JP2932531B2 - Liquid crystal device using antiferroelectric phase - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal element used for a liquid crystal display device, a liquid crystal optical shutter, and the like, and relates to a liquid crystal element using a novel antiferroelectric phase with improved display characteristics. Things.

(Prior Art) In recent years, an electro-optical element using a ferroelectric liquid crystal has attracted attention. The characteristics of the electro-optical element using ferroelectric liquid crystal are as follows.
The response is much faster than that of an electro-optical device using a conventional nematic liquid crystal, and the device has bistability. As an electro-optical element capable of exhibiting such characteristics of a ferroelectric liquid crystal, a surface-stabilized ferroelectric liquid crystal (hereinafter, SSFLC)
There is an element. This device is said to be the device closest to practical use among devices (US Patent No. 4, 367,924) developed by Clerk et al.

The switching principle of the director in the SSFLC element is
When the ferroelectric liquid crystal is held between cells (cell gap of about 0.5 to 2 μm) that are thin enough to lose the helical structure, a bistable state of liquid crystal molecules appears. That is, 2
In one stable state, the liquid crystal molecules are in a uniform state in which the directions of the directors, which are unit vectors in the major axis direction of the liquid crystal molecules, are different.

Since the ferroelectric liquid crystal has spontaneous polarization and has bistability as described above, high-speed response and memory properties can be realized. Therefore, application to a high-density large-screen display or a high-speed optical shutter has been considered. SSFLC elements utilizing this bistable state have made great progress with the recent development of liquid crystal materials. However, this SSFL is used for displaying high-density large-screen displays.
In order to apply the C element, it is necessary to improve display characteristics such as having a higher contrast, a high-speed response, a more clear voltage threshold, and being able to realize bistability even in a thick cell. is there.

Recent studies have revealed that it is necessary to control the structure of the liquid crystal layer in order to improve contrast and responsiveness. Although the structure of the ferroelectric liquid crystal layer varies depending on the method of the alignment treatment, it is general that the ferroelectric liquid crystal layer has a chevron structure in which a pair of parallel glass substrates has a “<” shape. In many cases, zigzag defects occur due to the misalignment of the "<" shape of the chevron structure, and light leaks through these defects to greatly reduce contrast. It is also clear that the response speed is higher when the liquid crystal layer has a bookshelf structure than when it has a chevron structure. For this reason, a bookshelf structure that is substantially perpendicular to a pair of glass substrates is desired as a structure of a ferroelectric liquid crystal layer that does not generate zigzag defects.

In a conventional ferroelectric liquid crystal, it is generally known that an electric field does not change the structure of a liquid crystal layer. In some cases, the structure of the liquid crystal layer was changed by applying a voltage with a specific waveform, voltage, and frequency to the ferroelectric liquid crystal.However, the inclination of the liquid crystal layer in the chevron structure slightly changed with respect to the normal to the substrate. Or, the inclination does not change, but the direction of the liquid crystal layer is uniform. As a method for obtaining a device having a bookshelf layer structure, oblique vapor deposition of SiO ₂ [Japanese Journal of Applied Physics (Japanese Journal)
al. Applied Physics, Vol. 27, PP L725, 1988, and Japanese Journal of Applied Physics, Vol. 27, PP L1993, 1998], but are difficult to implement industrially.

Many ferroelectric liquid crystal compounds have been synthesized since Clark et al. Announced the SSFLC element, and in recent years, a liquid crystal compound having an antiferroelectric phase has attracted attention (Japanese Patent Application Laid-Open No.
213390, Japanese Journal of Applied Physics Vol. 27, PP L729, 1988). The characteristics of the antiferroelectric phase (phase) include a threshold voltage characteristic, an apparent tilt (angle between a normal line of a square liquid crystal layer (layer) and an average major axis direction of liquid crystal molecules). ), Three stable states (two uniforms and a third state), etc., have been clarified, but no knowledge of the structure of the liquid crystal layer has been obtained. The present inventors measured the relationship between the tilt angle and the applied voltage, obtained a threshold DC voltage for switching of liquid crystal molecules, and determined the structure of the liquid crystal layer at an applied DC voltage slightly higher than the threshold voltage by X-ray diffraction. As a result of analysis using the apparatus, it was confirmed that the liquid crystal layer had a chevron structure. Further, texture observation confirmed that many zigzag defects existed in the liquid crystal layer.

