Energy Grows For Coating

There were plenty of surprises at drupa, among the most striking being offset curing using ultraviolet light generated by light emitting diodes—versions of the same low-energy, solid-state lights used in household accent lighting and digital printers. Interest in LED for UV curing stems from its low energy requirements—20% to 25% of that required by conventional UV curing lamps—and the elimination of ozone and heat output. LED lamps are also instant-on, with no warm-up period required before going on impression.

Ryobi showed UV curing in action in the fifth unit of a 525GX 5-color 13×19´´ press, running Toyo FD LED ink and a lamp developed by Panasonic. Ryobi reported that it has tested LED UV curing at speeds up to 16,000 sph.

IST Metz presented a demonstration of its entrance into UV curing via LED. The firm says it has been working on LED based UV curing technology over the past several years, primarily for the inkjet market, where this technology is currently used.

“We clearly acknowledge the exciting potential that exists for this technology in the area of reduced energy costs, reduced heat and instant start capabilities on sheetfed litho applications,” says IST America's Bill Bonallo, who notes his firm continues development of LED UV for offset.

Toyo debuted its FD LED series sheetfed offset inks at drupa, designed for use on thin paper. “Although the FD LED Series achieves the same level of ink performance as UV curable inks dried using conventional UV lamps, it is lined up as a next-generation technology due to the fact that it reduces environmental impact by conserving energy,” says a Toyo spokesperson. “It is aimed squarely at users focused on printing innovation.”

In a backgrounder on UV, from which the following explanation is drawn, Grafix explains the basics of UV curing. UV curable inks use low-molecular organic compounds that produce photo-polymerization reactions under ultraviolet light, all of which are cured through polymerization during printing and drying. This eliminates volatile evaporation of solvents.

Another key characteristic is instant drying. The rapid drying of regular inks involves heating with a hot-air dryer to speed up solvent evaporation, producing CO2 emissions from the electricity or gas used to heat the air. Although UV curing produces CO2 as a result of the usage of UV lamps, the amount is greatly reduced.

The popularity of the UV process and its rapid adoption was reflected in presses on display at drupa, and in the configurations of machines going into the field. At drupa Heidelberg, for example, showed various configurations of its new XL 75 29´´ press with UV coating and curing integrated into the line, and controls built into the central console. Heidelberg has its own branded DryStar UV curing system, integrated into the press and Prinect control console, engineered with the lamps at what it calls a “very small distance between UV dryer and sheet” to increase dryer output significantly and allow top production speeds in UV printing. Dryers previously had to be switched off when washing the blanket to guard against an explosion; Heidelberg says its Instant Start speeds resumption of curing after wash-up. Dryer settings can be saved with other parameters of a job and recalled, helpful when presses have complex dryer configurations.

At drupa, Heidelberg presented its DryingMonitor. Available for the XL105 beginning in September, it measures drying quality—but only for infrared curing of aqueous coated sheets so far. Based on the amount of coating applied, sensors at delivery and drying units help calculate amount of water introduced by the coating, the volume of air and the temperature and humidity of the incoming and outgoing air. A survey by Heidelberg revealed that, in practice, most dryers are operated at a 20% to 25% higher output than is actually necessary because operators had no means of assessing drying quality objectively.

Grafix says it has addressed energy usage and start-up speed issues through a more efficient yield of radiation and an optimum reflector geometry that ensures consistent drying and low energy consumption at the same time. This is optimized by continuous power control (from 30 % to 100 %) and through standby regulation down to 30 % of the lamp power.

At drupa, Air Motion Systems presented its third generation UV curing system, P3, with improvements addressing issues related to speed of start-up, reducing energy usage (up to 45% over comparable systems, says AMS), and improving reliability.

“With P3 we are solving the long-term durability and energy questions associated with UV,” says Steve Metcalf, president and CEO. Maintaining the consistency of UV lamps over time, to deliver consistent curing, was among the technical issues Air Motion Systems addressed through a MAX (for multi-axial motion) designed to maximize thermal durability of moving components, “self-healing” shutters that maintain alignment of reflectors despite ongoing physical stress inherent in an operating press (vibration, etc.), and in-line anodes that protect against water corrosion of internal components. The P3 UV System is equipped with enhanced double-parabolic reflection geometry—a key feature that allows it to reduce electrical energy consumption.

For specialty work with concentrations in printing on plastics and heat-sensitive materials, Air Motion Systems offers Cool Impression—an impression cylinder cooling system. It directs chilled high-velocity air at impression cylinders from underneath, in an area where sheets don't travel. Cooling is controlled in each print unit independently.

Like most UV curing system providers, Air Motion Systems says it works will with all leading press manufacturers. It is the single North American manufacturer to KBA for UV and IR curing systems. KBA's line of VariDry UV and IR dryers, offered worldwide, are based on AMS technology. AMS began working with Komori in 2005 offering its Peak UV and IR packages for Komori half-size and 40´´ Lithrones. AMS became preferred supplier to MLP in 2005 offering a tailored set of Peak UV and IR dryers for the Mitsubishi line of sheetfed presses.

