JPH07128650A - Liquid crystal display device and its driving method and its production - Google Patents

Abstract

PURPOSE:To suppress the generation of domains at the time of voltage impression by forming ruggedness on the surfaces of the coating layers on at least one of the substrate side. CONSTITUTION:This liquid crystal display device is constituted by holding a chiral nematic liquid crystal between a pair of substrates 2, forming electrodes 3 on the substrate 2 and forming the coating layers 4 on at least one of the substrate sides. The surfaces of the coating layers 4 has the ruggedness.The size of the domains generated at the time of voltage impression by the rugged shapes on the coating layers 4 is reduced and the domains are made visually negligible. Further, the liquid crystal is obliquely oriented in the microregions by the rugged shapes. The satd. voltage at which the domains disappear is thereby lowered. In addition, driving is executed between the state A and the state B after the domains are erased (state C) by impressing the voltage higher in the absolute value than the satd. voltage thereto at the time of starting in the driving method of the liquid crystal display device. As a result, the generation of the domains is suppressed and the display having high image quality is obtd.

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, a driving method thereof and a manufacturing method thereof.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device, the surface of a substrate is subjected to alignment treatment such as rubbing to make the liquid crystal in the cell into a monodomain. The structure of a typical TN (twisted nematic) type liquid crystal display device is shown in FIG. The liquid crystal molecules 5 are twisted by 90 ° between the two substrates 2 having the transparent electrodes 3. In order to obtain this liquid crystal alignment, the alignment film 6 is usually provided on the surface of the substrate 2 by rubbing treatment or the like. The two polarizers 1 are arranged so that their absorption axes coincide with the major axis direction of the liquid crystal molecules on the substrate surface (that is, the two polarizers 1
Are orthogonal to each other). The linearly polarized light that has passed through the polarizer 1 has its plane of polarization rotated (rotation) along the twist of the liquid crystal array.
Then, the light passes through the polarizer 1 on the opposite side (transmission). Next, when a voltage is applied, the alignment of the liquid crystal molecules 5 changes due to the dielectric anisotropy, and the rotation of the plane of polarization (optical rotation) disappears. The linearly polarized light incident from one of the polarizers 1 cannot pass through the polarizer 1 on the opposite side, and black display is obtained (blocked). However, the conventional mono-domain liquid crystal display device has a drawback that the viewing angle dependence of the display is large.

On the other hand, Kobayashi et al.
Announced N (Amorphous Twisted Nematic) liquid crystal display (SID '93 DIGEST p
622-625). In the a-TN type liquid crystal display device, since the liquid crystal molecules 5 on the coating layer 4 not subjected to the alignment treatment are adsorbed randomly as shown in FIG. 2, there are innumerable micro twist regions. Therefore, the viewing angle is wide and T
Alignment treatment such as rubbing, which is indispensable for N-type liquid crystal display devices, is unnecessary, and it is excellent as a display device.

[0004]

However, the above-mentioned a-T
In the N-type liquid crystal display device, domains are generated when a voltage is applied. For this reason, (1) there is leakage light and the contrast is reduced (2) the domain becomes display uneven in the halftone (3)
A hysteresis phenomenon (hysteresis) in the transmittance T-applied voltage V characteristic
There are issues such as the existence of.

Since the a-TN type liquid crystal display device is not subjected to alignment treatment such as rubbing, the tilt angle (pretilt angle θp) of the liquid crystal molecules 5 with respect to the substrate is approximately 0 °. When a voltage is applied, a reverse tilt domain in which the tilt angle of the liquid crystal molecules 5 is opposite between the domain | and the domain ‖ shown in FIG. 3, and the image quality is degraded. Also, as shown in FIG. 1, due to the leakage light between the domains 12,
Since the transmittance-applied voltage characteristic 7 when the voltage rises and the transmittance-applied voltage characteristic 8 when the voltage falls are different, halftone display is not possible.

The present invention solves the above-mentioned problems.
An object of the present invention is to provide a driving method of a liquid crystal display device that suppresses domain generation when a voltage is applied, a high image quality a-TN type liquid crystal display device that suppresses domain generation, and a manufacturing method thereof.

