Method for manufacturing a shadow mask by resist etching

Abstract: A steel sheet (1) of thickness 20-80 µm is coated on each surface with a resist layer (2), e.g. of casein, and (Fig 1) one surface only is patternwise exposed to light through a glass mask (31), the resultant pattern of holes is developed (baked) and the unpatterned resist (2) is covered by coating or adhesive with a non-etchable layer of a resin (5), the patterned resist (2) is etched, e.g. with ferric chloride, and the resists and resin layer removed to provide a shadow mask (1) having etched through-holes. In a variant (Fig 4) a large opening (311) 3 -5 times the thickness of the sheet is patterned in a resist (21) on one side, one or more small openings (321, 322) patterned opposite thereto on the other resist, and etching is performed from each side; a layer of non-etchable material (4) is coated on the second side and into the small holes before a final etching from the first side; a large through-hole is formed. The resin covering (5) must resist pressure of etching solution and have strength to maintain the flatness of the sheet (1) and can be alkali- or solvent-soluble, UV-setting or hot-melt; an adhesive film should be anti-acid. The holes can be formed as a slot or slit and they have satisfactory accuracy of shape and dimension. The masks can be used for a large color cathode ray tube.

Description: The present invention relates to a method of manufacturing a shadow mask for color CRT, and in particular to a method for manufacturing a thin-plate shadow mask of 20 - 80 µm in thickness and, more specifically, an effective method of manufacturing a thin-plate type aperture grill in the form of slits. With the recent increase of large-size CRT display units for color television and the like, there are now strong demands on large-size shadow masks. To produce lightweight shadow masks, thin plate of 20 - 80 µm in thickness is now widely used. To manufacture a shadow mask of conventional type using a base material of 130 - 150 µm in thickness, an electrode base material 1 is cleaned up (a) as shown in Fig. 2, and resist 2 is coated on both surfaces of the base material 1 (b). Using a glass mask 3, the resist 2 on both surfaces is exposed to light (c). After developing the resist 2, patterning is performed, and an etching film is produced through baking (d). Then, etching is performed from both surfaces of the base material 1. After forming an opening (e), the resist 2 is removed (f). This is called one-step etching method. If this method is applied to thin plate material of 20 - 80 µm, surface flatness cannot be maintained because of spraying pressure during etching, and shape and dimensional accuracy of the etching hole thus completed are sometimes not satisfactory. There is another method, by which an electrode base material 1 is cleaned up (a), and resist 2 is coated on both surfaces of the base materials 1 (b) as shown in Fig. 3, Using a glass mask 3, the resist 2 on both surfaces is exposed to light (c). After developing the resist 2, patterning is performed, and an etching film is prepared through baking (d). Then, etching is performed only cn one surface of the base material 1 to prepare hole (e). An anti-etching packing material 4 is filled into this hole (f), and etching is performed again from the side opposite to the hole (g), and the resist 2 is removed (h). This is called two-step etching method. When this method is applied to thin plate base material of 20 - 80 µm, it is not possible to obtain cross-sectional shape as desired. The latter is disclosed in the Japanese Laid-Open Patent Publication No. 61-130492 and others. When the thickness of the base material is as thin as 20 - 80 µm as described above, the plate thickness is relatively too thin to form an etching hole of 60 - 250 µm in width, and the desired cross-sectional shape cannot be prepared by the conventional two-step etching method as shown in Fig. 3. (The etching hole penetrates the material before the desired cross-sectional shape is obtained.) By the one-step etching method shown in Fig. 2, the product of good quality in terms of shape, linearity and dimensional accuracy of etching hole cannot be obtained because the base material is too thin to have sufficient strength and surface flatness cannot be maintained during etching. It is also known, see U.S.-A-4,755,257, to form an etching hole from only the resist pattern side of the base material while attaching a reinforcing support member directly on the other surface without coating the other surface with a resist layer. In this case, however, the edge shape of the through-hole on the other surface becomes inferior because there is no resist layer on the other surface, and the shape, linearity and dimensional accuracy of the etching hole is poorer. This is not desirable. Further, the reinforcing support member is subject to heat treatment through resist coating, patterning and baking. As a result, thermal expansion and thermal contraction occur, and the shadow mask is deformed. Also, a force may be applied during detachment, and the shadow mask is also deformed. The deformation of the shadow mask leads to warping and distortion of the product, and this makes it difficult to manufacture the product with high dimensional accuracy and better uniformity. It is