JPH08313908A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display device of high quality having a wide visual angle and good display characteristics without an irregular display state. CONSTITUTION: This method includes a process to inject a liquid crystal in a liquid crystal state into the space between a pair of substrates 1a, 1b and to heat-treat the substrates 1a, 1b and the liquid crystal over the N-I temp. The surfaces of the substrates where the liquid crystal is to be in contact with are not subjected to orientation treatment. The liquid crystal molecules 5 in the liquid crystal display device are not oriented in a specified direction but distributed in all directions with same probability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal display device, and more particularly to a method of manufacturing a liquid crystal display device capable of improving a viewing angle.

[0002]

2. Description of the Related Art Generally, a liquid crystal display device performs display by changing the direction of liquid crystal molecules arranged in a certain direction by the action of an electric field and controlling transmitted light. Therefore, in the state where there is no external action, for example, in the state where there is no electric field, it is necessary to arrange the liquid crystal molecules in a specific direction in advance. Usually, in order to keep the liquid crystal molecules aligned, the substrate surface in contact with the liquid crystal molecules is subjected to an alignment treatment.
Examples of this type of orientation treatment include so-called rubbing treatment in which an organic film such as polyimide is applied to the surface of the substrate and the surface is rubbed in one direction with a cloth or the like, formation of a vapor deposition film for depositing an inorganic substance or an organic substance, and formation of an LB film. Etc. However, when such an alignment treatment is performed, the liquid crystal is aligned in a certain direction, so that the brightness and darkness of the display are reversed depending on the direction and angle at which the liquid crystal display screen is viewed, and the viewing angle is limited. It had the drawback of having a dependency. Also,
When rubbing treatment is applied, dielectric breakdown occurs in the alignment film on the substrate due to static electricity due to friction, and partial alignment defects may occur.
When a driving element or wiring is arranged on the surface of the substrate as in the active matrix driving method, there are problems that the element may be broken or the wire may be broken, and dust may be generated during rubbing to cause display failure. Was.

Japanese Laid-Open Patent Publication No. 6-194655 proposes a liquid crystal display device and a method of manufacturing the liquid crystal display device which can improve the viewing angle dependency of the liquid crystal display device and the problems caused by rubbing treatment. The liquid crystal display device proposed in Japanese Patent Laid-Open No. 6-194655 has a liquid crystal layer provided between a pair of substrates that are not subjected to an alignment treatment for aligning the liquid crystal molecules in a predetermined direction. On the surface of the substrate, the liquid crystal molecules have uniform orientation in all directions, and when the entire substrate is viewed, the liquid crystal molecules do not have a uniform orientation. However, in the minute region, the liquid crystal molecules are oriented in a certain direction and form a multi-domain alignment state in which the direction is different for each minute region. Due to the chiral pitch of the liquid crystal, this multi-domain orientation shows a constant twist angle in the direction perpendicular to the substrate surface. In the liquid crystal display device having this multi-domain alignment state, since the liquid crystal molecules are oriented in all directions, uniform viewing angle characteristics can be obtained in all directions.

The manufacturing method disclosed in Japanese Unexamined Patent Publication No. 6-194655 discloses a general TN (twisted nematic).
It is almost the same as the manufacturing process of a liquid crystal display device. The difference is that since the surface of the substrate is not subjected to the alignment treatment, the rubbing process can be omitted, and the temperature of the substrate and the liquid crystal is changed from the liquid crystal phase state to the isotropic liquid state (N-
It is to perform the injection while heating and maintaining the temperature above point I).

[0005]

However, when the substrate and the liquid crystal are heated and held and the liquid crystal is injected between the substrates, when the general vacuum injection method is used, the liquid crystal is kept in a vacuum state.
-In order to heat and hold above point I,
Part of the components of the liquid crystal is volatilized or decomposed, resulting in a change in the composition ratio of the liquid crystal. In particular, in the case of a liquid crystal exhibiting a fast response speed, since a large amount of low-molecular liquid crystal having high volatility is contained, the liquid crystal composition ratio changes remarkably. When the liquid crystal with the changed composition ratio is injected between the substrates, the liquid crystal composition ratio is partially different in the screen of the liquid crystal display device, and when it is driven as a liquid crystal display device, display unevenness and contrast unevenness occur, resulting in good display characteristics. Was difficult to obtain. In addition, the physical properties of the liquid crystal before injection, for example,
Since the NI point, the drive voltage value, or the specific resistance value changes, stable operation becomes difficult, the target specifications are not achieved, and the liquid crystal and the substrate are heated in a vacuum state.
There is also a problem that productivity is impaired because a complicated device and complicated work are required.

