JPH06250186A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To provide the ferroelectric liquid crystal element which realizes a sufficiently wide driving margin in obtaining good images within the range of use environment temps. CONSTITUTION:This liquid crystal element is constituted by holding a chiral smectic liquid crystal 15 between substrates 11a and 11b formed with electrodes 12a, 12b and uniaxial orientation films 14a, 14b and satisfies the relations THETA<alpha+delta and delta<alpha, THETA>thetaa>THETA/2, THETAXdelta>70, THETAXdelta/Ps>20 when the tilt angle of the liquid crystal in the temp. range from 10 deg.C to 5 deg.C is defined as THETA ( deg.c), the angle of inclination of the liquid crystal layer as delta ( deg.C), the apparent tilt angle as thetaa ( deg.C) and the magnitude of the spontaneous polarization of the liquid crystal compsn. as Ps(nC/cm<2>).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element used in a liquid crystal display element, a liquid crystal optical shutter or the like, and more particularly to an element using a ferroelectric liquid crystal having spontaneous polarization.

[0002]

2. Description of the Related Art Conventionally, liquid crystals have been applied as electro-optical elements in various fields. Most of the liquid crystal elements currently in practical use are, for example, M. Sch.
adt) and W. Helfri
ch) "Applied Physics Letters"
("Applied Physics Letter
s ") Vo.18, No.4 (1971.2.15)
P. 127-128 "Voltage Depend"
ent Optical Activity of a
Twisted Nematic Liquid Cr
TN (Twisted Nem)
atic) type liquid crystal is used.

These are based on the dielectric alignment effect of liquid crystals, and utilize the effect that the average molecular axis direction is directed in a specific direction by an applied electric field due to the dielectric anisotropy of liquid crystal molecules. The optical response speed limit of these devices is said to be milliseconds, which is too slow for many applications.
On the other hand, in the application to a large flat panel display, the driving by the simple matrix method is the most effective in consideration of the price and the productivity. In the simple matrix method,
An electrode configuration in which a scan electrode group and a signal electrode group are configured in a matrix is adopted, and for driving thereof, an address signal is sequentially and selectively applied to the scan electrode group and a predetermined information signal is applied to the signal electrode group. The time-division driving method is adopted in which the signals are selectively applied in parallel in synchronization with the address signal.

However, when the above-mentioned TN type liquid crystal is adopted for the element of such a driving system, the scan electrode is selected and the signal electrode is not selected, or the scan electrode is not selected and the signal electrode is selected. A finite electric field is applied to the region (so-called “half-selected point”).

If the difference between the voltage applied to the selection point and the voltage applied to the half selection point is sufficiently large and the voltage threshold value required to align the liquid crystal molecules perpendicularly to the electric field is set to an intermediate voltage value, The display element works normally,
When the number of scanning lines (N) is increased, the whole screen (1
The time (duty ratio) in which an effective electric field is applied to one selection point during scanning of a frame decreases at a rate of 1 / N.

For this reason, the voltage difference as an effective value applied to the selected point and the non-selected point when repetitive scanning is performed is
As the number of scanning lines increases, the number becomes smaller, and as a result, deterioration of image contrast and crosstalk are inevitable drawbacks.

Such a phenomenon is caused by a liquid crystal having no bistability (a stable state in which the liquid crystal molecules are aligned horizontally with respect to the electrode surface, and a vertical state only while an electric field is effectively applied). This is an essentially unavoidable problem that occurs when driving (that is, repeatedly scanning) using the temporal accumulation effect.

In order to improve this point, the voltage averaging method,
The two-frequency driving method and the multi-matrix method have already been proposed, but none of them is sufficient, and the increase in the screen size and the density of the display element is stopped because the number of scanning lines cannot be increased sufficiently. This is the current situation.

In order to improve the drawbacks of the conventional liquid crystal device, the use of a liquid crystal device having bistability is explained by Clark and Lagerw.
all) (JP-A-56-1072).
16 publication, U.S. Pat. No. 4,367,924, etc.).

Ferroelectric liquid crystals having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) are generally used as the bistable liquid crystal.

This ferroelectric liquid crystal has a bistable state consisting of a first optical stable state and a second optical stable state with respect to an electric field, and therefore the optical modulation used in the above-mentioned TN type liquid crystal. Unlike the element, for example, the liquid crystal is oriented in the first optically stable state with respect to one electric field vector, and the liquid crystal is oriented in the second optically stable state with respect to the other electric field vector. Further, this type of liquid crystal has a property (bistability) of taking one of the two stable states described above in response to an applied electric field and maintaining the state when no electric field is applied.

In addition to the above-mentioned characteristic of having bistability, the ferroelectric liquid crystal has an excellent characteristic of high-speed response. This is because the spontaneous polarization of the ferroelectric liquid crystal and the applied electric field act directly to induce the transition of the alignment state.
It is 3 to 4 orders faster than the response speed due to the effect of the dielectric anisotropy and the electric field.

As described above, the ferroelectric liquid crystal potentially has extremely excellent characteristics, and by utilizing such characteristics, many of the problems of the above-mentioned conventional TN type element can be solved. A fairly substantial improvement is obtained. In particular, it is expected to be applied to high-speed optical optical shutters and high-density, large-screen displays.

In the case where the above-mentioned simple matrix display device is constituted by an element in which the ferroelectric liquid crystal layer is sandwiched between a pair of substrates, for example, JP-A-59-193426 and JP-A-59-193427 are disclosed. JP-A-60-1560
The driving method disclosed in Japanese Patent Laid-Open No. 46, Japanese Patent Laid-Open No. 60-156047, or the like can be applied.

FIG. 5 is an example of a waveform diagram of the driving method. FIG. 6 is a plan view of an example of a ferroelectric liquid crystal panel in which matrix electrodes are arranged. In the liquid crystal panel 51 of FIG. 6, the scanning lines of the scanning electrode group 52 and the data lines of the information electrode group 53 are wired so as to intersect with each other, and the ferroelectric property is provided between the scanning line and the data line at the intersection. Liquid crystal is arranged.

