JPH04304293A - Ferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain the title composition excellent in high-speed response characteristics and orientation properties and having a wide operating temperature range by incorporating a chiral dopant into a base liquid crystal containing a specified compound and showing a smectic C(SC) phase. CONSTITUTION:The title composition is made by mixing a base liquid crystal which contains a compound selected from compounds of formula I (wherein R and R are each independently 4-12C alkyl), formula II (wherein R and R are each independently 4-12C alkyl or alkoxyl), formula III (wherein R<5> and R<6> are each independently 4-12C straight-chain alkyl), and formula IV (wherein R<7> and R<8> are each independently 4-12C straight-chain alkyl) and shows a smectic C(SC) phase; and a chiral dopant comprising an optically active compound.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a novel ferroelectric liquid crystal composition useful as an electro-optical display material.
In particular, the present invention provides a ferroelectric liquid crystal composition that has excellent responsiveness compared to conventional liquid crystal materials and is useful as a material for liquid crystal display elements.

0002

[Prior Art] Liquid crystal display elements that are currently widely used are:
Twisted nematic (TN) type, which mainly uses nematic liquid crystal, or super twisted type
It is called a nematic (STN) type, and although it has many advantages, it has a major drawback that its response speed is much slower than that of light-emitting display systems such as CRT, and its application is difficult. There were major limitations. Although other liquid crystal display systems are being studied from various angles, the reality is that little improvement has been made in their response characteristics.

However, recently discovered liquid crystal display elements using ferroelectric chiral smectic liquid crystals have become capable of responding at least 100 times faster than conventional TN type display elements. Furthermore, it has been revealed that because it has bistable properties, it can retain its display even when the power is turned off. For this reason, it has great potential for use in large-screen high-resolution displays, flat-screen televisions, optical shutters, printer heads, etc., and active research and development is currently being conducted to put it into practical use.

The liquid crystal phase of the ferroelectric liquid crystal belongs to the tilted chiral smectic phase, and among them, the chiral smectic C (hereinafter abbreviated as SC*) phase, which has the lowest viscosity, is practically desirable. Many liquid crystal compounds exhibiting an SC* phase (hereinafter referred to as SC* compounds) have already been synthesized and studied, but none with sufficient properties to be used as optical switching elements for ferroelectric liquid crystal displays is yet known. It has not been done. Therefore, by mixing with other liquid crystal compounds, SC*
It is used as a liquid crystal composition that exhibits a phase (hereinafter referred to as SC* liquid crystal composition). Studies on such SC* liquid crystal compositions are being actively conducted, and currently, a chiral dopant consisting of an optically active compound is added to a base liquid crystal exhibiting a non-chiral smectic C (hereinafter abbreviated as SC) phase. The most common method is to As a result, it has become possible to obtain SC* liquid crystal compositions that have characteristics such as high-speed response, good alignment, and a wide operating temperature range.

[0005]

[Problem to be solved by the invention] However, the above S
The response speed of C* liquid crystal compositions is still not sufficient, and the reality is that even faster response is desired. It is known that in order to increase the response speed of a ferroelectric liquid crystal composition, it is necessary to increase the spontaneous polarization or decrease the viscosity of the liquid crystal composition. Among these, when the spontaneous polarization is increased too much, it tends to have an adverse effect on memory properties, etc., and the reality is that the spontaneous polarization cannot be increased beyond a certain level. Therefore, it is necessary to reduce the viscosity of the liquid crystal, and for this purpose, it is most important to reduce the viscosity of the base liquid crystal that accounts for the majority of the SC* liquid crystal composition.

[0006] The problem to be solved by the present invention is to provide a ferroelectric liquid crystal composition that contains a base liquid crystal with low viscosity and a chiral dopant, has excellent high-speed response and orientation, and has a wide operating temperature range. It is in.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides the following ferroelectric liquid crystal composition. That is, (1) ■ General formula (I)

[0008]

[C5]

(In the formula, R1 and R2 each independently represent an alkyl group having 4 to 12 carbon atoms, preferably a linear alkyl group having 4 to 12 carbon atoms.)
A compound represented by, ■ General formula (II)

0010

[C6]

(In the formula, R3 and R4 each independently represent an alkyl group or an alkoxyl group having 4 to 12 carbon atoms, but preferably R3 represents a linear alkyl group having 4 to 12 carbon atoms.) and R4 represents a linear alkoxyl group having 4 to 12 carbon atoms.

