JPH1124033A - Liquid crystal display - Google Patents

Abstract

(57) Abstract: Provided is a liquid crystal display device capable of performing time-division driving at a high duty even if display driving is performed by controlling an effective value of a driving voltage. Liquid crystal molecules are aligned in one of a first metastable state and a second metastable state according to a metastable state selection voltage applied after application of a reset voltage, and the alignment state in the metastable state is an effective state of a drive voltage. A liquid crystal display device is constituted by the liquid crystal cell 10 and the polarizing plates 21 and 22 that change according to the value, and the electro-optical characteristics of the display device including the liquid crystal cell and the polarizing plate in which liquid crystal molecules are aligned in the first metastable state. And selectively using electro-optical characteristics of a display device including a liquid crystal cell in which liquid crystal molecules are aligned in a second metastable state and a polarizing plate;
For the liquid crystal, a liquid crystal material having a value of dielectric anisotropy ΔΔ of 10 or more and having a fast reset response was used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device capable of performing high-duty time-division driving.

[0002]

2. Description of the Related Art There are two types of liquid crystal display devices: a transmissive type that displays by using light from a backlight, and a reflective type that displays by using external light such as natural light or indoor illumination light. . In these liquid crystal display devices, a polarizing plate is arranged on the front side and the back side with a liquid crystal cell interposed therebetween, and in the reflection type liquid crystal display device, a reflecting plate is arranged on the back side of the back side polarizing plate. It is configured. Some reflection-type liquid crystal display devices include only one polarizing plate. In this reflection-type liquid crystal display device, a polarizing plate is arranged on the front side of a liquid crystal cell, and on the back side of the liquid crystal cell. It is configured by disposing a reflection plate.

In a liquid crystal cell used in these liquid crystal display devices, electrodes are formed on respective surfaces facing each other, and liquid crystal is applied between a pair of substrates each having an alignment treatment on the surface on which the electrodes are formed. The liquid crystal molecules are aligned in a predetermined alignment state (for example, a twist alignment state) in which the alignment direction in the vicinity of each substrate is regulated by the alignment film.

The liquid crystal display device is driven by applying a drive voltage corresponding to display data between electrodes of each pixel portion of a liquid crystal cell, and when a voltage is applied between the electrodes, liquid crystal molecules are not voltage-marked. The alignment state is changed so as to rise from the initial alignment state to the substrate surface, and light transmission is controlled according to the alignment state.

The above-mentioned liquid crystal display devices include those using a simple matrix type liquid crystal cell and those using an active matrix type liquid crystal cell.
The simple matrix method is advantageous in that the structure of the liquid crystal cell is extremely simple and can be obtained at low cost.

[0006]

However, in a liquid crystal display device using a simple matrix type liquid crystal cell, a writing voltage is applied between electrodes (between a scanning electrode and a signal electrode) of each pixel portion of the liquid crystal cell. By controlling the effective value of the driving voltage applied to the liquid crystal layer, the display is driven by changing the alignment state of the liquid crystal molecules due to the electric field induction of the liquid crystal molecules according to the effective value of the driving voltage, so that light is emitted. When performing a display in which the transmission state is controlled stepwise, if the number of time divisions increases, it becomes impossible to increase the difference between the effective values corresponding to each step. The operating voltage margin (difference in the effective value of the voltage for displaying each gradation) when driving the liquid crystal cell is reduced, and clear stepwise display cannot be performed.

For this reason, in a liquid crystal display device using a simple matrix type liquid crystal cell, it is difficult to perform high-duty time-division driving, and therefore it is difficult to increase the number of pixels to achieve high definition of a display image. Was.

The present invention uses a liquid crystal cell driven by controlling the effective value of a drive voltage, while increasing the operating voltage margin with respect to the drive duty.
It is an object of the present invention to provide a liquid crystal display device capable of performing time-division driving at a high duty and realizing display of a high-definition image having a large number of pixels.

[0009]

A liquid crystal display device according to the present invention comprises a liquid crystal cell having a nematic liquid crystal layer sandwiched between a pair of substrates having electrodes formed on opposing surfaces, and at least a surface of the liquid crystal cell. At least one polarizing plate disposed on the side, and the liquid crystal layer orients the liquid crystal molecules between the electrodes of the pair of substrates such that the long axes of the molecules are substantially perpendicular to the substrate surface. After applying the reset voltage, one of a lower first metastable state selection voltage and a second metastable state selection voltage different from the first metastable state selection voltage is selectively applied. By doing so, the liquid crystal molecules are aligned in one of a first metastable state in which the liquid crystal molecules are aligned in a predetermined state and a second metastable state in which the liquid crystal molecules are aligned in a state different from the first metastable state, The first and second semi-low The liquid crystal molecules have a property that the alignment state of the liquid crystal molecules changes by electric field induction of the liquid crystal molecules according to the effective value of the driving voltage in each state, and the nematic liquid crystal has a dielectric anisotropy Δε value of 10 or more. It is characterized by being made of a material.

In the liquid crystal display device of the present invention, the liquid crystal molecules are aligned in one of the first and second metastable states, and the alignment state of the liquid crystal molecules in each metastable state is determined according to the effective value of the driving voltage. A liquid crystal cell in which liquid crystal molecules are aligned in the first metastable state and a polarizing plate when the first metastable state is selected. When the second metastable state is selected, the display device has the electro-optical characteristics of a liquid crystal cell in which the liquid crystal molecules are aligned in the second metastable state and a polarizing plate.

That is, this liquid crystal display device has the electro-optical characteristics of two display devices having different alignment states of liquid crystal molecules of a liquid crystal cell.
Controlling a plurality of transmission states of the transmission states to be controlled stepwise using one electro-optical characteristic, and controlling other plural transmission states using the other electro-optical characteristic. Can be.

Therefore, according to this liquid crystal display device, the number of stages in the transmission state is controlled by using the one electro-optical characteristic, that is, by controlling the light transmission state by selecting the first metastable state. And when utilizing the other electro-optical characteristic, that is, when controlling the light transmission state by selecting the second metastable state, and therefore, in each metastable state. Since the number of driven stages is reduced, time-division driving with a small number of stages can be performed in each metastable state.

Therefore, according to this liquid crystal display device,
Although the liquid crystal cell driven by controlling the effective value of the driving voltage is used, the operating voltage margin for the driving duty can be increased, and time-division driving at a high duty can be performed.

The rewriting of the display of the liquid crystal display device is performed by first resetting the alignment state of the previous liquid crystal molecules by applying the reset voltage, and by applying the first or second metastable state selection voltage. After selecting such a metastable state, the writing is performed by applying a writing voltage for obtaining the next writing state. In the present invention, the liquid crystal of the liquid crystal cell has a dielectric anisotropy Δε of 10 or more. Since the liquid crystal material is used, it is possible to reset the alignment state of the liquid crystal molecules before the application of the reset voltage with good responsiveness.

Therefore, according to the liquid crystal display device of the present invention, the application time of the reset voltage for resetting the alignment state of the liquid crystal molecules can be shortened, and the switching time of the metastable state can be shortened. High-duty time-division driving is possible, and a high-definition image with a large number of pixels can be displayed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a liquid crystal display device according to the present invention, first and second liquid crystal molecules are aligned by selective application of a first or second metastable selection voltage after application of a reset voltage. A liquid crystal cell including a liquid crystal layer that is oriented in one of a metastable state and an electric-field-induced alignment state corresponding to an effective value of a driving voltage after the metastable state is selected, wherein the first and second liquid crystal cells are used. By controlling the metastable state of the second and the alignment state according to the effective value of the driving voltage, the first and second states are controlled.
In each of the metastable states, the light transmission state is controlled in a plurality of stages, and in each metastable state, time-division driving of a small number of stages can be performed, and the liquid crystal cell In the liquid crystal, the value of the dielectric anisotropy Δε is 10
By using the above liquid crystal material, the reset of the alignment state of the liquid crystal molecules by the application of the reset voltage can be performed with good responsiveness, thereby enabling time-division driving at high duty.

In the liquid crystal display device according to the present invention, the liquid crystal layer of the liquid crystal cell may be arranged such that the liquid crystal molecules are oriented at approximately 0 ° to approximately 1 ° in one direction with respect to the alignment processing direction of one of the substrates.
A non-twisted or twisted splay alignment initial alignment state at a twist angle of 80 °, wherein the first metastable state is such that the liquid crystal molecules are further twisted approximately 180 ° in the one direction from the initial alignment state. In the alignment state in which the splay distortion has been eliminated by the alignment, the second metastable state is such that the liquid crystal molecules are twisted by about 180 ° in the direction opposite to the one direction from the initial alignment state to eliminate the splay distortion. The alignment state.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a reflection type liquid crystal display device will be described below with reference to the drawings. FIGS. 1A and 1B are perspective views showing a basic configuration of a liquid crystal display device according to a first embodiment of the present invention. FIG. 1A shows an initial alignment state, FIG. 1B shows a first metastable state, and FIG. Shows a metastable state.
FIG. 2 is a sectional view of the liquid crystal display device.

