JPH0457020A - Ferroelectric liquid crystal element and antiferroelectric liquid crystal element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ferroelectric liquid crystal element and an antiferroelectric liquid crystal element, and more specifically, a ferroelectric liquid crystal element that enables high contrast and high quality display. The present invention relates to liquid crystal elements and antiferroelectric liquid crystal elements.

[Prior art] Conventionally, the use of a liquid crystal element having bistability has been proposed by Clark (C
1ark) and Lagerwall
) (Japanese Unexamined Patent Publication No. 56-107216, US Pat. No. 4,367,924, etc.). As a liquid crystal element having this bistability, a ferroelectric liquid crystal having a chiral smectic C phase (SmC") or H phase (SmH*) is generally used. This ferroelectric liquid crystal is sensitive to electric fields. has a bistable state consisting of a first optically stable state and a second optically stable state, and therefore the conventional TN
Unlike optical modulators in which a type of liquid crystal was used, for example, the liquid crystal is oriented in a first optically stable state for one electric field vector, and in a second optically stable state for the other electric field vector.
The liquid crystal is aligned in an optically stable state. Furthermore, this type of liquid crystal has the property of very quickly taking one of the above two stable states in response to an applied electric field, and maintaining that state when no electric field is applied. By utilizing such properties, considerable essential improvements can be obtained with respect to many of the problems of the conventional TN type device described above.

For the above-mentioned ferroelectric liquid crystal, a method is known in which a uniaxial two-way west direction treatment is applied to the substrate surface in order to obtain alignment performance. Examples of the uniaxial alignment treatment include a method of rubbing the substrate surface in one direction with a bead, cloth, or paper, and a method of obliquely vapor depositing SiO or SiO2 on the substrate surface.

Furthermore, recently, it has been proposed to use a polymer liquid crystal with uniaxial alignment as an alignment film, which has the advantage of improving the uniform alignment of ferroelectric liquid crystals compared to the alignment treatment method described above. It has been reported.

In addition, focusing on liquid crystal materials, it has been reported that materials exhibiting a phase series as shown in formula (I) below significantly improve uniaxial alignment, and are widely used in ferroelectric liquid crystal devices. .

Iso, →ch→SmA　→SmC”→Cryst.

(I) In the formula, ch represents a cholesteric phase, SmA represents a smectic A phase, and SmC'' represents a chiral smectic C phase.

[Problems to be Solved by the Invention] However, it is possible to combine the above-mentioned polymeric liquid crystal film and a ferroelectric liquid crystal having a phase series of formula (I) to turn light on and off using the electro-optic effect of the ferroelectric liquid crystal. When attempting to obtain a ferroelectric liquid crystal element with high contrast, there are the following drawbacks.

That is, like a conventional transmission type ferroelectric liquid crystal element, a pair of polarizing plates are placed outside the liquid crystal cell in a cross-niffle relationship, and the polarization axis of one of the polarizing plates is set to have bistability. , and a ferroelectric liquid crystal element having a configuration in which one of the molecular axes of ferroelectric liquid crystal molecules having a phase series represented by formula (I) coincides with the molecular axis, and using the polymer liquid crystal film as an alignment film. As explained in FIG. 3 below, it was difficult to obtain a state in which light is blocked (a "dark" state).

The present invention has been made to improve the drawbacks of the prior art, and provides a ferroelectric liquid crystal element or an antiferroelectric liquid crystal element using a polymer liquid crystal film as an alignment film.
The object is to provide a high-contrast liquid crystal element that can obtain good optical "bright" and "dark" states.

[Means for Solving the Problems] That is, the first aspect of the present invention is to provide a pair of substrates with mutually crossed transparent electrodes and a uniaxial polymer liquid crystal on the transparent electrodes on at least one of the substrates. In a ferroelectric liquid crystal element in which a ferroelectric liquid crystal film is formed and a ferroelectric liquid crystal is arranged between the pair of substrates with a film thickness set to be sufficiently thin to release the helical structure of the ferroelectric liquid crystal, the ferroelectric liquid crystal is a chiral smectic liquid crystal and does not have a smectic A phase at a temperature higher than the chiral smectic phase.