accordingly an objection of the present invention to provide a shadow mask, which is satisfactory in terms of shape, linearity and dimensional accuracy of etching hole in case an electrode base material is 20 - 80 µm in thickness, and especially a thin-plate type aperture grill. Another object of the invention is to provide a shadow mask, in which etching hole having dimension larger than the thickness of the electrode base material, i.e. 20 - 80 µm is formed with satisfactory linearity, dimensional accuracy and cross-sectional shape. These objects are achieved by the method of manufacturing a shadow mask of Claim 1. The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 represents a manufacturing process of manufacturing a shadow mask, according to the present invention; Figure 2 shows a manufacturing process by a conventional one-step etching from both sides; and Figure 3 represents a manufacturing process by a conventional two-step etching method from both surfaces. In the method of the invention, an electrode base material 1 of 20 - 80 µm in thickness is used as shown in Fig. 1, and the base material 1 is cleaned up as shown in Fig. 1 (a). Then, resists 21 and 22 are coated on both surfaces of the base material 1 as shown in Fig. 1 (B). Using a glass mask 31 with an electrode pattern, the resist 21 on one surface is exposed to light as shown in Fig. 1 (c), while the resist 22 on the other surface is exposed to light using a glass mask 32 without an electrode pattern. Then, as shown in Fig. 1 (d), the resists 21 and 22 are developed, and patterning and drying are carried out to form an etching film. Thus, the resist 22 on the opposite side with no exposure of electrode pattern remains all over the surface. Next, as shown in Fig. 1 (e), the resist 22 on the unexposed portion is covered with a resin layer 5, which has anti-etching property and is resistible to spraying pressure during etching and has strength enough to maintain surface flatness of the base material 1 to eliminate unstability of the base material 1 caused by spraying pressure during etching. As shown in Fig. 1 (f), etching is performed only on one side of the base material from the side of the patterned resist 21, and the base material 1 is etched and penetrated. After etching is done as desired, the reinforcing resin layer 5 and the resists 21 and 22 are removed as shown in Fig. 1 (g). Thus, a shadow mask is obtained, which has satisfactory quality in terms of shape, linearity, dimensional accuracy of etching hole. In a modification of Fig. 1 (e), a reinforcing resin without anti-etching property may be used as the reinforcing resin layer 5 and may be covered with an anti-etching film. In a further modification, instead of providing the reinforcing resin layer 5, a reinforcing adhesive film with an anti-etching property may be used to cover the resist 22 on the unexposed side. The resin layer 5 must have the above property, and it is preferably alkali-soluble. Solvent-soluble resin such as nitrocellulose type, novolak type, etc., UV-setting resin such as oligoester acrylate type, or holt melt resin such as rosin-polyester type may be used. As the above anti-etching film or reinforcing adhesive film with anti-etching property, there are an anti-acid adhesive film such as polyester type or polyethylene-polypropylene type. In this case, it is preferable to use an adhesive, whose adhesive strength is decreased by heat setting, heat foaming processing and ultraviolet ray irradiation for easier detachment. The present invention, in which etching is performed from only one side with the patterned resist, is superior to the known method to etch by one step from both surfaces of the base material of the same thickness in terms of shape and linearity of the etching hole. Because etching is performed from one side, the difference between the width of the resist pattern and the dimensional width of the through-hole of the product becomes larger. (This difference is referred to as 'etching compensation' hereinafter). Thus, etching time is made relatively longer, and irregularities of etching surface is flattened, resulting in better linearity. That is, the etching compensation is larger than in the etching from both surfaces. Because a reinforcing layer to maintain flatness of the base material is used to resist spraying pressure during etching and to eliminate unstability of the base material by spraying pressure during etching, it is possible to manufacture a product with higher dimensional accuracy and better uniformity. By contrast, in the manufacturing method of the present invention, not only is one surface of the electrode base material provided with a reinforcing layer, but also there is a resist layer between the reinforcing layer and the base material. Thus, the edge shape of the through-hole on the other surface is formed better and it is possible to form an etching hole with better shape, linearity and dimensional accuracy. When the reinforcing layer is a resin layer, it can be removed at the same time as the resist layer by a resist-removing solution, and a detaching force is not applied on the base material. Further, when the reinforcing layer is an adhesive film, it is detached after heat setting processing, heat foaming processing or ultraviolet irradiation, and almost no physical