JP3143061B2 - Antiferroelectric liquid crystal property improver and antiferroelectric liquid crystal composition containing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an antiferroelectric liquid crystal property improving agent and an antiferroelectric liquid crystal composition containing the same.

[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. The thin film transistor method has a complicated structure and a low production yield, resulting in high cost.

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.

[0007] 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 has been trial-produced. No. 107216, but 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 represented by the following formula, the molecular orientation of the antiferroelectric liquid crystal becomes a first stable state [FIG. 3 (a)] when no electric field is applied, and the transmittance of the liquid crystal electro-optical device becomes first. And the liquid crystal becomes a second stable state [FIG. 3 (b)] in which the molecular orientation in one electric field direction differs from the first stable state when an electric field is applied. The transmittance of the electro-optical device shows a second stable state (3 in FIG. 1D), and a third molecular orientation stable state different from the first and second stable states in the other electric field direction [FIG.
(C)], which means that the transmittance of the liquid crystal electro-optical device shows a third stable state (1 in FIG. 1D). The applicant of the present invention has applied for a liquid crystal electro-optical device utilizing the tristable state as Japanese Patent Application No. 63-70212 and published as Japanese Patent Application Laid-Open No. 2-153322.

The characteristics of the antiferroelectric liquid crystal exhibiting a tristable state will be described in more detail. Clark / Ragawell (Cla
In the surface-stabilized ferroelectric liquid crystal device proposed by rk-Lagawall, two ferroelectric liquid crystal molecules are uniformly aligned in one direction in the S ^* C phase as shown in FIGS. 2A and 2B. It has a state and is stabilized in one of the states depending on the direction of the applied electric field, and that 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. 1D.

Further, when a voltage sufficiently higher than the threshold value of (+) or (-) is applied, FIGS.
The liquid crystal molecules are inclined in the same direction and are arranged in parallel as shown in FIG. 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.

In the SmC ^* A phase of the “anti” ferroelectric liquid crystal, the “anti” ferroelectric phase in the absence of an electric field and the two ferroelectric phases depending on the polarity of the applied electric field are stable, and the “anti” ferroelectric phase is stable. And high-speed switching in the microsecond order between the three stable states with a DC threshold value between the two ferroelectric phases. That is, the molecular arrangement of the liquid crystal changes according to the polarity and magnitude of the applied electric field, and the optic axis of the liquid crystal can be changed to three states. By sandwiching such three states of the liquid crystal between a pair of polarizing plates, It can be used as an electro-optical display device. When the light transmittance is plotted against the applied voltage of the AC triangular wave, a double hysteresis as shown in FIG. 4 is shown. This double hysteresis is shown in FIG.
As shown in (1), a memory effect can be realized by applying a bias voltage 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 first 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 that can achieve 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) and 2) H. Orih
ara et al., Japan J. et al. Appl. Ph
ys., 29, L-333 (1990), and based on the "anti" ferroelectric properties, the S ^* CA phase (Anti
ferroelectric Smatic C
^* Phase) has been named inventors, the liquid crystal phase is in the S ^* (3) phase (herein for performing switching between three stable states is defined as SmC ^* A phase display) and.

"Anti" ferroelectric phase SmC ^* A showing tristable state
Are in the phase series, JP-A-1-316367, JP-A-1-316372, 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 discloses JP-A-2-40625. JP-A-2-153322
And Japanese Patent Application Laid-Open No. 2-173724.

The material characteristics required for the antiferroelectric liquid crystal used in the above-mentioned display device mainly include 1) an operating temperature range, 2) a response speed, 3) a hysteresis characteristic, and 4) a display contrast.

Although these antiferroelectric liquid crystals have a shorter optical response time than conventional liquid crystals, they have attracted attention as one that opens up the possibility as a high-speed device.
The shorter the optical response time is, the wider the application of the liquid crystal is. Therefore, the reduction of the response time is an important theme.
Further, a potential problem of the antiferroelectric liquid crystal is that the threshold voltage is too high, and it is important to lower the threshold voltage.

