One of the important required steps to eliminate a web-coating defect is to insure that correct name is initially given to the observed defect. This is important because there is no standard naming convention for the many defects that can be created in the web coating process. These defects often have rather nebulous, hard‑to‑define characteristics. As a result, there are a wide variety of names for the same defect, the same name may be given to different defects and defects that appear similar can have a wide variety of causes. Typically, the first observer of the defect gives it a descriptive name, which then becomes the official name. The second observer may give it a different name. Thereby giving the same defect two names.
As a result, giving an incorrect name to a defect can seriously complicate the defect elimination process. The name often implies a cause and suggests a process to eliminate the defect. For example a bubble is a clear round spots with no coating in the final coated film. They are caused by air bubbles in the coating, which inhibit the wetting of the substrate under the bubble. Thus naming a defect as a bubble implies eliminating air in the coating, which may not be the cause and can result in wasted effort and not solving the problem. Also, since the same defect may have many names it complicates searching the literature to get useful information. Another factor is, that there may be a lot of information on the previous defect reduction efforts. However; without the correct name it can be difficult to find the information needed for a rapid solution to a problem.
Table 1 list the 14 names that are routinely used to describe a defect that is a series of lines running in the machine direction down the web. The most widely used name is ribbing but all of the others are in use.
There are several actions that can be taken to minimize this defect. Do not initially give the defect a name. Characterize the defect by physical appearance, visually with a microscope and by chemical analysis. Check references attached for defect information to help identify the defect. Develop an internal database to store results for later retrieval. The next blog post will present more details on developing a personal defect database.
Table 1: Various names for the ribbing defect
Ribbing Barring Coating Lines Comb lines Corduroy Md lines Phonographing PuckersRake lines Railroad Tracks Rib pattern
Defect References
Cohen, E.D., Gutoff E. B, Coating and Drying Defects Troubleshooting Operating Problems, second edition, John Wiley and Sons, New York, 2006.
R. Duane Smith, ed, Roll and Web Defect Terminology, 2nd Ed. TAPPI Press Copyright: 2007
Cohen, E. D, “AMICAL Defects Lexicon”, AIMCAL, Charlotte, NC. www.AIMCAL.org
McCrone Atlas of Microscopic Particles www.mccroneatlas.com/