Material Retention: A Novel Approach to Performance of Pigment Coating Colors Part 1. Laboratory Evaluation, 2006 Coating & Graphic Arts Conference

To eliminate a misting problem at 1800 m/min, a mill had reduced the starch proportion in the more critical topside formulation. For reasons of economy and printability, an increase in the starch level was desired.

It is known that certain additives that influence rheology can also reduce misting. Hyper-branched polymers are selectively constructed using polyvalent building blocks. The advantage of this procedure is that a well-defined molecular structure with respect to molecular weight and hydrophilic/hydrophobic regions can be generated. During pilot trials using a formulation containing 4 parts starch as a co-binder, one specific hyperbranched polymer significantly outperformed two other rheology modifiers with respect to misting reduction.

In another pilot series, an LWC formulation with 5 parts starch plus 7 parts latex could be run without misting at 1700 m/min and 8 g/m² coat weight. However, a reversal in the binder composition to 7 parts starch plus 5 parts latex led to misting under the same conditions. The addition of 0.4 parts of the same hyper-branched polymer to the latter formulation not only eliminated the misting but also enabled the speed to be increased to 1950 m/min despite the fact that due to hydrodynamics the coat weight had increased to 10 g/m² per side.