Preventive maintenance for inkjet printers

by all | 7 February 2014 8:30 am

By Bob Flipse
Too often, by the time a wide-format inkjet printer is serviced, it is in a state of crisis that could have been prevented. While most drivers know to get their car’s oil changed periodically, many people still do not think about printers in the same way—despite the fact their printer, unlike their car, can make a lot of money for them. The need for preventive maintenance is not merely cosmetic—e.g. preventing operators from placing solvent-soaked cloths or splashing ink on the printer—but also, more importantly, mechanical.

Much like owning a car and occasionally taking it to an automotive specialist, printer owners can do their own ‘oil changes,’ performing basic maintenance in between major service intervals. Like a car, an inkjet printer contains critically important fluid systems that need to be kept clean for optimal performance and longer operating life. Unlike a car, where most such systems are sealed, a wide-format printer’s caps, capping maintenance stations and/or printheads are exposed to outside air and contaminants during—and sometimes after—printing.

The major components of a solvent-based inkjet printer are the media transport and take-up system, the carriage and positioning, the electronics and controls and, responsible for the most maintenance service calls, the ink system.

Checking components
Each printer has its own maintenance routine, but a number of practices will apply to almost any printer, regardless of its manufacturer. One way to consider how the technology works and what is going on throughout the printer is to work from the end of the system, back to the beginning.

The waste bottle is the end of the line, as it is where wasted ink goes after the printheads are cleaned, the nozzles are washed and/or the printheads are primed. The ink is pulled through the printheads and pushed into the bottle by way of a pumping mechanism. If the bottle becomes full or if the service line that feeds into it is gummed up, the printer can become clogged.

Most printers use a pull-through pump system that draws ink through each printhead to prime them and keep the ink flowing, but for this process to be effective, there needs to be a good seal between the cap and the printhead. Typically, the printhead has a flat surface and the cap is like a rubber boot that seals the connection.

If the seal is not good, air leaks may occur whenever the pump tries to pull ink through the printhead. When such leaks happen, the printhead will not be primed, as no ink can be pulled through it. And during cleaning cycles, air leaks will prevent the printhead from being cleaned.

There are several causes of cap/printhead seal problems. For one thing, rubber caps will deteriorate over time with constant exposure to solvents and heat. Old and worn-out caps should be replaced.

There may also be poor alignment of the caps and printheads. If the caps do not seal the printheads in the correct position, there will be air leaks. So, it is important to perform a capping station alignment.

There can be problems with the capping station motor. While the specifics vary from printer to printer, some models use motors or belts to raise or lower the caps during and after printing. If this process encounters a problem, the solution is to repair or replace the motor assembly or its affected parts.

Poor cap maintenance can result in dried ink and pigments crusting right where they need to be sealed, at the cap-to-printhead interface. Additionally, failure to keep the caps clean will result in much faster degradation, as the crust will become abrasive, at which point cleaning it with solvent and swabs can tug bits off of the cap, resulting in premature failure. It is important to swab the caps gently and regularly instead.

There will be an accumulation of pigment both in the cap itself and below it, so a recommended maintenance solution should be used to wash the caps in sufficient quantity to run right down to the waste bottle. This will thin the accumulation and help avoid clogging caused by waste ink.

When capping units become old, dirty or misadjusted, the printheads can dry out because the pumps cannot prime them, leading to a starvation of ink. When the pumps cannot push fluids into their containers, the printheads and the capping station will become clogged, leading to a ‘constipated’ system that eventually will not print at all.

Another crucial component of the ink system is the wiper/wiping station. On most printers, this involves a rubber blade that wipes across the printheads periodically during printing. If the wipers are allowed to crust with dry ink, it can be transferred to the printheads, pressing dried particles of ink pigments into their orifices, with disastrous results.

So, wipers should be treated with the same care as the caps. Though they are not ‘seal-critical,’ any inefficiencies in wiping will have a significant negative effect on print quality.

Maintaining flow
It is essential to keep ink flowing and the printheads wet. Even busy sign shops can have down days where not much is being printed, so it is important to continue daily maintenance, running a set of colour bars corresponding to the printer’s capabilities.

With cyan, magenta, yellow and key/black (CMYK) printing, for example, this will involve approximately 153 x 305-mm (6 x 12-in.) blocks with 100 per cent of each colour. If light cyan and magenta are added, they should be 153 x 203-mm (6 x 8-in.) blocks with the light colours at only 40 per cent density, to assure the ink colours are being used by the raster image processor (RIP). The same goes for orange, green or white ink.

