Patent GB-762404-A (GB)
Title: Improvements in or relating to the etching of metals
IPC: C23F1/42
Filed: 1954-05-06
Abstract: 762,404. Etching. DOW CHEMICAL CO. May 6, 1954 [May 20, 1953]. No. 13298/54. Class 100(2) An etching bath comprises the following ingredients, in proportion by weight:- (1) Nitric acid 2-14 per cent, preferably 5-11 per cent, desirably 10 per cent, (2) A dioctyl sulphosucinate or dioctyl sulposuccinic acid 0.005-0.1, preferably 0.01-0.4, of the weight of nitric acid, (3) Diethyl benzene 2-15 per cent, preferably 4-9 per cent, and not more than 3.5 times as much as the nitric acid; ortho-, meta, para-diethyl benzene or mixtures thereof may be used, (4) Watersoluble gum (e.g. gum arabic, maraya), gelatin, dextrin, or methyl cellulose, the proportions being, for gum 0.1-1.0. gelatin, 0.002-0.015, dextrin 3.0-7.0. methyl cellulose 0.0007-0.01, of the ratio of the sulphosuccinate to the nitric acid, (5) water. The bath is used for etching objects, such as printing plates, of an alloy containing at least 80 per cent magnesium. The object of adding ingredient (4) is to increase the depth of etching in enclosed parts of closed letters and between adjacent letters in a word, which depth is less than that attained in large open areas of the plate. Examples of etching baths are:- (A) 40 litres of water at 85‹F., 6.45 litres technical grade 42‹ Be + nitric acid, 744 grams 25 per cent aqueous solution of sodium dioctyl sulphosuccinate, 4.96 litres commercial diethyl benzene (60 per cent meta-, 30 per cent para-, 10 per cent ortho-diethyl benzene), and water at 85-90‹F. to make up to 62 litres, giving a composition of 9.6 per cent nitric acid, 6.8 per cent diethyl benzene, 0.29 per cent sulphosuccinate,. to which is added 93 grams of dextrin in 2 per cent aqueous solution, giving a concentration of 0.145 per cent. (B) oT a mixture of 9.6 per cent nitric acid, 6.8 per cent diethyl benzene, 0.29 per cent sodium dioctyl sulphosuccinate is added 186 millilitres of 2 per cent aqueous solution gum arabic, producing 0.0058 per cent concentration. (C) 40 litres of water at 85‹F., 6.4 litres of s.g. 1.42 nitric acid, 3.2 litres diethyl benzene, 96 grams sodium dioctyl sulphosuccinate in 2 litres of water, water at 85- 90‹F. to make up to 64 litres, 96 millilitres 2 per cent aq. sol. gum arabic giving a concentration of 0.003 per cent. (D) 64 litres made up as in C, add 208 millilitres 2 per cent aq. sol. gum arabic giving a concentration of 0.0052 per cent. (E) 40 litres of water, 6.48 litres 42‹ Be + nitric acid, 186 grams sodium dioctyl sulphosuccinate in 2 per cent aq. sol., 4.96 litres diethyl benzene, water to make up volume to 62 litres, 93 millilitres of 0.1 per cent aq. sol gelatin to a resulting concentration of 1.45 X 10<SP>-4</SP> per cent. (F) 62 litres made up as in E, add 93 millilitres of 0.05 per cent aq. sol. gelatin to a resulting concentration of 7.2 x 10<SP>-5</SP> per cent. (G) 6.4 litres nitric acid s.g. 1.42, 96 grams sodium dioctyl sulphosuccinate, 3.2 litres commercial diethyl benzene s.g. 0.87, water to make up to 64 litres. The resulting composition is 9.5 per cent nitric acid, 0.15 per cent sulphosuccinate, 4.2 per cent diethyl benzene, to which is added 0.0128 grams methyl cellulose of 4,000 cps grade giving a concentration of 0.00002 per cent. In all the above examples, the ingredients are mixed together in an etching tank provided with splash paddles for agitating and splashing the bath against the work to be etched, and are added in the order given, except-that dextrin and gum arabic are added together with the diethyl benzene. The above baths are used, for example, to etch a photoprinted plate 0.064" x 5" x 9" of composition 3 per cent aluminium, 1 per cent zinc, 0.15 per cent manganese, remainder magnesium, the resist being a polyvinyl resin base on one face and comprising printed matter in 6 and 8 point type. Before etching, the resist face is cleaned with cotton soaked in an aqueous solution of 4 oz. potassium permanganate and 4 oz. sodium hydroxide per gallon, or a 10 per cent aqueous solution of nitric acid. Etching is described as performed in the various baths at temperatures ranging from 70‹-93‹F. for from 4-5.5 minutes. The resultant etching depth is 0.018- 0.0205 inch in the open area and 0.003- 0.014 inch in and between letters . Specification 703,814 is referred to. Reference has been directed by the Comptroller to Specification 703,815.