JP3184446B2 - Antiferroelectric liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel antiferroelectric liquid crystal composition which exhibits an antiferroelectric phase near room temperature.

[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 crystal was introduced in 1975 by Meyor.
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. 3B) 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 (2 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 (3 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 stable liquid crystal molecules in which the ferroelectric liquid crystal molecules are uniformly aligned in one direction in the S * C phase as shown in FIGS. 2 (a) and 2 (b). State, and depending on the direction of the applied electric field,
The state is stabilized in one of the states, 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, the molecules are reversed in each adjacent layer 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 exhibiting this molecular arrangement corresponds to 1 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 stabilized, 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. 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 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 .; Appl. Phys. ,
28, L- 1265 (1989) and 2) H.E. Ori
hara et al. , Japan J .; Appl. P
hys. , 29, L-333 (1990), and based on the "anti" ferroelectric properties, the S * CA phase (Ant
iferoelectric Smatic C *
However, the present inventors have defined the liquid crystal phase as an S * (3) phase (referred to as an SmC * A phase in this specification) because the liquid crystal phase performs switching between three stable states.

"Anti" ferroelectric phase SmC * showing tristable state
Liquid crystal compounds having A in a phase series are disclosed in Japanese Patent Application Laid-Open Nos. Hei 1-331667 and Hei 1-316372 filed by the present inventors.
JP-A-1-316339, JP-A-2-28128
And Japanese Patent Laid-Open No. 1-213390 such as Ichihashi,
As a liquid crystal electro-optical device utilizing a tristable state, the present applicant has disclosed in Japanese Patent Application Laid-Open Nos. 2-40625 and 2-1533.
No. 22 and Japanese Patent Application Laid-Open No. 2-173724 propose new proposals.

The material characteristics required for the antiferroelectric liquid crystal used in the above-described display device (optical device) are mainly as follows.
1) operating temperature range, 2) response speed, 3) hysteresis characteristic, 4) display contrast, and the like.

The tilt angle (tilt angle) is the tilt angle in the direction of the long axis of the molecule as shown in FIG. 3. In the above-described liquid crystal display device using an antiferroelectric liquid crystal, a dark state occurs when no electric field is applied. When using a cell assembled so that the tilt angle θ is 45 ° when an electric field is applied, the light transmittance becomes maximum. However, at present, a normal antiferroelectric liquid crystal compound or composition has a tilt angle of about 30 ° and an antiferroelectric liquid crystal having a tilt angle θ of 45 ° has not been obtained.
In order to improve the light transmittance, antiferroelectric liquid crystals having a large tilt angle are desired. Although the tilt angle changes depending on the temperature, in practice, there is heat from the backlight. Therefore, there is a demand for a liquid crystal compound or composition whose tilt angle is as little as 45 ° at 30 ° C. or higher than room temperature.

On the other hand, it is also important to improve the response speed of the liquid crystal display element together with the tilt angle. However, if a viscosity reducing agent is added to improve the response speed, the tilt angle is reduced, and the contrast is reduced. There is a problem that it causes a decrease. As described above, the tilt angle and the response speed are in a trade-off relationship.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to provide an antiferroelectric liquid crystal composition which exhibits an antiferroelectric phase near room temperature, has a sufficient tilt angle and also has a high response speed. is there.

[0022]

Means for Solving the Problems The present invention provides the following general formula (1)

Embedded image (Wherein m is an integer of 4 to 16, n is an integer of 4 to 12, X ₁ , X ₂ and X ₃ are elements independently selected from the group consisting of H and F, and Y is —COO -Or -O-,
Cf is a CH ₃ group or a CF ₃ group, and * indicates an optically active center. An antiferroelectric liquid crystal composition containing at least one compound represented by the formula (1), wherein the tilt angle at 30 ° C. is 30 to 50 degrees, and the response speed τ is 5 to 30 μsec. The present invention relates to an antiferroelectric liquid crystal composition characterized by the following.

The antiferroelectric liquid crystal compound represented by the general formula (1) is used in an amount of 0.1 wt.
% Or more, preferably 0.1 to 40 wt%, particularly preferably 1.0 to 20 wt%, can improve the tilt angle and the response speed.

Further, the antiferroelectric liquid crystal composition of the present invention comprises:
(A) The following general formula (1)

Embedded image (Wherein m is an integer of 4 to 16, n is an integer of 4 to 12, X ₁ , X ₂ and X ₃ are elements independently selected from the group consisting of H and F, and Y is —COO -Or -O-,
Cf is a CH ₃ group or a CF ₃ group, and * indicates an optically active center. A) a compound represented by the following general formula (2):

Embedded image (Wherein, R _C m _{H 2m + 1} - or _CH 2 = CH (C
H _{2) m} -, X is H or F, m, n, Cf and * are as defined above. ) Can also be achieved.

The antiferroelectric liquid crystal compound represented by the general formulas (1) and (2) is preferably 0.1 wt% or more with respect to other liquid crystal compositions, especially the antiferroelectric liquid crystal composition. Is 0.1 to 60% by weight, particularly preferably 1.0 to 4% by weight.
By using 0 wt%, the tilt angle can be improved.

