Curing the drying problem

It comes as no surprise that packaging converters are under increasing pressure from their clients to produce work that meets an increasing number of requirements. While the essential role of packaging arguably shielded many converters during the economic crash, brand-owners now expect to see their marketing budgets stretched further without a compromise on the quality of the printed product.

Short turnaround times, high print quality and strong durability are just several values the end products are expected to have. This is all well and good, but when a job is "needed yesterday" without any compromise on the quality, packaging converters are required to turn to the technology available to them to meet these goals.

While drying and curing technology offers established means of increasing a product's speed to market, there are a number of unique technologies that fall into this sector, operating in distinctly different ways.

UV growth
While ultra-violet curing is used in a raft of applications such as the flexographic package printing of folding cartons, this has been mainly confined to the role of varnishing. Now, an increasing number of press manufacturers are adopting UV curing for a wider gamut of package printing, ranging from cartons to labels and other flexible packaging materials. With more than 2,000 label presses currently utilising UV curing, it is clear that we're looking at a burgeoning market.

UV and electron beam curing offer a number of advantages for packaging converters. The immediate curing of inks, varnishes and coatings, in turn, enables the operator to progress with other finishing processes without a costly drying period.

Another benefit of instant curing, in this context, is the impact it has on preventing the growth of ink dots on the substrate. Curing ensures that the print remains sharp and bright, especially in instances where the substrate being used has absorbing qualities.
Chris Davies, marketing manager at Etiquette, a UK specialist in label production, says there are an increasing number of areas where UV offers notable advantages over other curing methods.

"UV flexographic printing of folding cartons can offer superior graphics and print quality when compared with offset, coupled with the ability to print heavy reverses and small type on- line work and colour consistency," she states. "In addition, there is also excellent scuff and run resistance with no clean=up between shifts. UV inks and curing are also considered environmentally friendly, with curing virtually instantaneous while the inks used do not contain any VOCs. With cost cutting paramount, wasted ink is kept to a minimum and the paperboard that comes with UV inks can be sold to scrap recyclers. Finally, the de-inking process is a relatively simple process and most scrap with UV ink can be recycled into fine grade paper," says Davies.

However, the efficiency of an ink system when reacting with UV energy, which forms a "cross-linked network" is heavily dependent on a number of factors. In particular, the thickness of UV-curable material is dependent upon the customer's needs, as well as the intensity of the light source. That aside, the concentration of photo-initiators and pigments is the responsibility of the ink manufacturer .

Extreme cure
Etiquette, based in Wrexham, is an established label converter and equipment supplier. It currently uses a GEW VCP advanced compact, fully air-cooled UV curing system. The VCP, which cures the ink between each printing station, also offers 'extreme cure' reflectors, with the ability to cure the most demanding applications.

Etiquette will also be taking delivery of a new GEW E2C curing and drying system, which is pitched as the most powerful low energy UV system for narrow web presses. The E2C made its at Labelexpo Europe earlier this year.

According to David Lyus, marketing manager at GEW, the E2C has enabled users to "substantially increase their profit margins" by producing high quality labels at full production speeds while using as little as 90W/cm of UV power. The company's new Rhino electronic control for the EC2 technology is claimed to enable packaging printers to cut their power usage in this area by nearly half.

Lyus tells Converting Today that this "highly efficient UV drying system" can withstand daily use in high ambient temperatures and humidity while job security on-press is additionally safeguarded. This is ensured as the Rhino power supplies are immune to damage from mains power spikes, dips, dropped phases and shorting to ground.

"Print room conditions can be arduous for electronic equipment so the power supplies are housed in a compact enclosure with full mains power distribution that protects against airborne contaminants whilst ensuring optimum cooling inside," he explains.

Ink developments
In the inks sector, Agfa is one major manufacturer that has been extensively developing low migration (LM) UV-curable inkjet inks specifically for food packaging.

While the so-called traditional printing and toner-based digital print technologies call on physical barriers, primers and in some cases, in-line laminates, to eliminate migration, UV inkjet looks elsewhere. It is a burgeoning technology as it can print onto a wealth of substrates, coupled with high speeds. However, using primers and in-line laminating units would compromise these advantages. As a result, these inks are targeted at food and drink applications printed using single-pass systems.

Hot air? While UV curing is becoming increasingly commonplace for many packaging converters, it is far from a broad-brush answer to every requirement. Another process is infra-red drying. Its main drawback is that it is slower than other forms of drying because the energy absorbed by the printed image is low, resulting in a longer turnaround time. As a result, we often only see infra-red drying utilised in sheetfed production and on paper stock, which eliminates a large number of possible packaging applications.

Hot air drying is held back as the ink can often curl, lose moisture or lose its gloss level. This is also considered to be a costly approach due to the heating involved.

Finally, electron beam curing (EB) is another process, which can cure thick films, even when working with opaque surfaces, This makes it ideal for curing adhesives that are used in lamination. It is capable of drying all colours at the same speed, polymerising the ink in the process.

"The full range of printing technologies are today employing energy curing of their inks," says David Helsby, president of RadTech Europe, the association that promotes UV and EB curing. "The key drivers are packaging innovations such as the shift from rigid to flexible materials; faster high volume print without reduced print quality; brand-owners' requirements for just-in-time delivery; and the need to reduce overall packaging costs today.

"However, unlike many drying methods, EB generates very little heat and works well with specific chemistries, but the key drawback is that it's an expensive process. Capital investment costs are considered high and recouping that significant expense is probably beyond the average packaging converter.

"A vacuum chamber is needed," adds Helsby, "as is the high voltage power supply and the need to create an inert atmosphere. Because of the unsurpassed characteristics of the resulting coating and the environmentally friendly aspects, issues such as energy consumption and avoiding waste water and waste gases will become increasingly important in the future."

Not all packaging is converted from a printed sheet on a conventional press. Air Control Industries (ACI) specialises in industrial air movement products. Its JetPlate and CanTunnel bottle and can drying offerings are "energy efficient", blower powered air delivery systems. They can be specified as enclosed units that house air delivery systems and blower in a single moisture containing, noise reducing cabinet. ?The JetPlate comprises facing plenums that deliver air and act as guide rails.

According to the manufacturer, their close proximity to the bottles and the air slot pattern ensure efficient air delivery and effective moisture removal. ACI's CanTunnel system passes cans through the machine, delivering air to remove and subsequently contain moisture.