The image coming out of the wide format inkjet printer may seem the same but as the saying goes, there are many ways to skin a cat, Wayne Robinson looks at the different technologies
Wide format inkjet printing has made massive strides in quality and productivity over recent years, and is now seen by commercial and quick printers alike as a profit centre in its own right. Posters, banners and display graphics used to be the preserve of the sign industry, but now with a decent wide format printer and rip costing as little as $20,000, and with most printers already having some knowledge of digital files, and a ready bunch of customers, the opportunity clearly exosts to add another arrow to your quiver.But where do you start, and with wide format printers costing anything from $20,000 to $500,000 and a wide array of different technologies to choose from? The key is application and markets. Clearly a copyshop branching out into a few posters will have different requirements to a printer looking to break into the real estate display graphics market. Any company today looking to move into wide format printing has a huge choice, a choice made greater in recent years through the entry into the market of big hitters such as Agfa, EFI and HP, all of whom are investing major resources into what they believe will be a significant growth area in coming years, even though wide format printing has outgrown all other sectors of print every year for the past decade.
Nozzles
The method of transferring the ink from the printer to the media may not be top of your agenda, but surprisingly there are three quite distinct technologies here; continuous inkjet, thermal inkjet and piezo inkjet.
• Continuous inkjet – as the name indicates the ink drops are emitted from the nozzle in a continuous stream during printing. The ink that is being used to print head straight for the media, while the ink aimed at the non- ink areas is deflected back to the kink reservoir. Continuous inkjet is a quick process as it can deliver a high volume of print in a short space of time, and as such is used in the very side format printing systems, three to five metre wide. On the flip side it is not easy to position the ink droplets as accurately as in other processes, and ink consumption tends to be high.
• Thermal inkjet – also known as Bubblejet, as the ink is heated rapidly in the print head to the point that it forms a gas bubble which then shoots out of the nozzle. This system has no moving parts, so is robust and durable, and prints aqueous and solvent inks without becoming caked or blocked.
• Piezo inkjet - An electric charge is sent through a piezo crystal in the nozzle causing it to expand and fire out the ink onto the media. The process is inherently precise, which means high resolutions are possible, with tightly defined text and photo quality images. This is due to the droplet size being finely controlled, with different droplet sizes being fired onto the media, delivering precise tonal values. Many Epson printers use piezo heads, part of the reason why Epson has taken the proofing market and agency with such force.
The Inks
Inks are crucial in wide format printing, and are essentially divided into indoor and outdoor, then subdivided into resolution required, and their ability to withstand climatic conditions.
• Dye based inks – can attain high resolution as the ink colour particle is located within a water based solution, which breaks down on impact with the media, so providing a smooth continuous tone image, with photo quality reproduction. However they can only be used for indoor applications as they will fade rapidly in sunlight and wash away in rain, and even indoors they may need laminating, as a spilt beverage for instance will make them run.
• Pigment inks – contain large colour pigments, and can withstand bleaching by the sun, so used for outdoor applications, and also for indoors.
There are three types of pigment inks:
• Water based – slow drying times means they are only used for less productive systems,, but for low level output applications they are perfectly acceptable
• Solvent based – the colour pigment is dissolved in a solvent. Rapid drying enables high speed printing, more than 400 sqm an hour is possible, with three year light fastness. Vibrant colours are achieved. You will need an exhaust system to remove the solvent, but new solvent lite, or eco solvent systems are appearing, which do away with much of the exhaust requirement, although they may struggle to achieve the same brilliant colours.
• UV cured – Immediate drying and highly vibrant colours with no solvent issues mean there is a bright future for UV wide format, and this is where much of the r+d money is going from the major developers. Flatbed printers have been the prime location for UV inks, as the UV will bind to a variety of substrates not just paper or board, such as wood, metal and glass, however roll to roll printers are also starting to appear with UV inks.
