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crazypigeon
September 21st, 2006, 08:54 AM
Well, I have a few badly yellowed computers, which is kind of a bummer. I was just wondering what causes yellowing....anyone know?

Luke
September 21st, 2006, 09:04 AM
Googled and found something:


All hard plastics (...) will yellow when left in direct sunlight, though obviously it's most noticeable in white plastic. It's a chemical change caused by ultraviolet radiation from the Sun, but unfortunately there is very little you can do to restore toys that have been damaged this way.

They also say there, that there are rumors, that whitening toothpaste can get yellow off plastic.
You should find a lot about yellowing on google.

Terry Yager
September 21st, 2006, 09:06 AM
http://experts.about.com/q/Transformers-2137/Yellowing-White-Plastic.htm

--T

ziloo
September 21st, 2006, 12:00 PM
I remember a similar discussion a while back:

http://www.vintage-computer.com/vcforum/showthread.php?t=2812&highlight=yellowing

Hope it helps!

Jorg
September 21st, 2006, 02:28 PM
Well, as a polymer engineer I should have to be able to comment- but most is said already.

The high energy UV radiation is breaking bonds in the polymer chains, which causes degradation and discoulouring.

It penetrates into the surface, so the affected layer must be romoved to have any effect.

carlsson
September 21st, 2006, 03:23 PM
Is the research going towards new polymers that won't break due to UV radiation, or is that just about impossible to do something about?

Vlad
September 21st, 2006, 03:36 PM
I've heard of UV protected plastics, but it was being used in stuff like outdoor chiars and such....

-VK

Jorg
September 21st, 2006, 05:21 PM
I've heard of UV protected plastics, but it was being used in stuff like outdoor chiars and such....

-VK

Yes, there are a range of UV additives available, but they add to the costs. In outdoor materials you need to do it as the damage to the polymer also affects the material strength.
Try a hammer on a ten year old outdoor chair...

crazypigeon
September 21st, 2006, 05:43 PM
Well the main question I ment to ask was:
I have all my old computers setup in my ex-closet (who puts clothes in their closetn anyway :) ) and I have a bunch of flouresent (is that how you spell it? :P) lights shining on them, and I just want to be sure that i'm not yellowing them even more than they already are.

Terry Yager
September 21st, 2006, 05:45 PM
Yes, there are a range of UV additives available, but they add to the costs. In outdoor materials you need to do it as the damage to the polymer also affects the material strength.
Try a hammer on a ten year old outdoor chair...

Hey, I just blew a slat in my 7-year-old wood/cast-iron park bench the other day. I hate to junk it, but I hate even more the idea of fixing it...

--T

nige the hippy
September 22nd, 2006, 12:56 AM
We had a local car paint specialist mix up cans of "IBM White" for plastic (most ibm stuff actually used to be painted on top of the plastic anyway, I wonder how many other manufacturers did the same?).

Stuff used to look like new, I'm not sure, but I think the slightly textured finish was down to an additive.

I think ordinary car paint flakes off plastic, so you need the proper stuff.

carlsson
September 22nd, 2006, 07:41 AM
.. and since computers of today mostly are ugly boxes without souls, nobody will care 20 years from now which type of plastic the case is made of and whether they are yellowed or not. ;-)

Jorg
September 22nd, 2006, 10:26 AM
Well the main question I ment to ask was:
I have all my old computers setup in my ex-closet (who puts clothes in their closetn anyway :) ) and I have a bunch of flouresent (is that how you spell it? :P) lights shining on them, and I just want to be sure that i'm not yellowing them even more than they already are.

Well, if you want to avoid yellowing, fluorescent lights (TL) are a bad idea. They work by putting a voltage on quicksilver vapor, and that produces UV light (185 and 254 nm). The inside of the tube has a poweder coating, that glows in the visible spectrum when hit by UV light.
TL therefore have a noticable amount of UV leakage. Better use bulbs- they are on the other end of the spectrum.
ats
Any decent pc case is made of ABS plastic. This should be not too difficult for paint adhesion, but it needs to be cleaned pretty well. Try some paint on PU basis. Car paint is for steel... maybe it works when you primer the case first, thats always a good idea.

compu_85
September 23rd, 2006, 08:36 AM
So sunlight is bad for plastics... what about fluorescent light?

EDIT: Hellow, my name is Jason, and I'd like to read the post directly above mine, which answers my question....

-Jason

Terry Yager
September 23rd, 2006, 09:04 AM
It's the UV radiation which causes a chemical change in the plastic, so anything that generates a lot of UV can lead to yellowing, including flourescent tubes.

As for paint, I've found that Krylon works great on most plastics. It costs a little more, but well worth it.

--T

Jorg
September 23rd, 2006, 09:04 AM
Uhm. Do you read this topic?