Electrophotographic image forming method

An electrophotographic image forming method which comprises the steps of:

• virtually face-to-face contacting an electrostatic charge receiving dielectric member with a photosensitive member and applying a direct current voltage of a first polarity therebetween under dark conditions and of a valve sufficient to cause air breakdown discharges between the members under such dark conditions whereby to charge the surface of the dielectric member with charges of first polarity;
• short circuiting the photosensitive member and the dielectric member and effecting the illumination of the photosensitive member until the electric field within the photosensitive member becomes substantially zero while said photosensitive member and dielectric member are held in virtual contact;
• applying a direct current voltage of a second polarity opposite said first polarity between the photosensitive member and the dielectric member simultaneously with the exposure of said photosensitive member to a light image original while said virtual contact is maintained thereby forming on said dielectric member an electrostatic latent image;
• developing the latent image with toner;
• transferring the developed image onto a copy member;
• cleaning residual toner remaining on the dielectric member;
• and
• applying direct current voltages alternately of first and second polarities between the photosensitive member and the dielectric members with said members being in virtual contact simultaneously with the illumination of the photosensitive member thereby erasing residual charges of both first and second polarities remaining on the dielectric member.

An electrophotographic image forming method which comprises the steps of:

• virtually face-to-face contacting an electrostatic charge receiving dielectric member with a photosensitive member wherein said dielectric member includes a dielectric layer formed of an electrically conductive member and said photosensitive member includes a photoconductive layer on an electrode layer, and applying therebetween under dark conditions a direct current voltage Vap1 of a first polarity and of a value sufficient to cause air breakdown discharges in the air gap therebetween whereby to charge the surface of the dielectric member with charges of first polarity to a surface potential V.sub.T1 satisfying the equation:
• ##EQU11## wherein .chi.p, .chi.d and .chi.a are the air gap equivalent thicknesses in microns of said photoconductive layer, dielectric layer and air gap respectively;
• Vb (.chi.a) being air breakdown discharge initiating voltage in accordance with Paschen Law and in the relationship of 312+6.2 .chi.a with .chi.a;
• and the voltage Vap1 being such that the product of .chi.d/(.chi.p+.chi.d) and Vap1 is greater than the product of .chi.d/(.chi.p+.chi.d) and {(.chi.p+.chi.d+.chi.a)/.chi.a}Vb (.chi.a);
• short circuiting the photosensitive and dielectric members and effecting the full surface illumination of the photosensitive member until the electric field within the photosensitive member becomes substantially zero while said members are held in virtual contact;
• applying a direct current voltage Vap2 of second polarity between the photosensitive member and the dielectric member simultaneously with the exposure of the photosensitive member to the light image of an original whereby the surface potential VT2 of the dielectric member at portions corresponding to non-exposed areas satisfies the equation:
• ##EQU12## wherein the maximum value of the voltage Vap2 applied without causing charges of a second polarity to be transferred onto the non-exposed area of the dielectric member is when VT2 in said equation becomes zero;
• and
• applying a direct current voltage Vr of the first polarity simultaneously with the illumination of the photosensitive member wherein said voltage satisfies the equation:
• ##EQU13##

An electrophotographic image forming method in which an electrostatic charge receiving dielectric member is held in virtual contact with a photosensitive member, the method comprising in sequence;

• the first step of applying a direct current voltage Vap1 of a first polarity between the photosensitive member and the dielectric member under dark conditions, said photosensitive member including a photoconductive layer on a light transparent electrically conductive electrode member and said dielectric member including a dielectric layer on an electrically conductive member, said voltage being of sufficiently high value to cause air breakdown discharges in the air gap between the photosensitive and dielectric members whereby to charge the surface of the dielectric member with charges of first polarity to a surface potential VT1 satisfying the equation:
• ##EQU14## wherein .chi.p, .chi.d and .chi.a are the air gap equivalent thicknesses in microns of said photoconductive layer, dielectric layer and air gap respectively;
• Vb (.chi.a) is the air breakdown discharge initiating voltage in accordance with Paschen Law and in the relationships of 312+6.2 .chi.a with .chi.a;
• and Vap1 being such that the product of .chi.d/(.chi.p+.chi.d) and Vap1 is greater than the product of .chi.d/(.chi.p+.chi.d) and {(.chi.p+.chi.d+.chi.a)/.chi.a}Vb (.chi.a);
• the second step of short circuiting the photosensitive and dielectric members and effecting the full surface illumination of the photosensitive member until the electric field within the photosensitive member becomes substantially zero while both of said members are held in virtual contact;
• the third step of applying a direct current voltage Vap2 of a second polarity opposite to said first polarity between the photosensitive member and the dielectric member simultaneously with the exposure of the photosensitive member to a light image of an original whereby the surface potential VT2 of the dielectric member of portions corresponding to non-exposed areas satisfies the equation:
• ##EQU15## wherein the maximum value of the applied voltage Vap2 without causing charges of second polarity to be transferred onto the non-exposed areas of the dielectric member is when VT2 in the equation becomes zero;
• the fourth step of separating the dielectric member from the photosensitive member and developing the latent image formed on the dielectric member;
• the fifth step of transferring the developed image onto a copy paper;
• the sixth step of cleaning residual toner on the dielectric member;
• and
• the seventh step of alternately applying direct current voltages of first and second polarities between the photosensitive and dielectric members while in virtual contact with each other and while effecting the illumination of the photosensitive member simultaneously therewith, the applied voltage satisfying the equation:
• ##EQU16## wherein the variable of the equation is of opposite sign for voltages of first and second polarities.

An electrophotographic copying method employing a photosensitive member including a photoconductor layer backed by an electrically conductive electrode and a dielectric layer backed by an electrically conductive electrode, said method comprising:

• positioning said members with said layers in face-to-face virtual contact;
• while said layers are in virtual contact applying between said electrodes with said photoconductor layer unilluminated a voltage of a first polarity and of a value sufficient to cause gaseous discharges between said layers to change said dielectric layer and thereafter removing said voltage and fully illuminating said photoconductive layer until the electric field therein is substantially zero and then simultaneously exposing said photoconductor layer to a light image and applying between the electrodes a voltage of a second polarity opposite to said first polarity and of a value sufficient to cause gaseous discharges between the layers corresponding to the light exposed areas of the photoconductor layer whereby to produce an electrostatic latent image on said dielectric layer;
• separating said members and at least partially removing said latent image from said dielectric layer;
• and
• repositioning said members with said layers in virtual contact and simultaneously illuminating said photoconductor layer and applying between said electrodes a direct current voltage of said first polarity whereby to erase residual charges on said dielectric layer.