JPH09176650A - Antiferroelectric liquid crystal composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an antiferroelectric liquid crystal compound which has a wide range of temperature at which the composition is in an antiferroelectric liquid crystal phase, a high speed of optical response and satisfactory display characteristics by using a combination of two specified antiferroelectric liquid crystal compounds. SOLUTION: This antiferroelectric liquid crystal composition comprises an antiferroelectric liquid crystal compound represented by formula I (wherein X is CH3 , C2 H5 or CF3 ; R<1> is a 3-14C alkyl; R<2> is a 3-10C alkyl; and Y is a single bond, O or COO, provided that the H atoms in the benzene ring may be replaced by halogens or CH3 groups) and an antiferroelectric liquid crystal compound represented by formula II (wherein X' is CH3 , C2 H5 or CF3 ; R<3> is a 3-14C alkyl; R<4> is a 3-10C alkyl; Y' is a single bond, O or COO, and one of A<1> and A<2> is one or two bivalent six-membered ring groups having paraconfigurations to each other and selected from among a benzene ring, a cyclohexane ring and a dioxane ring and the other is a cyclohexane ring or a dioxane ring; provided that hydrogen atoms in the six-membered rings of A<1> and A<2> may be replaced by halogen atoms or CH3 groups).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antiferroelectric liquid crystal composition suitable for use in a high speed optical shutter utilizing the response of an antiferroelectric liquid crystal to an electric field.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays have come to be widely used as display elements by taking advantage of their features such as thinness, light weight, and low power consumption. Most of these display devices use TN using nematic liquid crystal. (Twisted Nem
atic) type is generally adopted. In the TN type display method, since the driving is based on the anisotropy of the relative permittivity of the liquid crystal, the response speed is slow, and there is a need for improvement.

On the other hand, a liquid crystal device using a chiral smectic C (abbreviated as S _C ^* ) liquid crystal exhibiting ferroelectricity found by Meyer et al. Has a high-speed response / memory which cannot be achieved by a nematic liquid crystal. Since these properties are utilized, application research for ferroelectric liquid crystal displays is being energetically carried out. However, it is difficult to realize the good orientation and memory properties required for this display method in an actual cell, and there are problems such as being vulnerable to external shocks, and there are many problems to be solved. It is left.

On the other hand, according to Chandani et al., The aforementioned S _C ^*
Antiferroelectric phase (S _CA ^* phase) showing tristable state on low temperature side of phase
Was found. This antiferroelectric liquid crystal shows a thermodynamically stable phase in which dipoles are arranged antiparallel in each adjacent layer,
It causes an electric field-induced phase transition between the antiferroelectric phase and the ferroelectric phase, which is characterized by a clear threshold value and a double hysteresis characteristic with respect to the applied voltage. Studies on new display methods have begun by applying this switching behavior.

[0005]

When an antiferroelectric liquid crystal is applied to a high-speed optical shutter, the conventionally known antiferroelectric liquid crystal material has an antiferroelectric phase against an electric field in a temperature range and a room temperature range. It is not always preferable in terms of the optical response time (τ), the refractive index anisotropy (Δn) related to display characteristics, and the tilt angle (θ) in the ferroelectric phase induced by the electric field. In view of such a situation, the present invention widens the temperature range in which the antiferroelectric phase is exhibited, accelerates τ,
It is an object of the present invention to provide an antiferroelectric liquid crystal composition in which Δn and θ are optimized.

[0006]

The present invention provides at least one antiferroelectric liquid crystal compound represented by the general formula (1) as defined in claim 1 and an antiferroelectric liquid crystal represented by the general formula (2). An antiferroelectric liquid crystal compound containing at least one kind of dielectric liquid crystal compound. By combining these two kinds of liquid crystal compounds, it is possible to obtain an antiferroelectric liquid crystal high-speed optical shutter exhibiting a wide antiferroelectric phase temperature range, a high optical response speed, and good display characteristics.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The above general formulas (1) and (2)
The compound represented by the formula: JP-A-1-139551, JP-A-1-316372, and JP-A-3-123
No. 759, JP-A-3-197444, and JP-A-3-292388, or by combining known organic synthesis unit reactions with the methods described in these publications. it can.

The proportion of the compound represented by the general formula (1) in the antiferroelectric liquid crystal composition of the present invention is 5 to 50% by weight.
The ratio of the compound represented by the general formula (2) in the antiferroelectric liquid crystal composition of the present invention is 30 to 95 wt.
% Is preferred.

Preferred specific examples of the compound represented by the general formula (1) are general formulas (1-1) to (1) described in claim 2.
It is at least one kind selected from the group consisting of the compounds represented by (1-26). A preferred specific example of the compound represented by the general formula (2) is the general formula (2-
It is at least one kind selected from the group consisting of the compounds represented by 1) to (2-7).

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The composition described in this example is Δn: 0.14, θ: 2 from the relationship with the driving method and chromaticity.
2.5 ° is preferred.

Measurement of phase transition temperature and identification of phase
C, observed by a polarizing microscope.

