'... Transparent electrode, 4.4'...
・Organic alignment film subjected to alignment treatment, 5... Ferroelectric liquid crystal phase, 6... Spacer for keeping cell thickness constant, 7... Ferroelectric Liquid crystal molecules, 8...
...Spontaneous polarization, 9...C director-1)0
... Cone, 1) ... Layer, 12 ...
...Layer normal, 13...Tilt angle θ of the molecule with respect to the layer normal, 14...Liquid crystal molecule whose long axis of the molecule is tilted by 10 degrees with respect to the layer normal, 15・・・・・・Liquid crystal molecules whose long axis is tilted by 1θ with respect to the layer normal, 16・・・・・・
Dipole moment pointing toward the surface of the paper, 17...
...Dipole moment pointing toward the back of the paper, 18
・・・・・・Direction of the two polarizing plates. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1 θ so
iθO Ib I 4 Nau CIV) vt2 Fig. 2 OSθ Iθ0 Ihi 4-4 Clause (IV) W death, l Fig. 3 θ , so
1004 Hireito 4 Naru (V/1)
The W Sha! ≦Figure 4 0 60 lθρ Chiral A minute ψwt name Figure 5 Figure 6 Figure 7

Claims (5)

[Claims] (1) A liquid crystal composition characterized in that 30 to 70 wt % of at least one type of liquid crystal compound exhibiting an achiral smectic C phase is added to a liquid crystal composition exhibiting a ferroelectric liquid crystal. (2) The general formula of a liquid crystal compound exhibiting a non-chiral smectic C phase is represented by ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, in the formula, R and R' represent an alkyl group, an alkoxy group, or an acyloxy group.) A liquid crystal composition according to claim (1), characterized in that: (3) The liquid crystal composition according to claim 1 or 2, characterized in that the helical pitch of the liquid crystal composition exhibiting ferroelectric liquid crystal is elongated. (4) The general formula of a liquid crystal compound exhibiting a non-chiral smectic C phase is ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (However, in the formula, R, R', R'', R The liquid crystal composition according to claim 1, wherein ``'' represents an alkyl group, an alkoxy group, or an acyloxy group. (5) The liquid crystal composition according to claim 1 or 4, characterized in that the helical pitch of the liquid crystal composition exhibiting ferroelectric liquid crystal is elongated.