Electrophotographic process and apparatus

A process for forming an electrophotographic image on a photosensitive plate having a conductive base, a photoconductive layer overlying said base and exhibiting p-type or n-type semiconductivity and an insulative layer overlying said photoconductive layer, said photosensitive plate being characterized in having carrier charge of a polarity corresponding to the conductivity type of said photoconductive layer injectable from said conductive base into said photoconductive layer and bound in the region of the interface between said insulative and photoconductive layers, said process comprising the steps of:

• a. applying a first charge of a polarity opposite to the conductivity type of said photoconductive layer substantially uniformly onto said insulative layer to inject and bind carrier charge in the region of the interface between said insulative and photoconductive layers,
• b. then exposing said photoconductive layer to a pattern of image light while applying a corona discharge of a polarity opposite to that of said first charge onto said insulative layer and then,
• c. exposing said photoconductive layer to activating light to discharge bound carrier charge remaining in the region of said interface and form a high contrast electrostatic image,
• d. visualizing said electrostatic image by applying a developer onto said insulative layer,
• e. transferring said visualized image onto a transfer sheet and fixing the visualized image, and
• f. cleaning the surface of said insulative layer to remove residual developer and enable the repetitive use of said photosensitive plate.

A process for forming an electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of an original to be copied comprising the steps of:

• a. applying a first predetermined charge onto a photosensitive plate having a conductive base, a photoconductive layer overlying said base and an insulative layer overlying said photoconductive layer;
• b. then exposing said photoconductive layer to the light and dark image patterns of said original while applying a second charge onto said insulative layer, said second charge being applied in an amount relative to said first predetermined charge so that in areas exposed to the light image patterns of said original said first charge is neutralized and replaced with a charge of a polarity opposite to that of the first charge, and that in areas exposed to the dark image patterns said first charge is not completely neutralized;
• and then
• c. exposing said photoconductive layer to activating light to form a high contrast electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of said original to be copied.

A process for forming an electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of an original to be copied comprising the steps of:

• a. applying a first predetermined charge onto a photosensitive plate having a conductive base, a photoconductive layer overlying said base and exhibiting p-type or n-type semiconductivity, and an insulative layer overlying said photoconductive layer, said photosensitive plate being characterized in having carrier charge of a polarity corresponding to the conductivity type of said photoconductive layer injectable from said conductive base into said photoconductive layer and bound in the region of the interface between said insulative and photoconductive layers, said first predetermined charge being of a polarity opposite to the conductivity type of said photoconductive layer to inject and bind carrier charge in the region of the interface between said insulative and photoconductive layers;
• b. then exposing said photoconductive layer to the light and dark image patterns of said original while applying a corona discharge onto said insulative layer, said corona discharge being applied in an amount relative to said first predetermined charge so that in areas exposed to the light image patterns of said original said first charge is neutralized and replaced with a charge of a polarity opposite to that of the first charge, and that in areas exposed to the dark image patterns said first charge is not completely neutralized;
• and then
• c. exposing said photoconductive layer to activating light to discharge bound carrier charge remaining in the region of said interface and form a high contrast electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of said original to be copied.

An apparatus for forming an electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of an original to be copied comprising:

• a. a photosensitive plate having a conductive base, a photoconductive layer overlying said base, and an insulative layer overlying said photoconductive layer;
• b. charging means for applying a first predetermined charge uniformly onto said insulative layer;
• c. first means for exposing said photoconductive layer to light and dark patterns of said original whle applying a second charge onto said insulative layer, said first means including means for applying said second charge in an amount relative to said first predetermined charge so that in areas exposed to the light image patterns said first charge is neutralized and replaced with a charge opposite to that of said first charge, and that in areas exposed to the dark image pattern said first charge is not completely neutralized;
• and
• d. second means for thereafter exposing the photoconductive layer to activating light to form a high contrast electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of said original image to be copied.

