Patent GB-1065771-A (GB)
Title: Recording carriers and recording apparatus therefor
IPC: G03G5/08
Filed: 1964-03-16
Abstract: 1,065,771. Semi-conductor devices. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. March 16, 1964 [March 16, 1963; April 27, 1963; May 2, 1963 (2); June 17, 1963; June 21, 1963; Sept. 21, 1963 (2); Oct. 25, 1963; Oct. 28, 1963], No. 11021/64. Heading H1K. Means for electrostatically recording a light pattern or electric signals comprises an insulating carrier coated with a mixture containing semi-conductor and insulating material. The semi-conductor is not activated in such a way as to make it luminescent. According to the invention, if an insulating support 6, Fig. 2, carrying such a mixture 5 is placed between two oppositely charged electrodes 7, 8, the lower surface of the insulator 6 acquires a charge opposite to that of the adjacent electrode 8, in accordance with normal electrostatic principles, but the upper surface of the mixture 5, owing to the passage of electric charges into the semi-conductor material, acquires a charge similar to that of the electrode 7 and thus both faces of the combination acquire similar charges. Suitable semi-conductor materials are Ge, Si, Se, CuO 2 , ZnO, PbO, NiO, CdS, ZnSe and anthracene, and insulating materials may be glass, porcelain, silicone resin, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyvinyl butyral and wax. The magnitude and permanence of the charge may be influenced by the inclusion in the mixture of a fluorescent phosphor such as zinc or cadmium sulphide, a ferro-electric substance such as BaTiO 3  or a metal such as copper which develops a photo-electric effect through contact with the semi-conductor. Exposure to light appreciably affects the charge acquired by these latter mixtures and Fig. 16 shows the charge, plotted vertically, in relation to time when subjected to a steady potential difference of up to 800 volts. Curve 55 shows the positive charge resulting from the presence of the semi-conductor material in the mixture. Fluorescent phosphor material results in an opposite charge as shown in curve 56. Both of these curves are obtained under dark conditions and, with both substances in the mixture, give a resultant curve 57. The semiconductor material is uninfluenced by light but the phosphor material is particularly sensitive and its charge moves to curve 58, so that under light conditions the resultant curve becomes 59. If now a transparent upper electrode is used and a light pattern is applied to the mixture while subjected to a potential difference for a time p, for example, the charge in the dark areas is positive, as indicated by curve 55, while that in the light areas is negative as shown by curve 59. As applied to electrophotography, a sheet of paper, which constitutes the insulating support, carries a mixture incorporating two such substances and, when exposed, carries a latent image in which light and dark areas have opposite charges. This may be " developed " by a charged resin powder which is subsequently fixed by heat. The presence of opposite charges results in a very sharp image with clear boundaries and enables either a positive or negative image to be obtained according to the nature of the charge given to the powder. A mixture of semi-conductor and insulating material carried on a film support and thus exhibiting the uniform charge effect of Fig. 2, may be used for recording electric signals, such as video or sound, by using roller-type electrodes. Playback is effected by an electrostatic pick-up.