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FLEXO Magazine : August 2014
and contrasts conventional UV flexo printing with LED UV flexo printing. Variables ana- lyzed include: • Energy consumption • Substrate temperature under lamp • Ink color gamut (impacted by ink opacity) • Curing speed • Curing effectiveness • Ink composition distinctions • Ink cost One of the most notable disadvantages of conventional UV printing is the substantial heat generated by the lamps. This is partic- ularly problematic when working with heat sensitive sub- strates like film. Films generally are made from a polymer, whereas paper is generally made from trees. Plastic is much more susceptible to heat damage, therefore making it prob- lematic with conventional UV film printing or packaging. Because of this, only certain types of films can be used. The thinner the film, the more likely it will shrink or break on press. The heat limits the type of substrate convention- al UV can print on—exemplified by the lack of ability to print on heat shrinkable sleeves, also known as shrink sleeves. Shrink sleeves are made from thin plastic polymer that has the ability to mold to a product when heat is applied. LED UV runs much cooler but it also pro- duces light in a different portion of the UV spectrum. The actual unit produces signifi- cantly less heat than that of conventional UV. They both have different UV wavelengths and the photosensitive composition of the ink must be customized to the curing system. Therefore, most conventional UV ink systems do not work the same with LED lamps and in turn, the ink must be reformulated to be compatible with the LED UV wavelength. With these changes in ink composition comes differences in ink viscosity and ink opacity. This change directly affects the ink gamut after print, either increasing, decreasing or altering it completely. A color gamut for a printer is a visual representation of what the printer can print. This affects the quality of the work when color matching the final product to the image that the printer or the client has digitally represented on screen or in a proof. There are some significant challenges to UV curing. Among them: UV inks cost more than conventional (water or solvent based) inks, and lamps and energy consumption are expensive in comparison to simply drying. In addition to standard flex- ographic print, flexographic food packaging runs the risk for potential migration of uncured material from the substrate to the food, poten- tially causing contamination. Ultraviolet cur- able inks do not make sense for all packaging applications but in many cases, UV inks could be more widely used in the industry to take advantage of UV benefits. Printers now have an option to choose to use conventional UV or LED UV, and this knowl- edge will allow printers to justify their choice. UV CURING: MERCURY VAPOR The primary method of UV curing in flex- ography is the use of mercury vapor lamps. Mercury vapor lamps are efficient in compar- ison to standard lights. One of the advantages to mercury vapor is the lifetime of the bulb— about 24,000 hours with a clear, bright white output. After 24,000 hours, the bulb starts to dim and curing quality diminishes. They are a high intensity light, most widely used in factories, warehouses and sports arenas as bright overhead lights. The conventional mercury vapor lamps produce UV light in AUGUST 2014 | FLEXO 31 April 27 – BALTIMORE / USA April 30 – BALTIMORE / USA May 21 – BAD OEYNHAUSEN / GERMANY May 22 – BAD OEYNHAUSEN / GERMANY June 25 – JAK ARTA / INDONESIA September 17-18 – CHARLOTTE / USA September 18-21 – ISTANBUL / TURKEY September 26 -30 – TAIPEI / TAIWAN October 13 – JEDDAH / SAUDI ARABIA October 15 – RIYADH / SAUDI ARABIA October 20-22 – MINNEAPOLIS / USA November 14-17 – SHANGHAI / CHINA Enjoy 100% print quality! twin_check 2.0 WORLD TOUR 2014 increasing Productivity and Quality solutions iPQ_solutions More than 600 satisfied customers rely on our modularity: iPQ www.eltromat.de/en/worldtour2014 Be part of the show: iPQ_2x9"_Nr36_EN_140709.indd 1 09.07.14 14:13 Lena Haidar (left) and Natalee Consulo, presenting the findings of their report at Forum 2014.