JPH1068920A - Production of liquid crystal electro-optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a liquid crystal electro-optical element using a ferroelectric liquid crystal which shows first to third stable states according to electric fields, by heating the ferroelectric liquid crystal to change into an isotropic liquid, filling the space between substrates with the isotropic liquid, and cooling the liquid to change into a chiral smectic phase. SOLUTION: A ferroelectric liquid crystal 6 in which the molecular orientation shows different first to third stable states when no electric field is applied or an electric field in one direction or an electric field in other direction is applied, respectively, is heated to obtain an isotropic liquid. The obtd. isotropic liquid is supplied to fill the space between a pair of electrode substrates 1, 2 and cooled to obtain a chiral smectic phase of the ferroelectric liquid crystal 6. By changing the liquid crystal into an isotropic liquid, it can be easily supplied to fill between the electrode substrates 1, 2. By cooling after filling, the ferroelectric liquid crystal 6 is changed into a chiral smectic phase having desired three states. The cooling process is preferably carried out at 0.1 to 1.0 deg.C/min cooling rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a liquid crystal electro-optical device.

[0002]

2. Description of the Related Art As an electro-optical device using a liquid crystal, D is used.
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, those using such a nematic liquid crystal have a drawback that the response speed is extremely slow, from several milliseconds to several tens of milliseconds.

Against this background, a ferroelectric liquid crystal having a high-speed response has been developed, and several high-speed electro-optical devices using the ferroelectric liquid crystal have already been proposed. For example,
As disclosed in JP-A-56-107216, a twisted structure is solved 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 (1), there is one that utilizes a transient molecular scattering state that occurs when the polarity of an applied electric field is inverted.

[0004]

However, the conventional ferroelectric liquid crystal has problems in that it realizes a stable molecular alignment with a clear contrast between light and dark in the absence of an electric field, and that a clear threshold characteristic appears. is there. The present inventors have conducted intensive research on such a problem,
We have developed a ferroelectric liquid crystal having the following structural formula. In this ferroelectric liquid crystal, the molecular orientation shows a first stable state when no electric field is applied, and the molecular orientation shows a second stable state different from the first stable state when an electric field is applied in one electric field direction, It shows 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 other electric field direction.

An object of the present invention is to facilitate the manufacture of a liquid crystal electro-optical element using such a ferroelectric liquid crystal.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, the ferroelectric liquid crystal is heated and filled as a isotropic liquid between a pair of electrode substrates. And cooling the ferroelectric liquid crystal into a chiral smectic phase. By heating the ferroelectric liquid crystal into an isotropic liquid in this manner, the filling between the electrode substrates can be facilitated. By cooling after the filling, the ferroelectric liquid crystal is turned into a chiral smectic phase. Thus, a liquid crystal having the desired three states can be obtained.

It is desirable that the cooling be performed at a rate of 0.1 to 1.0 ° C. per minute, as in the second aspect of the present invention.

[0008]

FIG. 1 shows the structure of a liquid crystal electro-optical device according to an embodiment of the present invention. For example, 2μ
m, and a spontaneous polarization of at least 50 nC /
The ferroelectric liquid crystal material 6 of cm ² or more is sealed. As the ferroelectric liquid crystal material, a liquid crystal material having a structural formula shown in Chemical Formula 1 (TFM)
HPPOBC).

[0009]

Embedded image

[0010] [4- (1- t ri f luoro m ethyl h epty
loxycarbonyl) p henyl 4'- o ctyloxy b iphenyl -
4- c arboxylate] electrode substrate 1 is formed an electrode 1a made of a transparent shaped conductive film such as along indium oxide or tin oxide on the inner surface of the transparent substrate 1c transparent like glass or resin as in Figure 1 . The other electrode substrate 2 has the same configuration.

On the inner surfaces of the transparent electrodes 1a and 2a of the conductive film, there are arranged polymer film alignment films 1b and 2b that have been subjected to an alignment treatment for aligning liquid crystal molecules in parallel with the substrate. Also, in addition to this, rubbing treatment on the electrode substrate, or oblique deposition of silicon oxide or the like on the surface, or
In general, those which align liquid crystals, such as treatment with a surfactant, can be applied.