In FIG. 5A, S _S is a selected scan waveform applied to the selected scan line, S _N is an unselected scan waveform not selected, and I _S is applied to the selected data line. selection information waveform (black), I _N represents the non-selection information signal applied to the data line which is not selected (white). Further, in view as _{(I S -S S) (I} N -S S) is the voltage waveform applied to pixels on a selected scanning line, the voltage (I _S -S
_The pixel to which _S ) is applied is in a black display state and the voltage (I
_The pixel to which _N −S _S ) is applied has a white display state.

FIG. 5B shows the drive waveform shown in FIG. 5A, which is a time-series waveform when the display shown in FIG. 7 is performed.

In the driving example shown in FIG. 5, the minimum application time Δt of the single polarity voltage applied to the pixel on the selected scanning line.
Corresponds to the time of the write phase t ₂ , and 1 line clear t ₁
The phase time is set to 2Δt.

The values of the parameters V _S , V ₁ and Δt of the drive waveform shown in FIG. 5 are determined by the switching characteristics of the liquid crystal material used.

FIG. 8 shows the transmittance T when the drive voltage (V _S + V ₁ ) is changed while keeping the bias ratio, which will be described later, constant.
Of VT characteristics, that is, VT characteristics. Here, Δt = 50 μsec, bias ratio V _I / (V _I + V _S ).
It is fixed at = 1/3. Positive side of Figure 8 is shown in FIG. 5 (I _N -S _S), the negative side waveform shown by (I _S -S _S) is applied.

Here, V ₁ and V ₃ are called the actual driving threshold voltage and the crosstalk voltage, respectively. In addition, V ₂ <V ₁ <
At V ₃ , ΔV = V ₃ −V ₁ is called a voltage margin, which is a voltage width capable of matrix driving. It can be said that V ₃ generally exists in driving the FLC display device. In particular,
A voltage value causing switching by V _B in the waveform of FIG. _{5 (A) (I N -S} S). Of course, it is possible to increase the value of V ₃ by increasing the bias ratio, but increasing the bias ratio means increasing the amplitude of the information signal, which causes an increase in image flicker and contrast. Is caused, which is not preferable.

In our study, the bias ratio is 1/3 to 1/4.
The degree was practical. By the way, if the bias ratio is fixed, the voltage margin ΔV strongly depends on the switching characteristics of the liquid crystal material, and it goes without saying that a liquid crystal material having a large ΔV is very advantageous for matrix driving.

At such a certain temperature, it is possible to write two states of "black" and "white" to the selected pixel depending on the two directions of the information signal, and the non-selected pixel is "black" or "white". The upper and lower limit values of the applied voltage that can maintain the “white” state and the width thereof (driving voltage margin Δ
V) is unique because there is a difference between the liquid crystal materials. In addition, since the drive margin also shifts depending on the change in the ambient temperature, in the case of an actual display device, it is necessary to set the optimal drive voltage for the liquid crystal material and the ambient temperature.

However, in practical use, when the display area of such a matrix display device is expanded, the difference in the environment in which the liquid crystal exists in each pixel (specifically, the difference in the temperature and the cell gap between the electrodes) is naturally large. Therefore, a liquid crystal having a small driving voltage margin cannot obtain a good image in the entire display area.

Generally, in the case of a liquid crystal element utilizing the birefringence of liquid crystal, the transmittance under the crossed Nicols is expressed by the following equation (1).

I / I ₀ = sin ² 4θ _a sin ² (Δnd / λ) π (1) In the equation (1), I ₀ is the incident light intensity, I is the transmitted light intensity, and θ _a
Is the apparent tilt angle defined below, Δn is the refractive index anisotropy, d is the thickness of the liquid crystal layer, and λ is the wavelength of incident light. Apparent tilt angle θ in the above-mentioned non-helical structure
_a appears as the angle in the average molecular axis direction of the twisted liquid crystal molecules in the first and second alignment states.
According to the equation (1), the apparent tilt angle θ _a is 22.5 °.
The maximum transmittance is obtained when the angle is, and the apparent tilt angle θ _a in the non-helical structure that realizes the bistability needs to be as close as possible to 22.5 °.

However, the alignment method that has been used so far, in particular, the alignment method using a rubbing-treated polyimide film is applied to the ferroelectric liquid crystal having the non-helical structure and exhibiting the bistability disclosed by Clark and Lagerwol. When applied, it had the following problems.

That is, an apparent tilt angle θ _a (1/2 of the angle formed by the molecular axes of two stable states) in _a ferroelectric liquid crystal having a non-helical structure obtained by aligning with a conventional rubbing-treated polyimide film. ) Is smaller than the tilt angle in the ferroelectric liquid crystal (angle Θ which is 1/2 of the apex angle of the triangular pyramid shown in FIG. 6). In particular, the apparent tilt angle θ _a of _a ferroelectric liquid crystal having a non-helical structure obtained by orienting with a conventional rubbing-treated polyimide film is generally about 3 ° to 8 °, and the transmittance at that time is at most 3-5.
It was about%.

However, the following was discovered in order to realize a display in which _a large apparent tilt angle θ _a is generated in the non-helical structure of the chiral smectic liquid crystal and a high-contrast image is displayed.

That is, the chiral smectic liquid crystal and the liquid crystal are opposed to each other with the liquid crystal held therebetween, and electrodes for applying a voltage to the chiral smectic liquid crystal are formed on the opposed surfaces, and the liquid crystal is aligned. In a liquid crystal device comprising a pair of substrates that have been subjected to an alignment treatment in which uniaxial alignment axes intersect each other at a predetermined angle, the pre-tilt angle of the smectic liquid crystal device is α, the tilt angle is Θ, and the tilt angle of the liquid crystal layer is ( If the angle between the liquid crystal layer and the substrate normal is δ, the smectic liquid crystal is a liquid crystal element having an alignment state represented by the following formula (2), and at least two liquid crystals in the alignment state are present. shows a stable state, and the tilt angle of the apparent theta _a is ½ of the angle between their optical axes and said chiral smectic liquid crystal tilt angle Θ satisfies the following equation (3) In a liquid crystal element having engagement, it displays a high contrast image is displayed revealed that be realized.

