JPH11166182A - Antiferroelectric liquid crystal composition excellent in low-temperature-side quality assurance temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an antiferroelectric liq. crystal compsn. which is excellent in low-temp.-side quality assurance temp. by specifying the ratio of the alignment darkness at a specified temp. of an antiferroelectric liq. crystal compsn. having no cooling hysteresis to the alignment darkness of the compsn. after being cooled to a specified temp. and the heated to another specified temp. to a specified value or higher. SOLUTION: This compsn. contains a compd. of formula I. Pref. this compsn. is a compsn. contg. 70-100 wt.% at least one compd. selected from compds. of formulas II, III, and IV, a compsn. contg. a compd. of formula I, II, or IV and 10-30 wt.% compd of formula V, a compsn. contg. a compd. of formula II, III, or IV and 30-40 wt.% compd. of formula V or VI, or a compsn. contg. a compd. of formula II, III, or IV, a compd. of formula V or VI, and a compd. of formula VII. The ratio (D1 /D20 ) of the alignment shadow (D1 ) of this compsn. at 40 deg.C to the alignment shadow (D20 ) of the compsn. at 40 deg.C after being cooled to -20 deg.C and then heated to 40 deg.C is 0.9 or higher. In the formulas, R<1> is 7-11C alkyl; R<2> is 2-6C alkyl; X is a single bond or the like; Y<1> to Y<3> are each H or F; Cf is CH3 or the like; m and v are each 6-9; and n, p, r, t, and a are each 7-11 or the like.

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 which is indispensable for a display using an antiferroelectric liquid crystal material and has a high rate of recovery from alignment deterioration when temperature changes.

[0002]

2. Description of the Related Art Liquid crystal display devices are 1) low-voltage operable 2).
Since it has excellent features such as low power consumption, 3) thin display, and 4) light receiving type, TN method, STN method,
A guest-host method has been developed and put into practical use.

However, those using nematic liquid crystals which are widely used at present have a response speed of several msec to several tens m.
There is a drawback of as slow as sec, and there are various restrictions in application.

[0004] In order to solve these problems, an active matrix system using an STN system or a thin-layer transistor system has been developed.
Although the display quality such as the display contrast and the viewing angle has become excellent, there are problems such as the need for high accuracy in controlling the cell gap and the tilt angle and the slow response.

For this reason, there is a demand for the development of a new liquid crystal display system having excellent responsiveness, and the optical response time is μs
Attempts have been made to develop ferroelectric liquid crystals capable of realizing ultra-high-speed devices as short as c-orders.

[0006] Ferroelectric liquid crystals were introduced in 1975 by Meyer.
DOBMMBC (p-decyloxybenzylidene-p-amino-2-methylbutylcinnamate) was synthesized for the first time (Le Journal de Phys).
sque, 36, 1975, L-69). In addition, 1
DOB by Clark and Lagwall in 980
Ferroelectric liquid crystals have attracted much attention since properties on display devices such as high-speed response of submicroseconds of AMBC and memory characteristics have been reported [N. A. Cla
rk, et al. , Appl. Phys. Lett. 3
6.899 (1980)]. However, their scheme includes
There are many technical issues for practical use, and there is almost no ferroelectric liquid crystal that satisfies the practical characteristics required for displays at room temperature, and it is effective and practical for controlling the alignment of liquid crystal molecules indispensable for display displays. The method was not well established.

Since this report, various attempts have been made from both sides of the liquid crystal material / device, and a display device utilizing switching between two twisted states as shown in FIG. 2 has been prototyped, and a high-speed electro-optical device using the same has also been developed. For example, JP-A-56
Although it is proposed in, for example, -107216, high contrast and proper threshold characteristics have not been obtained.

[0008] From such a viewpoint, other switching methods have been searched, and a transient scattering method has been proposed.
Then, in 1988, the present inventors reported a three-state switching method of a liquid crystal having a tristable state [A.
D. L. Chandani, T .; Hagiwara,
Y. Suzuki et al. , Japan. J. of
Appl. Phys. , 27, (5), L729-L7
32 (1988)].