Many of the conventionally developed antiferroelectric liquid crystal compositions have a low response speed in a temperature range of room temperature or lower, so that when a signal for causing a liquid crystal element to draw a moving image is applied, the contrast is reduced. And tended to be difficult to see.

In general, in an antiferroelectric liquid crystal, a threshold voltage or a saturation voltage required for a transition from an antiferroelectric phase to a ferroelectric phase increases with a decrease in temperature. In many cases, the limit of the supply voltage of the IC is exceeded. In the latter case, of course, it can be handled by increasing the breakdown voltage of the IC.
It's not a cost advantage.

[0022]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an antiferroelectric liquid crystal property improving agent which lowers the threshold voltage and the saturation voltage and improves the response speed at a temperature lower than the room temperature range. An object of the present invention is to provide a dielectric liquid crystal composition.

[0023]

Means for Solving the Problems A first aspect of the present invention is the following general formula [1]:

Embedded image (Wherein, Cf represents a CH ₃ group or a CF ₃ group;
Is an integer of 6 to 12, n is an integer of 2 to 10, and * represents an optically active carbon).

The second aspect of the present invention relates to an antiferroelectric liquid crystal composition comprising at least one kind of the property improving agent for antiferroelectric liquid crystal according to claim 1.

In the antiferroelectric liquid crystal composition, the compound represented by the general formula [1] is 0.1 to 20% by weight, preferably 0.5 to 1% by weight based on the antiferroelectric liquid crystal composition.
It is preferred to use 0% by weight.

The antiferroelectric liquid crystal property improving agent can be synthesized, for example, by the following method.

Embedded image (Wherein, Cf, m, n and * are the same as described above)

The method for measuring the electro-optical characteristics (threshold voltage, saturation voltage and response speed) of the liquid crystal in the present invention is as follows. A 2 μm thick liquid crystal cell having a rubbed polyimide alignment film on a transparent electrode substrate was filled with a liquid crystal composition in an isotropic phase to prepare a liquid crystal alignment cell.
The prepared liquid crystal cell was charged at 0.1 to 1.0 ° C / min. The liquid crystal is precipitated by gradually cooling at a temperature gradient of (2). This liquid crystal cell was placed in a polarizing microscope equipped with a photomultiplier tube in which two polarizing plates were orthogonal to each other so as to provide a dark field at a voltage of 0V. When the liquid crystal composition is in the anti-ferroelectric phase, the voltage is ± 40 V, 1 Hz
FIG. 5 is a graph of the relative transmittance of light when the triangular wave voltage is applied with respect to the applied voltage. As shown in the figure, it is characterized by having two substantially symmetrical hysteresis when a plus voltage is applied and when a minus voltage is applied. As shown in the figure, in the process of increasing (decreasing) the applied positive voltage (minus voltage), the voltage at which the relative transmittance becomes 10% is set to the threshold voltage V ₁ and the applied positive voltage (minus voltage). In the process of increasing (decreasing) the voltage, the voltage at which the relative transmittance becomes 90% is the saturation voltage V ₂ , and the applied plus voltage (minus voltage) is reduced (increased). in the process, the relative transmittance to define a voltage which is 90% and the threshold voltage V _3.

The response speeds τ, τr, and τd can be obtained from changes in the relative transmittance of light when a rectangular wave of ± 50 V as shown in FIG. 6 is applied to the cell. τ is transmitted from the ferroelectric state (specifically, at the end of the negative rectangular wave voltage) to the next ferroelectric state via the antiferroelectric phase state (specifically, by the application of the positive rectangular wave voltage, the relative transmission). (When the rate reaches 90%). τr is a time required for a transition from an antiferroelectric phase state (specifically, when a rectangular wave voltage is applied) to a ferroelectric state (specifically, when a relative transmittance reaches 90%). , Τd are the times required for transition from the ferroelectric state (specifically at the end of the rectangular wave voltage) to the antiferroelectric phase state (specifically, when the relative transmittance reaches 10%). In each case, the unit is μsec.
It is.

