JPH0815707A - Liquid crystal display device and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] The present invention eliminates the rubbing treatment that causes viewing angle dependence and causes product defects such as display defects and element destruction, and also makes it possible to eliminate the rubbing process.
No. 20 and Japanese Patent Application No. 5-326990, a liquid crystal display capable of suppressing display defects due to a reverse tilt that may occur in a liquid crystal cell having a multi-domain structure and controlling the amount of generation to improve display quality. An object is to provide an element and a manufacturing method thereof. A liquid crystal display device according to the present invention has a liquid crystal layer containing a liquid crystal material having a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton, and a pair of substrates sandwiching the liquid crystal layer. The method of manufacturing a liquid crystal display device according to the present invention comprises a step of preparing a liquid crystal material having a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton, and a pair of liquid crystal materials facing each other at predetermined intervals. Injecting between the substrates.

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 improving display quality and a manufacturing method thereof.

[0002]

2. Description of the Related Art A liquid crystal display device used in a liquid crystal display or the like, a so-called liquid crystal cell, changes a specific molecular arrangement of liquid crystal into another different molecular arrangement by an external action such as an electric field, and transmits an optical signal between them. The change in the physical characteristics is used as a visual change for display. In order to bring the liquid crystal molecules into a specific alignment state, it is common to perform an alignment treatment on the surface of the glass substrate that sandwiches the liquid crystal.

In a conventional twisted nematic (TN) type liquid crystal cell or the like, a so-called rubbing method in which a glass substrate sandwiching the liquid crystal is unidirectionally rubbed with a glass cloth is used as an alignment treatment.

The rubbing directions are performed so that the rubbing directions are orthogonal to each other between the upper and lower substrates, and when the liquid crystal cell is a negative display, a polarizing plate with parallel Nicol arrangement sandwiching the cells is used. The polarizers are arranged so as to be parallel to the direction, and in the case of positive display, the polarizing plates in the orthogonal Nicol arrangement are arranged so that their polarization axes are parallel to the rubbing direction of the substrate.

[0005]

When the alignment treatment is performed by such rubbing, since the alignment direction of the liquid crystal molecules is uniform, the angle at which the display is easily seen by the observer is within a specific angle range. The viewing angle characteristic is limited to.

For example, when an iso-contrast curve representing the viewing angle characteristic of a conventional twisted nematic liquid crystal cell (TN-LCD) is measured, the viewing angle region with high contrast is biased to a specific angle region. Therefore, such a liquid crystal cell has a viewing angle dependency that it is easy to see from one direction and hard to see from another direction.

When the liquid crystal cell having such a viewing angle dependency is used as a display device, the contrast is extremely lowered at a certain angle with respect to the display screen, and in extreme cases, the brightness and darkness of the display is reversed. .

The liquid crystal cell has a viewing angle characteristic because a pretilt is generated in liquid crystal molecules by rubbing. The direction in which the liquid crystal molecules have a pretilt corresponds to the vector direction for rubbing.

When a voltage is applied to the liquid crystal cell, the liquid crystal molecules rise in the pretilt direction.
When observed from the direction in which the direction becomes the electric vector of light, the optical rotatory property is easily eliminated.

Further, during rubbing, static electricity may be generated due to friction to cause dielectric breakdown in the alignment film, or defective alignment at that portion may cause display failure. In addition, the liquid crystal cell adopts the active drive method,
When rubbing a substrate having driving elements such as TFTs (thin film transistors) and wiring formed on the surface, static electricity due to rubbing may destroy the elements and wiring.

Further, a large amount of fine dust is generated during alignment film formation and rubbing, and the dust adheres to the substrate due to static electricity, which causes display defects such as gap defects of liquid crystal cells and black and white dots. Sometimes it is another problem.

[0012] The specification of Japanese Patent Application No. 4-236652 filed on September 4, 1992 by the same applicant as the present application and Japanese Patent Application No. 5-23652 filed by claiming the domestic priority of the application.
The specification of No. 210320 discloses a liquid crystal display element that does not require a rubbing treatment and a method for manufacturing the same in order to solve the above problems associated with rubbing.

In the method of manufacturing a liquid crystal display element (hereinafter referred to as a-TN display element) of the invention described in the specification of Japanese Patent Application No. 5-210320, the substrate is not subjected to alignment treatment such as rubbing. . 9 liquid crystal molecules between two transparent electrodes
To manufacture an a-TN display element twisted by 0 °, when the chiral pitch of the chiral nematic liquid crystal is p and the thickness of the liquid crystal layer in the direction sandwiched by the glass substrates is d, d / p = A liquid crystal having a chiral pitch p satisfying 0.25 is used.

