ASA exposure data / outdoor applications 1

[SolarWeenie]

Hello,

We are considering the use of ASA in an outdoor application. The material will not be loaded mechanically, with the exception of thermal expansion/contraction. It will be bonded to extruded polystyrene foam with a reactive hot melt polyurethane adhesive, so differential expansion stress is unlikely to be a problem.

The sole purpose of this material is to protect the underlying substrate from UV.

Exposure will be on a rooftop, direct and indirect UV,
-40*C -- +70*C, for 20+ years. Unacceptable failure modes are cracking, peeling, or thickness loss such that the underlying substrate is exposed to substantial UV.

Does this sound like a reasonable idea? Does anyone know of actual outdoor exposure data for this stuff for 10+ years in Arizona or Florida (or equivalant internationally)? What about actual outdoor applications? Some I have leads on is car and RV exteriors, antenna housings, and boat hulls. However I would like to find more specific examples that I can find and look at locally (San Francisco area).

Thanks!

 

[patprimmer]

It sounds like a reasonable idea, but you should continue with your homework.

BASF should be able to provide a lot of data.

ASA has a very good reputation for UV stability, although I think this is partly due to it's exceptional performance when compared to ABS, which is really very poor to UV.

ASA's main benifit in UV has more to do with it's colour retention rather than physical properties retention.

I know it failed in an outdoor swimming pool safety with intergrated solar pool heater application, but that was due to stress cracking of the glue jounts. The design did not allow enough for the vulnerability of ASA to solvent stress crack nor the amount of expansion to be accomodated. I don't think this will apply to your application as you seem to have the expansion issue under control. It would be a good idea to verify long term crack resistance of ASA with your adhesive system, as it might contain some solvents or free monomer after curing that might act as a solvent.

I would also consider PET with a good stabiliser system, and of course the champion of UV resistance, acrylic.

Acrylic would be my first choice, provided it's mechanical properties will withstand your environment. It might have a problem with hail damage.

What's wrong with a few heavy coats of good old fashioned acrylic paint

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Regards
pat

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[SolarWeenie]

Interesting idea with acrylic.

Paint is not an option as we require cure time in <10 minutes, it would have to be water based (foam can't take solvents), and the foam can only take 70*C so high temp drying is out. Also paint application is pretty messy.

However, laminating acrylic sheet is an option. 20-30 mil white would be ideal. The same weathering data requirements would apply and I haven't found much for acrylic, which seems more of a commodity material.

GE Plastics has a guide that ranks materials for weathering resistance. Top four are:

Teflon
PVDF (Kynar)
PMMA (Acrylic?)
ASA (Geloy, in their case)

Thanks for the help!

-Carl

 

[patprimmer]

Acrylic is used extensivly in outdoor signs, aircraft windows (since ww11), boat windscreens and automotive tail lights.

Some very old aircraft and boats still have original windows in good condition.

If you send your e-mail address to me at pprimmer@acay.com.au, I will dig up some data on weathering of acrylic, and scan then send it

eng-tips, by professional engineers for professional engineers

Regards
pat

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