The advantages of the liquid crystal device using the antiferroelectric phase are that it has a very clear threshold value for voltage and that it has memory properties even in a thick cell. From these two points, it can be said that the liquid crystal element using the antiferroelectric phase is greatly improved as compared with the element using the conventional ferroelectric phase. However, the structure of the liquid crystal layer in the antiferroelectric phase is a chevron structure as in the case of the conventional ferroelectric liquid crystal, and it is desired that the layer structure be a bookshelf structure in order to improve contrast and response speed. It is rare.

(Problems to be Solved by the Invention) Accordingly, an object of the present invention is to provide a liquid crystal device using an antiferroelectric phase having high contrast and high-speed response.

It is a further object of the present invention to provide a liquid crystal element using an antiferroelectric phase in which a liquid crystal layer has no or almost no zigzag defects.

Another object of the present invention is to provide a high-density large-screen display,
An object of the present invention is to provide a liquid crystal element using an antiferroelectric phase suitable for use in a high-speed optical shutter or the like.

An object of the present invention (means for solving the problem) includes a liquid crystal or a liquid crystal composition having an anti-ferroelectric phase (SmC _A ^*), an electrode, a pair of sandwiching the liquid crystal or liquid crystal composition In the antiferroelectric phase (SmC _A ^* ), a short rectangular wave having a DC voltage of at least twice the threshold voltage or a peak value of at least twice the threshold voltage and a frequency of 1 kHz or less is applied to the electrode. This is achieved by a liquid crystal element using an antiferroelectric phase characterized by temporarily changing the layer structure of the liquid crystal or liquid crystal composition from a chevron structure to a bookshelf structure by applying a triangular wave voltage.

Liquid crystal or liquid crystal compositions used in the present invention is required to have an antiferroelectric phase ^(* S _m C ^_A). For example, during the cooling process, an isotropic phase → a chiral nematic phase (N ^* )
→ Smectic A phase (S _A ) → Chiral smectic C phase (S _C ^* ) → Anti-ferroelectric phase (S _m C _A ^* ), but isotropic phase → Smectic A phase (S _A) ) → chiral smectic C phase (S _C ^* ) → antiferroelectric phase (S _m C _A ^* ), but is not limited thereto.

The liquid crystal or the liquid crystal composition having the above phase transition is held between a pair of substrates arranged in parallel with electrodes, and the liquid crystal or the liquid crystal composition is heated to be in an isotropic state, and then gradually cooled. the state of the liquid crystal or liquid crystal composition antiferroelectric phase ^(* S _m C ^_a) by.

In this state, the liquid crystal layer has a chevron structure in which a pair of substrates has a "-" shape. By applying a voltage higher than a certain voltage to the electrodes, the chevron structure changes to a bookshelf structure in which the liquid crystal layer is substantially perpendicular to the pair of substrates. When the electric field is turned off, the bookshelf structure changes to a chevron structure with a small inclination angle に 対 す る with respect to the substrate or a layer structure in which a chevron or bookshelf cannot be determined. FIG. 4 is an X-ray diffraction pattern showing the above change in the layer structure, which will be described in detail later. or,
The appearance of the zigzag defects, which are defects in the layer structure, was examined by texture observation.As a result, many zigzag defects were observed before the electric field was applied.However, the zigzag defects disappeared when the layer became a bookshelf structure due to the application of the electric field. did.
When the applied electric field is turned off, the bookshelf structure changes to a chevron structure with a small tilt angle に 対 す る with respect to the substrate or a layer structure in which chevron or bookshelf cannot be determined.
Surprisingly, no zigzag defects were observed in this layer structure.

In the present invention, to temporarily change the layer structure of the liquid crystal or the liquid crystal composition from the chevron structure to the bookshelf structure means that an electric field is applied to a liquid crystal element in which the liquid crystal layer has a chevron structure and an electric field has never been applied. This means changing to a bookshelf structure. Although the waveform and frequency of such an applied electric field are not particularly limited, a direct current, a short rectangular waveform, a triangular waveform, or the like can be used as the waveform.
The frequency is preferably 0 to 1 KHz. The applied voltage depends on the liquid crystal or liquid crystal composition to be used.However, since the liquid crystal layer temporarily changes from the chevron structure to the bookshelf structure, it is necessary that the voltage be sufficiently higher than the threshold value for switching of liquid crystal molecules. It costs. In the case of the liquid crystal having an antiferroelectric phase used in Example 1 described later in detail, the liquid crystal layer changes from a chevron structure to a bookshelf structure at an applied voltage of at least twice the threshold value for switching of liquid crystal molecules. Completely changed.

