JPH1138417A - Liquid crystal display device - Google Patents

Abstract

(57) [Problem] To provide a new mode liquid crystal display device having a response speed higher than that of a TN mode and a wide viewing angle. SOLUTION: A liquid crystal layer 10 made of a nematic liquid crystal material or a liquid crystal layer 10 made of a chiral nematic liquid crystal material having a positive dielectric anisotropy is formed on a pair of substrates 13 having electrodes for applying a voltage to the liquid crystal layer 10. 14 are formed. When a voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal cell 16, the liquid crystal molecules 10a are in a twisted vertical alignment state or a vertical alignment state.
(Vth1> Vth2 (small voltage)), the liquid crystal molecules 1
0a is a twisted horizontal alignment state. A liquid crystal display element is formed using the alignment state of these two liquid crystal molecules 10a.

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.

[0002]

2. Description of the Related Art Liquid crystals are used in a very wide range as display elements. Currently used liquid crystal display elements include:
Typical examples include a liquid crystal display element of a TN (twisted nematic) mode and a liquid crystal display element of an STN (super-twisted nematic) mode.

As shown in FIG. 7A, in a TN mode liquid crystal display device, since the rubbing directions of the upper and lower substrates are shifted by 90 °, the internal nematic or chiral nematic liquid crystal molecules 103 are also twisted by 90 °. It is in an oriented state. When the polarizing plates 101 and 102 of the upper and lower substrates are arranged with the polarization axes twisted by 90 °, the lower polarizing plate 1
The light transmitted through 01 is transmitted through the liquid crystal cell while being rotated along the twist of the liquid crystal molecules 103. Then, since the electric field vector of the light is parallel to the polarizing plate 102 above,
The light passes through the polarizing plate 102 above. As a result, a white state is obtained.

Here, as shown in FIG. 7 (b), when an electric field is applied in the vertical direction of the cell, the liquid crystal molecule 103 has a positive dielectric anisotropy. The orientation state is such that it is parallel to the electric field. In this state, since the liquid crystal molecules 103 are not twisted, no optical rotation occurs, and the light does not pass through the upper polarizing plate 102. As a result, a black state is obtained.

As described above, in the TN liquid crystal display element, monochrome display is enabled by turning on and off the voltage. However, in order to satisfy Morgan's limit, the cell thickness becomes as thick as about 5 μm.

Further, as shown in FIG. 8A, the STN mode liquid crystal display element has a rubbing direction of the upper and lower substrates of two.
The pitch is shifted by about 40 °, and the pitch of the internal chiral nematic liquid crystal molecules 113 is also compensated so that the twist angle becomes about 240 °. Then, a white state is obtained when no voltage is applied, but the mechanism is different from the TN liquid crystal display element.
The light transmitted through the lower polarizing plate 111 is converted into elliptically polarized light and transmitted through the upper polarizing plate 112.

Here, as shown in FIG. 8 (b), when an electric field is applied in the vertical direction of the cell, liquid crystal molecules 113 rise as in the TN liquid crystal display element, and light does not pass through the upper polarizing plate 112. As a result, a black state is obtained.

Further, recently, OCB (optically compen
A liquid crystal display device of a (sated birefringence) mode has been announced. As shown in FIG. 9A, the cell in this mode is composed of alignment films 121 and 122, bend cells 125 containing liquid crystal molecules 125a, polarizing plates 123 and 124, and biaxial films 126. Also, the alignment film 121.1
22 is parallel rubbing in which the rubbing directions are almost parallel.

The bend cell 125 is a TN cell (FIG. 8)
Unlike (a), a bias voltage is required. The bend cell 125 is provided for the upper and lower substrates 127 and 128.
It is oriented in two dimensions. Therefore, when no bias voltage is applied, the liquid crystal molecules 125a are in a splay alignment state. The liquid crystal molecules 1 in this splay alignment state
When a voltage is applied to 25a, it becomes one of three states: a splay alignment state, a twist alignment state, and a bend alignment state.

Therefore, by applying a bias voltage to the substrates 127 and 128 above and below the bend cell 125,
Bend orientation state as initial state (state I, FIG. 9B)
Need to be achieved. Then, the orientation of the liquid crystal molecules 125a is changed by the voltage change between the bend orientation state I (FIG. 9B) and the vertical orientation state II (FIG. 9).
By controlling between (c) and (c), the light transmittance is changed. The light transmittance when this bend cell 125 is used for a normally black liquid crystal display device is shown in FIG.
It becomes as shown in. It should be noted that I and II in the graph represent the above states I and II. (Uchida: "Development of Cell Technology Realizing Simultaneous Wide Viewing Angle and High-Speed Response", "Flat Panel Display '95", Nikkei BP, p.150, (1994))

[0011]

Since the response time of the liquid crystal cell becomes longer almost in proportion to the square of the thickness of the liquid crystal layer,
When fast response characteristics are required, such as in a liquid crystal television, the thickness of the cell must be reduced to about several μm.

In this respect, in the conventional TN mode liquid crystal cell, since it is necessary to satisfy Morgan's limit, the thickness of the liquid crystal layer is as thick as about 5 μm, and the response speed is slow. Also,
The above-mentioned conventional STN mode liquid crystal cell has a slow response speed due to a large twist angle.

