JPS63191891A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prepare a ferroelectric liq. crystal display device which operates over a wide temp. range and enables a high speed response, by using a particular liq. crystal compd. having strong biphenyl or terphenyl conjugation. CONSTITUTION:A liq. crystal display device comprising a liq. crystal compsn. composed of at least one compd. of formula I (wherein l is 0 or 1; R is alkyl or alkoxy and R' is acyloxy or carbonyloxy, optically active acyloxy or carbonyloxy) having strong conjugation. Since the ferroelectric liq. crystal compsn. used in the above device contains a biphenyl or terphenyl liq. crystal material mixed therein, it has a structure similar to that of a rigid body by virtue of the conjugation stronger than that of conventional ester liq. crystal materials, which renders the liquid compsn. advantageous from the viewpoint of elasticity and enables a remarkable increase in the electrooptical response speed. Thus, it becomes possible to prepare a display device having an excellent display quality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application ``The present invention relates to a liquid crystal display device using a liquid crystal composition containing a novel liquid crystal substance, and particularly to a ferroelectric liquid crystal display device.

Conventional technology In recent years, liquid crystal displays have become widely used not only in watches and desks, but also in video equipment, and liquid crystal color televisions have also begun to appear on the market.Currently, color display liquid crystal panels use nematic liquid crystals. The mainstream is dominated by things.However,
The characteristics of nematic liquid crystals are far from ideal and include many problems. Ferroelectric liquid crystals have characteristics that nematic liquid crystals do not have, such as fast response speed and memory performance, making them ideal for display devices. Applications are being considered and research is progressing in many fields (for example, optronics, 198
3. Arashi 9) The ferroelectric liquid crystal will be explained below with reference to the drawings. Figure 6 is a schematic diagram of ferroelectric liquid crystal molecules. Ferroelectric liquid crystal is usually a liquid crystal with a layered structure called smectic liquid crystal, and the liquid crystal molecules are θ with respect to the layer normal direction.
It has a tilted structure. Furthermore, ferroelectric liquid crystal molecules are usually composed of optically active liquid crystal molecules that are not racemic.

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

As shown in Figure 6, the ferroelectric liquid molecules have spontaneous polarization, and in the chiral smectic C phase, they can move freely outside the cone 10 in Figure 6. The direction of the molecular long axis is slightly shifted for each layer, and the structure as a whole has a twisted structure. Next, we will discuss the display principle of ferroelectric liquid crystals. FIG. 7 is a diagram showing the operating principle of a ferroelectric liquid crystal. Figure 7(a) shows a state with no voltage applied;
(in Figure 7) is when a voltage is applied from the back side of the paper to the front side.
Figure 7 (C1 is a diagram of the principle of operation when voltage is applied in the opposite direction. 14 is a liquid crystal molecule whose long axis of the molecule is tilted by 10 degrees with respect to the layer normal, and 15 is a liquid crystal molecule whose long axis is tilted by 1 θ degree. , 16 is the dipole moment facing toward the front of the page, 17 is the dipole moment facing toward the back of the page, and 1 is the direction of the two polarizing plates.0 Ferroelectric liquid crystal with transparent electrodes. When sandwiched between glass substrates and the thickness of the panel is less than the helical pitch, the helix unravels as shown in Figure 7 fal, and the molecules +
It is divided into a region tilted by θ degrees and a region tilted by 1θ degree. Up and down!
By applying a voltage from the back of the paper surface to the front surface between the electrodes, the seventh
As shown in Figure (bl), the entire cell becomes a monodomain tilted by +θ degrees. Also, when a reverse voltage is applied, the entire cell becomes a monodomain tilted by -0 degrees as shown in Figure 7 tc+. Therefore, the electro-optic effect When applying a ferroelectric liquid crystal to a display device, the following conditions are required for the liquid crystal material: can give.