Nordson, another UV curing system supplier exhibiting at drupa, says it has addressed energy consumption issues with an eUV energy saving UV control system. The lamps shut down quickly during makeready and setup, then just before the press is ready to move into impression, an Express Restart delivers UV output quickly using conventional lamps. eUV can be integrated into the press control or managed directly by the press operator using the Nordson Spectronic system.

Ink manufacturers have been hard at work developing inks for both digital and for web and sheetfed offset. UV curable and hybrid inking systems have been experiencing 10% growth in recent years. Unique combinations of coatings, with reticulation and other texture effects, have added to the appeal.

The evolution of inks from hybrid versions—conventional inks with some UV photoinitiators to trigger curing—to pure UV formulations, is still progressing. Experts advise printers to make sure they know what they are getting in their ink formulations, to assure compatibility with their press rollers and blankets.

At drupa, Flint Ink debuted its Inuline dual ink/varnish system. The name stands for two systems: the first a special printing ink, Novavit F770 Inuline, which Flint says penetrates particularly quickly, is highly pigmented and has a wax-free formulation, and Ultraking Inuline, a corresponding UV varnish. The dual system permits application of a UV varnish directly inline on a conventional sheetfed offset printing ink without using a primer. A second element of the Inuline system delivers extremely high gloss rates with a water-based coating. The same Novavit F770 is used, this time combined with a special Novaset 7302/100 water-based coating.

Flint also offers the line of ArrowLith UV curable inks for use on coldset webs and newspaper presses. Recipient of a 2005 PIA/GATF InterTech Technology Award, the inks were the first UV products suitable for coated and supercalendered substrates as well as newsprint. With a tack similar to conventional news ink, the inks have opened he door for coldset and newspaper operations to move into commercial insert work.

On the LED front, Toyo's debut of the FD-LED UV curable inks was accompanied by an explanation of how LED inks and the LED-based process will differ from conventional UV:

Conventional UV lamps use arc discharge luminescence, notes Toyo, while LEDs harness the electroluminescence of semiconductors. This is what makes LED cut energy costs. The light emitted by LEDs does not contain any infrared, so the amount of heat generated is minimal. This makes it possible to print onto films and materials with a low level of heat resistance and minimizes effects of heat on the press, rollers and blankets.

LEDs have a substantially longer life—roughly 12 times as long—compared to other UV lamps, so they need to be changed much less frequently. And LEDs can be turned on and off instantly, eliminating the need for warm up and cool down periods, as with conventional lamps. Since UV curing units are compact, they don't take up lots of space, so they can fit into smaller presses, and have already made a mark in digital presses. Toyo says the range of emission wavelengths for LEDs shows much sharper peaks compared to UV lamps. As a result, Toyo had to develop and optimize new pigments, resin monomers and photo-polymerization initiators to create its FD LED inks. “The collaboration between such new inks and systems will bring about major innovations in conventional UV printing systems, making it possible to save both energy and space,” says a Toyo spokesperson.

UV cured inks and coatings can simplify dry trap printing, and allow for contrasting coating finishes. At drupa, Grebe showed its Weilburger Graphics Senolith Twin Effect coatings. Special coating effects continue to be fashionable and finished printed products are booming, says the company. But many printers are unprepared in technical terms to execute them. Many coating effects require double coating systems or have to be produced off-line at high cost or by means of several machine runs. Twin Effect Coatings simplify the process, allowing matt-gloss and structure-gloss effects to be achieved using printing systems with only one coating unit. Grebe says the effects are created as perfectly as matched coating systems, consisting of an offset printing ink, which is processed in the printing unit and can thus produce the very fine structures, and a dispersion coating in two different qualities. The matte or structure effects are defined via the offset printing ink components. A final overcoat of the whole surface with gloss lacquer brings out the different coating effects and protects the print.

On the digital front at drupa, Atlantic Zeiser showed its Smartcure series LED UV curable inkjet ink, a second generation version. The firm says inks have been developed in-house for difficult surfaces such as cotton, plastics or varnished media. Triangle Digital INX partnered with LED curing specialist Summit UV to develop Evolve UV four-color inkjet ink, shown running with single-pass through-cure with Xaar 1001 piezoelectric printheads. “We've been working with LED-cure inks for some time,” said Ken Kisner, TDI's Sr. VP, CTO “but at slower speeds. A key to this technology's success is formulating Evolve UV to work with Summit UV's unique, new LED. It has the ideal UV wavelength and, importantly, ample power.”

SunJet, the inkjet ink unit of Sun Chemical, also announced at drupa the development of new ink chemistry specifically designed for curing under exposure to UV light from LED. In lab tests line speeds in single pass applications have hit 300 fpm.

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