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FLEXO Magazine : March 2011
Technologies & Techniques Solvent-Free Lamination on Water-Based Inks A Matter of Chemistry and evolving Technology By giancarlo Caimmi and Brooke Mullins Increasing interest in coating and lamination have marked the conversion of flexible substrates in North America over the last 10 years, with converters recognizing significant op- portunities to create profits. Small and mid-sized converters in particular are attracted to the opportunity to expand their in-house capabilities by including coating and lamination in their processes. Major converters have focused on new technologies, new developments and new methods with the aim of improving quality and cutting production costs. Energy savings and emission reduction have garnered attention from all converters regardless of size, and “being green” is the catch-phrase of the new century. Green and SoLvent-Free Solvent-free lamination, which has been available since the 1980s, presents opportunities for creating profit and cutting production costs today. It requires a low investment in equip- ment, offers energy savings of up to 80 percent and has no emissions, making it the perfect technology to consider in the current economic climate. In solvent-free lamination, the resin at the base of the adhesive formulation is not dissolved in a solvent or dispersed in water: The “cur- ing” is produced by a chemical reaction and adhesive is coated in a 100-percent solid state. Although solvent-free lamination pro- duces no emissions, there are a few side effects to be considered. Lamination is performed with a low initial tack and very low shear resistance, so machinery needs to be adjusted accordingly to guarantee proper tension control. Curing takes time as the chemical reaction expands the size of the molecules and transitions adhesive from fluid to solid. Yet despite the wait for curing, the pros of solvent-free lamination outnumber the cons, which is why the consumption of solvent-free adhesives has increased on a global scale, with significant growth in North America in particular. The U.S. and Canada are well-known as countries where flexo printing technology is winning the race in flexible packaging. Both countries have stringent local and national regulations regarding emissions. The U.S. comprises a significant market share of water-based inks, with more printers using these inks than in any other country. Therefore, it is easy to see where converters involved in the use of water-based inks saw an opportunity in solvent-free lamination: Water-based inks and solvent-free lamination seem like the perfect “green” marriage. There is one challenge, however. The chemistries of water- based inks and solvent-free adhesives are not perfectly com- patible. Many water-based inks contain amines, which are introduced into the ink formulation to help with wet out and to solubilize the resin to alter the dry rate. Residual amines Moving Toward a Solvent-Free Future • Solvent-free lamination requires a low investment in equipment, offers energy savings of up to 80 percent and has no emissions • The chemistries of water-based inks and solvent-free adhesives are not perfectly compatible, but technol- ogy is evolving to overcome this challenge. • Advancements in water-based resins, pigment dis- persion technologies and the solvent-free adhesives themselves have allowed for a greater latitude in formulation. nordmeccanica demonstration at 2010 earth Day event. Photos: nordmeccanica remain in the inks after the drying process and can react with the isocyanate contained in the solvent-free adhesive and inhibit curing. This results in partially uncured adhesive and incomplete lamination bonding, which is why substrates printed with water-based inks and laminated to films using solvent-free adhesives are not known for reaching lamination bonds at the high end of the curve. In recognition of the poten- tial market in solvent-free adhesives, adhesive manufacturers, ink manufactures and machinery manufacturers have been working hard to solve this problem. Solvent-free lamination requires solid technology and state- of-the-art equipment for coating and lamination. The adhesive is coated at high viscosity, and it is paramount to maintain a constant coating weight during a production run to reach target bonds and optics. Laminating substrates by using adhesives with a significantly low shear resistance requires machinery built according to the highest standards in web- handling technology. These considerations are critical when laminating water-based printed films, especially water-based printed bio-degradable films. It has been proven that laminating-machine technol- ogy, once properly engineered, makes it possible to handle combinations of webs, inks and adhesives. A proper coating technology such as the patented 5 Roller System will guar- antee constant coating weight in both web directions. Of course, final bond results are in the hands of adhesive and ink manufacturers because the chemistry of both products is what makes it possible to achieve significant results. To testify to the importance of cooperation among play- ers within the flexo industry, Nordmeccanica and Dow have joined forces with their technical partners to create annual Earth Day events. The Earth Day events of 2009 and 2010, held at the Nordmeccanica location in Edgewood, N.Y., allowed participants from all over the U.S. to discuss and demonstrate the state 50 FLeXO MArCh 2011 www.flexography.org FLX_March11.indd 50 3/18/11 1:33 PM