JPH0559366A - Ferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain a low-viscosity ferroelectric liquid crystal composition, containing a specific matrix liquid crystal and a chiral dopant composed of an optically active compound, capable of exhibiting ferroelectricity within a wide temperature range and excellent in responsiveness. CONSTITUTION:The objective liquid crystal composition comprising (A) a matrix liquid crystal, containing (i) a fluorophenyloxymethylenebiphenyl derivative of formula I (R<1> and R<2> are 4-12C alkyl) and (ii) a fluorine-containing biphenyl derivative of formula II (R<3> and R<4>) are 4-12C straight-chain alkyl, 4-12C alkoxy or alkenyloxy) and capable of exhibiting a smectic C phase and (B) a chiral dopant composed of an optically active compound. The above-mentioned liquid crystal composition is suitable as a material for liquid crystal display elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal composition useful as an electro-optical display material, and more specifically, it has excellent responsiveness as compared with conventional liquid crystal materials and is a constituent material of liquid crystal display devices. The present invention provides a ferroelectric liquid crystal composition useful as the above.

[0002]

2. Description of the Related Art Liquid crystal display devices that are widely used at present are mainly TN type devices using nematic liquid crystals or S-type devices.
Although it is called a TN type and has many advantages, it has a major drawback in that its response is significantly slower than that of a light emitting type display system such as a CRT.
Therefore, its application is greatly limited. Various other liquid crystal display systems have been studied, but the reality is that the response has not been improved so much.

However, a liquid crystal display device using a ferroelectric chiral smectic liquid crystal that has recently been discovered has been possible to achieve a 100 times faster response than a conventional TN type display device or the like. Furthermore, it has been revealed that the display memory can be obtained even when the power is turned off due to the bistability. Therefore, it is highly applicable to large-screen high-resolution displays, thin-screen TVs, optical shutters, printer heads, etc., and currently, active development and research is being conducted toward its practical application.

The liquid crystal phase of the ferroelectric liquid crystal belongs to the tilt type chiral smectic phase, but among them, the chiral smectic C (hereinafter abbreviated as SC ^* ) phase having the lowest viscosity is practically desirable. A large number of liquid crystal compounds exhibiting an SC ^* phase (hereinafter referred to as SC ^* compounds) have already been synthesized and studied, but none of them have properties sufficient for use as an optical switching element for a ferroelectric liquid crystal display. unknown. Therefore, it is used as a liquid crystal composition that exhibits an SC ^* phase when mixed with another liquid crystal compound (hereinafter referred to as SC ^* liquid crystal composition).

Such an SC ^* liquid crystal composition has been actively studied, and at present, a chiral compound composed of an optically active compound is added to a matrix liquid crystal exhibiting a non-chiral smectic C (hereinafter abbreviated as SC) phase. A method of adding a dopant is common. This has made it possible to obtain SC ^* liquid crystal compositions having properties such as high-speed response, good orientation, and a wide operating temperature range.

[0006]

However, the above-mentioned S
It is difficult to say that the C ^* liquid crystal composition has sufficient responsiveness, and further high-speed responsiveness is desired. It is known that in order to accelerate the response in the ferroelectric liquid crystal, it is necessary to increase the spontaneous polarization of the liquid crystal composition or decrease the viscosity.
However, if the spontaneous polarization is too large, the memory property is adversely affected. Therefore, the spontaneous polarization cannot be increased beyond a certain level. Therefore, it is necessary to reduce the viscosity of the liquid crystal composition, and for that purpose, it is most important to reduce the viscosity of the base liquid crystal that occupies most of the SC ^* liquid crystal composition.

The problem to be solved by the present invention is to provide a SC ^* liquid crystal composition having a high driving speed, a good orientation and a wide driving temperature range by adding a chiral dopant to a host liquid crystal having a low viscosity. To do.

[0008]

The present invention provides a first SC ^* liquid crystal composition in order to solve the above problems.

That is, (1) general formula (I)

[0010]

[Chemical 4]

(In the formula, R ¹ and R ² each independently represent an alkyl group having 4 to 12 carbon atoms, preferably a linear alkyl group having 4 to 12 carbon atoms). Compounds represented and general formula (II)

[0012]

[Chemical 5]

(In the formula, one of R ³ and R ⁴ represents a linear alkyl group having 4 to 12 carbon atoms, and the other represents an alkoxyl group or alkenyloxy group having 4 to 12 carbon atoms. Preferably, R ³ represents a straight-chain alkyl group having 4 to 12 carbon atoms, and R ⁴ represents a straight-chain alkoxyl group having 4 to 12 carbon atoms.) Smectic C A matrix liquid crystal exhibiting a (SC) phase,
And (2) to provide a ferroelectric liquid crystal composition containing a chiral dopant composed of an optically active compound.

