NL8204678A - METHOD FOR MANUFACTURING A COLOR SCREEN. - Google Patents

Description

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Method of manufacturing a color display.

The invention relates to a method of manufacturing a color display device 5, which devices comprise a pair of electrodes, respectively, applied to opposing surfaces of two base plates spaced parallel to each other, a thin color filter layer being formed on at least one of the electrodes and wherein liquid crystal material 10 fills the space between the electrodes and can be controlled in terms of light transmittance or light reflection by the voltage applied between the electrodes. In particular, the invention relates to a method of manufacturing such devices, characterized in that the color filter layer is formed using an appropriate dyeing method.

The color display is used or suitable for use in computer system display devices, television receivers, video monitors and many other devices. For this reason, much research has been done and development work has been carried out with regard to such a color screen.

An example of the color display is shown in Figures 1 and 2. A pair of base plates 21 are placed parallel to each other with their inwardly facing surfaces carrying groups of narrow electrodes 22. Thin electrodes of color filter layers 23 are deposited on the electrodes of one of the groups, these layers representing the photometrically primary colors, ie red (R), green (G) and blue (B). The space between the base plates 21 is filled with liquid crystal material 24 and sealed with a spacer 25 placed on the edge of the plates.

As can be seen from Fig. 1, the color display comprises a number of small areas 11, each corresponding to the picture elements forming an original picture. The small 8204678 * 2 areas 11 contain said color filter layers 23R, 23G and 23B which act as a set of three primary colors.

In operation, a voltage is applied between the electrode 22 and the group of colored electrodes 22 which is separated from the first electrode by the interposed liquid crystal material so that a color image can be presented on the base plate 21 using a controlled change in the degree of transmittance or the degree of reflection of the liquid crystal material 24.

The quality of the performance of such a color display depends on the structure and the nature of the color filter layer. The following conditions are known and are believed to be essential in the manufacture of the color filter layer.

First, the layer must be thin enough to keep the driving voltage low which would otherwise increase due to the thicker layer present between the pair of electrodes. The layer thickness should be sufficiently small compared to the thickness of the layer of the liquid crystal material. According to reported test results, the thickness of the color filter layer is preferably 0.6 µm or less.

It is further necessary that the number of small areas of the filter layer can be successively colored with different colors and with sufficient accuracy.

This is absolutely necessary for a clear color image of a complicated pattern.

Thirdly, the colors of the filter layers must be pure and the shades thereof must be well balanced. This is a prerequisite for high fidelity in the reproduction of the color image.

Fourth, the said layers should not be uneven in thickness. Such inequality would result in the drive voltage being uneven between the 35 layers of different colors. Generally, the unevenness should be less than 1X of the thickness of the liquid crystal layer.

The fifth requirement is a practicable mass production that reduces costs.

However, none of the hitherto known methods have successfully fulfilled the said conditions. For example, screen printing that can reduce production costs cannot produce thin filters. Also, the degree to which the thickness of the layers is the same cannot be improved by this printing method. In the so-called "multilayer membrane interference" method, the electrodes are repeatedly vacuum-coated with suitable metal oxides. However, the multi-color filter produced by this method inevitably has a great thickness and is furthermore impractical due to its high production costs.

An object of the invention is to provide a method for manufacturing color display devices, which method according to the invention is characterized by a step in which paint-receiving layers formed on electrode surfaces are painted, so that all disadvantages of known methods are eliminated at once.

Another object of the invention is to provide a method suitable for manufacturing a plurality of color filter layers in such a manner that a plurality of thin, paint-receiving layers formed on thin electrodes of a color display device are grouped in a number of subgroups so as to be dyed in a predetermined color arrangement using predetermined dyes selected for each of the subgroups, respectively.

According to the invention, the filter layers can be made thin enough for a low drive voltage and they can also be accurately painted with a clear difference in colors from one another. The unevenness in thickness between the layers is less than + 0.04 µm. The color purity, 8204678 4, as well as the color balance are also satisfactory despite the simple manufacturing process which allows for mass production with low production costs.

Other objects and advantages will become apparent in the following description of a preferred embodiment shown in the drawing.

Fig. 1 is a horizontal sectional view of an example of a color display device viewed in the direction of arrows I-I in FIG. 2; FIG. 2 is a vertical sectional view of the direction viewed in the direction of arrows II-II in FIG. 1;

Fig. 3 to 9 show successively in partial vertical section one of the steps which together form an embodiment of the method according to the invention; and

Fig. 10 shows the color purity coupled with a color balance of the color filter layers produced by the method presented in FIGS. 3-9.

As shown in Figure 3, an electrically conductive layer having a thickness of about 0.1 µm is formed on a glass base plate 21 by vacuum depositing a layer of metal or metal oxide such as SnO 2 or 1 2 0 3 and then the layer is etched in the usual manner by the photo-etching process to thereby form a plurality of narrow electrodes 22.

