KR0183205B1 - Fabrication method for liquid crystal cell - Google Patents

Abstract

Amorphous twisted nematic liquid crystal cell joins the substrates 10 and 11 coated with a polysiloxane material to form a liquid crystal cell, and injects liquid crystal at room temperature to the nematic transition temperature (T _NI ) or higher. After heating, it is produced by slowly cooling to room temperature. As the liquid crystal cell cools, many domains are formed in the cell. The domains are continuously distributed with adjacent domains. The liquid crystal directors in each domain also have a continuous distribution with a slight angle difference with the upper and lower adjacent domains formed in the same domain. Becomes In order to continuously distribute the orientation of the liquid crystal molecules between adjacent domains, ultraviolet rays are irradiated to the liquid crystal cell before or after the injection of the liquid crystal to impart a pretilt of an appropriate size and direction.

Description

Liquid Crystal Cell Manufacturing Method

1 is a view showing a process of forming a domain by cooling the twisted nematic liquid crystal cell.

FIG. 2 is a diagram illustrating a process of forming domains by cooling an amorphous twisted nematic liquid crystal cell. FIG.

3 is a view showing a method of manufacturing an amorphous twisted nematic liquid crystal cell according to the first embodiment of the present invention.

4 is a view showing a method of manufacturing a twisted nematic liquid crystal cell according to a second embodiment of the present invention.

5 is a graph showing the relationship between the ultraviolet irradiation energy versus the pretilt angle of the amorphous twisted nematic liquid crystal cell manufactured according to the present invention.

6 is a diagram showing a relationship between voltage vs. transmittance of an amorphous twisted nematic liquid crystal cell manufactured according to the present invention.

7 is a graph showing the contrast ratio according to the viewing angle of the Amorphous twist nematic liquid crystal cell manufactured according to the present invention.

* Explanation of symbols for main parts of the drawings

10: first substrate 11: second substrate

20: alignment film 30: liquid crystal molecules

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a method for manufacturing an amorphous twisted nematic liquid crystal cell having a randomly distributed multidomain.

Twist nematic (TN) liquid crystal cells mainly used as liquid crystal display (LCD) have many problems in their viewing angle characteristics. In particular, the light transmittance is distributed symmetrically in the viewing angle in the left and right directions, but the light transmittance is distributed asymmetrically in the viewing angle in the up and down directions, so that the image is inverted and eventually the viewing angle is narrowed.

To solve this problem, a multi-domain liquid crystal compensating a viewing angle by forming a pixel into two or more domains having different alignment directions and pretilt sizes. Cells have been proposed.

However, in the method of manufacturing the multi-domain liquid crystal cell, in order to change the rubbing direction according to the domain of the substrate, after rubbing the domain using a photoresist as a mask, the photoresist is removed. The process becomes complicated, such as dusting and electrostatic charges caused by rubbing, which lowers the yield and damages the thin film transistor for operating each pixel of the liquid crystal display. In addition, each pixel must be composed of four or more domains in order to eliminate the inversion of the image, but this operation is substantially very difficult and the manufacturing process is very complicated.

Therefore, in order to overcome the above-mentioned difficulty, an amorphous TN (a-TN) liquid crystal cell has been proposed. The state of the liquid crystal molecules in the a-TN liquid crystal cell does not exist in the long range order of the directors of the nematic liquid crystal molecules, but in the local region, the continuous short-range order ( short range order). In addition, the a-TN liquid crystal cell has a very large number of domains. In the a-TN liquid crystal cell, a liquid crystal is injected at a temperature higher than the nematic transition temperature (T _NI ) into the liquid crystal cell whose orientation direction is not determined, and then the cell is cooled again to a room temperature below the nematic transition temperature (T _NI ). Is formed. At this time, the liquid crystal injected into the liquid crystal cell at a high temperature maintains an isotropic phase, but begins to form an anisotropic phase as the temperature is lowered to the nematic transition temperature (T _NI ). Many domains with different orientation directions are formed. The reason why the liquid crystal is injected at a high temperature higher than the nematic transition temperature (T _NI ) is to remove the nematic properties of the liquid crystal and to generate the alignment and the alignment film dragging shape caused by the flowing effect of the liquid crystal when the liquid crystal is injected. It is to prevent.

