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August 2009

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Subject:
From:
Nicholas Redgrave-Plumb <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Nicholas Redgrave-Plumb <[log in to unmask]>
Date:
Fri, 21 Aug 2009 11:31:14 +0100
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The only way I can see for the propellant causing this kind of problem  
is if the nozzle of the spray can is too close to the substrate whilst  
spraying. I note several suggestions in the posted responses of  
expensive elevated IR curing ovens etc. for IB31 but these are really  
not necessary as this material is dry to the touch/"tack" dry in only  
minutes, dry in 24 hours and cured/fully optimised in 7 days. This  
would undoubtedly be accelerated by an elevated cure but it shouldn't  
really be necessary. So all you should really need is simple drying  
cabinet at ambient temperature just to take the solvent vapours away.

Otherwise, it could be "champagning" or "solvent-popping" which are  
terms to describe a condition where the surface of the coating  
material partially cures leaving solvent still trapped inside the wet- 
film. The solvent has to go somewhere so it finds it's way out through  
the surface and in doing so makes multiple small holes.

To avoid this problem should be a matter of going back to basics.  
Review the coating procedure, make sure the operators are properly  
trained (and not getting the spray nozzle too close to the substrate).  
If the volumes justify the use of a purpose-built spray booth for  
conformal coating with intrinsic safety features and laminar air-flow/ 
extraction then it might be worth going in that direction.

But there should be a simple solution to this problem because the  
usage of HumiSeal 1B31 globally, in both liquid and aerosol cans is  
massive.

Nick Plumb
Gen3 Systems Limited
Farnborough, United Kingdom

_________________________________


On 20 Aug 2009, at 19:17, Inge wrote:

> Good Evening,
> we use small cans filled with 1B1 conformal coating for handspraying  
> boards. The guys are not satisfied with the result, because  
> sometimes the result is matte. Microscope photos show thousands of  
> microscopic bubbles in the coating. I suspect that it's included  
> driving gas. Or wrong handling the spray can.Anyone out there with  
> experience? How do you avoid this problem?
> /Inge
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