In addition, when the liquid crystal layer is thick, the viewing angle dependency is deteriorated, and the color and brightness change depending on the viewing direction and angle, making it difficult to realize a wide viewing angle.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a novel mode liquid crystal display device having a response speed higher than that of a TN mode and a wide viewing angle. .

[0015]

According to a first aspect of the present invention, there is provided a liquid crystal display device comprising a liquid crystal layer made of a nematic liquid crystal material or a chiral nematic liquid crystal material having a positive dielectric anisotropy. In a liquid crystal display element in which a liquid crystal layer is held between a pair of substrates having electrodes for applying a voltage to the liquid crystal layer, the liquid crystal layer has a structure in which the liquid crystal molecules are at least twisted vertically in accordance with the magnitude of the applied voltage. A liquid crystal material capable of taking a state and a twisted horizontal alignment state, and using two states of a twisted horizontal alignment state and a twisted vertical alignment state of the liquid crystal molecules of the liquid crystal layer,
It is characterized in that the display state of the pixel is switched.

According to the above configuration, by applying a bias voltage to a liquid crystal layer made of a liquid crystal material having a positive dielectric anisotropy, the liquid crystal molecules of the liquid crystal layer are twisted in a vertical orientation according to the magnitude of the applied voltage. State and twisted horizontal alignment state.

Thus, the display state of the pixel can be switched using the two states of the twisted horizontal alignment state and the twisted vertical alignment state of the liquid crystal molecules of the liquid crystal layer. Therefore, a liquid crystal display device of a new mode using the alignment state of these two liquid crystal molecules can be formed.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first aspect, the pair of substrates have substantially the same rubbing direction, and In the pair of polarizing plates provided one by one on the substrate, the polarizing axis of one polarizing plate substantially coincides with the rubbing direction, and the polarizing axis of the one polarizing plate is orthogonal to the polarizing axis of the other polarizing plate. The thickness between the pair of substrates is smaller than the thickness determined by the limit of Morgan.

According to the above configuration, in addition to the function of the first aspect, the rubbing directions of the pair of substrates of the liquid crystal molecules of the liquid crystal layer made of a liquid crystal material having a positive dielectric anisotropy are substantially the same. For this reason, the splay alignment state is taken when no voltage is applied, which is the initial state, the twisted vertical alignment state is taken when a voltage equal to or higher than the threshold voltage Vth1 is applied, and the skew is applied when the threshold voltage Vth2 (Vth1> Vth2) is applied. It takes a horizontal alignment state.

Thus, when a voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal layer to bring the liquid crystal molecules into a twisted vertical alignment state, the polarization axes of the polarizing plates are orthogonal, and the liquid crystal display element is brought into a black state. can do. When the voltage applied thereafter is set to the threshold voltage Vth2 and the liquid crystal molecules in the liquid crystal layer are in a twisted horizontal alignment state, the liquid crystal display element can be brought into a white state. Here, the reason for the white state is that the liquid crystal cell is thinner than the thickness determined by Morgan's limit (for example,
(3 μm or less), the light rotates in the liquid crystal layer halfway along the liquid crystal molecules, but cannot travel along the liquid crystal molecules to the end due to a large twist angle of the liquid crystal molecules. This is for transmission.

As described above, the switching of the display state of the pixel can be performed using the two states of the liquid crystal layer of the liquid crystal layer, that is, the twisted horizontal alignment state and the twisted vertical alignment state. Therefore, a liquid crystal display element of a new mode using the alignment state of these two liquid crystal molecules can be formed.

Further, by making the liquid crystal cell thinner (for example, 3 μm or less) than the thickness determined by the limit of Morgan, the response speed can be made higher than that of the conventional TN mode liquid crystal display device, and the wide field of view can be obtained. Corners can be secured. Further, a sufficient contrast can be secured.

According to a third aspect of the present invention, in order to solve the above-mentioned problems, in addition to the constitution of the first or second aspect, the liquid crystal layer further comprises a photosensitive monomer and the liquid crystal layer. The liquid crystal molecules are irradiated with ultraviolet rays in a state where a voltage is applied so as to be in a twisted horizontal alignment state.

According to the above configuration, in addition to the function of the first or second aspect, a photosensitive monomer is mixed in the liquid crystal, a voltage higher than the threshold voltage Vth1 is applied, and the liquid crystal molecules are twisted in the vertical alignment. After being in a state, perform ultraviolet exposure,
By stabilizing the liquid crystal molecules in a twisted vertical alignment state, the alignment state when the applied voltage is set to the threshold voltage Vth2 can be stabilized in a twisted horizontal alignment state.

Thus, the applied voltage is reduced to the threshold voltage Vth2.
After that, the alignment state of the liquid crystal molecules can be stabilized to a twisted horizontal alignment state, so that a white state can be displayed continuously. Therefore, an image can be displayed by using the liquid crystal display element for a simple matrix or an active matrix.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first or second aspect, the liquid crystal layer has a twisted horizontal alignment state of liquid crystal molecules of the liquid crystal layer. The twist angle is approximately 18 between the pair of substrates.
It is characterized in that a chiral agent is added so as to be 0 °.

According to the above configuration, in addition to the function of the first or second aspect, a chiral agent is added to the liquid crystal, and
By making the liquid crystal twisted by 0 °, the alignment state when the applied voltage is set to the threshold voltage Vth2 can be stabilized to a twisted horizontal alignment state.

