JPS63256923A - Production of liquid crystal cell - Google Patents

Abstract

PURPOSE:To prevent generation of remaining air bubble by deaerating the inside of a vacuum vessel and liquid crystal cell while heating the liquid crystal cell and maintaining liquid crystal cell substrates at a prescribed temp., then bringing the liquid crystal injection port of the liquid crystal cell into contact with a liquid crystal and injecting the liquid crystal into the cell. CONSTITUTION:The liquid crystal substrates 13 and 15 are sealed therebetween by a sealing agent 17 except the liquid crystal injection port 21 and heating plates 29, 29 are brought into tight contact with both sides of the liquid crystal cell 11 (empty cell) the gap spacing of which is maintained by a gap material 19. The heating plates are made into sandwich structure in which both sides of heating elements 23 are sandwiched by metallic sheets 25, 27, by which supporting and heating of the liquid crystal cell are executed simultaneously and the uniform heating and temp. control of the liquid crystal cell are facilitated. Aluminum sheets, copper sheets, etc., are used for the metallic sheets. Nichrome wires, sheathed wires, heat pipes, etc., are used for the heating elements 23. The liquid crystal cell subjected to heating and holding is immersed in the liquid crystal so that the liquid crystal is injected therein. Generation of air bubbles is thereby effectively prevented and the quick operation for injection of the liquid crystal is permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a liquid crystal cell, and more particularly to a method for injecting liquid crystal into a liquid crystal cell.

BACKGROUND OF THE INVENTION Conventionally, a vacuum injection method has been mainly used as a method for injecting liquid crystal into a liquid crystal cell. In the vacuum injection method, the inside of the liquid crystal cell is evacuated to a vacuum, the injection port of the liquid crystal cell is immersed in the liquid crystal in the liquid crystal tank, and the liquid crystal is poured into the liquid crystal cell using the pressure difference between the inside and outside of the liquid crystal cell. This is a method of injecting into

FIG. 2 is an explanatory diagram showing an example of the conventional vacuum injection method, in which the liquid crystal cell 11 and the liquid crystal tank 39 containing the liquid crystal 37 are
It is arranged in a vacuum chamber 31. The liquid crystal tank 39 is placed on a pedestal 41 that is vertically movable. In the liquid crystal cell 11, the inside of the seal portion 17 is a region into which liquid crystal is to be injected, and 21 is a liquid crystal injection port. Figure 3 shows the second
This is a cross-sectional view showing a method of holding the liquid crystal cell 11 shown in the figure, in which the liquid crystal inlet 21 is closely held from both sides by glass plates 43.43 so as to protrude from the ends of the glass plates 43.4:3.

In this state, first, the pump 33 is used to evacuate the inside of the vacuum chamber 31 and the inside of the liquid crystal cell. Next, the pedestal 41 holding the liquid crystal tank 39 is moved upward, and the liquid crystal injection port 21 is immersed in the liquid crystal 37. After this, open the leak valve 35,
Air or nitrogen gas or the like is gradually introduced into the vacuum chamber 31 to return it to normal pressure, and the liquid crystal 37 is injected from the liquid crystal injection port 21 using the pressure difference with the vacuum inside the liquid crystal cell II. Note that 19 in FIG. 3 indicates upper and lower substrates 13.1 constituting the liquid crystal cell 11.
This is a gap material for keeping the gap between the holes uniform.

However, when a plastic film is used as a liquid crystal cell substrate, problems may arise with the vacuum injection method described above.

When a plastic film is used as a liquid crystal substrate, unlike the case of a glass substrate, some distortion occurs in the entire cell after the upper and lower substrates are bonded together. This is thought to be caused by the elasticity of the upper and lower substrates when heat curing the sealant to bond the upper and lower substrates together.
This problem arises when a uniaxially stretched film, such as an axially stretched polyethylene terephthalate film, is used. Especially S
T N (Super Twisted Nemati
In a liquid crystal element having a structure in which the liquid crystal is largely twisted between the upper and lower substrates, as typified by the c) method, this phenomenon is noticeable when the upper and lower film substrates are bonded together with their stretching axes shifted (for example, by 10 to 20 degrees). .

In the STN type liquid crystal cell, as shown in FIGS. 4 and 5, significant distortion occurs in the direction of the misalignment angle of the stretching of the upper and lower substrates.

When liquid crystal is injected into such a liquid crystal cell using the conventional method, air bubbles 45 remain in the liquid crystal cell as shown in FIG. 6, making it difficult to produce a good cell.

In addition to being caused by distortion of the liquid crystal cell, bubbles are also likely to occur when the cell itself becomes larger, and the result is that the air inside the cell is not sufficiently removed. to cause.

However, sufficient deaeration takes a lot of time, resulting in a decrease in work efficiency.

In addition, if the degree of vacuum in the vacuum chamber is increased and the pressure inside the chamber is lowered, the low molecular components in the liquid crystal will evaporate, changing the characteristics of the liquid crystal and causing a great negative effect on the drive characteristics. Optimum conditions are set for the deaeration time, taking into consideration work efficiency. This optimal range depends on the liquid crystal material and the area of the liquid crystal cell, but it is approximately 1O-2t at the degree of vacuum.
orr order, and the evacuation time is within 2 hours.

The present invention provides a method for injecting liquid crystal into a liquid crystal cell using a plastic film as a substrate, effectively preventing the generation of residual bubbles even under normal deaeration conditions. It is.

