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Summary:
Water-based inks represent an exciting trend in the world of packaging industry and provide a technology for printers to eliminate VOCs (volatile organic compounds) emissions. There has been significant growth in the usage of waterbased ink in the flexo packaging market, such as labels, corrugated products, paper products, and some of the polyethylene products. Over the years, ink manufacturers have worked to improve ink properties in order to achieve better print quality. Rheological properties have major impacts on flow of inks and are fundamental in determining ink transfer in flexo printing. Of special interest are how waterbased flexo inks behave and whether the rheological characterization has any power in predicting press performance of inks. In this paper, measurements of rheological properties of six water-based flexographic inks are discussed. A Flexo trial was performed on a three-color ComCo Commander flexographic press. Print performance was analyzed and interpreted, and was correlated to ink rheology data. Comparisons were made between fresh and aged inks of the same color, as well as between different colors. Water-based flexo inks exhibit viscoelastic behavior under oscillatory and steady shear. The creep test also shows the viscoelastic behavior of these inks. It was found that rheological properties of an ink are more related to varying ink formulation, such as the choice of binder polymers, pigments, and the presence of additives in a system. A difference on the press performance was noted between the fresh and aged inks. Better print fidelity and higher print density was found in less shear-thinning inks, and print qualities are also related to ink viscoelasticity.