Thus, the applied voltage is reduced to the threshold voltage Vth2.
After that, the alignment state of the liquid crystal molecules can be stabilized to a twisted horizontal alignment state, so that a white state can be displayed continuously. Further, occurrence of disclination in the white state can be prevented. Therefore, an image can be displayed by using the liquid crystal display element for a simple matrix or an active matrix.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first aspect, the pair of substrates have substantially the same rubbing direction, and Is characterized in that a dichroic dye is added.

According to the above configuration, in addition to the effect of the configuration of claim 1, when a dichroic dye having a rod-like structure is used, the dye molecules have a property of being oriented in parallel with the liquid crystal molecules. When the alignment state of the liquid crystal molecules is changed, the alignment direction of the dye also changes. Since this dye is colored or not depending on the direction, it is possible to switch between coloring and non-coloring of the cell by applying a voltage.

Thus, by adding a dichroic dye to the liquid crystal cell in which the alignment directions of the liquid crystal molecules are almost the same, when a voltage higher than the threshold voltage Vth1 is applied, the liquid crystal molecules have a twisted vertical alignment. In this state, light is transmitted without being absorbed by the dichroic dye, so that a white state can be obtained. When the applied voltage is the threshold voltage Vth2, the liquid crystal molecules are in a twisted horizontal alignment state, and light is absorbed by the dichroic dye, so that a black state can be obtained.

Therefore, since black-and-white display can be performed stably, an image can be displayed using the liquid crystal display element in a simple matrix or an active matrix.
Further, since it is not necessary to provide a polarizing plate, it can be used for a reflective display.

According to a sixth aspect of the present invention, there is provided a liquid crystal display device according to the first or second aspect, further comprising a splay alignment when the liquid crystal molecules of the liquid crystal layer are in a twisted horizontal alignment state. Before the transition to the state starts, a reset pulse having a waveform and a voltage having a voltage and an application time sufficient to maintain the twisted horizontal alignment state is applied.

According to the above configuration, in addition to the function of the first or second aspect, a voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal display element, and the liquid crystal molecules are turned into a twisted vertical alignment state to a black state. After that, the applied voltage is set to the threshold voltage Vth2, and the liquid crystal molecules are turned into a white state with twisted horizontal alignment. Thereafter, the liquid crystal molecules can be maintained in the twisted horizontal alignment state by applying a reset pulse to the liquid crystal layer before the transition of the liquid crystal molecules from the twisted horizontal alignment state to the splay alignment state starts.

Thus, the applied voltage is reduced to the threshold voltage Vth2.
Then, since the alignment state of the liquid crystal molecules can be maintained in a twisted horizontal alignment state, a white state can be displayed continuously.

Therefore, an image can be displayed by using the liquid crystal display element for a simple matrix or an active matrix.

According to a seventh aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first or second aspect, the reset pulse is periodically applied.

According to the above configuration, in addition to the function of the first or second aspect, a voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal display element, and the liquid crystal molecules are turned into a twisted vertical alignment state to a black state. After that, the applied voltage is set to the threshold voltage Vth2, and the liquid crystal molecules are turned into a twisted horizontal alignment state and a white state. Thereafter, before the transition of the liquid crystal molecules from the twisted horizontal alignment state to the splay alignment state starts, the liquid crystal molecules can be maintained in the twisted horizontal alignment state by periodically applying a reset pulse to the liquid crystal layer. it can.

As a result, the applied voltage is reduced to the threshold voltage Vth2.
After that, since the alignment state of the liquid crystal molecules can be maintained in a twisted horizontal alignment state, a white state can be displayed continuously and more stably.

Therefore, an image can be displayed using the liquid crystal display element in a simple matrix or an active matrix.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

First, the basic configuration of the liquid crystal cell according to the present embodiment will be described with reference to FIG.

The liquid crystal cell 16 according to the present embodiment has two glass substrates 1 and 2 facing each other. In addition, if it has translucency and insulating properties, the glass substrate 1
Instead of 2, a substrate made of a resin such as polymethyl methacrylate may be used.

On the surface of the glass substrate 1, a plurality of transparent electrodes 3 made of, for example, indium tin oxide (ITO) are provided.
Are formed parallel to each other with a thickness of 1000 °.
On the electrodes 3..., For example, oblique evaporation of SiO ₂ ,
The transparent insulating film 4 (A2014, manufactured by Nissan Chemical Industries, Ltd.) is
It is laminated with a thickness of 00 °. In the formation of the insulating film 4, after spin coating of the insulating film solution, 200
Firing at 90 ° C. for 90 minutes. However, the insulating film 4 is not essential.

On the other hand, on the glass substrate 2, a plurality of transparent electrodes 5 made of the same material and the same thickness as the electrodes 3 are arranged parallel to each other so as to be orthogonal to the electrodes 3.
A transparent insulating film 6 of the same material and the same thickness as the insulating film 4 is laminated thereon. However, the insulating film 6 is not essential.

On the insulating films 4 and 6, alignment films 7 and 8 (SE-77) which have been subjected to a uniaxial alignment process such as a rubbing process.
92, manufactured by Nissan Chemical Industries, Ltd.) with a thickness of 500 mm. The alignment films 7 and 8 are formed by applying a soluble polyimide film, polyamic acid, or the like to a substrate by a roll coating method, a spin coating method, or the like. In this embodiment mode, the alignment film is formed by spin coating at 180 ° C. for 90 minutes after spin coating.

