Printing plates prepd. by etching through photosensitive coating - using an intermediate coating to protect the etched borders

摘要

In a photoengraving process, a base (1) is first coated with a material (2) which can be secured by a leaching agent which does not attach the base (1). A photosensitive coating (3) is then applied and selectively exposed to produce a required image. Non exposed zones of the photosensitive coating are dissolved away, the exposed parts of the first coating are then leached away, and the correspondingly exposed parts of the base are etched away to the appropriate depth, after which the residual coatings are removed. Used esp. for selectively etching hard or expensive materials, e.g. silicon, tantalum or Pt/Au alloys, either as solid blocks or as supported coating (4) typically 1500-3000 angstroms thick on a base of e.g. glass. Produces a sharper image than processes where the photosensitive layer is in direct contact with the base, because a more etch resistant coating can be maintained adjacent to the rims of the etched base.