[0007]

A liquid crystal display device of the present invention comprises a chiral nematic liquid crystal sandwiched between a pair of substrates, electrodes are formed on the substrates, and at least one of the substrates is coated. A liquid crystal display device having a layer is characterized in that the surface of the coating layer has irregularities. Furthermore, the spontaneous pitch p of the chiral nematic liquid crystal and the distance d between the pair of substrates are approximately d = p /
It is characterized by being 4. Furthermore, the unevenness on the surface of the coating layer is not anisotropic.

In the driving method of the present invention, a chiral nematic liquid crystal is sandwiched between a pair of substrates, electrodes are formed on the substrates, and a coating layer is formed on at least one of the substrates. In the method for driving a liquid crystal display device, the driving voltage when the liquid crystal display device is started is equal to or higher than the saturation voltage in absolute value, and the off voltage when the liquid crystal display device is driven is equal to or higher than the threshold voltage in absolute value. Characterize. Furthermore, in the method for driving a liquid crystal display device having an uneven surface on the coating layer, the drive voltage at the time of starting the liquid crystal display device is an absolute value equal to or higher than the saturation voltage of the liquid crystal display device, The off-voltage at the time is an absolute value which is equal to or higher than the threshold voltage of the liquid crystal display device.

Further, in the method for manufacturing a liquid crystal display device of the present invention, a chiral nematic liquid crystal is sandwiched between a pair of substrates, electrodes are formed on the substrates, and a coating layer is provided on at least one substrate side. In the method for manufacturing a liquid crystal display device in which the above is formed, an uneven surface is formed on the surface of the coating layer. Furthermore, it is characterized in that an uneven surface is formed on the surface of the coating layer by a stamping method. Further, it is characterized in that an uneven surface is formed by mixing fine particles into the coating layer. Further, it is characterized in that an uneven surface is formed by mixing a polymer material having a side chain into the coating layer. Further, the invention is characterized in that the coating layer having an uneven surface is formed by depositing an organic or inorganic material on a substrate.

[0010]

In the driving method of the liquid crystal display device of the present invention, as shown in FIG. 1, after the domain is erased by applying a voltage whose absolute value is the saturation voltage or more at the time of starting (state C), state A and state B
Drive between. As a result, the generation of domains can be suppressed, and high-quality display can be obtained. The saturation voltage is the voltage when the domain disappears and the transmittance change is 95% or more, and the threshold voltage is the voltage when the transmittance change is 10%.

In the liquid crystal display device of the present invention, the size of the domain generated when a voltage is applied can be reduced by the uneven shape on the coating layer 4, and the domain can be visually ignored. Further, due to the uneven shape, the liquid crystal can be tilted and aligned in a micro area, and the saturation voltage at which the domain disappears can be reduced.

Further, by carrying out the above two inventions at the same time, it is possible to completely suppress the generation of domains and obtain a high quality display.

According to the method of manufacturing a liquid crystal display device of the present invention, the unevenness on the coating layer 4 can be industrially easily manufactured.

[0014]

【Example】

(Example 1) Polyimide SP-740 (manufactured by Toray) was applied onto the glass substrate 2 having the ITO transparent electrode 3 by a spin coating method, and cured at 250 ° C for 1 hour in a constant temperature bath to form a coating layer 4. The polyimide coating layer has a cell gap of 3.5μ without being subjected to orientation treatment such as rubbing.
m sandwich type cell was prepared. The chiral nematic liquid crystal used in this example is a nematic liquid crystal ZLI.
Spontaneous pitch 14μ obtained by adding 0.57 wt% of chiral agent S-811 (manufactured by Merck) to -1132 (manufactured by Merck).
m liquid crystal material.

The sandwich type cell is set on a heater plate, and the liquid crystal phase-isotropic phase transition temperature of 100 or more is set.
The chiral nematic liquid crystal was injected in the isotropic phase state at ℃. After the injection, the liquid crystal panel was manufactured by cooling to room temperature, and the polarizers 1 were attached so as to be orthogonal to each other to obtain a liquid crystal display device for testing.