Here, the pretilt angle is 1 ° to 10 °.
Good degree. Note that the alignment film 7 used in the present embodiment is used.
・ Pretilt angle (catalog value) of material 8 is 7 ° to 8
°.

A polarizing plate 11 is provided on the surface of the glass substrate 1 opposite to the side on which the electrodes 3 are formed.
On the other hand, a polarizing plate 12 is provided on the surface of the glass substrate 2 opposite to the side on which the electrodes 5 are formed.

As described above, the glass substrate 1, the electrodes 3,...
An electrode substrate (substrate) 13 is formed by the insulating film 4, the alignment film 7, and the polarizing plate 11. On the other hand, an electrode substrate (substrate) 14 is formed by the glass substrate 2, the electrodes 5,..., The insulating film 6, the alignment film 8, and the polarizing plate 12.

The electrode substrates 13 and 14 are maintained at substantially uniform intervals by the 1.4 μm spacers 15 scattered, and are bonded together by the sealant 9.
Here, particularly in the present embodiment, as shown in FIG.
In the electrode substrates 13 and 14, the rubbing directions of the alignment films 7 and 8 substantially match (θ: shift angle in the rubbing direction, 0 <θ <1).
0 °), the polarization axis of the polarizing plate 12 is
(Φ: the angle between the polarization axis and the rubbing direction, 0 <φ <θ), and the polarizing axis of the polarizing plate 11 is disposed so as to be orthogonal to the polarizing axis of the polarizing plate 12. I have.

In the space formed between the electrode substrates 13 and 14 which is kept constant at a cell thickness of 1.4 to 1.5 μm, a positive dielectric anisotropy composed of the liquid crystal molecules 10a (FIG. 1) is provided. The liquid crystal layer 10 is formed by injecting a nematic liquid crystal material (E8, manufactured by Merck) having the following formula (1) from an injection port (not shown). After the formation of the liquid crystal layer 10, the injection port is sealed with a sealing agent.

Note that the liquid crystal cell 16 of the present embodiment
The rubbing direction is almost parallel to the CB mode liquid crystal cell (FIG. 9A), but the biaxial film 1
The difference is that 26 is not used, and that the polarizing axis of one of the polarizing plates and the rubbing direction are almost the same, and the other is provided so as to be orthogonal to those directions.

Next, the operation of the liquid crystal cell 16 of the present embodiment will be described with reference to FIG. 1 and FIGS.

When a voltage is gradually applied while observing the liquid crystal cell 16, the following phenomenon is observed.

(1) 0V When no voltage is applied to the liquid crystal cell 16, that is, in the initial state, the alignment state of the liquid crystal molecules 10a is splay alignment (FIG. 1 (a)). Therefore, since the polarizing axes of the polarizing plates 11 and 12 are arranged so as to be orthogonal to each other, no light is transmitted and the light is turned to a black state (FIG. 4A). Further, even when the liquid crystal cell 16 is observed from directly above or obliquely, there is no light leakage and the liquid crystal cell 16 is in a black state.

(2) 0 V to 3 V A voltage is applied to the liquid crystal cell 16 to gradually increase the voltage. At this time, when the liquid crystal cell 16 is observed from directly above, it is in a black state, but when obliquely observed, it can be seen that light is transmitted. At this time, the alignment state of the liquid crystal molecules 10a is a state in which the major axis is starting to be parallel to the electric field.

(3) 3 V to 5 V (threshold voltage Vth1) When the applied voltage is further increased, a black and round domain D1 starts to be generated from several places of the liquid crystal cell 16 as compared with no voltage application (FIG. 4B). . This domain D1 is black even when viewed obliquely. After that, when the voltage is further increased gradually, the domain D1 grows until the entire surface of the liquid crystal cell 16 is covered by about 5 V (threshold voltage Vth1), and the entire surface of the liquid crystal cell 16 becomes black (FIG. 4C). . At this time, the alignment state of the liquid crystal molecules 10a is twisted vertical alignment or vertical alignment (having a twist angle of 0 °) (FIG. 1B).
Note that the nail in FIG. 1B indicates a liquid crystal molecule 10a in which the head of the nail is tilted away from the paper surface.

(4) Very small voltage (1 V or less, threshold voltage Vth2
(Immediately) Then, when the applied voltage is changed from 5 V (threshold voltage Vth1) to a very small voltage (threshold voltage Vth2) of 1 V or less in the above state (FIGS. 1B and 4C), light is emitted. Transmissive, liquid crystal cell 1
6 becomes white (FIG. 4D). At this time, the alignment state of the liquid crystal molecules 10a is a twisted horizontal alignment (FIG. 1C). Note that the nail in FIG. 1C is a liquid crystal molecule 1 in which the head of the nail is tilted away from the paper surface.
0a is shown.