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

■ The response speed τ of the ferroelectric liquid crystal to the electric field is τmiη
/Ps-E However, 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 by a stable two-state a (bistable five-state). According to C1erk et al., in order to realize this state, it is necessary to make the cell gap d smaller than the spiral vinyl and unwind the spiral. F. Knee, Clark, Nis, Tee, Raghaval; Apple, Fizz, Left 0.1 Tech 899 (1980) (N, A, C1
erk, S, T, La (erwallHAp
H.

Phys, L-ett, 36 899 (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 pinch of the ferroelectric liquid crystal phase.

■ 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 anthropomorphism (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, Is o-*Ch-*SmA-esmc*However, Is
o; isotropic liquid Ch; cholesteric phase 3 mA; smectic human phase SmC*; chiral smectic C phase is desirable.

Furthermore, among the liquid crystal materials with the above phase series, C
It is believed that the longer the h-phase pitch, the better the alignment state.

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

There are only a few conventional ferroelectric liquid crystal materials that are practical in terms of temperature range, and at present there are almost no materials that meet all of the above conditions and can be put to practical use. Furthermore, in the past, ferroelectric liquid crystal materials using chemically stable ester compounds were used for soil.

The characteristics of a mixed system using conventional ester compounds are shown below.

50wt% Transition temperature Iso -* Ch -* SmA -*
SmC*73℃ 67℃ 57℃ Response speed (25℃) 1.2m5ec (24Vpp) The rjiS point that the invention aims to solve Conventional ferroelectric liquid crystal materials use chemically stable ester compounds. were the majority.

However, ester compounds have a problem in that although they have high SmC properties, they also have high viscosity and considerably poor electro-optical response characteristics. Therefore, the ferroelectric liquid crystal composition of the present invention uses a strongly conjugated biphenyl-based or terphenyl-based liquid crystal compound to provide a ferroelectric liquid crystal display with excellent display quality that operates in a wide temperature range and can respond at high speed. It provides equipment.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a strongly conjugated liquid crystal material such as biphenyl or terphenyl, which can be used in a wide temperature range. Excellent operating speed and fast response.

The present invention provides a ferroelectric liquid crystal display device with improved display quality.

Function: Since the ferroelectric liquid crystal composition used in the ferroelectric liquid crystal display device of the present invention is a mixture of biphenyl-based or terphenyl-based liquid crystal materials, it has a stronger conjugate system than conventional ester-based liquid crystal materials, making it more rigid. It has a structure close to that of , which is advantageous in terms of elasticity and has an extremely fast electro-optical response speed. As a result, a display device with extremely excellent display quality can be obtained.

Embodiment A liquid crystal display device according to an embodiment of the present invention will be described 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 is a polarizing plate, 2 is a glass substrate, 3 is a transparent electrode, and 4
numeral 5 represents an organic polymer film subjected to alignment treatment by rubbing, numeral 5 represents a ferroelectric liquid crystal layer, and numeral 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, the phase transition temperature was determined by tex using a polarizing microscope.
Measurements were performed by ture observation and DSC (differential scanning calorimeter).

Example 1 The compound described in claim (1) is a compound represented by formula (1), and this compound is mixed with an ester compound (I[) exhibiting a non-chiral smectic C phase. The phase transition temperature and response speed of the component mixture system were measured. Figure 1 shows the concentration dependence of spontaneous polarization at 25°C and response speed when 24V99 is applied, and Figure 2 shows the phase diagram of this mixed system. For comparison, the response speed of a mixed system of an ester-based chiral smectic liquid crystal compound and a non-chiral ester compound having the same chiral properties is shown below.

1200μ5 at a concentration of non-chiral component of 50wt%
EIC* The biphenyl mixture of this example showed a high-speed response of 120 μsec under the same conditions.

......(1) Example 2 The compound according to claim 11 is a compound represented by formula (1), and this compound is a phenylpyrimidine-based compound exhibiting a non-chiral smectic C phase. Compound (II
The phase transition temperature and response speed of the two-component mixed system containing I) were measured. Figure 3 shows spontaneous polarization at 25°C and 24VI
) shows the concentration dependence of the response speed when +1 is applied, and the fourth
The phase diagram of this mixed system is shown in the figure. The biphenyl-based mixture of this example has a non-chiral component of 65μ at 50wt%.
It showed a high-speed response of sec.

