PRESS DRYING/CURING--The ABCs of Press Drying

BY SCOTT POLK

For printers looking for a cure to their press drying woes, it would be wise to brush up on your alphabet skills. That's because the current solutions have names like UV, IR, WIR, EB and TDS. And if that sounds like a bunch of hot air, well, that's another option, too.

Though this multitude of choices can be staggering to someone not versed in the world of sheetfed and web press drying systems, it is also a blessing since the different options have pluses and minuses that benefit a variety of applications.

Ultraviolet (UV) curing is a favorite among printers because of its instant curing properties, the elimination of spray powder and the ability to achieve high gloss. Baldwin Technology offers two UV systems, filtered and unfiltered, depending on the customer's requirement, relates John Chapman, director of drying and ink systems.

The filtered system consists of a medium-pressure mercury vapor UV lamp that produces approximately 25 percent UV output, 25 percent white light and 50 percent infra-red (IR). In some UV curing processes, such as plastic, foil or lightweight substrates, the heat of IR causes problems. To alleviate this, Baldwin Technology places quartz filter tubes in front of the UV lamp. De-ionized water is pumped through these tubes, allowing pure UV to emit while filtering out 90 percent of the IR, resulting in a cool substrate. There is no need for shutters in this system.

In heavyweight and nonheat-sensitive substrates, unfiltered UV offers the ultimate curing process. Utilizing the same lamp as the filtered system, a perfect cure for inks and coatings can be achieved. To protect the press and operators, the system is both water- and air-cooled, and includes water-cooled shutters to allow the lamps to stay on when the press is not in motion.

"Generally a printer will put in the system best suited to his production," Chapman remarks. "Points that should be considered whether to go IR or UV will depend on end-result requirements."

Another vendor that praises the benefits of UV curing is Prime UV. The company was founded 14 years ago when UV curing was primarily used on sheetfed and label presses. To make the transition to today's web offset presses, Prime UV had to develop a high-intensity, finely focused UV dryer that could be installed on commercial web and high-speed direct mail presses running 2,000 fpm, as well as folding carton and flexo packaging presses running at 1,500 fpm. Because of this development, the UV printing process has become the drying system of choice for all direct mail, security printing, sheetfed offset printing on plastic substrates and folding carton web printing.

"Typically, the capital cost of a complete UV system for a high-speed commercial web press is less than $250,000. For a half-web, or direct mail press, the cost of a wet trapping UV system is less than $100,000," notes Prime UV President Elinor Midlik. "The printer's cost for a UV system is approximately 30 percent of an installed hot-air system. Capital savings are in the neighborhood of 70 percent. Return on investment is less than two years and many times only one year."

Midlik reports that the fastest growing curing/drying technology is the UV process, with a 10 to 12 percent increase in sales every year of the past decade. This popularity is due, in part, to the environmental benefits of the process.

Prime UV has expanded its product offerings with the Diamond Series. It is designed to fit interstation on sheetfed perfectors, as well as commercial web presses and provides high-intensity UV curing of both the top and bottom side of the web, at speeds of up to 2,600 fpm.

Another new offering is the Wide Web UV Processor, designed to be installed after the coating unit on wide-web flexo and offset packaging presses. Available in widths from 30˝ to 125˝ wide, the Wide Web cures high-gloss coatings on preprinted linerboard, multiwall bags, flexible packaging films and bags, folding cartons and corrugated stocks.

"Current industry trends are very strong for UV in the commercial printing market," Midlik notes. "UV lacquer coatings on cover stock, brochures, advertising and posters continue to be the strongest market."

Another feather in the cap of UV curing is its environmental benefits. Since the inks, varnishes and adhesives are 100 percent solids, no volatile organic compounds (VOCs) are generated. This eliminates the need for expensive solvent recovery and solvent destruction systems, reports UV Technology Project Engineer Mark Tausch.

UV Technology's newest equipment offering deals with flexographic printing using UV curable inks, varnishes and adhesives. Recent innovations and improvements that have been made by the flexographic press manufacturers, he contends, have generated print quality that rivals or surpasses that of offset and letterpress. The improvements in the UV curing systems and instant cure of the UV-curable inks, varnishes and adhesives allow these improved presses to run in excess of 750 fpm with excellent print quality and no waiting for post curing before the product can be shipped.

"These features, combined with the ease to change between substrate types and entire print jobs in as little as 20 minutes for an eight-color press, are making flexographic printing presses configured with high-performance UV curing systems the technology of choice to commercial printers," Tausch notes.

IST America offers a variety of products for UV, as well as IR and WIR (short wave infra-red) systems. Andrew Stott, vice president of sales, remarks that UV is best suited for all applications. However, it is used extensively for non-absorbent substrates like plastics, foil-lined papers and boards, and coated stocks. This is because conventional inks dry by absorption and oxidation and, when there is no absorption, then the drying times are considerably extended. Also, for the brightest gloss results with lacquers, total UV applications with interstation curing gives the best result.

IR, on the other hand, is used to accelerate the drying of conventional inks and mainly works by increasing the pile temperature to help the inks to set quicker in the stack. This technique does not normally reduce the levels of spray powder needed to prevent set-off. WIR systems are similar to IR, but are used to dry water-based coatings over conventional inks.

