| abstract |
This invention relates to a method of forming a selectively perforate membrane suitable for high resolution screen printing by homogeneously irradiating a sheet of synthetic resin, e.g., a polycarbonate resin, with heavy fission fragments whereupon the sheet is selectively irradiated in an oxygen atmosphere with electromagnetic radiation less than 4,000A (or a high intensity electron beam) to enhance the etch rate of those damage tracks lying within the electromagnetically irradiated area of the sheet. Apertures less than 200A in diameter then are etched through the sheet in areas of dual irradiation whereupon etching is abruptly terminated and the sheet is annealed at a temperature above 80*C to obliterate fission track damage. The selectively apertured sheet then is etched again to enlarge the apertures to a diameter between 1,000A and 100,000A. |