JPH08333576A - Antiferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE: To obtain an antiferroelectric liquid crystal composition incorporated with cyclohexyl-terminated liquid crystal compound(s), improved in memory margin at lower temperatures including room temperature, and thus having excellent display performance useful for display devices. CONSTITUTION: This antiferroelectric liquid crystal composition comprises (A) pref. 10-90 (more pref. 20-80)wt.% of at least one kind of compound of formula I ((m) and (n) are each an integer of 4-14; X<1> and X<2> are each H or F; Y<1> is a single bond, O, OCO or COO; * denotes an optically active center), (B) pref. 5-60 (more pref. 10-50)wt.% of at least one kind of compound of formula II (X<3> and X<4> are each H or F; Y<2> is the same as Y<1> ), and (C) pref. l-30 (more pref. 3-20)wt.% of at least one kind of compound of formula III (X<5> is H or F; Y<3> is the same as Y<1> ; Z is a single bond, COO or OCO; Cf is CH3 or CF3 ).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel antiferroelectric liquid crystal composition.

[0002]

2. Description of the Related Art Liquid crystal display devices have 1) low voltage operability and 2)
It has excellent features such as low power consumption, 3) thin display, 4) light receiving type, etc., so far, TN method, STN method,
A guest-host method has been developed and put to practical use.

However, a nematic liquid crystal that is widely used at present has a response speed of several msec to several tens m.
However, it has a drawback of being slow and has various restrictions in application.

In order to solve these problems, an active matrix method using an STN method or a thin layer transistor method has been developed.
Although display qualities such as display contrast and viewing angle have been improved, problems such as high precision required for control of the cell gap and tilt angle and a rather slow response have become problems. The thin film transistor method has a complicated structure, has a low manufacturing yield, and is consequently expensive.

Therefore, there is a demand for the development of a new liquid crystal display system having excellent responsiveness, and the optical response time is μse.
Attempts have been made to develop a ferroelectric liquid crystal that enables an extremely high speed device that is as short as c order.

Ferroelectric liquid crystals were first described in 1975 by Meyor.
DOBAMBC (p-decyloxybenzylidene-p-amino-2-methylbutyl cinnamate) was synthesized for the first time by (Le Journal de Phy).
sique, vol. 36, 1975, L-69). In addition, 1
DOB by Clark and Lagwall 980
Ferroelectric liquid crystal has become a focus of attention since the characteristics of display devices such as submicrosecond fast response of AMBC and memory characteristics have been reported [N. A. Cla
rk, et al. , Appl. Phys. Lett. Three
6.899 (1980)]. But in their scheme,
There are many technical challenges toward practical use, and there are few ferroelectric liquid crystals that satisfy the practical characteristics required for displays, especially at room temperature, and they are effective and practical for controlling the alignment of liquid crystal molecules that are essential for display displays. The method was not established either.

Since this report, various attempts have been made from both sides of the liquid crystal material / device, and a display device utilizing switching between twisted two states has been prototyped. A high-speed electro-optical device using the display device is also disclosed in, for example, Japanese Patent Laid-Open No. 56-56. No. 107216, etc., but high contrast and proper threshold characteristics have not been obtained.

From this point of view, other switching methods have been searched and a transient scattering method has been proposed.
Then, in 1988, the inventors of the present invention reported a three-state switching method for a liquid crystal having three stable states [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" means a liquid crystal in which an antiferroelectric liquid crystal is sandwiched between a first electrode substrate and a second electrode substrate which is arranged 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 indicated by, the molecular orientation of the antiferroelectric liquid crystal becomes the first stable state [Fig. 3 (a)] when there is no electric field, and the transmittance of the liquid crystal electro-optical device is the first. 2 (1 in FIG. 1D) and the molecular orientation becomes a second stable state [FIG. 3 (b)] different from the first stable state in one electric field direction when an electric field is applied. The transmittance of the electro-optical device shows the second stable state (2 in FIG. 1D), and the third molecular orientation stable state different from the first and second stable states with respect to the other electric field direction [FIG.
(C)], which means that the transmittance of the liquid crystal electro-optical device exhibits the third stable state (3 in FIG. 1D). Regarding the liquid crystal electro-optical device utilizing the tri-stable state, the present applicant has filed as Japanese Patent Application No. Sho 63-70212 and is disclosed as Japanese Patent Application Laid-Open No. 2-153322.

The characteristics of the antiferroelectric liquid crystal exhibiting the 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 ferroelectric liquid crystal molecules are uniformly oriented in one direction as shown in FIGS. 2 (a) and 2 (b) in the S * C phase. State, and depending on the direction of the applied electric field,
It is stabilized in one of the states, and that state is maintained even when the electric field is cut off.