Θ <α + δ and δ <α (2) Θ> θ _a > Θ / 2 (3) Hereinafter, this will be outlined. Smectic liquid crystals generally have a layered structure, but from SmA phase to SmC
When the phase or the SmC ^* phase is changed, the layer spacing is shortened, so that the layer 31 has a bent structure (chevron structure) at the center of the upper and lower substrates as shown in FIG.

As shown in FIG. 2, the bending direction is in the portion 32 in the orientation state (C1 orientation state) which appears immediately after the transition from the high temperature phase to the SmC ^* phase, and in the C1 orientation state when the temperature is further lowered. There can be two cases in the case of the portion 33 of the orientation state (C2 orientation state) that appears in a mixed manner. Furthermore, when a combination of a specific alignment film and a liquid crystal is used, the transition from the C1 alignment state to the C2 alignment state is unlikely to occur, and depending on the liquid crystal material, the C2 alignment state does not occur at all. Particularly when a high pretilt alignment film is used and the relationship of Θ <α + δ is satisfied, the contrast of the C1 alignment is very high and the contrast of the C2 alignment is low. Therefore, if a high pretilt alignment film is used as the display element, the entire screen is unified into the C1 alignment state, and the two states of high contrast are used as the two states of black and white display, a display of higher quality than before can be obtained. The pretilt will be described below.

As described above, C1 is produced without producing the C2 orientation state.
It is concluded that the following conditions must be satisfied in order to realize the oriented state. That is, as shown in FIG. 3, the directors near the substrate in the C1 and C2 orientations are on the cone 41 shown in FIGS. 3 (a) and 3 (b), respectively. As is well known, the rubbing causes the liquid crystal molecules at the interface of the substrate to form an angle called pretilt with respect to the substrate, and the direction of the liquid crystal molecules heads toward the rubbing direction (direction of arrow A in FIG. 3). It is suitable for holding up (making it look like the tip is floating). By the above,
The following formula (4) must be established among the tilt angle Θ, the pretilt angle α, and the layer tilt angle δ of the liquid crystal.

In the case of C1 orientation Θ + δ> α In the case of C2 orientation Θ−δ> α (4) Therefore, the condition for producing C1 orientation without causing C2 orientation as described above is expressed by the following equation (5). Represented.

Θ−δ <α, that is, Θ <α + δ (5) Furthermore, due to a simple consideration of the torque received when the interface molecule moves from one position to the other position by the electric field, the interface molecule is easily switched. As a condition, the following expression (6) is obtained.

Α> δ (6) Therefore, in order to form the C1 orientation state more stably, it is effective to satisfy the relationship of the expression (6) in addition to the expression (5).

As a result of further experiments under the conditions of the equations (5) and (6), the apparent tilt angle θ _a of the liquid crystal was
It increases from about 3 ° to 8 ° in the conventional case where the conditions of the expressions (5) and (6) are not satisfied to about 8 ° to 16 ° when the conditions of the expressions (5) and (6) are satisfied. It was empirically obtained that the following relational expression (7) holds between the liquid crystal tilt angle Θ and the liquid crystal tilt angle Θ.

Θ> θ _a > Θ / 2 (7) As described above, if the conditions of the expressions (5), (6) and (7) are satisfied, a display in which a high-contrast image is displayed can be realized. Became clear.

This point will be further described. (5)
In the orientation state represented by the formula, there are four states in the C1 orientation state.

FIG. 4 is a schematic view showing the arrangement of directors at respective positions between the substrates in each state of C1 orientation. In the figure, 45 to 48 are views in which the director is projected on the bottom surface of the cone in each state and viewed from the bottom surface direction. 45 and 46 are spray states, 47 and 48 are uniform states (bistable state) This is the arrangement of directors. As can be seen from the figure, in the two states 47 and 48 of the uniform, the position of one of the upper and lower liquid crystal molecules is replaced with the position of the spray state,
The director is not twisted between the upper and lower boards.

In the uniform orientation state, the relational expression (7) holds, and the apparent tilt angle θ _a of the liquid crystal is large,
A high contrast can be realized.

Further, cross rubbing in which the rubbing directions of the upper and lower substrates are shifted in the range of 1 ° to 25 ° (crossing angle) in order to stably form the C1 uniform orientation state and obtain good orientation is also very effective. .

[0043]

In practice, when the operating temperature range of the display is set to about 5 to 35 ° C., the ambient temperature of the liquid crystal device itself becomes about 10 to 50 ° C. due to heat accumulation from the periphery of the device. . In the current situation, it is not possible to maintain a good image quality in all the temperature ranges in a display using an ordinary ferroelectric liquid crystal. Particularly, securing a driving margin in a high temperature region has become a major issue.

At a temperature near room temperature, even if a good image with high contrast in the C1 uniform orientation state can be realized,
In a high temperature range, the orientation is often in a splay orientation state.
Therefore, in the high temperature range, the driving margin is greatly reduced,
It was hard to say that good images and drive margins were realized within the operating environment temperature range.

[0045]

Means and Actions for Solving the Problems The present inventors have
As a result of intensive studies to solve the above problems, as to the reduction of the driving margin at a high temperature, the relationship between the tilt angle (Θ) of the liquid crystal composition and the tilt angle (δ) of the layer was focused, and the tilt angle (Θ) And layer inclination angle (δ), spontaneous polarization (P
Focusing on the relationship of s), it was discovered that an element having a wide driving margin at high temperature can be obtained if certain conditions are satisfied in the element configuration according to the present invention.