In the prior art described above, there is no example of obtaining a liquid crystal element in which the liquid crystal layer has a bookshelf structure by applying an electric field as in the present invention, and by changing the liquid crystal layer from a chevron structure to a bookshelf structure, There is no example of removing zigzag defects in the layer. According to the present invention, a liquid crystal layer having a bookshelf structure and having a zigzag defect removed can be easily obtained for the first time.

As described above, when an electric field is applied to the liquid crystal layer to temporarily change from the chevron structure to the bookshelf structure and then cut off the electric field, the liquid crystal layer is changed from the bookshelf structure to the chevron structure having a small inclination angle に 対 す る with respect to the substrate, the chevron structure or the bookshelf. The structure changes to a liquid crystal layer structure that makes it difficult to determine the structure. The liquid crystal element can be actually used from this state. In actual use, the voltage applied to the electrode of the liquid crystal element only needs to be larger than the threshold value for switching of liquid crystal molecules, and was used to temporarily change the above liquid crystal layer from the chevron structure to the bookshelf structure. It need not be as high as the applied voltage.

The layer structure of the antiferroelectric phase ^(* S _m C ^_A), as in the conventional ferroelectric liquid crystal can be classified into the chevron structure and a bookshelf structure. The chevron structure refers to a state in which the liquid crystal layer is bent in a “<” shape with respect to the substrate as shown in FIG. 5A. The bookshelf structure indicates a state where the liquid crystal layer is perpendicular to the substrate as shown in FIG. 5B or a state where the liquid crystal layer is inclined with respect to the substrate as shown in FIG. 5C. 5A, 5B and 5C show a cross section of the liquid crystal element, 10 is a substrate, and 12 shows one of the liquid crystal layers. In FIG. 5A, the liquid crystal layer is inclined by ψ with respect to the normal line of the substrate 10. It has been found that the following relationship exists between the X-ray diffraction pattern showing the liquid crystal layer structure obtained using the X-ray diffraction measurement system shown in FIG. 1 and the liquid crystal layer structure. That is, the X-ray diffraction pattern of the liquid crystal layer having a chevron structure is, as shown in FIGS. 2A and 2B,
Usually has two peaks. On the other hand, the X-ray diffraction pattern of the liquid crystal layer having the bookshelf structure usually has a single sharp peak as shown in FIG. 2C. In this specification, the chevron structure and the bookshelf structure are defined as follows.

(1) The X-ray diffraction pattern of the liquid crystal layer
As shown in the figure, when the liquid crystal layer has two or more peaks, the liquid crystal layer has a chevron structure.

(2) When the X-ray diffraction pattern of the liquid crystal layer has only one sharp peak as shown in FIG. 2C, the liquid crystal layer has a bookshelf structure.

(3) When the X-ray diffraction pattern of the liquid crystal layer has two or more peaks that cannot be clearly separated as shown in FIG. 2D, the liquid crystal layer has a chevron structure or a bookshelf structure. This is determined by the half width of the peak of the X-ray diffraction pattern. That is, a sufficiently high voltage (preferably at least twice the threshold) is applied to the liquid crystal element until an X-ray diffraction pattern having one sharp peak as shown in FIG. 2C is obtained. In this applied state, the liquid crystal layer has a bookshelf structure. The half width (P _B ) of one sharp peak of the X-ray diffraction pattern obtained in this way is measured. Next, to measure the half width of the X-ray diffraction pattern of the liquid crystal to be determined whether the bookshelf structure or a chevron structure layer (P _S). If P _S is less than twice the P _B, and the liquid crystal layer is a bookshelf structure.
When P _S is more than twice P _B , the liquid crystal layer is assumed to have a chevron structure.