The above-mentioned "having a tristable state" refers to a liquid crystal in which an antiferroelectric liquid crystal is sandwiched between a first electrode substrate and a second electrode substrate disposed with a predetermined gap. In the electro-optical device, a voltage for forming an electric field is applied to the first and second electrode substrates.
When a voltage is applied as a triangular wave shown in (A), the molecular orientation of the ferroelectric liquid crystal becomes a first stable state (FIG. 3 (a)) when no electric field is applied, as shown in FIG. The transmittance of the liquid crystal electro-optical device is in the first stable state [2 in FIG. 1 (D)].
In addition, when an electric field is applied, the molecular orientation becomes the second stable state (FIG. 3B) different from the first stable state in one electric field direction, and the transmittance of the liquid crystal electro-optical device becomes the second stable state.
1 (D), and a third molecular orientation stable state (FIG. 3 (c)) different from the first and second stable states with respect to the other electric field direction. This means that the transmittance of the liquid crystal electro-optical device shows a third stable state [1 in FIG. 1 (D)]. The applicant of the present invention has disclosed a liquid crystal electro-optical device utilizing this tristable state in Japanese Patent Application No.
No. 70212 and published as JP-A-2-153322.

The characteristics of the antiferroelectric liquid crystal exhibiting a tristable state will be described in more detail. Clark / Lagerval (C
In the surface-stabilized ferroelectric liquid crystal device proposed by L.Lark-Lagawall, two stable alignments in which ferroelectric liquid crystal molecules are uniformly aligned in one direction in the S ^* C phase as shown in FIGS. A state is shown, and the state is stabilized to one of the states depending on the direction of the applied electric field, and the state is maintained even when the electric field is cut off.

However, in practice, the orientation state of the ferroelectric liquid crystal molecules shows a twisted two state in which the director of the liquid crystal molecules is twisted, or shows a Chevron structure in which the layer is bent in a square shape. In the case of the Chevron layer structure, the switching angle becomes small and causes a low contrast, which is a major obstacle for practical use. On the other hand, in the SmC ^* A phase in which the “anti” ferroelectric liquid crystal shows a tristable state, in the above-mentioned liquid crystal electro-optical device, when there is no electric field, as shown in FIG. The dipoles of the liquid crystal molecules are arranged to be antiparallel to each other and cancel each other. Therefore, the spontaneous polarization is canceled in the entire liquid crystal layer. The liquid crystal phase showing this molecular arrangement corresponds to 2 in FIG.

Further, when a voltage sufficiently higher than the threshold value of (+) or (-) is applied, FIGS.
Are tilted in the same direction and arranged in parallel. In this state, the dipoles of the molecules are also aligned in the same direction, so that spontaneous polarization occurs and a ferroelectric phase is formed.

That is, SmC ^* A of the “anti” ferroelectric liquid crystal
In the phase, the “anti” ferroelectric phase in the absence of an electric field and the two ferroelectric phases due to the polarity of the applied electric field are stabilized, and the “anti” ferroelectric phase and the two ferroelectric phases are separated by a DC threshold value. The operation is performed between stable states. Due to the change in the liquid crystal molecule arrangement accompanying the switching, the light transmittance changes in a double hysteresis shown in FIG. As shown in FIG. 4A, a memory effect can be realized by applying a bias voltage to this double hysteresis and further superimposing a pulse voltage.

In the "anti" ferroelectric liquid crystal, an image can be displayed by alternately using both the positive side and the negative side of the hysteresis. Can be prevented. Further, the layer of the ferroelectric phase is stretched by the application of an electric field, and a bookshelf structure is formed. On the other hand, the "anti" ferroelectric phase in the third stable state has a similar bookshelf structure.
Since the layer structure switching by the application of the electric field gives dynamic shear to the liquid crystal layer, alignment defects are improved during driving, and good molecular alignment can be realized.

As described above, the "anti" ferroelectric liquid crystal is
It can be said that this is a very useful liquid crystal compound capable of 1) high-speed response, 2) high contrast and a wide viewing angle, and 3) excellent alignment characteristics and a memory effect.

