Doug
Stainless steel ovens would seem a good idea - even for those using
conventional coatings because of solvent resistance. This would also help
when you come to routine maintenance and need to "strip" the coating gunge
from the surfaces.
It might help to note that moisture curing materials were developed in order
to accelerate curing whilst avoiding the use of 2 part formula's and the
inherent difficulties that these pose. However, moisture cured materials are
loaded with TDI (toluene di-isocyanate) which is a slight health hazard and
should be handled in "sealed, automated equipment" or the operators should
wear self-contained suits. (That will help keep you out of the consequential
liability front.)
Switching to UV curables does not aid your fast cure requirement. As it is
so difficult to bend light - at least that's what I read! - curing under
components is a major problem and it becomes necessary to add secondary cure
mechanisms to the formulation which impact other areas: pot life, shelf life
and "keep in the dark". Your equipment becomes more expensive and fume
extraction is a must, as ozone is a harmful by-product of UV light
generation.
Having said all that, there is a very good 1 part solventless silicone
moisture/UV combination curing material that works well - offline for more
info please. Your equipment budget will need to be analysed further as I
guess you have to change the oven at least.
It would help to learn however, the reason for the original coating
selection. Can you inform us?
As a guide, polyurethane's exhibit very good chemical and salt resistance
yet retain repairability. They are tough and provide good moisture
resistance. There are formulas around that are 1 part, free of isocyanates
and cure to handling condition at room temperature in less than 1 hour -
again, for more info, off-line please.
From your company title, I guess you are making luminescent displays for
out-door use, sports stadiums that sort of thing? We have a major customer
who had a curious problem with ants crawling up the support poles and
nesting in the electronics housing. The guy called me to complain that the
ants were "eating (our) coating and why don't (we) put an insecticide in the
product?"
I pointed out that modifying the coating by adding an insecticide may well
reduce the performance of the coating and anyway, that what he was seeing
was more probably (and was!) the formic acid from the ants dissolving the
electronics, starting with the coating of course!! They were using a 1 part
acrylic coating so I recommended they switch to the 1 part urethane and the
problem was solved.
I have a great story on this event for those who would like a copy, ask me
offline.
If it will help, I always prefer to get the designer, the production/process
engineer and the QA engineer together for the discussion, because each has a
different requirement and some compromise is usually required to achieve a
satisfactory solution (if you will pardon the pun?)
I hope this helps, let me know more if you can.
Regards,
Graham Naisbitt
[log in to unmask]
WEB: http://www.concoat.co.uk
CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK
Tel: +44 (0) 1276 691100 Fax: +44 (0) 1276 691227
----- Original Message -----
From: Hooper Doug <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 10, 2000 6:43 PM
Subject: [TN] Conformal Coating Cure Process
> I am looking for information relating to curing conformal coating using a
> one-part moisture cure polyurethane material. My ovens are rusting to
> pieces. I operate them with 50%-60%RH at 180F. I want cure the CC as
> quickly as possible - which is why the environment in the oven operates
> at these conditions. Is there a better way to cure or do I need to buy
> stainless steel ovens? Different CC material? What about a UV cure
> followed by a RT humid environment added afterwards?
>
> Douglas A. Hooper, Sr.
> Luminescent Systems Inc.
> [log in to unmask]
>
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