JPH08211393A - Method for manufacturing liquid crystal electro-optical element - Google Patents

Abstract

(57) Abstract: Molecular orientation exhibits a first stable state when there is no electric field, and a second stable state where the molecular orientation is different from the first stable state when an electric field is applied in one electric field direction. , Facilitating the production of a liquid crystal electro-optical element when a ferroelectric liquid crystal whose molecular orientation exhibits a third stable state different from the first and second stable states when an electric field is applied in the other electric field direction To do. SOLUTION: The above-mentioned ferroelectric liquid crystal is heated and filled as an isotropic liquid between a pair of electrode substrates, and then cooled to make the ferroelectric liquid crystal into a chiral smectic phase to form a liquid crystal cell.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal electro-optical device.

2. Description of the Related Art As an electro-optical device using a liquid crystal, D
Electro-optical devices using nematic liquid crystals such as SM type, TN type, G / H type and STN type have been developed and put into practical use. However, all of those using such a nematic liquid crystal have a drawback that the response speed is extremely slow from several msec to several tens msec. Against this background,
A ferroelectric liquid crystal having a high-speed response has been developed, and some high-speed electro-optical devices using the ferroelectric liquid crystal have already been proposed. For example, as shown in JP-A-56-107216, a twist structure is unraveled by the force of a wall surface and two molecular orientations parallel to the wall surface are changed by the polarity of an applied electric field, or JP-A-60-195521. As shown in Japanese Patent Laid-Open Publication No. 2003-242242, there is one utilizing a transient molecular scattering state that occurs when the polarity of an applied electric field is reversed.

However, in the conventional ferroelectric liquid crystal, there are problems in that a stable molecular orientation with a clear contrast of light and dark in the absence of an electric field is realized and a clear threshold characteristic appears. is there. The present inventors, as a result of earnest research on such problems,
We have developed a ferroelectric liquid crystal with a structural formula as described below. In this ferroelectric liquid crystal, the molecular orientation exhibits a first stable state when there is no electric field, and the second molecular orientation shows a second stable state which is different from the first stable state when an electric field is applied in one electric field direction, When an electric field is applied in the other electric field direction, the molecular orientation shows a third stable state different from the first and second stable states. An object of the present invention is to facilitate the manufacture of a liquid crystal electro-optical element using such a ferroelectric liquid crystal.

In order to achieve the above object, in the invention described in claim 1, the above-mentioned ferroelectric liquid crystal is heated to fill it as an isotropic liquid between a pair of electrode substrates, and thereafter, It is characterized by cooling the ferroelectric liquid crystal to a chiral smectic phase. By heating the ferroelectric liquid crystal to make it an isotropic liquid in this manner, it is possible to facilitate filling between the electrode substrates, and by cooling after filling, the ferroelectric liquid crystal is made to have a chiral smectic phase. Thus, a liquid crystal having the above-mentioned desired three states can be obtained. The cooling is preferably performed at a rate of 0.1 to 1.0 ° C. per minute as in the invention described in claim 2.

FIG. 1 shows the structure of a liquid crystal electro-optical device which is an embodiment of the present invention. For example, 2μ
A spontaneous polarization of at least 50 nC / is provided between two electrode substrates 1 and 2 which are spaced apart by m and are arranged in parallel with each other.
The ferroelectric liquid crystal material 6 of cm ² or more is sealed. As the ferroelectric liquid crystal material, a liquid crystal material (TFM) having a structural formula shown in Chemical formula 1 is used.
HPOBC).

