GB954052A - Electrostatographic methods and apparatus therefor - Google Patents

Abstract

954,052. Developing electrostatic latent images. RANK-XEROX Ltd. May 3, 1960 [May 7, 1959], No.15529/60. Heading G2H. An electrostatographic method comprises the step of causing dry finely divided toner particles which are sufficiently conductive to be chargeable by induction and which are borne upon a similarly conductive donar member to come into and out of contact with an electrostatographic surface bearing a latent electrostatic image so that particles are transferred towards the electrostatographic surface in a configuration governed by the electrostatic field existing between the surface and toner particles. As applied to a xerographic machine, a xerographic plate 11, Fig. 1, has a photoconductive insulating layer 12, e.g., of selenium, anthracene, sulphur, phosphor, or zinc oxide suspended in a binder such as acrylic resin. The machine has a sensitizing station 15, exposure station 16, development station 17, a transfer station 18 where a developed image is transferred e.g. to a paper web, and a cleaning station 20. An endless belt 9 of conductive material passes over rollers 7 and 8; roller 7 of conductive material is connected to a potentiometer 5 across battery 4. Powder 3 is supplied to the belt 9 by a cloud generator 10. The powder and belt 9 are relatively more conductive than the layer 12, e.g., the resisitivity of the layer 12 is at least 10<SP>12</SP> ohms-centimetre, whereas the belt may be 10<SP>-4</SP> ohms-centimetre. The particles of powder are charged,e.g., by feeding at turbulent rates through a fine tube or tubes, thus causing the particles to adhere to the surface of belt 9. A low potential applied to belt 9 through potentiometer 5 results in the induction of changes in the powder which are opposite in polarity to the changes making up the image on the layer 12, thereby causing attraction of particles to the charged image areas. Uncharged area of the layer 12 may be developed by applying to the powder a bias substantially equal to the level of change on the surface being developed and of the same polarity of the change on such surface. In this case, a driven brush 33, Fig. 2, having bristles 35 is loaded with developer particles from a black 42 by a loader 44 and a bias is applied to brush 33. Powder 26 deposits in the areas of no charge, while no powder deposits in areas of charge 25. The bristles 35 may be metal wires, natural and synthetic furs rendered conductive or carbon wool. In another modification, a photo conductive insulating layer 23 Fig, 3, on a conductive backing member 22 is earthed by lead 27 and contacts an insulating web 50, e.g., of pre-dried paper or insulating plastic material. Developer particles 57 carried by a web 53 are earthed through roller 54, thus causing the particles to be deposited on the web 50 as an image 51 in a configuration following the charged image areas on the layer 23. The particles 57 are fused by heat or vapour, thus bonding image 51 permanently to the surface of web. The web 50 may be wound on a spool, not shown, or cut into lengths. Developer powder which may be used in each of the embodiments include graphite, lampblack, and charcoal of a size less than zomicrous. Specification 696,515 is referred to.