Starch in the topcoat reducing starch-induced print mottling to enable higher starch use in the top coating of sheet offset papers and folding boxboard

It was evident from the many laboratory tests and trials in two paper mills that top coating colours can contain much higher amounts of starch than previously assumed without having adverse effects on print quality. The starch-containing coating colours caused no problems in the coating machines of the project partners - neither during colour preparation and processing nor during coating. The print quality of samples produced in the project was comparable to that of the commercial references. A slightly reduced optical quality and few coat ruptures were the only problems noticeable when using more starch in the top coating. Because the mottling results of samples had differed very little, it was generally difficult to establish correlations between the starch type or starch modification and print mottling - both on laboratory and on mill scale. It was evident, though, that the use of e. g. coating colours with high solids content and of a good-quality coating base leads to satisfying print results. The industry's widespread prejudice against starch use because it is suspected of having adverse effects on print quality could not be confirmed by the pilot plant and mill trials conducted in the project.