(5) Very small voltage (1 V or less, threshold voltage Vth2
(Several seconds later) When the applied voltage is set to a very small voltage (threshold voltage Vth2) of 1 V or less, the alignment state of the liquid crystal molecules 10a becomes a twisted horizontal alignment state (FIG. 1C) and becomes a white state (FIG. 4C). (D))
Thereafter, with time, black and round domains D2 begin to grow from several places of the liquid crystal cell 16 in the white state (FIG. 4).
(E)). After a further time, the domain D2 covers the entire surface of the liquid crystal cell 16 and becomes the same black state as the initial state (FIG. 4 (f)). At this time, the alignment state of the liquid crystal molecules 10a has returned to the splay alignment, which is the initial alignment state (FIG. 1A). Note that the small voltages (1) of (4) and (5)
V or less, the threshold voltage Vth2) may be 0V.

As described above, by applying a voltage higher than the threshold voltage Vth1 to the liquid crystal cell 16 according to the present embodiment, the alignment state of the liquid crystal molecules 10a is twisted vertical alignment or vertical alignment (FIG. 1B). ) And a black state (FIG. 4 (c)) can be achieved, and then the applied voltage is reduced to a very small voltage (threshold voltage Vth
2), the alignment state of the liquid crystal molecules 10a becomes a twisted horizontal alignment (FIG. 1C) and a white state (FIG. 4D).
Can be achieved. Therefore, a liquid crystal display element of a new mode using the two alignment states of the liquid crystal molecules 10a can be formed.

Here, the orientation of the liquid crystal molecules 10a will be supplemented.

The liquid crystal molecules 10 in the white state (4)
When microscopic observation was performed to examine the orientation state of a, FIG.
The disclination D3 shown in FIG. Then, in (4), the liquid crystal cell 16 is brought into the white state in two ways: (A) the liquid crystal molecules 10a are twisted and horizontally aligned; and (B) the liquid crystal molecules 10a are tilted in random directions. If the orientation is (B), the texture must be such that the direction parallel to the polarization axis of the polarizing plate becomes dark, but such a phenomenon has not been observed. Therefore, it is considered that the alignment state is (A).

Further, since disclination D3 occurs in the orientation state of (A), the white state assumes an orientation state twisted by 180 ° (FIG. 1 (c)). , A left 180 ° twist exists, and the disclination D3 is considered to appear at the boundary.

Next, in order to check the orientation state of the round and dark domain D1 in (3), the voltage was set to 5 V in (3).
(Threshold voltage Vth1), and the voltage was set to 0 V (threshold voltage Vth2) at the stage when the domain D1 started to grow slightly. At this time, the part that was the domain D1 became white, and the other parts became the same state as the black initial state.

From this, the domain D1 is closely related to the 180 ° twisted structure in the white state, and the alignment state of the liquid crystal molecules 10a at that time is vertical alignment as shown in FIG. It is considered that a vertical alignment state is obtained.

The liquid crystal layer 10 in the white state (4)
Includes a mixture of right-handed and left-handed liquid crystal molecules 10a and a disclination D3 (FIG. 5).
The following two methods are conceivable in order to prevent the occurrence of the disclination D3.
The first method unifies the twist direction of the liquid crystal molecules 10a to one of the twists by gradually increasing the shift angle θ of the rubbing directions of the electrode substrates 13 and 14 from 0 °. The second method is to increase the ratio of the chiral nematic liquid crystal material occupying the liquid crystal layer 10 to increase the twisting force of one of the liquid crystal layers 10 and unify the twisting direction of the liquid crystal molecules 10a to one of them.

However, when an image is actually displayed using this mode for a simple matrix or an active matrix, the white state of (4) must be maintained.

Therefore, as a method for stabilizing the white state,
The following four methods are conceivable.

(A) Method of Applying Reset Pulse A voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal cell 16 to change the liquid crystal molecules 10a into a twisted vertical alignment state or a vertical alignment state (FIG. 1 (b)). After the state is changed to (FIG. 4 (c)), the applied voltage is set to the threshold voltage Vth2, and the liquid crystal molecules 10a are turned into a twisted horizontal alignment (FIG. 1 (c)) to form a white state (FIG. 4 (c)).
(D)), and then apply a reset pulse. Here, the reset pulse to be applied has a magnitude (voltage equal to or higher than the threshold voltage Vth1) and an application time sufficient to bring the liquid crystal molecules 10a into a twisted vertical alignment or a vertical alignment state (FIG. 1B). Any voltage pulse may be used, and it may be applied before the alignment state of the liquid crystal molecules 10a shifts from twisted horizontal alignment to splay alignment. For example, it may be applied every frame (16 ms).

In this embodiment, as shown in FIG. 6A, a rectangular wave voltage pulse is applied periodically alternately in a positive and negative manner in consideration of DC balance. At this time, the change in the transmittance of the transmitted light was as shown in FIG. The transmittance of the transmitted light gradually increases from the application end point (T0) of the voltage pulse to reach 100%, and rapidly decreases from the application start point (T3) to reach 0%. Thus, the white state could be displayed continuously. The detailed experimental results will be described later.

(B) Method of Mixing Photosensitive Monomer in Liquid Crystal Layer and Irradiating Ultraviolet Light Photosensitive monomer is mixed in liquid crystal layer 10, a voltage higher than threshold voltage Vth 1 is applied, and liquid crystal molecules 10 a are twisted in a vertical alignment state. Alternatively, the liquid crystal molecules 10a are stabilized in the twisted vertical alignment state or the vertical alignment state by performing ultraviolet exposure after the vertical alignment state (FIG. 1B) is changed to the black state (FIG. 4C). After the applied voltage is set to the threshold voltage Vth2, the alignment state is a twisted horizontal alignment of a white state (FIG. 1).
(C)) can be stabilized.