Therefore, the present invention relates to a method for manufacturing a liquid crystal display device, and more specifically, in a method for manufacturing a liquid crystal display device capable of improving a viewing angle, a uniform and minute multi-domain alignment state is formed without changing the liquid crystal composition. You can
Provided is a method for manufacturing a liquid crystal display device having a wide viewing angle, which has good display characteristics and enables stable display driving.

[0007]

In order to achieve the above object, in the present invention, a liquid crystal is injected in a liquid crystal phase state between a pair of substrates whose contact surfaces are not subjected to an alignment treatment, It is characterized in that a step of heat-treating the substrate and the N-I point or more is performed.

Further, after injecting the liquid crystal in a liquid crystal phase state between a pair of substrates having an insulating film whose contact surface with the liquid crystal is not subjected to an alignment treatment, the liquid crystal and the substrate are heat-treated at a point above the NI point. It is characterized in that the step of performing is performed.

Immediately after injecting the liquid crystal in the liquid crystal phase between the substrates, the liquid crystal is injected radially from the liquid crystal injection holes and in the stripe shape along the pixel or the electrode, which is referred to as flow orientation as shown in FIG. Unevenness occurs in the entire liquid crystal display device, and a uniform multi-domain alignment state is not formed.

This flow alignment is caused by the flow alignment of the liquid crystal when the liquid crystal is injected. Therefore, when the liquid crystal is injected between the substrates that have not been subjected to the alignment treatment, the liquid crystal does not have a constant alignment regulating force, so that the flow alignment effect is large when the liquid crystal is injected, and this flow alignment is likely to occur. When a liquid crystal display device having this flow orientation is operated for display, the shape of the flow orientation appears white on the display screen, resulting in display unevenness, resulting in poor display quality.

Therefore, in the present invention, it is possible to eliminate such flow orientation by injecting the liquid crystal between the substrates in a liquid crystal phase state and then heat-treating the liquid crystal and the substrate to a temperature above the NI point. It was made.

[0012]

In the manufacturing method of the present invention, since the liquid crystal is injected between the substrates in the liquid crystal phase state, it is not necessary to heat the liquid crystal before the injection, and the composition ratio of the liquid crystal caused by the volatilization or decomposition of the liquid crystal. Also, no change in physical properties occurs. Therefore, the liquid crystal between the substrates after injection maintains a uniform liquid crystal composition ratio, and stable display driving can be performed without causing contrast unevenness or display unevenness.

[0013]

EXAMPLES Examples of the present invention will be shown below. FIG. 1 is a schematic sectional view of a liquid crystal display device according to the present invention. Insulating films 3a made by applying polyimide on the transparent electrodes 2a, 2b made of indium tin oxide (ITO) on the substrate surfaces of the substrates 1a, 1b made of transparent glass substrates,
3b is formed. Note that alignment treatment such as rubbing is not performed on the insulating film. The distance between the substrate 1a and the substrate 1b is 3.2.
Both substrates are bonded to each other so as to have a thickness of 5 μm by a sealing material 8 so that the liquid crystal layer 4 is provided between the substrates. Liquid crystal layer 4
Is a nematic liquid crystal to which a chiral substance is added to form a chiral nematic liquid crystal, and the distance between the substrate 1a and the substrate 1b is 3.
The chiral pitch was set to 9.75 μm so that a 120 ° twist was obtained at 25 μm. The NI point of this chiral nematic liquid crystal is 92 ° C. In this example, a vacuum injection method was used to inject a chiral nematic liquid crystal in a liquid crystal phase state between the substrates at 25 ° C. and then seal the substrate.

In the liquid crystal display device obtained by the above manufacturing method, the polarizing plates 6a and 6b are arranged so that their absorption axes are orthogonal to each other, and a voltage is applied. The flow orientation due to the flow orientation effect between the substrates generated during the injection was observed. The flow alignment is oriented radially from the liquid crystal injection holes 7 or along the pixels and electrodes, and in this state, a uniform and fine multi-domain alignment state is not obtained. The liquid crystal display device having such a flow orientation was placed in a constant temperature bath at 150 ° C. for a heat treatment time of 0 minutes (slow cooling is performed when the state changes to an isotropic liquid state), 5 minutes, 15 minutes. , 30 minutes, 1 hour,
It was gradually cooled to room temperature in a constant temperature bath. As a result, 5
In the liquid crystal display device subjected to the heat treatment for more than a minute, the flow alignment disappeared, and the liquid crystal layer 4 between the substrates formed a fine multi-domain alignment state with a twist angle of 120 °. Since the chiral nematic liquid crystal between the substrates is vacuum-injected at room temperature of 25 ° C., it has a uniform liquid crystal composition ratio, and as a matter of course, the physical property values such as the NI point are the initial values of the liquid crystal before the liquid crystal injection. It did not differ from the physical properties. However, when the heat treatment time was 0 minutes, the liquid crystal display device formed a multi-domain alignment state, but the flow alignment did not disappear. Therefore, it is necessary to select the optimum heat treatment time for eliminating the flow orientation depending on the type of insulating film material and liquid crystal material used.

