How does an old, aged, damaged, dirty, contaminated or bad PCR affect your print/copy quality and machine. January 2020 Week 4

Probably one of the areas in a digital copier or laser printer that is neglected the most in relation to the importance of the device  is the overall condition and operation  of the Primary Charge Roller, so lets look at one does the PCR in the machine when it is not well looked after, or what are the signs and causes of a PCR wearing out.

Lets first in a nutshell look at the role or functioning of the PCR. The job of the PCR is to provide and even electrical charge to the outer coating of the OPC (Organic Photo Conductor) Drum, and this electrical charge is then discharged when it comes into contact with the laser beam that shines on it, and produces and electrical or latent image in the shape/s of the image one is printing, the toner is then repelled by the charged areas of the OPC Drum, and this is the white areas of print on the page, and the toner adheres to the discharged areas, forming a visible image, be it on a Black & White/Monochrome print or a colour print. The PCR also discharges the OPC Drum with an AC (Alternating Current), just before it recharges the drum, and this discharge ensures that there is no residual electrical charge on the image areas of the drum that were just printed.

Firstly as most PCRs have a rubber coating as the main component that transfers the electrical charge to the OPC drum, one needs to be sure that the PCR one is purchasing and installing in your machines you service is manufactured using high grade rubber. At CET we use only the highest grade of rubber raw materials from Japan, and the PCRs are manufactured under the strictest environmental and Quality Controls, as small things such as the curing temperatures and there must be zero humidity are critical to ensuring there is even curing of the rubber when the PCRs are molded. The accuracy of the molding with the metals PCR shaft to be exactly in the centre so as to ensure the PCR runs 100% smoothly against the OPC Drum. If not, then there will be an uneven charge delivered to the drum and one will get an uneven print on the page. The PCR will also more than likely damage the drum well before the actual life of the OPC drum too, if not well manufactured.

As there is an electrical charge delivered through the PCR to the OPC Drum, the rubber used to manufacture the PCR is impregnated with carbon, allowing it to conduct electricity from the centre shaft, through the rubber to the OPC Drum surface. Every model of digital copier/laser printer is designed with a specific voltage that is applied to the PCR in order to achieve the desired charge on the OPC Drum surface, so the electrical resistance of the PCR rubber is critical, as if the resistance of the PCR is too high the charge delivered to the OPC Drum will be too low, and one will get background on the prints, and if the resistance is too low, too much voltage will be applied to the OPC Drum and the prints will be light, and one may even get a short circuit, where sparks are produced between the PCR shaft and the OPC Drum, severely damaging the OPC Drum surface.

What actually happens to the PCR rubber as it gets older? As the rubber PCRs as used in most makes of copier and laser printer are the rubber PCT that runs on the surface of the drum, there is spring pressure pressing the PCR against the OPC Drum so the rubber on the PCR compacts or compresses slightly all the time, so with time on every rotation the PCR compacts slightly and with time will reduce in diameter. Then, as there is a relatively high electrical charge of between 500VDC and 1500VDC depending on the machine, this electrical charge causes the rubber to perish, decay, degrade, or degenerate, whatever one may refer to the degradation of the rubber, so the overall strength and conductivity of the PCR will reduce over time.

The PCR has a far smaller diameter than the OPC Drum, so rotates many more times per rotation of the OPC Drum too. As the PCR rubber degenerates, it tends to conduct less electricity, causing the prints to start producing background print, and technicians often look for other causes such as blaming the toner, or developer if there is developer in the machine. As the PCR runs against the OPC drum, and the only drive that causes the PCR to rotate is the friction against the OPC drum, so on long print runs, the PCR will also heat up from the friction between the OPC drum and the PCR.

The background on the prints can be rectified by cleaning or replacing the PCR, but worse still if the PCR rubber has severely decayed, gaps or splits in the rubber of the PCR, then arcing may occur between the PCR and the OPC drum, this is when sparks form from short circuit between the PCR shaft and the OPC drum due to there being no insulation or resistance between the PCR shaft and the OPC drum, and this will go through the OPC layer on the drum, damaging the drum permanently.

Lets then look at a few points here that one should take into consideration regarding the PCR in the digital copier/laser printer, and that is that the PCR should always be kept as clean possible to ensure optimum performance. Once the life of the PCR is over, one should replace the PCR with only a quality PCR, such as those manufactured by CET. This will maintain the print quality plus will extend the OPC drum life in most cases too.