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June 2008

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Graham Naisbitt <[log in to unmask]>
Date:
Mon, 9 Jun 2008 16:34:40 +0100
Content-Type:
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text/plain (148 lines)
You see - there are all the "Depends" you could wish for - despite the  
poor spelling.

Only one little extra titbit - urethanes often/usually contain  
isocyanates that would require/mandate you to provide the operators  
with artificial respiration equipment, not entirely dissimilar to what  
Buzz Aldrin had to wear on the moon! I exaggerate just a tad.

Graham N


On 9 Jun 2008, at 13:53, Douglas O. Pauls wrote:

> Mike,
> As others have said, the two don't mix.  I have tried to clean  
> silicones
> from spray equipment and you can never get it down enough such that it
> does not cause fisheyes and other coating problems.  Save yourself a  
> whole
> lot of problems and simply get new equipment.  If you cannot go this
> direction, then I would suggest that you use naphtha as a cleaning
> solvent.  It seems to be more effective than other solvents on  
> silicone
> residues.  Then follow the naphtha cleaning with alcohol cleaning.   
> You
> would probably need to clean your exhaust stacks too.  Replacing  
> might be
> easier and cheaper in the long run.
>
> You did not say what kind of silicone you were going from (solvent  
> vs 100%
> solids) and what kind of urethane you are going to (solvent-borne  
> (notice
> the proper spelling) vs. two part reactive).  Where you may not have  
> had
> an environmental exhaust permit issue before, you may have one now  
> if you
> are going to a VOC-based solvent urethane.  Check with your local  
> EPA or
> DNR.
>
> Someone else brought up the dreaded "O word" - OSHA.  Check what  
> personal
> protective equipment you will need.   Many of the urethanes have  
> higher
> health impact ratings than silicones.
>
> Urethanes and silicones have dramatically different properties in  
> terms of
> chemical resistance, thermal performance and rigidity.  Have you  
> checked
> with the designers to determine if there is any impact to form, fit or
> function that this change represents?
>
> Urethanes and silicones flow differently, have you figured in the  
> time to
> retrain your operators on the new methods?
>
> Urethanes and silicones look and feel different in their finished  
> form.
> Are you ready for the change in workmanship standards?  Have you  
> accounted
> for the re-training time for your inspectors?
>
> Urethanes and silicones have completely rework and repair procedures.
>
> What does the end user think about the change?
>
> Are you ready for the culture change?  The material switch is  
> relatively
> easy.  It's changing the culture that is a cast iron *^%*#^(*#.
>
> Doug Pauls
>
>
>
>
> Mike Johnson <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 06/06/2008 10:04 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Mike Johnson <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] Changing conformal coating from silicone to urethane...
>
>
>
>
>
>
> We are considering changing our pcb conformal coating process from a
> silicone base material to a urethane base material.  Other than a  
> thorough
> cleaning of our machine, replacing material delivery lines, complete
> disassembly and cleaning of nozzles, ordering new nozzles to meet
> viscosity requirements of new material if necessary, are there other
> concerns we should be addressing?
>
> Mike
>
>
>
>
>
>
> ***
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