The optical rotatory power is not limited to 90 degrees. When the chiral pitch of the chiral nematic liquid crystal is p and the distance between the transparent substrates is d, p and d are set such that 0.15 <(or ≈) d / p <(or ≈) 0.75. It is disclosed that a value may be selected. That is, it is shown that a liquid crystal cell that does not require a rubbing treatment can be obtained by using a liquid crystal having a chiral pitch p defined by a desired twist angle of the cell and a cell thickness d.

According to the method of the invention of this prior application, a multi-domain which is a set of minute regions having a specific alignment direction of liquid crystal molecules is formed, and the alignment directions are randomly present in all directions. The chiral nematic liquid crystal rotates the polarization axis of incident light as a whole by a predetermined angle. Positive display can be realized by using a pair of deflection plates in this liquid crystal cell.
A liquid crystal display device having uniform viewing angle characteristics can be obtained.

In such a multi-domain liquid crystal display device, a completely isotropic viewing angle characteristic, that is, a characteristic in which the viewing angle characteristic is uniform in all directions (excluding the limitation of the viewing angle characteristic due to the characteristics of the polarizing plate itself) is obtained. To this end, in the multi-domain on the substrate, liquid crystal molecules must be aligned in a certain direction in each domain, and in addition, all directional components must exist in the liquid crystal molecule alignment direction of the multi-domain as a whole with equal probability.

June 29, 1993 by the same applicant as the present application
The specification of Japanese Patent Application No. 5-159606 filed on the date and the Japanese Patent Application No. 5-159606 filed by claiming domestic priority.
In the specification of -326990, an optical polarization storage film is formed on a substrate surface, and a positive alignment treatment corresponding to individual micro regions of a multi-domain is performed to ensure a constant alignment of each micro region. An excellent liquid crystal display device that realizes omnidirectional alignment of the entire domain (hereinafter, SMD-
It is called a TN display element. ) Is disclosed.

A-TN disclosed in the specifications of these earlier applications
In the display element and the SMD-TN display element, the rubbing process is not performed, so that the liquid crystal molecules do not have a pretilt angle. If there is no pretilt, a reverse tilt may occur when a voltage is applied to the liquid crystal cell, and in that case, the interface in which the tilt of the liquid crystal molecules is reversed appears as a line defect.

Particularly, when the applied voltage is near the threshold voltage, innumerable defects are generated, and the defect positions move around with the passage of time or changes in the applied voltage, so that the presence of defects is easily visually recognizable. At the same time, since light scattering occurs and the contrast also deteriorates, the display quality of the liquid crystal display device is significantly deteriorated.

The state of this display defect in the conventional a-TN display device is shown in FIG. 5 (A), (B),
(C) is a display surface of a liquid crystal cell, which is a photograph of changes in display defects when V ₁₀ , V ₅₀ , and V ₉₀ , which are voltages that give transmittances of 10%, 50%, and 90% to the liquid crystal cell, are applied. It is an enlarged photograph. Here, V ₁₀ is 2.1 V and V ₅₀ is 2.7.
V and V ₉₀ correspond to 3.6V.

In the photograph, display defects are observed as elongated white lines. At V ₁₀ , the most defects are generated, and the defects decrease as the voltage increases. When such a defect occurs, hysteresis occurs in the light transmittance-voltage characteristic of the liquid crystal cell, and there is also a drawback that good gradation display cannot be performed.

The object of the present invention is to provide viewing angle dependence,
It eliminates the need for rubbing that causes product defects such as display defects and element destruction.
No. 210320 and Japanese Patent Application No. 5-326990 discloses a liquid crystal display device using a liquid crystal cell having a multi-domain structure, which can suppress display defects due to reverse tilt and control the amount of generation to improve display quality. An object of the present invention is to provide a liquid crystal display device that can be improved and a manufacturing method thereof.

[0023]

A liquid crystal display device according to the present invention comprises a liquid crystal layer containing a liquid crystal material to which a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton is added, and a pair of liquid crystal layers sandwiching the liquid crystal layer. And a substrate.

In the method of manufacturing a liquid crystal display device according to the present invention, a step of preparing a liquid crystal material in which a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton is added, and the liquid crystal material are arranged facing each other at predetermined intervals. And a step of injecting it between the pair of substrates thus formed.

