I am in charge of coating operations at my plant. We produce and paint plastic products for domestic use. The products are coated. The coating thickness is critical for the performance of the product. I need a measuring technique for quality control. I have experienced great difficulty in measuring the thickness of an epoxy-amine coating on a polyethylene teraphthalate substrate. What kind of thickness measurement devices should I be looking for? E. B.
Because of the nature of the substrate, finding film thickness measuring devices for plastics presents a tough problem. Unfortunately, the old standby magnetic gages will not work. Film thickness measuring devices can be destructive and nondestructive. Destructive testing often involves cutting and sectioning. Testing can be done by making a V-shaped cut in the film and then measuring the film microscopically. You can hang plastic blanks or test samples on the conveyor line and make micrometer measurements or you can cut them and make microscopic cross-section measurements. Nondestructive measurements can be made on plastics using beta backscattering devices. You can also use ultrasonic thickness gauges. Suppliers of film thickness measuring devices can be found online at www.pfonline.com/suppliers.html or listed under Testing Equipment, thickness of coating (pg 433-436) in the Products Finishing 2004 Directory & Technology Guide.