In the present embodiment, the nematic liquid crystal material E
8 was added with a photosensitive monomer of 1%, a voltage higher than the threshold voltage Vth1 was applied, and the liquid crystal molecules 10a were twisted in a vertical alignment state or a vertical alignment state (FIG. 1B), and ultraviolet rays were irradiated at 4 mW / cm ^2. For 3 minutes. Thus, after the applied voltage is set to the threshold voltage Vth2, the alignment state of the liquid crystal molecules 10a can be stabilized to a twisted horizontal alignment state (FIG. 1C), and a white state can be displayed continuously. did it. The voltage applied to bring the liquid crystal molecules 10a into a twisted vertical alignment state or a vertical alignment state (FIG. 1B) may be a reset pulse as shown in FIG. 6A.

(C) A method of adding a chiral agent to the liquid crystal material so that the twist of the liquid crystal molecules becomes 180 ° d (cell thickness) / P (spiral pitch) ≒ 1/2, that is, 1
A liquid crystal material to which a chiral nematic liquid crystal material is added so as to be twisted by 80 ° is injected into the liquid crystal layer 10. Thus, the liquid crystal cell 16 is in a white state in an initial state where no voltage is applied. Then, even when a voltage is gradually applied to the liquid crystal cell 16, the domain D1 shown in FIG.
And gradually changes to a dark state as the major axis of the liquid crystal molecules 10a stands parallel to the direction of the electric field. Furthermore, the white state is returned immediately after the voltage is cut off. That is, the initial alignment state of the liquid crystal molecules 10a can be horizontal alignment (FIG. 1C), and the white state can be stabilized.

(D) Method of Adding Dichroic Dye A liquid crystal material added with a dichroic dye is injected into a liquid crystal cell without a polarizing plate. When a voltage higher than the threshold voltage Vth1 is applied to such a liquid crystal cell, the alignment state of the liquid crystal molecules becomes a twisted vertical alignment state or a vertical alignment state (FIG. 1B), and light is not absorbed by the dichroic dye. Through. Further, when the applied voltage is a threshold voltage Vth2, the alignment state of the liquid crystal molecules becomes a twisted horizontal alignment state (FIG. 1C), light is absorbed by the dichroic dye, and a black state is obtained.

In this embodiment, the nematic liquid crystal material E
8, 2% of a dichroic dye was added and injected into the liquid crystal cell 16. In addition, the polarizing plates 11 and 12 were removed from the upper and lower electrode substrates 13 and 14. In addition, the liquid crystal cell as described above can be used for a reflection type display because a black and white display can be performed without adding a polarizing plate by adding a dichroic dye to the liquid crystal.

Here, experimental results on the response speed, luminance and contrast of the liquid crystal cell according to the present embodiment will be shown. The liquid crystal cell used had a cell thickness of 1.4 μm and was driven at 35 ° C. As the reset pulse to be applied, a rectangular wave of 10 V and 500 μs was periodically applied alternately in a positive and negative manner every 50 ms (FIG. 6B).

Response speed (cell thickness: 1.4 μm) Time from the end of the voltage pulse until the transmittance becomes 10% T0 → T1 7.8ms Time when the transmittance changes from 10% to 90% T1 → T28 .2 ms The time during which the transmittance changes from 90% to 10% after the application of the voltage pulse T3 → T4 34 μs

Brightness and contrast (brightness and contrast in white state and black state) Bright state 76 cd / m ² Dark state 0.5 cd / m ² Contrast 152: 1

The response speed when the cell thickness of the liquid crystal cell is 2.6 μm is also shown. The conditions are the same as those described above.

Response speed (cell thickness 2.6 μm) Time from the end of the voltage pulse until the transmittance becomes 10% T0 → T1 16.0 ms Time when the transmittance changes from 10% to 90% T1 → T2 15 0.0ms The time when the transmittance changes from 90% to 10% after applying a voltage pulse T3 → T4 290 μs

As described above, in the liquid crystal cell according to the present embodiment, by applying a voltage equal to or higher than the threshold voltage Vth1, the liquid crystal molecules 10a are twisted in a vertical alignment state or a vertical alignment state (FIG. 1B). As a result, the black state (FIG. 4C) can be stably achieved, and thereafter, the applied voltage is reduced to the threshold voltage Vth2.
By setting (Vth1> Vth2), the liquid crystal molecules 10a are turned into a twisted horizontal alignment state (FIG. 1C) and a white state (FIG. 4C).
Since (d)) can be stably achieved, a liquid crystal display device of a new mode using the alignment state of these two liquid crystal molecules 10a can be formed.

By making the liquid crystal cell thin as a parallel rubbing cell having a cell thickness of 3 μm or less, a faster response and a wider viewing angle than a TN mode liquid crystal display element can be secured. Further, a sufficient contrast can be secured.

The liquid crystal cell according to the present embodiment only needs to have a cell thickness of 3 μm or less, but realizes faster response characteristics by further reducing the cell thickness to 1.5 μm or less. be able to.

