JPH06192657A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal composition having a new phase series, i.e., the fourth phase series by mixing two specified compounds with each other. CONSTITUTION:The composition is prepared by mixing 80-40 pts.wt. compound of formula I (wherein R1 and R2 are each 4-18 C n-alkyl; and * represents asymmetry) with 20-60 pts.wt. compound of formula II (wherein R3 and R4 are each 4-18C n-alkyl; and * represents asymmetry). It is required that the optical purity of each compound should be at least 80%ee, that the compound of formula II should be an R isomer when the compound of formula I is an R isomer, and that the compound of formula II should be an S isomer when the compound of formula I is an S isomer. This composition can develop an antiferroelectric phase in two temperature regions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition having two kinds of antiferroelectric phases having three optical stable states (tristable states).

[0002]

2. Description of the Related Art As a conventional liquid crystal element, a method called TN (twisted nematic) type is widely used (M. Schadt and W. Herfrich, Applied Physics Le.
tters. Vol. 18, No. 4, pp. 127-128). TN
Type liquid crystal device is a device in which nematic liquid crystal is sealed between a pair of transparent electrode substrates and arranged so that liquid crystal molecules are twisted by 90 ° between the upper and lower substrates, and the twisted structure disappears by application of an electric field to transmit light. Alternatively, it is cut off and the light and dark are displayed.
However, when the TN type liquid crystal element is applied to a liquid crystal display device having a matrix electrode structure in which a band-shaped scanning electrode group and a signal electrode group are arranged orthogonally, the response speed is slow,
The voltage-light transmittance characteristic does not have sufficient nonlinearity,
Therefore, there is a problem that the pixel density of the matrix cannot be increased, and the field of application is greatly limited under the present circumstances. Under such circumstances, ferroelectric liquid crystals synthesized by Meyer et al. Have been attracting attention (Le Jou
rnal de Physique, Volume 36, March 1975, L-6
9 to L-71). The most widely studied at present is a ferroelectric liquid crystal device having bistability (for example, Japanese Patent Publication No. 63-22287, U.S. Pat. No. 436).
7924). Bistable liquid crystals include optically active chiral smectic C phase (SmC *) or H phase (S
Liquid crystals with mH *) are known, which form a unique helical structure in the bulk state. When this is sandwiched between substrates that are separated by a distance short enough to suppress the spiral structure, the liquid crystal exhibits two stable states with respect to an electric field. That is, the liquid crystal is aligned in the first optically stable state with respect to the electric field in one direction and in the second optically stable state with respect to the electric field in the opposite direction. It can switch between two optically stable states. Moreover, this switching speed is extremely faster than that of the TN type liquid crystal element, and there is an advantage that it has the property of maintaining each stable state even when the electric field is removed. FIG. 1B shows a change in optical transmittance when a triangular wave electric field shown in FIG. 1A is applied to a display device using this liquid crystal. On the other hand, in recent years, an antiferroelectric liquid crystal having three optically stable states has been presented, and has been attracting attention as a liquid crystal exhibiting a better electro-optical effect (AD Cha.
ndani, E. Gorecka, Y. Ouchi, H. Takezoe and A. Fuku
da, Jpn. J. Appl. Phys., 28 (1989) L1265). This liquid crystal is in a first optical stable state when there is no electric field, in a second optical stable state when an electric field in one direction is present, and in a third optical stable state when an electric field is in the opposite direction. The three stable states can be switched at high speed depending on the orientation and strength of the electric field applied. Furthermore, the optical transmittance change between the three stable states with respect to the applied voltage shows a hysteresis shifted on the voltage axis (for example, when the applied electric field is increased to change from the first stable state to the second stable state). When,
Conversely, the voltage at which the optical transmittance changes differs when the applied electric field is reduced to change from the second stable state to the first stable state.) Realization of the device is expected. In FIG. 1 (c),
A change in optical transmittance when a triangular wave electric field shown in FIG. 1A is applied to a display device using this liquid crystal is shown. A liquid crystal compound having a liquid crystal phase S * (3) showing a tristable state in a phase series is disclosed in Japanese Patent Application Laid-Open Nos. 1-331667 and 1-316767 filed by the present applicant.
-316372, JP-A-1-316339, JP-A-2-28128, and Ichihashi et al. JP-A-1-213390.
The present applicant has made new proposals for liquid crystal electro-optical devices utilizing tristable states in JP-A-2-40625, JP-A-2-153322, and JP-A-2-173724. By the way, an element using an antiferroelectric liquid crystal having these three optically stable states (tristable states) needs to apply a voltage equal to or higher than the threshold voltage in order to achieve a desired electro-optical response. The thickness of the cell currently used is 2 μm or more, and if the thickness is less than 2 μm, it is difficult to make the cell thickness uniform and the cost becomes high. The threshold voltage in the antiferroelectric phase of the currently known antiferroelectric liquid crystal is 20 to 30 when enclosed in a cell having a cell thickness of 2 μm.
V or more (that is, an electric field of 10 to 15 v / μm is required). Further, when driving, a positive voltage and a negative voltage are alternately applied, so that the driving circuit needs ± 30 V, that is, a withstand voltage of 60 V or more. An IC that can withstand such a voltage becomes a special one, and an inexpensive circuit cannot be assembled. Therefore, an antiferroelectric liquid crystal having a low threshold voltage has been desired, but a technology regarding an antiferroelectric liquid crystal having a low threshold voltage has not been disclosed yet. On the other hand, the conventional antiferroelectric liquid crystal
The phase sequence is

