- June 13, 2012, Mark Miller
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Within all coating matters, scientific application of process and material understanding is critical to success. The amount of care applied to understanding each step in the fluid coating process provides a reduction in error to the process overall.
Typically process engineers want to attack a coating defect or manufacturing issue with a concentration at the coating station. “If the fluid is applied to the web at the coating station, and a defect exists, then this is where I start,” states the emergent engineer. But sometimes the fault of the coating issue does not lie out where you can see it. When working on a coating defect, it behooves a process engineer to understand every step before and after the coating station.
OK, so let’s say we have a coating streak in a slot die coating of a typical adhesive coated tape. Should I start by adjusting the slot die to remove the streak? That depends. Does the adhesive have particles in it? Maybe the filter is not adequate. Was the substrate inspected before loaded on the unwind stand? Maybe the streak is a latent defect in the underlying film. Does the fluid have a ‘shelf-life’ before the particles settle out of suspension? Maybe the streak occurs after a specific amount of production time.
My point is – for as much time and attention that is spent on the coating station, it would reduce overall defect chasing by having protocols in place to remove defects that develop in the other areas of the coating process. Applying the tried and true scientific method to each of the critical areas of operation (substrate, fluid, fluid delivery, coating, and curing) will save an engineer headaches down the road. There are two important methods for tracking down these defects and understanding the root cause: (1) Design of Experiments (DOEs) that include variables outside the coating station to capture more information; and (2) a process journal that coating operators keep by the line to document changes that may not be captured with Statistical Process Control (SPC) from the web machine trends.
These methods will help you track the information, make appropriate changes, and improve performance of the web coating process. Move in a scientific method and quality will improve, and so will the bottom line. If you have applied these techniques, let me know and contact Mark D. Miller, Founder and CEO of Coating Tech Service, LLC (www.coatingtechservce.com) at email@example.com or (612) 605-6019.