Embedded image [4- (1- t ri f luoro m ethyl h eptyloxycarbony
l) p henyl 4'- o ctyloxy b iphenyl -4- c arbox
ylate] As shown in FIG. 1, the electrode substrate 1 has an electrode 1a made of a transparent conductive film such as indium oxide or tin oxide along the inner surface of a transparent glass or resin transparent substrate 1c. The other electrode substrate 2 has the same configuration. On the inner surfaces of the transparent electrodes 1a and 2a of the conductive film, alignment films 1b and 2b of a polymer film which have been subjected to an alignment treatment for aligning liquid crystal molecules in parallel with the substrate are arranged. In addition to the above, rubbing treatment on the electrode substrate, oblique vapor deposition of silicon oxide or the like on the surface, treatment with a surfactant, or the like for generally aligning liquid crystals can be applied. The electrode substrates 1 and 2 are combined in parallel so that liquid crystals are arranged in one direction. After that,
The ferroelectric liquid crystal material of the formula is heated to be an isotropic liquid and is injected between the electrode substrates 1 and 2 by utilizing a capillary phenomenon, and then the whole liquid crystal cell is heated at 0.1 to 1.0 ° C. per minute. After cooling, the chiral smectic C phase is cooled. As a result of such cooling, the ferroelectric liquid crystal molecules 20 in the chiral smectic C phase are oriented as shown in FIG. 2A due to the large polarization of the liquid crystal molecules themselves and the order of the liquid crystals. The polarizing plates 4 and 5 on the outer sides of the electrode substrates 1 and 2 are arranged so as to be orthogonal to each other. Furthermore, the polarizer (P) of this polarizing plate is oriented such that the long axis direction of the liquid crystal molecules in the absence of an electric field forms an angle of 0 ° (180 °). An external power supply 3 including a drive circuit is connected to the transparent electrodes 1a and 2a, and a voltage waveform as described later is applied to the liquid crystal. Next, the operation of the above device will be described with reference to FIGS. 2 (a), 2 (b) and 2 (c).
Here, each left figure is a plan view of the apparatus, and each right figure is a side view. Liquid crystal molecules 20 between the substrates 1 and 2 when no electric field is applied
Are aligned in the normal direction of the smectic layer 10, and FIG.
The alignment state shown in (a) is shown. At this time, the spontaneous polarization of the liquid crystal molecules is directed leftward (or rightward) in the upper half of the device (cell) and rightward (or leftward) in the lower half, that is,
If it is explained on the cone where the ferroelectric liquid crystal molecules move (Fig. 2
(A) The right figure), the molecule is located above (or below) the cone in the upper half of the cell, and below (or above) the cone in the lower half, and the cumulative value of spontaneous polarization in the cell thickness direction becomes zero. Become. Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper surface is applied, the spontaneous polarization direction 30 of the liquid crystal molecules is aligned with the electric field direction 40. Along with this, the liquid crystal molecules are realigned as shown in FIG. At this time, the liquid crystal molecules form a tilt angle θ with respect to the layer normal direction. Incidentally, the tilt angle of the ferroelectric liquid crystal material of Formula 1 is 10 ° C. to 31 ° C. within the temperature range of 70 ° C. to 110 ° C. Then, when an electric field sufficient to rotate the liquid crystal molecules from the back side of the paper to the front side is applied, the spontaneous polarization 30 is aligned with the electric field direction 40. Along with this, the liquid crystal molecules are realigned as shown in FIG. At this time, the liquid crystal molecules form a tilt angle of −θ from the layer normal direction.
Thus, the optical axis of the liquid crystal can be changed to three states depending on the polarity and magnitude of the applied electric field. By sandwiching a liquid crystal having such three states between a pair of polarizing plates 4 and 5, it can be used as an electro-optical device. For example,
As shown in FIG. 2 (a), the polarizer (P) of the polarizing plate and the liquid crystal molecule major axis direction are installed so as to form an angle of 0 °. The linearly polarized light that has passed through the polarizer (P) in this state passes through the liquid crystal, but is blocked by the analyzer (A), resulting in a dark state. Further, in the case of FIG. 2B in which an electric field is applied from the front side to the back side of the paper surface, the light passing through the polarizer (P) is generally elliptically polarized light due to the birefringence effect of the liquid crystal. Since this light component passes through the analyzer (A), it is in a bright state. In the case of FIG. 2C in which an electric field is applied from the back side of the paper to the front side, the light passing through the polarizer (P) is generally elliptically polarized light due to the birefringence effect of the liquid crystal. The component of this light also passes through the analyzer (A), and thus becomes a bright state. Next, the voltage-transmittance curve of this device will be described. The polarizer (P) is installed so that the direction of the long axis of the molecule with respect to the polarization axis of the polarizer (P) is 0 °, and the threshold is a voltage at which the luminance changes by 10%. FIG. 3 shows a voltage waveform used for the measurement, the applied pulse width is 1 msec, and the voltage is repeatedly applied at a constant cycle. The