JPH01198682A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device having memory properties and excellent threshold characteristic, providing wide gap margin, by sandwiching a liquid crystal layer containing a specific ferroelectric liquid crystal compound not forming racemic modification in a chiral part between substrates. CONSTITUTION:The aimed device obtained by sandwiching a liquid crystal layer which comprises ferroelectric liquid crystal composition shown by formula I (R is alkyl, alkoxy, acyloxy or carbonic acid ester; X is optically active alkyl, halogenated alkyl, alkoxy, acyloxy or alkoxycarbonyl) and not forming racemic modification in a chiral part in between a pair of substrates having electrodes opposing the liquid crystal layer and 3-5mum gap. The composition is optionally blended with one or more ferroelectric liquid crystal compounds shown by formula II and not forming racemic modification in a chiral part as a compound having the opposite direction of twisting.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display device containing a novel liquid crystal composition, and particularly to a ferroelectric liquid crystal compound.

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.

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 times and memory properties. Research is progressing from various fields with possible applications to display devices (Obtronics, 1
983, No. 9).

The ferroelectric liquid crystal will be explained below while referring to the drawings. FIG. 3 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. Furthermore, ferroelectric liquid crystal molecules are usually composed of optically active molecules that are not racemic pairs.

In Figure 3, 1 is a liquid crystal molecule, 2 is spontaneous polarization, and 3 is C
The director 24 is a cone, 5 is a layer structure, 6 is a layer normal direction, and 7 is an inclination angle θ.

As shown in Figure 3, ferroelectric liquid crystal molecules have spontaneous polarization, and in the chiral smectic C phase, ferroelectric liquid crystal molecules have a tertiary polarization.
The direction of the molecular long axis is slightly shifted for each layer that can freely move outside the conical shape 4 (cone) in the figure, and the structure as a whole has a twisted structure.

Next, we will discuss the display principle of ferroelectric liquid crystal.

FIG. 4 is a diagram showing the operating principle of a ferroelectric liquid crystal. Figure 4 (a
) is a state in which no voltage is applied, FIG. 4(b) is a diagram of the operating principle when a voltage is applied from the front to the back of the page, and FIG. 4(C) is a diagram of the operating principle when a voltage is applied in the opposite direction.

In FIG. 4, 8 is a liquid crystal layer, 9 is a spontaneous polarization, 10 is a liquid crystal molecule, 11 is a perpendicular direction of the layer, 12 is an electric field, 13 is a polarization axis of a lower polarizer, 14 is an upper analyzer, 15 indicates an electric field. When a ferroelectric liquid crystal is sandwiched between a glass substrate with transparent electrodes and the thickness of the panel is made less than the helical pitch, the helix unwinds and the molecules move against the layer as shown in Figure 4(a). +θ
It is divided into a region tilted by 1 degree and a region tilted by 1θ degree. By applying a voltage between the upper and lower electrodes from the front to the back of the paper, the
As shown in b), the entire cell becomes a monodomain tilted by +θ degrees.

Furthermore, when a reverse voltage is applied, the entire cell becomes a monodomain tilted by 1θ degree as shown in FIG. 4(C). Therefore, if we use birefringence or dichroism due to electro-optic effect, +θ
Light and darkness can be expressed by two tilted states.

When applying a ferroelectric liquid crystal to a display, the following conditions are required for the liquid crystal material.

(2) Exhibits a ferroelectric liquid crystal phase (eg, 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 response speed on the order of several μsec, it is necessary to have a large spontaneous polarization Ps.

(2) As described above, the optical response of a ferroelectric liquid crystal is first realized in two stable states (bistable 5 states). According to C1ark et al., in order to achieve this state, it is necessary to make the cell gap d less than the spiral pitch and unwind the spiral [for example, F. Nee, Clark, Nis.

Tea, Raghaval: Apple, Huiz, Let, , 3
6899 (1980) (N, ^, CIark,
S,T.

Lagerwa 11; APH, Phys, Let
t, , 36899 (1980) > 3. Therefore, in order to utilize a cell with a thick cell gap that is easy to manufacture, 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, I s o -+C
h-+smA-+SmC*However, Iso: isotropic liquid Ch: cholesteric phase SmA: smectic A phase SmC*: chiral smectic C phase is preferable.Furthermore, among liquid crystal materials having the above phase series, It is believed that the longer the pitch of the Ch phase, the better the alignment state.

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

Problems to be Solved by the Invention 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, many ferroelectric liquid crystal materials must be mixed while taking into consideration all aspects such as the left and right pitch direction, size, and polarity of spontaneous polarization in the cholesteric phase and chiral smectic C phase. However, there is a problem in that it is difficult to obtain a practical ferroelectric liquid crystal composition, and at present, bistability can only be obtained in a thin region with a cell gap of about 2 μm.