In the liquid crystal device using the antiferroelectric phase of the present invention, switching between the two uniforms can be performed at high speed while maintaining the liquid crystal layer having the bookshelf structure. It is considered that the switching between the two uniforms in the liquid crystal device using the antiferroelectric phase of the present invention proceeds by the same mechanism as the switching between the two uniforms in the chiral smectic C phase. The conventional chiral smectic C phase liquid crystal layer has a chevron structure, and its switching mechanism is known in detail. Switching between two uniforms is faster when the liquid crystal layer has a bookshelf structure than when the liquid crystal layer has a chevron structure, see Japanese Journal of Applied Physics Vol 26.p
p, L21-24, 1989. However, there is no practical method for easily manufacturing a conventional liquid crystal element in which a liquid crystal layer in a chiral smectic C phase has a bookshelf structure. However, in the present invention, the liquid crystal layer can be easily changed from the chevron structure to the bookshelf structure by applying an electric field, so that a liquid crystal element capable of performing switching between two uniforms at high speed can be easily manufactured. can do.

As described above, according to the present invention, a liquid crystal element using an antiferroelectric phase having high contrast and high-speed response can be obtained by temporarily changing the structure of the liquid crystal layer from a chevron to a bookshelf structure by applying an electric field. Accordingly, a liquid crystal element using an antiferroelectric phase having excellent display characteristics can be realized.

The liquid crystal having special properties used in the present invention may be a single substance or a mixed composition.

A compound effective as a liquid crystal having an antiferroelectric phase used in the present invention is, for example, a known 4- (1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4 having the following chemical structural formula. Carboxylate (compound A).

C ₈ H ₁₇ O-Ph-Ph-COO-Ph-COO-C ^* H (CH ₃ ) C ₆ H ₁₃ Ph; benzene ring C ^* ; asymmetric carbon Then, it can be used as a liquid crystal composition having an antiferroelectric phase. Examples of the compound to be mixed include a compound group (compound B) represented by the following general formula.

RO-Ph-Ph-COO-R ^* RCOO-Ph-Ph-COO-R ^* RO-Ph-COO-Ph-COOR ^* RO-Ph-OCO-Ph-R ^* RO-Ph-Ph-COO-Ph- _{^{OR * RO-P ym -Ph-}} OR * R; alkyl group Ph; benzene ring R ^*; substituents P _ym containing an asymmetric carbon; specific examples of the pyrimidine ring the general compounds of the formula (B) is For example, the following compounds may be mentioned, but the present invention is not limited thereto.

_{C 7 H 15 -Ph-Ph-} COO-CH 2 C * H (CH 3) C 2 H 5 C 8 H 17 -COO-Ph-Ph-COO-CH 2 C * H (CH 2) C 3 H 6 _{C 8 H 17 O-Ph-} COO-Ph-COO-CH 2 C * H (CH 3) C 2 H 5 C 9 H 19 O-Ph-OCO-Ph-CH 2 C * H (CH 3) C 2 _{H 5 C 8 H 17 O-} Ph-Ph-COO-Ph-O-CH 2 C * H (CH 3) C 2 H 5 C 11 H 29 O-P ym -Ph-O-CH 2 C * H ( OCH ₃ ) C ₂ H ₅ The liquid crystal composition having an antiferroelectric phase which is a mixture of the compound A and the compound B used in the present invention varies depending on the type of the compound B, but one or more of the compound B is added. Can be made. The mixing ratio of the compound A and the compound B is such that the compound A is 2 to 80% by weight, preferably 3% by weight in the liquid crystal composition.
It is preferable to mix them so as to be about 70% by weight.

Examples of the ferroelectric liquid crystal or the ferroelectric liquid crystal composition used in the present invention are as described above. However, these compounds or mixtures are used when an antiferroelectric phase is caused to undergo a phase transition from an isotropic phase in a temperature decreasing process. (S _m C _a ^*) must be present.

The anti-ferroelectric phase ^(* S _m C ^_A) is a phase showing the following properties.

(1) The extinction position of the liquid crystal element using the antiferroelectric phase (SmC _A ^* ) which is aligned in parallel is the normal direction of the liquid crystal layer and the liquid crystal layer when the liquid crystal element is viewed from above when no electric field is applied. (Hereinafter, the term “normal direction of the liquid crystal layer and the direction parallel to the liquid crystal layer” refers to the case where the liquid crystal element is viewed from above).