1 and 2 are diagrams illustrating a process of forming nematic phases of liquid crystal molecules in a liquid crystal cell when the TN liquid crystal cell and the a-TN liquid crystal cell are cooled to a room temperature at a high temperature higher than the nematic transition temperature T _NI . In the drawing, the alignment film 20 applied to the first substrate 10 and the second substrate 11 of the liquid crystal cell is a polyimide, and is oriented by rubbing to the first substrate and the second substrate of the TN liquid crystal cell. The direction is determined, and no orientation direction is formed on the first substrate and the second substrate of the a-TN liquid crystal cell.

When the liquid crystal is injected at a high temperature above the nematic transition temperature T _NI , the liquid crystal molecules in the cell form an isotropic phase because the nematic properties of the liquid crystal are removed. At this time, in the TN liquid crystal cell, the liquid crystal molecules near the substrate are oriented in a state having a constant pretilt by the alignment force of the alignment film applied to the substrate, but in the a-TN liquid crystal cell, the alignment force is not applied to the alignment film applied to the substrate. Therefore, the liquid crystal molecules on the substrate surface form an isotropic phase similarly to the liquid crystal molecules in the cell.

When the isotropic cell is slowly cooled to a room temperature below the nematic transition temperature (T _NI ), in the TN liquid crystal cell, nucleation starts from the surfaces of the substrates 10 and 11, and the monodomain is distributed throughout the cell. (mono-domain) is formed, but in the a-TN liquid crystal cell, nucleation starts from a bulk region in the center of the cell instead of the surfaces of the substrates 10 and 11, thereby forming a multidomain cell. That is, the surface of the alignment layer 20 on which the a-TN liquid crystal cell is not rubbed does not play a role in nucleation.

Columns formed in the e-TN liquid crystal cell are domains having different viewing angles, and each column is twisted 90 degrees from the first substrate to the second substrate by a dopant.

As described above, in the a-TN liquid crystal cell, a large number of columns, that is, a large number of domains having different viewing angles, are formed to improve viewing angle characteristics. In addition, in the a-TN liquid crystal cell manufacturing process, there is no need to perform rubbing on the alignment film formed on the substrate, which not only simplifies the manufacturing process but also causes problems such as dust and static electricity generated during rubbing of the alignment film. Problems such as a decrease in yield or breakage of the substrate can be prevented.

However, in the manufacturing method of an a-TN liquid crystal cell using polyimide as the alignment film as described above, the liquid crystal is injected in the isotropic phase, and the alignment is generated, that is, the alignment film attracting phenomenon, that is, when the liquid crystal is injected into the liquid crystal cell The liquid crystal should be injected at a high temperature above the nematic transition temperature (T _NI ) to prevent the alignment film from being damaged by friction between the alignment film and the alignment film and to prevent order from being imparted to the liquid crystal. However, the liquid crystal injection step is performed by integrating and sealing a liquid crystal cell and then injecting the liquid crystal in a state in which the liquid crystal cell is kept at a low pressure close to vacuum. Therefore, there is a problem that the liquid crystal molecules injected at a high temperature are volatilized or deformed by low pressure.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing Amorphous twisted nematic liquid crystal cell, which is easy to manufacture and forms a multidomain cell composed of many domains, thereby improving viewing angle characteristics.

Another object of the present invention is to prevent the volatilization and deformation of the liquid crystal molecules generated when the liquid crystal is injected at a high temperature by injecting the liquid crystal at room temperature.

In order to achieve the above object, the liquid crystal cell manufacturing method according to the present invention comprises the steps of coating the alignment film on the first substrate and the second substrate, and then bonding to form a liquid crystal cell, and injecting liquid crystal into the liquid crystal cell; After heating the cell injecting the liquid crystal and slowly cooling to room temperature again, and irradiating the liquid crystal cell with ultraviolet rays to give a pretilt direction and size. The alignment film applied to the substrate is a polysiloxane material, and when the liquid crystal is injected, the liquid crystal molecules are aligned in a direction perpendicular to the substrate in the cell. When the liquid crystal cell is heated and then cooled to room temperature again, the liquid crystal cell becomes an amorphous twisted nematic liquid crystal cell composed of a very large number of domains having different alignment directions.

