Abstract

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.

Library of Congress Subject Headings

Flexography--Quality control; Flexography--Equipment and supplies--Testing; Printing plates--Testing; Gearing

Publication Date

12-1-2000

Document Type

Thesis

Department, Program, or Center

School of Print Media (CIAS)

Advisor

Lee, Barry

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: Z252.5.F6 W57 2000

Campus

RIT – Main Campus

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