Surface smoothness: determination of sheet topography using Shadow Moire method.

APPLICATION: The Shadow Moire method can characterize dimensional instability problems in lightweight papers in a non-contact, nondestructive manner.

The Shadow Moire system can be used to characterize the surface topography of paper and to study the problems of dimensional instabilities. Armed with this technique, we performed a number of experiments. One experiment illustrated the usefulness of the tool in measuring not only curl but also the directionality of curl. The technique was also used to separate curl and cockle in terms of an appropriate length scale, for which several types of filtering and computational techniques were utilized.

To determine the influence of changing humidity on cockle, we subjected a sample of paper to cyclic humidity conditions ranging from 50% to 85% RH at a constant ambient temperature. The surface topography of the sheet was measured after each humidity cycle. The results showed that the most severe cockle occurs during the first cycle, after which the change in cockle is relatively slight. Consequently, if paper is stored in a warehouse in which the humidity is constantly changing, even the first cycle of change will be detrimental to the dimensional stability of the paper. View this paper online at http://www.tappi.org/index.asp?pid=32225&ch=1

Barry Hojjatie is an assistant professor and engineering coordinator in Physics/Engineering, Valdosta State University, 1500 Patterson St., Valdosta, GA 31698. Douglas W. Coffin is an associate professor of Paper Science and Engineering, Miami University, Oxford, Ohio 45056. Email Hojjatie at [e-mail] and Coffin at [e-mail].