The electrode substrates 1 and 2 are combined in parallel so that liquid crystals are arranged in one direction. Thereafter, the ferroelectric liquid crystal material of the formula (1) is heated and injected as an isotropic liquid between the electrode substrates 1 and 2 by utilizing the capillary phenomenon. Cool slowly at 0 ° C. and cool to 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:
Figure 2 due to the large polarization of the liquid crystal molecules themselves and the order of the liquid crystal
Orientation is performed as shown in FIG.

The polarizers 4 outside the electrode substrates 1 and 2
5 are arranged orthogonally. Further, the direction of the long axis of the liquid crystal molecules in the absence of an electric field is set to an angle of 0 ° (180 °) with the polarizer (P) of the polarizing plate. Transparent electrode 1a,
An external power supply 3 including a drive circuit is connected to 2a.
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 FIG.
This will be described with reference to (b) and (c). Here, each left drawing shows a plan view of the apparatus, and each right drawing shows a side view. At the time of no electric field, the liquid crystal molecules 20 between the substrates 1 and 2 are aligned in the normal direction of the smectic layer 10 and show the alignment state shown in FIG. At this time, the spontaneous polarization of the liquid crystal molecules is
The left half (or right) in the upper half and the right (or left) in the lower half, that is, on a cone on which ferroelectric liquid crystal molecules move (FIG. 2 (a) right), 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, the integrated value of the spontaneous polarization in the cell thickness direction becomes zero.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper 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. By the way 1
The tilt angle of the ferroelectric liquid crystal material of the formula is from 70 ° C. to 110 ° C.
10 ° C to 31 ° C within the temperature range of

Next, when an electric field sufficient to rotate the liquid crystal molecules from the back side to the front side of the paper is applied, the spontaneous polarization 30 is aligned with the electric field direction 40. As a result, the liquid crystal molecules are
Reorient as shown in (c). At this time, the liquid crystal molecules form a tilt angle of -θ from the normal direction of the layer. In this way, the optical axis of the liquid crystal can be changed into three states depending on the polarity and magnitude of the applied electric field.

By sandwiching such a liquid crystal having three states between a pair of polarizing plates 4 and 5, the liquid crystal can be used as an electro-optical device. For example, as shown in FIG. 2A, the polarizer (P) of the polarizer and the liquid crystal molecule major axis direction are arranged so as to form an angle of 0 °. In this state, the linearly polarized light that has passed through the polarizer (P) passes through the liquid crystal but is blocked by the analyzer (A), and becomes a dark state.

In the case of FIG. 2B in which an electric field is applied from the front side to the back side of the paper, the light passing through the polarizer (P) is generally elliptically polarized due to the birefringence effect of the liquid crystal. Since this light component passes through the analyzer (A), it becomes a bright state. FIG. 2 shows an electric field applied from the back side to the front side.
In the case of (c), the light that has passed through the polarizer (P) generally becomes elliptically polarized light due to the birefringence effect of the liquid crystal. Since this light component also passes through the analyzer (A), it becomes a bright state.

Next, a voltage-transmittance curve of the present apparatus will be described. The polarizer (P) is set so that the polarization axis of the polarizer (P) and the direction of the molecular major axis in the absence of an electric field are at 0 °, and the threshold is a voltage at which the luminance changes relatively by 10%. FIG. 3 shows the voltage waveform used for the measurement, the applied pulse width is 1 msec,
It is applied repeatedly at a constant cycle. The optical response at this time is shown in FIG. It can be seen that the state is dark when there is no electric field, but is bright when voltage is applied.

FIG. 5 shows a plot of light transmittance versus voltage when the electric field is applied. Voltage 0
As the voltage increases from (V), the threshold value 1 is exceeded, and the state rapidly changes from a dark state to a bright state, but thereafter becomes constant. next,
As the voltage is decreased, the state changes from the bright state to the dark state at the threshold 2 after the threshold 1 at the time of the voltage increase has passed.