In other words, in a display device with a conventional configuration, considering the memory and threshold characteristics of the ferroelectric liquid crystal material, it is necessary to make the cell thickness extremely thin and uniform, about 2 μm. There was a set point during the short and so on.

The present invention solves the above problems, and the cell thickness is 3 to 5.
The purpose of this invention is to provide a liquid crystal display device with high display quality in a thick region of μm.

Means for Solving the Problems In order to solve the above problems, the liquid crystal display device of the present invention has the following features:
It has a structure in which a ferroelectric liquid crystal compound having a biphenyl skeleton is used as a component of the liquid crystal composition.

That is, the liquid crystal display device of the present invention has a large amount of (R is an alkyl, alkoxy, acyloxy, carbonate ester group,
X represents an optically active alkyl, halogenated alkyl, alkoxy, acyloxy, alkoxycarbonyl group,
), the liquid crystal layer is made of a liquid crystal composition containing at least one kind of ferroelectric liquid crystal compound in which the chiral part does not form a racemic body, and the liquid crystal layer has an electrode facing the liquid crystal layer and has a gap of 3 to 5 μm. The liquid crystal composition is sandwiched between a pair of substrates, and if necessary, the liquid crystal composition is a ferroelectric liquid crystal compound having a reverse twist direction, with a large amount (R is alkyl, alkoxy, acyloxy, carbonate). ester group, X represents an optically active alkyl, halogenated alkyl, alkoxy, acyloxy, alkoxycarbonyl group), and contains at least one type of ferroelectric liquid crystal compound in which the chiral moiety does not form a racemate; Further, if necessary, the liquid crystal composition may contain a liquid crystal compound exhibiting a non-chiral smectic C phase, such as a large amount or (R1, R2, R3, and R4 represent alkyl, alkoxy, acyloxy, or carbonate groups). It contains a liquid crystal compound or liquid crystal composition represented by:

Effect The present invention has the above-described structure, so that the gap is 3 to 5 μm.
However, it is possible to easily fabricate a cell that exhibits memory properties and good threshold characteristics and has a uniform gap between the upper and lower substrates, and to obtain a liquid crystal display device with high display quality without short circuits between the upper and lower substrates.

Example Example 1 An embodiment of the present invention will be described below with reference to the drawings.

The structure of the liquid crystal display device used for measurement in this example is shown in FIG. 5, where 21a and 21b are polarizing plates,
22a and 22b are glass substrates, 23a and 23b
24a and 24b are SiO columns formed by oblique evaporation, 25 is a liquid crystal layer, and 26 is a spacer for keeping the cell thickness constant. Injecting a liquid crystal composition using a ferroelectric liquid crystal compound into such a device,
Its threshold characteristics and response speed were measured. Further, the phase transition temperature was measured by texture observation using a polarizing microscope and by DSC (differential scanning calorimeter).

FIG. 1 shows the dependence of the threshold voltage V90% on the cell thickness gap. An apparatus having the structure shown in FIG. 5 was used, and the thickness of the SiO oblique evaporation film was 200 OA. Components, component ratio, transition temperature and 44 of the liquid crystal composition used
The response speed at VDrj is as follows.

1) Component: 5wt% i) Transition temperature (°C) I s□ −+ Ch rate → SA → 3C
m − * Cryi) Response speed 100μsec (Gap 3.2μ11, Film thickness 2
000 people, orthorhombic cell) From Figure 1, it can be seen that the threshold voltage at a gap of 2 to 3 μm shows gap (cell thickness) dependence, whereas at a gap of 3 μm, the threshold voltage depends on the gap (cell thickness).
Threshold voltage V90 during the same pulse at ~4 μm
There was almost no difference in percentage, and we were able to obtain a very wide gap margin.

FIG. 2 shows the threshold characteristics of this ferroelectric liquid crystal material at a gap of 5 μm. 0 is the maximum relative brightness when voltage is applied and represents the bulk response,
X is the relative brightness after scanning a series of measurement waveforms for 1000 lines, and represents a memory response.

From FIG. 2, relatively steep threshold characteristics could be obtained even with a gap of 5 μm.

Examples 2 to 7 Using the same liquid crystal display device as in Example 1 above, using the ferroelectric liquid crystal composition shown in Table 1 as the ferroelectric liquid crystal material, the response speed was determined in the same manner as in Example 1. When I measured it,
As shown in Table 1, almost the same results as in Example 1 were obtained.

