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July 2001

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Subject:
From:
Phil Kinner <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 19 Jul 2001 15:53:24 +0100
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Doug,

Shame I am not included in Graham's "Coating Room work naked bonus" -
but merely trapped away in my office!

I should say that blushing is almost exclusively humidity related.  The
cooling effect caused by the atomisation of the solvents causes
condensation of the excess humidity.  The rate of evaporation of the
solvent will probably affect the degree of effect though... (did I get
those the right way round?)

Switching to a solvent such as 2-pentanone (MPK) which is a) more
volatile than say xylene, and b) is probably a weaker solvent for say an
acrylic could potentially cause worsening of any blushing, bubbling in
the coating and cobwebbing (weaker solvent = higher solids content at
low spray viscosity).

Let us know how you get on.

Best Regards,

Phil Kinner
Concoat Ltd

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: 19 July 2001 13:38
To: [log in to unmask]
Subject: Re: [TN] White residue from conformal coating

Graham,
Thanks for the insights on the "blush" phenomena.  How interesting that
it
comes up in the same discussion as your "work naked bonus".

Is there any link between the type of solvent in the coating and blush,
or
is it exclusively humidity related?  One project that has been suggested
for me is to replace the toluene and xylene we use as acrylic thinners
with
methyl propyl ketone.  If such a switch were made, would you expect a
greater or lesser susceptibility to blush, or is it immaterial (no pun
intended).

Doug Pauls
Rockwell Collins

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