Chester Carlson and Xerography

The xerographic process, which was invented by Chester Carlson in 1938 and developed and commercialized by the Xerox Corporation, is widely used to produce high-quality text and graphic images on paper.

Carlson originally called the process electrophotography. It’s based on two natural phenomena: that materials of opposite electrical charges attract and that some materials become better conductors of electricity when exposed to light. Carlson invented a six-step process to transfer an image from one surface to another using these phenomena.

First, a photoconductive surface is given a positive electrical charge. The photoconductive surface is then exposed to the image of a document. Because the illuminated sections (the non-image areas) become more conductive, the charge dissipates in the exposed areas. Negatively charged powder spread over the surface adheres through electrostatic attraction to the positively charged image areas. A piece of paper is placed over the powder image and then given a positive charge. The negatively charged powder is attracted to the paper as it is separated from the photoconductor. Finally, heat fuses the powder image to the paper, producing a copy of the original image.

Six Step Process:

  1. Charge

Inside every copier and laser printer is a light-sensitive surface called a photoreceptor. It consists of a thin layer of photoconductive material that is applied to a flexible belt or drum. The photoreceptor is insulating in the dark, but becomes conducting when it is exposed to light. It is charged in the dark by applying a high DC voltage to adjacent wires, which produces an intense electric field near the wires that causes the air molecules to ionize. Ions of the same polarity as the voltage on the wires deposit on the photoreceptor’s surface, creating an electric field across it.

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