JPS6223849B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a flat display element using a liquid display medium such as a liquid crystal, and particularly to a method for manufacturing a large flat display element in which the spacing between substrates is made uniform.

Generally, when manufacturing a display element in which a liquid display medium is sealed in a cell with two substrates facing each other with a predetermined gap between them, it is basic to make the spacing between the substrates uniform throughout the device. is important.

For example, in a liquid crystal display element, when a voltage is applied between electrodes attached to the inside of both opposing substrates, the time response of the optical change that occurs in the liquid crystal greatly depends on the spacing between the substrates, so this spacing is uniform. If this is not maintained, variations will occur in the response time of the liquid crystal, and display performance will be significantly reduced. Therefore, it is necessary to construct cells by interposing spacers with high dimensional accuracy between the substrates to maintain uniformity in the spacing between the substrates. As such a spacer material, a fibrous material such as glass fiber or a powder such as alumina is used. A common method for constructing cells is to apply an adhesive containing these minute spacers to the periphery of the substrate and harden the adhesive while applying pressure (for example, as described in Japanese Patent Application Laid-Open No. 1983-1989).
No. 60598), in the case of large substrates, spacers are further spread over the entire substrate surface to make the substrate spacing uniform. However, especially with large substrates, it has been extremely difficult to obtain cells with such uniform substrate spacing. This is because conventional methods were unable to apply pressure uniformly to the substrate. In other words, molds and presses have traditionally been used to apply pressure to the substrate, but since there are limits to their flatness and pressure accuracy, it is not only impossible to eliminate warping and bending of the glass substrate. However, the effect of the spacers dispersed on the substrate could not be fully exploited.

In order to overcome these drawbacks, a method of applying fluid pressure to the substrate has been developed, and this method uses fluid pressure to press a pressurizing body that is easily compatible with the substrate against the substrate. A sufficient effect cannot be obtained unless the body is made almost the same shape as the substrate, and it is difficult to heat the substrate to harden the adhesive.

The present invention has been made by focusing on the problems of the conventional method. When bonding substrates, the pressure in the space between the substrates is reduced at least at the final stage of the curing process of the adhesive. The purpose of the present invention is to solve the above-mentioned problems by performing adhesion while applying pressure using atmospheric pressure.

Hereinafter, the present invention will be explained based on the drawings. 1st
The figure shows an example of a display element using a liquid display medium.
It shows a cross section of a main part of a large liquid crystal display element, and FIG. 2 is a bottom view showing the back side of the upper substrate. To explain the structure, numerals 1 and 2 are large glass substrates (approximately 100 x 200 mm ² ), and on the inner surface of each electrode 3 formed of a transparent conductive film such as a number pattern is adhered. A transparent insulating liquid crystal alignment control film 4 is formed thereon. A spacer 5 is provided between the upper substrate 1 and the lower substrate 2 to maintain a distance of about 10 μm, and the periphery of the spacer 5 is sealed with an adhesive 6 including the spacer. Liquid crystal 7 is injected into this sealed gap from injection port 8 and sealed with adhesive.

According to the conventional device manufacturing method, spacers 5 are spread on the inner surface of either of the upper and lower substrates 1, 2, and adhesive 6 is applied to the periphery of the other substrate, and then the two are overlapped and molded or pressed. The adhesive is heated and cured by raising the overall temperature while applying pressure.

In contrast, in the present invention, after the upper and lower substrates are stacked in the same manner as in the conventional method, the peripheral edge portions are first temporarily bonded at a temperature lower than the curing temperature of the adhesive 6. Next, the gap between the substrates is evacuated by an oil rotary pump using the liquid crystal injection port 8 to bring the inside into a vacuum state. At this time, due to the pressure difference generated inside and outside the element, the upper and lower substrates are compressed with a pressure of approximately 1 kg/cm ² , and the spacing between the substrates is forcibly made almost completely equal to the diameter of the spacer. While maintaining the element in this state, it is heated to the curing temperature of the adhesive 6 to complete curing and perform the main bonding. After this, the vacuum inside the device is broken and the process is completed.

It has been confirmed that such a method is extremely effective in making the substrate spacing uniform. This is because the pressure applied to the substrate is highly uniform, which cannot be achieved with conventional molds or presses, and as a result of crimping being performed under uniform pressure, warping and bending of the substrate is minimized. This is presumed to be because the element is formed in the state.
Furthermore, in the method of the present invention, there is no restriction on the size of the substrate in principle, which is also a feature not found in conventional methods using molds or presses.

The present invention will be explained below using examples.

Example A large liquid crystal display element was manufactured by the above method. The size of the glass substrate used was 100×200 mm ² and the thickness was 1 mm. First, as shown in FIG. 1, fine glass fibers with a diameter of 10 μm and a length of about 50 μm are placed in a mesh pattern on the surface of one substrate, for example, the upper substrate 1, on which the transparent electrode 3 and the liquid crystal alignment control film 4 are formed. Using a standard film with a spacing of 37μm
Spray at a density of 1.5 sticks/mm ² . An epoxy adhesive is applied by printing to a predetermined area around the periphery of the other lower substrate, except for a portion of the liquid crystal injection port 8 (to be described later), that is, a width of about 2 mm, and the lower substrate 2 is placed facing and fixed to the upper substrate. Heat the cell configured like this at 60℃ for 30 minutes,
Perform temporary gluing. Next, using the liquid crystal inlet 8 as an exhaust port, the inside of the cell is evacuated by an oil rotary pump. At this time, a silicone rubber tube 9 was used as the exhaust pipe, and was fixed to the exhaust port portion with an adhesive. To explain in detail the connection between the exhaust port and the exhaust pipe, the silicone rubber pipe 9 has an outer diameter of 4 mm, for example.
Using a tube with an inner diameter of 2 mm, cut a slit with a width of just under 2 mm and a length of 10 mm from the end face along the axis of the tube as shown in Figure 3, and insert the temporarily bonded substrate into this slit. The liquid crystal injection port 8 is made to face the hole of the silicone rubber tube 9. Thereafter, an adhesive 10 is applied to the contact portions between the silicone rubber tube 9 and the substrates 1 and 2.

