| 摘要 |
883,942. Photoetching materials. RADIO CORPORATION OF AMERICA. Feb. 24, 1958 [March 1, 1957], No. 5971/58. Drawings to Specification. Class 98(2). A sheet as of silver or copper having a .photosensitive surface portion, or else a sheet of photosensitive glass, is characterized by a coating of insulating material which may have a finely divided photoconductor dispersed therein on the photosensitive surface; and use thereof comprises charging the insulating coating, projecting a light image thereon to form a complementary electrostatic image, forming a powder image corresponding thereto, exposing with light to which such powder image is opaque to harden the photosensitive surface imagewise, removing the powder image and the insulating coating, and subsequently etching through the hardened image. Typographic, lithographic or gravure printing plates or printed circuits may result from such use. In an embodiment of the invention the metal surface of a copper-clad phenolic resin sheet is coated with a specified glue-albumin-bichromate solution, dried, overcoated with a silicone resin containing zinc oxide in toluene, the latter is evaporated and a corona discharge is applied in darkness, the metal being grounded; a light image from a 35 mm. transparency is then projected on to the charged surface to leave the charge only on the dark areas, and a mixture of magnetic particles with opaque powder is applied thereto; exposure is then made from a mercury vapour lamp, the powder mixture is removed with a magnetic brush and the silicone coating with toluene, after which unhardened areas of the bichromate layer are removed with warm water, the remaining areas baked and the metal etched. In a further embodiment a perforated template is placed in contact with the insulating coating and the electrostatic charge pattern formed directly through the holes of the template.
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