(2) Apparent tilt angle of liquid crystal molecules in a liquid crystal device that uses an antiferroelectric phase (SmC _A ^* ) that is aligned in parallel, ψ (the angle between the normal direction of the liquid crystal layer and the average long axis direction of the liquid crystal molecules) ) Has a hysteresis with respect to the DC applied voltage as shown in FIG. Further, as shown in FIG. 3, such a liquid crystal element has a clear threshold value for a DC applied voltage.

(3) When an electric field of a threshold value or more is applied to a liquid crystal element that is parallel-aligned and uses an antiferroelectric phase (SmC _A ^* ), the liquid crystal molecules are in a uniform state similarly to the chiral smectic C phase.

Observation of the liquid crystal device while holding the liquid crystal device that uses the antiferroelectric phase (SmC _A ^* ) aligned in parallel between the orthogonal polarizers shows that the extinction position is the normal direction of the liquid crystal layer and the liquid crystal when no electric field is applied. The direction parallel to the layer. Therefore, when no electric field is applied, the major axes of the liquid crystal molecules are apparently arranged parallel to the normal direction of the liquid crystal layer. When a DC voltage equal to or higher than the threshold voltage is applied to the liquid crystal element, the liquid crystal molecules are inclined at a certain angle from the normal direction of the liquid crystal layer, and a uniform state is observed in a normal chiral smectic C phase. That is, the anti-ferroelectric phase ^(* S _m C ^_A) is (are oriented normal to the direction of the liquid crystal layer apparent crystal molecules) and two uniform states conventionally known, one new state
Having. This new state is called a third state. One feature of the antiferroelectric phase ^(* S _m C ^_A) is to have a as the three stable states (3 referred to as a stable state). Currently, the three anti-ferroelectric phase having a stable state (S _m C _A ^*) is often unsure detailed structure of but models like FIG. 6 is considered (Japanese Journal of Applied Physics, Vol 28, pp L1265, 19
89). FIG. 6 is a view of the liquid crystal element as viewed from above. The center of FIG. 6 shows the third state, and the major axes of the liquid crystal molecules are in opposite directions in the adjacent liquid crystal layer.
The dipole moment is canceled between adjacent liquid crystal layers. The right end and the left end in FIG. 6 show a uniform state.

Still another characteristic of the liquid crystal device using an antiferroelectric phase (SmC _A ^* ) exhibiting a tristable state is that the apparent tilt angle (ψ) of the liquid crystal molecule is, as shown in FIG. Have two hysteresis and a well-defined DC voltage threshold. That is, when a DC electric field in a certain direction is applied to the electrodes of the liquid crystal element to increase the voltage, the apparent tilt angle (point A in FIG. 3) which was initially 0 ° C. is slightly increased up to the voltage V _1. changes to, started to change in the voltage V ₁ (3
(Point B in the figure) As the voltage is further increased, the apparent tilt angle changes rapidly. A sudden change in the tilt angle of the apparent to increase the voltage up to V ₂ ceased (C point of FIG. 3), is hardly a change in the tilt angle also apparent increase more voltage (of FIG. 3 D point). Begins to decrease a voltage from this state, but hardly changed tilt angle of apparent at first, the tilt angle of the apparent when a voltage up to the voltage V ₃ decreases begins to change (Fig. 3 E point). Furthermore the tilt angle of the apparent and continues to decrease the voltage changes rapidly, ceased abrupt change in the tilt angle of the apparent in voltage V ₄ (F of FIG. 3
Point) Then, when the voltage is lowered to OV, the apparent tilt angle gradually decreases and becomes almost 0 at 0V. It is different from the voltage V ₁ and V ₄ and the voltage V ₂ and V _3, the tilt angle of the apparent exhibits hysteresis with respect to the applied DC voltage. Even when the direction of the applied electric field is reversed, the same phenomenon as described above appears. However, the direction of the change in the apparent tilt angle is opposite to the above. That is, in FIG. 3, when an electric field reverse to the above is applied and the voltage is increased and then decreased, the apparent tilt angle becomes point A →
It changes from point B '→ point C' → point D '→ point E' → point F '→ point A. Since the tilt angle of the apparent changes rapidly to changes in the voltages V ₁ to V _2, the liquid crystal element using an antiferroelectric phase (SmC _A ^*) has a threshold value of the definite applied DC voltage.

