A short story of the Selenium Photo-sensitive Drum.
2014-12-15 by howard.chester@...
This is to reference to the discussion about LASER Printer build
A short story of the Selenium Photo-sensitive Drum.
In the seventies, small Company offices saw the birth of the Photocopier.
These used a Selenium coated drum, charged up to about 3,000V(3Kv) by a
Corona wire near the drum. The rotating drum was exposed to a thin line
of light produced by a set of scanning mirrors and constant focus lenses.
The areas exposed to light areas in the image, discharges the 3Kv charge
on the charged drum. This is called the Latent Image. The drum is immersed
In a liquid mixture of developer and toner, whereby the toner is attracted to
Charged (un-exposed) areas on the drum. The drum now passes a 1,000 (1Kv) transfer corona wire behind the paper, transferring the latent image to the surface of the paper. The final stage is to evaporate the clear developer and fuse theToner, in the fusing heaters.
A major improvement was to add Arsenic to the Selenium Drum, improving
theDrum sensitive to blue colours (this is the reason that forms and notes
were required to be filled-in and signed with black ink as a Blue signature "dissapears"!).
The next major improvement was the "Dry Copier", eliminating the
Stinky liquid developer. This of course led on to the modern LASER copier, this
still uses the Selenium / Arsenic drum but digital image detection, processing
and LASER drum scanning is used to produce the latent image.
This point also highlights the Drums lack of sensitivity to Blue / UV LASERS
A few tips when handling the drum
1) Selenium is EXTREMELY TOXIC!!!. Handle with gloves and mask.
Selenium in a heavy Metal and as such accumulates in the body, similar
to Mercury. Effects may only become apparent Years later.
2) The drum surface is damaged by the sweat and oil from fingerprints,
Use gloves.
3) In my years as a Photo-Copier Tech, small scratches on the drum surface
were removed with a "steel-wool" type cotton based copper cleaner. The
Drum is lightly polished in an up and down motion from top to bottom.
Rinse with IPA(Iso-Propal Alcohol).
(DO NOT USE STEEL WOOL! this is for descriptive purpose only). This
Process could only used 3 times before replacing the drum.
I hope these notes prove useful and informative to all,
Chester