21 March 2016 Analogue Printing Technologies

The choice of UV inks is spreading

Commercial printers looking at a move into UV printing have a greater choice of suppliers to choose from, but cannot expect the price to match that of conventional inks. But price is not the only issue.

The cost of ink has always been held up as the major barrier to companies transitioning to new generation UV printing. It is reckoned to be three time the price of more conventional inks and while the price differential is narrowing as volumes increase and new suppliers enter the market, UV cured ink will always be more expensive simply because the recipe for the ink includes photo initiating compounds.

These are the materials which form the chemical lattice to trap colour on the surface of the substrate, the key to UV printing. But the price is falling. One expert reckons that parity with conventional UV inks is possible.

Part of the cost issue was also related to shipping costs from Japan. Komori’s H-UV process was developed between the press manufacturer, Baldwin and Toyo as ink supplier. While Toyo has acquired UV ink specialist Arets in Belgium, it has taken time to start production in Europe.

Likewise Ryobi introduced LED UV curing in 2008, developing that process with Panasonic and with Dainippon Ink and Chemicals as inks supplier. DIC operates in Europe as Sun Chemical and this company is now starting to produce new generation UV inks in Europe.

“It has been developed as an ink for single-lamp systems,” says Jonathan Sexton, marketing director for narrow web and screen at Sun Chemical. “It will be launched at Drupa and is already undergoing beta testing.”

A four-colour set for LED UV has also been developed and will be produced in Europe. Its testing phase is a little behind the single-lamp version, but will be available at Drupa. “We know this is a product that works,” says Sexton. “It is cost effective in Europe for printing on paper and on some of the more common plastics.”

The rise of retro fit systems will expand the opportunity for all ink makers because printers will not be as tied to the press supplier.

Komori, for example, tests and approves inks for its H-UV system passing Huber inks as suitable, the first to receive the endorsement. The ink will work with the other single lamp systems as these are fitted into existing presses.

“We have had questions like this in the last couple of months,” says Huber UK’s offset technical manager Richard Gill. “We would advise a printer to talk to chemistry and ink suppliers to get as much advice as possible.”

That would include the suitability of roller coverings, fount solutions and blanket washes both for the press and to work with the ink.

“With a retrofit system, printers are more able to work with their existing ink suppliers than having to work with the suppliers recommended by the press manufacturer,” he points out.

Currently the field for LED sensitive litho inks is dominated by Flint Group, which has its UV technology centre in Trelleborg, Sweden and production there and in the US. This produces the LED inks that companies like Blackmore, ABC Print Group, B&B Press and Vario Press are using in the UK. But there is far greater demand from outside this country.

Countries are attracted to UV for different reasons. Japan, because of the energy saving aspect that legislation dictates; Hongkong because rapid processing of work in progress frees up space in tiny factories increasing the ability to work round the clock; India because power shortages limit the number of working days.

And in Europe there has been an environmental aspect from Switzerland and Germany, a quality aspect from France and now speed of turnaround driving take up in Germany. “In India,” says Richard Wilson, global sheetfed technical coordination of UV for Flint, “there are three new presses with LED and 30 that are being prepared for retrofits.”

At this early stage, inks from different manufacturers may give completely different results. Finding the right combination of fount, blanket and ink may need determination. All suppliers are prepared to work with printers to achieve this. There is a much narrower band for ink water balance for example.

“We are working with the machine manufacturers,” says Flint Group’s Wilson. “The Flint ink will work on 65-70% of all non absorbent surfaces as well as paper and board. We also have a series for IML plastics and now a low migration LED ink that has been certified by ISEGA.”

No packaging printers have committed to LED curing because the ink has not been available, and the ink suppliers need demand for the printers, a classic Catch-22.

There are, Wilson continues, fluorescent and metallic colours available, as well as different varnishes for dedicated coaters and duct application. It is not discolouration that is the barrier here, it is the high cost of some of these coatings.

And while this is an LED ink, there are uses printing with the Xcura ink on single-lamp systems. All the inks, he stresses, conform to Eupia standards over the safety of the compounds used.

Printers cannot expect any kind of UV to be a drop in replacement for a conventional ink. It will be necessary for any printer to adjust tone curves on the CTP having profiled the press with the new inks. Unlike the first generation of UV inks, these do not result in excessive dot gain. If anything the ink prints sharper, pinned to the surface of the substrate.