The liquid crystal phase showing a tristable state of the "anti" ferroelectric liquid crystal is described in 1) A. D. L. Chandani
et al., Japan J. et al. Appl. Phys., 2
8, L-1265 (1989); Orihar
a et al., JapanJ. Appl. Phys.,
29, L-333 (1990),
The S ^* CA phase (Antife) for its “anti” ferroelectric properties
rroelectric Smectic C ^* phase) to be named but the present inventors have found that this crystal phase is defined as S ^* (3) phase for performing switching among the three stable states.

Liquid crystal compounds having an "anti" ferroelectric phase S ^* (3) exhibiting a tristable state in a phase series are disclosed in Japanese Patent Application Laid-Open Nos. Hei 1-331667, Hei 1-316372 and Hei 1-3316372, filed by the present inventors. There are JP-A-1-316339, JP-A-2-28128 and JP-A-1-213390 such as Ichihashi. As a liquid crystal electro-optical device utilizing a tristable state, the applicant of the present invention has disclosed JP-A-2-40625. Kaihei 2-153322
And Japanese Patent Application Laid-Open No. 2-173724.

When an "anti" ferroelectric liquid crystal is applied to a liquid crystal display, 1) operating temperature range, 2) response speed, 3).
It is difficult to satisfy all of spontaneous polarization, 4) hysteresis characteristics, 5) initial alignment, etc. with a single liquid crystal, and usually prepared as a dozen or more types of mixed liquid crystal.

At present, in order to improve the initial alignment of an antiferroelectric liquid crystal composition, the mixing ratio of a liquid crystal compound having a CF ₃ group bonded to asymmetric carbon to a liquid crystal compound having a CH ₃ group is about 7%. : 3, it is known that relatively good initial orientation can be obtained as compared with other ratios (Preliminary proceedings of the 20th Liquid Crystal Symposium, P.272). However, it is known that such a good orientation is not always maintained, but deteriorates due to heat history. It is understood that the reason for this is due to a defect that occurs when the layer structure formed in the smectic phase expands and contracts due to a change in temperature. Due to the disorder of the alignment state due to the defect, the angle between the optical axis of the liquid crystal and the polarizing plate is shifted, and light leakage occurs in the dark state. As a result, the value of the contrast represented by the ratio of the amount of light transmitted between the bright state and the dark state decreases, and when viewed as an actual display, the sharpness of the displayed image is impaired. To solve this problem, we have proposed a composition in which the temperature dependence of the layer spacing is extremely small.However, such a material does not necessarily show good display performance when used for a display. In practice, the types of liquid crystals that can be used are considerably limited.

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an antiferroelectric liquid crystal composition which can maintain good alignment regardless of the temperature change of the smectic layer interval and which has an excellent quality assurance temperature on the low temperature side. With the goal.

[0021]

First A solution for the present invention is a dark oriented at 40 ° C. of no antiferroelectric liquid crystal composition cooled history and D _1, cooling the antiferroelectric liquid crystal composition to -20 ° C. when the dark orientation was D ₂₀ at the 40 ° C. warmed to up to 40 ° C. after,

## EQU3 ## The present invention relates to an antiferroelectric liquid crystal composition having an excellent low temperature side quality assurance temperature, wherein D (−20 ° C.) = D ₁ / D ₂₀ is 0.9 or more.

The second aspect of the present invention is that the darkness of orientation of the antiferroelectric liquid crystal composition having no cooling history at 40 ° C. is D _1, and the antiferroelectric liquid crystal composition is cooled to −40 ° C. and then heated to 40 ° C. When the orientation dark at 40 ° C. is D ₄₀ ,

## EQU4 ## The present invention relates to an antiferroelectric liquid crystal composition having an excellent low-temperature-side quality assurance temperature, wherein D (−40 ° C.) = D ₁ / D ₄₀ is 0.9 or more.

