Rheological Studies of Two-Component Inks for Pad Printing on Lenses

摘要

Pad printing is used for colour printing on lenses as it has the ability to print onto curved surfaces and characteristics that are ideally suited to high precision: thin ink films, excellent dot reproduction, the ability to print fine line rulings, superior registration and no moire. The dimensions and the quality of the printed dot, hence the quality of the entire image, is determined by the ink characteristics, the pad surface characteristics, the engraving definitions, the lens surface characteristics and the pad press parameters. The technological status of the cliche plate and silicone pad development as well as printing press parameters are not limiting factors. For an experienced pad press operator it is feasible to combine the different, and generally conflicting parameters and come to an acceptable printing result. The ink characteristics, however, are the least controlled, and yet they have an enormous impact on not only the printing behaviour, but also on the final dot definition and colour quality. A limiting factor is the availability of inks with appropriate printing characteristics. Up to now two-component inks for printing on lenses have been developed for their adhesion and hydro expansion behaviour, rather than to accommodate printing requirements. The aim of these rheological studies is to establish the connection between ink printing behaviour and ink rheology. The approach is, firstly, to study the rheological behaviour of the ink and its main components, such as the binders and slurries, and secondly to find a rheological procedure to simulate the behaviour of the ink during printing.