An apparatus for forming an electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of an original to be copied comprising:

• a. a photosensitive plate having a conductive base, a photoconductive layer overlying said base and exhibiting p-type or n-type semiconductivity, and an insulative layer overlying said photoconductive layer, said photosensitive plate being characterized in having carrier charge of a polarity corresponding to the conductivity type of said photoconductive layer injectable from said conductive base into said photoconductive layer and bound in the region of the interface between said insulative and photoconductive layers;
• b. charging means for applying a first predetermined charge substantially uniformly onto said insulative layer, said first predetermined charge being of a polarity opposite to conductivity type of said photoconductive layer to inject and bind carrier charge in the region of the interface between said insulative and photoconductive layers;
• c. first means for exposing said photoconductive layer to the light and dark image patterns of said original while applying a corona discharge onto said insulative layer, said first means including means for applying said corona discharge in an amount relative to said first predetermined charge so that in areas exposed to the light image patterns of said original said first charge is neutralized and replaced with a charge of a polarity opposite to that of the first charge, and that in areas exposed to the dark image patterns said first charge is not completely neutralized;
• and
• d. second means for exposing said photoconductive layer to activating light to discharge bound carrier charge remaining in the region of said interface and form a high contrast electrostatic image having areas of opposite polarity corresponding to the light and dark image patterns of said original to be copied.

An electrophotographic copying device which comprises:

• charging means for applying a primary charge on the surface of a photosensitive plate, which plate comprises a base, a photoconductive layer and a translucent insulating layer overlaid thereon;
• means for simultaneously exposing an original image and for applying a corona discharge onto the surface of said charged insulating layer;
• means for forming a high contrast static image of the original image on the surface of said insulating layer by uniformly irradiating the whole surface of said insulating layer, thereby activating the photoconductive layer;
• developing means for visualizing said static latent image;
• means for transferring said visualized image onto copying material;
• and
• cleaning means for removing residual developer from the surface of said insulating layer remaining after the transfer of the image, whereby the photosensitive plate is prepared for repeated use.

An apparatus for forming an electrostatic image comprising:

• a. a photosensitive plate having a conductive base, a photoconductive layer overlying said base and exhibiting p-type or n-type semi-conductivity and an insulative layer overlying said photoconductive layer, said photosensitive plate being characterized in having carrier charge of a polarity corresponding to the conductivity type of said photoconductive layer injectable from said conductive base into said photoconductive layer and bound in the region of the interface between said insulative and photoconductive layers;
• b. charging means for applying a first charge of a polarity opposite to the conductivity type of said photoconductive layer substantially uniformly onto said insulative layer to inject and bind carrier charge in the region of the interface between said insulative and photoconductive layers;
• c. means for exposing said photoconductive layer to a pattern of image light while applying a corona discharge of a polarity opposite to that of said first charge onto said insulative layer;
• and
• d. means for exposing said photoconductive layer with activating light to discharge bound carrier charge remaining in the region of said interface and form a high contrast electrostatic image.

An apparatus for forming an electrophotographic image comprising:

• a. a photosensitive plate having a conductive base, a photoconductive layer overlying said base and exhibiting p-type or n-type semiconductivity and an insulative layer overlying said photoconductive layer, said photosensitive plate being characterized in having carrier charge of a polarity corresponding to the conductivity type of said photoconductive layer injectable from said conductive base into said photoconductive layer and bound in the region of the interface between said insulative and photoconductive layers;
• b. charging means for applying a first charge of a polarity opposite to the conductivity type of said photoconductive layer substantially uniformly onto said insulative layer to inject and bind carrier charge in the region of the interface between said insulative and photoconductive layers;
• c. means for exposing said photoconductive layer to a pattern of image light while applying a corona discharge of a polarity opposite to that of said first charge onto said insulative layer;
• d. means for exposing said photoconductive layer with activating light to discharge bound carrier charge remaining in the region of said interface and form a high contrast electrostatic image;
• e. developing means for visualizing said electrostatic image;
• f. means for transferring said visualized image onto a copy sheet;
• and
• g. cleaning means for removing from said photosensitive plate residual developer remaining after the transfer of the visualized image whereby said photosensitive plate is prepared for repeated use.