Note i) Composition of the non-chiral component Sl: S2: (R1, R2, R3, R4 represent alkyl, alkoxy, acyloxy, carbonate groups) As described above, according to each of the above examples, the non-chiral component has a biphenyl skeleton. By using a ferroelectric liquid crystal compound, memory properties were exhibited even in a region with a relatively thick gap, and good threshold preference could be obtained with a gap of 3 to 5 μm regardless of the structure of the optically active group of the chiral component.

In the liquid crystal display device of the present invention, in order to control the alignment of the ferroelectric liquid crystal compound in the liquid crystal layer, an organic alignment film such as a polyimide polymer may be coated on the surfaces of the pair of substrates. For example, a dichroic dye such as an anthraquinone dye may be included.

Effects of the Invention As described above, the present invention uses a ferroelectric liquid crystal compound having a biphenyl skeleton as a component of a liquid crystal composition, exhibits memorability and good threshold preference at a gap of 3 to 5 μm, and has an extremely high A wide gap margin can be obtained, and a liquid crystal display device with no short circuit between the upper and lower substrates can be obtained, and device design can be facilitated from the viewpoint of panel manufacturing.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the gap (cell thickness) and threshold voltage in the liquid crystal display device of Example 1 of the present invention, and FIG.
The figure shows the relationship between applied voltage and relative brightness in the liquid crystal display device of Example 1, Figure 3 is a schematic diagram showing a cone showing the operating range of molecules of a ferroelectric liquid crystal compound, and Figure 4 is a diagram showing a cone showing the operating range of molecules of a ferroelectric liquid crystal compound. FIG. 5 is an exploded perspective view of a liquid crystal display device used in each embodiment of the present invention. 21a, 21b - polarizing plate, 22a, 22b - glass substrate, 23a, 23b... transparent electrode, 24a, 2
4b-... Oblique evaporation SLO column, 25... Liquid crystal layer,
26...Spacer. Agent Yoshi Morimoto Buddhist painting 1 volume 1 - ~ Yabb (JL IN) (MEVX) Fig. 2 1 egg 27rJ1 pressure (Vn Fig. 3 Fig. 4

Claims (1)

[Claims] 1. The general formula is ▲ Numerical formula, chemical formula, table, etc. ▼ (R is alkyl, alkoxy, acyloxy, carbonate group, X is optically active alkyl, halogenated alkyl, alkoxy, acyloxy, alkoxy A liquid crystal layer comprising a liquid crystal composition containing at least one type of ferroelectric liquid crystal compound represented by (representing a carbonyl group) in which the chiral moiety does not form a racemic body, is provided with an electrode facing the liquid crystal layer. A liquid crystal display device sandwiched between a pair of substrates with a gap of 3 to 5 μm. 2. Liquid crystal compositions are ferroelectric liquid crystal compounds with opposite twist directions, and have general formulas such as ▲mathematical formulas, chemical formulas, tables, etc.▼ (R is alkyl, alkoxy, acyloxy, carbonate group, X is 2. The liquid crystal according to claim 1, which contains at least one ferroelectric liquid crystal compound represented by an optically active alkyl, halogenated alkyl, alkoxy, acyloxy, or alkoxycarbonyl group, and whose chiral moiety does not form a racemate. Display device. 3. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 4. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 5. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 6. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 7. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 8. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 9. The liquid crystal display device according to claim 1 or 2, wherein the optically active group X is represented by ▲a mathematical formula, a chemical formula, a table, etc.▼. 10. Claims 1 to 10, wherein the liquid crystal composition contains at least one liquid crystal compound exhibiting a non-chiral smectic C phase.
9. The liquid crystal display device according to any one of 9. 11.A liquid crystal compound exhibiting a non-chiral smectic C phase whose general formula is ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (R1 and R2 represent alkyl, alkoxy, acyloxy group, carbonate ester group) 11. The liquid crystal display device according to claim 10, using: 12. As a liquid crystal compound exhibiting a non-chiral smectic C phase, the general formula is ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ and ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (R1, R2, R3, R4 are alkyl, alkoxy, 11. The liquid crystal display device according to claim 10, using a composition of a liquid crystal compound represented by acyloxy or carbonate group. 13. The liquid crystal display device according to any one of claims 1 to 12, wherein the surfaces of the pair of substrates are obliquely evaporated to control the orientation of the ferroelectric liquid crystal compound. 14. The liquid crystal display device according to claim 13, wherein the obliquely evaporated material is SiO. 15. The liquid crystal display device according to claim 1, further comprising an organic alignment film coated on the surfaces of the pair of substrates. 16. Claims 1 to 1, wherein the liquid crystal layer contains a dye exhibiting dichroism.
16. The liquid crystal display device according to any one of 15.