by Dr. John Wyhof :Technical Director of the Imaging Supplies Division of Static Control
An OPC will degrade from: frictional wear, chemical degradation, light fatigue and electrical fatigue.
Background, wear lines and light print will indicate the end of photoreceptor life.
The CTL surface naturally wears as it is in contact with the developing toner, the paper at transfer, the wiper blade during cleaning and the charge roller during charging. It is also subject to physical
mishandling, light fatigue and additional chemical degradation during the remanufacturing process.
In general the toner and cleaning blade contribute most to the wear. A toner formulated without the proper lubricating additives will more rapidly degrade a drum. Specific additives are used to both prevent the toner from sticking to the drum and to lubricate the drum so that the wiper works effectively. High iron oxide toners, will wear a drum more rapidly.
Using rough paper, excessively thick paper and envelopes will also wear the drum more rapidly.
Wiper blades with rough or wavy edges will wear and scratch the drum surface allowing toner to adhere. Higher cleaning blade pressure on the drum is normally used with small particle size
“micro” toners to clean the drum. This will usually result in higher wear rates. At the transfer step frictional contact between the drum and paper causes wear.
The toner transfer efficiency; is the ratio of toner transferred to the paper to toner developed on the drum. It will directly affect drum wear. For example, a toner with only 88% transfer efficiency
will leave twice as much toner on the drum as a toner with 94% transfer efficiency. It is this toner remaining after transfer which must be cleaned by the wiper blade. The type of image printed, text or graphics, and the percent coverage of print on the page will significantly affect the transfer efficiency and wear of the drum. A drum will show signs of physical wear about half way through its normal life. There is usually a slight decrease in density and toner usage.
Generally, aftermarket drums are designed to be more sensitive to laser light, or “hotter”, than the OEM drum. This property gives the drum its “long life” feature as the normal wear affects will not be observable to the user until later in the life of the drum.
Light and electrical fatigue occurs when the OPC no longer fully discharges the surface with exposure to the laser beam. The dark area print density becomes lighter and the text characters
appear “thinner”. The drum appears to become less sensitive to light or “cooler” as the carrier generation efficiency and the charge mobility are decreased. Drum wear should be measured in terms of drum rotations. Short print runs of one or two pages can result in more drum rotations
per page than long print runs and give the effect of shorter drum life. A general rule may be 75,000 – 100,000 drum rotations for a typical drum before failure
Recollected by: Ricardo Zevallos Cruz
Copier Technician from Lima Peru