Patent GB-1165405-A (GB)
Title: Electrophotography
IPC: G03G21/00
Filed: 1966-07-12
Abstract: 1,165,405. Electro-photographic processes. CANON CAMERA CO. Inc. July 12, 1966 [July 12, 1965; Oct. 28, 1965; Dec.1, 1965; Feb. 23, 1966], No.31329/66. Heading G2H. An electro-photographic member consists of a conductive layer, a photo-conductive layer, and an insulating layer. Either or both the conductive layer and the insulating layer are translu-. cent. The member is such that upon the application to the insulating layer of a positive or negative charge, according to whether the photoconductive layer is N-type or P-type respectively, charges of opposite polarity are even in the absence of activating radiation injected into the photoconductive layer from the conductive layer and bound in the region of the interface between the photo-conductive layer and the insulating layer, and is such that the insulating layer can support said charges without breakdown. Such a member is claimed in Specification 1,165,407. In use the member is charged, then simultaneously imagewise exposed and reverse charged, and then (preferably) uniformly exposed to increase contrast. Dependent upon the construction of the apparatus and of the member, the member may be exposed either through the conductive layer or through the insulating layer. In the apparatus shown in Fig. 11 the electro-photographic member is in the form of a cylinder. Primary charging takes place by means of corona charger 4t. The simultaneous secondary reverse charging and imagewise exposure takes place through the open shield of coratron 8t. Following this the material is uniformly exposed by tungsten illumination 23t. The elctrostatic image is then developed by charged toner particles applied by magnet brush 15t. At the next station the developed image is transferred by coratron 10t to a charge receiving base 11t. This base is then passed over an infrared heated roller 18t to produce the final copy. The electro-photographic cylinder is subjected to an A. C. discharge 20t and remaining developer particles removed by brush 22t. The cycle is thus completed. The alternative apparatus of Fig. 12 and of Fig. 13 (not shown) makes use of an electro-photographic member having an opaque insulating layer. The exposure takes place here through the conductive backing. In use the corona charger 23 is passed across the electro-photographic member B to apply the primary charge from section 23 ab, In the next stage imagewise exposure takes place through the travelling optical system 18b which is scanned across the under surface of the electro-photographic member. Facing magnets 24b and 25b in the optical system and in the corona charger from means by which the corona charger 23 may be synchronously scanned with the optical system during secondary charging from section 23bb., The final stage of overall illumination of the plate B is acheived by means of an internal lamp 21b (not shown). Normal processes of development may then be used to produce a developed image on the upper surface of the electro-photographic member B. The process may of course be used in ordinary daylight. In these processes a high primary charge and high secondary charge give enhanced contrast, but it is possible to degrade the contrast by having an excessive secondary charge.