In the process of applying a voltage to the plus (or minus) side from the state of the antiferroelectric phase, there is a phenomenon that the relative transmittance gradually increases before the transition to the ferroelectric phase.
In actual state of applying the large V ₁ is less than the DC bias voltage than V ₃ denotes a display, it means that is driven by applying a pulse voltage, light leakage in the antiferroelectric state causes a decrease in contrast. Light leakage in the antiferroelectric state was quantitatively evaluated as follows. The relative transmittance in the process of applying a voltage to the plus (or minus) side from the no-voltage state was second-order-differential to the applied voltage, and the voltage at which the value at this time became 2 was obtained. Then, a relative transmittance at a corresponding voltage was obtained from a relative transmittance-applied voltage curve, and this value was defined as a pot bottom ratio. The smaller the pot bottom ratio, the less light leakage.

[0030]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by this.

Production Examples (Production of antiferroelectric liquid crystal property improver of the following formula used in Examples 1, 2 and 3)

Embedded image The reaction formula is shown below. 0.3 g of R-form 2-octanol was dissolved in 100 ml of dichloromethane, and 0.24 g of triethylamine and 0.09 g of dimethylaminopyridine were dissolved.
Was added and stirred well. 0.87 g of 4-octylphenylbenzoic acid chloride was added little by little to this solution, and the mixture was stirred at room temperature under a nitrogen atmosphere for about 15 hours. The reaction solution is developed in water, and the aqueous layer is neutralized with a 0.1N aqueous HCl solution and a 0.1N aqueous NaOH solution to extract an organic solvent layer. The organic solvent layer is dried using an excess amount of magnesium sulfate, and then dichloromethane is distilled off. The crude product was subjected to silica gel chromatography (developing solvent: hexane / ethyl acetate = 10.0: 0.
Separate in 5). Recrystallization from ethanol gave 0.26 g of 4-octylphenylbenzoic acid 2-octanol ester as the target compound.

[0032]

Embedded image

Comparative Example 1 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-decyloxybiphenyl-4-carboxylate

Embedded image And 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-undecyloxybiphenyl-4-carboxylate

Embedded image And 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-decylbiphenyl-4-carboxylate

Embedded image Were mixed at a weight fraction of 28.7: 31.7: 39.6 to produce an antiferroelectric liquid crystal composition. The antiferroelectric liquid crystal composition is injected into a 2 μm-thick cell made of glass with a transparent electrode which has been coated with polyimide and rubbed, and subjected to phase transition temperature (data at the time of temperature increase, ° C) is as shown in the table below.

[Table 1]

Further, 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 3 shows the response speeds τr, τd, and τ at ° C. Further, Table 4 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

Example 1 With respect to the antiferroelectric liquid crystal composition prepared in Comparative Example 1,

Embedded image Was added at a weight fraction of 5% to produce an antiferroelectric liquid crystal composition.

Table 2 shows the phase transition temperature (° C.) measured by the above method when the temperature of the antiferroelectric liquid crystal composition was raised.

[Table 2]

Further, at 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 3 shows the response speeds τr, τd, and τ at ° C. Further, Table 4 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

[0038]

[Table 3]

[Table 4]

Comparative Example 2 4- (2-octyloxycarbonyl) phenyl-4 '
-N-nonyloxy-2-fluorobiphenyl-4-carboxylate

Embedded image And 4- (2-octyloxycarbonyl) 3-fluorophenyl-4'-n-nonyloxy-2-fluorobiphenyl-4-carboxylate

Embedded image Was mixed at a weight fraction of 50.0: 50.0 to prepare an antiferroelectric liquid crystal composition.

Table 5 shows the phase transition temperature (° C.) measured by the above method when the temperature of the antiferroelectric liquid crystal composition was raised.

[Table 5]

Further, at 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 7 shows the response speeds τr, τd, and τ at ° C. Table 8 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

Example 2 With respect to the antiferroelectric liquid crystal composition prepared in Comparative Example 2,

Embedded image Was added at a weight fraction of 5% to produce an antiferroelectric liquid crystal composition.

