Analysis of Dot Gain Produced by Interactions of Flexo Plate and Anilox Roll Screen Frequencies

Abstract

Flexography prints on non-absorbent as well as absorbent substrates using liquid ink. With developments in photopolymer plate and anilox roll manufacturing technology, we can print half tone with screen frequencies exceeding 150 LPI (Lines per Inch) where the print quality can be comparable with offset printing results. This has helped flexographic printer to reproduce black-and-white, single color tone and full color graphic original, satisfying the printing and packaging needs of many customers. But unlike other printing technologies in flexographic printing screen frequency of plate i.e. image carrier and engraving line frequency of anilox roll collectively affect smoothness and uniformity of reproduced half tone image. Furthermore the LPI of screen used in plate making also adds to variation in tonal reproduction. In the presented work 3 line frequencies expressed in CPI (Cells per Inch) of anilox roll and 5 screen frequency of image carrier are selected and their effect on print characteristics is studied using plot of theoretical dot area against apparent dot area. Given the sizable capital investment involved in manufacturing of anilox roll, this work is appropriately directed at finding optimum combination of screen frequency and line frequency required in minimizing secondary moire and maintaining print quality without varying screen angle and engraving angle.