[0084]

As described above, the liquid crystal display element according to the first aspect of the present invention comprises a liquid crystal layer made of a nematic liquid crystal material or a chiral nematic liquid crystal material having a positive dielectric anisotropy. In a liquid crystal display element held between a pair of substrates each having an electrode for applying a voltage to the layer, the liquid crystal layer has at least liquid crystal molecules in a twisted vertical alignment state and a twisted horizontal alignment according to the magnitude of the applied voltage. In this configuration, the display state of the pixel is switched using two states of a twisted horizontal alignment state and a twisted vertical alignment state of the liquid crystal molecules of the liquid crystal layer.

Therefore, the switching of the display state of the pixel can be performed by using two states of the liquid crystal molecules in the liquid crystal layer, that is, the twisted horizontal alignment state and the twisted vertical alignment state. Therefore, there is an effect that a liquid crystal display element of a new mode using the alignment state of these two liquid crystal molecules can be formed.

As described above, in the liquid crystal display element of the second aspect of the present invention, in addition to the configuration of the first aspect, the pair of substrates has substantially the same rubbing direction, and A pair of polarizing plates provided one by one, while the polarization axis of one of the polarizing plates substantially coincides with the rubbing direction,
The polarizing axis of the one polarizing plate is orthogonal to the polarizing axis of the other polarizing plate, and the thickness between the pair of substrates is smaller than the thickness determined by the limit of Morgan.

Therefore, in addition to the effect of the structure of claim 1, when a voltage equal to or higher than the threshold voltage Vth1 is applied to the liquid crystal layer to bring the liquid crystal molecules into a twisted vertical alignment state, the polarization axes of the polarizing plates become orthogonal. Therefore, the liquid crystal display element can be brought to a black state. Further, the voltage applied thereafter is changed to a threshold voltage Vth2.
When the liquid crystal molecules in the liquid crystal layer are in a twisted horizontal alignment state, the liquid crystal display element can be in a white state.

Therefore, the following effects are obtained.
The switching of the display state of the pixel can be performed using the two states of the twisted horizontal alignment state and the twisted vertical alignment state of the liquid crystal molecules of the liquid crystal layer. Therefore, a liquid crystal display element of a new mode using the alignment state of these two liquid crystal molecules can be formed. Further, the liquid crystal cell is thinner than the thickness determined by Morgan's limit (for example, 3 μm).
m or less), the response speed can be made higher than that of the conventional TN mode liquid crystal display element, and a wide viewing angle can be secured. Further, a sufficient contrast can be secured.

According to a third aspect of the present invention, as described above, in addition to the constitution of the first or second aspect, the liquid crystal layer contains a photosensitive monomer, and the liquid crystal of the liquid crystal layer has In this configuration, ultraviolet rays are irradiated in a state where a voltage is applied so that molecules are in a twisted horizontal alignment state.

Therefore, in addition to the effect of the configuration of claim 1 or 2, after the applied voltage is set to the threshold voltage Vth2,
Since the alignment state of the liquid crystal molecules can be stabilized to a twisted horizontal alignment state, a white state can be continuously displayed. Therefore, there is an effect that an image can be displayed by using the liquid crystal display element for a simple matrix or an active matrix.

As described above, in the liquid crystal display device according to the fourth aspect of the present invention, in addition to the configuration of the first or second aspect, the liquid crystal layer may include a twist angle in a twisted horizontal alignment state of the liquid crystal molecules of the liquid crystal layer. Is a configuration in which a chiral agent is added so that the angle between the pair of substrates becomes substantially 180 °.

Therefore, in addition to the effect of the configuration of claim 1 or 2, after the applied voltage is set to the threshold voltage Vth2,
Since the alignment state of the liquid crystal molecules can be stabilized to a twisted horizontal alignment state, a white state can be continuously displayed. Further, occurrence of disclination in the white state can be prevented. Therefore, there is an effect that an image can be displayed by using the liquid crystal display element for a simple matrix or an active matrix.

As described above, in the liquid crystal display element according to the fifth aspect of the present invention, in addition to the structure of the first aspect, the pair of substrates has substantially the same rubbing direction, and the liquid crystal layer has In this configuration, a dichroic dye is added.

Therefore, in addition to the effect of the structure of claim 1, by adding a dichroic dye to a liquid crystal cell in which the alignment directions of liquid crystal molecules are substantially the same, the threshold voltage V
When a voltage of th1 or more is applied, the liquid crystal molecules are in a twisted vertical alignment state, and light is transmitted without being absorbed by the dichroic dye, so that a white state can be obtained. When the applied voltage is the threshold voltage Vth2, the liquid crystal molecules are in a twisted horizontal alignment state, and light is absorbed by the dichroic dye, so that a black state can be obtained.

Therefore, since a monochrome display can be stably performed, an effect can be obtained that an image can be displayed by using the liquid crystal display element in a simple matrix or an active matrix. In addition, since it is not necessary to provide a polarizing plate, there is an effect that it can be used for a reflective display.

According to the liquid crystal display element of the invention of claim 6, in addition to the constitution of claim 1 or 2, when the liquid crystal molecules of the liquid crystal layer are in a twisted horizontal alignment state, the liquid crystal display element changes to a splay alignment state. Before the start of the transition, a reset pulse having a waveform having a voltage and an application time sufficient to maintain the twisted horizontal alignment state is applied.

Therefore, in addition to the effects of the first and second aspects, when the applied voltage is the threshold voltage Vth2, the alignment state of the liquid crystal molecules can be maintained in a twisted horizontal alignment state. The white state can be displayed continuously.

