An Investigation into the effect of plate hardness, and surface speed differential on flexographic gear marking

Publication Year:
2000
Usage 658
Downloads 634
Abstract Views 24
Repository URL:
https://scholarworks.rit.edu/theses/3796
Author(s):
Wirojrungson, Wisit
Tags:
Printing
thesis / dissertation description
Gear marking is a print defect in flexography. It appears as a uniformly spaced pattern of lateral alternating dark and light bands along the web length corresponding to the distance between gear teeth. A comprehensive definition characterizes gear marking as a regular pattern attributable to metal burrs, nicks, debris, or other flaws that lead to unsmooth movement somewhere in the mechanical system of the press. Gear marking can be caused by a multitude of different factors. In most cases, gear marking results from more than one phenomenon. The objective of this study was to investigate some factors that were expected to contribute to both the causes and the severity of flexographic gear marking. The factors studied (independent variables) included plate hardness, and surface speed differential between the plate image area and the substrate when gear mark severity was the dependent variable of the study. The test target were designed and printed on the RIT's Mark Andy 4120 System narrow-web press. To study the effect of plate hardness, three plate types with different hardness, 40 Shore A, 50 Shore A, and 60 Shore A, were used. To study the effect of surface speed differential, two types of stickybacks, 0.015 inch and 0.020 inch, were used to create variations in surface speed differentials. Six pressruns were performed; the first three pressruns were of three plate hardness mounted on 0.015-inch stickybacks and the others were of three plate hardness mounted on 0.020-inch stickybacks. A group of thirty observers at the Rochester Institute of Technology were asked to participate in press sheet visual evaluation by ranking six sample press sheets in terms of gear mark severity. The Verity IA software was used to measure the horizontal bar defect indices on sample sheets of six pressruns for the quantitative analysis of gear mark severity. The results indicated that plate hardness and differential in surface speed affected the gear mark severity in flexography significantly. A lower plate hardness will produce more noticeable in gear marking than a higher one. A higher differential in surface speed will produce more noticeable in gear marking than a lower differential.