Opening of subsecuent PU coating

[handlecuinba]

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

 

[Suilven]

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.