force is applied on the base material. Therefore, the shadow mask is not deformed during detaching. The product is neither warped nor distorted, and it is possible to manufacture the product with higher dimensional accuracy and better uniformity. One example of the method of the invention will now be described below. Example Using a base material of 35.5cm in size and 60 µm in thickness, made of low carbon mild steel, a casein resist was coated on both sides of the base material. After drying, the resist on one side of the base material was patterned. It was baked, and a rosin-polyester resin of hot melt type was coated on the resist surface on the other side in a thickness of 200 - 500 µm. Then, the patterned side was etched by a spraying method using ferric chloride of 60°C liquid temperature and 46°Baume specific gravity as etching solution. Thus, a penetrating slit was prepared. After etching, it was washed with water. The resist and the resin were removed using an alkaline solution. After washing and drying, the width and linearity of the slit were measured. The results are compared with the results of a conventional one-step etching method in the table below. Manufacturing method Dimensional accuracy σ Linearity Rz Rmax Conventional method 0.20 1.09 µm 1.28 µm The present invention 0.12 0.63 µm 0.75 µm As it is evident from this table, compared with the conventional one-step etching method from both sides of the base material, the dimensional accuracy and linearity were about twice as good in the present invention. Here, the dimensional accuracy σ is expressed by light transmittance of (several) slits in a limited region, and it is the standard deviation for 100 pieces. R z and R max showing the linearity are defined by the Japanese Industrial Standard (JIS B 0601; 1982). The electrode plate was destroyed, and the roughness of the cross-section was measured. In this case, etching compensation of the resist pattern was set to 30 µm, and this was larger than the etching compensation in the conventional one-step etching from both sides. As the reinforcing resin, a rosin-polyester resin was used; this has anti-etching property and is resistible to spraying pressure during etching and has strength enough to maintain the surface flatness of the base material. Preferably, it is alkali-soluble and easy to form on the resist. The rosin-polyester resin and used here melts at about 120°C, and it was coated on the resist in molten condition. After coating, the rosin-polyester resin is solidified in the range from normal temperature to etching temperature. It has sufficient reinforcing property, good anti-etching property and is alkali-soluble. In the above example, the etching solution temperature was 60°C, and the specific gravity of the etching solution was 46°Baume, while the same results were obtained from the solution temperature was 50-75°C and specific gravity was 45 - 49°Baume.

Claims: A method of manufacturing a shadow mask of 20-80 µm in thickness, wherein a reinforcing layer is applied to one side of an electrode base material, a patterned resist layer is provided on the other side, and etching is performed only from the side of the patterned resist layer, characterised in that an unpatterned resist layer is provided on said one side of the electrode base material between said base material and the reinforcing layer, and said reinforcing layer is further provided with an anti-etching property. A method of manufacturing a shadow mask according to Claim 1, wherein said reinforcing layer is formed from a reinforcing resin having an anti-etching property. A method of manufacturing a shadow mask according to Claim 1, wherein said reinforcing layer is formed from a reinforcing resin and is covered with an adhesive film having an anti-etching property. A method of manufacturing a shadow mask according to Claim 1, wherein said reinforcing layer is formed from an adhesive film covering said unpatterned resist layer and having anti-etching and reinforcing properties. A method of manufacturing a shadow mask according to Claim 2 or 3, wherein the resin layer is made of an alkali-soluble resin. A method of manufacturing a shadow mask according to Claim 2 or 3, wherein the resin layer is made of a solvent-soluble resin. A method of manufacturing a shadow mask according to Claim 2 or 3, wherein the resin layer is made of a UV-setting resin. A method of manufacturing a shadow mask according to Claim 2 or 3, wherein the resin layer is made of a hot melt resin. A method of manufacturing a shadow mask according to Claim 3 or 4, wherein the adhesive film is an anti-acid adhesive film. A method of manufacturing a shadow mask according to Claim 3 or 4, wherein the adhesive for the adhesive film is used, whose adhesive strength is decreased by heat setting processing, heat foaming processing or ultraviolet irradiation. A method of manufacturing a shadow mask according to any of Claims 1 to 9, wherein the shadow mask is formed in shape of a slit.

Inventors: IKEMAGI TAKESHI, NAKAMURA OSAMU, IKEMAGI, TAKESHI, NAKAMURA, OSAMU, Ikemagi, Takeshi, c/o Dai Nippon Printing CO., LTD, Nakamura, Osamu, c/o Dai Nippon Printing CO., LTD
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON PRINTING CO., LTD.
Application year: 1992
Main classification: G03F1
IPC codes: H01J9, G03F1