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Home  > Forum  > Coatings & raw material failures  > Peeling of clear lacquer from base coat

Monday, 17 June 2019

Peeling of clear lacquer from base coat

7 Posts

Friday 28 March 2008 1:00:00 am

Please provide if possible literature references on the subject of peeling of clear lacquers from basecoats. Coating types: powder coatings, polyester based. Substrate: automotive and industrial finishes.

Thanks.

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Monday 31 March 2008 1:00:00 am

Please adv the type of additives used with the ratio of any anti settling/anti sagging addtive used.

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Thursday 03 April 2008 1:00:00 am

Please explain your problem in detail. Type of resin used, system followed, solvents used etc. for further assistance.

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Friday 04 April 2008 1:00:00 am

Thanks for feed-back.
The failure concerns decorative steel coils for outdoor displays. Originally the items were powder coated (primed)with a greyish epoxy-polyester, aluminumpigmented base-coat and then topcoated with a polyester clear coat (powder). The base-coat primer has now been replaced with a pure polyester powder coating, but the topcoat lacquer still detaches.
We suspect that the aluminum pigmentation is to blame, as ESEM-analyses show that the aluminum seems to concentrate on top of the basecoat (leafing aluminum?). Leafing aluminum is "wetted" with pastes (sterates) and surfactants. Is this assumption correct? Could the problem be solved by changing to non-leafing aluminum or is it better to use normal automobile repair products (wet paints) for the purpose?

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Friday 04 April 2008 1:00:00 am

.... The panels are made of elctrogalvanized coils and phosphated before application of base-coat. The surface of the base-coat under the peeled clear laquer shows traces of zinc corrosion products.

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Tuesday 15 April 2008 1:00:00 am

I see that you don't have a reply yet. Adhesion of powder topcoat to a basecoat is always more difficult than using a "wet" coating-topcoat. But if you insist to make a go of your system, try low molecular weight, and fit-for purpose lower Tg polyester. Check flexibility-may need additon of flexible polyester or additive AND check your dry film thickness-it could be over optimum. Guide: must always be less than the basecoat.

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Saturday 19 April 2008 1:00:00 am

Use urethaned polyester, this polymer increase the adherence between base and clearcoats.

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Friday 09 May 2008 1:00:00 am

Thanks to all for the feed-back. We'll continue and test other binder compositions,including wet paints.

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