"In our view, UV is the fastest-growing technology and our yearly sales increase in UV systems confirm this view," Stott concludes. "Apart from the obvious traditional markets, UV offers considerable advantages to the commercial printer, whether it be sheet or web printing."

New technologies from IST include dichroic glass reflectors for low heat transfer (IR), but maximum UV reflection, stepless lamp control linked to press speed to optimize UV output to curing needs and units for web presses that do not require extraction to atmosphere.

There's no acronym involved, but Grafix North America believes it has combined the best of all the coating processes with its innovative CoCure process. It provides—in one in-line press pass—a level of gloss and rub resistance previously thought to be obtainable only when running on a double coater or a full UV press. For existing UV coated work or to create a new market niche by providing customers with the uniqueness of UV, the CoCure process is a proven, cost-effective method. Printers with existing tower coater-equipped presses can produce a UV coated sheet in-line without an excessive capital investment in equipment or having to dedicate the press to UV work only.

"The CoCure process has proven to be an economical and competitive method of printing on non-porous substrates, such as plastics, credit cards, metallized foils and other synthetic substrates," relates COO Jeff Miller. "The market opportunities that were once only available to all UV presses cannot be capitalized on by the general commercial printer. This creates tremendous ROI statistics enabling medium-sized printers to further utilize their sheetfed press investment."

Miller adds that CoCure has been installed in the Heidelberg, Komori and MAN Roland showrooms and won the GATF InterTech Award in 1999.

William Fuchs, president of Fuchs DeVries Inc., reports that many of his customers look for versatility in drying systems. The demand is for systems that allow the printer to use various types of coatings on a variety of paper stocks and cure the coatings at maximum press speeds without any risk of picking or blocking the loads. As a result, the company designed a drying package known as the Total Drying System (TDS).

"It is a custom-designed system to meet each printer's unique needs," Fuchs informs. "We also engineered the system to operate via PLC controls and touchscreens. This allowed us to integrate our software with that of the press manufacturers, and now our systems operate within the press control consoles. This integration includes IR, hot air and UV."

The majority of Fuchs DeVries' customers are requesting IR and hot-air drying systems for water-based products. However, with the advent of hybrid inks and coatings, UV curing appeals to printers who desire to UV coat in-line and attain the level of gloss that can be achieved with off-line or second-pass coating.

"We are still supplying more high-volume hot-air drying systems for water-based coating applications versus IR and UV systems. However, the interest and inquiries for UV have increased dramatically," Fuchs reports. "Unfortunately, after the printer investigates what the costs and certain requirements are regarding UV, the decision to move forward in purchasing and implementing the system is sometimes delayed until more thorough investigation is made and return on investment is calculated."

Accel Graphic Systems offers the Tempest hot-air dryer, which uses PTC thermistors instead of IR elements to accelerate the drying process. Heat is generated when an electrical current is applied to the thermistor. Thermistors are self-regulating semiconductors that use a phenomenon called autostabilization to maintain a constant temperature without the need of a thermostat. This approach to drying eliminates the risk of fire because the thermistors approach, but never reach, the temperature where they could ignite paper. This is combined with warm air to accelerate the drying process. It is as effective as IR for drying inks (excluding UV) and water-based coatings, and is much safer, according to Accel. It does not dry UV inks or coatings.

"Because more printers are doing multicolor work, dryers are becoming necessary for faster turnaround time and higher quality printing," points out Vice President Lance Carpenter. "Drying systems also reduce spray powder usage and setoff blocking."

Energy Sciences manufactures electron beam (EB) systems, which are similar to UV in that they use energy to cross link/cure the ink, coating or adhesive. It does so instantly without heat or light. However, EB systems are currently only available for mid- to wide-web presses. Narrow-web EB systems are still in development, reports Rick Sanders, sales and marketing manager for North America.

"My experience indicates that UV currently offers the most potential for the commercial printing industry, but some commercial printers are looking at EB," he notes. "One of the drivers to energy-curable processes is the desire to get away from solvents and VOCs."

Energy Sciences' newest offering is the EZCure EB system. It is a low-cost, compact EB system designed for high-speed curing of coatings and adhesives on flexographic and rotogravure presses.

Another vendor, Printing Research, is designing more powerful drying systems and is more closely targeting the spectrical output of its emitters, reports John Aylor, director of technical sales. The company is also refining its air management systems to control the higher temperatures generated by the improvements. It is also working on improving its Cold Cure UV systems to further decrease heat exposure to plastic substrates, thereby improving the stability of the material during printing and coating processes.

"New and different substrates are being used today," Aylor notes. "Many types of plastics are being printed and coated, bringing with them the problem of controlling their stability in the presence of the heat generated by the dryers in combination with the pressure applied in the impression nips."

SpeedyDry ink conditioner reduces drying times on coated and uncoated, alkaline and acidic, natural and synthetic stocks, Tyvek, polyester and vinyl. Drying times for felt stocks were reduced from 26 hours to 11⁄2 hours, acidic stocks from 24 hours to 3 hours, and coated stocks from 3 hours to 45 minutes.