Examples of the other liquid crystal compositions include Japanese Patent Application Nos. 7-248636 and 7-179 filed by the present applicant.
No. 520, No. 7-179519, No. 7-162859
Nos. 7-161412, 7-161410, 7-161409, 7-146866, and 7-1
No. 46862, No. 7-1468661, No. 7-1400
No. 01, No. 7-126025, No. 7-115208
Nos. 7-94293, 7-93115, 7-
No. 77349, No. 7-74480, No. 6-28739
9, 6-277114, 6-277113,
6-277111, 6-277110, 6-
277109, 6-243320, 6-248
No. 649, No. 6-234220, No. 5-215060
And the known antiferroelectric liquid crystal compounds and compositions.

[0027]

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

Comparative Example 1 A basic antiferroelectric liquid crystal composition (a) shown in the following Chemical Formula 5 was prepared.

Embedded image

Example 1 100 parts by weight of a basic antiferroelectric liquid crystal composition (a) having the composition shown in Chemical Formula 5 was added to the following formula of the present invention.

Embedded image Was mixed with 8 parts by weight of a liquid crystal compound represented by the formula (1) to obtain a novel antiferroelectric liquid crystal composition (A).

The response speed τ and tilt angle θ of this antiferroelectric liquid crystal composition (A) are as shown in the following table.

[Table 1]

On the other hand, the response speed τ and the tilt angle θ of the basic antiferroelectric liquid crystal composition (a) are as shown in the following table.

[Table 2]

When the tilt angles of the antiferroelectric liquid crystal composition (A) of Example 1 of the present invention and the basic antiferroelectric liquid crystal composition (a) of Comparative Example 1 are compared, Tables 1 and 2, and As is clear from FIG. 6, the antiferroelectric liquid crystal composition (A) of the present invention.
It can be seen that the tilt angle was improved and the response speed was hardly reduced as compared with the basic antiferroelectric liquid crystal composition (a) at 5 to 30 ° C.

Example 2 100 parts by weight of the basic antiferroelectric liquid crystal composition (a) having the composition shown in Chemical Formula 5 was added to the following formula of the present invention.

Embedded image Was mixed with 8 parts by weight of a liquid crystal compound represented by the formula (1) to obtain an antiferroelectric liquid crystal composition (B). The tilt angle and response speed at that time are as shown in the table below.

[0034]

[Table 3]

As is clear from Tables 2 and 3 and FIG. 7, the product of Example 2 is 30 to 30 times larger than that of Comparative Example 1.
It can be seen that the tilt angle at 40 ° C. is greatly improved.

Comparative Example 2 The following formula was added to 70 parts by weight of the basic antiferroelectric liquid crystal composition (b) having the composition shown in the following chemical formula 9.

Embedded image Was mixed to obtain an antiferroelectric liquid crystal composition of Comparative Example 2. Table 4 shows the tilt angles.

Embedded image

[0037]

[Table 4]

[0038]

According to the present invention, a liquid crystal composition having an improved tilt angle at a practical temperature of 30 ° C. without deteriorating the response speed can be provided.

[Brief description of the drawings]

FIG. 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 an optical response characteristic in a tristable state.

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

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

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.

FIG. 5A 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.

FIG. 6 is a graph showing the tilt angle at each temperature of the antiferroelectric liquid crystal composition (A) of Example 1 and the basic antiferroelectric liquid crystal composition (a) as a control.

FIG. 7 is a graph showing the tilt angle at each temperature of the antiferroelectric liquid crystal composition (B) of Example 2 and the basic antiferroelectric liquid crystal composition (a) as a control.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Osamu Nonaka 3-5-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Inside Showa Shell Sekiyu KK (72) Inventor Hiroyuki Mogami 3-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Showa Shell Sekiyu KK (56) References JP-A-7-316101 (JP, A) JP-A-5-65486 (JP, A) JP-A-6-184536 (JP, A) JP-A-6-145111 (JP, A) JP-A-4-268389 (JP, A) JP-A-3-109369 (JP, A) JP-A-9-40953 (JP, A) JP-A-9-165356 (JP, A) JP-A-9-53073 (JP, A) JP-A-8-295666 (JP, A) JP-A-8-291138 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 19 / 02 C09K 19/28 CA (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] [Claim 1] The following general formula (1) (Wherein m is an integer of 4 to 16, n is an integer of 4 to 12, X ₁ , X ₂ and X ₃ are elements independently selected from the group consisting of H and F, and Y is —COO -Or -O-,
Cf is a CH ₃ group or a CF ₃ group, and * indicates an optically active center. An antiferroelectric liquid crystal composition containing at least one compound represented by the formula (1), wherein the tilt angle at 30 ° C. is 30 ° or more and 50 ° or less, and the response speed τ is 5 μsec or more and 30 μsec or less. An antiferroelectric liquid crystal composition characterized by the following.