The present invention further provides a second SC ^* liquid crystal composition.

That is, (1) the compound represented by the general formula (I), the compound represented by the general formula (II) and the general formula (III)

[0016]

[Chemical 6]

(In the formula, one of R ⁵ and R ⁶ represents a linear alkyl group having 4 to 12 carbon atoms, and the other represents an alkoxyl group or alkenyloxy group having 4 to 12 carbon atoms. Preferably, R ⁵ represents a straight-chain alkyl group having 4 to 12 carbon atoms, and R ⁶ represents a straight-chain alkoxyl group having 4 to 12 carbon atoms). An SC ^* liquid crystal composition containing the host liquid crystal shown, and (2) a chiral dopant composed of an optically active compound.

The content of each compound in the base liquid crystal is 5 to 40% by weight of the compound represented by the general formula (I) in the base liquid crystal showing the SC phase of these liquid crystal compositions, and the general formula (II). The compound represented by the formula (10) is preferably in the range of 10 to 50% by weight, and when the compound represented by the general formula (III) is used, its content is 2% in the host liquid crystal.
The range of 0 to 70% by weight is preferable.

The compound represented by the general formula (I) used in the SC ^* liquid crystal composition of the present invention is a compound exhibiting an SC phase in a wide temperature range and a high temperature range, and is a very tricyclic compound. Since it has a low viscosity, it is an excellent compound for forming a matrix liquid crystal showing an SC phase (hereinafter, abbreviated as SC matrix liquid crystal).

The compound represented by the general formula (I) does not show a smectic A (SA) phase in the high temperature region of the SC phase. Generally, an optically active compound that induces a large spontaneous polarization, such as a chiral dopant, tends to expand the SA phase and eliminate the chiral nematic (N ^* ) phase by adding the compound to a liquid crystal composition. There are many things to show.

In the ferroelectric liquid crystal, the phase series having the SA phase and the N ^* phase in the high temperature region of the SC ^* phase is said to be necessary for obtaining good orientation. Therefore, the compound represented by the general formula (I) is particularly preferable in order to obtain a liquid crystal composition having such a phase series.

In the SC ^* liquid crystal composition of the present invention, the compound represented by the general formula (I) is contained as a main component of the host liquid crystal, but if the content is less than 5% by weight, the effect is small. If it exceeds 40% by weight, the melting point of the host liquid crystal tends to be high, and crystals tend to precipitate easily. Therefore, it is preferably contained in the host liquid crystal in an amount of 5 to 40% by weight.

Table 1 shows typical examples of the compounds represented by formula (I).

[0024]

[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) is a compound having a low melting point and a very low viscosity. Many of these compounds show or do not show the SC phase in a relatively low temperature range, but when added to the liquid crystal composition, they do not lower the temperature range of the SC phase so much that the matrix having a low viscosity is used. It is an excellent compound for obtaining liquid crystals.

In the liquid crystal composition of the present invention, the compound represented by the general formula (II) is also contained as a main component of the host liquid crystal, but if the content is 10% by weight or less, the effect is small and 50% by weight. %, The temperature range of the SC phase of the host liquid crystal tends to be too low. Therefore, it is preferable to contain the host liquid crystal in the range of 10 to 50% by weight.

Table 2 shows typical examples of the compounds represented by the general formula (II).

[0029]

[Table 2]

The compound represented by the general formula (III) is
Since it is a compound having an SC phase in a temperature range from room temperature to a slightly high temperature and having a relatively low viscosity, it is the most used compound as a base liquid crystal in a ferroelectric liquid crystal at present.

The second SC ^* ferroelectric liquid crystal composition of the present invention comprises a compound represented by the general formula (I) and a general formula (II).
By containing the compound represented by the general formula (III) as the third component in addition to the compound represented by
It is possible to improve the compatibility of the liquid crystal composition and obtain a liquid crystal composition having a very low melting point.