Further, the second aspect of the present invention is to form transparent electrodes that cross each other on a pair of substrates and a polymer liquid crystal film having uniaxiality on the transparent electrodes on at least one of the substrates, This is an antiferroelectric liquid crystal element characterized by disposing an antiferroelectric liquid crystal having three stable states between them.

The present invention will be explained in detail below.

In the present invention, it is preferable that an alignment film subjected to uniaxial alignment treatment is formed between a transparent electrode formed on at least one substrate and a polymer liquid crystal film, and that the uniaxial alignment treatment is a rubbing treatment.

Further, the liquid crystal element has a pair of polarizers whose polarization axes are in a crossed nicol relationship with each other, and the direction of the polarization axis of one of the polarizers substantially coincides with the axial direction in the uniaxial alignment process. Preferably.

The ferroelectric liquid crystal used in the present invention preferably has a cholesteric phase at a higher temperature than a chiral smectic phase.

Next, optical characteristics of the ferroelectric liquid crystal element and antiferroelectric liquid crystal element of the present invention will be explained.

First, before explaining the optical characteristics of the liquid crystal element of the present invention, we will explain the conventional ferroelectric liquid crystal element, that is, uniaxial polymer liquid crystal (PLC).
The optical properties of a liquid crystal element using a ferroelectric liquid crystal (FLC) having a phase series as shown in the above formula (I) are determined as follows.
This will be explained based on the diagram.

In Fig. 3, assuming that the PLC serving as the alignment film is uniaxially aligned in the direction of 101, which is the rubbing axis and the average molecular axis of the polymer liquid crystal, the FLC also changes to the SmA phase in the process of slow cooling from the Tokichi phase. oriented in the 101 direction. Therefore, in the SmC'' phase, the average molecular axes 102 and 10 of the ferroelectric liquid crystal tilted by the tilt angle θ centering on the January direction.
It has an average molecular axis in either direction of 2'.

The FLC takes a bistable state in these two directions, is oriented in one direction depending on the polarity of voltage application, and maintains this state even after the voltage is removed. Furthermore, as shown in FIG. 3, the two states can be achieved by arranging the polarizer P and the analyzer A in a crossed nicol relationship in the direction of the polarization axis 103 of the polarizer and the polarization axis 104 of the analyzer. It becomes optically distinguishable.

Without a uniaxially oriented PLC, orientation in the 102 direction would provide an optically "dark" state, and orientation in the 102' direction would provide an optically "bright"state;
Since birefringence occurs due to PLO oriented in the 01 direction, coloring occurs even when the FLC is oriented in the 102 direction, making it impossible to obtain an optical "dark" state, and as a result, the contrast due to FLC switching is significantly reduced. do.

The present invention eliminates the above-mentioned drawbacks, and the optical characteristics of the ferroelectric liquid crystal element and antiferroelectric liquid crystal element of the present invention are shown based on FIGS. 1 and 2.

First, the FLC used in the ferroelectric liquid crystal element of the first aspect of the present invention is an FLC that does not have a smectic A phase (SmA), and has, for example, the following phase series.

Iso, →ch→SmC"→Cryst,
(2) As in the case of Fig. 3 mentioned above, in Fig. 1,
When FLC is heated to the isokichi phase and then slowly cooled, first c
It is oriented in the orientation direction 101 of PLC in the h phase. Next, since there is no SmA phase, the smectic layer is formed in the SmC'' phase, and its normal direction is along the PLC orientation axis '101.
Unlike, FLC(7), if the temperature change of the cone angle (or tilt angle) is small, the cone angle is 1Ω5 in the center direction just below the phase transition temperature in the Sm(: ” phase.
) The average molecular axes 102 and 102' are FLC (7) A bistable or substantially bistable state is obtained.

When a polarizer P and an analyzer A are placed above and below this cell as shown in FIG.
Optically "bright" optical characteristics can be obtained in the dark J and 102' orientation directions, and a high contrast liquid crystal element can be obtained.

Next, the optical characteristics of the antiferroelectric liquid crystal element according to the second aspect of the present invention will be explained using FIG.

The liquid crystal used here is not a conventional FLc (but is an antiferroelectric liquid crystal (AFLC) described in the following literature, which has three stable states.

(1) Chandani, Hagiwara, Suzuki, Ouchi.