Threshold voltage 2.2V, saturation voltage 6.5V
When an active element (thin film transistor TFT) was used for the a-TN type liquid crystal display device of No. 1 and a voltage of 7V was applied at the time of start-up, followed by driving with an off voltage of 2.5V and an on voltage of 5V, a contrast of 1:45 was obtained Was given. The halftone display was also good, and no history phenomenon was observed.

(Embodiment 2) A glass substrate 14 having an ITO transparent electrode coated with an epoxy resin 13 has a diameter of about 1
A coating layer was formed by pressing a stamp with countless 0 μm hemispherical projections (FIG. 4).
A sandwich type cell having a cell gap of 3.5 μm was produced using this substrate. The chiral nematic liquid crystal used in this example is a liquid crystal material with a spontaneous pitch of 14 μm in which 0.57 wt% of the chiral agent S-811 is added to the nematic liquid crystal ZLI-1132.

The sandwich type cell was set on a heater plate, and a liquid crystal phase-isotropic phase transition temperature of 100 or higher was set.
The chiral nematic liquid crystal was injected in the isotropic phase state at ℃. After the injection, the liquid crystal panel was manufactured by cooling to room temperature, and the polarizers 1 were attached so as to be orthogonal to each other to obtain a liquid crystal display device for testing.

When the active element was driven at an off voltage of 2 V and an on voltage of 5 V, a contrast of 1:50 was obtained. The halftone display was also good, and no history phenomenon was observed.

(Example 3) Polyimide SP-740 mixed with glass spheres 16 having a diameter of about 1.5 μm was applied onto a glass substrate 14 with an ITO transparent electrode by spin coating and cured in a constant temperature bath at 250 ° C. for 1 hour. Then, a coating layer having an uneven shape was formed (FIG. 5). With this substrate,
A test liquid crystal display device was produced in the same manner as in Example 2.

When the active element was driven at an off voltage of 2 V and an on voltage of 5 V, a contrast of 1:48 was obtained. The halftone display was also good, and no history phenomenon was observed.

Example 4 An organic solution in which the concentration of polyimide RN-626 (manufactured by Nissan Kagaku) having side chains 17 for vertically aligning the liquid crystal molecules 5 was 0.25 wt% with respect to the solvent was transparent by spin coating. Apply to the electrode-equipped substrate 14,
The coating was cured in a constant temperature bath at 200 ° C. for 1 hour to form a coating layer with side chains 17 protruding (FIG. 6). Using this substrate, a test liquid crystal display device was manufactured in the same manner as in Example 2.

When the active element was driven at an off voltage of 2 V and an on voltage of 5 V, a contrast of 1:52 was obtained. The halftone display was also good, and no history phenomenon was observed.

Example 5 A small amount of SiO19 was vertically vapor-deposited on a substrate 14 with a transparent electrode in vacuum to form a coating layer having irregularities (FIG. 7). With this substrate,
A test liquid crystal display device was produced in the same manner as in Example 2.

When the active element was driven at an off voltage of 2 V and an on voltage of 5 V, a contrast of 1:45 was obtained. The halftone display was also good, and no history phenomenon was observed.

Example 6 The surface of a substrate coated with polyimide SP-740 was ion-etched in a low vacuum to form a coating layer having irregularities (FIG. 8). Using this substrate, a test liquid crystal display device was manufactured in the same manner as in Example 2.

When the active element was driven at an off voltage of 2 V and an on voltage of 5 V, a contrast of 1:45 was obtained. The halftone display was also good, and no history phenomenon was observed.

Example 7 The liquid crystal display device manufactured in Example 2 was driven in the same manner as in Example 1, and the ratio was 1:75.
High contrast was obtained. The halftone display was also good, and no history phenomenon was observed.

[0029]

As described above, according to the present invention, a driving method of an a-TN type liquid crystal display device which suppresses domain generation when a voltage is applied, and a high image quality a-TN type liquid crystal display device which suppresses domain generation and the same are provided. It realizes the manufacturing method.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmittance T-applied voltage V characteristic of an a-TN type liquid crystal display device.

FIG. 2 is a schematic cross-sectional view of an a-TN type liquid crystal display device.

FIG. 3 is a diagram showing the behavior of liquid crystal molecules when a voltage is applied in an a-TN type liquid crystal display device.

