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PRESSROOM: A COAT OF MANY COLORS

Mar 1, 1999 12:00 AM


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A printer's ability to utilize a growing range of press-applied coatings is evolving into a central production capability to meet increasingly demanding customer requirements. Today the question is not whether or not to coat, but rather which coatings to apply in order to achieve specific results. The pervasiveness of on-press coating is illustrated by the large percentage of new sheet-fed presses equipped with coating towers.

"About 85 percent of Heidelberg's six-color and up 40-inch presses are now purchased with coating towers, including a few multiple inline configurations for packaging applications," reports John Dowey, director of marketing for the company's Speedmaster presses. "Ninety-plus percent of those machines are equipped for aqueous coating, with the balance outfitting for UV coating." "In the half-size press range, such as the Speedmaster 74, the number of presses equipped with coating capability drops to around 70 percent," adds Dowey.

Other press manufacturers report the same trend. "Nine out of 10 of the 40-inch, six-color presses installed by Komori over the past two years were equipped with coating capability," according to Harry A. McMillan, Komori America's executive vice president. Noting that relatively few 28-inch machines go into the packaging industry (in which almost every press has coating capabilities), McMillan adds that about 80 percent of Komori's half-size presses are coating equipped.

Most other sheet-fed press manufacturers report similar percentages. Rudy Valenta, manager corporate sales at MAN Roland, notes that all of the Roland 900 series are shipped with tower coaters. These presses are available in 44-, 51- and 56-inch models. While an increasing number of new presses are being equipped with coating capability, Jack Bronson, sales manager of Dahlgren, notes a similar interest in upgrading older equipment. "Commercial printers are finding that they may be at a competitive disadvantage without coating capabilities.

Those without this capability realize that they will need to add coaters to their existing presses at some time in the future."

For retrofits, Dahlgren offers a blanket coating unit used in conjunction with the last printing station so that the unit may be used as a coater or printer. This approach, which limits the printing capacity of the press, reportedly can be overcome with Dahlgren's LithoPlus unit, which makes it possible to use the last unit simultaneously as a coater and printing station--a feature especially attractive for four-unit presses.

About 85 percent of Dahlgren's installations are currently used for aqueous coating, although there is a growing interest in UV, reports Bronson.

Packaging web presses--offset, flexo and gravure--are frequently equipped with coaters in a variety of configurations. Publication webs used for catalog and magazine printing are rarely, if ever, coating equipped. Heatset webs, such as the Heidelberg M 600, doing high-end work such as brochures and annual reports, often are equipped with aqueous coaters. So why are interest? The use of coatings has grown rapidly over the past few years, according to Komori's McMillan, because of the wide range of product and productivity enhancements that the technology offers.

Creating eye-appealing gloss with spot, pattern or full sheet coating is a long-standing application going back to the earliest days of varnishing. Similarly, coatings are used to protect a variety of printed products, from covers to packages.

In commercial printing, coaters often are used to increase efficiencies, observes McMillan. Sheets can be dropped out of the delivery, flipped over and put back through the press after a short drying cycle, eliminating the long waiting time otherwise required, according to Heidelberg's Dowey.

"Printers have discovered that coatings can help move the job through the shop, getting sheets back on press or into the bindery quickly," comments McMillan. These "productivity" enhancers can be very light coatings formulated for quick setup, giving protection to the wet ink underneath without materially affecting the gloss or appearance of the sheet. MAN Roland's Valenta adds that coatings increase slip and eliminate spray powder, speeding jobs through the bindery. This is a difficult productivity improvement to measure, according to the sales manager, but it's real nevertheless.

Aqueous coatings are clearly the most widely used. UV is gaining in popularity, and electron beam curing is limited to a small number of packaging web installations. Each of these types of coating has its own set of characteristics and its own group of enthusiastic proponents.

Collectively, these coating types are pushing previously dominant solvent-based coatings and varnishes into limited niche markets as printers adapt to meet stricter environmental regulations and the customers' need for high-quality appearance and product protection. What was once a simple off-line varnish approach has evolved into complex on-press chemistry, in some cases involving double in-line coating.

"Coating is a fast-moving and situation-specific field, making it difficult to be knowledgeable across the spectrum of the technology," notes Mike Hecht, industry consultant, coating/drying guru and sometime curmudgeon.

"Coating is at the tail end of the press, but it is the coater after the last print station and the dryer system prior to the delivery pile that can determine the efficiency and productivity of a printing press. Coating adds versatility to print--the ability to create special effects of market value to the printers' customers. But coating must be approached with knowledge as well as TLC--tender loving care," Hecht emphasizes.