In the liquid crystal display device of this embodiment, as shown in FIGS. 1 and 2, polarizing plates 21 and 22 are disposed on the front side and the back side of the liquid crystal cell 10 and the polarization on the back side. A reflection plate 30 is arranged behind the plate 22, and a driving system 40 for driving the liquid crystal cell 10 is connected to the liquid crystal cell 10.

As shown in FIG. 2, the liquid crystal cell 10 has a pair of transparent substrates 11 and 14 having transparent electrodes 13 and 14 on the inner surface and alignment films 15 and 16 on which an alignment process is performed. A liquid crystal 18 is sandwiched between the substrates 12, and the pair of substrates 11 and 12 are joined via a frame-shaped sealing material 17, and the liquid crystal 18 is surrounded by the sealing material 17 between the substrates 11 and 12. Is enclosed in a closed area.
The alignment films 15 and 16 are horizontal alignment films made of polyimide or the like, and the alignment is performed by rubbing the film surfaces in a predetermined direction.

The liquid crystal cell 10 is of a simple matrix type, and a transparent electrode 13 provided on a front substrate 11 has a plurality of scanning electrodes formed along one direction (left and right directions in FIG. 2). The transparent electrodes 14 provided on the electrodes and the back substrate 12 are a plurality of signal electrodes formed along a direction substantially orthogonal to the scanning electrodes 13.

Further, the liquid crystal cell 10 has the liquid crystal 1
8, a nematic liquid crystal having a twist orientation by adding a chiral agent was used. The nematic liquid crystal used in this example had a viscosity of 30 c at room temperature.
It is made of a liquid crystal material having a dielectric anisotropy Δε of 10 or more, which has physical properties of not less than p and an elastic constant ratio K33 / K11 of 1.5 or more. The liquid crystal material preferably has a viscosity of 30 to 45 c.
p, and the elastic constant ratio K33 / K11 is desirably in the range of 1.5 to 2.2.

In the liquid crystal layer of the liquid crystal cell 10, in the initial alignment state, the liquid crystal molecules have a non-twist alignment (twist angle) of 0 ° to 180 ° in one direction with respect to the alignment processing direction of one of the substrates. Angle is 0 ° orientation) or in a splay orientation state in which the orientation is twisted.

The liquid crystal cell 10 applies a reset voltage of a sufficiently high voltage to the liquid crystal layer so that the liquid crystal molecules rise and align substantially perpendicularly to the surfaces of the substrates 11 and 12, and then applies a reset voltage lower than the reset voltage. Is applied, the liquid crystal molecules are further twisted by about 180 ° from the initial alignment state in the one direction (the same direction as the twist alignment direction in the initial alignment state), and the liquid crystal molecules are twisted to eliminate the splay distortion. 1 after the application of the reset voltage, and the application of a selection voltage of another predetermined value lower than the reset voltage causes the liquid crystal molecules to move from the initial alignment state in a direction opposite to the one direction (the first direction). (A direction opposite to the twist orientation direction in the metastable state of (1)) is twisted at an angle twisted by approximately 180 ° to achieve a second metastable state in which splay distortion is eliminated, and The alignment state of the liquid crystal molecules in the first and second metastable states has an alignment state induced by an electric field that changes according to an effective value of a driving voltage applied according to display data.

In this embodiment, the twist angle of the liquid crystal molecules in the initial alignment state is set to approximately 90 °. Therefore, the first metastable state is a state in which the liquid crystal molecules are subjected to the alignment treatment of one of the substrates. A state in which the liquid crystal is twist-oriented in one direction with a twist angle of approximately 270 ° based on the direction,
The second metastable state is a state in which the liquid crystal molecules are twist-aligned with a twist angle of about 90 ° in a direction opposite to the first metastable state with respect to the alignment processing direction of the one substrate.

In FIG. 1, reference numerals 11a and 12a denote alignment directions of the substrates 11 and 12 of the liquid crystal cell 10 (the alignment films 15 and 12).
16 rubbing directions), and in this embodiment,
The alignment film 15 of the front substrate 11 is subjected to an alignment process in a direction shifted approximately 45 ° counterclockwise as viewed from the front side with respect to the horizontal axis x of the screen of the liquid crystal display device and from the lower left to the upper right of the screen. The orientation film 16 of the rear substrate 12 is oriented in a direction deviated clockwise by approximately 45 ° from the horizontal axis x when viewed from the front side and in a direction from the upper left to the lower right of the screen. That is, the orientation direction 11 of both substrates 11 and 12
a and 12a are directions substantially orthogonal to each other.

In this embodiment, a liquid crystal 18 to which a chiral agent having a counterclockwise twist orientation is added as viewed from the surface side is used. Therefore, the liquid crystal molecules of the liquid crystal cell 10 are: In the initial alignment state, the liquid crystal is twist-aligned with a splay distortion in a counterclockwise direction (the twist direction given by the chiral agent) with a twist angle of about 90 ° when viewed from the surface side.

In this initial alignment state, the liquid crystal molecules are aligned in the respective alignment processing directions 11 near the substrates 11 and 12.
a, 12a, and the direction indicated by the broken line arrow in FIG. 1A with reference to the alignment processing direction of one of the substrates, for example, the alignment processing direction 12a of the back substrate 12, that is, the chiral agent. Is a splay alignment state in which the liquid crystal molecules are twist-oriented at a twist angle of about 90 ° in the twist direction given by.

The initial alignment state is a state that is not actually used for display. The liquid crystal cell 10 changes the alignment state of the liquid crystal molecules of each pixel portion to the first and second metastable states described above. The display is driven while being oriented.

The first metastable state and the second metastable state are such that the twist angle of the liquid crystal molecules is approximately 1 from the initial alignment state.
This is a state in which the splay distortion is eliminated by changing by 80 °, and the twist angle in the twist direction given by the chiral agent with respect to the orientation processing direction 12a of the backside substrate 12 is +, and the twist angle is given by the chiral agent. Assuming that the twist angle in the direction opposite to the twist direction (direction in which the twist by the chiral agent is released) is minus, the first metastable state is a twist orientation in which the twist angle is changed by + 180 ° with respect to the initial orientation state. The second metastable state is a twist alignment state in which the twist angle has changed by -180 ° with respect to the initial alignment state.

The switching of the alignment state from the initial alignment state to the first and second metastable states is performed between the electrodes (between the scanning electrode 13 and the signal electrode 14) of each pixel portion of the liquid crystal cell 10.
First, a splay distortion elimination voltage of a sufficiently high voltage value at which the liquid crystal molecules rise and align substantially perpendicular to the surfaces of the substrates 11 and 12 is applied, and then a selection voltage of a predetermined value is applied between the electrodes. Done by

That is, after the liquid crystal molecules are vertically aligned with respect to the surfaces of the substrates 11 and 12 by applying the splay distortion elimination voltage, a selection voltage having a predetermined value lower than the splay distortion elimination voltage (hereinafter referred to as a first voltage). When a liquid crystal molecule is twisted at a twist angle (90 ° + 180 ° = 270 °) obtained by adding a twist of approximately 180 ° to the twist angle in the initial alignment state when a metastable state selection voltage is applied. To eliminate the splay distortion and enter the first metastable state.

In the first metastable state, the liquid crystal molecules are aligned along the respective alignment processing directions 11a and 12a near the two substrates 11 and 12, and the alignment processing direction of one of the substrates, for example, With reference to the orientation processing direction 12a of the back substrate 12, in the twist direction indicated by the broken arrow in FIG. 1B, that is, in the counterclockwise direction (the twist direction given by the chiral agent) when viewed from the front side, approximately 2
It is in a state of being twist-oriented at a twist angle of 70 °.

After the liquid crystal molecules rise and align substantially perpendicular to the surfaces of the substrates 11 and 12 by application of the splay distortion elimination voltage, a selection voltage having a predetermined value lower than the splay distortion elimination voltage (hereinafter referred to as a first voltage). When a metastable state selection voltage is applied, the liquid crystal molecules have a twist angle (9) obtained by subtracting a twist of approximately 180 ° from the twist angle in the initial alignment state.
(0 ° −180 ° = −90 °), the liquid crystal is oriented in a twisted state, the splay distortion is eliminated, and a second metastable state is set.

In the second metastable state, the liquid crystal molecules are aligned along the respective alignment processing directions 11a and 12a in the vicinity of the two substrates 11 and 12, and the alignment processing direction of one of the substrates, for example, With reference to the orientation processing direction 12a of the back substrate 12, the twist direction indicated by the broken arrow in FIG. 1C, that is, the clockwise direction as viewed from the front side (the direction opposite to the twist direction given by the chiral agent)
In addition, it is in a state of being twist-oriented at a twist angle of about 90 °.