The method for measuring the orientation darkness is as follows. That is, a 2 μm-thick liquid crystal cell formed of a glass with a transparent electrode and having a polyimide film formed thereon and subjected to a rubbing treatment is filled with a liquid crystal composition to be measured in an isotropic phase. Next, aging is performed by applying an electric field at a temperature 30 ° C. lower than the upper limit temperature of the antiferroelectric phase. The cell is gradually cooled at a temperature gradient of 2.0 ° C./min, and the orientation dark D ₁ at 40 ° C. is measured. Next up to -T ° C 2.0 ° C / mi
n, gradually heated to 40 ° C., applied an electric field, aged, and again oriented dark D _{T at} 40 ° C.
Is measured.

The T ° C. is −20 ° C.
If ₁ / D ₂₀ is 0.9 or more, even when used in this antiferroelectric liquid crystal composition obtained it may be cooled to approximately -20 ° C. atmosphere, to be able to guarantee the quality understood. Further, the T ° C. is -40 ℃, if D ₁ / D ₄₀ at this time is 0.9 or more, this antiferroelectric liquid crystal composition obtained may be cooled to approximately -40 ℃ It was found that the quality could be guaranteed even when used in an atmosphere.

In the present invention, the expression that there is no cooling history means that there is no history of cooling to a temperature lower than 40 ° C. after the liquid crystal composition was injected into the cell.

The antiferroelectric liquid crystal composition is specifically represented by the following general formula (1)

Embedded image (Wherein, R ¹ is an alkyl group having 7 to 11 carbon atoms, the alkyl group may contain a double bond, R ² is an alkyl group having 2 to 6 carbon atoms, and X is a single bond. , O, CO
A group selected from the group consisting of O and OCO;
¹ , Y ² and Y ³ are each independently selected from the group consisting of hydrogen and fluorine atoms, Cf is a CH ₃ group or a CF ₃ group, and * represents an asymmetric carbon. ) Can be achieved.

The compound of the general formula (1) is preferably present in an amount of 70 to 100% by weight in the total antiferroelectric liquid crystal composition.

The antiferroelectric liquid crystal composition may contain a racemic liquid crystal compound in an amount of 3 to 15% by weight. Further, these antiferroelectric liquid crystal compositions include, for example, Japanese Patent Application Nos. 6-248649, 6-277110, and 6-2.
No. 77111, No. 6-277113, No. 6-277114
No., 6-287399, 7-148662, 8-1
27788, 8-143642, 8-320947
No., 9-242143, reference number HP0002251
1 to 3% by weight of the liquid crystal property improver described in -1.

In the antiferroelectric liquid crystal composition of the present invention, the compound represented by the general formula (1) is preferably a compound represented by the following general formula (5):

Embedded image Wherein t is a number selected from the group consisting of integers from 7 to 11, and u is a number selected from the group consisting of integers from 2 to 6. ),

Embedded image (Wherein v is a number selected from the group consisting of integers from 6 to 9, w is a number selected from the group consisting of integers from 2 to 6), and a compound represented by the general formula ( 7)

Embedded image (Where a is a number selected from the group consisting of integers from 7 to 11 and b is a number selected from the group consisting of integers from 2 to 6). And at least one compound selected from the group consisting of:

The antiferroelectric liquid crystal composition of the present invention includes:
The compound represented by the general formula (1), preferably the compound represented by any of the general formulas (5), (6) and (7) is added to the compound represented by the following general formula (2)

Embedded image (Wherein, m is a number selected from the group consisting of integers from 6 to 9, and n is a number selected from the group consisting of integers from 2 to 6). By containing it, an antiferroelectric liquid crystal composition having a higher recovery rate can be obtained.

Furthermore, in the present invention, (a) a compound represented by the general formula (1), preferably the aforementioned general formula (5),
A liquid crystal composition containing at least one compound represented by any of (6) and (7) or (b) a compound represented by the general formula (1), preferably the above-mentioned general formulas (5), (6),
A liquid crystal composition containing at least one compound represented by any of (7) and at least one compound represented by the general formula (2) is added to a liquid crystal composition represented by the following general formula (3)

Embedded image (Wherein, p is a number selected from the group consisting of integers from 7 to 11 and q is a number selected from the group consisting of integers from 2 to 6). By doing so, an antiferroelectric liquid crystal composition having an even higher recovery rate can be obtained.

