Paint is Fading Looking for Test 4

[Cervantis]

I have been asked to investigate a problem that involves fading of paint when exposed to sunlight for longer than 3 weeks. The surface material is Aluminum. The paint color is black. The product comes in already painted, and we affix it to another part. But after 3 weeks the painted surfaces changes from Black to Grey. We suppect that the UV additive was not used, but we can't figure out how to tell with a simple quick test. We have a UV chamber, but this test is 500 hours or 20 days. Any IDEAS on how to test a painted surface for UV protection quickly.

I thought I would use the most powerful tool in the universe, ENG-TIPS.com to find a conclusion to this conundrum.

Best,

Cervantis

 

[Compositepro]

20 days IS the quick test.

 

[unclesyd]

You might want to look at a gloss meter, there are several types that will normally tell you pretty quick if a coating is starting to fail.
If you have the UV Fadeometer there are accelerated tests that you can use.

http://www.glossmeters.com/

http://acceleratedclimate.com/equipement.htm

Is the paint chalking or just turning gray.

 

[Cervantis]

Thanks Compositepro and Unclesyd, I do appreciate your responces. I am also looking at our "little angels" spaying something on the aluminum plate before they are exposed to the sunlight. The intermitten pattern of affect is perplexing. I like the Gloss Meter idea.

Thanks,

JOHN

 

[lawayosh]

Presume that exposure is to sunlight if UV is causing the fading. What type of coating is your supplier using? If you have the ability to specify the coating it could solve the problem.

Yosh

 

[CoryPad]

How about testing the coating for presence or absence of a UV stabilizer? Gas chromatography/mass spectrometry would be one technique. What is your commercial arrangement with the paint supplier? What do you specify, and how?

 

[hokie66]

What type coating has been used? Epoxies are the worst for fading and chalking.

 

[rhodie]

Organic pigments will fade and oxidize must more quickly in direct sunlight than inorganic pigments.

Confirm with the paint/coating manufacturer than an inorganic black is being specified.

Also, if your aggregate material is Al, make sure that a zinc binder or cobalt drier ingredient in the coating is not galvantically acting to create the oxidization.

 

[Cervantis]

Well it has been several months since the original post. You learn new things given time and effort. Here for the groups information that I will share for your future reference is what we have learned/I have learned. The ALUMINUM plate is not "painted" as I was led to believe early on. The Stainless plate is "painted". These are aluminum, and are "annodized" and/or stained in a "type" of "ink". There was a significant improvement once we discussed the issue with the vendor. And after running dozens of UV chamber 500 hour tests on every lot number we could find, track, or dig up, we were able to isolate, identify, quarantine, seperate and remove the "good" from the bad. Our discoveries were within a certain time frame, as those from before the X time frame and those after the X time frame had similar outcomes of not "fading". Those within the X time frame,in general "flopped". We are looking at other options that will make this a "never event" for the future and are currently running very agressive testing to make sure our decisions are correct for the long haul. We are also making corrections in incoming inspections that will give us the added comfort zone for the issue. It was a new issue for us, and I thank the community for your input, williness to share your skills, talent, and knowledge with an "rookie".

Best,

Cervantis

 

[CoryPad]

Thanks for returning and providing an update.

 

[jedward]

One very uv resistant type of paint is use for spray painting of wood stoves.
I have used it exposed to high intensity arc lamps illumination at a few solar constants for over 10,000 hours with "no change".
I suggest you look at this type of source for the paint.

 

[boothuk]

I seriously doubt that any coating would show no deterioration after 10k hours to Xenon Arc.

I don't know your end use, but powder coatings (PE) show very good resistance to natural sunlight. I am referring to architectural grades.

For future reference, you may check the 'fingerprint' of the material using FTIR analysis methods, however, i'm not sure how good this would be for an anodised finish.

 

[Cervantis]

Thank you again to all for your time and your input. This is one of the best spots on the NET for honest and worthwhile information. The architectural variety is what we are going to be using in the future.

 

[boothuk]

Cervantis, are where are you based?

Have you ever heard of 'Qualicoat'? This is an accepted standard in Europe & M.E. for architectural specifications. Some of the biggest manufacturers of PC are members, i.e. Jotun Powder Coatings UK/Thai/Dubai, Akzo Nobel Powder Coatings UK/Turkey/Egypt/Dubai, Sonneborn & Rieck etc.

Maybe it's worth looking at their spec for their benchmarks on anodising (chrome free) and powder coatings.

The latest spec is edition 12.

 

[Cervantis]

Thank you Boothuk for the information. I am here in the US.
I am familar with AKZO NOBEL POWDER COATINGS. We should be getting in the new product soon, and I will give all an update on our findings. The preliminary testing was very favorable for this "new" style we are going to. I have moved on to other issues/head aches like inconsistencies in DYE pressed parts. I am sure there will be a post sometime in the future on this "diddy". Thanks to all again for your time shared on this concern and for all the great information.

Cervantis

 

[jedward]

For boothuk primarily
I have used "black stove paint" for the interior and exterior walls of our solar simulators that use 4200 Watt xenon lamps, a type used in theater projections systems. The walls are about 15 to 20 inches from the lamp and show minimal discoloration after 15 years of operation of 50 hours per week.
The choice was somewhat accidental but was selected for high temperature stability- based on home use on a wood stove.

 

[unclesyd]

You might want to look at products from the Dampney Co. I have used a number of their products with excellant results. They did have very knowledgeable and helpful technical support.

http://www.dampney.com/Products/Products.asp?ProductID=36

 

[boothuk]

Jedward,

I suppose the end use and type of paint used is feasible. Did you calculate the CIELAB or are you making a visual comparison? What was the gloss retention of the coating like? Apologies for being so dismissive, I have a tendancy to focus on the abilities of powder coatings only, as per experience.

 

[jedward]

boothuk
-visual estimate, reflectivity went from about 10% to perhaps 40% over the full time period.(>80,000 sun hours).
-this is a very extreme exposure.
- using Z306 or L300 could be considered but probably out of the question by cost reasons. Stuff is for thermal control of spacecraft.

 

[Cervantis]

Update:

Our new upgraded material is now in house. We begin our QUV testing today. I will have results on this new lot in 22 days and let the group know where we stand.

PS..I have a new post in Polymer Eng if anyone wishes to chime in.

Thank you again to all for your kindness, interest, and willingness to share the vast wealth of collected combined knowledge.

Cervantis