Drum wear is one of the most expensive factors in remanufacturing a cartridge and it’s beneficial to take a look at different angles from time to time. There have been some misconceptions about the thickness of OPC drum coatings around the remanufacturing industry and although different drum manufactures use different qualitydrumcoatings you should also be aware that even new drum can be down on what could be seen as the desired thickness to get best results

The specification for the thickness of the working coatings on both OEM and aftermarket 30mm (SX, EX, NX, WX, 8100, 4000 etc.,) and 24mm (PX, AX, VX, 1200 etc.,) OPC’s are almost identical. The difference between the two products is that the OEM OPC’s have approximately 6-10µ (microns) base coat or etch coating which anchors the coatings to the aluminium (see Photo 1).

The aftermarket drums are usually made from anodised aluminium tube which allows for the working layers to be fixed directly to the tube. The down side of this is that there can be some reflection of the laser beam from the aluminium base which causes fringes of interference and some loss of resolution. There may be some loss of quality when comparing to OEM standard or at least this is the claim of companies who are now working on a new generation drum with a substrate made of conductive resin. Specifications on the thickness of the Charge Generation Layer (CGL) and the Charge Transfer Layer (CTL) are not usually over approximately 27-28µ as this can cause distortion of the image. (see Photo 2)

The numbers that remanufacturers should keep in mind are:
* An aftermarket OPC drums when new are approximately 27-28µ and they fail at around 11-12µ. That’s a wear layer of around 15µ and this applies to both 30mm and 24mm diameter drums. (see Photo 3)
* Remember that OEM’s have an additional 6-9µ under coating which takes their new thickness to 35-36µ and fail thickness to around 19-20µ’s.

Also keep in mind that coating thickness varies from one end of the OPC to the other, varying sometimes up to 3-4µ’s from end to end and some times more than this on longer drums such as BX, WX, and 8100. This occurs due to the dipping process used in manufacturing the drum. Coating thickness can also vary amongst OPC manufacturers as can the type of coating that they use. To give you some idea of comparison on sizes, the average human hair is 50µ in diameter. It is very difficult, some would say impossible, to pick up measurements of a few microns through visual inspection only.

Previous figures had stated that 24mm drums had average thicknesses of 48µ for aftermarket and 57µ for OEM. I believe that these measurements came about through zeroing an Eddy Current Meter on a 30mm OPC and then using this as a standard to measure both the 30mm and the 24 mm size. So the golden rule if you’re using an Eddy Current Meter to measure drum coating thickness is that you must zero your meter on a blank drum the same diameter as the one you’re about to test (see Photo’s 4 and 5)

The refrain from those that have been in the industry since the days of the SX cartridge is ‘how come they can’t make the newer OPC’s do the 8 to 10 cycles that the old SX drum could”. The OPC drum coating thickness on an SX drum is the same as for all OPC’s, as stated above, approximately 27-28µ for aftermarket and 35-36µ for OEM.

As remanufacturers are aware, one of the reasons for not being able to get multiple cycles from such cartridges as VX, HP1200(X size) etc. is because these cartridges are using PCR toner transfer technology. This is a high wear factor technologyy, plus these cartridges use a similar amount of toner to that of the SX, with a smaller drum diameter. The EX cartridge had an extra 100 grams of toner when compared to the SX cartridge, which used corona wire toner transfer technology, with consequently less wear and tear up against the drum.

It is possible to get multiple OPC drum cycles on some cartridges that use PCR toner transfer technology and this is because of the balance between toner quality, toner load, drum diameter, print speed and cartridge design. This is proven by the LX cartridge, where an OPC drum was able to be used for about 5-6 cycles. Again, these drums have the same thickness of coating as other OPC’s. The internal design of the LX helped to lessen the impact of the PCR and tranfer roller because the OPC gear cogs helped air to exit outside the main print zone and the design of the combing and foam in the cartridge helped block air flow round the PCR (less air turbulance, less wear).

Over the years, Canon has been able to come up with higher printer speed, better design and much finer toner to offset the problems of PCR and transfer roller wear. Design and the advent of chemical toner has helped OPC wear enormously, as have developments in the formulation of OPC drum coatings. This can be compared in the difference between the EX cartridge (6,800 pages) and the HP4300 (18,000 pages), with both cartridges having approximately the same coating thickness on the drum.

All in all, OPC drum manufacture hasn’t changed nearly as much as toner technology and the design of cartridges over the past 10 years.

© 2004 all rights reserved, Terry Mehan.

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