Further, the first metastable state and the second metastable state can be switched from one to the other, and even if the liquid crystal molecules are oriented in either metastable state, First, liquid crystal molecules are placed between the electrodes 13 and 14 on the substrate 1.
By resetting the metastable state by applying a reset voltage of a sufficiently high voltage that rises and orients substantially perpendicular to the 1,12 planes, and then applies the first or second metastable state selection voltage, In addition, the alignment state of the liquid crystal molecules can be switched from one metastable state to the other metastable state.

Note that the first metastable state selection voltage and the second
The metastable state selection voltage is determined by the properties of the nematic liquid crystal used, the properties of the chiral agent, and the amount added.
The first metastable state selection voltage is almost 0 V (a value to which almost no voltage is applied), and the second metastable state selection voltage is a tilt angle in which almost all liquid crystal molecules are almost the same as or close to the pretilt angle in the initial alignment state. And a voltage whose absolute value is higher than the first metastable state selection voltage.

FIG. 3 shows the alignment state of the liquid crystal molecules in the initial alignment state, the reset state, and the first and second metastable states as viewed from the lower edge direction of the liquid crystal cell 10 (the direction orthogonal to the horizontal axis x). FIG. 18a is a schematic diagram, and 18a indicates liquid crystal molecules.

As shown in this schematic diagram, the initial alignment state (the liquid crystal molecules are twisted with a twist angle of approximately 90 ° counterclockwise when viewed from the front side with respect to the alignment processing direction 12a of the back substrate 12). State) indicates that both substrates 11 and 12
Are aligned so as to rise obliquely at a pretilt angle of about several degrees toward the alignment processing directions 11a and 12a with respect to the surfaces of the substrates 11 and 12 respectively, but the twisted liquid crystal is aligned. This is a state in which the tilts of the pretilts on the respective substrates 11 and 12 are opposite to each other when the molecules are developed so that the respective molecular long axes are on the same plane. A state in which the tilt angle decreases as the distance from the substrates 11 and 12 increases, and the direction of inclination with respect to the surfaces of the substrates 11 and 12 is reversed with respect to the middle of the liquid crystal layer thickness (point where the tilt angle becomes 0 °) ( (With splay distortion).

The reset state is set between the two substrates 11,
The liquid crystal molecules (not shown in the figure) near 12 are in a state that is almost the same as the initial alignment state (for each substrate 1).
1 and 12 surfaces are oriented so as to rise obliquely at a pre-tilt angle of about several degrees toward the alignment processing directions 11a and 12a), but almost at least a certain distance from the substrates 11 and 12 Liquid crystal molecules of the substrate 1
It is in a state of being oriented so as to rise almost perpendicularly to the 1 and 12 planes.

Further, the first metastable state (the state in which the liquid crystal molecules are twisted in one direction at a twist angle of about 270 °) corresponds to the state in which the liquid crystal molecules in the vicinity of the substrates 11 and 12 are in the initial alignment state. It is almost the same as the above, but the liquid crystal molecules are twisted by about 180 ° more than the initial alignment state and are in a twisted state. Therefore, the liquid crystal molecules in the twisted state are aligned such that their respective molecular long axes are on the same plane. Since the tilt direction of the liquid crystal molecules 18a is the same when viewed in a developed state, the first metastable state is a twist alignment state without splay distortion.

In the second metastable state (the liquid crystal molecules are
Is a state in which the liquid crystal molecules are twisted at a twist angle of about 90 ° in the direction opposite to the metastable state of the liquid crystal molecules). The angle is approximately 1 in the direction opposite to the twist direction in the first metastable state from the initial orientation state.
The liquid crystal molecules 18a are twisted and twisted by 80 °, and therefore, when the liquid crystal molecules in the twisted alignment are developed so that the respective molecular major axes are on the same plane, the tilt direction of the liquid crystal molecules 18a is the same. Therefore, the second metastable state is also a twist alignment state having no splay distortion.

The first and second metastable states are respectively
The twisted state of maintaining the twist angle of the liquid crystal molecules 18a in the metastable state is maintained. In any metastable state, the tilt angle of the liquid crystal molecules 18a, that is, the substrate 1
The rising angle with respect to the surfaces 1 and 12 changes according to the effective value of the driving voltage applied between the electrodes 13 and 14 (however, the alignment state of the liquid crystal molecules near the substrates 11 and 12 hardly changes).

Of the alignment states of the liquid crystal molecules in the first and second metastable states shown in FIG. 3, the alignment state shown on the upper side corresponds to the case where the effective value of the driving voltage is a relatively small value. Of the liquid crystal molecules (first writing state) when the effective value of the driving voltage is a certain high value. In any metastable state, the liquid crystal molecules maintain the twist alignment state in the metastable state, and induce the electric field of the liquid crystal molecules according to the effective value of the drive voltage, so as to respond to the effective value of the drive voltage. Rise orientation.

The driving voltage is a voltage whose effective value changes within a range lower than the voltage value of the reset voltage, and the first and second metastable states correspond to the effective value of the driving voltage. Although the tilt angle of the liquid crystal molecules changes, the twist alignment state is maintained as it is. In any metastable state, the liquid crystal molecules 18a are made almost perpendicular to the substrates 11 and 12 by applying the reset voltage. The state is maintained until the metastable state is reset by the rising orientation.

That is, the liquid crystal layer of the liquid crystal cell 10
After applying a reset voltage between the electrodes 13 and 14 of the pair of substrates 11 and 12 so that the long axis of the liquid crystal molecules is substantially perpendicular to the surfaces of the substrates 11 and 12, a reset voltage of a lower value is applied. By selectively applying one of the first metastable state selection voltage and a second metastable state selection voltage different from the first metastable state selection voltage, the liquid crystal molecules are maintained in a predetermined state. Orienting first metastable state and this first metastable state
The liquid crystal molecules are aligned in one of a second metastable state and an alignment state different from the metastable state of the liquid crystal, and the electric field of the liquid crystal molecules according to the effective value of the driving voltage in each of the first and second metastable states It has the property that the alignment state of the liquid crystal molecules changes by induction.

In FIG. 1, 21a and 22a are:
The transmission axes of a pair of polarizing plates 21 and 22 disposed on the front side and the back side with the liquid crystal cell 10 interposed therebetween are shown. In this embodiment, the front polarizing plate 21 is connected to the transmission axis 21a by the liquid crystal cell. 10 are arranged in a direction substantially parallel to or substantially perpendicular to the orientation processing direction 11a of the front substrate 11 (direction substantially parallel in the figure), and the rear polarizing plate 22 is connected to the front polarizing plate 21 by the transmission axis 22a. Are arranged in a direction substantially perpendicular to the transmission axis 21a.

This liquid crystal display device uses external light such as natural light or indoor illumination light to reflect light incident from the front side with a reflector 30 disposed on the back side to display an image. The driving is performed by driving the liquid crystal cell 10 by the driving system 40.

The drive system 40 selects each pixel row of the liquid crystal cell 10 in a predetermined selection order, and applies the reset voltage, the first and second reference voltages between the electrodes of each pixel section of the selected pixel row. A metastable state selection voltage for selecting one of the stable states and a write voltage according to the write data are applied. The liquid crystal molecules in each pixel portion of the liquid crystal cell 10 are almost vertical by the application of the reset voltage. And the previous written state (the metastable state and the alignment state of the liquid crystal molecules in that state) is reset, and the first and second states are set in accordance with the metastable state selection voltage applied thereafter. And the orientation state is changed in the metastable state according to the effective value of the drive voltage determined by the write voltage.

Prior to the start of driving of the liquid crystal display device, the liquid crystal molecules in all the pixel portions of the liquid crystal cell 10 are aligned in the above-described initial alignment state (alignment state having splay distortion). At the start, when the first reset voltage is applied, the voltage is used as the splay distortion elimination voltage to orient the liquid crystal molecules so as to rise almost vertically, which is the same state as when the metastable state is reset.

In the liquid crystal display device, the liquid crystal molecules in each pixel portion of the liquid crystal cell 10 are aligned in one of the first and second metastable states, and the tilt angle of the liquid crystal molecules in each metastable state is driven. The light transmission state is controlled by changing the effective value of the voltage. When the first metastable state is selected, the liquid crystal molecules are turned on one side with reference to the alignment processing direction of one of the substrates. The display device has electro-optical characteristics of a display device comprising a liquid crystal cell and a polarizing plate twisted with a twist angle of about 270 ° in the direction, and when the second metastable state is selected, the liquid crystal molecules are aligned with the one substrate. In the direction opposite to the first metastable state with respect to the processing direction, approximately 9
It has electro-optical characteristics of a display device comprising a liquid crystal cell twisted at a twist angle of 0 ° and a polarizing plate.

