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Introduction to HP A4 series monochrome laser printers

Most HP printers are based on Canon print engines surrounded by HP electronics. Most recent HP printers feature a Canon innovation that has been labelled as the Instant-on fuser or fixing film fuser. This technological feature distinguishes Canon and HP laser printers from most others in the market today. The fixing assembly or fuser is the component that melts the toner and fixes it onto the paper: it is the component that is most likely to wear and is the most expensive part in any printer maintenance kit. HP has used fixing-film fusers in most of its A4 printer models since the introduction of the HP 5P, HP 4000 and HP 5000 laser printers. The principal components of this fuser design (as implemented in a HP 4000 fuser) are pictured in the section entitled: Does your printer have a problem?

The fuser in a laser printer usually incorporates two rollers: an upper fuser roller or hot roller and a lower fuser roller or pressure roller. The upper roller is usually made of aluminium and takes the form of a hollow cylinder about 20 to 30mm in diameter and about 300mm long. It is coated with a non-stick surface such as Teflon. A heating element (halogen bulb) is mounted longitudinally along the central axis of the roller. The operation of the heating element is governed by a thermistor that rests on the outside surface of the upper fuser roller to monitor its temperature. The lower fuser roller consists of a metal core covered with a silicon rubber sleeve.

When the printer is operating, the paper is fed between the two fuser rollers rather like clothes through an old-fashioned clothes wringer. Most laser printers take 10 to 20 seconds to warm-up before they are ready to start printing. The elapsed time represents the time taken to heat the aluminium hot roller in the fuser to a temperature of 185 degrees Celsius. This time lapse only occurs before the first page is printed: - after that the fuser is already at the operating temperature. However, the initial delay can be annoying if one is in a hurry to print a few important pages. It is particularly annoying if you are only using the printer to produce one or two pages intermittently, eg when printing sales invoices. You always seem to be waiting for the printer to warm-up. Canon developed the instant-on fuser or fixing film fuser as the solution to this problem.

The Canon/HP design replaces the upper fuser roller with a fixing film assembly an aluminium core, a metal strip heating element and a thermistor enclosed inside a cylindrical plastic film coated with a non-stick surface. The plastic film spins on the aluminium housing as the fuser rotates. The plastic film is quite thin, has a low latent heat and reaches operating temperature almost immediately the heating element is activated. Hence, we have the instant-on fuser. This design also protects the thermistor from the effects of toner spills as it is covered by the plastic film rather than being mounted on the external surface of the hot roller.

The fixing film is no ordinary plastic tube: it is made of quite special materials and it is extruded in a special way. To date, most after-market manufacturers have not been able to duplicate the quality and durability of the Canon product. Further, the film is lubricated with a special lubricant to enable it to rotate smoothly on the aluminium housing. The lubricant has to withstand sustained heat and pressure when the fuser is operating and Canon has kept the composition of the lubricant secret. Many after-market lubricants work well initially but breakdown after a few months in operation. The genuine plastic film and the lubricant are not sold separately: one has to buy a complete, genuine fixing film assembly from HP or Canon to replace a worn unit.

The need to use only genuine spare parts tends to raise the cost of fuser repairs relative to other fuser designs such as Lexmark. It is possible to buy good quality after-market parts for Lexmark fusers that will perform and last well in operation. If one damages the plastic fixing film in a Canon or HP printer, eg by accidentally feeding a staple or paper clip through the printer, then one must replace the whole fixing film assembly, even if the fuser is almost new. Moreover, the plastic film seems to be relatively fragile and more easily damaged than a Teflon-coated aluminium hot roller.

The earlier designs of fixing film fusers have a single heating element. They tend to accumulate toner at either end of the rollers. The toner is abrasive and can produce excessive wear on ends of the plastic film. This can abrade the non-stick coating and the ends of the cylindrical film tend to disintegrate: the film shrinks in length and this can lead to it sliding backwards and forwards along the aluminium housing. Later designs, eg the HP 4100 fuser, have multiple heating elements that are independently controlled. This facilitates more even heating of the plastic film and a longer lasting product. The quality and coating of the film have also been improved. The improved film design is also used in the HP LaserJet 2200 whereas the original film is used in the HP 2100.

The HP LaserJet 5000 and 5100 A3 printers use a fixing film fuser. However, all of HP?s heavy-duty, high-output A3 printers such as the HP 8000, 8100 and 8150 still use a more conventional fuser with a Teflon-coated aluminium hot roller and a silicon rubber pressure roller. The colour LaserJet printers use two silicon sleeved metal rollers that are both heated by halogen heating lamps.

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