However, in reality, the alignment state of the ferroelectric liquid crystal molecules shows a twisted two-state in which the director of the liquid crystal molecules is twisted or a chevron structure in which the layers are bent in a V shape. With the Sieblon layer structure, the switching angle becomes small, which causes low contrast, which is a major obstacle to practical use. On the other hand, in the SmC * A phase in which the "anti" ferroelectric liquid crystal shows a tristable state, in the liquid crystal electro-optical device, when there is no electric field, the molecules in the adjacent layers move in opposite directions as shown in FIG. The tilts are arranged antiparallel, and the dipoles of the liquid crystal molecules cancel each other out.
Therefore, the spontaneous polarization is canceled in the entire liquid crystal layer. The liquid crystal phase showing this molecular arrangement corresponds to that in FIG. 1D.

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

In the SmC * A phase of the "anti" ferroelectric liquid crystal, the "anti" ferroelectric phase when there is no electric field and the two ferroelectric phases depending on the polarity of the applied electric field are stable, and the "anti" ferroelectric phase 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 alignment of the liquid crystal changes depending on the polarity and magnitude of the applied electric field, and the optical axis of the liquid crystal can be changed into 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, the double hysteresis as shown in FIG. 4 is shown. As shown in FIG. 4A, a bias voltage is applied to this double hysteresis to superimpose a pulse voltage, and a memory effect can be realized.

In the "anti" ferroelectric liquid crystal, since image display can be performed by alternately using both positive and negative hysteresis, image afterimage phenomenon due to accumulation of internal electric field due to spontaneous polarization occurs. Can be prevented. Further, by applying an electric field, the layer of the ferroelectric phase is stretched to form a Bookshelf structure. On the other hand, the first stable state “anti” ferroelectric phase has a similar Bookshelf structure.
Since the layer structure switching by the application of the electric field gives a 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 it is a very useful liquid crystal compound that can realize 1) high-speed response, 2) high contrast and wide viewing angle, and 3) good alignment characteristics and memory effect.

Regarding the liquid crystal phase showing the tristable state of "anti" ferroelectric liquid crystal, 1) A. D. L. Chandani
et al., Japan J. 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), the S * CA phase (Anti) associated with the "anti" ferroelectric property.
ferroelectric Smatic C *
The present inventors defined the liquid crystal phase as S * (3) phase (referred to as SmC * A phase in this specification) because the liquid crystal phase switches between tristable states.

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

The material characteristics required for the antiferroelectric liquid crystal used in the above-mentioned display device (optical device) are mainly 1) operating temperature range, 2) response speed, 3) hysteresis characteristic, 4) display contrast, etc. Can be mentioned. Regarding the hysteresis characteristic of 3), the memory margin is defined as a standard showing the width of the hysteresis. The larger the memory margin, the more suitable for the display.

In the currently developed anti-ferroelectric liquid crystal display, the display quality is not sufficient in terms of high definition and high quality as compared with the display performance of the TFT liquid crystal display, and the above-mentioned important driving characteristics There is a strong demand for improvement methods. It has been found that a single compound antiferroelectric liquid crystal compound is very difficult to satisfy these performances.

[0020]

The object of the present invention is to:
Another object is to provide a novel antiferroelectric liquid crystal composition having excellent display performance that can be sufficiently used for a display.

[0021]

[Means for Solving the Problems] As a result of diligent investigation of the above problems, a liquid crystal compound having a cyclohexyl group at the terminal was added to an antiferroelectric liquid crystal composition to obtain a memory in a low temperature range including room temperature The inventors have found that the margin is improved and have completed the present invention.

That is, the present invention provides (A) the following general formula [1]

[Chemical 4] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y ¹ is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
(B) The following general formula [2]

Embedded image (In the formula, m is an integer of ^{4 to} 14, n is an integer of ^{4 to} 14, X ³ and X ⁴ are groups independently selected from the group consisting of H and F, and Y ² is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
And (C) the following general formula [3]

[Chemical 6] (In the formula, m is an integer of 4 to 14, X ⁵ is H or F,
Y ³ is a group selected from the group consisting of a single bond, O, OCO and COO, Z is a single bond, COO or OCO, Cf is CH ₃ or CF ₃ , and * represents an optically active center. . And an antiferroelectric liquid crystal composition containing at least one compound represented by the formula (1).

Examples of the compound represented by the above general formula [1] are shown below.

[Chemical 7]

Embedded image

[Chemical 9]

Examples of the compound represented by the above general formula [2] are shown below.

[Chemical 10]

[Chemical 11]

[Chemical 12]

Examples of the compound represented by the above general formula [3] are shown below.

[Chemical 13]

Embedded image

[Chemical 15]

Embedded image

[Chemical 17]

Embedded image

[Chemical 19] In the formula, R ¹ represents C _m H _{2m + 1 and} R ² represents C _n H _{2n + 1} .

The reason why the three components are required is that the memory margin at room temperature or less is remarkably reduced only with both the first component (CF ₃ compound) and the second component (CH ₃ compound). If only the first component (CF ₃ compound) is used (that is, the second component is not contained), the alignment contrast is lowered. A combination of only the first component and the third component, or a combination of only the second component and the third component can increase the memory margin, but is unbalanced and not preferable.