The method for manufacturing a liquid crystal cell according to the present invention includes creating a vacuum in a liquid crystal cell in which at least one of the upper and lower substrates is made of a plastic substrate, and bringing the liquid crystal injection port of the liquid crystal cell into contact with the liquid crystal in the liquid crystal tank. In the method of injecting liquid crystal into a liquid crystal cell, the liquid crystal cell is heated and the liquid crystal cell substrate is kept at a predetermined temperature while the vacuum chamber and the liquid crystal cell are degassed, and then the liquid crystal injection port of the liquid crystal cell is brought into contact with the liquid crystal. It is characterized by liquid crystal injection.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating a method for heating and maintaining a liquid crystal cell according to the present invention, and corresponds to FIG. 3 described in the section of the prior art. Note that the plan view of the liquid crystal cell is the same as that in FIG. 2. The liquid crystal inlet 21 is connected between the liquid crystal substrate 13° and 15°.
The heating plates 29 and 29 are sealed on both sides of the liquid crystal cell 11 (empty cell) with the gap distance maintained by the gap material 19. The heating plates 29.29 have a sandwich structure in which the heating element 23 is sandwiched between metal plates 25.27 on both sides.

If such heating plates 29, 29 are used, the liquid crystal cell can be supported and heated at the same time, and moreover, uniform heating of the liquid crystal cell and temperature fFIHR can be easily achieved.

As the metal plates 25 and 27, aluminum plates, copper plates, etc. are used.

As the heating element 23, a nichrome wire, a sheathed wire, a heat pipe, etc. are used. Note that, in FIG. 1, the power input section for the heating element and the like are omitted.

The heated and maintained liquid crystal cell is immersed in the liquid crystal 37 to inject the liquid crystal as described with reference to FIG.

Note that the heating method is not limited to the above, and any method can be used as long as it can heat the entire liquid crystal cell substrate to a desired temperature, such as a method using an infrared lamp or microwave.

An aluminum plate with a thickness of 2I1wn is used, and heating plates 29 and 29, each having a structure using nichrome wire as a heating element to uniformly heat the entire aluminum plate, are placed on both sides of the liquid crystal cell as shown in Figure 1. It was placed in a vacuum chamber as shown in Figure 2.

Then, while maintaining the surface of the liquid crystal cell substrate at a temperature of 150° C. or less, I X 10-" to 5 X 10-"
After degassing the inside of the vacuum chamber and the liquid crystal cell and degassing the liquid crystal 37 at the same time at a vacuum degree of rr for 1.5 to 2 hours, heating of the heating plate 29 was stopped. Thereafter, the pedestal 39 was moved, and after the liquid crystal injection port 21 was immersed in the liquid crystal 37, the leak valve 35 was opened to perform liquid crystal injection.

In this method, when liquid crystal was injected while varying the substrate surface temperature, the liquid crystal cell It was confirmed that a good liquid crystal cell could be produced without any air bubbles remaining inside.

Here, the degassing effect within the liquid crystal cell increases as the heating temperature becomes higher, but there is a limit due to the heat resistance of the plastic film substrate.

For example, the heat resistance temperature of a uniaxially stretched polyethylene terephthalate film is 150°C, and if it exceeds this temperature, it exceeds the thermoplastic limit. Further, at 120° C. or higher, although it is within the heat resistance limit, thermal strain between the upper and lower substrates tends to occur, making it difficult to maintain a uniform gap over the entire cell. From the following two points of view, in the present invention, the heating temperature is preferably 150°C or lower, preferably 120°C or lower. Furthermore, if the heating temperature is too low, the heating effect will not work effectively and sufficient deaeration will not be possible.

As mentioned above, a liquid crystal cell made of a plastic substrate before liquid crystal is injected has some distortion throughout the cell, but after liquid crystal is injected, a liquid crystal cell consisting of a plastic substrate has some distortion between the liquid crystal and the side substrate. It is possible to obtain a liquid crystal cell with a uniform gap that is completely compensated by the acting attractive force.

According to the present invention, by heating and deaerating a plastic film liquid crystal cell substrate and then injecting liquid crystal, it is possible to create a liquid crystal cell with distortion or a size of about 640 x 400 dots or larger. Because it effectively prevents the generation of bubbles in liquid crystal cells with large area and capacity, and allows liquid crystal injection to be performed in a short time, it is possible to improve yields, improve reliability, and improve reliability compared to conventional liquid crystal cell manufacturing methods. Uniform display quality is achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a method of heating and holding a liquid crystal cell in the method of the present invention. FIG. 2 is an explanatory diagram showing a liquid crystal injection method according to the present invention and a conventional method. FIG. 3 is an explanatory diagram showing a conventional method of holding a liquid crystal cell. FIGS. 4 and 5 are explanatory diagrams showing the state of distortion occurring in the liquid crystal cell before liquid crystal injection. FIG. 6 is an explanatory diagram showing the generation of bubbles in the conventional method. 11...Liquid crystal cell 13.15...Liquid crystal substrate 1
7...Sealant 21...Liquid crystal injection port 23...
・Heating element 25.27...Metal plate 29...Heating plate 31...Vacuum chamber 37...Liquid crystal Fig. 1 Fig. 3 Fig. 2 □. Figure 4 Figure 5 Figure 6 Figure 1o holder

Claims (1)

[Claims] 1. In the method of injecting liquid crystal into the liquid crystal cell by creating a vacuum in the liquid crystal cell in which at least one of the upper and lower substrates is made of a plastic substrate, and bringing the liquid crystal injection port of the liquid crystal cell into contact with the liquid crystal in the liquid crystal tank, the method described above. A liquid crystal cell characterized in that after heating the liquid crystal cell and degassing the inside of the vacuum chamber and the liquid crystal cell while keeping the liquid crystal cell substrate at a predetermined temperature, the liquid crystal is injected by bringing the liquid crystal injection port of the liquid crystal cell into contact with the liquid crystal. Production method.