05 September 2018 Analogue Printing Technologies

LED success requires the partnership approach

The shortage in supply of photointiators has highlighted how UV printing is more sensitive to the balance between inks, rollers and other consumables to achieve quality on press.

LED UV is unlike conventional litho. It is not a process where a printer can easily switch between ink and consumable suppliers in search of a lower price. Instead in order to achieve decent results, the technology demands a partnership approach between inks, plates, blankets and rollers. That favourite wash, used for many years on a succession of sheetfed presses, will no longer work on the new LED equipped press.

This partly explains why European ink makers were wrong footed when first H-UV and then LED UV were introduced from Japan. The inks begin as more expensive because of the inclusion of photoinitiators, the compounds that react to UV light to form an interlinked polymer lattice to trap the ink pigments on the surface of the paper.

This is why UV is so good on uncoated paper. The ink does not sink into the paper. Instead it creates a bright, high lift image on the the surface of the substrate that does not rub off and feels completely dry. This also means less ink is used on these absorbent surfaces.

Photoinitiators are sought after products, not just in print. This makes them expensive, the more so after factories closed in China this summer and new regulations were introduced in Europe. Some products used in Japan cannot be used in Europe. At first suitable inks had to be imported from Toyo, Sakata and INX, adding to the cost.

European ink makers have responded with Huber, Flint and Sun Chemical (subsidiary of Japan’s Dainippon Ink & Chemicals), making inks and coating that work at the appropriate wavelengths. Toyo has come back with the acquisition of Arets, a Belgian ink producer that had specialised in UV inks and T&K Toka with the acquisition of VanSon Inks at the end of last year.

There is a clear belief that UV inks are going to be big. Komori promoted the idea of packaged products to ensure that H-UV would work and Flint has collaborated with AMS on installations of its LED technology. The reason for this approach is that printers have a narrower operating window with UV than with conventional litho inks.

Graham Punchard, director and general manager in charge of rollers at BFS Pressroom Chemicals, says that “LED has become quite a big part of our business now. “We seem to have most of the products needed in our portfolio and they work together.” Key is a roller product that is different to anything else on the market and which works well with the UV technology. It is supplied as part of the start up configuration by OEM press suppliers he says. One of these is Komori where BFS has been collaborating since the early days of H-UV.

“We are trying to get people moving into the sector to recognise the importance of having a matched package and knowing that all the products work together. We are seeing some phenomenal results when they do.”

One of the first Komori H-UV customers he says has only changed ten rollers in the four years of running the press. “A lot of conventional customers are changing rollers a lot more frequently than that,” says Punchard.

This longevity requires a good maintenance routine as well as working with approved consumables. It means keeping on top of the filtration of fount solutions. New rollers will need proper conditioning, he says to prevent them taking in too much of what is a more ‘aggressive’ ink. Hardness values will end to be checked “If this is done correctly, the rollers will keep working for a lot longer,” Punchard says. “You need them to carry the specific amount of ink or water. Not all products operate with the necessary precision.”

Problems arise when printers do not heed the advice, decide to work with suppliers who lack the necessary experience or understanding, or want to keep using products they have relied on for many years, but which no longer work in the harsher UV conditions. “Security of supply is also important. You cannot chop and change between products. There can be unexpected knock on effects from choosing the wrong wash,” he adds. “Take advice: most manufacturers will be able to supply a product that works.”

The ink manufacturers are in prime position to dispense the recommendations needed. Like BFS, Sun Chemical was part of the H-UV roll out, subsequently moving into LED, says Jonathan Sexton. “Today we are hearing more about LED than about H-UV: we are seeing a lot ofHeidelbergs going in across the world.” The UK is lagging in terms of take up he adds. “Sometimes the UK can be very innovative, other times UK printers can be conservative and take longer to pick up on a trend.”

IF LED is established in commercial printing, it has still to make the breakthrough in carton printing. One reason is that low migration inks are not as widespread or as generally available as they need to be. Availability and demand is also restricted by the choice of photo initiators and therefore the cost of the inks. “Low migration requires a polymeric photo initiator which is more expensive than standard photo initiators,” he says.

There is a limited take up to date, a customer in Spain, one that plans to use a LED UV Heidelberg for food packaging. The risks are high. “I imaging there will be people who introduce into the market something they says is useful for food packaging, but which might not be suitable.”

The state of knowledge is such that marketing claims need to be checked out he says. For example, the stated energy saving benefits need to be tempered by understanding the comparison and also that savings can be obtained by switching to a high efficiency single lamp system rather than a multiple lamp.

“It is very hard to get any accurate data from people, whether moving from standard UV to LED UV or from people switching from commercial printing to LED UV. And the cost calculations are even more complex.” The additional cost of the ink is set against savings in energy, lack of spray powder, seals and so on together with more intangible benefits.

But this counts as nothing compared to the astronomic cost of an LED cured varnish. These require even more refined photoinitiators, or acceptance of a yellowing effect. A compromise from Sun is a varnish where yellowing has been minimised and which is not as expensive as some LED UV varnishes. Many users are using LED to cure the four process colours with a standard UV varnish cured by a single lamp in the delivery.

This is becoming standard practice in flexographic printing, the latest sector to succumb to the charms of LED UV. Again the UK has lagged behind others, in this case the US which had never adopted UV flexo in the way that European label printers have and which leaped directly to LED UV. Inkjet technology on digital presses is likely to help prepare the way for LED UV in this area, but so too will the purchasing decisions of multinational groups where matched production facilities may be needed.

A handicap may be that multiple lamps will be needed on a label press to cure each colour in turn. But a convertor can switch one unit at a time Amanda Jones, marketing manager of Paragon Inks, points out. The Scottish company produces flexo inks for labels and uses the same pigmentation for both standard UV cured by medium pressure mercury vapour lamps and LED cured UV. Lamp manufacturers like IST and GEW are producing units which can run either technology.

A printer can start with one or two units, perhaps for white where LED seems to have an advantage, while keeping conventional lamp units to handle the varnish problem or for special colours where lower demand for the LED equivalent keeps the price high.

“LED UV is a natural progression as regards UV curing,” she says. “It can cure different ink film weights more easily and with more consistency. With mercury lamps there is always a question about degradation: Are we sure that the ink has been cured fully. LED UV provides stability of output. It amounts to a better platform for printers. “We have customers that are saving 30% in run time because they are not getting the warm up and cool down periods.”

There is also the question of the future status of mercury. Under EU regulations it has been allowed on industrial equipment where there has been no viable alternative. A revision to those regulations is now due and the status of some mercury lamp installations at least will be called into question.

A bigger issue says Jones is ignorance. “We need to dispel the fear factor. It is a minority of printers that have so far gone for it, others are sitting on the fence to watch. But there is nothing to fear, the US industry has embraced LED UV completely.”

There is also a dedicated ink for printing plastic, justifiable where sufficient volume is printed. Like Punchard, Sexton’s message is that switching to LED UV will mean a learning curve and there may have to be compromises. He says: “Printers must learn what works for them.”

“Everyone is building up more know­ledge of what works and what doesn’t,” says Punchard. Month by month that is happening. LED UV will not be the panacea for print’s problems. For some work it will be too expensive or too limited, but in others LED UV will be unbeatable.

Gareth Ward

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