optical response at this time is shown in FIG. It can be seen that it is in a dark state when there is no electric field, but is in a bright state while a voltage is applied. FIG. 5 shows a plot of light transmittance with respect to voltage when this electric field is applied. When the voltage is increased from 0 (V), the threshold value of 1 is exceeded and the dark state is rapidly changed to the bright state, but thereafter, it becomes constant. Next, when the voltage is reduced, the threshold value 1 at the time of increasing the voltage is passed, and then the threshold value 2 changes from the bright state to the dark state. When the voltage is further reduced, the threshold value 3 is exceeded again and the dark state is changed to the bright state, but thereafter it becomes constant. Next, when the voltage is increased, it can be seen that after the threshold value 3 at the time of the voltage decrease, the threshold value 4 changes from the bright state to the dark state. Thus, with a clear threshold,
There is a large hysteresis. Next, the temperature dependence of the response speed of this device was measured using the ferroelectric liquid crystal material represented by Chemical formula 1. The response speed was defined as the time required for the light transmittance to change to 90% after voltage application. The measured voltage waveform is a square wave of 10 Hz and the voltage is 30 (V).
Is. FIG. 6 shows the temperature dependence of the response speed. It shows a high-speed response in the μsec range. Regarding the orientation of the liquid crystal molecules, the twisted state observed with the conventional ferroelectric liquid crystal when no electric field was applied was observed, and only one stable orientation state was observed. The orientation of the previous chiral smectic C phase can be reproduced by increasing the temperature after cooling once to bring it into a crystalline state and then changing the temperature to a chiral smectic C phase. In the above-described embodiment, the polarizer (P) of the polarizing plate and the molecular long axis direction in the absence of an electric field form an angle of 0 ° (180 °), but for example, 22.5 °, 45. ° or 90 °
May be configured to form an angle of, for example, 22.5
In the case of °, when the electric field is applied, one electric field direction shows a dark state, the other electric field direction shows a bright state, and when there is no electric field, it shows an intermediate state. This configuration (22.5
The molecular orientation of the three states was confirmed by the transmittance and the polarization reversal current with respect to the triangular wave voltage. The voltage waveform used for the measurement is a triangular wave voltage of ± 30 (V) and 10 (Hz). The transmittance and polarization reversal current at two temperatures when this waveform is applied are shown in FIGS. 7 and 8. In the figure, (a) shows the applied voltage waveform, (b) shows the transmittance, and (c) shows the polarization reversal current waveform. The transmittance (b) clearly shows a dark state in the negative range, an intermediate bright state in the 0 volt range, and a bright state in the positive range. Regarding the polarization reversal current (c),
It can be seen that the peaks of the polarization reversal current waveforms respectively appear corresponding to the above state changes. In addition, the electrode substrate 1,
2, a plurality of stripe-shaped transparent electrodes 1a, 2a are formed in parallel as shown in FIG.
The electrodes of the substrate 2 are arranged so as to be orthogonal to each other, and an external power source including a circuit capable of being dynamically driven is connected to the electrodes to form a matrix type display device. It is also possible to drive using the hysteresis characteristics shown. Here, the line sequential method of the dynamic driving method will be described. As an example, 1/3
The bias method will be described with reference to FIG. X indicates an electrode (scan electrode) that is line-sequentially scanned, and Y indicates an electrode (signal electrode) to which a signal voltage is applied. The points marked with ○ indicate points to be displayed (selected points), and the points without marks indicate points to retain the display (non-selected points). + For the electrode selected in the scan electrode
2V is applied, and 0V is applied to the non-selected electrodes.
On the signal electrode side, -1V is applied to the selected electrode and + 1V is applied to the non-selected electrode. In this way, a voltage of 3V is applied to the selected points, and -1 is applied to the other non-selected points.
V or + 1V will be applied. When the dynamic driving is performed as described above, the bias voltage is applied to the non-selected points, so that it is necessary that the bias voltage is not more than the threshold voltage range applied to the non-selected points. Further, the voltage applied to the non-selected point is set between the threshold value 1 and the threshold value 2 in FIG. 5, the voltage between threshold values 2 and 3 is set at the dark display point, and the voltage applied to the bright display point is set as the threshold value. If it is set higher than 1, it is possible to easily carry out dynamic driving with a high contrast ratio and capable of maintaining display. The present invention is not limited to the transmissive type in which display is performed by illumination from the back surface, but can be applied to the reflective type in which light from the entire surface is reflected. By the way, as the liquid crystal material having a large spontaneous polarization used in the device of the present invention, the following structural formula (TFMNPOBC) can also be used.