That is, this liquid crystal display device has the electro-optical characteristics of two display devices having different alignment states of liquid crystal molecules in a liquid crystal cell. Can be controlled using one electro-optical characteristic, and the other plural transmission states can be controlled using the other electro-optical characteristic.

In this case, in the above embodiment, the front side polarizing plate 2
1 with respect to the direction of the transmission axis 21a.
And the transmission axis 22a of the back-side polarizing plate 22 is set to a direction substantially perpendicular to the transmission axis 21a of the front-side polarizing plate 21. Display in a twisted nematic mode (hereinafter referred to as TN mode) both when the metastable state is selected to control the transmission state and when the second metastable state is selected to control the transmission state. Can be.

That is, in any of the first and second metastable states, the linearly polarized light that has passed through the front polarizing plate 21 and entered the liquid crystal cell 10 is transmitted by the liquid crystal cell 10 due to the birefringence of the liquid crystal layer. Is rotated in accordance with the twist alignment state of the above, and the light is incident on the rear polarizing plate 22, and the transmission is controlled by the rear polarizing plate 22. And the back side polarizing plate 2
The light transmitted through 2 is reflected by the reflection plate 30 and is transmitted through the back-side polarizing plate 22, the liquid crystal cell 10, and the front-side polarizing plate 21 in order and emitted.

In this liquid crystal display device, the first
When the metastable state of is selected, the alignment state of the liquid crystal molecules is
Since the twisted state has a large twist angle of about 270 °, the optical rotation differs for each wavelength light due to the optical rotation dispersion in the birefringence action of the liquid crystal layer, so that each wavelength light passes through the back-side polarizing plate 22 with a different transmittance. Then, this back side polarizing plate 22
The light transmitted through becomes a colored light having a color corresponding to the ratio of the intensities of the respective wavelength lights constituting the light.

As described above, when the first metastable state is selected, the display in the TN mode is a color display in which a colored display is obtained, and the display color is the electrode 13, 1
It changes according to the effective value of the drive voltage applied between the four.

That is, the liquid crystal molecules rise and align according to the effective value of the driving voltage while maintaining the alignment state in the metastable state. When the alignment state of the liquid crystal molecules changes in this way, the liquid crystal layer corresponding to the alignment state changes. Since the optical rotation of each wavelength is changed by the change of optical rotation dispersion according to the change of birefringence, the color of the colored light can be changed by controlling the effective value of the drive voltage, and therefore, one pixel Can display multiple colors.

In the color display, light is colored by utilizing the birefringent action of the liquid crystal layer of the liquid crystal cell 10 and the polarizing action of the pair of polarizers 21 and 22. Since light absorption is smaller than that of coloring light, even a reflective liquid crystal display device can increase the transmittance of display light to obtain a bright colored display.

On the other hand, when the second metastable state is selected, the alignment state of the liquid crystal molecules is a twist alignment state in which the twist angle is substantially 90 °, and the display in the TN mode at this time is a normal TN mode. This is basically the same as the case of the liquid crystal display device of the type. In the liquid crystal display device of this embodiment, the front-side polarizing plate 21 and the rear-side polarizing plate 22 are respectively connected to the transmission axes 21a, 21a.
When the tilt angles of the liquid crystal molecules are close to the pretilt angle, white, which is an achromatic bright display, is displayed when the tilt angle of the liquid crystal molecules is close to the pretilt angle. The rate decreases, and black, which is an achromatic dark display, is finally displayed.

In this case, the liquid crystal molecules rise and align according to the effective value of the driving voltage, and the birefringence of the liquid crystal layer changes accordingly. Therefore, the transmission of light is controlled by controlling the effective value of the driving voltage. By controlling the state step by step, monochrome display with gradation can be performed.

The above-mentioned initial alignment state, that is, the state in which the liquid crystal molecules are twist-aligned at a twist angle of about 90 ° with a splay distortion is not used for actual display, but this initial alignment state is also used in the TN mode. In this state, the display can be obtained.

FIGS. 4 and 5 show the orientation directions 11a and 12a of the substrates 11 and 12 of the liquid crystal cell 10 and the transmission axes 21a and 22a of the front and back polarizers 21 and 22, respectively, as shown in FIG. And the change of the light emission rate and the display color with respect to the driving voltage of the liquid crystal display device in which the value of Δnd (the product of the refractive index anisotropy Δn of the liquid crystal and the liquid crystal layer thickness d) of the liquid crystal cell 10 is selected to be about 1000 nm. 4A and 4B show the voltage-emission rate characteristic diagram and the CIE chromaticity diagram in the first metastable state, and FIGS. 5A and 5B show the second metastable state. FIG. 3 is a voltage-emission rate characteristic diagram and a CIE chromaticity diagram in FIG. In the chromaticity diagrams of (b) of each drawing, W indicates an achromatic color point.

The voltage-emission rate characteristic in the first metastable state is a characteristic as shown in FIG. 4A, and the change of the display color with respect to the driving voltage is as shown in FIG. Value is 1.9
Red is applied when a voltage of 5 V is applied, and blue when an effective value of 2.98 V is applied.

The red coordinate values of x and y are as follows:
x = 0.353, y = 0.350, and the Y value (brightness) is 28.54. The x, y coordinate values of the blue are x = 0.274, y = 0.296,
The Y value is 11.64.

The voltage-emission rate characteristics in the second metastable state are as shown in FIG. 5A, and the change in display color with respect to the driving voltage is as shown in FIG. 5B. White when an effective value of 1.55 V is applied, and an effective value of 3.0.
Black when a voltage of 7 V is applied.

Note that the x, y coordinate values of the above white are:
x = 0.317, y = 0.341, and the Y value is 34.
41. Further, the x, y coordinate values of the above black are:
x = 0.271, y = 0.290, and the Y value is 1.8
3.

That is, the liquid crystal display device displays red and blue by selecting the first metastable state and displays white and black by selecting the second metastable state.
In addition to white and black display, which is the basis of display, two color display of red and blue can be performed.

When the power of the liquid crystal display device is turned off, the first
Or, the alignment state of the liquid crystal molecules in the second metastable state is
The liquid crystal returns to the initial alignment state in a few seconds to several minutes (depending on the characteristics of the nematic liquid crystal used and the characteristics and addition amount of the chiral agent) due to spontaneous discharge, and the entire screen is in the initial alignment state when no voltage is applied (see the above embodiment). Then it becomes white).

The liquid crystal display device has the electro-optical characteristics of two display devices having different alignment states of the liquid crystal molecules of the liquid crystal cell. Since a plurality of transmission states can be controlled using one electro-optical characteristic and another plurality of transmission states can be controlled using the other electro-optical characteristic, all stages of the transmission state can be controlled. The number is determined when the one electro-optical characteristic is used, that is, when the transmission state is controlled by selecting the first meta-stable state, and when the other electro-optical characteristic is used, that is, when the second meta-stable state is used. When the state is selected and the transmission state is controlled, it can be sorted, and therefore, the number of stages driven in each metastable state decreases, so in each metastable state,
Time-division driving with a small number of stages can be performed.

Therefore, according to the liquid crystal display device described above, it is possible to increase the operating voltage margin with respect to the driving duty of the liquid crystal cell 10. That is, in the case of a liquid crystal display device that performs two-color display of red and blue in addition to the above-described white and black display, the effective value of the drive voltage is changed to red by selecting the first metastable state. 1.95V when displaying black
1.55V and 3.07V when the second metastable state is selected to display blue and white.
Therefore, the difference between the effective values of the two drive voltages in each metastable state, that is, the operating voltage margin, is set to 1.03 V in the first metastable state.
(= 2.98V-1.95V) and 1.52V (= 3.07V-1.55V) in the second metastable state, which is sufficiently large.

Therefore, according to the above liquid crystal display device,
Even when the liquid crystal cell 10 is of a simple matrix type driven by controlling the effective value of the driving voltage, the operating voltage margin is increased with respect to the driving duty, and time-division driving at a high duty becomes possible. be able to.

The display of the liquid crystal display device can be rewritten by first resetting the alignment state of the previous liquid crystal molecules by applying the reset voltage, and by applying the first or second metastable state selection voltage. Is performed by applying a write voltage for obtaining the next write state after the metastable state is selected. In this liquid crystal display device, the liquid crystal of the liquid crystal cell 10 has a dielectric anisotropy Δε of 10 or more. Since the liquid crystal material described above is used, the reset of the alignment state of the liquid crystal molecules by the application of the reset voltage can be performed with good responsiveness.

That is, the liquid crystal cell 1 of the above liquid crystal display device
When three types of liquid crystal materials having different physical properties were prepared as the liquid crystal 18 to be sealed in 0, and the responsiveness of the liquid crystal material when the reset voltage was applied was examined, the results shown in the following table were obtained. Obtained.

[0074]

[Table 1]

As can be seen from this table, the dielectric anisotropy Δε
The liquid crystal material A or liquid crystal material B having a small value of 6.2 or 7.4 has a low reset response, whereas the liquid crystal material C having a large value of dielectric anisotropy Δε of 12.7 has a high reset response.

