GB813803A - Improvements relating to etch-resistant materials and etching methods - Google Patents

Abstract

813,803. Etching. SAUNDERS-ROE Ltd. Aug. 31, 1956 [Aug. 31, 1955], No. 25054/55. Class 100(2) An etching resist consists of a solution of bitumen and oil-reactive resin. The solvent may be xylene. The bitumen may be that known under the Registered Trade Mark "Gilsonite", and may be present in the proportions 7¢-20 per cent, preferably 10 per cent, of the resin. The resin may be a phenolic resole, an alkyl resin, or a maleic resin, e.g. the reactive resin based on para tertiary butyl phenol, or a glycerol esterified resin modified maleic resin. An example is 10 parts pure phenolic resole, 100 parts Gilsonite bitumen. For etching a metal surface, the design area is masked, the resist coated over the unmasked surface, and the mask removed, e.g. the outline of the design is printed, the surface is covered with a transparent material, such as Saro-film, and the material is removed from the non-design areas. Alternatively, the resist may be applied by hand. Example. In a method of reducing the thickness of part of the area of a sheet of aluminium, the sheet is given a hot alkaline wash, a dilute nitric acid wash, a cold water rinse, and dried. The design is litho-printed on the sheet, which is then sprayed with Saro-film, and dried for 30 minutes at ambient temperature. The film is cut by hand round the printed area and that part covering the area not to be etched is peeled off, leaving a mask. The sheet is. sprayed with a primer and airdried at 70‹F., and is then covered with the resist in a series of thin coats, being dried between each coat at 70‹F. for 30 minutes. The mask is removed and the sheet dried in air for 12 hours, and then etched at 70‹C. with a 10 per cent solution of caustic soda to which may be added wetting and oxidizing agents as desired. The sheet is then rinsed in cold water, then in 5 per cent aqueous solution of nitric acid at room temperature to remove black oxides and neutralize caustic soda action, then in hot water, then in an agitated bath of xylene at 20-50‹C to remove the resist. The bitumen is recovered by distillation for re-use. The solvent can be used continuously. The primer may be removed or not from the sheet. Alternatively, the mask may be applied by fitting a suitably-shaped piece of masking tape to the sheet before applying the resist.