Embedded image [4- (1- t ri f luoro m ethyl n onyloxy carbony
l) p henyl 4'- o ctyloxy b iphenyl -4- c arbox
ylate] FIG. 11 shows the transmittance characteristic and the polarization reversal current characteristic when a triangular wave voltage (± 30 V, 10 Hz) is applied to this liquid crystal material, and shows the same three states as those of the above-mentioned liquid crystal material. Further, as another liquid crystal material having a large spontaneous polarization, one having the following structural formula (MHPOBC) can also be used.

Embedded image [4- (1- m ethyl h eptyloxy carbonyl ) p henyl
4'- o ctyloxy b iphenyl -4- c arboxylate] shows the transmission characteristics and polarization reversal current characteristics when the same is applied to the triangular wave voltage to the liquid crystal material 12, have been obtained three states described above. Next, FIG. 13 shows the value of the spontaneous polarization Ps at which the three states of the transmittance appear for the above three liquid crystal materials. All three types of liquid crystals show three states when they have a large spontaneous polarization of 50 (nC / cm ² ) or more. A general triangular wave method was used for measuring the spontaneous polarization. In addition to the above three liquid crystal materials, other liquid crystal materials have the following structural formula (TFMH
B2FDB) can be used.

[Chemical 4] [4- (1- t ri f luoro m ethyl h eptyloxy carbony
l) -4'- b iphenyl 2 - f luoro -4- d ecyloxy
b enzoate] The phase transition of this compound was measured by differential thermal analysis (DSC) and texture observation under a polarizing microscope. Here, Cry: crystal phase, SmC ^* : chiral smectic C phase (ferroelectric liquid crystal phase), SmA: smectic A
Phase, I: indicates an isotropic liquid phase. When the spontaneous polarization of this compound in the ferroelectric smectic phase was measured using a general triangular wave method, the characteristics shown in FIG. 14 were obtained. Also,
The appearance of the above-mentioned three states extends over the entire area of the ferroelectric smectic phase, that is, over the range of about 4 [nC / cm ² ] to about 80 [nC / cm ² ] in terms of the magnitude of spontaneous polarization.
Note that FIG. 15 shows the transmittance characteristic (b) and the polarization inversion characteristic (c) when the triangular wave voltage (a) is applied at 55 ° C., and it can be seen that the three states described above are shown. Further, among the above four kinds of compounds, TFMHPOB is used for increasing the room temperature of the ferroelectric smectic phase temperature range and expanding it.
C, MHPOBC and TFMHB2FDB were mixed in the following ratios, and TFMHPOBC ...... 20% MHPOBC ...... 46% TFMHB2FDB ...... 34% The phase transition was measured by differential thermal analysis (DSC) and a polarization microscope. The result was obtained. The mixture was sealed in a liquid crystal cell, the transmittance characteristics and the polarization reversal current when a triangular wave voltage was applied were measured, and the appearance of the three states was examined. Was observed. 16 shows a structure of a liquid crystal electro-optical device which is another embodiment of the present invention. In the present embodiment, for example, spontaneous polarization is at least 50 nC / cm between two electrode substrates 1 and 2 which are spaced apart by 2 μm and arranged in parallel with each other.
^Two or more ferroelectric liquid crystal materials in which a dichroic dye is dissolved 6'are sealed. As the ferroelectric liquid crystal material, for example, the above-mentioned four liquid crystal materials (TFMHPOBC, TFMN) are used.
POBC, MHPOBC, TFMHB2FDB). Further, as the dichroic dye, for example, S-334 (azo black dichroic dye) manufactured by Mitsui Toatsu Co., Ltd. is used, and the ferroelectric liquid crystal is heated to an isotropic liquid phase,
2 wt% of the dichroic dye is added and dissolved. After that, after injecting between the electrode substrates 1 and 2 by utilizing the capillary reduction, the entire liquid crystal cell is gradually cooled at 0.1 to 1.0 ° C. per minute and cooled to a chiral smectic C phase. As a result of such cooling, the ferroelectric liquid crystal molecules 20 that have become the chiral smectic C phase are oriented as shown in FIG. 17A due to the large polarization of the liquid crystal molecules themselves and the order of the liquid crystals. In addition, in this embodiment, the polarizing plate 5 is arranged only outside the electrode substrate 2. Further, the direction of the major axis of the liquid crystal molecule in the absence of an electric field is 0 ° (180
