COLOR FILTER

Abstract: A color filter comprising a transparent base plate (1) having provided thereon a porous active membrane layer (2) formed by active alumina, active silica. or a mixture thereof, a colored region or pattern (5) formed by a dye (4) deposited into micropores (3) of the active membrane layer, and a coating layer (6) sealing the upper portion of the micropores (3). This color filter can be prepared relatively easily, possesses excellent resistances to heat, water, chemicals, solvent, etc., and is suitable as a display for various devices, particularly a liquid crystal display.

Description: The present invention relates to a method for forming a color filter comprising a transparent substrate with a porous activated film oxide layer, a colored portion or pattern of the dye fixed in the minute pores of the activated film oxide layer, and a coating layer sealing the upper portions of the minute pores of said activated film oxide layer. JP-A-53 099 822 discloses a multi-colour filter which is made by forming an Al-oxide layer on a transparent substrate or on a transparent conductive layer formed on said substrate, coloring the Al-oxide layer and covering it with a masking layer. The Al-oxide layer is formed by anodic oxidation. JP-A-53 110 379 discloses a photomask comprising a transparent substrate, an Al-film and a resist film partially covering said Al-film. Those parts of the Al-film which are not covered by the resist film are converted into transparent Al₂O₃ by anodic oxidation. The elder, but postpublished EP-A-112 695 describes a method for making a multicoloured member wherein said member comprises a transparent substrate, a metallic Al-film which is made porous by different methods, e.g. by anodic oxidation, and a sealing layer. It is the object of the present invention to provide a method for forming a color filter which is superior in resistivity to heat, water , etc. and can provide a pattern having a sharply defined contour and enable the presentation of a variety of colors. Furthermore, the method should be relatively simple and easy in manufacture. According to the invention a method for forming a color filter is provided wherein a layer of colloidal alumina or colloidal silica or a mixture thereof is applied on a transparent substrate, thereafter drying then sintering the layer to form thereby a transparent activated film layer on said substrate with a number of minute pores therein, then applying a dye to said activated film layer uniformly or in a pattern and, subsequently applying a transparent sealing coating over the dyed avtivated film layer. The invention is advantageously developed by the measures mentioned in the subclaim. Fig. 1 is a schematic enlarged cross-sectional view of a color filter obtained by the method of the present invention. Fig. 2 is a schematic cross-sectional view of an example of a liquid crystal display pannel which employs a color filter obtained by the method of the present invention. One embodiment of the present invention will be explained in detail below. For clarity of illustration the drawing is exaggerated with the relative dimensions of the component parts being neglected. Referring to Fig. 1, there are shown a transparent substrate 1, an activated film layer 2 formed thereon, a colored portion or pattern 5 formed by the dye 4 fixed in a plurality of minute pores 3 of the activated film layer 2, and a coating layer 6 on the activated film layer 2. The transparent substrate 1 is a plate commonly used in liquid crystal display devices. Usually a glass plate may advantageously be used. The activated film layer 2 formed on the transparent substrate 1 is made of activated alumina or activated silica or a mixture of both these substances. To form the activated film layer 2, colloidal alumina or colloidal silica or a mixture thereof is first applied to the surface of the transparent substrate and dried and then sintered at 350° C to 850° C for 10 minutes to 180 minutes.The activated film layer 2 formed in this manner is transparent with a number of minute pores 3 formed therein, constituting a layer to be dyed. Desirably the activated film layer 2 has a thickness of 0.5 µ m to 10 µm, preferably 1.5 µm to 5 µm in consideration of the transparency, surface hardness, receptivity of dyes and other qualities thereof. A greater thickness renders the activated film layer milky and opaque, whereas a smaller thickness makes it impossible to obtain a required density of the coloration. The dye 4 which is fixed in the minute pores 3 of the activated film layer 2 to form a colored area or pattern 5 can be a sublimable dye and/or a thermo-diffusible and evaporable dye, etc. In practice, disperse dyes, oil-soluble dyes which do not contain metal, cation dyes, etc. are used. Dyeing with the above-mentioned dyes may be conducted with an ink containing a dye at such a temperature as to cause the dye to be thermally transferred into the minute pores, for example, at 100° C to 250° C for several to 60 minutes. The temperature varies with different kinds of dyes. To form the colored portion or pattern 5 on the activated film layer 2 any of the following methods may be employed. (1) Method wherein the acitvated film layer is dipped in a dye solution. (2) Method wherein a dye solution is sprayed over the activated film layer. (3) Method wherein a dye solution is applied to the activated film layer. (4) Method wherein a mask having a pattern formed therein is placed on the upper surface of the activated film layer and a sheet of transfer material printed with dye is placed on the mask and heated and pressed so as to cause the dye thereon to be transferred onto the activated