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FLEXO Magazine : September 2009
76 FLEXO SEPTEMBER 2009 www.flexography.org TECHNOLOGIES & TECHNIQUES is shown in Figure 3 for a litho press with front-end coater. The saving comes from lower speed second foil stamping steps or elimination of the foil film lamination process for foil board. Flexo presses, on the other hand, are ready to take advan- tage of the in-line capability without any modification to the press as shown in Figure 4. Compared to flexo's in-line hot foil stamping, the cost saving with UV metallic coatings comes from faster (i.e. normal) line speed and elimination of all the waste of hot foil film. The waste of the hot foil film (or the cold- foil film in the cold-foil transfer process) can amount to the same linear footage as the primary web in most cases. UV inks work best with the UV metallic coating due to the inherent immediate and short-distance curing mechanism. Oil-based oxidative inks could be used, but the offset can be a problem because of the slow drying process and may cause dry-back (gloss-back) issues when coated directly with UV topcoat. A water-based topcoat can be used, but brilliancy will be affected. All UV systems throughout this in-line foil-on- demand process produce the best foil-like effect and best surface protection. Appropriate procedures and precautions should be taken if oil-based inks and water-based coating are used in the process. The most popular form of UV metallic coating is the fluid version, which offers more brilliancy when delivered through coating application methods, e.g. flexographic, blanket or roller coaters (verses a paste form that is delivered through ink train units of a lithographic or offset presses). It is also applied at a higher coating weight than regular UV flexo inks to achieve a maximum brilliancy. Some manufacturers can provide many tips and best practices that will help make the transition to these coatings easier and enable all the poten- tial advantages. In some cases, changes in color separation and/or switching to solid instead of screening for silver image might be advised to maintain the intended visual effect. THE SUSTAINABILITY ADVANTAGE In 1992, Radtech Associates commissioned Beloit Corp. to perform a study to confirm that UV/EB-curable technology, including coating and inks, are recyclable. (The reprinted article appeared in the May/June 2005 Radtech Report). This independent evaluation for recyclability confirmed that UV metallic coatings are a sustainable alternative to hot foil stamping and foil board lamination and offers converters the green advantages listed below: • Full recyclability • 100 percent non-volatile and UV-curable • Reduction of carbon footprint by eliminating laminating step • Reduction of waste via application to areas requiring metallized effect • Substantial reductions in energy demand • Reduced transportation cost and emission • Positive performance advantages and economical returns • Brilliance equal to foil board COMPARISON TO TRADITIONAL FOIL In folding carton applications, foil lamination, hot foil stamping, and---the latest addition to the mix---cold foil transfer all can create great brilliance because they are derived from metalized film products. However, as efficient as these processes are, they are not without drawbacks, some of which are listed in Table 1. TABLE 1. Disadvantages of Traditional Foil Application Processes Foil Lamination Foil Stamping Cold Foil Transfer Cost-intensive process Slow process Specialty transfer foil Limited graphics Labor and cost intensive Slower line speed Covers the whole application area Off-line process Print resolution limited Long lead times Printability issues Waste on non-image area Double bumps for white Waste on non- image area Inventory for foil film Adhesion with Inks Inventory for foil films Curling with thin paperboard Difficult for recycling at best Not RFID ready through film FIGURE 3. In-line "foil-on-demand" schematics using UV metallic coatings at the front end coater of a litho printing press. FIGURE 4. UV metallic coatings in-line and press ready for flexo without any modification.