The compound represented by the general formula (2) can be contained in an amount of 10 to 30% by weight, preferably 12 to 28% by weight based on the whole antiferroelectric liquid crystal composition. The compound represented by the general formula (3) is used in an amount of 30 to 40% by weight, preferably 31 to 40% by weight based on the total antiferroelectric liquid crystal composition.
３４34% by weight.

Furthermore, in the present invention, (a) a compound represented by the above general formula (1), preferably at least one compound represented by any of the following general formulas (5), (6) and (7) (B) a compound represented by the general formula (1), preferably at least one compound represented by any of the general formulas (5), (6) and (7) Or a liquid crystal composition containing at least one compound represented by the general formula (2), or (c) a compound represented by the general formula (1), preferably the general formulas (5), (6), A liquid crystal composition containing at least one compound represented by any one of (7) and at least one compound represented by the general formula (2) and at least one compound represented by the general formula (3) has the following general formula Equation (4)

Embedded image (Wherein, r is a number selected from the group consisting of integers from 7 to 11 and s is a number selected from the group consisting of integers from 2 to 6). By doing so, an antiferroelectric liquid crystal composition having an extremely high recovery rate can be obtained.

The compound represented by the general formula (4) can be contained in an amount of 10 to 30% by weight, preferably 13 to 28% by weight based on the whole antiferroelectric liquid crystal composition. When the compound represented by the general formula (7) accounts for 3 to 15% by weight based on the total antiferroelectric liquid crystal composition, the compound represented by the general formula (7) may be in a racemic form.

The composition of the antiferroelectric liquid crystal composition of the present invention comprises an antiferroelectric liquid crystal compound in which the side chain of the asymmetric carbon is a trifluoromethyl group and an antiferroelectric liquid crystal compound in which the side chain of the asymmetric carbon is a methyl group. A mixture with a ferroelectric liquid crystal compound is desirable from the viewpoint of alignment darkness, and the preferable ratio is 6: 4 to 7: 3.

[0036]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 An antiferroelectric liquid crystal composition having the following composition was prepared.

Embedded image The maximum temperature of the antiferroelectric phase of this composition is 99.2 ° C., the orientation dark D ₁ is 69, the orientation dark D ₄₀ is 71, and D ₁ /
D ₄₀ = 0.97. Therefore, it can be guaranteed that the antiferroelectric liquid crystal composition can be used in an environment up to −40 ° C.

Example 2 An antiferroelectric liquid crystal composition having the following composition was prepared.

Embedded image The maximum temperature of the antiferroelectric phase of this composition is 95.5 ° C., the orientation dark D ₁ is 80, and the orientation dark D _{40 at} −40 ° C. is 84, so that D ₁ / D ₄₀ = 0. .93.

Example 3 An antiferroelectric liquid crystal composition having the following composition was prepared.

Embedded image The maximum temperature of the antiferroelectric phase of this composition is 95.7 ° C., the orientation dark D ₁ is 80, and the orientation dark D _{40 at} −40 ° C. is 83, so that D ₁ / D ₄₀ = 0. .96.

Example 4 The following chemical structural formula was applied to the antiferroelectric liquid crystal composition of Example 2.

Embedded image A new antiferroelectric liquid crystal composition was prepared by mixing a liquid crystal compound of the formula (1) with a weight fraction of 10: 1. The maximum temperature of the antiferroelectric phase of this composition is 94.1 ° C.
₁ is 79, the orientation darkness at −40 ° C. is D ₄₀ = 85, so D ₁ / D ₄₀ = 0.93.

Example 5 An antiferroelectric liquid crystal composition having the following composition was prepared.

Embedded image The maximum temperature of the antiferroelectric phase of this composition is 94.1 ° C., the orientation dark D ₁ is 90, and the orientation dark D _{40 at} −40 ° C. is 92, so that D ₁ / D ₄₀ = 0. .98.

Example 6 An antiferroelectric liquid crystal composition having the following composition was prepared.