Angle). An external power supply 3 including a drive circuit is connected to the transparent electrodes 1a and 2a, and the voltage waveform as described above is applied to the liquid crystal.
Next, referring to FIG. 17 (a),
This will be described with reference to (b) and (c). Here, each left figure is a plan view of the apparatus, and each right figure is a side view. When no electric field is applied, the liquid crystal molecules 20 between the substrates 1 and 2 are aligned in the normal direction of the smectic layer 10 and have the alignment state shown in FIG. At this time, the spontaneous polarization of the liquid crystal molecules is directed to the left (or right) in the upper half of the device (cell) and to the right (or left) in the lower half, that is, on the cone where the ferroelectric liquid crystal molecules move. In the upper half of the cell, the molecule is located above (or below) the cone, and in the lower half below (or above) the cone, and spontaneously in the cell thickness direction. The integrated value of polarization becomes zero. At this time, the dichroic dye 21 is dispersed in the liquid crystal molecules 20,
The liquid crystal molecules 20 are oriented in the same direction as the long axis direction. Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper surface is applied, the spontaneous polarization direction 30 of the liquid crystal molecules is aligned with the electric field direction 40. As a result, the liquid crystal molecules are shown in FIG.
Reorient as in (b). At this time, the liquid crystal molecules form a tilt angle θ with respect to the layer normal direction. By the way, the tilt angle of the dichroic dye dissolved in the ferroelectric liquid crystal material of Formula 1 is 10 ° to 31 ° within the temperature range of 70 ° C to 110 ° C. Also in this case, the dichroic dye 21 moves according to the movement of the liquid crystal molecules 20. Next, when an electric field sufficient to rotate the liquid crystal molecules from the back side of the paper to the front side is applied, the spontaneous polarization 30
Follow the electric field direction 40. Along with this, the liquid crystal molecules are realigned as shown in FIG. At this time, the liquid crystal molecules form a tilt angle of −θ from the layer normal direction. Also in this case, the dichroic dye 21 moves according to the movement of the liquid crystal molecules 20. In this way, the optical axis of the liquid crystal is set to 3 depending on the polarity and magnitude of the applied electric field.
It can be changed to a state. By attaching the polarizing plate 5 to the liquid crystal having such three states, it can be used as an electro-optical device. For example, as shown in FIG. 17A, the polarizer (P) of the polarizing plate and the liquid crystal molecule long axis direction are arranged so as to form an angle of 0 °. In this state, the linearly polarized light passing through the polarizer (P) has a polarization direction that coincides with the absorption axis of the dichroic dye and is absorbed, so that it becomes a dark state.
17B in which an electric field is applied from the front side to the back side of the paper surface.
17 and when an electric field was applied from the back side of the paper to the front side.
In the case of (c), since the polarization direction of linearly polarized light passing through the polarizer (P) does not match the absorption axis of the dichroic dye,
Light is transmitted and it becomes a bright state. The polarizing plate 5 may be provided outside the electrode substrate 1. The optical response, the light transmittance, the temperature dependence of the response speed, the orientation of the liquid crystal molecules, and the like in this embodiment are substantially the same as those in the above embodiments. In addition, in this embodiment, the polarizer (P) of the polarizing plate and the molecular long-axis direction (dichroic dye molecule long-axis direction) in the absence of an electric field form an angle of 0 ° (180 °). However, for example, it may be configured to form an angle of 45 ° or 90 °. For example, in the case of 90 °, when an electric field is applied, one electric field direction shows a dark state and the other electric field direction shows a bright state. , Shows an intermediate state when there is no electric field 2
It is possible to display gradation in stages. Further, the dichroic dye is not limited to the azo type dichroic dye, and an anthraquinone type dichroic dye having good light resistance can also be used.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a liquid crystal electro-optical device showing an embodiment of the present invention.

