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Polyester based high-gloss coil coating is too rough

January 22, 2012

Q. We have encountered a problem of rough finish on a high gloss polyester coil coating.
I have re checked the grind of the wet paint and it is below ten microns, way below the application thickness of twenty microns. The peak metal temperature is maintained at two hundred thirty two °C. What could be the possible cause of this problem, can anyone help?

Francis Tubbali
Development Chemist - Dammam, KSA

January 25, 2012

Unfortunately, you have supplied insufficient data for anyone to advise you on your problem.
Please supply the following info:
1)Is this a recent phenomenon?
2)Did it occur only when a new batch of paint was incorporated into your coating system?
3)Is your coating system utilising solvent or water based material?
4)What colour is the paint blacks can flocculate i.e. look bitty.
If a waterborne coating is contaminated by carry-over from a pretreatment process then this may also be the cause of your problem?
However, your coating supplier should be on-site to ascertain and rectify your problem!!!
To help yourself I would take paint samples from the coating plant and flow it out on glass alongside a fresh sample from an unopened stock container... if more than one batch in stock, include these also. After allowing them to air-dry in a dust free space, bake them in a laboratory oven or similar... but not your processing oven. Report your observations.

Terry Hickling
Birmingham, United Kingdom

February 10, 2012

We have encountered this problem with great frequency, polyester coatings being a significant part of our business. Make sure you are getting enough kiss on your applicator roll, if using zinc phosphate treatment, is it dry enough. Does your coating supplier under stand coil coating intimately, we purchase from a multitude of suppliers interchangeable coating systems mainly polyester basecoats for print systems, one supplier will blister the alternates under the same conditions will not, due to one supplier being cheap on their solvent package which will work over a one treatment, complex oxide, but not for instance zinc phosphate.

Hope this helps

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada

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