Many phases including a smectic A phase and a chiral smectic C phase have been known as a smectic phase so far. However, an antiferroelectric phase (S _m C _A ^* ) having a tristable state is as follows. Different.

7A and 7B show the relationship between the liquid crystal layer 14 and the liquid crystal molecules 16 when the liquid crystal element is viewed from above.

As shown in FIG. 7A, the smectic A phase is a phase in which liquid crystal molecules are arranged in parallel to the normal direction of the liquid crystal layer. In smectic A phase, extinction position when no electric field is applied, like the anti-ferroelectric phase ^(* S _m C ^_A) is a direction parallel to the normal direction and the liquid crystal layer of the liquid crystal layer. However, the apparent tilt angle of the liquid crystal molecules has no hysteresis with respect to the DC applied voltage, and has no threshold value with respect to the DC applied voltage.

As shown in FIG. 7B, the chiral smectic C phase is a phase in which liquid crystal molecules are inclined by an apparent tilt angle (ψ ′) from the normal direction of the liquid crystal layer. The SSFLC element in the chiral smectic C phase has bistability, and when an electric field is applied, the liquid crystal molecules switch between the bistable state, that is, between two uniforms. or,
As shown in FIG. 7C, the relationship between the pulse voltage and the apparent tilt angle has a threshold value for the pulse voltage and one hysteresis.

Antiferroelectric phase ^(* S _m C ^_A) is more as mentioned, it is clearly different from the smectic phase are known prior to beginning a smectic A phase and chiral smectic C phase.

As a material of the pair of parallel substrates used in the present invention, glass, plastic, or the like is preferably used, and a transparent electrode is preferably disposed. It is preferable that an organic polymer film rubbed on both surfaces or one surface of a pair of parallel substrates is formed as an alignment film. As the organic polymer film, it is preferable to use a polyimide film, a polyamide film, a polyvinyl film, a nylon film, or the like. Further, instead of the organic polymer film, an inorganic thin film such as yttrium or silicon oxide (SiO, SiO ₂ ) may be formed on one or both surfaces of a pair of parallel substrates. Furthermore, it is also possible to align the liquid crystal by adopting a temperature gradient method when the liquid crystal is sandwiched between a pair of parallel substrates to form an element, and in this case, the alignment can be performed without performing the alignment treatment on the parallel substrate. is there.

The transparent electrode used in the present invention is preferably an ITO film, a NESA film, or the like.

In the present invention, the gap between the parallel substrates, that is, the cell gap varies depending on the use of the liquid crystal element, but is preferably 0.5 to 300 μm. In particular, when used as an element for a display device, the thickness is 1.5 to 10 μm, particularly preferably 1.5 to 5 μm.

(Effect of the Invention) The present invention comprises a liquid crystal or a liquid crystal composition having an antiferroelectric phase and a pair of substrates having electrodes and sandwiching the liquid crystal or the liquid crystal composition. In the antiferroelectric phase, a voltage is applied to the electrodes. A liquid crystal device using an antiferroelectric phase characterized by temporarily changing the layer structure of the liquid crystal or liquid crystal composition from a chevron structure to a bookshelf structure by applying a liquid crystal, which has high contrast and high-speed response. It is excellent in display characteristics, such as having a display, and is suitable for use in high-density large-screen displays, high-speed optical shutters, and the like.

(Examples) The present invention will be described more specifically with reference to the examples.

Example 1 As a liquid crystal, 4- (1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate was used. The phase transition temperature is isotropic → SmA 149 ° C,
^{SmA → SmC * 121 ℃, SmC} * → SmC A * 116 ℃, S m C A * → crystal 7
2 ° C. After a pair of 150 μm-thick glass substrates with ITO were coated with polyimide, only one of the pair of substrates was rubbed, and liquid crystal was injected between the pair of substrates to form a liquid crystal cell. The cell gap was 6 μm. The liquid crystal cell was heated until the liquid crystal became an isotropic phase, and then the liquid crystal cell was gradually cooled at a rate of 1 ° C./min to uniformly align the liquid crystal parallel to the glass substrate to obtain a sample for X-ray diffraction. X-ray diffraction is Ru
-200 (manufactured by Rigaku Corporation). The temperature control of the liquid crystal cell was performed using a temperature control unit having an accuracy of ± 0.1 ° C.

