JPH02151683A - Ferroelectric liquid crystal composition and liquid crystal display device - Google Patents

Abstract

PURPOSE:To make it possible to prevent a ferroelectric liquid crystal composition from undergoing deterioration of the properties with the lapse of time and thereby keep the properties well by adding an epoxy compound to the composition. CONSTITUTION:At least one epoxy compound is added to a ferroelectric liquid crystal composition. For example, when 0.3wt.% epoxy compound is added to a ferroelectric liquid crystal material, the threshold value characteristics of the liquid crystal can keep steepness even after 700hr.

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 more particularly to a ferroelectric liquid crystal composition and 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 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 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 (for example, Obtronics, 1983).
, Na9), ferroelectric liquid crystal will be explained below with reference to the drawings. Figure 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.

In FIG. 3, 7 is a liquid crystal molecule, 8 is spontaneous polarization, 9 is a C director, 11O 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 3, ferroelectric liquid crystal molecules have spontaneous polarization, and in the chiral smectic C phase, 1, 3,
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. 4 is a diagram showing the operating principle of a ferroelectric liquid crystal. Figure 4(a) shows the state where no voltage is applied;
FIG. 4(C) shows the principle of operation when voltage is applied from the front to the back of the paper, and FIG. 4(C) shows the operating principle when voltage is applied in the opposite direction.

In Figure 4, 14 indicates that the long sleeve of the molecule is +θ with respect to the layer normal.
Tilt liquid crystal molecule, 15, the long sleeve of the molecule with respect to the layer normal is -
The liquid crystal molecules are tilted by θ, 16 is a dipole moment facing towards the front of the paper, 17 is a dipole moment facing towards the back of the paper, and 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 4(a), resulting in a region where the molecules are tilted by +θ degrees with respect to the layer and a region where the molecules are tilted by +θ degrees. Divided into tilted areas. By applying a voltage from the surface of the paper between the upper and lower electrodes to the back side, the entire cell becomes a monodomain tilted by +θ degrees as shown in FIG. 4(b). Furthermore, when a reverse voltage is applied, the entire cell becomes a monodomain tilted by 1θ degree as shown in FIG. 4(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 a ferroelectric liquid crystal to a display, the following conditions are required for the liquid crystal material.

(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 However, η; viscosity Ps; spontaneous polarization E: given by the applied electric field. Therefore, in order to achieve a high response speed 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 C1ark et al., in order to realize this state, it is necessary to make the cell gap d less than the helical pitch p and unwind the helix. N.

Knee, Clark, Nis, Tee, Raghaval; Apple;
Fizz, Rhett, 36 899 (1980) (N, A
, C1ark, S.T.

Lagerwall HA pH, Phys.

Lett, 36 899 (1980)) Therefore,
In order to utilize a cell with a thick cell gap that is easy to manufacture, it is necessary to increase 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, if the phase series of the ferroelectric liquid crystal material is, for example, chiral smectic C phase, I s o-+Ch-esmA-+smc*However, summer
Oi isotropic liquid Ch; cholesteric phase SmA; smectic A phase SmC*; chiral smectic C phase are 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 above four conditions, we must take into consideration the left and right direction of the pitch, the size, the polarity of spontaneous polarization, etc. in the cholesteric phase and chiral smectic C phase of many individual ferroelectric liquid crystal materials. However, 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. It is. In addition, the long-term stability of properties such as bistability and dark value properties is also an important issue.

Problems to be Solved by the Invention In conventional display devices, the characteristics of the ferroelectric liquid crystal element deteriorate over time, and as a result, there is a problem in that it is difficult to maintain good initial characteristics.

In view of the above problems, the present invention provides a liquid crystal composition for eliminating changes in characteristics over time, and a liquid crystal display device using the liquid crystal composition.

Means for Solving the Problems In order to solve the above problems, the liquid crystal composition and liquid crystal display element of the present invention are characterized in that they use a ferroelectric liquid crystal composition containing at least one type of epoxy compound. It has the characteristic of being able to eliminate changes over time.

Function The present invention provides a liquid crystal composition whose characteristics do not change over time by using the above-mentioned liquid crystal composition, and further provides a liquid crystal display device with high display quality.

Example First, the physical properties of the ferroelectric liquid crystal material used in this example are shown below.

