Inkjet’s rivers of ink – Print21 magazine article

For commercial printers getting into wide format, the bewildering variety of inks can be confusing: solvent, aqueous, UV and now latex from HP in machines that run five, six, or up to ten colours. You can drown in the detail. In this second instalment of a ‘How-To Guide’, Patrick Howard looks at the how wide format colour flows.

For offset printers accustomed to treating ink as a commodity, the variety and diversity of inkjet inks can come as a surprise. Inkjet inks are primarily divided between pigment and dye, water-based and solvent. Pigment inks retain their colour for longer, especially in outdoor applications, while dye-based ink has a much wider colour gamut. Solvent inks are easier to image and faster than aqueous inks with a growing trend towards eco-solvent. Then there is HP latex ink.

Most ‘poster’ graphics, (wide format as opposed to so-called large format) inkjet machines use aqueous inks; wider professional high-production inkjets mainly use solvent, eco-solvent and UV-curable inks. Aqueous inkjet printers are the most common for ‘shop-front’ businesses or commercial printers that want to add wide format paper-based graphics to their offering. The machines from such manufacturers as HP, Canon and Epson are relatively inexpensive, but tend to be too slow for higher productivity work.

Most aqueous prints require coating or laminating for outside display. They are ideally suited for indoors point-of-sale but they fade in sunlight. Photo posters are usually printed aqueous inkjet. Being water-based, the inks are safe and can be used in the print shop in the same way they are used at home on desktop applications.

Stepping up a notch
Printers who want to get into supplying the high production and signage market are likely to investigate large format solvent inkjets from suppliers such as Seiko, Roland, Mimaki and Mutoh. Most solvent inks are pigment-based, although they can be dye-based too. Pigments are preferred for outdoor applications in order to retain rightness and colour; dye-based inks fade under UV light. For printers using solvent inks, the choice comes down to ‘hard’ or highly vaporous solvent inks and eco-solvent or ‘mild’ solvent inks.

‘Hard’ solvent ink is the workhorse of the wide-format industry, or has been for many years, enabling printers to output on practically any substrate without any need for preparation. It ‘bites’ into vinyl, is completely waterproof, able to image at high speed and is relatively inexpensive. Heat driers are almost standard equipment on the machines. The big downside is that the solvents let off toxic fumes that require major ventilation in enclosed spaces. Health and safety requirements have tightened up in recent years and the popularity of ‘hard’ solvents has declined. Certainly any printer entering the market now would be well advised to investigate alternatives such as eco-solvent.

Same, same but safer
Eco or low-solvent inks have been growing in popularity. While they still emit fumes, they are of much lower toxicity than ‘hard’ solvents. Many eco-solvent machines are used in enclosed spaces without the benefit of special ventilation. They have most of the benefits of the harsher liquids with few of the disadvantages. Although prices have steadily fallen over time, they still come at a premium.

At the same time, UV-curable inks made from acrylics have become more popular, especially in niche markets. Using a built-in UV lamp, the inks are ‘cured’ and ready to handle straight away. Because there are no solvents there is less of a ventilation problem but the pay-off is that UV-cured inks lack ‘bite’. They sit on top of the substrates and if it’s a flexible surface, lifting and cracking can be a problem. Often UV-cured inkjets are used to image rigid substrates where speed and registration are the primary concerns.

HP latex ink is now being heralded as the way forward for a water-based ink that can take on the solvents at their own game. There’s no doubt it is extremely safe and doesn’t crack on flexible substrates. It has the advantage of no fade in outdoor settings without the need for coating or laminating, and there are no reports of lifting on flexible surfaces even though it does not penetrate. For anyone entering the market, the HP offering bears investigation.