Patent GB-1221333-A (GB)
Title: Improved electrophotographic process
IPC: G03G13/22
Filed: 1968-02-05
Abstract: 1,221,333. Electro-photographic processes. CANON CAMERA CO. Inc. Feb.5, 1968 [Feb.4, 1967; Aug.2, 1967(3); Nov.4, 1967, No.5682/68. Heading G2H. An electro-photographic process comprises the steps of exposing a layer of photo-conductive material having a dark resistivity of less than 10<SP>15</SP> ohms. cm to a light image, thus forming a latent conductivity image, charging the image, and developing the image with charged particles. The layer of photo-conductive material is carried on an insulating layer having a resistivity of at least 10<SP>8</SP> ohms. cm or, on a conductive layer covered by a barrier insulating layer. In one example, using an n-type photo-conductive layer 1 Fig. 1(a), e.g. ZnO in a binder on an insulating support 2 the layer is exposed to light. Holes or electrons are formed at the surface at the illuminated portion L, such that negative charges in this portion pass to the positive electrode R, Fig. 3, leaving a positive charge in the portion L while the support 2 is negatively charged. In another example, using a thin insulating layer 6 Fig.3(a), a photo-conductive layer 7 of ZnO in a binder, and a conductive support 8. Upon exposure to a pattern of light carriers P are formed near the surface of layer 7 Fig.3(b). When the layers are passed through a negative electrode 11, Fig.4, and a positive electrode 11<SP>1</SP>, the layer 7 becomes positively charged, while the layer 6 becomes negatively charged. The layer 6 preferably has a resistivity greater than 10<SP>10</SP> ohm. cm and a light transmissivity of at least 50%. Many examples of the compositions of suitable photo-conductive layers using ZnO are given (see Division H1). These compositions are formed into emulsions using an ultrasonic disperser or a ball mill and coated on art paper to a thickness of 6 to 8Á. and then dried. Alternatively, the dispersions are coated on tracing paper or an aluminium plate. Many examples are also given of organic resin binders which may be used for the photo-conductive and barrier layers together examples of sensitizers. The charging of the exposed layer is effected by rollers (R 1 R<SP>1</SP>) Fig.2 (not shown) connected to a D.C. source of about 800 volts. This produces a potential difference of 100 volts on the unexposed portions and about 400 volts on the exposed portions. The rollers (R 1 R<SP>1</SP>) may have 4 cores of iron, aluminium, copper, and semi-conductive metal covers (3 1 3<SP>1</SP>). An insulating liquid, such as (Registered Trade Mark) "Shell-Sol" may be present between the electrodes and photo-conductive layer during charging. The charging electrodes may also be formed by a magnetic brush composed of magnetic powder on a magnet coated with semi-conductive material Fig.7 (not shown). These electrodes can also be used as developing electrodes when using a liquid developer. In a further embodiment, Fig.8, (not shown) roller (R11) has a network mesh (3c) wound thereon with a coating (4c) of charge controlling material. The mesh may be of iron, steel, aluminium silk screen, stainless steel screen, fibres rendered conductive by graft carbon. The charge controlling material may be polyester, polyethylene, cellulose acetate, fluorine containing resin, ethyl cellulose, or (Registered Trade Mark) "Sellotape". An A.C. voltage source (v 2 ) Fig. 11 (not shown) may be used in place of a D.C. source.