That is, according to the present invention, a chiral smectic liquid crystal is opposed to the liquid crystal with the liquid crystal sandwiched therebetween, and electrodes for applying a voltage to the liquid crystal are formed on the opposing surfaces, respectively, and the liquid crystal is uniaxially oriented. In a liquid crystal device including a pair of substrates whose alignment axes are crossed or parallel to each other at a predetermined angle, a pretilt angle of the liquid crystal device is α (degrees) in a temperature range of 10 ° C to 55 ° C. When the tilt angle of the liquid crystal is Θ (degree) and the tilt angle of the liquid crystal layer is δ (degree), the liquid crystal has an alignment state represented by the following formula (I), and at least two stable states are obtained in this alignment state. The tilt angle θ _a (degree), which is 1/2 of the angle formed by these optical axes, and the tilt angle Θ satisfy the relationship of the following formula (II), and Θ <α + δ and δ <α _{(I) Θ> θ a>} Θ / 2 (II Furthermore, the magnitude of spontaneous polarization of the liquid crystal composition Ps (nC /
cm ² ), Ps, Θ and δ at 55 ° C. are the following formulas (III) and (IV)

[0047]

[Equation 3] A liquid crystal element characterized by satisfying the relationship

In the present invention, Ps, Θ and δ at 55 ° C. are expressed by the following formulas (V) and (VI).

[0049]

[Equation 4] It is preferable to satisfy the relationship of
The phase transition temperature from the smectic A phase to the chiral smectic C phase is preferably 60 ° C. or higher.

As described above, a major factor for reducing the driving margin in the high temperature region is that the C1 uniform orientation state becomes unstable and the splay orientation state is likely to appear.

The inventors have found that the tilt angle δ of the liquid crystal layer showing the clarity of the chevron structure, the magnitude of the tilt angle Θ which is the angle between the two stable state positions of the switching of the liquid crystal molecules by the electric field, and the substrate interface. When the relationship between the three liquid crystal physical property parameters of the spontaneous polarization magnitude Ps of the liquid crystal composition, which is the largest parameter expressing the electrical interaction with the liquid crystal molecules from, deviates from a certain optimum range, the C1 uniform orientation state becomes We have found the fact that it becomes unstable and the driving margin in the high temperature range is greatly reduced.

That is, the present inventors repeated experiments such as measurement of high temperature driving margin for various liquid crystal devices in which many liquid crystal compositions and device configurations were combined, and as a result, the above formulas (I) and (II) were obtained. And satisfy the above (II
By satisfying the relation of the formula (I), more preferably the formula (V), and further satisfying the formula (IV), more preferably the formula (VI), the C1 uniform orientation state can be stabilized even in a high temperature range. It has been found that it is possible to secure a sufficient drive margin in the high temperature range.

In the present invention, the reason why the relation of each parameter at 55 ° C. is shown is that the ambient temperature of the liquid crystal element itself is about 50 ° C. under a high temperature (35 ° C.) use environment, so that it is favorable near 50 ° C. This is because in order to guarantee the image quality and the driving margin, it is necessary to have a good image quality and the driving margin above the upper limit environmental temperature.

At this time, at least a driving voltage margin exists at 55 ° C., and if the driving voltage margin at 55 ° C. is 3.4 V or more, a wide driving margin sufficient to display a good image at 50 ° C. It is known that

In the present invention, as one of the conditional expressions for having the orientation state, a constant lower limit value is given to the pretilt angle α such that δ <α (I).

By setting α to be larger than the lower limit value as described above, the state of the C1 uniform orientation is stabilized as described above. At the time of driving, splay alignment may appear in the original C1 uniform alignment although it is a minute region.

As a condition for preventing this, it is possible to satisfy the condition of the following formula (VII) Θ <α (VII) in the entire temperature range for displaying an image. When this condition is not satisfied, that is, when Θ is α or more, C1 splay alignment tends to be mixed during matrix driving.

At another low temperature (about 10 ° C.)
Even under the condition (1), a region exhibiting a C2 alignment state as a non-favorable alignment state other than the C1 uniform alignment that can obtain a good image during matrix driving may appear although it is slight. This phenomenon has a great influence on the driving conditions such as the driving voltage and the frequency, but it appears only when δ of the liquid crystal material is considerably smaller than Θ, and as a condition for preventing this, Under low temperature (about 10 ° C.) condition, it is preferable to satisfy the condition of the following formula (VIII) δ> θ / 3 (VIII), more preferably the formula (IX) δ> θ / 2 (IX).

FIG. 1 is a sectional view schematically showing an example of the liquid crystal element of the present invention. This liquid crystal element includes a chiral smectic liquid crystal 15 and a liquid crystal 15 as shown in FIG.
Electrodes 1 for sandwiching and facing each other and applying a voltage to the chiral smectic liquid crystal on the facing surfaces, respectively.
2a and 12b are formed, and a pair of substrates 11a and 11b that have been subjected to an alignment treatment in which uniaxial alignment axes for aligning liquid crystals intersect each other at a predetermined angle.

The substrates 11a and 11b are made of glass plates, and are made of In ₂ O ₃ or ITO (Indium Ti).
n Oxide) and other transparent electrodes 12a and 12b. And, on it, S of 200-3000Å thickness
Insulating film 13a such as iO ₂ film, TiO ₂ film, Ta ₂ O ₅ film
13b and 50-1000Å made of polyimide
Thick orientation control films 14a and 14b are laminated respectively. Here, a thin film of tantalum oxide is formed on the glass substrates 11a and 11b provided with the transparent electrodes 12a and 12b by a sputtering method, and a polyamic acid manufactured by Hitachi Chemical Co., Ltd., represented by the following structural formula 1 is formed on the thin film. 1% N of LQ1802
The MP solution is applied by a spinner and baked at 270 ° C. for 1 hour.

[0061]

[Chemical 1]

The alignment control films 14a and 14b have a crossing angle of 6 ° counterclockwise with respect to the alignment control film 14a on the upper side with respect to the alignment control film 14b on the upper side. Uniaxial alignment treatment to have
And rubbing treatment so that the same direction (arrow A direction)
I am doing it. Hereinafter, the intersection angle will be defined in this way. The distance between the substrates 11a and 11b is set to a distance small enough to suppress the formation of the helical alignment structure of the chiral smectic liquid crystal 15, for example, 0.1 to 3 μm. Here, it is 1.2 to 1.3 μm. This distance is held by the bead spacers 16 (silica beads, alumina beads, etc.) arranged between the substrates 11a and 11b.