The reset response time of the liquid crystal materials A, B, and C (the time required for the liquid crystal molecules to rise substantially vertically) is about 4 msec when the reset voltage is set to 50 V, and the liquid crystal material A has a reset response time of about 4 msec. B is about 4 msec when the reset voltage is 40 V, and liquid crystal material C is about 2 msec when the reset voltage is 40 V.

As described above, the liquid crystal material C has a reset response almost twice as fast as the liquid crystal materials A and B. Therefore, when the liquid crystal material C is used, the liquid crystal molecules C The application time of the reset voltage for resetting the alignment state can be shortened, and the switching time of the metastable state can be shortened. Since the first or second metastable state selection voltage applied after the application of the reset voltage is a very low voltage, the liquid crystal molecules in which the previous alignment state has been reset have good responsiveness in the first or second liquid crystal molecules. Oriented to a metastable state.

Therefore, according to the liquid crystal display device described above, time-division driving with a higher duty can be performed, and a high-definition image having a large number of pixels can be displayed. Note that the liquid crystal material C shown in the above table has a dielectric anisotropy Δε value of 12.
7, if a liquid crystal material having a value of Δε of 10 or more is used, the reset voltage application time for resetting the alignment state is sufficiently shortened to shorten the meta-stable state switching time. Can be.

The above liquid crystal display device has a liquid crystal cell 10
Is divided into groups of a plurality of rows, and for each frame, driving for resetting the pixel unit of each row of the one pixel row group, selecting a metastable state, and writing the pixel units of all the pixel rows is performed. It is desirable to drive the display by the method.

According to this driving method, the reset and the metastable state selection time secured in one frame need only be the time required for resetting and the metastable state selection of each pixel row in one group, so that one frame is shortened. Thus, the frame frequency can be increased.

Further, according to this driving method, writing to the pixel row in which the metastable state is selected, resetting of the remaining pixel rows of the group and selection of the metastable state are completed, and thereafter, each pixel in this group is set. Since the sequential writing to the row is started and the writing period to the pixel row is started, the new writing is performed even in the pixel row in which the reset and the metastable state selection are first performed in the group. The idle time is very short, so that no screen flicker occurs.

According to this driving method, the pixel rows are divided into groups so that the number of pixel rows in one group is selected so as to obtain a high frame frequency, and the number of groups is necessary to rewrite an image for one screen. It is preferable to select the number of frames so as not to increase too much.

To give an example, simple matrix type liquid crystal cells include those having 32, 64, 128, etc. pixel rows. For example, the liquid crystal cell has 64 pixel rows. In such a case, it is preferable to divide the pixel rows into groups of eight rows, and if the number of pixel rows in one group is about eight, a sufficiently high frame frequency can be obtained.
If 64 lines are divided into groups of 8 lines, an image for one screen is rewritten in about 8 to 9 frames, so that screen switching is good. That is, for example, when the frame frequency is 1
/ 30 sec, if the number of frames required to rewrite an image for one screen is 8 to 9 frames, 1
Approximately three to four screens can be rewritten per second, so that screen switching can be made good.

In the above liquid crystal display device, when the first metastable state is selected, the display colors are red and blue. The display color is obtained by changing the value of Δnd of the liquid crystal cell 10. Can be chosen arbitrarily.

Further, the liquid crystal display device of the above embodiment performs display in the TN mode when any of the first and second metastable states is selected, and performs display in the first metastable state. Is a color display, and the display in the second metastable state is a black-and-white display. At least the direction of the transmission axis 21a of the front polarizing plate 21 is set to the alignment processing direction 11a of the front substrate 11 of the liquid crystal cell 10. If the direction is obliquely intersected, the display in both the first and second metastable states can be color display in the birefringence effect mode.

In this liquid crystal display device, the viscosity of the liquid crystal 18 of the liquid crystal cell 10 at room temperature is 30 cp or more (preferably in the range of 30 to 45 cp) and the elastic constant ratio K
Since a liquid crystal material having a physical property of 33 / K11 of 1.5 or more (preferably in the range of 1.5 to 2.2) is used, the alignment state of the liquid crystal molecules in the first and second metastable states described above. The liquid crystal molecules are aligned with the effective value of the driving voltage in the metastable state, and a highly reliable display operation is performed while reliably maintaining the selected metastable state. Can be made.

FIGS. 6A and 6B are perspective views showing a basic structure of a liquid crystal display device according to a second embodiment of the present invention, wherein FIG. 6A shows an initial alignment state, FIG. 6B shows a first metastable state, and FIG. Indicates a second metastable state.

The liquid crystal display device of this embodiment has a liquid crystal cell 1
The twist angle of the liquid crystal molecules in the initial alignment state of 0 is approximately 3
The other configuration is the same as that of the first embodiment, and the liquid crystal material used for the liquid crystal cell 10 is also the same.

In this embodiment, as shown in FIG. 6, the alignment processing direction 11a of the front substrate 11 of the liquid crystal cell 10 is substantially counterclockwise with respect to the horizontal axis x of the screen of the liquid crystal display device when viewed from the front side. The direction is shifted by 15 ° from the lower left to the upper right of the screen.
a is approximately 1 clockwise with respect to the horizontal axis x when viewed from the front side.
The direction is shifted by 5 ° and is directed from the upper left to the lower right of the screen. That is, the alignment processing directions 11a and 12a of the substrates 11 and 12 are directions intersecting each other at an angle of about 30 °.

In this embodiment, the liquid crystal cell 1
The liquid crystal of 0 is a liquid crystal added with a chiral agent having a counterclockwise twist alignment as viewed from the surface side. Therefore, in the initial alignment state, the liquid crystal molecules have a splay distortion when viewed from the surface side. It is twist-oriented with a twist angle of about 30 ° in the counterclockwise direction (the twist direction given by the chiral agent).

In this initial alignment state, the liquid crystal molecules are aligned in the respective alignment processing directions 11 near the substrates 11 and 12.
a, 12a, and the direction indicated by the dashed arrow in FIG. 6A based on the alignment processing direction of one of the substrates, for example, the alignment processing direction 12a of the back substrate 12, that is, the chiral agent. Is a splay alignment state in which the liquid crystal molecules are twist-oriented at a twist angle of about 30 ° in the twist direction given by the above.

In each of the first and second metastable states, the twist angle of the liquid crystal molecules is approximately 18 degrees from the initial alignment state.
In this embodiment, the twist angle of the liquid crystal molecules in the initial alignment state is almost 3 °.
In the first metastable state, the liquid crystal molecules are twist-aligned at a twist angle of about 210 ° in the twist direction given by the chiral agent with respect to the alignment processing direction of one of the substrates. In the metastable state of 2, the liquid crystal molecules are twist-aligned with a twist angle of about 150 ° in a direction opposite to the twist direction given by the chiral agent with respect to the alignment processing direction of the one substrate.

That is, in the first metastable state, the liquid crystal molecules are aligned along the respective alignment directions 11a and 12a in the vicinity of the substrates 11 and 12, and
The orientation processing direction of one of the substrates, for example, the back substrate 1
6, the twist direction indicated by the broken arrow in FIG. 6B, that is, the counterclockwise direction as viewed from the surface side (the twist direction given by the chiral agent)
In addition, it is in a twist-oriented state with a twist angle of about 210 °.

The second metastable state is that the liquid crystal molecules are
In the vicinity of the two substrates 11 and 12, the alignment is performed along the respective alignment processing directions 11 a and 12 a, and the alignment processing direction of one of the substrates, for example, the alignment processing direction 12 a of the back substrate 12 is set as a reference in FIG. In the twist direction indicated by the dashed arrow in c), that is, in the clockwise direction (the direction opposite to the twist direction given by the chiral agent) when viewed from the surface side, the twist is oriented at a twist angle of about 150 °.

The first metastable state and the second metastable state are the same as in the first embodiment.
Resetting the meta-stable state by applying a reset voltage having a value that causes the liquid crystal molecules to rise and orient substantially perpendicular to the 1,12 surfaces,
Thereafter, by applying the first or second metastable state selection voltage, one metastable state is switched to the other metastable state.

The first metastable state selection voltage is substantially 0 V, and the second metastable state selection voltage is such that most of the liquid crystal molecules are aligned at an inclination angle which is almost equal to or close to the pretilt angle in the initial alignment state. Lower value.

In this embodiment, the front polarizing plate 21
Is arranged so that its transmission axis 21a is displaced substantially 45 ° counterclockwise as viewed from the front side with respect to the horizontal axis x of the screen, and the back-side polarizing plate 22 has its transmission axis 22a set to the horizontal axis x. On the other hand, they are arranged in a direction shifted clockwise by approximately 45 ° clockwise when viewed from the front surface side.
1a is the alignment processing direction 1 of the front substrate 11 of the liquid crystal cell 10.
1a (approximately 15 ° counterclockwise with respect to the horizontal axis x when viewed from the front side)
(The direction shifted) at a crossing angle of about 30 ° with respect to the oblique direction, and the transmission axis 22a of the back-side polarizing plate 22 is substantially orthogonal to the transmission axis 21a of the front-side polarizing plate 21. .

