Polymerization of Sheet-Fed Offset Ink Vehicles, 2003 Advanced Coating Fundamentals Symposium Proceedings

The final drying of sheet-fed offset prints involves an oxygen-induced polymerization of drying oils e.g. alkyd resin and triglycerides such as linseed oil. This reaction has been studied in model systems using FTIR. The decrease in unsaturation with time was followed. A comparison with the reduction of monomer characterized by GPC showed that the experimental technique well described the rate of polymerization.

The effect of various amounts of ink constituents such as catalytic driers, antioxidants and ink oils on the rate of polymerization was determined. Ink oils studied were mineral oil, soya bean oil and a monoester used as a replacement for mineral oil in vegetable-oil based inks.

It was found that the polymerization showed an initial phase with no or very limited polymerization followed by a rapid polymerization. The catalytic driers strongly reduced the initial phase while it was highly increased by antioxidants and moderately increased by ink oils. A general conclusion emerging from this work was that the rate of chemical drying of sheet-fed offset prints is highly determined by ink composition and changes in ink composition due to ink setting.