When the voltage is further reduced, the threshold value 3 is passed again, and the state changes from the dark state to the bright state, but thereafter becomes constant. Next, as the voltage is increased, it can be seen that the state changes from the bright state to the dark state at the threshold 4 after passing the threshold 3 at the time of the voltage decrease. Thus, there is a clear threshold and a large hysteresis. Next, the temperature dependence of the response speed of the device using the ferroelectric liquid crystal material of Formula 1 was measured. The response speed is defined as
It was the time required for the light transmittance to change to 90%.
The measured voltage waveform is a 10 Hz square wave with a voltage of 30
(V). FIG. 6 shows the temperature dependence of the response speed. μ
This shows a fast response in the sec range.

Further, regarding the orientation of the liquid crystal molecules, the twisted state observed in the conventional ferroelectric liquid crystal in the absence of an electric field was not observed, but only one stable alignment state was observed.
Once cooled and brought into a crystalline state, the temperature is raised and the orientation of the previous chiral smectic C phase can be reproduced as the chiral smectic C phase. In the above embodiment, the polarizer (P) of the polarizing plate and the molecular major axis direction in the absence of an electric field make an angle of 0 ° (180 °). However, for example, 22.5 °, 45 ° ° or 90 °. For example, in the case of 22.5 °, when an electric field is applied, one of the electric field directions indicates a dark state, the other electric field direction indicates a bright state, and In the case of an electric field, the intermediate state is shown.

With this configuration (22.5 °), the molecular orientation in three states was confirmed by the transmittance with respect to the triangular wave voltage and the polarization reversal current. The voltage waveform used for the measurement is ± 30 (V), 1
It is a triangular wave voltage of 0 (Hz). FIGS. 7 and 8 show transmittance and polarization reversal current at two temperatures when this waveform is applied. In the figure, (a) shows the applied voltage waveform, (b) shows the transmittance, and (c) shows the domain-inverted current waveform. The transmittance (b) clearly appears as a dark state in a minus range, an intermediate bright state in a 0 volt range, and a bright state in a plus range. Regarding the polarization inversion current (c), it can be seen that the peaks of the polarization inversion current waveform appear respectively in accordance with the state change.

As shown in FIG. 9, a plurality of stripe-shaped transparent electrodes 1a and 2a are formed in parallel on each of the electrode substrates 1 and 2 so that the electrodes of the substrate 1 and the substrate 2 are orthogonal to each other. A matrix type display device is formed by arranging and connecting an external power supply including a circuit that can be dynamically driven to the electrodes, and driving using the hysteresis characteristic shown by the voltage-transmittance curve is performed. Can also.

Here, the line sequential method of the dynamic driving method will be described. As an example, the 1/3 bias method will be described with reference to FIG. X indicates an electrode (scanning electrode) scanned line-sequentially, and Y indicates an electrode (signal electrode) to which a signal voltage is applied. A mark indicates a point to be displayed (selected point), and a mark without a mark indicates a point to maintain the display (non-selected point). A voltage of +2 V is applied to an electrode selected as a scanning electrode, and a voltage of 0 V is applied to a non-selected electrode. On the signal electrode side, -1 V is applied to the selected electrode, and +1 V is applied to the non-selected electrode.
Is applied. As described above, a voltage of 3V is applied to the selected point, and -1V or + 1V is applied to the other non-selected points.
Is applied.

When performing the dynamic driving as described above,
Since the bias voltage is also applied to the non-selected points, it is necessary that the bias voltage is lower than the voltage threshold applied to the non-selected points. Further, the voltages applied to the non-selected points are set to the threshold 1 and the threshold 2 shown in FIG.
If a voltage between the thresholds 2 and 3 is set at a point for dark display and a voltage applied to a point for bright display is set higher than the threshold 1, the contrast ratio is high and the display can be held. Dynamic driving can be easily performed.

The present invention can be applied not only to the transmission type in which the display is made by illumination from the back, but also to the reflection 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, one having the following structural formula (TFMNPOBC) can be used.

[0028]

Embedded image

[0029] [4- (1- t ri f luoro m ethyl n onyl
oxy carbonyl) p henyl 4'- o ctyloxy b iphenyl -
4- c arboxylate] shows the transmission characteristics and polarization inversion current characteristics of the liquid crystal material to a triangular wave voltage (± 30 V, 10 Hz) upon application of a 11 shows the same three states and the liquid crystal material described above.