Effects of the Invention As described above, the present invention uses a highly conjugated phenyl-based or terphenyl-based liquid crystal compound as a ferroelectric liquid crystal material, so that it can easily operate in a wide temperature range including room temperature and has a high-speed response. The present invention provides a ferroelectric liquid crystal display device with excellent display quality.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of the concentration dependence of response speed and spontaneous polarization of a ferroelectric liquid crystal cell in Example 1 of the present invention, FIG. 2 is a phase diagram of a mixed system in Example 1 of the present invention, and FIG. The figure is a characteristic diagram of the concentration dependence of response speed and spontaneous polarization of a ferroelectric liquid crystal cell in Example 2 of the present invention, Figure 4 is a phase diagram of a mixed system in Example 2 of the present invention, and Figure 5 is A block diagram of a ferroelectric liquid crystal cell, 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...with respect to the layer normal of the molecule (aj angle θ
, 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 Haka1 person No. 11!
1 0 9 ΔO chiral 8 to VV e % Figure 2 o so
wt% of ttv compound (°X) Figure 3 θ so
to. Change + thing (π) Wtl Figure 4 o z ,
to6il:,+thing <x) wt3 Figure 5 Figure 6

Claims (9)

[Claims] (1) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, in the formula, l is an integer of 0 or 1, R is an alkyl group,
R' represents an alkoxy group, and R' represents an acyloxy group, a carbonyloxy group, or an optically active acyloxy group or carbonyloxy group. ) A liquid crystal display device characterized by using a liquid crystal composition containing at least one type of strongly conjugated compound as represented by the following. (2) A liquid crystal display device according to claim (1), characterized in that R is an optically active 2-methylbutyl group (numerical formula, chemical formula, table, etc.). (3) A liquid crystal display device according to claim (1), characterized in that R is an optically active 2-octyl group (numerical formula, chemical formula, table, etc.). (4) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, in the formula, l is an integer of 0 or 1, R is an alkyl group,
R' represents an alkoxy group, and R' represents an acyloxy group, a carbonyloxy group, or an optically active acyloxy group or carbonyloxy group. ) and general formulas ▲mathematical formulas, chemical formulas, tables, etc. 1. A liquid crystal display device comprising a liquid crystal composition containing at least one compound represented by the following formulas. (5) The liquid crystal according to claim (4), which uses a liquid crystal composition in which R is an optically active 2-methylbutyl group ▲ Numerical formula, chemical formula, table, etc. ▼ Display device. (6) In the general formula, R is an optically active 2-octyl group ▲ mathematical formula,
A liquid crystal display device according to claim (4), characterized in that a liquid crystal composition having a chemical formula, a table, etc. is used. (7) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, in the formula, l is an integer of 0 or 1, R is an alkyl group,
There are strongly conjugated compounds represented by an alkoxy group (where R' is an acyloxy group, carbonyloxy group, or an optically active acyloxy group or carbonyloxy group) and general formulas ▲ mathematical formulas, chemical formulas, tables, etc. ▼ ( However, the liquid crystal composition is characterized in that it uses a liquid crystal composition containing at least one compound each represented by the formula (wherein R″ and R′″ each represent an alkyl group, an alkoxy group, or an optically active alkyl group or an alkoxy group). LCD display device. (8) The liquid crystal according to claim (7), characterized in that a liquid crystal composition in which R in the general formula is an optically active 2-methylbutyl group (numerical formula, chemical formula, table, etc.) is used. Display device. (9) In the general formula, R is an optically active 2-octyl group ▲ mathematical formula,
A liquid crystal display device according to claim (7), characterized in that a liquid crystal composition having a chemical formula, a table, etc. is used.