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Summary:
The rheological properties of keyless and conventional lithographic printing inks from U.S, European, and Japanese sources have been characterized using a Carri-Med stress-controlled rheometer. The Herschel-Bulkley equation was used to fit the experimental data in the low to medium shear rate region, from which the shear thinning index, the consistency index, and the dynamic yield value were obtained. It has been shown that a high degree of linear correlation and a distinct difference between keyless inks and conventional inks exists. It has also been shown that the dynamic yield value of a conventional ink is higher than that of a keyless ink with the same consistency index. A high degree of linear correlation between thixotropy indices and shear thinning indices was observed for all inks. From a rheological perspective, keyless inks can be engineered from standardized, measurable parameters without the need for extensive and expensive on-press trial and error testing.