Shoulder Angle Determination with Flexographic Photopolymer Plate Material

The shoulder angle and relief depth of dots on photopolymer plate material are hypothesized to be critical variables in flexographic continuous tone image reproduction. Prior to this research, shoulder angle had never been measured and therefore, only educated guesses could be made about how the plate making variables of face and back exposure effect shoulder angle. By utilizing scanning electron microscopy, the physical dot shoulder angle of various face and back exposure combinations were measured and statistically analyzed. The resulting printing dot areas were also measured and statistically analyzed. The following conclusions were drawn: ( as face exposure time increases, shoulder angle increases, ( as dot area increases, shoulder angle increases, ( conventional 150 line screening results in greater shoulder angles than stochastic screening, ( less face exposure results in larger differences in shoulder angle by dot area, ( as shoulder angle increases, dot gain increases, within a given relief, ( both dot gain and shoulder angle plateau at the midtones.