The liquid crystal display device of this embodiment has a liquid crystal cell 1
Since the initial alignment state of the liquid crystal molecules of 0 is a splay alignment state in which the liquid crystal molecules are twist-aligned with a twist angle of about 30 ° in one direction with reference to the alignment processing direction 12a of one substrate (here, the back substrate) 12, When the metastable state of 1 is selected, a display comprising a liquid crystal cell and a polarizing plate in which liquid crystal molecules are twist-aligned in one direction with a twist angle of about 210 ° in one direction with respect to the alignment processing direction 12a of the one substrate 12. When the device has the electro-optical characteristics and selects the second metastable state, the liquid crystal molecules are substantially aligned in the direction opposite to the first metastable state with respect to the alignment processing direction 12a of the one substrate 12. It has electro-optical characteristics of a display device comprising a liquid crystal cell twisted at a twist angle of 150 ° and a polarizing plate.

In this embodiment, the direction of the transmission axis 21a of the front-side polarizing plate 21 is set to a direction obliquely shifted at an intersection angle of about 30 ° with respect to the alignment processing direction 11a of the front-side substrate 11 of the liquid crystal cell 10. , The transmission axis 22a of the rear polarizing plate 22
Since the direction is set substantially perpendicular to the transmission axis 21a of the front polarizing plate 21, the second metastable state is selected even when the transmission state is controlled by selecting the first metastable state. Also, when controlling the transmission state by using the display device, color display in the birefringence effect mode can be performed.

The color display in the birefringence effect mode will be described. In either of the first and second metastable states, linearly polarized light transmitted through the front polarizing plate 21 and transmitted through the liquid crystal cell 10 is transmitted. In the process, each wavelength light becomes elliptically polarized light having a different polarization state due to the birefringence action of the liquid crystal layer, and each wavelength light passes through the back-side polarizing plate 22 with a transmittance according to each polarization state, The light transmitted through the back-side polarizing plate 22 becomes colored light having a color corresponding to the light intensity ratio of each wavelength light constituting the light. This colored light is reflected by the reflection plate 30, and is transmitted through the rear-side polarizing plate 22, the liquid crystal cell 10, and the front-side polarizing plate 21 in order and emitted.

As described above, the color display in the birefringence effect mode uses the birefringence of the liquid crystal layer of the liquid crystal cell 10 and the polarization of the pair of polarizing plates 21 and 22 to color light. Therefore, light absorption is smaller than that in which light is colored by using a color filter. Therefore, even in a reflection type liquid crystal display device, a light color display can be obtained by increasing light transmittance.

The above-mentioned initial alignment state, that is, the state in which the liquid crystal molecules are twist-aligned with a splay distortion at a twist angle of about 30 ° is not used for an actual display as described above. In this state, a display in the birefringence effect mode can be obtained.

In the liquid crystal display device, the first
(A state where liquid crystal molecules are twisted at a twist angle of about 210 ° in one direction) is selected.
The alignment state of the liquid crystal molecules is different from that when the second metastable state (the state in which the liquid crystal molecules are twisted at a twist angle of about 150 ° in the opposite direction to the first metastable state) is selected,
Accordingly, the liquid crystal layer exhibits different birefringence,
Different colors can be displayed when the metastable state is selected and when the second metastable state is selected.

Further, in this liquid crystal display device, the electrodes 13, 14 are provided in any of the first and second metastable states.
The birefringence of the liquid crystal layer changes due to a change in the tilt angle of the liquid crystal molecules in accordance with the effective value of the driving voltage applied between them, and the polarization state of each wavelength light incident on the back-side polarizing plate 22 changes accordingly. Therefore, by controlling the effective value of the drive voltage, the color of the colored light can be changed, and therefore, a plurality of colors can be displayed in one pixel portion.

FIGS. 7 and 8 show that the twist angle of the liquid crystal molecules in the initial alignment state of the liquid crystal cell 10 was set to approximately 30 ° as in this embodiment, and the alignment direction 1 of both substrates 11 and 12 was changed.
1a, 12a and transmission axes 21 of front and back polarizing plates 21, 22
a and 22a are set as shown in FIG. 6, and the change of the light emission rate and the display color with respect to the drive voltage of the liquid crystal display device in which the value of Δnd of the liquid crystal cell 10 is set to about 800 nm is shown. FIGS. 7A and 7B show the voltage-emission rate characteristic diagram and the CIE chromaticity diagram in the first metastable state, and FIGS. 8A and 8B show the second metastable state. It is a voltage-emission rate characteristic diagram and a CIE chromaticity diagram. In the chromaticity diagrams of (b) of each figure, W is an achromatic color point.

The voltage-emission rate characteristics in the first metastable state are as shown in FIG. 7A, and the change of the display color with respect to the drive voltage is as shown in FIG. 7B. The value is 1.4
Red is applied when a voltage of 6 V is applied, and white when an effective value of 2.00 V is applied.

The x, y coordinates of the red color are x
= 0.432, y = 0.391, and the Y value (brightness)
Is 20.29. The x, y coordinate values of the white are x = 0.290, y = 0.319, and the Y value is 29.70.

Further, the voltage-emission ratio characteristic in the second metastable state is a characteristic as shown in FIG. 8A, and the change of the display color with respect to the driving voltage is as shown in FIG. Red when an effective value of 1.46 V is applied, and an effective value of 2.
It is blue when a voltage of 00V is applied.

Note that the red x, y coordinate value is x
= 0.424, y = 0.399, and the Y value is 21.3.
It is one. Also, the x, y coordinate values of the blue are x =
0.249, y = 0.267, and the Y value is 11.32.
It is.

That is, the liquid crystal display device displays red and white by selecting the first metastable state and displays red and blue by selecting the second metastable state.
For example, color display in which an image is displayed in red and blue on a white background can be performed.

In the liquid crystal display device of this embodiment, the effective value of the drive voltage is changed to the second metastable state even when the first metastable state is selected and red and white are displayed. When displaying red and blue, it is sufficient to set the two values of 1.46 V and 2.00 V. Therefore, the difference between the effective values of the two drive voltages in each metastable state, that is, the operating voltage margin, is set. , 0.51 V (= 2.00 V-1.46 V) in any of the first and second metastable states.

The two effective values when selecting and displaying the first metastable state and the two effective values when selecting and displaying the second metastable state are the same (1). .46V and 2.00V), so that display driving is also facilitated.

FIGS. 9A and 9B are perspective views showing the basic structure of a liquid crystal display device according to a third embodiment of the present invention. FIG. 9A shows an initial alignment state, FIG. 9B shows a first metastable state, and FIG. Indicates a second metastable state.

The liquid crystal display device of this embodiment has a liquid crystal cell 1
The twist angle of the liquid crystal molecules in the initial alignment state of 0 is approximately 7
The other configuration is the same as that of the first embodiment, and the liquid crystal material used for the liquid crystal cell 10 is also the same.

In this embodiment, as shown in FIG. 9, the orientation processing direction 11a of the front substrate 11 of the liquid crystal cell 10 is substantially counterclockwise as viewed from the front side with respect to the horizontal axis x of the screen of the liquid crystal display device. The direction is shifted from the lower left to the upper right of the screen by a direction shifted by 35 °.
a is approximately 3 clockwise with respect to the horizontal axis x when viewed from the front side.
The direction is shifted by 5 ° and is directed from the upper left to the lower right of the screen. That is, the alignment processing directions 11a and 12a of the substrates 11 and 12 are directions intersecting each other at an angle of about 70 °.

In this embodiment, the liquid crystal cell 1
The liquid crystal of 0 is a liquid crystal added with a chiral agent having a counterclockwise twist alignment as viewed from the surface side. Therefore, in the initial alignment state, the liquid crystal molecules have a splay distortion when viewed from the surface side. It is twist-oriented with a twist angle of approximately 70 ° in the counterclockwise direction (the twist direction given by the chiral agent).

In this initial alignment state, the liquid crystal molecules are aligned in the respective alignment processing directions 11 near the substrates 11 and 12.
a, 12a, and the direction indicated by the broken line arrow in FIG. 9A with respect to the alignment processing direction of one of the substrates, for example, the alignment processing direction 12a of the back substrate 12, that is, the chiral agent. Is a splay alignment state in which the liquid crystal molecules are twist-oriented at a twist angle of about 70 ° in the twist direction given by (1).