When voltage is applied to a liquid crystal cell injecting a liquid crystal having a negative dielectric anisotropy, liquid crystal molecules are oriented in a horizontal direction with the substrate to form a multi-domain, and a liquid crystal cell in which a liquid crystal with a positive dielectric anisotropy is injected is irradiated for a predetermined time. Then, an appropriate pretilt size is imparted to the alignment film to form a multidomain.

Hereinafter, a method of manufacturing a liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a view illustrating a method for manufacturing an amorphous twisted nematic liquid crystal cell according to Embodiment 1 of the present invention. First, after the alignment layer 20 is applied to the first substrate 10 and the second substrate 11, The liquid crystal cells are bonded together to form a liquid crystal cell. The alignment layer 20 applied to the substrates 10 and 11 is a polysiloxane based material, and the chemical formula below shows an example of polysiloxane cinnamate. When the polysiloxane material is used as the alignment layer, breakage of the alignment layer due to the drag phenomenon of the liquid crystal may be prevented when the liquid crystal is injected.

Polysiloxane Cinnamate I:

Polysiloxane Cinnamate II:

Z = OH, CH ₃ or a mixture of OH and CH ₃ ,

m = 10-100,

l = 1 to 11,

L = 0 or 1,

K = 0, 1 or 2,

X, X ₁ , X ₂ , Y = H, F, Cl, CN, CF ₃ , C _n H _{2n + 1} or OC _n H _{2n + 1} (n = 1 to 10)

Some of the alignment films made of polysiloxane material have a pretilt angle close to 90 ° in the initial state, that is, without the ultraviolet light, as shown in FIG. 5, but the size of the pretilt angle gradually increases as the ultraviolet light is irradiated. Becomes smaller.

Therefore, as shown in FIG. 3 (a), liquid crystals having a negative dielectric anisotropy (Δε) due to the pressure difference in a state in which the pressure in the liquid crystal cell coated with the polysiloxane material is kept at a low pressure close to vacuum, for example, ZLI When -4801-000 (Nematic Transition Temperature; T _NI = 90 ° C) is injected, a 90 ° pretilt angle is determined on the alignment film 20 applied to the substrates 10 and 11 to be injected into the cell. The liquid crystal molecules 30 are aligned with the substrate as shown in FIG. 3B. At this time, a chiral dopant is added to a liquid crystal so that d / p = 1/4. Here, d is a liquid crystal cell gap, and d is about 5 탆, and p is the pitch of the liquid crystal. Since the injection of the liquid crystal is performed at room temperature, unlike the conventional a-TN, the liquid crystal molecules 30 excited by the high temperature during the injection of the liquid crystal are not volatilized or denatured by low pressure.

After heating the liquid crystal cell at a temperature of about nematic transition temperature (T _NI ) in an oven and slowly cooling to room temperature, nuclei are formed in the liquid crystal cell as shown in FIG. As a result, a multi-domain liquid crystal cell composed of a large number of domains is formed. Thereafter, when the liquid crystal cell is irradiated with unpolarized ultraviolet rays for a predetermined time as shown in FIG. 3 (d), a pretilt angle direction is formed on the alignment layer of the liquid crystal cell, and the liquid crystal molecules are oblique in a state perpendicular to the substrate. It is in a state.

Since the above-mentioned multidomain is a-TN, the liquid crystal director in the liquid crystal cell tends to align the liquid crystal molecules 30 oriented at the time of nucleation in the same direction by the pretilt angle direction formed by irradiation of ultraviolet rays. The liquid crystal directors of the domains adjacent to each other are continuously distributed in a shape twisted finely with the directors of the adjacent domains. Also, in each domain, the liquid crystal directors are continuously distributed at minute angles with the upper and lower liquid crystal directors adjacent to each other in the domain.