"The equipment is important, but the key to success is in the relationship between the printer and the coating materials' manufacturer," notes Komori's McMillan. "All the mystery of coating takes place in the bottle."

One of the difficulties that press manufacturers encounter when selling a coater-equipped press is to translate the customers' requirements into the proper equipment configurations.

The most productive results usually are obtained when a printer creates and works with a strategic partnership team that includes press coating and dryer equipment manufacturers as well as ink, coating materials, chemistry and substrate suppliers. Active customer participation on the team is useful to ensure that all end-product requirements will be met. The coating team plays a key role in equipment and materials selection, as well as providing continuing operating assistance.

For many commercial printers, coating simply means using aqueous solutions, adding a coating tower, dryer and press extension between the last printing unit and the press delivery. There are, however, a variety of other configurations and materials to meet specific end-product requirements enabling printers to differentiate their capabilities.

Although aqueous coating dominates the market, there is a growing interest in UV primarily because it provides the highest gloss. However, two coating towers and an IR dryer, as well as a UV dryer are required. Two coating towers are required because wet lithographic inks and UV coating solutions basically are incompatible.

With a double coater, the first coating unit puts down a primer that provides a barrier between the wet litho inks and the UV coating, which is put down in the second tower. This approach requires a higher level of capital investment and has higher operating costs than aqueous, but is claimed to provide higher gloss and more flexibility in using coatings to achieve special effects. In addition to putting down primer and UV coating, double coaters are used for applying double thick blister coating, micro-fragrances, scratch-off gaming cards and a variety of specialty packaging coatings.

On-press sheet-fed UV coating also requires a shadowless delivery gripper system on the press. This is necessary to avoid shadows on the coated sheet during the curing exposure, which results in wet coating remaining on the sheet.

The delivery end of the press should be high-temperature prepared and corrosion-resistant in order to prevent damage from the UV curing system.

The sheet guides in the delivery, which are floating the sheets along on a cushion of air, require a water-cooling jacket in order to remove heat from the delivery area. Some sheet-fed press manufacturers routinely equip all of their presses with these features. They are essential to the successful installation of a UV coating system.

When selecting a coating system, printers must decide if the coating is to be accomplished with a standard set of rubber or chrome rollers or with the use of a laser-engraved anilox roller and a chamber-type doctor blade. The advantage of the anilox roller approach is that it is possible to apply heavier coating weights, as well as to more precisely meter and control the thickness of the coating being laid down.

Anilox systems are said to be largely independent of press speed and are less affected by coating solution viscosity fluctuations. The chambered doctor blade and anilox roller system finds application with specialty coatings such as metallics, some matte coating materials, blister coats and moisture, as well as other barrier coating materials.

For routine aqueous coatings, many believe that the roller coating approach, although less precise, is nevertheless better because there are fewer consumable items such as seals, wiper and scraper blades. Standard rollers also take far less time to clean than chambers and anilox rollers. Anilox coating is more commonplace in packaging applications than it is in commercial printing.

Cosmetic and high-end packaging producer Arkay Packaging's recent installation of an MAN Roland 700 combination press for its Hauppauge, NY plant illustrates the variety of configurations possible. Arkay's press consists of seven offset units and two flexo or anilox tower coaters, extended delivery, UV and IR drying, computerized inking and TriServices temperature controls. The configuration has been instrumental in printing high-end metallics and pearlescents and moving work from gravure, reducing start-up costs.

Another approach to utilizing UV is a hybrid technology called Co-cure. The printing inks used are a mixture of standard offset pigments and a vehicle with UV reactive components. Using the hybrid inks, four or more colors are put down in normal sequence, dried, UV coated and cured. The advantage of the approach is that it keeps the drying and coating processes at the end of the press. Heidelberg's Dowey reports that this process produces some eye-popping materials.

One of the problems in coating is the time and expense required to make a rubber or photopolymer coating plate for spot or pattern coating. Spot and/or pattern coating is done with a relief plate that must register precisely with the printed material. Achieving this can be difficult, costly and take an inordinate amount of time in the production schedule. To overcome this problem, consultant Hecht has developed and patented an approach simply known as "Mike's Method." This process, which is installed in more than 100 packaging plants, involves a press-coater calibration, a specific method or process, and materials.

The first step in Mike's Method is to use a series of test plates to calibrate the coater to the printing units, in effect establishing a coater profile. Using the profile, a "Mike plate" is made on a CAD/ CAM plotter-cutter in the die shop. With the plotter-cutter, extremely intricate designs and/or multiple ups can be produced for a 40-inch press. This takes about 15 minutes to 20 minutes. It's also possible to cut the plate manually.