Table 6 shows the phase transition temperature (° C.) measured by the above method when the temperature of the antiferroelectric liquid crystal composition was raised.

[Table 6]

Also, at 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 7 shows the response speeds τr, τd, and τ at ° C. Table 8 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

[0045]

[Table 7]

[Table 8]

Comparative Example 3 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-decyloxybiphenyl-4-carboxylate

Embedded image And 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-undecyloxybiphenyl-4-carboxylate

Embedded image And 4- (1,1,1-trifluoro-2-hexyloxycarbonyl) phenyl-4'-n-decylbiphenyl-4-carboxylate

Embedded image And 4- (2-octyloxycarbonyl) phenyl-
4'-n-nonyloxy-2-fluorobiphenyl-4
-Carboxylate

Embedded image And 4- (2-octyloxycarbonyl) 3-fluorophenyl-4'-n-nonyloxy-2-fluorobiphenyl-4-carboxylate

Embedded image And 20.1: 22.2: 27.7: 15.
An antiferroelectric liquid crystal composition mixed at a ratio of 0: 15.0 was produced.

Table 9 shows the phase transition temperature (° C.) measured by the above method when the temperature of the antiferroelectric liquid crystal composition was raised.

[Table 9]

Also, at 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 11 shows the response speeds τr, τd, and τ at ° C. Table 12 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

Example 3 The antiferroelectric liquid crystal composition prepared in Comparative Example 3 was

Embedded image Was added at a weight fraction of 5% to produce an antiferroelectric liquid crystal composition.

Table 10 shows the phase transition temperature (° C.) measured by the above method when the temperature of the antiferroelectric liquid crystal composition was raised.

[Table 10]

Also, at 70 ° C., 50 ° C., 30 ° C. and 20 ° C.
Table 11 shows the response speeds τr, τd, and τ at ° C. Table 12 shows the threshold voltage V ₁ , the saturation voltage V ₂ , and the pot bottom ratio at 50 ° C. and 30 ° C.

[0052]

[Table 11]

[Table 12]

[0053]

An antiferroelectric liquid crystal composition comprising only a system having a trifluoromethyl group in an optically active site, an antiferroelectric liquid crystal composition comprising only a system having a methyl group, and an antiferroelectric liquid crystal containing both Regarding any of the compositions, the liquid crystal property improver of the present invention can increase the electro-optical properties, that is, the response speed, reduce the threshold voltage, the saturation voltage, and reduce the anti-ferroelectric state. The light leakage phenomenon (pot bottom property) at the time of applying a voltage was able to be improved.

[Brief description of the drawings]

FIG. 1 A is a triangular wave applied, B is a commercially available nematic liquid crystal, C is a bi-state liquid crystal, D is a tri-stable liquid crystal,
Each optical response characteristic is shown.

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

FIG. 3A shows three stable alignment states of antiferroelectric liquid crystal molecules. B shows three-state switching corresponding to each of (a), (b) and (c) of A and a change in liquid crystal molecular arrangement.

FIG. 4 is an applied voltage-light transmittance characteristic diagram showing that light transmittance changes due to double hysteresis of antiferroelectric liquid crystal molecules with respect to applied voltage.

FIG. 5 shows a model of a hysteresis curve of relative transmittance with respect to a triangular wave applied voltage.

FIG. 6A shows a relationship between applied voltage and time, and FIG.
Is a graph showing a response state of liquid crystal molecules when the applied voltage is applied.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsuyoshi Yoshida 3-5-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Inside Showa Shell Sekiyu KK (72) Inventor Yoshinori Nagoya 3-5-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Showa (56) References JP-A-2-202851 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 19/54 C09K 19/20 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] [Claim 1] The following general formula [1] (Wherein, Cf represents a CH ₃ group or a CF ₃ group;
Is an integer of 6 to 12, n is an integer of 2 to 10, and * represents an optically active carbon). 2. An antiferroelectric liquid crystal composition comprising at least one kind of the property improving agent for antiferroelectric liquid crystal according to claim 1.