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FLEXO Magazine : September 2009
www.flexography.org SEPTEMBER 2009 FLEXO 65 TECHNOLOGIES & TECHNIQUES responsibility of the print and graphic communications industry through sustainable green printing practices." The SGP would like to see maximum use of environmentally friendly materials from the print and graphic communications industry. For this reason, it is important to try to replace ink resins made of fossil raw materials with environmentally friendly ones produced from renewable resources. One of the promis- ing new raw materials is corn. Annual production of corn is 560 million metric tons, with half of that amount produced in the U.S. alone.4 The main polymer present in corn is starch. Starch decomposition and derivatization leads to many useful materials used in fluid ink formulations. Dry grinding of corn leads to ethanol production, which may be used as an ink sol- vent or co-solvent. Corn starch can be hydrolyzed to dextrose. Fermentation of dextrose to lactic acid opens possibilities of making chemicals based on lactic acid. PLA (polylactic acid) is a thermoplastic biodegradable polymer which has been successfully used to make biodegradable films for packag- ing, plastic trays, and bottles. Currently, PLA costs more than petroleum derived commodity plastics, but because of its mass production and the possibility to be derived from agricultural residues, it is possible that its price will drop. It is expected that its demand will grow annually by 25 percent5. The drawback of PLA is that it is marginally soluble in solvents used in the ink industry6. It needs to be further de- veloped in order to find application for printing inks. Another application for starch in inks is that it can be plasticized with glycerol and copolymerized with e-caprolactone to form bio- degradable water-based polyurethanes. A sodium alginate mixture with coconut oil along with naturally occurring plant colorants (henna, safflower, turmeric, and goldenrod) as pig- ments have been used to make a screen printing ink7. Polyhydroxyalkanoates (PHAs), along with PLA, polyglycolic acid (PGA), and apolylactic-co-glycolic acid have been recent- ly used for formulating water-based flexo inks in their natural form or formulated with a triblock compound, to improve the stability of flexo inks8. Sakata Ink in Japan claimed successful production of water-based flexo inks based on similar chemis- try. Ink was made of polylactic acid (PLA) and other biodegrad- able polymers, such as polylactic co- glycolic acid, polyglycolic acid, polyvinyl alcohol, and polybutylene succinate which can be used individually or in combinations. Self-dispersible biode- gradable polyesters creating emulsion polymer particles were patented9. They may be useful in biodegradable inks formula- tions with water and ethanol as solvents. Currently, there are few biodegradable polymers available that can be used in the ink industry, mostly due to cost. Biode- gradable polymers must be either enzymatically degraded, or serve as a carbon source for microorganisms10. Polyhydroxyl- actanoate and its copolymers may be used as resins for water- based flexo inks. Poly (3-hydroxybutyrate) (PHB) and copolymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) are other suitable polymers, which can be obtained by bacterial fermen- tation under modified fermentation conditions. Metabolix fer- mented glucose to polyhydroxybutyrate valerate (commercial name Biopol) in a commercial fermentation plant11. The biodegradable packaging market is growing rapidly in advanced countries, especially in the U.S. It will experience an annual growth rate of 22 percent according to one study13. Biodegradable packaging is aiming to use films made of bio- degradable polymers, but it only makes sense to print on them with biodegradable inks. This packaging is printed most often in the U.S. using flexo because of its simple working principle (Figure 1). Flexography is more efficient, more cost effective and more versatile than other printing processes. The prospect of biodegradable packaging using water-based inks offers flexographic printers an opportunity to develop a new pack- age printing market and can provide environmentally friendly products for consumers. But still water-based inks, which most people consider to be more environmentally benign, contain raw materials that are petrochemical-based14. EXPERIMENTAL MATERIALS SBS and CNB substrates were used as substrates for print- ing. Water-based ink includes materials listed in Table 1. with their purpose. TABLE. 1 Water-based ink ingredients and their purpose in formulation Ingredient Purpose Pigment Dispersion Colorant JONCRYL 77 Hard film forming emulsion for water and rub resistance Luron binder Readily bio-degradable resin JONCRYL 2153 Hard letdown emulsion for drying speed and ink stability JONCRYL 60 Transfer, gloss and resolubility JONCRYL WAX 26 Rub and scratch resistance Surfactant (DF-75) Improve wetting and ink leveling Antifoam Foam control Water Diluent INK FORMULATION Ink was blended in 500mL batches in a laboratory electric ink mixer (high speed disperser) with the spindle speed of 1500rpm for approxi- mately 10 minutes. The starting formula- tion was taken from the BASF formulating guide15 for water- based packaging inks (Table 2). Luron binder (15.42 percent solids) replaced JONCRYL® 77 (45.9 percent solids) resin according to the ratios given in Table 2. The Luron binder is the aqueous colloidal solution of an albuminous condensa- tion product from BASF Corp. According to BASF this resin is readily biodegradable16. Luron binder was of much lower solids content than acrylic Joncryl resin; therefore it was not possible to adjust all of the inks to the same value, if higher solids were needed (see Table 3). FIGURE 2. Comco Commander flexo press at Western Michigan University's Printing Pilot Plant.