The thinner layer of ink that can be applied means much brighter results on uncoated papers especially and for subjects that can sometimes be difficult to print, architectural structures for example.

The inks will need to be stored separately from standard inks, if only to avoid potential confusion – the print equivalent of filling a diesel car with four star petrol. But there are no special requirements, says Richard Gill. “It’s about sensible housekeeping measures,” he says. “Switching to printing with new generation UV need not be terrifying.”

Some of the issues relating to the use of UV inks are not the problem that perhaps they were a generation ago. Despite early concerns he says the ink has no greater tendency to mist than any other inks at high press speeds, nor he says are ink agitators necessary with the latest Huber inks, which are developed to flow faster. “Printers want the same sort of performance with UV inks as they receive with conventional inks,” he says.

However, the laws of physics and chemistry may prevent this. The effectiveness of the curing process will depend on the power of the UV source and the distance between that source and the ink layer.

Press speed may need to be adjusted to compensate and ensure a full cure takes place. The thickness of ink on the substrate may also affect this. If a full cure does not take place immediately, the inks may mark.

Paul English, European sales director of UV inks for Huber, points out that the UK lags behind other countries, perhaps because there is greater margin in commercial print in Europe and price pressures a little less.

This helps promote investment because there is a foreseeable return. The ROI model in the UK is more complex, made more so by the widespread use of UV in packaging.

Huber, he explains, will be introducing an LED UV sensitive ink at Drupa. “There is not much difference between single lamp and LED systems, a slight difference in the photo initiators, but there is a French customer printing with LED UV on our HS-UV inks,” he says.

“The use of both kinds of UV is growing rapidly in mainland Europe because of the benefits from not using spray powder and being able to convert faster. And the ink, being sensitive to certain wavelengths of UV light, will stay open in the duct. And we will see a slight gloss improvement in the ink because it does not get absorbed into the substrate.”

Some companies have been advised to change lighting or to apply a UV filtering film at considerably less expense, though this is not essential.

That said, the technology is not infallible. While adhesion is much better on hard to print on substrates than with conventional inks, rub tests may be necessary to establish this. Likewise, it will be important to check the effectiveness of curing.

Mercury vapour lamps have a finite life and will degrade, reducing the amount of energy reaching the paper, affecting the thoroughness of the cure. The life of the lamp was put at 1,200 hours, though again this is being extended and many printers have experience beyond this.

As with conventional inks, it may be better to run certain materials and coverage levels at below top speeds for optimal results. The earlier LED UV systems were restricted in this way: there was a window of operation in this regard.

But that is no longer the case and the promise of more powerful LEDs will remove any lingering doubts as well as give ink makers greater latitude in producing inks for different materials. Sun’s first LED UV ink is suited to papers and the most friendly plastics, says Sexton.

It is not suitable for packaging applications and certainly would not pass food proximity testing. Sun Chemical has developed LED UV inks that meet these requirements in flexo applications and is working on a suitable ink for offset litho but this is 6-12 months away, says Sexton.

It is likewise working on varnishes that retain clarity. UV varnishes have greater reflectance values than any aqueous seal. Those for new generation UV have, however, been associated with yellowing. This is no longer the case for single-lamp systems.

“The big challenge is LED because the formulations we have leads to yellowing. The materials we have today are not working very well and we will need shorter wave length lamps to overcome this,” he explains. “They are coming.”

And perhaps coming quickly. English says that Huber is in discussion with a varnish supplier that reckons to have cracked the problem. “They are claiming to have a duct applied varnish that will cure and will cure at speed. We were also told that this was not possible because of the narrow band of the UV energy. We plan to test this in the very near future.”

The alternative approach is to place an LED UV unit ahead of the coater which applies a conventional UV varnish and is cured by conventional lamps. This is equally an approach which can be effective for doped lamp UV.

Flint Group can also supply varnishes and coatings that do not discolour. Given the size of its investment into this sector that is hardly surprising. It has seen been in discussion with press manufacturers and knows that new generation UV is going to be a very big market.

Says Wilson: “We have had LED inks for two years now and it’s a key strategic area for Flint. We want to be seen as the the world leader.”

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Flint Group

Flint Group

Flint has led the way with LED UV inks, and now Sun Chemical and Huber are among those planning to introduce LED UV compatible inks at Drupa.

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