JPH08113784A - Improver for liquid crystal characteristic - Google Patents

Abstract

PURPOSE: To obtain an improver for liquid crystal characteristics, comprising a compound having a specific structure, capable of remarkably improving the memory margin of an antiferroelectric liquid crystal composition and sufficiently usable for a display. CONSTITUTION: This improver comprises a compound of formula I [(m) is an integer of 4-14; (n) is an integer of 0-13; X is a single bond, O, COO or OCO; (r) is 1 or 2; (p) is an integer of 2-12; Z is CH3 or CF3 ]. For example, a compound of formula II is cited as the compound of formula I. Furthermore, the improver is preferably added in an amount of 0.1-40wt.%, preferably 1-20wt.% based on a liquid crystal composition, especially an antiferroelectric liquid crystal composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal property improving agent. In particular, the present invention relates to a liquid crystal property improving agent suitable for improving the properties of antiferroelectric liquid crystals.

[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.

[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 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.

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 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)]. However, their scheme includes
There are many technical issues toward practical use, and there is almost no ferroelectric liquid crystal that satisfies the practical characteristics required for displays at room temperature. The method was not well established.

Since this report, various attempts have been made from both sides of liquid crystal materials / devices, prototype display devices utilizing switching between twisted two states have been manufactured, and high-speed electro-optical devices using the same have been 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.

[0008] From such a viewpoint, 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. 1D), and when an electric field is applied, the molecular orientation becomes a second stable state [FIG. 3 (b)] different from the first stable state in one electric field direction. The transmittance of the optical device shows the second stable state (of FIG. 1D), and the third molecular alignment stable state different from the first and second stable states with respect to the other electric field direction [FIG.
(C)] means that the transmittance of the liquid crystal electro-optical device shows the third stable state (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 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 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.

Further, when a voltage sufficiently higher than the threshold value of (+) or (-) is applied, 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. 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 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, 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.

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., 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 are mainly 1) operating temperature range, 2) response speed, 3) hysteresis characteristic, and 4) display contrast. 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 antiferroelectric display, compared with the display performance of the TFT display,
The display quality is not sufficient in terms of high definition and high quality, and there is a strong demand for a method for improving the above-mentioned important drive characteristics. It has been found that it is extremely difficult to satisfy these performances with a single compound antiferroelectric liquid crystal compound.

[0020]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a novel liquid crystal property improving agent for preparing a liquid crystal composition having a sufficient memory margin which can be sufficiently used for a display, particularly an antiferroelectric liquid crystal composition. There is a point to do.

[0021]

The present invention has the following general formula [I]:

Embedded image (In the formula, m is an integer of 1 to 14, n is an integer of 0 to 13, X is
Is a single bond, a group selected from the group consisting of O, COO and OCO, r is 1 or 2, p is an integer of 2 to 12, and Z is C.
H ₃ or CF ₃ ) is contained in the liquid crystal property improving agent.

The liquid crystal characteristic improving agent of the present invention is a liquid crystal composition,
Especially for antiferroelectric liquid crystal compositions, it is usually 0.1 to 4
The memory margin can be improved by adding 0 wt%, preferably 1 to 20 wt%.

The memory margin in the present invention was measured as follows. A liquid crystal cell having a cell thickness of 2.0 μm and having a rubbing-treated polyimide alignment film on a transparent electrode substrate was filled with the liquid crystal compound or the liquid crystal composition obtained in Example in an isotropic phase to prepare a liquid crystal thin film cell. The prepared liquid crystal cell was charged 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, the relative transmittance of light when a triangular wave voltage of ± 40 V and 1 Hz is applied to the cell is plotted against the applied voltage as shown in FIG. 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, increase (decrease) the applied positive voltage (minus voltage).
In the process, the voltage at which the relative transmittance becomes 10% is V ₁ , and the voltage at which the relative transmittance becomes 90% is V _{2 at} the process of increasing (decreasing) the applied positive voltage (minus voltage). The voltage at which the relative transmittance becomes 90% in the process of increasing (decreasing) the applied positive voltage (negative voltage) is defined as V ₃ . Also,
The width of hysteresis is defined as the memory margin M ₁ and the following equation.

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

Examples of the liquid crystal characteristic improving agent of the present invention are shown below.

[Table 1]

[Table 2]

[0025]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Comparative Example 1 An antiferroelectric liquid crystal composition was prepared by mixing the liquid crystal compounds shown below in the respective proportions shown below.

Embedded image Table 3 shows the data of the antiferroelectric liquid crystal composition thus obtained.

Example 1

[Chemical 4] Table 3 shows data of the antiferroelectric liquid crystal composition obtained by blending the both.

Example 2

Embedded image Table 3 shows data of the antiferroelectric liquid crystal composition obtained by blending the both.

Physical properties were measured by the above-mentioned measuring method 3.
Table 3 shows the memory margins at 0 ° C and 40 ° C.

[Table 3]

[0030]

[Effect] By using the liquid crystal property improving agent of the present invention, the memory margin of the liquid crystal composition, particularly the antiferroelectric liquid crystal composition, can be significantly improved.

[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.

Claims (1)

[Claims] 1. The following general formula [I]: (In the formula, m is an integer of 1 to 14, n is an integer of 0 to 13, X is
Is a single bond, a group selected from the group consisting of O, COO and OCO, r is 1 or 2, p is an integer of 2 to 12, and Z is C.
H ₃ or CF ₃ ). A liquid crystal property improving agent.