[Table 1] Iso: Isotropic phase Sm A: Smectic A phase SmC * α: Smectic Cα phase SmC *: Smectic C phase (ferroelectric phase) SmC * γ: Smectic Cγ phase SmC * A: Antiferroelectric phase However, there is no known antiferroelectric liquid crystal having a phase sequence other than this.

[0003]

[Object] It is an object of the present invention to provide a liquid crystal composition having a new type of phase series that has never existed before, that is, a fourth type of phase series. Another object of the present invention is to provide an antiferroelectric liquid crystal composition that exhibits a tristable state at a low threshold voltage.

[0004]

The present invention comprises (a) general formula (I)

[Chemical 7] (Wherein R ₁ and R ₂ are groups independently selected from the group consisting of n-alkyl groups having 4 to 18 carbon atoms, and * represents an asymmetric carbon) 80 to 40 parts by weight Department,
(B) General formula (II)

[Chemical 8] (Wherein R ₃ and R ₄ are groups independently selected from the group consisting of n-alkyl groups having 4 to 18 carbon atoms, and * represents an asymmetric carbon) 20 to 60 wt. And a liquid crystal composition having a optical purity of 80% e.
e or more, when the compound of general formula (I) is in the R form, the compound of general formula (II) is also in the R form, and when the compound of general formula (I) is in the S form, The present invention also relates to a liquid crystal composition exhibiting an antiferroelectric phase in two temperature regions, wherein the compound is also an S-form.

The liquid crystal composition of the present invention is a novel liquid crystal composition exhibiting an antiferroelectric phase in two temperature regions. This "having an antiferroelectric phase in two temperature regions" means that the phase sequence of the liquid crystal is

[Table 2] Is meant to indicate a new type of phase sequence. In other words, it means a new type of phase series in which the antiferroelectric phase appears in two regions, a high temperature side temperature region and a conventional antiferroelectric liquid crystal temperature region (low temperature side).

[0006]

【Example】

Example 1 (a) R-(-)-4 (1-) represented by the formula (III) that does not exhibit antiferroelectric phase (indicates ferroelectric phase and ferrielectric phase)
Methylheptyloxycarbonyl) phenyl 4'-octyloxycarboxybiphenyl-4-carboxylate [abbreviated as R-(-)-MHPOOCBC hereinafter]
80 parts by weight and R-(−)-4 (1-methylheptyloxycarbonyl) phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate having one antiferroelectric phase represented by the formula (IV) [hereinafter referred to as R-(-)-MH
Abbreviated as POCBC] 20 parts by weight were mixed to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 3] From this phase series, in the present embodiment, 74.8 ° C to 74.6 ° C.
At, a new antiferroelectric phase (SmC * A2) appeared.

(B) 70 parts by weight of R-(-)-MHPOOCBC was mixed with 30 parts by weight of R-(-)-MHPOCBC to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 4] From this phase series, in this example, 82.6 ° C to 78.8 ° C.
It can be seen that in Fig. 1, the antiferroelectric phase appears on the high temperature side.

(C) 60 parts by weight of R-(-)-MHPOOCBC was mixed with 40 parts by weight of R-(-)-MHPOCBC to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 5] From this phase series, in this example, 86.9 ° C to 82.2 ° C.
It can be seen that in Fig. 1, the antiferroelectric phase appears on the high temperature side.

(D) 50 parts by weight of R-(-)-MHPOOCBC was mixed with 50 parts by weight of R-(-)-MHPOCBC to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 6] From this phase series, in this example, 89.2 ° C to 85.0 ° C.
It can be seen that in Fig. 1, the antiferroelectric phase appears on the high temperature side.

(E) 40 parts by weight of R-(-)-MHPOOCBC was mixed with 60 parts by weight of R-(-)-MHPOCBC to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 7] From this phase series, in the present embodiment, 88.2 ° C to 85.3 ° C.
It can be seen that in Fig. 1, the antiferroelectric phase appears on the high temperature side.