Takezoe, Fukuda, etc. "Tri-stipple switching"
"In Surface Stabilized Ferroelectric Liquid Crystal with a Large Subontaneous Volatization" Japanese Journal of Applied Physics Vol. 27 p.
p, L 729-L732 (1988) [A, D
, L., Chandani, T., HagiwaraY.
,5uzuki, Y,0uchi, H,Takez
oe and A, Fukuda ;” Trista
ble Switching in 5 surface
5tabilized Ferroelectric L
iquid Crystals with a Lar
geSpontaneous Po1arizatio
n″Jpn, J, Appl Phys.

27pp, L729-L732 (198g)]
(2) A, D, L, Chandani, E, Bretzka, Yukio Ouchi.

Hideo Takezoe and Atsuo Fukuda “Collection of Lecture Proceedings of the 15th LCD Symposium”
Pages 310-311 (1989) In Figure 2, the directions indicated by 105, 105' and 105'' are the average molecular axes in the three states of AFLC, and 101 is the orientation direction of PLC and the normal to the smectic layer of AFLC. It is the direction.

Figures 5(a) and (b) show the AFL in the liquid crystal cell.
FIG. 2 is a schematic diagram showing the molecular orientation state of C. When the AFLC is released from its spiral shape, as shown in FIG. 5(b),
In the absence of an electric field, the molecules are arranged so that the directions of spontaneous polarization are opposite in each layer, and therefore, the overall average molecular axis direction coincides with the layer normal direction 101.

Therefore, as shown in FIG.
It becomes possible to obtain a "dark" state. Furthermore, the optical "bright" state can be switched in the direction of the average molecular axis shown in the 105 or 105' direction, depending on the polarity, by applying a desired electric field as in conventional FLC. That state is maintained. However, unlike conventional FLCs, the voltage at the center of switching hysteresis is not 0.sup., so it is generally necessary to apply an appropriate bias voltage.

[Example code] Hereinafter, the present invention will be explained in more detail.

Example 1 FIG. 4 is a sectional view showing one embodiment of the ferroelectric liquid crystal element of the present invention. The ferroelectric liquid crystal element shown in FIG.
A pair of upper substrate 21a and lower substrate 21b arranged in parallel,
Transparent substrates 22a and 22 wired to each glass substrate
It is equipped with b. A ferroelectric liquid crystal 23 having a non-helical structure having at least two stable states is arranged between the upper substrate 21a and the lower substrate 21b.

In the present invention, as the ferroelectric liquid crystal, chiral smectic C phase (SmC"), H phase (SmH") or ■ phase (S
Ni-do) can be used, and smectic A can be used on the high temperature side.
It is sufficient that the material does not have a phase, and it is preferable that the temperature dependence of the tilt angle is small in the vicinity of the phase transition temperature to the chiral smectic phase during the cooling process, in other words, it is desirable that the material has a strong first-order transition property.

The transparent electrodes 22a and 22b described above are made of ferroelectric liquid crystal 23.
In order to perform multiplexing driving, it is preferable that the wiring be arranged in a stripe shape, and that the stripe shapes be arranged to intersect with each other.

In the ferroelectric liquid crystal element shown in FIG. 4, the transparent electrode 22a
and 22b, alignment control films 24a and 24b made of polyimide resin with a film thickness of approximately 200 mm are arranged, and are subjected to a rubbing treatment in substantially parallel directions. Furthermore, polymer liquid crystal films 25a and 25b represented by the following structural formula (II) are disposed on the alignment control films 24a and 24b to a thickness of approximately 2000 nm.

In addition, 3 moj! A cyclohexanone solution containing 1.6% of 1.6-hexamethylene diisocyanate was applied onto the polyimide alignment film using a spinner. After drying, it was heat-treated at 90° C. for 3 days to obtain a crosslinked and oriented polymer liquid crystal film.

Further, alumina beads having an average particle size of about 2 pm were scattered on one glass substrate, and then the two glass substrates were stacked so that the respective wrappings were parallel to each other to create a cell.

Into this cell, a ferroelectric liquid crystal material r ZLI-4139J made by Merck & Co., Ltd., which exhibits the following phase transition, is injected under vacuum in a Tokichi phase, and then it can be oriented by slowly cooling it while applying a DC electric field. did it.