The first and second metastable states each have a twist angle of about 18 from the initial alignment state.
This is a state in which the splay distortion is eliminated by changing by 0 °. In this embodiment, the twist angle of the liquid crystal molecules in the initial alignment state is set to about 7 °.
Therefore, in the first metastable state, the liquid crystal molecules are twist-aligned at a twist angle of about 250 ° in the twist direction given by the chiral agent with respect to the alignment processing direction of one of the substrates. In the metastable state of 2, the liquid crystal molecules are twist-aligned with a twist angle of about 110 ° in a direction opposite to the twist direction given by the chiral agent with respect to the alignment processing direction of the one substrate.

That is, in the first metastable state, the liquid crystal molecules are aligned along the respective alignment directions 11a and 12a in the vicinity of the substrates 11 and 12, and
The orientation processing direction of one of the substrates, for example, the back substrate 1
2, the twist direction indicated by the dashed arrow in FIG. 9B, that is, the counterclockwise direction as viewed from the surface side (the twisting direction given by the chiral agent) with reference to the alignment processing direction 12a of FIG.
In addition, it is in a state of being twist-oriented at a twist angle of about 250 °.

The second metastable state is that the liquid crystal molecules are
In the vicinity of the two substrates 11 and 12, the alignment is performed along the respective alignment processing directions 11a and 12a, and based on the alignment processing direction of one of the substrates, for example, the alignment processing direction 12a of the back substrate 12, as shown in FIG. In the twist direction indicated by the dashed arrow in c), that is, in the clockwise direction as viewed from the surface side (the direction opposite to the twist direction given by the chiral agent), the twist is oriented at a twist angle of about 110 °.

The first metastable state and the second metastable state are the same as those in the first embodiment.
By resetting the metastable state by applying a reset voltage having a voltage value that causes the liquid crystal molecules to rise and orient substantially perpendicular to the surfaces 1 and 12 and then applying the first or second metastable state selection voltage, Is switched from the metastable state to the other metastable state.

The first metastable state selection voltage is substantially 0 V, and the second metastable state selection voltage is such that almost all liquid crystal molecules have an inclination angle which is almost the same as or close to the pretilt angle in the initial alignment state. It is a low value to orient.

In this embodiment, the front polarizing plate 21
Is arranged so that its transmission axis 21a is displaced substantially 45 ° counterclockwise as viewed from the front side with respect to the horizontal axis x of the screen, and the back-side polarizing plate 22 has its transmission axis 22a set to the horizontal axis x. On the other hand, they are arranged in a direction shifted clockwise by approximately 45 ° clockwise when viewed from the front surface side.
1a is the alignment processing direction 1 of the front substrate 11 of the liquid crystal cell 10.
1a (approximately 35 ° counterclockwise as viewed from the front side with respect to the horizontal axis x)
The transmission axis 22a of the rear-side polarizing plate 22 is in a direction substantially orthogonal to the transmission axis 21a of the front-side polarizing plate 21. .

The liquid crystal display device of this embodiment has a liquid crystal cell 1
Since the initial alignment state of the liquid crystal molecules of 0 is a splay alignment state in which the liquid crystal molecules are twist-aligned with a twist angle of about 70 ° in one direction with reference to the alignment processing direction 12a of one substrate (here, the back substrate) 12, When the metastable state of 1 is selected, a display comprising a liquid crystal cell and a polarizing plate in which liquid crystal molecules are twist-aligned in one direction with a twist angle of approximately 250 ° with respect to the alignment processing direction 12a of the one substrate 12 as a reference. When the device has the electro-optical characteristics and selects the second metastable state, the liquid crystal molecules are substantially aligned in the direction opposite to the first metastable state with respect to the alignment processing direction 12a of the one substrate 12. It has electro-optical characteristics of a display device comprising a liquid crystal cell twisted at a twist angle of 110 ° and a polarizing plate.

In this embodiment, the direction of the transmission axis 21a of the front-side polarizing plate 21 is set to a direction obliquely shifted at an intersection angle of about 10 ° with respect to the alignment processing direction 11a of the front-side substrate 11 of the liquid crystal cell 10. , The transmission axis 22a of the rear polarizing plate 22
Since the direction is set substantially perpendicular to the transmission axis 21a of the front polarizing plate 21, the second metastable state is selected even when the transmission state is controlled by selecting the first metastable state. Also, when controlling the transmission state by using the display device, color display in the birefringence effect mode can be performed.

In the liquid crystal display device of this embodiment,
The first metastable state (when the liquid crystal molecules are almost 2 in one direction)
When a twist orientation of 50 ° is selected) and a second metastable state (state in which liquid crystal molecules are twisted at a twist angle of approximately 110 ° in a direction opposite to the first metastable state) When the first metastable state is selected and when the second metastable state is selected, the alignment state of the liquid crystal molecules is different from when the liquid crystal layer is selected, and the liquid crystal layer exhibits different birefringence accordingly. Thus, different colors can be displayed.

Further, in this liquid crystal display device, the electrodes 13, 14 are provided in any of the first and second metastable states.
The birefringence of the liquid crystal layer changes due to a change in the tilt angle of the liquid crystal molecules in accordance with the effective value of the drive signal applied between them, and the polarization state of each wavelength light incident on the back-side polarizing plate 22 changes accordingly. Therefore, the color of the colored light can be changed by controlling the effective value of the drive signal, so that a single pixel portion can display a plurality of colors.

FIGS. 10 and 11 show that the twist angle of the liquid crystal molecules in the initial alignment state of the liquid crystal cell 10 was set to approximately 70 ° as in this embodiment, and the alignment processing directions 11a and 12a of the substrates 11 and 12 were the same. Transmission axis 2 of front and back polarizing plates 21 and 22
The directions of 1a and 22a are set as shown in FIG. 9, and the change of the light emission rate and the display color with respect to the drive voltage of the liquid crystal display device in which the value of Δnd of the liquid crystal cell 10 is set to about 900 nm is shown. FIGS. 10A and 10B show a voltage-emission rate characteristic diagram and a CI in the first metastable state.
FIGS. 11A and 11B are an E chromaticity diagram and a voltage-emission rate characteristic diagram and a CIE chromaticity diagram in the second metastable state. In the chromaticity diagrams of (b) of each figure, W is an achromatic color point.

The voltage-emission rate characteristics in the first metastable state are as shown in FIG. 10A, and the change of the display color with respect to the driving voltage is as shown in FIG. 10B. Red when a voltage of 1.53 V is applied, and an effective value of 2.0
It is orange when a voltage of 3 V is applied.

Note that the red x, y coordinate value is x
= 0.343, y = 0.322, the Y value is 24.31, and the orange x, y coordinate value is x = 0.32.
2, y = 0.378, and the Y value is 31.98.

Further, the voltage-emission rate characteristics in the second metastable state are as shown in FIG. 11A, and the change of the display color with respect to the driving voltage is as shown in FIG. 11B. And white when an effective value of 1.53 V is applied, and blue when an effective value of 2.03 V is applied.

The x, y coordinate values of the white are x
= 0.320, y = 0.349, the Y value is 34.36, and the blue x, y coordinate values are x = 0.260, y =
0.278, the Y value is 9.05.

That is, the liquid crystal display device displays red and orange by selecting the first metastable state, and displays white and blue by selecting the second metastable state. For example, a color display in which an image is displayed in red, orange, and blue on a white background can be performed.

In the liquid crystal display device of this embodiment, when the effective value of the drive voltage is changed to the second metastable state when the first metastable state is selected and red and orange are displayed. 1.53V and 2.03 when displaying white and blue
V. Therefore, the difference between the effective values of the two drive voltages in each metastable state, that is, the operating voltage margin is set to 0.50 V in both the first and second metastable states. (= 2.03V-1.53V)
Can be taken sufficiently large.

Also, the two effective values when the first metastable state is selected and displayed and the two effective values when the second metastable state is selected and displayed are the same (1). .53V and 2.03V), so that the display driving becomes easy.

As described above, the liquid crystal display devices of the second and third embodiments are also similar to those of the first embodiment.
It has the electro-optical characteristics of two display devices having different alignment states of liquid crystal molecules in a liquid crystal cell. Therefore, it is possible to control a plurality of transmissive states of one of the transmissive states to be controlled in a stepwise manner. Since the characteristics can be controlled and the other plurality of transmission states can be controlled using the other electro-optical characteristics, even if the liquid crystal cell 10 is of a simple matrix type, its driving duty is Thus, the operating voltage margin can be increased, and time-division driving with high duty can be performed.

In these liquid crystal display devices as well, if a liquid crystal material having a dielectric anisotropy Δε of 10 or more and a quick reset response is used for the liquid crystal 18 of the liquid crystal cell 10, the reset voltage can be reduced by applying a reset voltage. Resetting the alignment state of the liquid crystal molecules, selecting one of the metastable states by applying the first or second metastable state selection voltage, and then applying a write voltage for obtaining the next write state. At the time of display driving, the application time of the reset voltage can be shortened, and the switching time of the metastable state can be shortened. Can be realized.