The measurement system is shown in FIG. The measurement procedure for X-ray diffraction is described in Japanese Journal of Applied Physics, Vol. 27, pp L725, 1988 and Japanese Journal of Applied Physics, Vol. 27, pp L199.
3, according to 1988. That is, the Bragg angle of the liquid crystal was measured using a capillary sail initially filled with the liquid crystal. Next, the counter was set to the Bragg angle. An X-ray diffraction pattern was obtained by rotating α using the cell prepared in the above procedure. Here, α is the angle between the glass surface and the incident beam. The size of the X-ray beam is
1 mm ² . X-ray diffraction sets the temperature of the liquid crystal cell to 100 ° C (S
_(m C _A ^* phase) were measured for the case where no electric field was applied even once after the liquid crystal alignment, the case where the applied DC voltage was increased stepwise to 70 V, and the case where the applied voltage was finally released.

 The X-ray diffraction measurement conditions are as follows.

X-ray diffractometer; Ru-200 (manufactured by Rigaku Corporation), 60 KV, 20
0mA Target; Cu Filter; Ni Voltage; 50KV Current; 200mA Scan Speed; 4deg / min Sampling Rate; 0.1deg, conteniousscan Slit; DS0.5 ゜, RS0.3mm, SS0.5 ゜ Detector; PC An assembly diagram based on the left end of each X-ray diffraction pattern is shown. In FIG. 4, the vertical axis indicates the X-ray diffraction intensity, and the horizontal axis indicates the rotation angle α of the liquid crystal cell. FIG. 4 shows that as the applied voltage increases, the structure of the liquid crystal layer changes from a chevron structure to a bookshelf structure. At this time, the threshold voltage for switching the liquid crystal molecules is 27 V (V1 in FIG. 3), so that it is necessary to apply a voltage twice or more the threshold voltage in order for the layer to have a bookshelf structure. You can see that. When the voltage is released, the structure of the liquid crystal layer returns to the chevron structure defined by the present invention (70 → OV X in FIG. 4).
Line diffraction pattern).

Example 2 In the same procedure as in Example 1, a cell in which both the pair of glass substrates were rubbed and a cell in which one of the pair of glass substrates was rubbed were produced, and the layer structure was examined by X-ray diffraction.
When the temperature of the liquid crystal cell where both the pair of glass substrates are rubbed is maintained at 90 ° C (S _m C _A ^* phase) and no electric field has been applied once after the liquid crystal alignment, or when a DC voltage of 80 V is applied ,
An X-ray diffraction pattern was measured for each of the cases where the applied voltage was canceled. The respective results are shown in FIGS. 2A, 2C and 2B. The vertical axis in the figure indicates the X-ray diffraction intensity, and the horizontal axis indicates the rotation angle α of the liquid crystal cell. A liquid crystal cell in which only one of a pair of glass substrates is rubbed is kept at 90 ° C (S _m C _A ^* phase), a DC voltage of 80 V is applied from the state where no electric field is applied after liquid crystal alignment, and then the applied voltage is released. The X-ray diffraction pattern of the liquid crystal cell after the above is shown in FIG. 2D. 2D and 70 in FIG. 4
From the X-ray diffraction pattern of 0 V, it can be seen that the X-ray diffraction pattern of the liquid crystal element having the chevron structure after the application of the electric field in the single-sided rubbing cell slightly varies depending on the cell. 2B and 2D that the X-ray diffraction pattern of the liquid crystal element having the chevron structure after the application of the electric field is greatly different depending on the rubbing condition of the substrate.

Example 3 A relationship between an apparent tilt angle and an applied voltage at 100 ° C. was examined using a liquid crystal element obtained by rubbing only one of the substrates of Example 1. The apparent tilt angle was the angle between the normal direction of the liquid crystal layer and the extinction position. The measuring method was determined by applying a DC voltage to the liquid crystal element in a stepwise manner, and observing the extinction position at each voltage with a polarizing microscope having a polarizing plate orthogonal to the polarizing plate. Third result
Shown in the figure. From this figure, it can be seen that there is a threshold value for the DC voltage and a memory property. The threshold value for the DC voltage was 27 V (FIG. 3, V1).

