Electrophotographic image forming

DETAILED DESCRIPTION Generally speaking, in accordance with the invention, photoconductive image forming is provided by selectively transferring toner corresponding to an image from a conductive support to a transparent image forming substrate and transferring the adhered toner to a transfer medium.
The toner image is formed by exposing the toner to light from the opposite surface of the image forming substrate to lower the resistivity of exposed toner.
A bias voltage is applied between the image forming substrate and the electroconductive support.
Unexposed toner is not charged because its resistivity is too high and does not adhere to the substrate.
The exposed toner image which adheres to the substrate is transferred to a transfer medium.
In an alternative embodiment, a thin layer of charged toner is applied to an electroconductive substrate.
The layer of toner is exposed with a "negative" image which becomes oppositely charged and is removed to an intermediate transfer surface.
The unexposed toner remaining on the substrate is transferred to a transfer medium in the form of the desired image.
The image forming apparatuses in accordance with the invention include a two component magnetic brush for charging toner and contacting it to a transparent image forming substrate or electroconductive substrate.
An image writing exposure device is provided within the substrate to expose and thereby selectively reduce the resistivity of the exposed toner.
Exposed toner can then be oppositely charged and will adhere to the substrate in the form of an image which is transferred to a recording medium by an intermediate transfer device.
Improved toners suitable for use in image forming in accordance with the invention are azo-type metal dyes which have no absorption over the visible wavelength and can be sensitized to different exposure wavelengths.
In this manner, different color toners, sensitized to different wavelengths can be used to form multicolor images.
The toners can also be sensitized to the near infrared region so that inexpensive near infrared lasers can be utilized as the writing device