film layer through the mask. (5) Method wherein a dye is set in the cells of a gravure plate, which is brought into close contact with the surface of the activatd film layer and heated to transfer the dye in the cells to the activated film layer. (6) Method wherein a sheet of transfer material having a pattern formed thereon with dye is brought into close contact with the surface of the activated film layer and heated to transfer the dye on the sheet of transfer material to the activated film layer. (7) Method wherein the required portion of the activated film layer is dyed by heating. (8) Method wherein a pattern is directly printed on the activated film layer. (9) Method wherein the required portion of the activated film layer is dyed, with a resist having been applied to the other portions. (10) Method wherein the whole surface of the activated film layer is colored with a dye solution and the portions other than the required portion of the layer is decolorized. (11) Method wherein the activated film layer itself is formed into a pattern and the layer is dyed. (12) Method wherein a pattern is depicted on the activated film layer by hand. Of these methods, methods (1) (2) and (3) are more suitable for coloring the whole surface of the activated film layer uniformly while methods (4) (5) (6) and (7) are more suitable for coloring the pattern. The pattern to be formed by dyeing may be designed according to its use. According to this invention, dot patterns can be formed with ease. In this case, there are patterns of more than two colors, with the pattern of each color being formed at a position accurately coinciding with a corresponding pattern of a transparent electrically conductive film. The coating layer 6 is formed on the upper portion of the minute pores 3 of the activated film layer 2 having dye fixed therein so as to seal the pores. The coating layer 6 may be formed by applying a hard transparent resin such as acrylic, melamine, epoxy, silicone, polyimide, etc. to the above-mentioned activated film layer, and heating it at such a temperature as to cause the resin to be set. Besides the above-mentioned resins, the coating layer 6 may be formed by applying and heating an inorganic material such as sodium silicate, lithium silicate, etc. The coating layer 6 is a layer for preventing the dye molecules arrested in the minute pores of the activated film layer from being evaporated again and the dyed portions from becoming dirty. In order to form a transparent electrically conductive film having a desired pattern on the coating layer 6 of a color filter obtained by the present invention at a later step of the process, it is preferable that the coating layer should be made of a material having a good adhesivity to the material which forms the transparent electrically conductive film. Fig. 2 schematically shows an example in which a color filter of the above-mentioned construction is used in a liquid crystal display device. On the surface of a transparent base plate 10 there is formed a transparent electrode 11a, and a color filter 14 obtained by the method of the present invention is arranged to face the surface of the electrode across a space 13 formed by spacers 12, with a transparent electrode 11b being provided on the color filter 14, and liquid crystal is enclosed in the space 13. A polarizing plate 15 is arranged adjacent the outer surface of each of the base plate 10 and the color filter 14. An orientated film 16 covers each of the transparent electrodes 11a and 11b. The color filter obtained by the method according to the present invention has the following advantages. Since the activated film layer of activated alumina or activated silica is formed on the transparent substrate, the filter is superior to conventional color filters with respect to resistivity to heat, water, chemicals and solvents. Since the dye forming the colored portion or pattern is fixed in the individual independent pores of the above-mentioned activated film layer, there is no problem of bleeding and even those dyes which require a relatively high temperature and a long time can be used for coloration. Since it is possible to use any dye that can be fixed in the minute pores of the activated film layer, it is possible to express various colors. Furthermore, the method of coloring or forming patterns is simple and easy. The color filter obtained by the method according to the present invention is extremely excellent in resistivity to heat, water and chemicals, and relatively simple and easy to manufacture, so that it can be used very effectively as a color filter in liquid crystal display devices and other display devices.

Claims: A method for forming a color filter which comprises: applying a layer of colloidal alumina or silica or a mixture thereof on a transparent substrate; thereafter drying then sintering the layer to form thereby a transparent activated film layer on said substrate with a number of minutes pores therein; thereafter applying a dye to said activated film layer uniformly or in a pattern; and, subsequently applying a transparent sealing coating over the dyed activated film layer. The method of claim 1 further comprising applying dye in patterns of at least two colors to said activated film layer and applying thereover a transparent electrically conducting film with patterns thereon corresponding to each dye color with the color pattern of electrically conductive film pattern in registry.

Inventors: MASAKI, KENICHI 906, CO-OP NOMURAOIKE, MATSUMURA, KOZO, SUMI, TAKAO, TAKAOCHI, MINORU 3-B-802, 151-30
Applicants: NISSHA PRINTING CO., LTD.
Application year: 1985
Main classification: G02B5
IPC codes: G02B5, G02F1