| 摘要 |
819,067. Electroplating copper and chromium in succession. LEMOTAL S.A. Nov. 25, 1955 [Nov. 25, 1954], No. 33812/55. Class 41. [Also in Group XVI] A method of producing an offset planographic printing plate comprises the steps of electrolytically depositing a first copper coating 2 on a base-plate 1 from a cuprous solution, electrolytically depositing a further copper coating 3 over the first coating 2 from a cupric solution, electrolytically depositing over the coating 3 a thin film of chromium 4, interrupting the electrolysis, then resuming the electrolysis until a substantial chromium coating 5 has been deposited over the copper coating, and selectively removing portions of the chromium coatings in accordance with a pattern. In an example a base-plate 1 of zinc 114 cm. X 140 cm. was immersed in a bath containing 20 grams of cuprous cyanide, 15 grams of sodium cyanide, 15 grams of sodium hydroxide, 40 grams of sodium carbonate and 40 grams of Rochelle salt per litre of electrolyte, and a current of 500 amps. at 4 volts was passed for 30 minutes. The plate was then immersed in an electrolytic bath containing 250 grams of cupric sulphate per litre and a current of 300 amps. at 2.5 volts passed for 60 minutes. The plate was then buffed. The layer 4 was deposited from a bath containing 250 grams of chromic acid and 2 grams of sulphuric acid at 66 degrees Baume per litre at a temperature between 31 C. and 41‹ C. To deposit the layer 4 a current of about 3,500 amps. at 12 volts was passed for about 45 seconds after which electrolysis was suspended for about one minute. To deposit the layer 5 a current of about 3,000 amps. at 10 volts was passed for 10 minutes. After removal from the bath the plate was coated with a photographically sensitized layer 6 which was then exposed to light and developed by immersion in water to form a resist image which was then treated with a setting agent. The plate was then chemically etched to remove the chromium coatings from the parts of the plate not covered by the developed resist 6 which was finally completely removed. |
