Yellowed Polycarbinate

[TeamOutlaw]

Hopefully this is posted in the right section of the forum...

Wondering if you all have found any DIY "tricks" to help eliminate some of the "yellowing" caused by UV on backlit sign panels. We've encountered this a lot, but never really done any more that just clean them up with Simple Green etc. If they are bad enough...replace them.

I have a current job that has 6 pieces of white poly that aren't very old that they want to re-brand. Any "tricks" that you've found to help eliminate some of the yellowing? TIA

 

[Marlene]

by lexan with UV protection and make sure you have it sun side out. for old signs that are yellow, Spray Nine gets rid of most of the yellow but it wil come back as the old stuff had no protection.

 

[printhog]

Yellowing after 5 or 7 years is the reason we're all in business. Nothing lasts forever. "Time to buy a new sign Mr Customer"

The surface of poly decomposes with time and solar exposure. The headlights on cars are a good example of that. The very same process for those headlight restoral kits will work for signs. Sand with 600 then 1500, then 3000, and finish with a fine polish compound for plastic. Buy one of those Maguire's kits for detail.

Expect about a year of life for that polishing effort.

Sent from my SM-G900T using Tapatalk

 

[signbrad]

I've never known of any effective procedure for eliminating the yellowing that comes with polycarbonate as it ages. The UV layer that is applied to the face of exterior grade polycarbonate eventually degrades. Sometimes you can minimize the yellow look by reversing out first-surface vinyl, but the discoloration doesn't really go away. I can see where sanding and buffing might work temporarily, like printhog said. Presumably, though, this procedure will remove any trace of UV coating left. The only real way to eliminate the yellow is to replace the plastic. The discoloration is the trade-off for plastic that is difficult to break.

I have never done this, but it might be interesting to compare warranties for various brands that are made for being in the weather, to see where each one falls on the yellowing scale.
Here is a link to the warranty for the Lexan brand, which has been part of Sabic Innovative Plastics since 2007 (Sabic is a Saudi Arabian company, mostly owned by the government).

Lexan warranty:
http://bristolite.com/Interfaces/media/Lexan polycarbonate warranty.pdf

Brad in Kansas City

 

[Signchief]

Damn Saudis... The only thing better than their plastics is their pilots... Too soon?

 

[signbrad]

Acquiring General Electric's plastic division was a shrewd move by Sabic. It means Saudi Arabia now has the plastics production capability to go with the raw material that they already had—petroleum.

 

[Johnny Best]

And cheaper replacement of their cockpit plastic on their jets so their pilots can see better.

I think the polycarbonite with the Rino on the cover seems to hold up the best from yellowing.

 

[Fares Bayazeed]

Lexan.

 

[Johnny Best]

Makroln has the Rino Sheffield Plastics by Bayer

 

[myront]

We just went through this same scenario. This was patch of a patch of a patch. After cleaning it all off you could see several logos and text crisscrossing everywhere. We ended up throwing a coat of white vinyl with clear adhesive backing to it then apply the translucent logo decal.

 

[spectrum maine]

castrol super clean really removes a lot of yellow. you will be suprised how much yellow is on the cleaning rags.

 

[The Big Squeegee]

I have used vinegar on these old signs with a lot of success. MEK will take the remainder of the yellow off but MEK will dissolve the plastic so you have to use it aggressively for a short period. Clean off the MEK residue with alcohol water and soap mix. Cover with a UV protected laminate when done before applying new graphics.

You can also do this with headlamp covers followed up with a UV protecting polish. Do not use wax!

 

[Westcoast Sign Guy]

These are the pro's and con's of Polycarbonate vs Acrylic.

Quality Acrylic won't yellow but it can shatter.

I won't use Polycarb unless I REALLY have too

 

[Impactor]

Makroln has the Rino Sheffield Plastics by Bayer

That's an old sheet. They changed name in 2015.

Btw there are two types of polycarbonate : UV protected and standard.
UV protected can be coated but best is coextruded.
UV protected means there is a thin layer absorbing UV radiation so the rest does not yellow (so much), which is backed with a 10 or 15 year warranty.
If you manage to get the yellow off a yellowed PC sheet, then it means it was not UV protected, and you wash off dirt, and with more aggressive solvents you take off the top layer (20 micron typically).
When you do this with UV protected PC, it was an older sheet, or it was exposed to chemicals before, and will end up like a non-UV protected sheet