0012

[C7]

(wherein R5 and R6 each independently represent a straight-chain alkyl group having 4 to 12 carbon atoms) and general formula (III) b

[0014]

[Chemical formula 8]

(In the formula, R7 and R8 each independently represent a linear alkyl group having 4 to 12 carbon atoms.) The host liquid crystal exhibiting the (SC) phase and the (2
) provides a ferroelectric liquid crystal composition containing a chiral dopant consisting of an optically active compound, more preferably a matrix liquid crystal exhibiting a smectic C (SC) phase;
(1) 5 to 40% by weight of the compound represented by general formula (I), 10 to 80% by weight of the compound represented by general formula (II), and (2) general formula (III) a and general formula (III).
The present invention provides a ferroelectric liquid crystal composition containing 5 to 30% by weight of a compound selected from the group consisting of compounds represented by b).

The compound represented by the general formula (I) is a compound that exhibits an SC phase over a wide temperature range, especially up to a high temperature range, and has a very low viscosity as a tricyclic compound, so It is a compound suitable for the preparation of Also,
This compound has smectic A (SA) in the high temperature range of the SC phase.
Shows no phase.

On the contrary, when the compound represented by the general formula (III) a or the general formula (III) b is added to the liquid crystal composition, the temperature range in which the SA phase is exhibited is expanded, and the N phase is increased. shows a tendency to disappear easily. When these compounds are simultaneously added to a liquid crystal composition, a liquid crystal composition having an SA phase and an N phase in the high temperature range of the SC phase can be obtained.
Such a phase series is preferable in order to obtain good orientation.

The liquid crystal composition of the present invention contains a compound represented by the general formula (I) as a main component of the parent liquid crystal,
If the content is less than 5% by weight, the effect will be small, and 40
If the content exceeds 5% by weight, the melting point of the base liquid crystal increases and crystals tend to precipitate easily, so it is preferably contained in the base liquid crystal in an amount of 5 to 40% by weight. Examples of compounds represented by general formula (I) are shown in Table 1.

[0019]

[Table 1]

(In the table, Cr represents a crystalline phase, I represents an isotropic liquid phase, N represents a nematic phase, and SC represents a smectic C phase.) On the other hand, the compound represented by the general formula (II) Since it exhibits an SC phase in a low temperature range and has a relatively low viscosity, it is widely used as a component constituting the host liquid crystal.

The liquid crystal composition of the present invention contains the compound represented by the general formula (II) as a main component of the parent liquid crystal, but if the content is less than 10% by weight, the effect will be small;
If the amount exceeds 80% by weight, the temperature range of the SC phase of the parent liquid crystal tends to become too low.
It is preferable that the content is % by weight. Examples of compounds represented by general formula (II) are shown in Table 2.

[0022]

[Table 2]

(In the table, Cr represents the crystalline phase, I represents the isotropic liquid phase, N represents the nematic phase, SC represents the smectic C phase, and SA represents the smectic A phase.) Next, the general formula The compound represented by (III)a or general formula (III)b does not show an SC phase, but is a very low viscosity compound, and by adding this compound to a liquid crystal composition, it can be used to improve the liquid crystal composition. This greatly reduces viscosity and enables high-speed response.

The liquid crystal composition of the present invention has the general formula (III)
The parent liquid crystal contains a compound selected from the group consisting of compounds represented by a and general formula (III) b as a main component, but if the content is less than 5% by weight, the effect is small, and if the content is less than 30% by weight. Since the temperature range of the SC phase of the host liquid crystal tends to be too low,
It is preferable that the content is % by weight.

Examples of compounds represented by the general formula (III)a are shown in Table 3.

[0026]

[Table 3]

(In the table, Cr represents a crystalline phase, I represents an isotropic liquid phase, and S represents an unidentified smectic phase.) Examples of compounds represented by the general formula (III) b are shown in Table 4. show.

[0028]

[Table 4]

(In the table, Cr represents a crystalline phase, I represents an isotropic liquid phase, N represents a nematic phase, and SB represents a smectic B phase.) The characteristics of the SC* liquid crystal composition of the present invention are as follows: Its response speed is very high, and it is very suitable for device production as a material for actual liquid crystal display elements.

[0030]

[Examples] The present invention will be specifically explained below with reference to Examples, but the gist and scope of the present invention are not limited by these Examples.