[0025]

By adding a photopolymerizable acrylate resin material having a liquid crystal skeleton to the liquid crystal, it is possible to prevent display defects due to reverse tilt from appearing in a liquid crystal display device using the liquid crystal material. The amount of defects generated can be controlled by the applied voltage, and the defects can be fixed by photopolymerization.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display device according to an embodiment of the present invention and a method of manufacturing the same will be described with reference to the drawings.

The basic structure and the basic process of the liquid crystal element are described in Japanese Patent Application No. 5-210320 and Japanese Patent Application No. 5-210320.
It is based on 326990. FIG. 2A is a schematic sectional view of a liquid crystal display cell according to an embodiment of the present invention. A resin-added liquid crystal material 3 is sandwiched between transparent glass substrates 1 and 2, and polarizing plates 8 and 9 are provided on both sides thereof.

2 (B) and 2 (C) respectively show structural cross sections of a liquid crystal display element using a simple matrix driving method and an active matrix driving method. In the case of the simple matrix driving method, transparent electrode groups P such as ITO (indium-tin oxide) which intersect with each other are formed on a pair of substrates.

In the case of the active drive system, a film transistor (TFT) drive element Q formed by using amorphous a-Si or polycrystalline Si on one substrate surface and a metal such as Cr or Al. The formed wiring W, the transparent pixel electrode P, and the insulating protective film 10 are formed.

In the figure, a color filter layer and a light-shielding film called a black mask which are necessary for color display are omitted. For the production of this liquid crystal display device, the conventional process can be used as it is. However, the alignment film is not provided except when the optical polarization storage film described in the following examples is used. Further, in this embodiment, a normal alignment treatment such as rubbing is not performed. Therefore, there is no common single orientation direction over the entire surface of the substrate provided in a normal liquid crystal display device.

It should be noted that FIG.
The schematic sectional configuration shown in (A) is common, and in the embodiments of the present invention, a nematic liquid crystal, a cholesteric liquid crystal, or a chiral nematic liquid crystal obtained by adding a chiral agent to nematic liquid crystal is used as a liquid crystal base material. A photopolymerizable acrylate resin having a liquid crystal skeleton is added to this liquid crystal base material. Addition amount is 0.1 to 10.0
It is appropriately selected within the range of wt%.

Specifically, for example, as an additive, a resin-added liquid crystal material 3 having a liquid crystal skeleton having three rings in its skeleton and adding 3 wt% of a liquid crystalline diacrylate resin having an acryloyl group bonded to both ends thereof is prepared. .

The thickness d of the liquid crystal layer in FIG. 2A is 0 ≦ d / when the chiral pitch of the liquid crystal is p, as disclosed in Japanese Patent Application No. 5-210320 of the prior application.
The condition of p ≦ 0.75 is satisfied. Preferably, a liquid crystal cell is formed so as to satisfy a condition of 0.15 <d / p <0.75. Under this condition, the liquid crystal
It has an optical rotatory power with an angle of 270 degrees to 270 degrees. For example, in Japanese Patent Application No. 5-210320 of the prior application, d / p = 0.25
An example in which (corresponding to 90 degree twist) is selected is disclosed.

FIG. 1A is a schematic cross-sectional view showing an embodiment of injecting a liquid crystal material added with a diacrylate resin into a liquid crystal cell. The container 4 contains the liquid crystal material 3 to which the resin is added, and the liquid crystal material 3 is injected between both substrates. As the injection method, a method such as capillary phenomenon is used.

Since there is no unidirectional alignment structure on each substrate, the liquid crystal layer forms a multi-domain which is a set of minute micro-domains. In addition, Japanese Patent Application No. 5-210
As disclosed in No. 320, at the time of injecting liquid crystal, a liquid crystal material is heated to a phase transition temperature (N−I) or higher from both sides of a substrate by using a heating device such as a heater, and 0.5 ° C./injected after injection. A multi-domain liquid crystal layer having a more uniform domain size can be formed by performing a method of gradually cooling to a point below the NI point at a cooling rate of a minute.

Further, the liquid crystal cell 5 in which the resin-added liquid crystal material 3 is injected is irradiated with light from the outside by the method shown in FIG. 1B to polymerize the added photopolymerizable acrylate resin in the liquid crystal matrix material, Let it harden. In the case of a liquid crystalline diacrylate resin, light in the ultraviolet range is irradiated. Further, at the time of irradiation with this ultraviolet light, the electrodes of the substrates 1 and 2 (FIG. 2B,
A predetermined DC voltage or AC voltage is applied to (C). In this embodiment, alternating current is used. However, no voltage may be applied (voltage 0V).

