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 coloured ink are combined to make up near-photographic quality images.
The most powerful wide format inkjet printers in the world today use full-width, metres-wide arrays containing hundreds of printheads. They jet billions of drops per second, each directed to a precise location, producing hundreds of square metres 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 this system works perfectly, high performance machines like Onset flatbed printers can be in constant use around the clock producing thousands of square metres 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 pounds to replace. Protecting printheads from damage is key to getting maximum uptime out of a production machine.
What can go wrong?
These 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.
Extensive testing of waveform and ink properties, in combination with the printhead, are an integral part of the development process of all Fujifilm UV inkjet inks, in order to ensure flawless jetting performance. In addition, Fujifilm’s rigorous quality assurance and quality control processes ensure ultimate consistency between batches of ink. In addition, the ink formulations are developed to ensure the ink remains stable, with no change in fluid characteristics, over it’s lifetime.
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, or misfiring 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 colour 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, often necessitating 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.
Printhead and ink supply system damage
Incompatibilities between the chemistry used in an ink and the materials used in the construction of a printhead can actually cause damage to printhead components, and the printhead literally falls apart. Likewise, damage can occur to any part of the ink supply system, from the point of entry in the machine, to the printhead. Some ink suppliers may promise better adhesion to difficult substrates, but the same aggressive chemicals they use to etch into the material can cause internal damage to the printhead and ink supply system. There is also the possibility that the materials used in the printhead or ink supply system can cause the ink to gel or pigments to fall out of dispersion, blocking the ink supply or printhead. As part of the ink development process, Fujifilm tests the compatibility of the ink with printheads, plus the components of the ink supply system in printers, to eliminate the possibility of ink incompatibility or damage. This is a time-consuming procedure, but vital to ensure ongoing machine reliability.
Ink to ink compatibility issues
If an ink with different chemistry is used in a printer, ink to ink compatibility issues can occur. Reactions between incompatible ink components can cause gelling or pigment agglomeration, which can block nozzles and the ink supply system. This is especially likely where aggressive chemicals are used in inks to obtain adhesion to difficult substrates.
All Fujifilm UV inkjet inks are produced with proprietary dispersion technology to create stable, reliable inks that are designed to work perfectly with a particular printer. The benefits of using Fujifilm UV inkjet inks are not just limited to great print quality and performance; the benefits of the care and attention put into the ink development also include increased machine up-time (from increased machine reliability and reduced maintenance), lower cost in use by eliminating the need for printhead replacement, greater productivity and reduced media wastage.