Bob,
Unfortunately with accelerated testing, there is no formula for x hours =
y years. The test systems usually try to mimic the spectral output of the
sun and the intensity (irradiance) at ground level. The accelerated part
happens because they can expose at the Peak Natural Daylight Standard,
determined by the International Society of Illumination to be 0.68 W/m2 at
340 nm, for hours and not just for the typical minutes experienced each
day. Also, the systems use elevated temperatures along with periods of
condensation.
The data obtained is best used comparatively - if material A can survive
10X longer than material B in accelerated testing, then material A will
likely last 10X longer than material B with outdoor exposure.
ASTM G154 accelerated testing uses a UVA 340 nm lamp with a 0.89 W/m2 at
340 nm. The test conditions are 8 hours of UV at a controlled temperature
of 60C followed by 4 hours of condensation (deionized water) at 50C. They
usually report color and gloss values, and visual appearance (chalk,
crack, blister, check, flake).
So a 2000 hour test includes about 1400 hours of what is determined by the
illuminated society to be greater than peak sunlight exposure.
From my limited knowledge, and I don't claim to be any kind of a UV test
expert, it appears that a 1000 hour test is fairly common to determine how
well a paint or coating will hold up outdoors.
I cannot say if 2000 hours is sufficient for all applications. But, our
customers that are familiar with outdoor applications are satisfied with
this result.
As far as the pun, it was a Friday afternoon. Some weeks I have to revert
to sarcasm.
Lamar
From: Bob Landman <[log in to unmask]>
To: [log in to unmask]
Date: 11/12/2010 03:19 PM
Subject: Re: [TN] UV radiation and conformal coating
Sent by: TechNet <[log in to unmask]>
Good pun Lamar "shedding some light" but is a 2000 hr test sufficient? Is
the light level much more intense than standard sunlight intensity and if
so how much? (I don't have a copy of G154).
Bob Landman
Sent from my iPhone
On Nov 12, 2010, at 2:47 PM, Lamar Young <[log in to unmask]> wrote:
> Doug,
>
> I do not know of any papers specific to conformal coatings. And as far
as
> coatings other than Parylene, I think other manufactures should supply
> information. But, we know a bit about Parylenes and have performed
> several accelerated UV tests internally.
>
> It is fairly well known that the normal C, N, and D Parylenes do not
hold
> up well to outdoor sunlight exposure. However, Parylene HT (a
fluorinated
> version) that Kevin mentions below, is very UV stable. We have
performed
> accelerated UV exposure in a UV chamber with over 2000 hours ASTM G154
> with minimal impact (other Parylenes can't last to 100 hours). We have
> several successful outdoor projects with Parylene HT, such as coating
LED
> signs. So depending on the application and the coating, it may be
> possible.
>
> Hopefully this sheds some light on your question.
>
> Lamar
>
>
>
>
> From: "Glidden, Kevin" <[log in to unmask]>
> To: [log in to unmask]
> Date: 11/11/2010 08:30 AM
> Subject: Re: [TN] UV radiation and conformal coating
> Sent by: TechNet <[log in to unmask]>
>
>
>
> Doug,
>
> Sorry I can't offer any known articles, but I would be interested in
> seeing if there are any out there.
>
> Our vendor tells us that the urethanes will discolor to a yellow and
> eventually brown tint with continued UV exposure, and eventually be more
> susceptible to cracking. We've witnessed this on the coating build-up
of
> some fixtures we run through the UV tunnel multiple times.
>
> I have heard of a new parylene coating (parylene HT) that was developed
to
> have increased UV resistance, but I have not seen it used yet.
>
> Kevin Glidden
> Manufacturing Engineer
> Astronics Luminescent Systems Inc.
>
> -----Original Message-----
> From: Douglas Pauls [mailto:[log in to unmask]]
> Sent: Thursday, November 11, 2010 8:20 AM
> To: [log in to unmask]
> Subject: [TN] UV radiation and conformal coating
>
> Good morning all,
>
> Does anyone know of any papers on the effects of UV light on conformal
> coating? Not talking the cosmic radiation hard space kind. I know it
> would be wavelength and intensity specific. Got a question from one of
> our engineers and I, of course, gave the very intelligent answer of
"Beats
>
> me". But I have this wonderful resourse called Technet...............
>
> Doug Pauls
>
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