According to this embodiment, the voltage applied to the cell at the time of ultraviolet irradiation was 0V, 1V, 1.5V, 2V, 5V and 10V.
Each of the devices was prepared under the following six conditions. FIG.
6 is an enlarged photograph of a cell display surface when an a-TN display device is manufactured using the method described above. The photographs (A), (B), and (C) in FIG.
V ₁₀ , which is a voltage giving a transmittance of 50% and 90%,
It is obtained by application of V _50, V _90. Where V ₁₀ is 2.1
V and V ₅₀ correspond to 2.8V, and V ₉₀ corresponds to 3.8V. The state transferred to the three photographs is almost unchanged, and the defect state (white line-shaped objects in the photographs) is not changed by the voltage change. It can also be seen that the defect does not move around.

Therefore, the defect is not visually recognized, and the deterioration of the display quality described in the section of the problem to be solved by the invention can be prevented. Furthermore, since the occurrence of hysteresis can be prevented, a good halftone display can be obtained.

FIG. 4 is an enlarged photograph of the display surface when the voltage applied to the liquid crystal cell during irradiation of ultraviolet rays is changed.
In the photograph of FIG. 4 (A), 0 V, 1 B in (B), 1.5 V in (C), 2 V in (D), and 5 V in (E) are applied at the time of ultraviolet irradiation.

As can be seen from the photograph of FIG. 4, FIG.
The amount of defects is maximum when 1.5 V is applied, and the amount of defects decreases when a higher voltage is applied. The generation state of defects is changed by changing the cell applied voltage at the time of ultraviolet irradiation, so that the generation amount of defects can be controlled by the voltage.

Defects are less likely to be recognized due to the two functions of controlling the state of generation of defects by voltage application during light irradiation and fixing the defects by curing the resin by photopolymerization. In addition, Japanese Patent Application No. 5-210320 and Japanese Patent Application No. 5-3269
The optical deflection memory film disclosed in No. 90 may be formed on the surface of the substrate and subjected to a positive alignment treatment corresponding to each minute region of the multi-domain. Also in the device having such a configuration, the addition of the photopolymerizable acrylate resin having a liquid crystal skeleton can provide the same effect.

An example of the case where the positive alignment treatment using the optical polarization memory film is performed will be described below.

As the optical polarization memory film, one using (1) silicon polyimide doped with a diazoamine dye: Wayne M.A. Gibbons et al., NATURE
Vol. 351 (1991) p. 49, (2) Using PVA (polyvinyl alcohol) doped with an azo dye: Yasufumi Iimura et al .: 18th Liquid Crystal Symposium-The 64th Annual Meeting of the Chemical Society of Japan-, p. 34, Published September 11, 1992, The Chemical Society of Japan. Alternatively, Jpn. J. Ap
pl. Phys. Vol. 32 (1993) pp. L9
3-L96, (3) with photopolymerized photopolymers: Martin Schadt et al., Jpn. J. Ap
pl. Phys. Vol. 31 (1992) pp. 21
55-2164 etc. can be utilized.

FIG. 6 shows an apparatus for producing a substrate in which an alignment treatment is carried out for each minute region using a light polarization memory film.
The size of each micro area is designed so that a sufficiently large number of micro areas are included in each display pixel. For example,
When the size of one pixel is about 100 × 300 μm, the area of one pixel includes several to several tens of minute regions.

In order to fill a large area with minute areas having the same area, it is preferable that the shape of each minute area is a regular hexagon, a rectangle, a square, a parallelogram, a rhombus, a triangle or the like.

The laser light output from the laser light source 11 is first transmitted to the optical system (including, for example, an aperture having a predetermined shape and a lens) 1.
It is narrowed down by 2 and given a predetermined beam spot diameter with the polarization characteristics eliminated. Further, the laser beam is passed through a polarizing plate 13 having a polarization axis in a predetermined direction to obtain linearly polarized laser light 14. The linearly polarized laser beam 14 is applied to the surface of the transparent glass substrate 15 coated with the optical polarization memory film as a beam spot having an area corresponding to a predetermined minute region.