In the second liquid crystal composition of the present invention, the compound represented by the general formula (III) is contained as the main component of the host liquid crystal, but if the content is 20% by weight or less, the effect is small. Therefore, it is preferable to contain 20 to 70% by weight in the base liquid crystal.

In the SC ^* liquid crystal composition of the present invention, the following compounds are preferable among the compounds represented by the general formula (III).

(A) A compound of the general formula (IIIa) in which R ⁵ represents a linear alkyl group having 4 to 12 carbon atoms and R ⁶ represents a linear alkoxyl group having 4 to 12 carbon atoms.

(B) A compound of the general formula (IIIb) in which R ⁵ represents a linear alkyl group having 4 to 12 carbon atoms and R ⁶ represents a branched alkoxyl group having 4 to 12 carbon atoms.

(C) A compound of the general formula (IIIc) in which R ⁵ represents a linear alkyl group having 4 to 12 carbon atoms and R ⁶ represents a linear alkenyloxy group having 4 to 12 carbon atoms. .

(D) R ⁵ represents a linear alkoxy group having 4 to 12 carbon atoms, and R ⁶ has 4 to 12 carbon atoms.
A compound of the general formula (IIId) representing a straight chain alkyl group of

(E) R ⁵ represents a branched alkoxyl group having 4 to 12 carbon atoms, and R ⁶ has 4 to 12 carbon atoms.
A compound of the general formula (IIIe) representing a straight chain alkyl group of

(F) R ⁵ represents a linear alkenyloxy group having 4 to 12 carbon atoms, and R ⁶ has 4 to 4 carbon atoms.
General formula (IIIf) representing 12 linear alkyl groups
Compound of.

Examples of compounds of the general formulas (IIIa), (IIIb) and (IIIc) are listed in Tables 3 and 4.

[0041]

[Table 3]

[0042]

[Table 4]

The general formulas (IIId) and (IIIe)
Examples of compounds of (IIIf) and (IIIf) are listed in Table 5.

[0044]

[Table 5]

Among these compounds, the compound represented by the general formula (IIIa) is particularly preferable in the SC ^* liquid crystal composition of the present invention.

SC of the present invention containing such a compound
^* Liquid crystal compositions are characterized by low viscosity and very fast response.

As shown in the Examples below, 50% by weight of the compound represented by the general formula (I) and the general formula (I)
A base liquid crystal (B-1) consisting of 50% by weight of the compound represented by I) was prepared. 95% by weight of this host liquid crystal (B-1) and the formula (P) as a chiral dopant.

[0048]

[Chemical 7]

The SC ^* liquid crystal composition (M-1) containing 5% by weight of the optically active compound represented by the formula (3) showed a high-speed response of 33 μsec at 25 ° C.

On the other hand, a SC ^* liquid crystal composition (N containing 95% by weight of the base liquid crystal (B-2) consisting of the compound represented by the general formula (III) and 5% by weight of the compound of the above formula (P). In the case of -1), the response speed at 25 ° C. was 51 μsec, which was rather slow.

From this, it is clear that the SC ^* liquid crystal composition of the present invention has a very low viscosity.

Next, the compound 2 represented by the general formula (I)
5% by weight, 25% by weight of the compound represented by the general formula (II) and 50% by weight of the compound represented by the general formula (III)
A host liquid crystal (B-3) was prepared.

95% by weight of this host liquid crystal (B-3) and a chiral dopant of the formula (Q)

[0054]

[Chemical 8]

The SC ^* liquid crystal composition (M-3) composed of 5% by weight of the optically active compound represented by the formula (5) showed a high-speed response of 45 μsec at 25 ° C. This composition (M-3) had a melting point of 0 ° C., which was lower than that of (M-1), and there was no precipitation or phase separation even when it was left at a low temperature of 10 to 15 ° C. for a long time.

The present invention also provides a liquid crystal display device using the above SC ^* liquid crystal composition.

The SC ^* liquid crystal composition of the present invention is formed by coating an organic thin film of polyimide or the like and subjecting it to a treatment such as rubbing or the like, or two glass transparent substrates which are subjected to an orientation treatment such as oblique vapor deposition of SiO or the like. By enclosing between the electrode plates, it can be used as a liquid crystal display element. The thickness of the cell (liquid crystal layer) is preferably in the range of 1 to 20 μm, and 1.5 to
The range of 10 μm is particularly preferable.