Further, as another liquid crystal material having a large spontaneous polarization, one having the following structural formula (MHPOBC) can be used.

[0031]

Embedded image

[0032] [4- (1- m ethyl h eptyloxy carbony
l) p henyl 4'- o ctyloxy b iphenyl -4- c arbox
ylate] FIG. 12 shows transmittance characteristics and polarization reversal current characteristics when the above-mentioned triangular wave voltage is similarly applied to this liquid crystal material, and the above three states are obtained. Next, FIG. 13 shows the values 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 or more (nC / cm ² ) or more. Note that a general triangular wave method was used as a method for measuring spontaneous polarization.

Further, in addition to the above three liquid crystal materials, another liquid crystal material has the following structural formula (TFMHB2F
DB) can be used.

[0034]

Embedded image

[0035] [4- (1- t ri f luoro m ethyl h epty
loxy carbonyl) -4'- b iphenyl 2 - f luoro -4
- d ecyloxy b enzoate] became a phase transition of the compound differential heat content folding (DSC) results as measured by texture observation under a polarizing microscope in the following manner. Here, Cry; crystal phase, SmC ^* ; chiral smectic C phase (ferroelectric liquid crystal phase), SmA; smectic A
Phase, I: Indicates an isotropic liquid phase.

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. The appearance of the above three states extends over the entire ferroelectric smectic phase, that is, the magnitude of spontaneous polarization is about 4 [nC / cm ² ] to 80 [nC
/ Cm ² ]. FIG.
It shows the transmittance characteristic (b) and the polarization reversal characteristic (c) when the triangular wave voltage (a) is applied at 5 ° C., and it can be seen that the above three states are shown.

In order to raise the temperature range of the ferroelectric smectic phase to room temperature and to expand the temperature range, of the above four compounds,
TFMHPOBC, MHPOBC, TFMHB2FDB
The following three types were mixed at the following ratios, and TFHPOBC 20% MHPOBC 46% TFMHB2FDB 34% The phase transition was measured by differential thermal analysis (DSC) and a polarizing microscope to obtain the following results. Was.

[0038] The mixture was sealed in a liquid crystal cell, and 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. As a result, the three states were observed over the entire ferroelectric smectic phase temperature range. Was observed.

FIG. 16 shows the structure of a liquid crystal electro-optical device according to another embodiment of the present invention. In the present embodiment, a two-color ferroelectric liquid crystal material having a spontaneous polarization of at least 50 nC / cm ² is provided between two electrode substrates 1 and 2 spaced apart from each other by, for example, 2 μm. 6 ′ in which a sex dye is dissolved is sealed. As the ferroelectric liquid crystal material, for example, the above-mentioned four liquid crystal materials (TFMPOBC, TFMNPOBC, MHPOB)
C, TFMHB2FDB). Examples of the dichroic dye include, for example, S-33 manufactured by Mitsui Toatsu.
No. 4 (azo black dichroic dye) is used, and the ferroelectric liquid crystal is heated to an isotropic liquid phase, and 2 wt% of the dichroic dye is added and dissolved. Thereafter, the liquid crystal cell is injected between the electrode substrates 1 and 2 using capillary reduction, and then the entire liquid crystal cell is gradually cooled at a rate of 0.1 to 1.0 ° C. per minute to be 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:
Figure 1 due to the large polarization of the liquid crystal molecules themselves and the order of the liquid crystal
Orientation is performed as shown in FIG.

In this embodiment, the electrode substrate 2
The polarizing plate 5 is arranged only on the outside. Furthermore, the direction of the long axis of the liquid crystal molecules in the absence of an electric field is set to an angle of 0 ° (180 °) with the polarizer (P) of the polarizing plate. Transparent electrode 1
An external power supply 3 including a drive circuit is connected to a and 2a so that the above-described voltage waveform is applied to the liquid crystal.