In this example, the phase transition temperature was measured using a polarizing microscope equipped with a temperature control stage and a differential scanning calorimeter (DSC). In addition, “
%” shall all represent “% by weight”. (Example 1) A host liquid crystal (B
-1) was prepared with the following composition ratio. This mother liquid crystal (B-
1) is SC phase up to 56.5℃ and SA phase up to 60.0℃.
phase and N phase up to 64.0°C, and its melting point is -4
It was ℃.

[0032] The parent liquid crystal (B-1) is

[0033]

[Chemical formula 9]

It consists of the following. This mother liquid crystal (B-
1) Chiral dopant consisting of 80% and the following composition (
A) An SC* liquid crystal composition (M-1) consisting of 20% was prepared. This SC* liquid crystal composition exhibited an SC* phase up to 54.5°C, an SA phase up to 56.5°C, and an N* phase up to 61.0°C, and its melting point was -4°C.

Note that the chiral dopant (A) is

003
6]

[Chemical formula 10]

It consists of the following. (In the formula, Pr represents a propyl group.) Next, using this liquid crystal composition, a liquid crystal cell was created according to the following procedure.

First, ITO commercially available from EHC
A vapor-deposited glass plate (electrode area 70 mm2) was washed and dried. A polyimide forming solution "PIQ" (manufactured by Hitachi Chemical Co., Ltd.) was applied to this using a spinner coater to form a polyimide film (substrate A).

Similarly, a polyimide film containing a spacer was formed using the above polyimide forming solution mixed with a glass fiber spacer (substrate B).
. After rubbing substrate A and substrate B with nylon cloth, apply thermosetting epoxy adhesive to one substrate, and rub substrate A and substrate B so that the rubbing directions are parallel and opposite to each other. They were overlapped and left to stand at 80° C. for 3 hours to harden to form a cell.

[0040] The above liquid crystal composition was heated to form an isotropic liquid phase and then injected into the thus prepared cell.
Slow cooling was performed at a rate of 1°C per minute to separate the N* phase, SA phase, and S
The C* phase was oriented to obtain a liquid crystal display element. The thickness of this cell was measured and found to be 2.0 μm.

When a rectangular wave with an electric field strength of 10 Vp-p/μm was applied to this cell and its electro-optical response speed was measured, a high-speed response of 34 μsec at 25° C. was confirmed. The spontaneous polarization at this time was 18.9 nC/cm2, and the tilt angle was 24.7°. Contrast was good. (Example 2) 98% of the base liquid crystal (B-1) and the formula

0
042]

[Chemical formula 11]

S consisting of 2% of compound (C) represented by
A C* liquid crystal composition (M-2) was prepared. This SC* liquid crystal composition exhibits an SC* phase up to 57°C, an SA phase up to 59°C,
Each exhibited an N* phase up to 63.5°C, and its melting point was not clear.

The electro-optical response speed measured in the same manner as in Example 1 was 69 μsec at 25° C., confirming high-speed response. Also, the spontaneous polarization at this time is 4.1nC/c
m2, and the tilt angle was 25.0°. Contrast was good. (Example 3) The base liquid crystal (B-1) 98% and the formula

0
045]

[Chemical formula 12]

S consisting of 2% of compound (D) represented by
A C* liquid crystal composition (M-3) was prepared. This SC* liquid crystal composition exhibited an SC* phase up to 56.5°C, an SA phase up to 61°C, and an N* phase up to 63.5°C, and its melting point was not clear.

The electro-optical response speed measured in the same manner as in Example 1 was 96 μsec at 25° C., confirming high-speed response. Also, the spontaneous polarization at this time is 3.6nC/c
m2, and the tilt angle was 24.3°. Contrast was good. (Example 4) In Example 3, the SC* liquid crystal composition (
M-4) was prepared. This SC* liquid crystal composition exhibits an SC* phase up to 57°C, an SA phase up to 62.5°C, and an N phase up to 64°C.
*Each phase was shown, and the melting point was not clear. The electro-optic response speed measured in the same manner as in Example 1 was 2.
The response time was 37 μsec at 5° C., confirming high-speed response. Further, the spontaneous polarization at this time was 12.1 nC/cm2, and the tilt angle was 24.7°. Contrast was good. (Example 5) In Example 3, an SC* liquid crystal composition (M-5) was prepared using 90% of the base liquid crystal (B-1) and 10% of the compound (D). This SC* liquid crystal composition is 54.
It showed an SC* phase up to 5°C and an SA phase up to 63°C, and its melting point was not clear. The electro-optical response speed measured in the same manner as in Example 1 was as fast as 27 μsec at 25°C. Also, the spontaneous polarization at this time is 28.
The temperature was 0 nC/cm2, and the tilt angle was 22.0°. Contrast was good. (Example 6) The base liquid crystal (B
-2) was prepared with the following composition ratio. This mother liquid crystal (B-
2) is SC phase up to 52.5℃ and SA phase up to 62.0℃.
phase and N phase up to 67.5°C, and its melting point is -4
．． The temperature was 5°C.