Then, as shown in Fig. 4, the surfaces of the electrodes 22 as well as the uncovered surfaces of the glass between the electrodes are covered with a paint-taking agent 31 the thickness of which does not exceed 0.6 µm. Any suitable device, such as a turntable, can be used when applying the agent.

The agent contains a film-forming agent and a photosensitive agent, both of which are dissolved in a suitable solvent, such as water. The film-forming substance may be a water-soluble protein, for example, gelatin, or a resin, for example, 8204678-polyvinyl alcohol (hereinafter referred to as "PVA"). The photo-sensitive substance is, for example, a dichromate or a diazo compound.

After the paint-receiving layer 31 has dried, only the electrode surfaces are exposed to the light (U) by means of a shielding mask 32 of a desired pattern. Thus, only the portions of the paint-receiving layer on the electrodes 22 are cured and rendered insoluble. Portions of the layer that have not been exposed are then removed by dissolving the glass base plate as shown in Fig. 5.

The said film-forming substance, ie protein or PVA, is advantageous in the invention because the substance forms a thin and uniform layer that can be easily painted in deep colors. In the case where a much thinner layer and / or a much better paintability thereof are required, the paint-accepting agent 31 may contain an additive such as poly-dimethyldiacryl ammonium chloride, methyl glucose chitosamine or another organic polymer or other organic compound containing quaternary ammonium groups and / or contain amino groups in their molecules.

The paint-receiving layers 33 on the electrodes 22 are then covered with a lipophilic positive photoresist 34, as shown in Fig. 6. After the photoresist has dried, one of the pre-fabricated masks, 35, for one of the filter colors becomes red, green or blue, chosen to illuminate (U) the color-assuring layers 33R to be painted, for example, red. Only these layers 33R remain soluble due to the positive behavior of the photoresist so that they are dissolved in a developing process to leave temporary protective layers 36 as shown in Fig. 7.

Then, the paint-receiving layers 33R that are not covered with the temporary protective layers 36, 35 are painted with a solution of a suitable dye in a desired color depth. Red filter layers are thus formed on the selected electrodes. Finally, the protective layers 36 are removed using a suitable solvent.

The above steps are repeated for a second color (green) and a third color (blue) to form green filter and blue filter layers on preselected electrodes.

The dyes are preferably purified for use in order to obtain a deep dyeing of the layers 33 to allow them to be thinner thereby.

It is necessary to remove the usual additives commonly present in the dyes prepared for dyeing textile fibers.

The layers 23 thus painted can be fired if unfavorable swelling thereof is observed after dyeing. The firing will compress the swollen layers and make the layers thinner and stronger.

If necessary, an orientation membrane 26 can be formed on the color filter layers 33. This membrane gives the layers a function that improves an orientation of the liquid crystal material 24. The membrane will also act to prevent molecules of the dye from dissolving in the liquid crystal material. Suitable materials for forming the membrane are organic materials such as polyimide resin, polyacrylic resin, polyepoxy resin, PVA and organosilane resin, and inorganic electrically insulating materials such as SiO4. This material can be applied to the filter layers 33 by the turntable or by the vacuum coating method, both suitable for obtaining a thickness of the membrane not greater than 0.1 µm. Finally, a rubbing treatment is performed on the surfaces of the filter layers or of the orientation membrane as is common in liquid crystal display screens, and then a sealant 25 is screen printed onto the edge portions of the base plates 21, the sealant acting as 8204678 «5 9 7 a spacer that forms a space between the plates to be joined together. The liquid crystal material 24 will then be introduced into the space, as shown in FIG. 9. FIG. 10 shows a high color purity 5 accompanied by a good color balance of the filter layers produced by the above-described method.

Example 10 The transparent electrodes 22 of 1 ^ 0 ^ were formed on the base plate by a method common in the manufacture of electrodes for liquid crystal display screens. A coating solution was spread on the electrodes by the turntable device, which was prepared by adding 1 part by weight of ammonium chromate to 30 parts by weight of an adhesive solution whose viscosity was adjusted to 40 cp. The coating solution further contained a small amount of methyl glucose chitosamine. The thickness of the applied coating layer was adjusted to 1 µm. The layer was exposed to light 20 through the mask 32 after it was dried.

The parts of the layer 31 of the paint-receiving agent, that is, those parts that were directly above the electrodes 22, were thus cured or coagulated, while the rest of the layer which remained unexposed was dissolved in warm water just temperature of 50 ° C. The paint-receiving layers 33 were formed in the manner described above and further processed in the following manner.

