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In the field of plastic testing, reproducibility is usually emphasized in standard test methods. However, relevancy is at least equally important to end-use applications. In the field of surface testing, relevancy can sometimes be more difficult to achieve.
Both ASTM and nonstandard abrasion tests for plastics are compared with ANSI abrasion tests for photographic film. Mechanisms include falling carborundum, abrasive loaded wheels, soft-hair wheelbrush, and spherical stylus. All give similar rankings when testing simple plastics surfaces. Only the spherical stylus produces results reliably related to trade experience with the thin coatings on photographic films.
Lubricity is introduced relative to its effect on abrasion resistance and ease of product handling by mechanical equipment. The classical ASTM friction test for plastics is a sled test. A sled test's lack of relevancy to scratch testing exemplifies a breakdown of the classical laws of friction. In the photographic film field, a point-contact friction test is more correlative. The ANSI version of this, the Paper Clip Friction Test, is described, and correlations with scratch as well as with lubricant levels in molded plastics are presented.
abrasion, scratch, friction, wax, lubrication, photographic film
Technical associate, Eastman Kodak Co., Rochester, N.Y.