After connecting the silicone rubber tube 9 in this way, the end portion of the silicone rubber tube 9 is sealed after exhausting the air for several minutes. In this state, the spacing between the substrates is almost completely uniform to 10 μm, which is equal to the diameter of the glass fiber. While keeping the inside of the cell in a vacuum state,
C. for 1 hour to harden the adhesive on the peripheral edge of the substrate. After cooling, the vacuum inside the cell is broken and the exhaust pipe is removed. As the vacuum is broken and the pressure effect on the glass substrate is relaxed, the spacing between the substrates increases slightly in the center of the cell, but uniformity is maintained sufficiently.

In order to quantitatively examine the uniformity of the substrate spacing, the substrate spacing was measured at each point of the cell and its statistical variation was determined. Regarding the cell of this example, when the substrate spacing was measured at 100 locations, the average value < d
> was 11.9 μm, and the standard deviation σ was 1.10 μm. When crimping is done using the traditional method using a metal mold,
<d> is approximately 13.5μm, and the value of σ is 2.00
It was difficult to keep the thickness below μm. It can be seen that according to the present invention, the substrate spacing can be accurately controlled to a value close to the diameter of the spacer.

When liquid crystal was injected into the device manufactured by the above method, the response time was uniform over the entire display area. Even when a guest-host type liquid crystal was used as the injected liquid crystal, color unevenness did not occur in the display area.

In the above example, a minute glass fiber was used as the spacer material, but the present invention is not limited to this. Any material having a diameter may be used.

Regarding the density of spacers, if the density is too high, the spacers tend to overlap each other, and if it is too low, the effect will be weakened, and in either case, it will cause uneven substrate spacing. Therefore, it was optimal to set the number to about 1.5 lines/mm ² .

In addition, in the above embodiment, only the glass fiber was interposed between the upper and lower substrates, but in order to make the substrate spacing more uniform, an adhesive was further interposed in a minute part at the center of the cell, and then It may be crimped by any method. When crimping is performed with the inside of the cell in a vacuum state, the upper and lower substrates are forcibly fixed at the center of the cell by adhesive at a distance that is approximately equal to the diameter of the glass fiber, so that when the vacuum is broken after crimping, the substrate spacing is The uniformity of is further improved. However, in this case, the area of the adhesive needs to be kept as small as possible so as not to affect display quality.

Note that when reducing the pressure in the cell interior space, if the applied adhesive can withstand atmospheric pressure, the pressure may be reduced during the entire period of the adhesive curing process.
However, if the viscosity is lowered by heating and curing, such as with an epoxy resin, the pressure should be reduced after the viscosity increases and hardens again, and the reduced pressure state should be maintained until the resin is completely cured.

Furthermore, although the above embodiments have described the case where a glass substrate is used, according to the present invention, it is also possible to fabricate a bendable flat panel display element using, for example, a highly heat-resistant polymer film as a substrate. .

Furthermore, the present invention can also be applied to the production of display elements such as electrochromic elements and photochromic elements using liquid display media other than liquid crystals.

For example, when comparing an electrochromic device and a liquid crystal, an electrochromic device uses propylene carbonate containing LiClO ₄ as an electrolyte instead of liquid crystal, or has a layer of tungsten oxide for color development. However, the major structural difference is that electrochromic devices are made of a porous plate (0.2 to 0.3 mm thick) with many holes of a few microns in parallel between both substrates.
exists. Therefore, in this case, by interposing a spacer between each substrate and the porous plate, it can be manufactured in the same manner as a liquid crystal element.

As described in detail above, the present invention has made it possible for the first time to make the substrate spacing uniform in a flat panel display element filled with a liquid display medium, especially in a large flat panel display element. The present invention has extremely great practical value because a flat panel display element of any size with uniform display characteristics can be easily produced with good reproducibility without the need for molds or presses.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a large liquid crystal display element, Figure 2 is a bottom view showing the back side of the upper substrate, and Figure 3 is a partial cross-sectional view of the cell and exhaust pipe to show the state in which the exhaust pipe is attached to the cell. It is. DESCRIPTION OF SYMBOLS 1... Upper substrate, 2... Lower substrate, 3... Transparent electrode, 4... Liquid crystal alignment film, 5... Spacer, 6...
Sealing agent, 7...Liquid crystal, 8...Liquid crystal injection port, 9...
Silicone rubber tube, 10...Adhesive.

Claims (1)

[Claims] 1 A display in which two substrates are placed facing each other with a spacer interposed between them, and a space is formed between the substrates by bonding the peripheral edges while applying pressure to the substrates, and a liquid display medium is sealed within the space. 1. A method for manufacturing a display element, characterized in that the substrate is pressurized by reducing the pressure in the space at least at the end of the process of curing the adhesive.