In order to obtain a high contrast of the liquid crystal device, it is necessary to uniformly align the liquid crystal material. For this purpose, as the liquid crystal material, IN ^* -SA-S from the high temperature side is used.
It is said that it is necessary to show the C ^* phase sequence.
In a liquid crystal composition containing an optically active compound that induces a large spontaneous polarization, N ^{* in} the high temperature range tends to disappear,
The matrix liquid crystal in the SC ^* liquid crystal composition of the present invention has an N phase in a wide range of the SC phase in a high temperature range and does not have an SA phase or has a very narrow temperature range. Even if the compound is added, the above preferable phase series can be easily obtained, and therefore the orientation is excellent.

[0059]

【Example】

The present invention will be specifically described below with reference to examples, but the gist and scope of the present invention are not limited by these examples.

In the examples, the phase transition temperature was measured by using a polarizing microscope equipped with a temperature adjusting stage and a differential scanning calorimeter (DSC). Further, all "%" in the composition represent "% by weight".

(Example 1) No. 1 in Table 1 Compound of (I) -2 12.5% No. Compound of (I) -3 12.5% No. Compound of (I) -4 12.5% No. Compound of (I) -5 12.5% No. 2 in Table 2 Compound of (II) -1 12.5% No. Compound of (II) -2 12.5% No. Compound of (II) -3 12.5% No. A host liquid crystal (B-1) having an SC phase consisting of 12.5% of the compound (II) -4 was prepared.

This host liquid crystal (B-1) is S up to 65 ° C.
Phase C showed N phase up to 72 ° C.

Next, 95% of the base liquid crystal (B-1) and the formula (P) as a chiral dopant.

[0065]

[Chemical 9]

An SC ^* liquid crystal composition (M-1) consisting of 5% of the optically active compound represented by the formula: was prepared. This SC ^* liquid crystal composition (M-1) had an SC ^* phase of 50.
The SA phase was shown up to 5 ° C, and the N ^* phase was shown up to 58.0 ° C. The melting point was about 13 ° C.

Next, an ITO vapor-deposited glass plate (electrode area 70
mm ² ) was coated with a polyimide forming solution to form a polyimide coating (substrate A). Similarly, a spacer-containing polyimide coating was prepared using the above-mentioned polyimide-forming solution mixed with glass fiber spacers (substrate B). The substrates A and B are rubbed with a nylon cloth, a thermosetting epoxy adhesive is applied to one of the substrates, and the substrates A and B are superposed so that the rubbing directions are parallel and opposite to each other. Then, it was cured by heating to prepare a cell.

SC ^* liquid crystal composition (M-1) was injected into the cell thus obtained in a state of being heated to form an isotropic liquid (I) phase, followed by gradual cooling to obtain N ^* phase and SA. The liquid crystal display device was obtained by orienting the phase and the SC ^* phase. The orientation was very good. When the cell thickness of this liquid crystal display device was measured, it was about 2.0 μm.

This liquid crystal display device has an electric field strength of 10 V _pp /
When a rectangular wave of μm was applied and the electro-optical response speed was measured, a high-speed response of 33 μsec at 25 ° C. could be confirmed. At this time, the spontaneous polarization was 13.6 nC / cm ² and the tilt angle was 24.1 °. The contrast was very good.

Comparative Example 1 No. 3 in Table 3 Compound of (IIIa) -1 30% No. Compound of (IIIa) -2 20% No. Compound of (IIIa) -3 30% No. A base liquid crystal (B-2) consisting of 20% of the compound (IIIa) -4 was prepared.

An SC ^* liquid crystal composition (N-1) comprising 95% of the base liquid crystal (B-2) and 5% of the optically active compound of the formula (P) was prepared. This SC ^* liquid crystal composition (N-
1) SC ^* phase up to 46.5 ℃, SA up to 64.0 ℃
The phases showed N ^* phase up to 66.5 ° C., respectively.

Using this SC ^* liquid crystal composition (N-1), a liquid crystal display element was prepared in the same manner as in Example 1, and its electro-optical response speed was measured.
It was late for a second. Further, as compared with Example 1, since the chiral dopants used were the same and the same amount, the host liquid crystal (B-1) of Example 1 may have a lower viscosity than (B-2). it is obvious.