The chiral smectic liquid crystal 15 has a bistable alignment state. 17a and 17b are polarizing plates.

In this liquid crystal element, the above formulas (I) and (II) are satisfied.

The tilt angle Θ (degree), the layer tilt angle δ (degree), the pretilt angle α (degree), the apparent tilt angle θ _a (degree) and the Ps (nC / cm ² ) of the liquid crystal according to the present invention are It measured as follows.

Measurement of tilt angle Θ of liquid crystal While applying an AC voltage of ± 30 V to ± 50 V and 100 Hz between the upper and lower substrates of the FLC element, the crossed Nicols are placed, and the FLC element arranged between them is rotated parallel to the polarizing plate. Then, the first extinction position (the position where the transmittance is lowest) and the second extinction position are searched for while detecting the optical response with Photomal (manufactured by Hamamatsu Photonics KK). At this time, 1/2 of the angle from the first extinction position to the second extinction position is the tilt angle Θ of the liquid crystal.
And

Measurement of Apparent Tilt Angle θ _a After applying a single pulse having a threshold value of the liquid crystal, the FLC element placed between them under no electric field and under orthogonal crossed Nicols is rotated horizontally with the polarizing plate. After searching for the extinction position and then applying a pulse having a polarity opposite to that of the above-mentioned single-shot pulse, the second extinction position is searched for under no electric field. Apparent tilt angle θ _a of ½ of the angle from the first extinction position to the second extinction position at this time
And

Measurement of layer tilt angle δ Basically, the method disclosed by Clark and Lagerwol (Japan Display '86, Sep. 3).
0-Oct. 2, 1986, pp. 456-458) or the method of Ouchi et al. (JJAP, 27 (5) (1
988) pp. 725-728) was used.

A rotating anticathode type X-ray diffractometer manufactured by MAC Science Co. was used as a measuring device, and copper Kα ray was used as an analysis line. For the liquid crystal cell, 80 μm thick glass (trade name: Microsheet, manufactured by Corning Incorporated) was used as the substrate glass to reduce the absorption of X-rays as much as possible, and the other ordinary cell forming steps were used as they were. To measure the layer spacing of liquid crystal, apply bulk liquid crystal on the sample glass and perform 2 as in the case of normal powder X-ray diffraction.
It was determined by performing θ / θscan.

The tilt angle δ was measured by forming a cell with a gap of 80 μm using the same 80 μm thick glass as a spacer as described above, slowly cooling from the isotropic phase while applying a magnetic field in the direction parallel to the substrate in the electromagnet, and performing horizontal alignment. A treated cell was prepared. An X-ray detector was fitted to the diffraction angle 2θ for which the layer spacing was obtained, the cell was θ-scanned, and δ was calculated by the method described in the above document. The value of δ measured by this measuring method is unique to the liquid crystal composition, in which the cell thickness dependency is almost eliminated.

Measurement of spontaneous polarization Ps It was measured by the triangular wave method.

Measurement of Pretilt Angle α J. A. P. 19 (1980) No. 10, Sho
It was determined according to the method (crystal rotation method) described in rt Notes 2013.

That is, the rubbed substrates were bonded in parallel and in opposite directions to form a cell having a cell gap of 20 μm, and the ferroelectric liquid crystal CS-1014 manufactured by Chisso Corporation was compounded with a compound represented by the following structural formula in a weight ratio. A mixture containing 20% was filled as a standard liquid crystal and measured.

[0074]

[Chemical 2]

The mixed liquid crystal composition had a composition of 10
It shows a SmA phase at 55 ° C.

The measuring method is as follows: while rotating the liquid crystal cell in a plane perpendicular to the upper and lower substrates and including the alignment treatment axis,
Helium-neon laser light with a polarization plane that makes an angle of ° is emitted from the direction perpendicular to the axis of rotation, and the intensity of the transmitted light is increased by the photodiode through a polarizing plate that has a transmission axis parallel to the incident polarization plane on the opposite side. It was measured.

The angle formed by the angle at the center of the hyperbola group of transmitted light intensity formed by interference and the line perpendicular to the liquid crystal cell is φ.
_The pretilt angle α was obtained by substituting _X into the following equation.

[0078]

[Equation 5] n _o: ordinary refractive index n _e: extraordinary refractive index

[0079]

EXAMPLES Examples of the present invention will be described below.

Example 1 A liquid crystal compound having the following structure

[0081]

[Chemical 3] Liquid Crystal Compositions 1-A to 1-R were prepared using the above as a main component (however, 1-C is ZLI-3774 manufactured by Merck). The phase transition temperature of this liquid crystal composition and 30 ° C.
The spontaneous polarization (Ps), tilt angle (Θ), and layer tilt angle (δ) at 55 ° C. are shown below.

[0082]

[Table 1]

[0083]

[Table 2]

Next, the optical response of these liquid crystal compositions was observed using a cell prepared by the following procedure.

A thin film of tantalum oxide was formed on a glass substrate having a transparent electrode by a sputtering method, and polyamic acid LQ1 manufactured by Hitachi Chemical Co., Ltd., represented by the above structural formula 1, was formed on the thin film.
802 1% NMP solution is applied with a spinner and 270 ° C.
It was baked for 1 hour.

Next, this substrate was rubbed, and it had an intersection angle of 8 ° (described above) with another substrate subjected to the same treatment, and a gap of about 1.2 to 1.3 μm was formed so as to be in the same direction. A cell was created by keeping and pasting. The pretilt angle α of the cell was 18 ° by the crystal rotation method.

The liquid crystal compositions 1-A to 1-R were injected into this cell in an isotropic liquid state, and the liquid crystal composition 1-A to 1-R was injected at 25 ° C. from the isotropic phase at 20 ° C./h.
A ferroelectric liquid crystal element was prepared by gradually cooling to.

Using this ferroelectric liquid crystal element, the orientation at 30 ° C. and 55 ° C. was observed, and the drive margin ΔV (V was obtained with the drive waveform (1/3 bias ratio) shown in FIG.
_3- V ₁ ) was measured and driveability was observed (however, ΔT is V
₁ = 15V).