Therefore, an effect is obtained that an image can be displayed by using the liquid crystal display element in a simple matrix or an active matrix.

The liquid crystal display element according to the seventh aspect of the present invention has a configuration in which the reset pulse is periodically applied in addition to the configuration of the first or second aspect.

Therefore, in addition to the effect of the configuration of claim 1 or 2, after setting the applied voltage to the threshold voltage Vth2,
Since the alignment state of the liquid crystal molecules can be maintained in a twisted horizontal alignment state, the white state can be displayed continuously and more stably.

Therefore, an effect is obtained that an image can be displayed by using the liquid crystal display element in a simple matrix or an active matrix.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory diagrams showing alignment states of liquid crystal molecules of a liquid crystal display device according to an embodiment of the present invention, wherein FIG. 1A is an initial state, FIG. 1B is a state in which a voltage is applied, and FIG. ) Indicates a state where the application of the voltage is removed.

FIG. 2 is a cross-sectional view schematically showing a configuration of a liquid crystal cell using the liquid crystal display device of FIG.

FIG. 3 is an explanatory diagram showing a relationship between a rubbing direction and a polarization direction in bonding the electrode substrates of the liquid crystal cell of FIG.

4A and 4B are explanatory diagrams showing a state of a liquid crystal cell when a voltage is gradually applied while observing the liquid crystal cell of FIG. 2 from directly above, where FIG. 4A is an initial state, and FIG. (C) is a state in which a voltage is further applied, (d) is a state in which the voltage is removed, (e) is a state several seconds after the removal of the voltage, and (f) is a state in which the voltage is applied. Shows a state in which a further time has passed after the removal of.

FIG. 5 is a schematic diagram of disclination that appears when the voltage applied to the liquid crystal cell of FIG. 2 is removed.

6A and 6B are explanatory diagrams of operation timings showing a change in transmittance of a liquid crystal cell when a reset pulse is applied to the liquid crystal cell of FIG. 2; FIG.
(B) is a response waveform of the transmittance.

7A and 7B are explanatory diagrams schematically showing a conventional TN mode liquid crystal display element, in which FIG. 7A shows an alignment state of liquid crystal molecules when no voltage is applied, and FIG. 7B shows a liquid crystal when a voltage is applied. This is the orientation state of the molecule.

8A and 8B are explanatory views schematically showing a conventional STN mode liquid crystal display element, in which FIG. 8A shows an alignment state of liquid crystal molecules when no voltage is applied, and FIG. 8B shows a liquid crystal when a voltage is applied. This is the orientation state of the molecule.

9A and 9B are explanatory views schematically showing a conventional OCB mode liquid crystal display element, in which FIG.
(B) shows the alignment state of the liquid crystal molecules when no voltage is applied, and (c) shows the alignment state of the liquid crystal molecules when a voltage is applied.

FIG. 10 is a graph showing a voltage transmittance characteristic of a conventional OCB mode liquid crystal display element.

[Explanation of symbols]

 3.5 electrode 10 liquid crystal layer 10a liquid crystal molecule 11.12 polarizing plate 13.14 electrode substrate (substrate)

Claims (7)

[Claims] 1. A liquid crystal layer made of a nematic liquid crystal material or a liquid crystal layer made of a chiral nematic liquid crystal material having a positive dielectric anisotropy is held between a pair of substrates having electrodes for applying a voltage to the liquid crystal layer. In the liquid crystal display device, the liquid crystal layer is formed of a liquid crystal material whose liquid crystal molecules can take at least a twisted vertical alignment state and a twisted horizontal alignment state in accordance with the magnitude of an applied voltage; A liquid crystal display element characterized in that a display state of a pixel is switched using two states of a twisted horizontal alignment state and a twisted vertical alignment state of liquid crystal molecules. 2. The rubbing directions of the pair of substrates are substantially the same, and the pair of polarizing plates provided one by one on the pair of substrates is such that the polarization axis of one of the polarizing plates is in the rubbing direction. And that the polarization axis of the one polarizing plate is orthogonal to the polarization axis of the other polarizing plate, and that the thickness between the pair of substrates is smaller than the thickness determined by Morgan's limit. 2. The liquid crystal display device according to claim 1, wherein: 3. The liquid crystal layer is irradiated with ultraviolet rays in a state where a photosensitive monomer is added and a voltage is applied so that liquid crystal molecules of the liquid crystal layer are in a twisted horizontal alignment state. 3. The liquid crystal display device according to claim 1, wherein: 4. The liquid crystal layer according to claim 1, wherein a chiral agent is added so that a twist angle of the liquid crystal molecules in the liquid crystal layer in the twisted horizontal alignment state is approximately 180 ° between the pair of substrates. The liquid crystal display device according to claim 1 or 2, wherein 5. The liquid crystal display device according to claim 1, wherein the rubbing directions of the pair of substrates are substantially the same, and a dichroic dye is added to the liquid crystal layer. 6. When the liquid crystal molecules of the liquid crystal layer are in a twisted horizontal alignment state, the liquid crystal molecules have a voltage and an application time sufficient to maintain the twisted horizontal alignment state before the transition to the splay alignment state starts. 3. The liquid crystal display device according to claim 1, wherein a reset pulse having a waveform is applied. 7. The liquid crystal display device according to claim 6, wherein said reset pulse is applied periodically.