A method of observing with a polarization microscope will be described below. After a polyimide film is formed on a glass substrate provided with two transparent electrodes, a rubbing process is performed, and the glass substrate is bonded to a cell with a spacing of 2 μm using a spacer.
A sample liquid crystal is injected to create a liquid crystal thin film cell. Using a polarizing microscope with a hot stage, the prepared cells were arranged so as to be in a dark field in the absence of an electric field under crossed Nicols, and the phase was identified by observing the electric field response of the cells.

The measurement of τ was performed as follows. Align the oriented cell to a polarizing microscope with a photomultiplier,
Arranged to be a dark field when there is no electric field under crossed Nicols,
A pulse electric field of ± 50 V with a pulse width of 1 ms as shown in FIG. 1 was applied to this liquid crystal cell, and τ was measured from the change in the amount of transmitted light at that time.

The measurement of Δn was performed as follows. First,
The cell gap (d) was measured before injecting the liquid crystal into the cell. Next, liquid crystal is injected, and after the injection, the cell is heated to a temperature at which the liquid crystal composition changes to an isotropic liquid, and then 1 ° C.
Spectral transmittance was measured under crossed Nicols using a cell that was cooled to room temperature at 1 / min and oriented.
-Calculated d. Finally, Δn was calculated from the already measured d and Δn · d. The value of Δn described in this specification is at λ: 450 nm.

The measurement of θ was carried out as follows. The cell is arranged in the same way as when measuring τ, and the ferroelectric phase induced by applying a voltage to this liquid crystal cell appears, and the optical axis at that time and the optical axis during the antiferroelectric phase (when there is no electric field) The angle between and was measured by rotating the stage. The optical axis in the ferroelectric phase was set to a position (dark field) where the amount of transmitted light was the same as in the case of no electric field.

Example 1 Compounds No. 1 and N shown in Table 1
o.2, No.6, No.7, No.8, No.9, and No.1
0 was used to prepare liquid crystal composition No. 20 having the composition shown in Table 2. The phase transition temperature of antiferroelectric liquid crystal composition No. 20 is shown in Table 4, and τ, Δn and θ are shown in Table 5.

[0017]

[Table 1]

[0018]

[Table 2]

(Comparative Examples 1 and 2) Compound No. shown in Table 1
A liquid crystal composition comprising a compound represented by the general formula (1) having the composition shown in Table 2 using No. 1, No. 3, No. 4 and No. 5
No. 21 (Comparative Example 1) was used as a compound No. 6, No. 7, No.
A liquid crystal composition having the composition represented by the general formula (2) having the composition shown in Table 3 using Nos. 8, No. 9 and No. 10
No. 22 was produced. The antiferroelectric liquid crystal composition No.
The phase transition temperatures of No. 21 and No. 22 are shown in Table 4, and τ, Δn, and tilt angle are shown in Table 5.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

Comparing the example of the present invention with the comparative example, composition No. 21 has a slow τ, and both Δn and θ are large, which is not practical. Composition No. 22 has a low upper limit temperature showing an antiferroelectric phase, and has a small Δn, which is not practical.
It can be seen that only the composition No. 20 of the present invention has a wide temperature range in which the antiferroelectric phase is exhibited, τ is fast, and both Δn and θ have suitable values.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a waveform of a voltage applied to a cell and a transmitted light amount when measuring τ.

Claims (2)

[Claims] 1. An antiferroelectric material represented by the following general formula (1):
Represented by at least one liquid crystal compound and the following general formula (2)
Containing at least one antiferroelectric liquid crystal compound
An antiferroelectric liquid crystal composition characterized by the above. Embedded image(In the above formula, X is -CH_Three, -C_TwoH_Five, Or -CF
_ThreeAnd R is¹, R^TwoAre carbon numbers 3 to 14, 3 respectively
A linear or branched alkyl group of 10
Y represents a single bond, -O-, or -COO- group.
The hydrogen atom in the benzene ring group is a fluorine atom or chlorine.
Optionally substituted with atoms, bromine atoms, or methyl groups
Yes. )(In the above formula, X'is -CH_Three, -C_TwoH_FiveOr -C
F_ThreeAnd R^Three, R^FourAre carbon numbers 3 to 14, 3 respectively
A linear or branched alkyl group of 10
Y'represents a single bond, -O-, or -COO- group.
A¹, And A ^TwoAre benzene ring and cyclo
Selected from either xanthane ring or dioxane ring
Six divalent or monovalent divalent bonds with each other in para position
It consists of member ring groups. A¹And A^TwoThe total of 6-membered ring groups of
3 of them, 2 of which are benzene rings, and the remaining
One is either cyclohexane ring or dioxane ring
Is. A¹And A^TwoThe hydrogen atom in the 6-membered ring group of is
Fluorine atom, chlorine atom, bromine atom, or methyl group
It may be exchanged. ) 2. The antiferroelectric liquid crystal compound represented by the general formula (1) is at least one selected from the group consisting of compounds represented by the following general formulas (1-1) to (1-26). The antiferroelectric liquid crystal compound represented by the general formula (2) is selected from at least one compound selected from the group consisting of compounds represented by the following general formulas (2-1) to (2-7). The antiferroelectric liquid crystal composition according to claim 1. However, in the following general formula, R ¹ is selected from an alkyl group having 8, 9, 10, 11, 12 carbon atoms, and R ² is selected from an alkyl group having 4, 5, 6, 8 carbon atoms. Embedded image Embedded image Embedded image [Chemical 6] Embedded image