| 摘要 |
1,196,204. Etching. PUREX CORP. Ltd. 29 April, 1968, No. 20308/68. Heading B6J. [Also in Division C3] A masking composition used in etching processes comprises a block copolymer of styrene and butadiene together with a minor proportion of a polymer of α-methylstyrene. The composition is applied by spraying, brushing, flow coating, dipping or silk-screening to metal substrates, e.g. aluminium, aluminium alloys, or other ferrous and non-ferrous alloys, and after forming a pattern in the mask by, e.g. scribing, the un-masked areas are etched with acid or alkali. Specified etchants are potassium hydroxide, sodium phosphate, soda-ash and, preferably, sodium hydroxide at temperatures above 100‹ F. The polystyrene block of the copolymer has a minimum molecular weight of 5000, and the polybutadiene block has a minimum molecular weight of 15,000, while the ratio of styrene to butadiene is preferably between 2: 3 and 1: 4. The copolymer is present in the masking composition in 5 to 25% amounts by weight, and the α-methyl styrene polymer, which preferably has a molecular weight between 5000 and 60,000, is present in at least 2 parts per 100 parts of block copolymer. The balance of the masking composition is made up by organic solvent, and may also include 0À25 to 10% by weight of a phenolic resin, e.g. nonylphenolformaldehyde resin, and 0.025 to 1% of a metal oxide. The mask may be removed in a plurality of successive etching operations, each operation removing a layer of the mask. |