The idea is to force the printer to use the colours even if it is not printing at the time. The blocks can be scaled according to the width of the printer and the substrate. Printing full-width bars has proven to do the trick in helping unclog otherwise serviceable printheads.

Some inkjet printers even automatically produce a thin ‘confidence stripe’ along the edge of every graphic, to ensure all colours are being used all of the time. When the printer or RIP does not offer this feature, signmakers can simply create their own confidence stripes, about 12.7 mm (0.5 in.) wide, with all four to six colours, running the length of the graphic.

In some cases, printer manufacturers have configured their devices to bring up error messages and preventive maintenance flags, which should not be ignored. These are the equivalent to dealer-scheduled oil changes for cars.

When a printer will be unused for more than a month, the system should be flushed first. For this purpose, there are specific storage fluids that are not as volatile as maintenance solvents, will not dry out as quickly and will protect the printer longer.

Using OEM inks
Printers start with original equipment manufacturer (OEM) inks, which are highly recommended and, indeed, required to maintain warranties. OEM inks are formulated with the proper chemistry, viscosity, volatility and pigment particle size to flow optimally through the ink system and printheads.

This optimization relates not only to chemistry, but also to physics, as the ink flows from cartridges or tanks through lines and dampers with filters in them, then is jetted out of microscopic orifices at precisely the right size, time and direction to achieve a cleanly printed graphic. If the ink dries too quickly, it could coagulate on the printhead, either during printing or overnight while the printer sits idle. If it dries too slowly, on the other hand, the graphics might not dry before they wind up on the take-up system, at which point they could be ruined.

If the ink does not spread enough when it hits the substrate, it could cause banding. And if the particle size is too large or irregular, the printheads could become clogged. Even the temperature settings for heaters before, during and after printing come into play.

This is not to say all alternative inks are bad options, but simply to emphasize how not all inks are created equal.

Mechanical maintenance
As mentioned, there is less to worry about in terms of preventive maintenance when it comes to the non-ink-related mechanics of the system. The owner’s manual should be checked for specific details, materials and intervals.

The media transport and take-up system commonly features a media holder, pinch rollers and a heater platen. A blade should never be used to cut along the platen or it could become scratched.

All components should turn freely, without binding. Non-drying lubricants are preferable to gooey oils. The rollers should be cleaned to prevent clogs. And the belts need to be changed before they wear out.

The rail—usually aluminum—where the printhead carriage traverses back and forth will need to be kept free of contamination and lubricated occasionally with the manufacturer’s recommended product. The encoder strip—generally a clear plastic ‘ruler’ that helps the printer determine its position as it traverses across the substrate—should periodically be cleaned gently with isopropyl alcohol or a mix of soap and water, much like washing a car. If the strip’s ‘eye’ sensor were to become clouded or otherwise damaged, it would cause errors in printing.

A printer’s control panels are often membrane switches sensitive to human touch. If compromised, they may not work properly. Both multi-function and dedicated circuit boards need to be protected against static or voltage spikes at external cable junctions. Some systems are extremely delicate, requiring careful control of humidity levels.

Cosmetic care
While mechanical maintenance is more crucial in ensuring a printer continues to make money for its owner, cosmetic care is also important. After all, no one wants a scratched-up or scarred printer, even a used one, so proper care will help optimize the machine’s resale value.

Solvent-soaked cloths, syringes, pipettes, bottles or other maintenance items should never be placed on the printer. Plastic can melt and paint can become mottled.

If ink is splashed onto the printer, it should be wiped off quickly.

While specialized technicians will still occasionally be needed for deeper access to a printer’s mechanical and electronic workings, there is much that sign shop owners can do by themselves in terms of periodic maintenance and just taking care of their printers.

Preventive maintenance calibrations will help ensure faster, sharper printing and stave off expensive repairs. The price of printer failure, on the other hand, includes everything from wasted ink and materials to overtime for employees and downtime when customers cannot be served.

Bob Flipse is a partner at Grafx Network, which services wide-format printing equipment. This article is based on a seminar he recently presented on behalf of the Specialty Graphic Imaging Association (SGIA). For more information, contact him via e-mail at bob@grafxnetwork.com[6] and visit www.sgia.org[7].

Source URL: https://www.signmedia.ca/preventive-maintenance-for-inkjet-printers/

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