4 is a view showing a method of manufacturing an amorphous twisted nematic liquid crystal cell according to a second embodiment of the present invention. In this embodiment, a liquid crystal in which the dielectric anisotropy (Δε) of the liquid crystal injected into the liquid crystal cell is negative is used, and the liquid crystal is injected after irradiating ultraviolet rays. First, as shown in FIG. 4A, after the alignment film 20 is applied to the first substrate 10 and the second substrate 11, the unpolarized ultraviolet rays are irradiated to pretilt the surface of the alignment film 20. Determine each direction. Thereafter, when the liquid crystal is injected as shown in FIG. 4 (b), the liquid crystal molecules 30 are oriented perpendicular to the first substrate 10 and the second substrate 11 as shown in FIG. do. Subsequently, when the liquid crystal cell is heated to a temperature of Tn ₁ or more and then slowly cooled to room temperature, nuclei start to form in the liquid crystal cell as shown in FIG. The voltage is not applied to the liquid crystal cell at this time. When voltage is applied to the liquid crystal cell, the dielectric anisotropy (Δε) of the liquid crystal is negative, so that the liquid crystal molecules 30 are parallel to the substrates 10 and 11 due to the electric field between the substrates 10 and 11. Direction is oriented. In addition, since chiral dopant is added to the liquid crystal, when an electric field is applied, a large number of domains are formed in the cell in which the liquid crystal directors twisted vertically adjacent to each other are twisted at a fine angle, and the liquid crystal directors between the domains are also used. It becomes a shape twisted at a fine angle.

6 is a graph showing the relationship between the transmittance band voltage and the graph of the a-TN liquid crystal cell formed by the present invention, which is normally white mode. According to the drawing, it can be seen that the a-TN liquid crystal cell formed according to the present embodiment also changes the transmittance according to the application of a voltage as in the general TN liquid crystal cell.

7 is a graph showing a contrast ratio according to the viewing angle of the a-TN liquid crystal cell formed according to the present invention. Unlike the conventional TN liquid crystal cell, FIG. 7 shows not only the viewing angle in the horizontal direction but also the viewing angle in the vertical direction. It can be seen that the contrast ratio is symmetrical and the viewing angle characteristic is remarkably improved.

Since the method for manufacturing the Amorphous twisted nematic liquid crystal cell of the present invention forms a multi-domain liquid crystal cell composed of many domains without performing mechanical rubbing as described above, a reduction in yield occurring during rubbing and substrate Breakage can be prevented and the viewing angle characteristic can be significantly improved. In addition, since the liquid crystal is injected at room temperature, the liquid crystal can be prevented from being volatilized or deformed.

Although the present invention illustrates only preferred embodiments, the present invention is not limited to the above preferred embodiments. For example, an application to a preferred embodiment of the present invention, such as not only ultraviolet light not polarized by the ultraviolet light to be irradiated, but also linearly polarized ultraviolet light, may be used by those skilled in the art. Anyone can easily create using the concept of. Accordingly, the scope of the present invention should not be determined by the preferred embodiment described above, but should be determined by the appended claims.

Claims (10)

After applying the alignment film to the first substrate and the second substrate, and then bonded to form a liquid crystal cell, injecting the liquid crystal into the liquid crystal cell at room temperature, and heating the liquid crystal cell injecting the liquid crystal Liquid crystal cell manufacturing method consisting of a step of slowly lowering to room temperature. The method of claim 1, wherein the alignment layer is a polysiloxane material. After applying the alignment film to the first substrate and the second substrate, and irradiating light to the first substrate and the second substrate to give a pretilt angle direction to the alignment film, the first substrate and the second substrate Forming a liquid crystal cell by bonding the substrates, injecting a liquid crystal into the liquid crystal cell at room temperature, and heating the liquid crystal cell into which the liquid crystal is injected, and then cooling the liquid crystal cell to room temperature. . The method of claim 3, wherein the alignment layer is a polysiloxane material. 10. The method of claim 9, wherein the ultraviolet light is an unpolarized ultraviolet light. After applying the alignment film to the first substrate and the second substrate, and then bonded to form a liquid crystal cell, injecting the liquid crystal into the liquid crystal cell at room temperature, and heating the liquid crystal cell injecting the liquid crystal And cooling to room temperature and irradiating light to the liquid crystal cell into which the liquid crystal is injected to impart a pretilt angle direction to the alignment layer. The method of claim 6, wherein the alignment layer is a polysiloxane material. The method of claim 10, wherein the ultraviolet light is ultraviolet light that is not polarized light. The method of claim 3, wherein the light is ultraviolet rays. 7. The method of claim 6, wherein the light is ultraviolet light.