[0027]

[Table 1]

The method of measuring electro-optical characteristics in the present invention is as follows. A liquid crystal thin film cell was prepared by filling a liquid crystal cell having a rubbing-treated polyimide alignment film on a transparent electrode substrate and having a cell thickness of 2.0 μm with the liquid crystal composition obtained in Example in an isotropic phase. The manufactured liquid crystal cell was heated at 0.1 to 1.0 ° C./min. The mixture was gradually cooled with a temperature gradient of 2 to deposit. This liquid crystal cell was placed in a polarizing microscope 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 is in the antiferroelectric phase,
FIG. 5 is a graph of the relative transmittance of light when a triangular wave voltage of 40 V and 1 Hz is applied, with respect to the applied voltage. As shown in the figure, it is characterized by having two hysteresis which are substantially symmetrical when a positive voltage is applied and when a negative voltage is applied. As shown in the figure, in the process of increasing (decreasing) the applied positive voltage (negative voltage), the relative transmittance is 10%.
% Is V ₁ , the positive voltage (negative voltage) to be applied is increased (decreased), the voltage at which the relative transmittance is 90% is V ₂ , and the applied positive voltage (minus voltage) The voltage at which the relative transmittance becomes 90% in the process of increasing (decreasing) the voltage) is defined as V ₃ . Further, the width of hysteresis is defined as a memory margin M ₁ and the following equation.

[Equation 1] The larger the memory margin value, the better the display.

[0030]

EXAMPLES A composition containing a liquid crystal compound corresponding to each of the following general formulas [1] and [2] was used as a basic liquid crystal composition, and each liquid crystal compound corresponding to the general formula [3] was added thereto. Then, the antiferroelectric liquid crystal composition of Example 1 was prepared.

Embedded image

Example 1 Antiferroelectric liquid crystal compositions A, B, C, D and E were prepared by blending the following compounds in the basic antiferroelectric liquid crystal composition in the ratios shown below. .

[Chemical 21] FIG. 6 shows the memory margin measured by the above-mentioned measuring method.

The embodiments of the present invention will be described below. 1. (A) The following general formula [1]

[Chemical formula 22] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y ¹ is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
(B) The following general formula [2]

[Chemical formula 23] (In the formula, m is an integer of ^{4 to} 14, n is an integer of ^{4 to} 14, X ³ and X ⁴ are groups independently selected from the group consisting of H and F, and Y ² is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
And (C) the following general formula [3]

[Chemical formula 24] (In the formula, m is an integer of 4 to 14, X ⁵ is H or F,
Y ³ is a group selected from the group consisting of a single bond, O, OCO and COO, Z is a single bond, COO or OCO, Cf is CH ₃ or CF ₃ , and * represents an optically active center. . ) An antiferroelectric liquid crystal composition containing at least one compound represented by the formula (1). 2. The antiferroelectric liquid crystal composition according to item 1, wherein Z is a single bond in the compound of the general formula [3]. 3. In the compound of the general formula [3], Z is a single bond and C
The antiferroelectric liquid crystal composition according to item 1, wherein f is CF ₃ . 4. The antiferroelectric liquid crystal composition according to item 1, wherein Z is COO in the compound of the general formula [3]. 5. In the compound of the general formula [3], Z is COO and C
The antiferroelectric liquid crystal composition according to item 1, wherein f is CF ₃ . 6. The antiferroelectric liquid crystal composition according to the above item 1, 2, 3, 4 or 5, wherein the compound of the general formula [3] is contained in an amount of 1 to 30% by weight based on the total composition.

[0033]

[Effect] According to the present invention, the memory margin is significantly improved in a region below room temperature (25 ° C).

[Brief description of drawings]

FIG. 1A is an applied triangular wave, B is a commercially available nematic liquid crystal, C is a two-state liquid crystal, and D is a three-stable state liquid crystal.
The respective optical response characteristics are shown.

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

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

FIG. 4 is an applied voltage-light transmittance characteristic diagram showing that the “anti” ferroelectric liquid crystal molecule draws double hysteresis with respect to the applied voltage and the light transmittance changes.

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

FIG. 6 is a graph showing the relationship between temperature and memory margin of the basic liquid crystal composition and the antiferroelectric liquid crystal compositions of Compositions A to E of the present invention.

Claims (1)

[Claims] (A) The following general formula [1]: (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y ¹ is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
(B) The following general formula [2] (In the formula, m is an integer of ^{4 to} 14, n is an integer of ^{4 to} 14, X ³ and X ⁴ are groups independently selected from the group consisting of H and F, and Y ² is a single group. A group selected from the group consisting of a bond, O, OCO, and COO, and * represents an optically active center.),
And (C) the following general formula [3] (In the formula, m is an integer of 4 to 14, X ⁵ is H or F,
Y ³ is a group selected from the group consisting of a single bond, O, OCO and COO, Z is a single bond, COO or OCO, Cf is CH ₃ or CF ₃ , and * represents an optically active center. . ) An antiferroelectric liquid crystal composition containing at least one compound represented by the formula (1).