In FIG. 9, S _N , S _{N + 1} , and S _{N + 2} represent voltage waveforms applied to the scanning lines, and I represents voltage waveforms applied to typical information lines. (S _N -I) and (S
_{N + 1-} I) is a composite waveform applied to the intersection of the scanning lines S _N and S _{N + 1} and the information line I.

The measurement results in this example are shown below. The orientation here means the orientation of the C1 uniform orientation when not driven, and the drivability means the maintenance of the C1 uniform orientation when driven (switching). Shows the drivability.

The parameters of the driving voltage margin are
It is defined by (V ₃ −V ₁ ) / (V ₃ + V ₁ ), and the larger this value is, the larger the margin of the driving voltage is.

The ranks of orientation and driveability were as follows.

Orientation ○ C1 uniform orientation × Other than C1 uniform orientation (splay orientation) Driving property ○ Switching of C1 uniform orientation × Switching other than C1 uniform orientation (splay orientation)

[0094]

[Table 3]

[0095]

[Table 4]

As is clear from this example, liquid crystal compositions (1-A, 1-B, 1-D, 1-A, 1-B, 1-D, which satisfy the conditional expressions Θ × δ> 70 and Θ × δ / Ps> 20 in the present invention. 1-
E, 1-G, 1-H, 1-I, 1-J, 1-K, 1-
L, 1-O, 1-P, 1-Q) is a liquid crystal element containing
A driving voltage margin is secured at 55 ° C.

Furthermore, a liquid crystal composition (1-A, 1-B, 1-D, 1-) that satisfies Θ × δ> 90 and Θ × δ / Ps> 25.
G, 1-H, 1-I, 1-J, 1-K, 1-L, 1-
The liquid crystal element containing O) has a driving voltage margin of 3.4 V or more at 55 ° C., and can be a liquid crystal element having a sufficiently wide driving margin in a high temperature range.

However, the liquid crystal element containing the liquid crystal composition 1-B has a wide driving voltage margin at 55 ° C., but at 30 ° C., δ <α and Θ / 2 <θ _a <
Since the condition of Θ was not satisfied, uniform orientation was not obtained at 30 ° C. Further, the liquid crystal element containing the liquid crystal composition 1-C also has δ <α and Θ / 2 <θ at 30 ° C.
_Since the condition of _a <Θ was not satisfied, uniform orientation was not obtained at 30 ° C.

Example 2 Liquid crystalline compound having the following structure

[0100]

[Chemical 4] A liquid crystal composition 2-A having as a main component was prepared.

The following liquid crystalline compound was added to this liquid crystal composition 2-A.

[0102]

[Chemical 5] 99: 1, 98: 2, 97: 3, 95: 5, 92:
Liquid crystal composition 2-B, 2 mixed in a ratio of 8,90: 10
-C, 2-D, 2-E, 2-F, 2-G were created, respectively.

The phase transition temperature of this liquid crystal composition and 30
The spontaneous polarization (Ps) at 55 ° C and 55 ° C, the tilt angle (Θ), and the layer tilt angle (δ) are shown below.

[0104]

[Table 5]

Next, instead of using the liquid crystal composition used in Example 1, the liquid crystal compositions 2-A, 2-B, 2-C and 2 were used.
A ferroelectric liquid crystal device was produced in the same manner as in Example 1 except that -D, 2-E, 2-F and 2-G were injected into the cell.

Then, in the same manner as in Example 1, 30 ° C. and 5
The orientation and driveability at 5 ° C. were observed and the same evaluation was performed. The measurement results in this example are shown below.

[0107]

[Table 6]

As is clear from this embodiment, even if Θ and δ are almost the same, when the value of Ps is gradually increased, the driving voltage margin at high temperature (55 ° C.) decreases. . Further, a liquid crystal composition (2-A, 2-B, 2-C, 2- that satisfies the conditional expressions Θ × δ> 70, Θ × δ / Ps> 20 in the present invention.
The liquid crystal element containing D, 2-E) has a drive voltage margin at 55 ° C.

Furthermore, liquid crystal compositions (2-A, 2-B, 2-C, 2- that satisfy Θ × δ> 90 and Θ × δ / Ps> 25 are satisfied.
The liquid crystal element containing D) has a driving voltage margin of 3.4 V or more at 55 ° C., and can be a liquid crystal element having a sufficiently wide driving margin in a high temperature range.

Example 3 Liquid crystalline compound having the following structure

[0111]

[Chemical 6] A liquid crystal composition 2-A having as a main component was prepared.

The following liquid crystal compound was added to this liquid crystal composition 2-A.

[0113]

[Chemical 7] Were mixed at a ratio of 98: 2, 97: 3, 94: 6, 91: 9 to prepare liquid crystal compositions 3-A, 3-B, 3-C and 3-D, respectively.

The phase transition temperature of this liquid crystal composition and 30
The spontaneous polarization (Ps) at 55 ° C and 55 ° C, the tilt angle (Θ), and the layer tilt angle (δ) are shown below.

[0115]

[Table 7]

Next, instead of using the liquid crystal composition used in Example 1, the liquid crystal compositions 2-A, 3-A, 3-B and 3 were used.
A ferroelectric liquid crystal element was produced in the same manner as in Example 1 except that -C and 3-D were injected into the cell.

Then, in the same manner as in Example 1, 30 ° C. and 5
The orientation and driveability at 5 ° C. were observed and the same evaluation was performed. The measurement results of this example are shown below.

[0118]

[Table 8]

As is clear from this example, Θ × δ / Ps
However, if the values of Θ and δ are gradually reduced, the drive voltage margin at high temperature (55 ° C.) decreases. Further, a liquid crystal composition (2-A, 3-A, 3-B, 3- that satisfies the conditional expressions Θ × δ> 70 and Θ × δ / Ps> 20 in the present invention.
The liquid crystal element containing C) has a driving voltage margin at 55 ° C.

