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.
The rail where the printhead carriage traverses back and forth will need to be lubricated occasionally and kept free of contamination. File photos
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.
Daily printhead maintenance will include running a set of colour bars corresponding to the printer’s capabilities. Photos by Peter Saunders
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.