Even if an insulating film or liquid crystal different from the one used in this embodiment is used, the flow orientation disappears and becomes uniform by selecting the optimum heat treatment temperature and the optimum heat treatment time above the NI point. A minute multi-domain alignment state was formed by, and good display characteristics were obtained as in this example.

Here, the reason why the flow alignment disappears and a uniform and fine multi-domain alignment state is formed by performing the heat treatment is that the surface between liquid crystal molecules and the liquid crystal molecules are in contact with each other during liquid crystal injection. When the liquid crystal changes to the isotropic liquid state, the regulation force such as the adsorption force generated in the is temporarily released and becomes stable during the heat treatment or the process of slow cooling to room temperature. It is considered that the liquid crystal between the substrates disappeared and a uniform and fine multi-domain alignment state was obtained.

In the embodiment, the liquid crystal display device was placed in a constant temperature bath previously kept at a high temperature and heat treatment was performed. However, after the liquid crystal display device was placed in the constant temperature bath, the temperature was gradually raised to a set temperature. Also has the same effect. The optimum temperature setting for heat treatment is determined by the type of liquid crystal and insulating film used,
If the set temperature is too high, the quality of the insulating film and the sealing material may deteriorate, so 200 ° C. or less is desirable. In addition, the liquid crystal display device that has been heat-treated in a constant temperature bath is preferably cooled slowly because flow alignment does not remain and a uniform and fine multi-domain alignment state is not formed if the cooling speed to room temperature is too fast.

In the present embodiment, the insulating film is applied to the surfaces of both substrates, which are in contact with the liquid crystal,
The effect of the present invention was sufficiently obtained even when the insulating film was not applied to one or both substrates. However, in order to quickly eliminate the flow orientation, it is preferable to use an insulating film. In particular, when a polymer film such as polyimide or polyamic acid or polyamide containing an aliphatic or alicyclic molecular skeleton, which has a relatively weak adsorption force with liquid crystal, is used as an insulating film, the flow orientation disappears more effectively. did.

As described above, when the liquid crystal display device obtained by the manufacturing method of the present invention is actually operated for display, a uniform and minute multi-domain alignment state is formed, and therefore, a liquid crystal of good display having no viewing angle dependency. It was a display device. Further, there was no display unevenness such as contrast unevenness and brightness unevenness on the entire liquid crystal display screen, and there was no change in the NI point, the drive voltage, the specific resistance value, etc., so that stable display driving was possible.

[0020]

As described above, according to the present invention, there is no display unevenness such as contrast unevenness or brightness unevenness,
In addition, a liquid crystal display device having a wide viewing angle characteristic by a uniform and minute multi-domain alignment state, which performs stable display operation, can be manufactured more easily than the conventional manufacturing method.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic cross-sectional view of a liquid crystal display device according to a manufacturing method of the present invention.

FIG. 2 is a diagram showing an alignment state immediately after liquid crystal injection.

[Explanation of symbols]

 1a, 1b Glass substrates 2a, 2b Transparent electrodes 3a, 3b Insulating film 4 Liquid crystal layer 5 Liquid crystal molecules 6a, 6b Polarizing plate 7 Liquid crystal injection hole 8 Seal material 9 Alignment unevenness

Claims (2)

[Claims] 1. A liquid crystal is injected in a liquid crystal phase state between a pair of substrates whose contact surfaces are not subjected to an alignment treatment, and then the liquid crystal and the substrate are separated from each other in a liquid crystal phase state. A method for manufacturing a liquid crystal display device, which includes a step of performing heat treatment at a temperature not lower than a temperature at which a liquid is changed to an isotropic liquid state. 2. A liquid crystal is injected in a liquid crystal phase between a pair of substrates having an insulating film whose contact surface is not subjected to alignment treatment, and then the liquid crystal and the substrate are in a liquid crystal phase. A method for manufacturing a liquid crystal display device, which includes a step of performing heat treatment at a temperature equal to or higher than a temperature at which the state changes from the state of FIG.