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Opening of subsecuent PU coating

Opening of subsecuent PU coating

Opening of subsecuent PU coating

(OP)
After spaying a base coat of a 70 Shore crosslinked PU dispersion, allowing it to dry and embossed it @ 90°C and 150 Kg, we couldn't get an even spraying of subsecuent coats of some other PU's dispersions.

We have tried penetrators, tensoactives, soaps, solvents like IPA and Butilcellosolve with no good result at all, we still get the opening of the spayed coat.

But when we first pre-heated the base coated substrate, we could get an even aplication of the colour coat and the top coat.

Do you have any explanation of this fenomena and do you have any suggestions about how to improve the flow of subsecuent coats, because we consider pre-heating is no solution at all?

RE: Opening of subsecuent PU coating

Hi
we have experience of spraying thin film water based coating and experience similar results.
What is the subsiquent coating you are applying?
if it is a true water based PU then the coating actually cures from the substrate out hense the improved performance in application with a warm subtrate.
Some Pu's activate at lower surface temperature than others
Is it a OCS (oxygen crosslinked system) or a traditional oil modified Urithanes? this will have a heavy imfluence on its hanging and curing time.
Also the wft is critical some materials are capable of being applied at a much lower thickness.
Let me know what you are using and the ambient temps and we can give you more pointers.

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