Considerations on bulged-out print shoulders due to mesh depression and high ’emulsion over mesh’ in screen printing

Abstract

In screen printing sometimes at the edges of an ink deposit that is wider than a few millimetres a phenomenon occurs, which can be described as an elevated edge or better as bulging-out shoulders. This can be a print quality issue if subsequent overprints need to be carried out. The shoulder bulge-out effect typically occurs if the stencil build-up is not well adapted to the targeted type of print pattern (e.g. fine lines vs. large solid tone areas). The effect is described in screen printing textbooks and some scientific articles but not yet tackled theoretically. As an approach, here a simple model, assuming a quasi-infinite line as the pattern to be printed is used. The model combines the elongation of the mesh caused by the mesh tension and the additional stress applied by the squeegee with material properties and calculates the depression of the mesh towards the substrate during the squeegee movement between the two edges of the stencil opening. The developed relationship ends up in an equation that is solved numerically by means of a look-up-table (LUT) approach. Graphs are derived that show the dependencies on print line width, stencil build-up, stresses applied and materials used.