[0048] The base liquid crystal (B-2) is

[0049]

[Chemical formula 13]

It consists of: This mother liquid crystal (B-
2) An SC* liquid crystal composition (M-6) consisting of 80% and 20% of chiral dopant (A) was prepared. This SC* liquid crystal composition exhibits an SC* phase up to 50°C and an SA phase up to 58.5°C.
phase and N* phase up to 64.5℃, and its melting point is -
The temperature was 4.5°C. The electro-optical response speed measured in the same manner as in Example 1 was as fast as 37 μsec at 25°C. Further, the spontaneous polarization at this time was 16.8 nC/cm2, and the tilt angle was 22.2°. Contrast was good. (Example 7) An SC* liquid crystal composition (M-7) consisting of 98% of the base liquid crystal (B-2) and 2% of compound (C) was prepared. This SC* liquid crystal composition exhibited an SC* phase up to 53.5°C, an SA phase up to 61.0°C, and an N* phase up to 67.0°C, and its melting point was not clear.

The electro-optical response speed measured in the same manner as in Example 1 was 120 μsec at 25° C., confirming high-speed response. Also, the spontaneous polarization at this time is 3.
The temperature was 15 nC/cm2, and the tilt angle was 21.1°. Contrast was good. (Example 8) An SC* liquid crystal composition (M-8) consisting of 98% of the base liquid crystal (B-2) and 2% of compound (D) was prepared. This SC* liquid crystal composition maintains the SC* phase up to 52°C.
It showed an SA phase up to 63°C and an N* phase up to 67°C, and its melting point was not clear. The electro-optic response speed measured in the same manner as in Example 1 was 10 at 25°C.
The response time was 2 μsec, confirming high-speed response. Further, the spontaneous polarization at this time was 3.7 nC/cm2, and the tilt angle was 20.1°. Contrast was good.

[0052]

Effects of the Invention The ferroelectric liquid crystal composition of the present invention exhibits SC* over a wide temperature range and has low viscosity, allowing high-speed response. Therefore, the ferroelectric liquid crystal composition of the present invention is extremely useful as a material for optical switching elements for display.

Claims (4)

[Claims] Claim 1: (1)■General formula (I) [Formula 1] (wherein, R1 and R2 each independently have 4 to 4 carbon atoms)
represents 12 alkyl groups. ) compound represented by,■
General formula (II) [Formula 2] (wherein, R3 and R4 each independently have 4 to 4 carbon atoms
12 alkyl group or alkoxyl group. ) and ■ General formula (III)a [Formula 3] (wherein, R5 and R6 each independently have 4 to 4 carbon atoms)
Represents 12 linear alkyl groups. ) and the compound represented by the general formula (III)b [Formula 4] (wherein, R7 and R8 each independently have 4 to 4 carbon atoms)
Represents 12 linear alkyl groups. ) A ferroelectric liquid crystal composition containing a base liquid crystal exhibiting a smectic C (SC) phase, and (2) a chiral dopant consisting of an optically active compound. 2. The ferroelectric liquid crystal composition according to claim 1, wherein R3 is a linear alkyl group having 4 to 12 carbon atoms, and R4 is a linear alkoxyl group having 4 to 12 carbon atoms. thing. Claim 3: (1) A compound represented by general formula (I) is added to a base liquid crystal exhibiting a smectic C (SC) phase.
~40% by weight, 1 of the compound represented by general formula (II)
0 to 80% by weight and (2) 5 to 30% by weight of a compound selected from the group consisting of a compound represented by general formula (III) a and a compound represented by general formula (III) b. The ferroelectric liquid crystal composition described above. 4. A liquid crystal display element comprising the ferroelectric liquid crystal composition according to claim 1, 2 or 3 as a constituent element.