Example 4 Using a liquid crystal device in which only one of the substrates of Example 1 was rubbed, observation of the fixture was performed using a deflection microscope in which a polarizing plate was orthogonally arranged. Note that the temperature of the liquid crystal element was kept at 100 ° C. during microscopic observation. Immediately after the liquid crystal was aligned, many zigzag defects were observed in the liquid crystal element.
When this voltage was applied, the zigzag defect disappeared. Further, even when the voltage was cut off, the zigzag defect did not appear again in the liquid crystal element. Further, in the device having the zigzag defect immediately after the liquid crystal alignment, the contrast ratio between both uniforms was measured by applying a rectangular wave voltage of ± 35 V and measuring the contrast between the two uniforms. After applying a voltage of 70V to this cell to remove the zigzag defect, applying a rectangular wave voltage of ± 35V again and measuring the contrast between the two uniforms, the contrast ratio was improved to 60, showing a very high contrast. .

Example 5 The liquid crystal used was 4- (1-methylheptyloxycarbonyl) phenyl 4'-octyloxybienyl-4-carboxylate. Phase transition temperature isotropic phase → SmA phase 149 ℃, Sm
A → SmC ^* 121 ° C, SmC ^* → SmC _A ^* 116 ° C, SmC _A ^* → Crystal 72
° C. Inject liquid crystal into a pair of glass substrates with ITO,
The liquid crystal was uniformly aligned parallel to the substrate by a temperature gradient method. The cell gap was 2.5 μm. In this liquid crystal element, the threshold value for the DC voltage was 15V. The cell temperature was maintained at 70 ° C., and a response time was measured by applying a rectangular wave voltage having a voltage of ± 17 V and a frequency of 5 Hz. The response time when the above voltage was applied to the cell to which no electric field was applied after the liquid crystal alignment was 34 μs (microsecond). On the other hand, when a DC voltage of 80 V was once applied to the cell, the layer structure was changed to a bookshelf structure, and the above-described voltage was applied again, the response time was 27 μs (microsecond).

As described above, the response speed was increased by temporarily changing the layer structure from the chevron to the bookshelf structure by applying an electric field.

[Brief description of the drawings]

FIG. 1 is an X-ray analysis measurement system used for diffraction of a liquid crystal layer structure of a liquid crystal device using an antiferroelectric phase of the present invention, where α is a rotation angle, θ is a diffraction angle, Ki is an incident X-ray, and Ks Is a diffraction X-ray. FIGS. 2A, 2B, 2C, and 2D are X-ray diffraction patterns of a liquid crystal device using the antiferroelectric phase of the present invention. The horizontal axis represents the rotation angle of the liquid crystal device, and the vertical axis represents the X-ray diffraction intensity (cps). is there. FIG. 3 shows the relationship between the apparent tilt angle (φ) and the applied DC voltage of the liquid crystal device using the antiferroelectric phase of the present invention. FIG. 4 is an X-ray diffraction pattern when a DC voltage applied to a liquid crystal element using the antiferroelectric phase of the present invention is changed. FIGS. 5A, 5B, and 5C are cross-sectional views of a liquid crystal element schematically showing a layer structure of a smectic phase. FIG. 6 is a schematic view of the molecular arrangement of the liquid crystal element of the present invention when the liquid crystal element is viewed from above. 7A and 7B are schematic diagrams of the molecular arrangement of various liquid crystal phases when the liquid crystal element is viewed from above. FIG. 7C shows a hysteresis of a pulse voltage and a tilt angle of a ferroelectric liquid crystal element having no antiferroelectric layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1337 G02F 1/141

Claims (1)

(57) [Claims] 1. _A liquid crystal or liquid crystal composition having an antiferroelectric phase (SmC _A ^* ), and a pair of substrates having electrodes and sandwiching the liquid crystal or liquid crystal composition. _{In A} ^* ), by applying a DC voltage or a short-wave or triangular-wave voltage having a peak value of twice or more of the threshold voltage and a frequency of 1 kHz or less to the electrode, A liquid crystal device using an antiferroelectric phase, wherein a layer structure of a liquid crystal composition is temporarily changed from a chevron structure to a bookshelf structure.