Further, the liquid crystal element containing the liquid crystal composition (2-A, 3-A, 3-B) satisfying Θ × δ> 90 and Θ × δ / Ps> 25 has a driving voltage margin at 55 ° C. Is 3.4 V or more, and a liquid crystal element having a sufficiently wide driving margin in a high temperature range can be obtained.

Example 4 Liquid Crystal Composition 1-A, 1-B, 1-Used in Example 1
Using D, 1-I, 1-P, 1-Q and 1-R, a cell was prepared in the same manner as in Example 1 so that the intersection angle (described above) was 6 °. The pretilt angle α of the cell was 16 ° by the crystal rotation method.

Liquid crystal composition 1-A, 1-B, 1 was added to this cell.
-D, 1-I, 1-P, 1-Q, 1-R was injected into the cell to prepare a ferroelectric liquid crystal element.

Then, in the same manner as in Example 1, 30 ° C. and 5
The orientation and driveability at 5 ° C. were observed and the same evaluation was performed. The measurement results in this example are shown below.

[0124]

[Table 9]

As is clear from this example, a liquid crystal composition satisfying the conditional expressions Θ × δ> 70 and Θ × δ / Ps> 20 in the present invention even when the device structure according to the present invention is changed. (1-A, 1-B, 1-D, 1-
The liquid crystal element containing I, 1-P, 1-Q) has a drive voltage margin at 55 ° C.

Furthermore, a liquid crystal composition (1-A, 1-B, 1-D, 1-) that satisfies Θ × δ> 90 and Θ × δ / Ps> 25.
The liquid crystal element containing I) has a driving voltage margin of 3.4 V or more at 55 ° C., and can be a liquid crystal element having a sufficiently wide driving margin in a high temperature range.

However, the liquid crystal element containing the liquid crystal composition 1-B has a wide driving voltage margin at 55 ° C., but at 30 ° C., δ <α and Θ / 2 <θ _a <
Since the condition of Θ was not satisfied, uniform orientation was not obtained at 30 ° C.

Example 5 Using the ferroelectric liquid crystal device injected with the liquid crystal compositions 1-A to 1-R used in Example 1, the orientation at 30 ° C. and 55 ° C. was observed, and Is different from the drive margin ΔV with the drive waveform (1/3 bias ratio) shown in FIG.
(V ₃ −V ₁ ) was measured (where ΔT is V _I = 15V
Was set. ).

The method of evaluating the orientation and the drivability is the same as in Example 1.

The measurement results in this example are shown below.

[0131]

[Table 10]

[0132]

[Table 11]

As is clear from this example, a liquid crystal composition (1) which satisfies the conditional expressions Θ × δ> 70 and Θ × δ / Ps> 20 in the present invention even when the driving method waveform is changed. -A, 1-B, 1-D, 1-
E, 1-G, 1-H, 1-I, 1-J, 1-K, 1-
L, 1-O, 1-P, 1-Q) is a liquid crystal element containing
A driving voltage margin is secured at 55 ° C.

Furthermore, a liquid crystal composition (1-A, 1-B, 1-D, 1-) that satisfies Θ × δ> 90 and Θ × δ / Ps> 25.
G, 1-H, 1-I, 1-J, 1-K, 1-L, 1-
The liquid crystal element containing O) has a driving voltage margin of 3.4 V or more at 55 ° C., and can be a liquid crystal element having a sufficiently wide driving margin in a high temperature range.

However, the liquid crystal element containing the liquid crystal composition 1-B has a wide driving voltage margin at 55 ° C., but at 30 ° C., δ <α and Θ / 2 <θ _a <
Since the condition of Θ was not satisfied, uniform orientation was not obtained at 30 ° C. Further, the liquid crystal element containing the liquid crystal composition 1-C also has δ <α and Θ / 2 <θ at 30 ° C.
_Since the condition of _a <Θ was not satisfied, uniform orientation was not obtained at 30 ° C.

Example 6 Liquid Crystal Compositions 1-D, 1- used in Examples 1, 2 and 3
The values of the tilt angle Θ, the layer tilt angle δ, and the spontaneous polarization P _s of J, 1-K, 1-Q, 2-A, and 3-D at 10 ° C are shown below.

[0137]

[Table 12]

The same cells as those used in Examples 1, 2, and 3 into which these liquid crystal compositions were injected were sequentially subjected to matrix driving using the driving waveforms shown in FIG. 9 as in Example 1. . However, the bias ratio is 1/3, the drive voltage V ₁
Was fixed at 15 V and 20 V, and the speed was adjusted by changing ΔT for evaluation.

The results are shown below.

[0140]

[Table 13]

In the above table, the symbols o, Δ, and x represent the following contents.

When ΔTmin is the minimum value of the variable range of ΔT at which good switching between two stable states of C1 uniform orientation is ensured, ◯: C2 orientation does not appear even at ΔT of ΔTmin × 1.5 or less Δ : C2 orientation does not appear in ΔTmin, but ΔTmin
C2 orientation appears when driven with ΔT of × 1.5. ×: C2 orientation appears even with ΔTmin.

As is clear from this table, the liquid crystal composition in which δ is larger than Θ / 3 is a cell in which C2 orientation does not appear and good switching characteristics are obtained when V ₁ = 15 V driving at 10 ° C. .

A liquid crystal composition having δ larger than Θ / 2 is
The C2 orientation does not appear even when driving V ₁ = 20V.

On the other hand, in the liquid crystal composition (3-C) in which δ is smaller than Θ / 3, C2 is not exceeded even when driven at 15V.
Orientation appears, preventing good switching.

Comparative Example 1 Liquid Crystal Compositions 1-B and 1-C used in Example 1 were prepared at 45 ° C.
The values of the tilt angle Θ, the layer inclination angle δ, and the spontaneous polarization P _S at are shown below.

[0147]

[Table 14]

When the drivability was observed at 45 ° C. for the cell in which these liquid crystals were injected exactly as in Example 1, a splay alignment region appeared considerably and a large driving margin could not be obtained. This is Θ is α
This is because it is larger than (18 °).

