Inkjet Printability and Functional Properties of Synthetic Silicate-Filled Hydroxypropylated Starch-based Dispersion Coatings
Year: 2017
Journal: J. Imaging Sci. Technol., Volume 61, SEP
Authors: Mielonen, Katriina; Ovaska, Sami-Seppo; Koivula, Hanna M.; Jalkanen, Laura; Backfolk, Kaj
Three-ply paperboard was coated using hydroxypropylated starch (HPS) and styrene-butadiene latex as polymeric components and kaolin or synthetic layered silicate as the functional pigment. The coatings were designed to modify the surface characteristics of the substrate to enhance the printability and barrier properties and prevent the migration of mineral oil. The substrates were printed with aqueous dye-based inkjet inks and the ink-substrate interaction and print quality characteristics such as print density, mottling, bleeding, and wet and dry ink rub resistance were determined. The coated substrates showed extraordinarily high print density values and reasonable good dry rub resistance, but low wet ink adhesion, which was ascribed to dissolution of the coating-ink interface. Water vapor transmission rate (WVTR) determinations confirmed that the coatings were sensitive to moisture, since the WVTR values more than doubled when the relative humidity was increased from 50% to 75%. The highest print density (2.66 in the 100% black area) was achieved on silicate-filled coatings, which was 97% higher than that of the uncoated reference. On kaolin-containing coatings, the print density was 60% higher than that of the uncoated reference. The AFM images revealed not only that the starch-silicate coatings were remarkably smooth, but also that they were more homogeneous than the pure starch coating. Although the resistance of the studied coatings to liquid oils was in most cases only moderate, the migration of a gaseous mineral oil simulant through the coated sample was low. A small addition of synthetic silicate effectively prevented the migration of mineral oil in the liquid phase through coatings with a solely starch binder. This work demonstrates that starch-based coatings can be designed for high-quality inkjet printing with dye-based inks and that such coatings can simultaneously inhibit the migration of mineral oil in packaging applications, suitable for e.g., hybrid printing applications. (c) 2017 Society for Imaging Science and Technology.