By irradiation with the polarized laser beam 14, each irradiation minute area in the optical polarization storage film is oriented in a direction corresponding to the polarization direction of the polarizing plate 13. Glass substrate 15 is 2
It is arranged on a movable stage 16 movable in the dimensional directions X and Y. While moving the movable stage 16 and simultaneously rotating the polarizing plate 13 around the optical axis to change the polarization direction, the polarized laser beam 14 is irradiated in a pulsed manner over the entire optical polarization storage film on the substrate 15. In this way, an oriented structure having a large number of minute regions 17 as shown in FIG. 7 is obtained. The arrow in the figure indicates the orientation direction.

Alternatively, it is possible to memorize the orientations in a plurality of regions at one time by one laser irradiation using an apparatus provided with an optical system for enlarging the diameter of the laser beam and a polarizing plate photomask. It is possible to more easily prepare a substrate that has been subjected to different orientation processing for each minute region.

Even in a liquid crystal display device in which a minute area is positively oriented by using the optical polarization storage film by the above method, the amount of defects is suppressed by adding an acrylate resin material to the liquid crystal layer, and further ultraviolet irradiation is performed. It is possible to control the amount of defects generated by changing the cell voltage at that time.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0051]

By adding a small amount of the photopolymerizable acrylate resin to the liquid crystal, in the rubbing-free liquid crystal display element, various display defects caused by the occurrence of reverse tilt due to the absence of the pretilt angle are reduced to improve the display quality. Can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a liquid crystal display device according to an exemplary embodiment of the present invention.

FIG. 3 shows “a fine pattern formed on a substrate” on a display surface of a liquid crystal display device manufactured by a manufacturing method according to an embodiment of the present invention, which is taken by changing an applied voltage.
It is an enlarged photograph.

FIG. 4 shows “a fine pattern formed on a substrate” on a display surface of a liquid crystal display device produced by changing a voltage condition during irradiation of ultraviolet rays by a manufacturing method according to an embodiment of the present invention.
It is an enlarged photograph.

FIG. 5 a disclosed in the specification of Japanese Patent Application No. 5-326990
-"Represents a fine pattern formed on the substrate" on the display surface of the TN display device, which was taken by changing the applied voltage.
It is an enlarged photograph.

FIG. 6 is a perspective view of an apparatus for aligning a substrate of a liquid crystal display device according to an exemplary embodiment of the present invention.

FIG. 7 is an enlarged view showing an alignment treatment state of a substrate of a liquid crystal display device according to an embodiment of the present invention.

[Explanation of symbols]

 1, 2 Transparent glass substrate 3 Resin-added liquid crystal material 4 Container 5 Liquid crystal cell 6 Light source 7 Power source 8, 9 Polarizing plate 10 Insulation prevention film 11 Laser light source 12 Optical system 13 Polarizing plate 14 Linearly polarized laser light 15 Substrate 16 Movable stage 17 Micro region

Claims (9)

[Claims] 1. A liquid crystal display device comprising a liquid crystal layer containing a liquid crystal material having a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton, and a pair of substrates sandwiching the liquid crystal layer. 2. The liquid crystal display device according to claim 1, wherein the amount of the acrylate resin material added to the liquid crystal material is selected in the range of substantially 0.1 to 10.0 wt%. 3. The liquid crystal material includes a chiral nematic liquid crystal or a nematic liquid crystal, and the alignment direction of liquid crystal molecules of the liquid crystal layer is distributed macroscopically in almost all directions with equal probability with respect to the in-plane direction of the substrate. The liquid crystal display element according to any one of claims 1 and 2, which exhibits a substantially constant twist angle in a direction perpendicular to the substrate. 4. The liquid crystal display element according to claim 1, which has an alignment structure which is formed on at least one of the pair of substrates and has a large number of minute regions having different alignment directions. 5. A step of preparing a liquid crystal material to which a predetermined amount of a photopolymerizable acrylate resin material having a liquid crystal skeleton is added, and a step of injecting the liquid crystal material between a pair of substrates arranged to face each other at a predetermined interval. And a method for manufacturing a liquid crystal display device having the following. 6. The method for producing a liquid crystal display device according to claim 5, wherein the amount of the acrylate resin material added to the liquid crystal material is selected in the range of substantially 0.1 to 10.0 wt%. 7. The method of manufacturing a liquid crystal display device according to claim 5, further comprising a step of irradiating the liquid crystal layer with light to polymerize the acrylate resin material after the step of injecting the liquid crystal material. 8. The light according to claim 7, which is light in the ultraviolet region.
A method for producing the liquid crystal display element described. 9. The method of manufacturing a liquid crystal display element according to claim 7, wherein a predetermined voltage is applied between the substrates when the light is irradiated.