According to Hecht, the nature of the plate materials are such that they carry more coating materials than traditional plates while providing for a clean release. Users indicate that the Mike plate has run for one million to two million impressions.

The advantage of Mike's Method, according to Tom Meyers, vice president, marketing, Chicago Packaging Co., is that one can quickly produce a low-cost spot/pattern coater plate in-plant, off-press. The plate registers correctly, claims the exec, and runs well on press.

Electron beam (EB) technology is widely used across several industries. In the graphic arts, EB is used by material suppliers to coat substrates for printing, particularly those used in packaging applications. From the perspective of on-press printing and packaging industry applications, EB is limited to a few web installations and can best be described as a technology in waiting.

Electron beam installation requirements are such that the process is not considered to be suitable for sheet-fed presses. For web installations, capital equipment cost is relatively high and EB coatings and inks are more expensive than UV with little prospect for a change in that relationship. EB does have an advantage over UV in that the energy costs to operate the curing units are about half of the UV energy costs. EB industry forecasts indicate that the cost of the equipment will come down.

EB manufacturers also are talking about building units to fit narrow web presses. With the current growth in narrow and mid-width flexo equipment, this could result in making EB more attractive for label and some folding carton applications.

If EB does become more attractive for in-line coating, it is expected to appeal to food packagers for its lower odor and because it provides a more thorough cure, thereby improving physical properties such as scuffing. Until EB becomes cost-effective for on-line coating applications, however, the technology appears to be on the sideline, awaiting breakthrough developments.

While water-based materials dominate on-press coating, they also can be the source of nasty problems for printers. A common problem in the summer is heat blocking with water-based coatings--individual sheets meld together and become one solid mess.

The mess is created by a combination of environmental conditions and the fact that water-based coatings are thermoplastic and will re-soften with heat. This is a characteristic that can be minimized by effective drying of the coating during delivery to the load.

Many plants are not air and humidity conditioned, resulting in elevated temperatures and humidity for work in process. High humidity can cause a retardation of fountain solution evacuation from the ink film, causing the ink under the coating to set and dry more slowly. The combination of elevated heat and moisture, along with the pressure of a load, can result in coated sheets simply sticking together--a condition that can occur even under an ideal environment.

Blocking can, to a degree, be avoided by selection of the best water-based coatings for the environment. Coatings can be enhanced by various agents to improve heat block resistance. Ensuring that infrared and hot-air equipment is working at the correct temperatures also will help to avoid blocking.

Unless a plant is properly temperature- and humidity-controlled, special care must be given to the use of aqueous coatings during hot and humid summer days.

Water-based coating also can be the source of difficult latent problems for printers. A customer-okayed coated job can look good coming off press, only to become unacceptable days, weeks or even months after delivery. Ink colors can shift, fade or bleed.

While there are a number of potential culprits that might create this type of problem, the use of water-based coatings that are incompatible with the inks is the most common cause. When aqueous coatings are applied to a printed sheet, the coating "wets" the previously printed inks. If the components of the coating material and the wetted inks are uncompatible, the inks will bleed, shift in color or appear to yellow in the light-colored, pastel or tint areas.

To avoid the problem, specify bleed resistant colors when ordering ink that is to be aqueous coated. Inform coating and ink suppliers about job conditions, including furnishing sample stock to perform pre-production compatibility tests. Even then, there are no absolute guarantees because of the wide range of influences encountered during the production process. The pervasiveness of coating in many printing and packaging market segments does not mean that a majority of printers are proficient at it or that the opportunities presented by the technology are being fully exploited.

Background research suggests that creative emphasis on coating could boost many printers' productivity while enhancing their customers' products--plus providing a point of market differentiation. It is an opportunity worth investigating. Consider initiating a strategic partnership coating team for a coating payout.

Coating gets little respect--and less attention. Prepress workflow, computer-to-plate and other digital technologies are where the hypesters focus their attention--and with good reason. But in the short-run market, there may be more opportunity for profitable marketplace differentiation with coating technology than with digital technology. Virtually all package printers and a high percentage of commercial printers operating 29-inch and larger sheet-fed equipment offer coating capabilities. But, for the most part, it's a mundane coating targeted toward gloss and scuff resistance. There's much more that can be done. Relatively few commercial printers are taking advantage of the opportunities possible through innovative coating. Most are stuck in the coatings "commodity" trap. If you want to take advantage of this underserved market opportunity, here are a few tips. Create a coating team consisting of your key people, along with a full spectrum of coating and materials suppliers, then add in a customer or two. Develop a plan and take action. It could pay big dividends.