Example 2 The base liquid crystal (B-1) 95
% And formula (Q)

[0074]

[Chemical 10]

An SC ^* liquid crystal composition (M-2) consisting of 5% of the optically active compound represented by the formula: was prepared. This SC ^* liquid crystal composition has SC ^* phase up to 50.0 ° C and S up to 51.5 ° C.
Phase A showed N ^* phase up to 58.0 ° C.

The electro-optical response speed measured in exactly the same manner as in Example 1 was 41 μsec at 25 ° C., and a high-speed response could be confirmed. At this time, the spontaneous polarization was 11.2 nC / cm ² and the tilt angle was 24.6 °. The contrast was good.

(Example 3) No. 1 in Table 1 Compound of (I) -2 6.25% No. Compound of (I) -3 6.25% No. Compound of (I) -4 6.25% No. Compound of (I) -5 6.25% No. 2 in Table 2 (II) -1 compound 6.25% No. Compound of (II) -2 6.25% No. Compound of (II) -3 6.25% No. Compound of (II) -4 6.25% No. 3 in Table 3 Compound of (IIIa) -1 15.0% No. Compound of (IIIa) -2 10.0% No. Compound of (IIIa) -3 15.0% No. A base liquid crystal (B-3) consisting of 10.0% of the compound of (IIIa) -4 was prepared.

The host liquid crystal (B-3) exhibited an SC phase up to 50.5 ° C, an SA phase up to 52 ° C, and an N phase up to 61.5 ° C. The melting point was 0 ° C or lower. 95% of the base liquid crystal (B-3) and the formula (Q) as a chiral dopant.

[0079]

[Chemical 11]

An SC ^* liquid crystal composition (M-3) consisting of 5% of a compound represented by the formula: was prepared. This SC ^* liquid crystal composition has an SC ^* phase up to 51 ° C. and an SA phase up to 56.5 ° C.
Each shows N ^* phase up to 1 ℃, and its melting point is 0 ℃
It was below. Even when this liquid crystal composition was allowed to stand at 5 to 10 ° C for 1 month, phase separation and the like did not occur.

The electro-optical response speed measured in exactly the same manner as in Example 1 was a high speed of 46 μsec at 25 ° C. The spontaneous polarization at this time was 8.8 nC / cm ² , and the tilt angle was 23.4 °. The contrast was good.

[0082]

The ferroelectric liquid crystal composition of the present invention exhibits an SC ^* phase in a wide temperature range and is capable of high-speed response of 30 to 40 μsec. Therefore, it is extremely useful as a material for the optical switching element for display.

Claims (5)

[Claims] 1. A general formula (I): (In the formula, each of R ¹ and R ² independently has 4 to 1 carbon atoms.
2 represents an alkyl group. ) And a compound represented by the general formula (II): (In the formula, one of R ³ and R ⁴ has 4 to 12 carbon atoms.
Represents a straight chain alkyl group, and the other has 4 to 1 carbon atoms.
2 represents an alkoxyl group or an alkenyloxy group. A ferroelectric liquid crystal composition containing a compound represented by the formula (1) and a matrix liquid crystal exhibiting a smectic C phase, and (2) a chiral dopant composed of an optically active compound. 2. A compound represented by the general formula (III): (In the formula, one of R ⁵ and R ⁶ has 4 to 12 carbon atoms.
Represents a straight chain alkyl group, and the other has 4 to 1 carbon atoms.
2 represents an alkoxyl group or an alkenyloxy group. 3. The ferroelectric liquid crystal composition according to claim 1, containing a compound represented by the formula (1). 3. A compound represented by the general formula (II), wherein R ³ is a linear alkyl group having 4 to 12 carbon atoms, and R ⁴ is a linear alkoxyl group having 4 to 12 carbon atoms, and R ⁵ is a straight-chain alkyl group having 4 to 12 carbon atoms, and R ⁶ is a straight-chain alkoxyl group having 4 to 12 carbon atoms, containing a compound represented by the general formula (III). The ferroelectric liquid crystal composition according to claim 2. 4. A matrix liquid crystal exhibiting a smectic C phase,
5 to 40% by weight of the compound represented by the general formula (I), 10 to 50% by weight of the compound represented by the general formula (II),
The ferroelectric liquid crystal composition according to claim 2, which contains 20 to 70% by weight of the compound represented by the general formula (III). 5. A liquid crystal display device comprising the ferroelectric liquid crystal composition according to claim 1, 2, 3 or 4.