The liquid crystal display device of the second embodiment selects the first metastable state to display red and white, and
Is selected to display blue and black.
The liquid crystal display device according to the third embodiment displays the red and orange colors by selecting the first metastable state, and displays white and blue by selecting the second metastable state. The display color is determined by the value of Δnd of the liquid crystal cell 10 and the polarizing plates 21 and
The direction can be arbitrarily selected by changing the directions of the transmission axes 21a and 22a.

Further, in the liquid crystal display device of the present invention,
The initial alignment state of the liquid crystal cell 10 is not limited to the above-described first to third embodiments, and the liquid crystal molecules are oriented by approximately 0 ° in one direction with respect to the alignment processing direction of one of the substrates.
A non-twisted or twisted splay alignment state with a twist angle of about 180 ° is sufficient.

For example, the initial alignment state is such that all the liquid crystal molecules are aligned along the alignment processing direction of one substrate.
In a non-twist orientation state in which the twist angle is almost 0 °,
The first metastable state is a state in which the splay distortion is eliminated by twist orientation in one direction with a twist angle of about 180 ° in one direction with reference to the orientation processing direction of the one substrate, and the second metastable state is , Approximately 180 degrees in a direction opposite to the first metastable state with respect to the orientation processing direction of the one substrate.
This is a state in which splay distortion is eliminated by twist orientation at a twist angle of °.

For example, when the initial alignment state is a twist alignment state in which liquid crystal molecules are aligned in one direction with a twist angle of about 180 ° with respect to the alignment processing direction of one substrate, the first metastable state is obtained. The state is a state where the splay distortion is eliminated by twist alignment with a twist angle of about 360 ° in one direction based on the alignment processing direction of the one substrate, and the second metastable state is a state where all the liquid crystal molecules are aligned. Is a state in which non-twist alignment is performed along the alignment processing direction of the one substrate to eliminate splay distortion.

As described above, even when the initial alignment state and the first and second metastable states of the liquid crystal cell 10 are selected, at least the front side of the pair of polarizing plates 21 and 22 having the liquid crystal cell 10 interposed therebetween. If the direction of the transmission axis 21a of the polarizing plate 21 is set to a direction obliquely intersecting with the alignment processing direction 11a of the front substrate 11 of the liquid crystal cell 10, the first metastable state is selected and the transmission state is controlled. In both cases, the color display in the birefringence effect mode can be performed when the transmission state is controlled by selecting the second metastable state.

Further, the liquid crystal display device of each of the above embodiments is
Birefringence action of liquid crystal layer of liquid crystal cell 10 and pair of polarizing plates 2
The display is performed by utilizing the polarizing action of the liquid crystal cell 10 in addition to the polarizing action of the liquid crystal cell 10. Is also good.

This addition of a retardation plate is particularly effective in a liquid crystal display device which performs color display in the birefringence effect mode. Due to the birefringence of both the retardation plate and the liquid crystal layer of the liquid crystal cell 10, the polarization state of each is greatly changed and incident on the back-side polarizing plate 22.
The difference in the transmittance of each wavelength light passing through becomes large, so that the light transmitted through the back-side polarizing plate 22 becomes sharp colored light in which the difference in the intensity of each wavelength light constituting the light is large,
Further, with the change of the alignment state of the liquid crystal molecules according to the effective value of the driving voltage, the transmittance of each wavelength light and the difference between the transmittances greatly change, and the color of the colored light changes. Also increase.

The liquid crystal display devices according to the first to third embodiments are of a reflection type in which a reflection plate 30 is disposed on the back surface side. Transmission type liquid crystal display device (reflection plate 3
0) can also be applied.

Further, the present invention can be applied to a reflection type liquid crystal display device in which only one polarizing plate is provided, a polarizing plate is arranged on the front side of the liquid crystal cell, and a reflecting plate is arranged on the back side of the liquid crystal cell. In this case, a reflector may be provided on the outer surface of the back substrate of the liquid crystal cell, or an electrode provided on the inner surface of the back substrate may be formed of a metal film, and this electrode may also serve as the reflector. May be.

[0147]

The liquid crystal display device of the present invention has the electro-optical characteristics of two display devices in which the liquid crystal molecules of the liquid crystal cell have different alignment states from each other. A plurality of transmission states among the states can be controlled using one electro-optical characteristic, and the other plurality of transmission states can be controlled using the other electro-optical characteristic.

Therefore, according to this liquid crystal display device, the total number of stages of the transmission state can be divided into a case where the one electro-optical characteristic is used and a case where the other electro-optical characteristic is used. Therefore, since the number of stages driven in each metastable state is reduced, time-division driving with a small number of stages can be performed in each metastable state.

Therefore, according to this liquid crystal display device,
While using a simple matrix type liquid crystal cell driven by controlling the effective value of the driving voltage, the operating voltage margin for the driving duty is increased, and time-division driving at a high duty is possible. Can be.

The rewriting of the display of the liquid crystal display device is performed by first resetting the alignment state of the previous liquid crystal molecules by applying the reset voltage, and by applying the first or second metastable state selection voltage. After selecting such a metastable state, the writing is performed by applying a writing voltage for obtaining the next writing state. In the present invention, the liquid crystal of the liquid crystal cell has a dielectric anisotropy Δε of 10 or more. Since the liquid crystal material is used, it is possible to reset the alignment state of the liquid crystal molecules before the application of the reset voltage with good responsiveness.

Therefore, according to the liquid crystal display device of the present invention, the application time of the reset voltage for resetting the alignment state of the liquid crystal molecules can be shortened, and the switching time of the metastable state can be shortened. High-duty time-division driving is possible, and a high-definition image with a large number of pixels can be displayed.

[Brief description of the drawings]

FIG. 1 is a perspective view of an initial alignment state, a first metastable state, and a second metastable state, showing a basic configuration of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the liquid crystal display device.

FIG. 3 is a schematic diagram showing an alignment state of liquid crystal molecules in an initial alignment state, a reset state, and first and second metastable states of the liquid crystal display device.

FIG. 4 is a voltage-emission rate characteristic diagram and a CIE chromaticity diagram in a first metastable state of the liquid crystal display device.

FIG. 5 shows a voltage-emission ratio characteristic diagram and a CIE chromaticity diagram in a second metastable state of the liquid crystal display device.

FIG. 6 is a perspective view showing the basic configuration of a liquid crystal display device according to a second embodiment of the present invention, showing an initial alignment state, a first metastable state, and a second metastable state.

FIG. 7 is a voltage-emission ratio characteristic diagram and a CIE chromaticity diagram in a first metastable state of the liquid crystal display device.

FIG. 8 shows a voltage-emission rate characteristic diagram and a CIE chromaticity diagram in a second metastable state of the liquid crystal display device.

FIG. 9 is a perspective view showing the basic configuration of a liquid crystal display device according to a third embodiment of the present invention, showing an initial alignment state, a first metastable state, and a second metastable state.

FIG. 10 shows a voltage-emission ratio characteristic diagram and a CIE chromaticity diagram in a first metastable state of the liquid crystal display device.

FIG. 11 is a voltage-emission rate characteristic diagram and a CIE chromaticity diagram in a second metastable state of the liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal cell 18 ... Liquid crystal 21 and 22 ... Polarizer 21a, 22a ... Transmission axis 30 ... Reflector

Claims (2)

[Claims] 1. A liquid crystal cell having a nematic liquid crystal layer sandwiched between a pair of substrates having electrodes formed on opposing surfaces, and at least one polarizing plate disposed on at least the surface side of the liquid crystal cell. The liquid crystal layer, between the electrodes of the pair of substrates, after applying a reset voltage to orient the liquid crystal molecules so that the molecular long axis is substantially perpendicular to the substrate surface, the lower value of By selectively applying one of the first metastable state selection voltage and a second metastable state selection voltage different from the first metastable state selection voltage, the liquid crystal molecules are maintained in a predetermined state. Oriented in one of a first metastable state to be oriented and a second metastable state oriented in a different orientation state from the first metastable state, and in each of the first and second metastable states. Depending on the effective value of the drive voltage The nematic liquid crystal is made of a liquid crystal material having a value of dielectric anisotropy Δ１０ of 10 or more. Liquid crystal display device. 2. The liquid crystal layer according to claim 1, wherein the liquid crystal molecules are oriented at approximately 0 ° in one direction with respect to the alignment processing direction of one of the substrates.
Having a non-twisted or twisted splay orientation initial orientation state with a twist angle of about 180 °,
The metastable state is an alignment state in which liquid crystal molecules are further twisted by approximately 180 ° in the one direction from the initial alignment state to eliminate splay distortion, and the second metastable state is that the liquid crystal molecules are in the initial alignment state. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is in an alignment state in which the liquid crystal molecules are aligned by being twisted by about 180 [deg.] In a direction opposite to the one direction from the alignment state to eliminate the splay distortion.