GB1288945A - - Google Patents

Abstract

1288945 Electro-photographic processes, &c. RANK XEROX Ltd 16 Dec 1969 [16 Dec 1968] 61202/69 Heading G2H In an electro-statographic process allowing selective production of positive or negative copy from an original without changing the toner charge polarity, the photo-sensitive element comprises two photo-conductive layers sensitive in different spectral regions. As shown in the form of a drum 11, the element comprises first and second photoconductive layers 4 and 6, Fig.1 (not shown) on a conductive substrate 2 with optional insulative layers 3, 5 & 7. The drum 11 is cycled through the following processes:- a) uniform charging using corona device 12 simultaneously with uniform illumination with light which passes through the outer layers to produce free charge in photoconductive layer 4, b) imagewise exposure using similar light simultaneously with reverse charging using projector 38 or 39 and corona device 16, c) optional uniform exposure to light active in layer 4 to reverse the charge image and d) uniform exposure to light active in the outer photo-conductive layer 6 to erase the latent image. Known development, image transfer and drum cleaning processes are described. To effect the first charging step, corona charger 12 has an electro-luminescent panel 13 the inner face of which is transparent, electro-conductive and earthed. Reverse charging device 16 has an earthed electro-conductive glass plate 17 allowing projection therethrough of an image from either microfilm 42 moving at constant speed in synchronism with drum 11 or from a document placed on belt conveyer 46 moving at the same speed as the surface of drum 11. If a positive charge is applied to drum 11 initially then on development using a negatively charged toner a positive copy is produced from negative microfilm without application of step c) and a negative copy obtained when step c) is applied. In a second embodiment using a similar drum Fig.4 (not shown) an A.C. potential is applied to the second corona charger and the microfilm is arrested for projection of its image on to a Fresnel lens (82) from where it is projected on to the rotating drum (51) by scanning lens (84). For document projection, Fresnel lens (82) is removed and replaced by the document which is scanned by lamp (85) and lens (84).