FIG. 4 is a schematic cross-sectional view of a coating layer provided with unevenness by a stamp.

FIG. 5 is a schematic cross-sectional view of a coating layer mixed with glass spheres.

FIG. 6 is a schematic cross-sectional view of a coating layer applied with a polymer material having a side chain.

FIG. 7 is a schematic sectional view of a coating layer in which SiO is vertically vapor-deposited.

FIG. 8 is a schematic cross-sectional view of a coating layer subjected to etching.

FIG. 9 is a schematic cross-sectional view of a conventional TN type liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polarizer 2 ... Transparent substrate 3 ... Transparent electrode 4 ... Coating layer 5 ... Liquid crystal molecule 6 ... Alignment film 7 ... Transmittance T at the time of voltage rise-Applied voltage V characteristic 8 ... Transmittance T when voltage drops-Applied voltage V characteristic 9 ... Electric field direction 10 ... Tilt direction of liquid crystal molecule in domain | 11 ... Tilt direction of liquid crystal molecule in domain ‖ 12 ... Domain Boundary line between | and domain‖ (disclination line) 13 Epoxy resin 14 Glass substrate with transparent electrode 15 Polyimide 16 Glass sphere 17 Polyimide side chain 18 Polyimide main chain 19・ ・ SiO 20 ・ ・ Polyimide A ・ ・ ・ Off voltage B ・ ・ ・ On voltage C ・ ・ ・ Saturation voltage

Claims (12)

[Claims] 1. A liquid crystal display device comprising a chiral nematic liquid crystal sandwiched between a pair of substrates, electrodes formed on the substrates, and a coating layer formed on at least one of the substrates. A liquid crystal display device, wherein the surface of the coating layer has irregularities. 2. In the liquid crystal display device, a spontaneous pitch p of the chiral nematic liquid crystal and a distance d between the pair of substrates.
The liquid crystal display device according to claim 1, wherein is approximately d = p / 4. 3. The liquid crystal display device according to claim 1, wherein the irregularities on the surface of the coating layer have no anisotropy. 4. A method of driving a liquid crystal display device, which comprises a pair of substrates and a chiral nematic liquid crystal sandwiched between the substrates, electrodes are formed on the substrates, and a coating layer is formed on at least one of the substrates. In the liquid crystal display device, the drive voltage when the liquid crystal display device is started is equal to or higher than the saturation voltage in absolute value, and the off voltage when the liquid crystal display device is driven is equal to or higher than the threshold voltage in absolute value. Driving method. 5. A method of driving a liquid crystal display device having an uneven surface on the coating layer, wherein a drive voltage at the time of starting the liquid crystal display device is an absolute value equal to or higher than a saturation voltage of the liquid crystal display device. A method for driving a liquid crystal display device, wherein an off-voltage when the device is driven is equal to or higher than a threshold voltage of the liquid crystal display device as an absolute value. 6. A method of manufacturing a liquid crystal display device, comprising a pair of substrates and a chiral nematic liquid crystal sandwiched between the substrates, electrodes formed on the substrates, and a coating layer formed on at least one of the substrates. 2. A method for manufacturing a liquid crystal display device, which comprises forming an uneven surface on the surface of the coating layer. 7. The method for manufacturing a liquid crystal display device according to claim 6, wherein an uneven surface is formed on the surface of the coating layer by a stamping method. 8. The method for manufacturing a liquid crystal display device according to claim 6, wherein the uneven surface is formed by mixing fine particles in the coating layer. 9. The method for manufacturing a liquid crystal display device according to claim 6, wherein the uneven surface is formed by mixing a polymer material having a side chain in the coating layer. 10. The method of manufacturing a liquid crystal display device according to claim 6, wherein the coating layer having an uneven surface is formed by depositing an organic or inorganic material on a substrate. 11. Forming the coating layer on the substrate,
7. The method for manufacturing a liquid crystal display device according to claim 6, wherein an uneven surface is formed by depositing an organic or inorganic material on the surface of the coating layer. 12. The method for manufacturing a liquid crystal display device according to claim 6, wherein the surface of the coating layer is subjected to an etching treatment to form an uneven surface.