Kserograafia

Kserograafia, derived from the Greek words "xeros" (dry) and "graphein" (to write), is a dry photocopying process. It was invented by Chester Carlson in 1938 and later developed into the first commercial photocopier by the Haloid Company (now Xerox Corporation) in 1959. The core principle behind kserograafia is electrophotography, which utilizes the properties of static electricity and light.

The process begins with a specially coated drum, often made of selenium, which becomes photoconductive when exposed to light. First, the drum is electrostatically charged. Then, a light image of the original document is projected onto the drum. Areas of the drum that are exposed to light become conductive and lose their charge, while the areas corresponding to the dark parts of the original document retain their charge.

Next, a fine, dry powder called toner, which is oppositely charged to the residual charge on the drum, is cascaded over the drum's surface. The toner particles adhere only to the charged areas of the drum, forming a visible image. This toner image is then transferred to a sheet of paper, which has been given a stronger electrostatic charge. Finally, the paper with the toner image is passed through a heated fuser unit, which melts and fuses the toner particles permanently onto the paper, creating a copy of the original document. Kserograafia revolutionized document reproduction due to its speed, simplicity, and the dry nature of the toner, eliminating the need for liquid chemicals.