2 (a), (b) and (C) are diagrams showing alignment states of liquid crystal molecules in the device shown in FIG.

FIG. 3 is a voltage waveform diagram used for measuring the relationship between the liquid crystal voltage and the transmittance.

FIG. 4 is a diagram showing changes in transmittance when the voltage of FIG. 3 is applied to liquid crystal.

FIG. 5 is a diagram showing a relationship between a voltage of liquid crystal and a transmittance.

FIG. 6 is a characteristic diagram showing the relationship between the response speed of liquid crystal and temperature.

FIG. 7 is a diagram showing a transmittance and a polarization reversal current with respect to a triangular wave voltage.

FIG. 8 is a diagram showing the transmittance and polarization reversal current for a triangular wave voltage at a temperature different from that shown in FIG. 7.

FIG. 9 is a diagram showing another configuration of the liquid crystal electro-optical device of the present invention.

FIG. 10 is an explanatory diagram for explaining a dynamic driving method.

FIG. 11 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in another liquid crystal material.

FIG. 12 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in still another liquid crystal material.

FIG. 13 is a diagram showing the values of spontaneous polarization at which three states of transmittance with respect to three liquid crystal materials appear.

FIG. 14 is a diagram showing temperature dependence of spontaneous polarization in still another liquid crystal material.

15 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in the liquid crystal shown in FIG.

FIG. 16 is a configuration diagram of a liquid crystal electro-optical device showing another embodiment of the present invention.

17 is a diagram showing an alignment state of liquid crystal molecules in the device shown in FIG.

[Explanation of symbols]

1, 2 ... Electrode substrate, 1a, 2a ... Transparent electrodes, 1b, 2b
... Alignment film, 1c, 2c ... Transparent substrate, 4, 5 ... Polarizing plate,
6, 6 '... Ferroelectric liquid crystal, 10 ... Smectic layer, 20
... liquid crystal molecule, 21 ... dichroic dye, 30 ... spontaneous polarization direction,
40 ... electric field direction, 50 ... polarization direction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Yamamoto 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd. (72) Inventor Ichiro Kawamura 2-3-7 Marunouchi, Chiyoda-ku, Tokyo Showa Inside Shell Oil Co., Ltd.

Claims (2)

[Claims] 1. A molecular orientation exhibits a first stable state when no electric field is applied, and a molecular orientation exhibits a second stable state different from the first stable state when an electric field is applied in one electric field direction, and A ferroelectric liquid crystal (6) having a third stable state in which the molecular orientation is different from the first and second stable states when an electric field is applied in the direction of the electric field is provided between the pair of electrode substrates (1, 2). In the method for producing a liquid crystal electro-optical element, the ferroelectric liquid crystal is heated to fill the space between the pair of electrode substrates as an isotropic liquid, and then cooled to bring the ferroelectric liquid crystal into a chiral smectic phase. A method of manufacturing a liquid crystal electro-optical device, comprising: 2. The method for manufacturing a liquid crystal electro-optical device according to claim 1, wherein the cooling is performed at a rate of 0.1 to 1.0 ° C. per minute.