Example 2 R-(-)-4 (1-methylpentyloxycarbonyl) phenyl 4'-decyloxycarboxybiphenyl of the formula (V) showing no antiferroelectric phase (the ferroelectric phase is shown) -4-Carboxylate 60 parts by weight and R-(-)-MHPOCBC showing an antiferroelectric phase represented by the formula (IV)
40 parts by weight were mixed to prepare a liquid crystal composition. The phase sequence of this liquid crystal composition is as follows.

[Table 8] From this phase series, in this example, 86.4 ° C to 83.4 ° C.
At, a new antiferroelectric phase (SmC * A2) appeared.

Embodiment 3 FIG. 2 shows an overall configuration diagram of a liquid crystal element to which the present invention is applied. The liquid crystal element has a pair of electrode substrates 1 and 2 arranged in parallel at an interval of, for example, 10 μm, and an antiferroelectric liquid crystal 6 is sealed between the pair of electrode substrates 1 and 2. The electrode substrates 1 and 2 are formed by forming transparent electrodes 1a and 2a made of a transparent conductive film such as indium oxide or tin oxide on the inner surfaces of transparent substrates 1c and 2c made of transparent glass or resin. Alignment control films 1b and 2b are formed on the surfaces inside the electrodes 1a and 2a that come into contact with the liquid crystal 6. As the antiferroelectric liquid crystal 6, the high temperature side antiferroelectric phase of the liquid crystal compound of the present invention is used. Polarizing plates which are orthogonal to each other are arranged at 4 and 5. When a triangular wave voltage was applied to the liquid crystal device thus produced, an optical response with clear switching was obtained.

[0013]

[Effect] According to the present invention, a liquid crystal composition having a new type of phase series can be provided. The present invention can drive a liquid crystal element by using an antiferroelectric phase on the high temperature side, and a driving potential difference that is extremely lower than that of conventional antiferroelectric liquid crystal compositions. Therefore, the excellent electro-optical effect of the antiferroelectric liquid crystal can be sufficiently exerted by driving at a low voltage. Therefore, it is applied to a large-screen high-definition display device, a TV image display device, a liquid crystal optical shutter, or the like. , Exerts a remarkable effect.

[Brief description of drawings]

1A shows optical response characteristics of an applied triangular wave, FIG. 1B shows optical response characteristics of a liquid crystal showing two stable states, and FIG. 1C shows optical response characteristics of a liquid crystal showing a tristable state.

FIG. 2 is an overall configuration diagram of a liquid crystal element used in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode substrate 1a Transparent electrode 1b Alignment control film 1c Transparent substrate 2 Electrode substrate 2a Transparent electrode 2b Alignment control film 2c Transparent substrate 3 Power supply 4 Polarizing plate 5 Polarizing plate 6 Antiferroelectric liquid crystal

Claims (3)

[Claims] 1. (a) General formula (I): (Wherein R ₁ and R ₂ are groups independently selected from the group consisting of n-alkyl groups having 4 to 18 carbon atoms, and * represents an asymmetric carbon) 80 to 40 parts by weight Department,
(B) General formula (II): (Wherein R ₃ and R ₄ are groups independently selected from the group consisting of n-alkyl groups having 4 to 18 carbon atoms, and * represents an asymmetric carbon) 20 to 60 wt. And a liquid crystal composition having a optical purity of 80% e.
e or more, when the compound of general formula (I) is in the R form, the compound of general formula (II) is also in the R form, and when the compound of general formula (I) is in the S form, A liquid crystal composition exhibiting an antiferroelectric phase in two temperature regions, wherein the compound is also an S-form. 2. The formula (III): 80 to 40 parts by weight of 4- (1-methylheptyloxycarbonyl) phenyl 4'-octyloxycarboxybiphenyl-4-carboxylate represented by the formula (IV) A liquid crystal composition consisting of 20 to 60 parts by weight of 4- (1-methylheptyloxycarbonyl) phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate represented by the formula:
And above, when the compound of formula (III) is in the R form, formula (IV)
The compound of formula (I) is also in the R form, and the compound of formula (III) is also in the form of S when the compound of formula (III) is in the S form. A liquid crystal composition exhibiting an antiferroelectric phase in two temperature regions. . 3. Formula (V): 4- (1-methylpentyloxycarbonyl) phenyl 4′-decyloxycarboxybiphenyl-4-carboxylate represented by the formula (I
V) [Chemical 6] A liquid crystal composition consisting of 20 to 60 parts by weight of 4- (1-methylheptyloxycarbonyl) phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate represented by the formula:
When the compound of formula (V) is in the R form, the formula (IV)
The compound of formula (R) is also in the R form, and when the compound of formula (V) is in the form of S, the compound of formula (IV) is also in the form of S. A liquid crystal composition exhibiting an antiferroelectric phase in two temperature regions object.