In theory, inkjet technology is simple. A series of ink drops are jetted from a piezoelectric printhead onto the substrate beneath, without any direct contact between head and substrate. Tiny dots of different colored ink are combined to make up near-photographic quality images.
Paul Stinton, Technical Support Specialist at Fujifilm, explains the importance of using the right ink to avoid costly downtime and repairs to an inkjet printer
The most powerful wide format inkjet printers in the world today cover the full width of the printing bed containing hundreds of printheads. They jet billions of drops per second, each directed to a precise location, producing hundreds of square feet of high-resolution print per hour. The demands on printheads and ink performance are very high, and the relationship between ink and printhead is critical to the reliable production of consistently high-quality print.
When the system works perfectly, high performance machines like Onset flatbed printers can be in constant use around the clock producing thousands of square feet of print per day. But any issues with jetting can affect print quality, or stop print production all together.
Printheads are usually the most expensive part of the investment in a high performance inkjet printer, and can cost thousands of dollars to replace. Protecting printheads from damage is key to getting maximum uptime out of a production press. Here are some of the problems that can be caused by poorly designed inks:
Drop formation issues and unreliable jetting
Optimum jetting performance is critical to print quality and reliability, and is achieved through a combination of carefully tuned ink fluid characteristics, printhead performance and jetting waveform. Both ink and waveform need to be carefully matched to each other, and in turn to the printhead. Critical ink fluid characteristics include rheology, surface tension and specific gravity. Variations in the characteristics between inks can reduce jetting performance and lead to poor jetting accuracy or drop placement, reducing image quality; ink misting or overspray; and poor nozzle reliability, leading to missing nozzles mid-print.
Consistency of the ink fluid characteristics is also critical. Variation of the key ink fluid properties between ink batches can lead to unacceptable variation in jetting performance, leading to unpredictable results.
Nozzle blockage or deviating nozzles
A printhead nozzle can be just 25 microns (or smaller) in diameter, half the width of an average human hair. Particles that are too large or don’t have the right properties can cause blockages, resulting in non-firing or mis-firing nozzles. These appear as white streaks in a print and if there are too many the print becomes unsaleable. Often, these issues are caused by a poorly dispersed, or unstable ink. The pigment that is used to give the ink its color is made up of clumps of particles that have to be broken down small enough to pass through an inkjet nozzle, but in a low viscosity liquid there is a tendency for the particles to agglomerate or stick back together. They are also subject to gravitational settlement.
Missing or deviated nozzles caused by poor pigment dispersion are very difficult to recover – the procedures required to do so are time consuming, potentially damaging to the printhead, and have limited success rates. This often leads to costly printhead replacement. Poor pigment dispersion will also lead to frequent blocking of ink filters, restricting ink supply to the printheads, plus the cost and machine downtime required to replace the filters. In addition, agglomeration and gravitational settlement can lead to a build up of pigment particles in elements of the ink supply system such as valves and sub tanks, requiring cleaning or replacement.
PART 2 of Why reliable ink is important to the success of your business will be posted by May 7, 2015 in Inklings Blog