Electrostatic image transfer processes and apparatus therefor

Claim 1

A DEVICE FOR PRODUCING AN ELECTROSTATIC IMAGE ON A DIELECTRIC MEDIUM, COMPRISING: A ROTATING DRUM INCLUDING AN ELECTRICALLY CONDUCTIVE CYLINDER HAVING A LAYER OF PHOTOCONDUCTIVE MATERIAL COVERING A PORTION OF ITS OUTER SURFACE; MEANS FOR UNIFORMLY DISTRIBUTING A PREDETERMINED LEVEL OF CHARGE OF A GIVEN POLARITY OVER THE SURFACE OF SAID PHOTOCONDUCTIVE LAYER; MEANS FOR PROJECTING AN OPTICAL IMAGE ON THE CHARGED SURFACE OF SAID PHOTOCONDUCTIVE LAYER, A CORRESPONDING ELECTROSTATIC IMAGE THEREBY BEING FORMED ON SAID SURFACE; FIRST AND SECOND GUIDE ROLLER HAVING ELECTRICALLY CONDUCTIVE OUTER SURFACES ROTATABLY POSITIONED ADJACENT SAID DRUM, SAID ROLLERS HAVING THEIR RESPECTIVE AXES OF ROTATION PARALLEL TO THE AXIS OF SAID DRUM; A WEB OF DIELECTRIC MATERIAL PRESSED AGAINST A PORTION OF THE SURFACE OF SAID DRUM BY SAID GUIDE ROLLERS, SAID WEB MOVING INTO VIRTUAL CONTACT WITH SAID DRUM SURFACES AS IT PASSES OVER SAID FIRST GUIDE ROLLER AND BEING SEPARATED FROM SAID DRUM SURFACES AS IT PASSES OVER SAID SECOND GUIDE ROLLER, THERE BEING A MINUTE BUT FINITE GAP BETWEEN SAID WEB AND SAID DRUM SURFACE AT POINTS OF VIRTUAL CONTACT THEREBETWEEN; MEANS FOR CHARGING SAID WEB TO A PREDETERMINED POTENTIAL OF A POLARITY OPPOSITE TO SAID GIVEN POLARITY PRIOR TO INITIAL VIRTUAL CONTACT BETWEEN SAID WEB AND SAID DRUM; A VOLTAGE SUPPLY ELECTRICALLY CONNECTED TO THE OUTER SURFACE OF SAID FIRST GUIDE ROLLER, THE POTENTIAL APPLIED BY SAID VOLTAGE SUPPLY TO SAID FIRST GUIDE ROLLER BEING OF THE SAME POLARITY AS SAID GIVEN POLARITY AND HAVING A MAGNITUDE SUFFICIENT TO MAINTAIN THE TOTAL VOLTAGE ACROSS THE GAP BETWEEN SAID WEB AND SAID DRUM SURFACE, AS THE LATTER ARE MOVING INTO VIRTUAL CONTACT, BELOW THE MINUMUM BREAKDOWN VALUE, THE TRANSFER OF CHARGE BETWEEN SAID WEB AND SAID DRUM SURFACE THEREBY BEING INHIBITED; AND ELECTRICAL MEANS FOR MAINTAINING SAID CONDUCTIVE CYLINDER OF SAID DRUM AND THE OUTER SURFACE OF SAID SECOND GUIDE ROLLER AT SUBSTANTIALLY THE SAME POTENTIAL, WHEREBY THE ELECTROSTATIC IMAGE ON SAID PHOTOCONDUCTIVE LAYER IS TRANSFERRED TO SAID WEB.