Liquid crystal material: ZLI-3654 (MERCK)
o -1→c h-+S m A-1 groan S m C
*Tilt angle: 25" Ps: 29 nC/cm Further, the phase transition temperature when 0.3 wt% of Epicoat 828 (Yuka shell epoxy) is added as an epoxy compound is shown below.

The Iso-4Ch-+SmA SmC* phase transition temperature was measured by texture observation using a polarizing microscope and DSC (differential scanning calorimeter).

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

FIG. 1 shows the structure of a liquid crystal cell. Here, l
and 1' are polarizing plates, 2 and 2' are glass substrates, and 3 and 3.
' is a transparent electrode, 4 and 4' are column layers formed by oblique evaporation, or organic alignment film layers subjected to a certain alignment treatment, 5 is a ferroelectric liquid crystal layer, and 6 is for keeping the cell thickness constant. represents the spacer.

FIG. 2 shows the dark value characteristics of ferroelectric liquid crystal. Figure 2(a) shows ZLI-36 as a ferroelectric liquid crystal material.
When only 54 is injected into the cell, FIG. 2(b) shows that ZLI
-3654 with Epicoat 828 as an epoxy compound
This figure shows the dark value characteristics after 700 hours when a ferroelectric liquid crystal composition obtained by adding 0.3 wt% of is injected into a cell. The cell gap is 2 μm. 0 is the relative brightness of Max when voltage is applied and represents the bulk response, and X is the relative brightness after scanning a series of measurement waveforms for 1000 lines and represents the memory response. From Figure 2, it is clear that only the liquid crystal While the dark value characteristics after 700 hours in the case of injection have deteriorated, the dark value characteristics of the liquid crystal to which Epikote 828 is added maintains symmetrical and steep characteristics even after 700 hours. This is because the surface of the alignment film is modified with an epoxy compound.
This is thought to be due to the effect of relaxing interactions between the sides of liquid crystal molecules.

Furthermore, by adding the epoxy compound, each transition in the phase transition tends to approach a second-order transition, and therefore good results were also shown regarding the alignment of liquid crystal molecules.

In addition, Epicoat 801, 807, 808°815.8
15X, 816, 819, 827° 828XA, 834
,871,1001゜1002.1003,1031,
1055゜1004.1007.1009 (trade name of oil-containing shell epoxy), DER-132 (DOW
).

201, 206, 289 (Chissonox) also showed similar effects. In addition, the solid type was used after being dissolved in liquid crystal.

The liquid crystal material is not limited to ZLI-3654.

Effects of the Invention As described above, the present invention prevents deterioration of memory and dark value characteristics over time and maintains good characteristics by adding at least one type of epoxy compound to a ferroelectric liquid crystal composition. I was able to do that.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a ferroelectric liquid crystal cell in an example of the present invention, Fig. 2 is a block diagram showing the dark value characteristics of a ferroelectric liquid crystal composition, and Fig. 3 is a diagram of the behavior of ferroelectric liquid crystal molecules. An explanatory diagram showing a cone indicating a range, and FIG. 4 is a diagram of the operating principle of a ferroelectric liquid crystal. 1.1'...Polarizing plate, 2,2'...Glass plate, 3.3'...Transparent electrode, 4,4'...
...SjO column layer formed by oblique evaporation, or organic oriented Si, 5, which has been subjected to a certain orientation treatment
. . . Ferroelectric liquid crystal layer containing at least -aim epoxy compound, 6 . . . Spacer, 7 .
...Liquid crystal molecule, 8...Permanent dipole, 9...
...C director-110 ... Cone, 1
1... Layer structure, 12... Layer normal direction,
13... Tilt angle, 14... Liquid crystal molecule whose long axis is tilted by 10 degrees with respect to the layer normal, 15...
・Liquid crystal molecules whose long sleeves are tilted by 10 degrees with respect to the layer normal, 1
6...Dipole moment facing towards the front of the paper, 17...Dipole moment facing towards the back of the paper, 18...Direction of the two polarizing plates . Agent's name Patent attorney Shigetaka Awano Haka 1 name map - 仄 - 連 z, = 100) tsec ") - 1 evil τ gate 100. asec & p addition CV) 1F7 addition A (V)

Claims (2)

[Claims] (1) A ferroelectric liquid crystal composition characterized in that at least one type of epoxy compound is added to the ferroelectric liquid crystal composition. (2) A liquid crystal display device using the ferroelectric liquid crystal composition according to claim (1).