GB1238552A - - Google Patents

Abstract

1,238,552. Imaging methods and apparatus. LITTON BUSINESS SYSTEMS Inc. April 9, 1969 [April 22, 1968], No. 18270/69. Heading G2H. An apparatus for producing a visible image on dielectric material comprises means for producing a high frequency alternating field in the megacycle range, and means for producing a light pattern corresponding to the image on a photo-conductive member, such that when the field is applied to the material breaks in field intensity are produced which correspond to the light pattern and cause a change in appearance by dielectric heating in those areas subject to the higher intensities of field. As shown, a light pattern corresponding to an original is produced on a transparent layer 19 above a transparent conductive layer 21 and an insulating photo-conductive layer 22. A thermographic sheet 15, preferably of polar dielectric comprises one or more sheets of paper 16 each having a heat-sensitive layer 17 which changes visibly when its temperature is sufficiently elevated to expose a coloured surface on the sheet(s) 16. A high frequency voltage source 24 is connected between a conductive plate 23 for a time determined by a timer 25. The areas of layer 17 corresponding to the under illuminated areas 27 of the original negative become heated to produce an image Fig. 2 (not shown). A positive image may be produced by providing illumination according to Fig. 3 (not shown) wherein the light intensity (62) is greater than (G1). In a modification Fig. 8, an insulating photoconductive layer 44 impregnated in or coated in silk, or formed as a coating on glass is in contact with electrodes 42, 43 while exposed to an original 48. A conductivity pattern is formed along the layer 44 corresponding to the original which controls the density of the electrical field applied by source 45. In dark areas the field density is insufficient to heat the thermographic sheet. Positive and negative images may be formed as described with reference to Figs. 13 and 10 (not shown).