Phase transition temperature ('C) Next, when a polarizer and an analyzer were arranged as shown in Figure 1 and switched with a pulse of about 20 V, a nearly bistable orientation was obtained, and the contrast at that time was is about IO
Met.

Example 2 In the same cell as in Example 1, 4-(1-
Methylhebutyloxycarbonyl)hepnyl 4'-octyloxybiphenyl-4-carboxylate (MH
POBC) was vacuum injected under the Tokichi phase, and then
It was slowly cooled to C.

Phase transition temperature (°C) Next, in the arrangement shown in Fig. 2, switching was performed with approximately 4 square positive and negative pulses while applying a DC voltage of approximately 6 V, and a bistable orientation was obtained. The contrast at that time was about 20.

Comparative Example 1 In the same cell as in Example 1, a ferroelectric liquid crystal containing a phenylpyrimidine skeleton exhibiting the following phase transition series was added in the Tokichi phase,
The mixture was injected under vacuum and slowly cooled.

Phase transition temperature ('C) Next, with the arrangement shown in Figure 3, switching was performed using a pulse of about 20 V, and a bistable alignment was obtained, but both were colored and the contrast was about 2. Met.

[Effects of the Invention] As explained above, according to the present invention, in a ferroelectric liquid crystal element or an antiferroelectric liquid crystal element using a polymer liquid crystal film as an alignment film, high contrast and excellent uniform alignment can be achieved. It becomes possible to obtain a liquid crystal element of.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the optical characteristics of the ferroelectric liquid crystal element of the present invention, FIG. 2 is an explanatory diagram showing the optical characteristics of the antiferroelectric liquid crystal element of the present invention, and FIG. An explanatory diagram showing the optical characteristics of a liquid crystal element, FIG. 4 is a cross-sectional view of a liquid crystal cell of a ferroelectric liquid crystal element of the present invention, and FIGS.
b) is a schematic diagram showing the molecular orientation state of antiferroelectric liquid crystal in a liquid crystal cell. 101...Rubbing axis and polymer liquid crystal average molecular axis 1
02, 102'... Average molecular axis 103 of ferroelectric liquid crystal
... Polarization axis 104 of polarizer ... Polarization axis 105, 105', 105'' of analyzer ... Average molecular axis 21a, 21b of antiferroelectric liquid crystal - Substrate 22a, 22b - Electrode 23... Ferroelectric liquid crystals 24a, 24b-alignment films 25a, 25b...polymer liquid crystal film 26...antiferroelectric liquid crystal molecules 27...dipole

Claims (6)

[Claims] (1) A polymeric liquid crystal film having uniaxiality is formed on a pair of substrates with transparent electrodes crossing each other and the transparent electrodes on at least one of the substrates, and a ferroelectric liquid crystal spiral is formed between the pair of substrates. In a ferroelectric liquid crystal device in which a ferroelectric liquid crystal is disposed with a thickness set to be sufficiently thin to release the structure, the ferroelectric liquid crystal is a chiral smectic liquid crystal, and the ferroelectric liquid crystal is a smectic A liquid crystal at a higher temperature than the chiral smectic phase. A ferroelectric liquid crystal element characterized by having no phase. (2) The ferroelectric liquid crystal element according to claim 1, wherein an alignment film subjected to uniaxial alignment treatment is formed between the transparent electrode formed on at least one of the substrates and the polymer liquid crystal film. (3) Claim 1, wherein the uniaxial alignment treatment is a rubbing treatment.
Or the ferroelectric liquid crystal element according to 2. (4) A pair of polarizers whose polarization axes are in a crossed nicol relationship with each other, and the direction of the polarization axis of one of the polarizers substantially coincides with the axial direction in the uniaxial alignment treatment. The ferroelectric liquid crystal element described above. (5) The ferroelectric liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal has a cholesteric phase at a higher temperature than a chiral smectic phase. (6) forming transparent electrodes that cross each other on a pair of substrates and a uniaxial polymer liquid crystal film on the transparent electrodes on at least one substrate, and having three stable states between the pair of substrates; An antiferroelectric liquid crystal element comprising an antiferroelectric liquid crystal.