Next, the operation of the apparatus having the above-described structure will be described with reference to FIG.
A description will be given using (a), (b), and (c). Here, each left drawing shows a plan view of the apparatus, and each right drawing shows a side view. At the time of no electric field, the liquid crystal molecules 20 between the substrates 1 and 2 are aligned in the normal direction of the smectic layer 10 and show the alignment state shown in FIG. 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, on the cone on which the ferroelectric liquid crystal molecules move. (FIG. 17 (a) right), 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 spontaneously spontaneously in the cell thickness direction. The integrated value of the polarization becomes zero. At this time, the dichroic dye 21 is dispersed in the liquid crystal molecules 20 and faces in the same direction as the major axis direction of the liquid crystal molecules 20.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper 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, a dichroic dye dissolved in a ferroelectric liquid crystal material represented by Chemical Formula 1 has a tilt angle of 10 ° to 31 ° within a 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 to the front side is applied, the spontaneous polarization 30 is aligned with the electric field direction 40. As a result, the liquid crystal molecules are
Reorient as shown in (c). At this time, the liquid crystal molecules form a tilt angle of -θ from the normal direction of the layer. 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 can be changed into three states depending on the polarity and magnitude of the applied electric field.

A polarizing plate 5 is provided on the liquid crystal having such three states.
Can be used as an electro-optical device. For example, as shown in FIG. 17A, the polarizer (P) of the polarizing plate is arranged such that the major axis direction of the liquid crystal molecules forms an angle of 0 °. In this state, the linearly polarized light that has passed through the polarizer (P) is in a dark state because its polarization direction coincides with the absorption axis of the dichroic dye and is absorbed.

Further, in the case of FIG. 17 (b) in which an electric field is applied from the front side to the back side of the paper and in the case of FIG. 17 (c) in which an electric field is applied from the back side of the paper, the linearly polarized light passing through the polarizer (P) is Since the polarization direction of the light does not coincide with the absorption axis of the dichroic dye, light is transmitted and a bright state is obtained. The polarizing plate 5 may be provided outside the electrode substrate 1. Note that the optical response, the light transmittance, the temperature dependency 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 embodiment.

In this embodiment, the polarizer (P) of the polarizing plate and the direction of the long axis of the molecule when no electric field is applied (the long axis of the dichroic dye molecules) form an angle of 0 ° (180 °). Although the configuration is described, for example, the configuration may be such that an angle of 45 ° or 90 ° is formed. State when no electric field is applied.
It is possible to perform gradation display in stages.

The dichroic dye is not limited to an azo dichroic dye, and an anthraquinone dichroic dye having good light resistance can also be used.

[Brief description of the drawings]

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

2 (a), 2 (b), and 2 (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 a change in transmittance when the voltage shown in FIG. 3 is applied to a liquid crystal.

FIG. 5 is a diagram showing a relationship between a voltage of a 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 transmittance and polarization inversion current with respect to a triangular wave voltage.

FIG. 8 is a diagram showing transmittance and polarization reversal current with respect to 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 reversal current with respect to a triangular wave voltage in another liquid crystal material.

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

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

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

15 is a diagram showing transmittance and polarization reversal 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 according to another embodiment of the present invention.

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

[Explanation of symbols]

1, 2, ... electrode substrate, 1a, 2a ... transparent electrode, 1b, 2b
... Orientation films, 1c, 2c ... Transparent substrates, 4, 5 ... Polarizing plates,
6, 6 ': ferroelectric liquid crystal, 10: smectic layer, 20
... liquid crystal molecules, 21 ... dichroic dye, 30 ... spontaneous polarization direction,
40: electric field direction, 50: polarization direction.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Norio Yamamoto, Inventor 1-1-1, Showa-cho, Kariya, Aichi Prefecture Inside Denso Corporation (72) Inventor Ichiro Kawamura 2-7-3, Marunouchi, Chiyoda-ku, Tokyo Showa Shell Petroleum Co., Ltd.

Claims (2)

[Claims] 1. A molecular orientation shows a first stable state when no electric field is applied, a molecular orientation shows 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 and filled between the pair of electrode substrates as an isotropic liquid, and then cooled to turn the ferroelectric liquid crystal into a chiral smectic phase. A method of manufacturing a liquid crystal electro-optical device. 2. The method according to claim 1, wherein the cooling is performed at a rate of 0.1 to 1.0 ° C./min.