[0149]

As described above, according to the present invention, the relationship between the tilt angle (θ), the tilt angle (δ) of the liquid crystal layer, and the spontaneous polarization (Ps) is defined, whereby the high temperature environment It is possible to prevent a decrease in the driving margin below, to realize a good image with a high contrast in the C1 uniform orientation state within the operating environment temperature range, and to realize a wide driving margin, so that it can be used in a large screen display device. A good image can be obtained in the entire display area.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of a liquid crystal display of the present invention.

FIG. 2 is an explanatory diagram of C1 and C2.

FIG. 3 is an explanatory diagram showing a relationship among a tilt angle, a pretilt angle, and a layer tilt angle in C1 and C2 orientations.

FIG. 4 is a schematic diagram showing the arrangement of directors at various positions between substrates in each C1-oriented state.

FIG. 5 is a waveform diagram of a driving method used in the description of the conventional technique and in the fifth embodiment.

FIG. 6 is a plan view of a liquid crystal panel in which matrix electrodes are arranged.

FIG. 7 is a schematic diagram of a display pattern when actual driving is performed with the time-series driving waveform shown in FIG.

FIG. 8 is a (VT characteristic diagram) graph showing the change in transmittance when the drive voltage is changed.

FIG. 9 is a waveform diagram of the driving method used in the examples.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Electrode 13a, 13b Insulating film 14a, 14b Alignment control film 15 Chiral smectic liquid crystal 16 Bead spacer 17a, 17b Polarizing plate 31 Chevron structure 32 C1 alignment 33 C2 alignment 41 Cone 45, 46 Spray alignment state 47, 48 uniform alignment state 51 liquid crystal panel 52 scanning electrode group 53 information electrode group

Front Page Continuation (72) Inventor Shuji Yamada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yu Mizuno 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Ichiharu Katagiri 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A chiral smectic liquid crystal, and an electrode for applying a voltage to the liquid crystal is formed on each of the opposing surfaces of the chiral smectic liquid crystal while sandwiching the liquid crystal, and a uniaxial alignment axis for aligning the liquid crystal is formed. In a liquid crystal element including a pair of substrates that have been subjected to an alignment process of intersecting or parallel to each other at a predetermined angle, the pretilt angle of the liquid crystal element is α (degrees),
When the tilt angle of the liquid crystal is Θ (degrees) and the tilt angle of the liquid crystal layer is δ (degrees) in the temperature range of 10 ° C. to 55 ° C., the liquid crystal has an alignment state represented by the following formula (I). , And exhibit at least two stable states in this orientation,
The apparent tilt angle θ _a (degree), which is ½ of the angle formed by the optical axes, and the tilt angle Θ satisfy the relationship of the following formula (II), and Θ <α + δ and δ <α (I) Θ > Θ _a > θ / 2 (II) Furthermore, the magnitude of spontaneous polarization of the liquid crystal composition is defined as Ps (nC /
cm ² ), Ps, Θ and δ at 55 ° C. are expressed by the following formulas (III) and (IV) A liquid crystal element characterized by satisfying the relationship of. 2. Ps, Θ and δ at 55 ° C. are expressed by the following equations (V) and (VI): 2. The liquid crystal element according to claim 1, wherein the relationship is satisfied. 3. The liquid crystal device according to claim 1, wherein the liquid crystal has a phase transition temperature from a smectic A phase to a chiral smectic C phase of 60 ° C. or higher. 4. The tilt angle Θ in the temperature range of 10 ° C. to 55 ° C. satisfies the relationship of the following (VII) formula Θ <α (VII). Liquid crystal element. 5. A chiral smectic liquid crystal, and an electrode for applying a voltage to the liquid crystal, which is opposed to the liquid crystal with the liquid crystal sandwiched therebetween, and which has a uniaxial alignment axis for aligning the liquid crystal. In a liquid crystal element including a pair of substrates that have been subjected to an alignment process of intersecting or parallel to each other at a predetermined angle, the pretilt angle of the liquid crystal element is α (degrees),
When the tilt angle of the liquid crystal is Θ (degrees) and the tilt angle of the liquid crystal layer is δ (degrees) in the temperature range of 10 ° C. to 55 ° C., the liquid crystal has an alignment state represented by the following formula (I). , And exhibit at least two stable states in this orientation,
The apparent tilt angle θ _a (degree), which is ½ of the angle formed by the optical axes, and the tilt angle Θ satisfy the relationship of the following formula (II), and Θ <α + δ and δ <α (I) Θ > Θ _a > Θ / 2 (II) Furthermore, δ and Θ at 10 ° C. satisfy the following equation (VIII) δ> Θ / 3 (VIII). 6. A chiral smectic liquid crystal, and an electrode for applying a voltage to the liquid crystal is formed on each of the opposing surfaces of the liquid crystal while sandwiching the liquid crystal, and a uniaxial alignment axis for aligning the liquid crystal is formed. In a liquid crystal element including a pair of substrates that have been subjected to an alignment process of intersecting or parallel to each other at a predetermined angle, the pretilt angle of the liquid crystal element is α (degrees),
When the tilt angle of the liquid crystal is Θ (degrees) and the tilt angle of the liquid crystal layer is δ (degrees) in the temperature range of 10 ° C. to 55 ° C., the liquid crystal has an alignment state represented by the following formula (I). , And exhibit at least two stable states in this orientation,
The apparent tilt angle θ _a (degree), which is ½ of the angle formed by the optical axes, and the tilt angle Θ satisfy the relationship of the following formula (II), and Θ <α + δ and δ <α (I) Θ > Θ _a > Θ / 2 (II) Furthermore, δ and Θ at 10 ° C. satisfy the following equation (IX): δ> Θ / 2 (IX). 7. The δ and Θ at 10 ° C. are as follows (V
III) The liquid crystal element according to any one of claims 1 to 4, which satisfies a relation of δ> Θ / 3 (VIII). 8. The values of δ and Θ at 10 ° C.
X) The formula δ> Θ / 2 (IX) is satisfied, and the liquid crystal element according to any one of claims 1 to 4.