Embedded image The upper limit temperature of the antiferroelectric phase of this composition is 90.1 ° C., the orientation dark D ₁ is 76, the orientation dark D _{40 at} −40 ° C. is 101, and D ₁ / D ₄₀ = 0. 75. Further, in the method of measuring the dark orientation, rather than the -40 ℃ minimum cooling temperature, and -20 ° C., warmed to 40 ° C., orientation dark D ₂₀ measured at 40 ° C. is 84, this time D ₁ / D ₂₀ =
0.9. Therefore, it can be guaranteed that the antiferroelectric liquid crystal composition can be used in an environment up to −20 ° C.

[0043]

According to the present invention, it is possible to provide an antiferroelectric liquid crystal composition capable of recovering good alignment by applying an electric signal even when the alignment state changes due to heat history.

[Brief description of the drawings]

1 (A) shows an applied triangular wave, (B) shows a commercially available nematic liquid crystal, (C) shows a two-state liquid crystal, and (D) shows a tristable state liquid crystal. .

FIG. 2 shows two stable alignment states of ferroelectric liquid crystal molecules proposed by Clark / Lagerval.

FIG. 3A shows three stable alignment states of the “anti” ferroelectric liquid crystal molecules of the present invention. (B) shows the three-state switching and the change of the liquid crystal molecular arrangement corresponding to each of (a), (b), and (c) of A.

FIG. 4 is an applied voltage-light transmittance characteristic diagram showing that the “anti” ferroelectric liquid crystal molecules change their light transmittance by drawing a double hysteresis with respect to an applied voltage.

Claims (6)

[Claims] An anti-ferroelectric liquid crystal composition having no cooling history has a darkness of orientation at 40 ° C., D ₁ , and the anti-ferroelectric liquid crystal composition is cooled to −20 ° C. and then heated to 40 ° C.
When the dark orientation was D ₂₀ at ## EQU1 ## D (-20 ℃) = antiferroelectric superior in low temperature side quality assurance temperature D ₁ / D ₂₀ is equal to or less than 0.9 Liquid crystal composition. Wherein the dark orientation in 40 ° C. with no cooling history antiferroelectric liquid crystal composition as D _1, the anti-ferroelectric liquid crystal composition warmed to 40 ° C. After cooling to -40 ℃ its 40 ° C.
When the dark orientation was D ₄₀ at ## EQU2 ## D (-40 ℃) = antiferroelectric superior in low temperature side quality assurance temperature D ₁ / D ₄₀ is equal to or less than 0.9 Liquid crystal composition. 3. The antiferroelectric liquid crystal composition according to the following general formula (1): (Wherein, R ¹ is an alkyl group having 7 to 11 carbon atoms, the alkyl group may contain a double bond, R ² is an alkyl group having 2 to 6 carbon atoms, and X is a single bond. , O, CO
A group selected from the group consisting of O and OCO;
¹ , Y ² and Y ³ are each independently selected from the group consisting of hydrogen and fluorine atoms, Cf is a CH ₃ group or a CF ₃ group, and * represents an asymmetric carbon. 3. The antiferroelectric liquid crystal composition according to claim 1, which comprises at least one compound represented by the formula (1). 4. The following general formula (2): (Wherein, m is a number selected from the group consisting of integers of 6 to 9, and n is a number selected from the group consisting of integers of 2 to 6). 4. The antiferroelectric liquid crystal composition according to claim 3, which has an excellent low-temperature-side quality assurance temperature. 5. The following general formula (3): (Wherein p is a number selected from the group consisting of integers from 7 to 11, and q is a number selected from the group consisting of integers from 2 to 6). 5. The antiferroelectric liquid crystal composition according to claim 3, wherein the composition has an excellent low-temperature-side quality assurance temperature. 6. The following general formula (4): (Wherein, r is a number selected from the group consisting of integers from 7 to 11 and s is a number selected from the group consisting of integers from 2 to 6). 6. The antiferroelectric liquid crystal composition according to claim 3, wherein the composition has an excellent low temperature side quality assurance temperature.