On the paint-accepting layers 33, a lipophilic positive photoresist "0FPR" (a product of TOKYO OUKA LTD.) 30 was applied as a layer 34 using said dial and dried thereon. The layers 35R to be painted in a red color were selectively exposed to the light so that the photoresist present in the layers 35R decomposed and was removed by a developer solution to thereby leave the protective layers 36 8204678 8 for covering the layers other than the paint-receiving layers 35R. The latter were then painted using a red paint solution consisting of 1.5 parts of KAYAKALAN ORANGE RL (a dye manufactured by NIHON KAYAKU LTD., Which was purified using methanol, 2.0 parts of AMINYL BRILLIANT RED T -4B (a dye manufactured by SUMITOMO KAGAKU K0GY0 LTD.), 0.2 parts of AMYLAZIN (a diazo compound from DAIICHI K0GY0 SEIYAKU LTD.), 4 parts of sodium chloride and 100 parts of water. Dyeing was performed at 50 ° C for 20 minutes by keeping the object immersed in the solution and then the protective layers 36 were removed from the other paint-accepting layers 33 which were to be painted successively with a green paint solution and a blue paint solution.

The green paint solution consisted of 1.0 parts of SUMIN0L MILLING YELLOW MR (a paint manufactured by SUMITOMO KAGAKU K0GY0 LTD.) Which was also purified using methanol, 0.125 parts of SANDOLAN BRILLIANT BLUE N-5GM (one by SAND0Z LTD. manufactured paint-20 fabric), 1.0 parts citric acid and 110 parts water. Dyeing was carried out at 60 ° C for 20 minutes by keeping the object immersed in the solution.

The blue paint solution consisted of 1.0 parts of SANDOLAN CYANINE N-G 360% (a dye manufactured by SANDOZ LTD.) And 100 parts of water, and the dyeing was carried out at 50 ° C for 20 minutes also by immersion.

The paint-receiving layers 33, which had a thickness of 0.1 µm, swelled up in order to achieve a greater thickness of about 0.3 µm at the end of the paint treatments. Therefore, the layers were heated at 150 ° C for 20 minutes to compress them to about 0.2 µm thickness.

Then, the orientation membrane 26 was formed to cover the color filter layers 23 produced by painting and heating the paint-receiving layers 33 in the manner described above. A polyimide resin solution, 8204678 9 3 3 "diluted with N-methyl-2 pyrrolidone and DMAC, was used for the stated purpose and applied to the surfaces of the filter layers by means of the turntable. The orientation ** membrane had a thickness of 0. 1 µm and was fired at 200 ° C for 20 minutes.

In the event that the direct application of the polyimide solution will cause the dye to immigrate from the filter layer into the orientation membrane, it may be useful in preventing such immigration from applying a permanent protective membrane (not shown). between the orientation membrane and the filter layers.

The permanent protective membrane can be formed prior to forming the orientation membrane with an organic substance such as "POLYDULE" (a product of MIKUNI 15 PAINT LTD.) That does not allow the dye to pass through.

The scope of the invention is not limited to the example given. The paint-receiving layers 33 and the orientation membrane 26 can be made of any suitable material other than the glue solution and the polyimide resin solution, respectively. Layers 33 or the membrane can be water-soluble while the other is oil-soluble, or they can both be water or oil-soluble. When both are water-soluble, the solution for the orientation membrane 26 can be applied and dried quickly such that it prevents any immigration of the dyes that would otherwise occur in accordance with the combination of the materials. On the other hand, a negative photoresist can be used in forming said temporary protective layer (not the "membrane") instead of the exemplary positive photoresist. The composition and shape of the above-described glass base plates and the electrodes are also not limited to the examples mentioned, but can be varied to a wide extent, if necessary, to be applicable to many types of liquid 8204678

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». % 10 crystal displays. Therefore, it should be noted that the method of the invention also applies to the manufacture of a liquid crystal device containing color filter layers formed on thin film transistors.

8204678

Claims (5)

A method of forming color filter layers for a liquid crystal color display device, characterized by a step of forming receptive layers which are applied to each of at least one of two separate groups of fine electrodes, each group being supported by one of two freestanding base plates suitable for applying a liquid crystal material therebetween, and a step of painting the paint-accepting layers using 10 predetermined dusting solutions such that the layers are distributed over a number of subgroups of the color filter layers which are predetermined with respect to their colors. 2. A method according to claim 1, characterized in that the paint-receiving layers are hardened before the painting step is carried out. 3. A method according to claim 1, characterized in that the paint-receiving layers contain an organic polymer or a compound with a quaternary ammonium salt and / or an amino group in its molecule. Method according to claim 1, characterized in that the dye solution is prepared from (a) purified dye (s). 5. A method according to claim 1, characterized in that the color filter layers are covered with an orientation membrane suitable for improving the orientation of the liquid crystal material which occurs when a voltage is applied across the spaced electrodes, wherein the orientation membrane is also suitable for preventing the dye molecules from migrating into the liquid crystal material from the filter layers. 8204678 - / 2- Improvement of errata in the description associated with patent application No. 82-04678 Ned. Proposed by Applicant dd. December 13, 1982 Page 5, line 18: For "poly-dimethyldiacrylamonium chloride" - read "poly-dimethylallyl ammonium chloride"; Page 9, line 1: read --- DMAC (dimethyl acetamide) ---. y jev / bk