What causes this???

special K
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special K
Edited Date/Time 3/5/2020 6:51pm
What causes the plastic to swell on old bikes underneath decals on the fenders? Not a big deal on this bike because I’m going to put vintage sponsorship decals back on because I like the look. I think you can see the KYB spot in the photo for reference.
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DynoDan22
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DynoDan22 3/4/2020 8:54pm
3/4/2020 8:54pm Edited Date/Time 3/4/2020 8:55pm
I think the area under the decal is not affected by the shrinkage caused by sunlight and UV rays. I think that over time the plastic shrinks and dries out leaving a "raised" portion under the decal but this raised portion was actually the original thickness of the fender when new. Just thinking out loud but I've seen this behavior in super-tough nylon which I believe to be close to what the plastic is made of.
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PN27416
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PN27416 3/5/2020 1:39pm
3/5/2020 1:39pm
DynoDan22 wrote:
I think the area under the decal is not affected by the shrinkage caused by sunlight and UV rays. I think that over time the plastic...
I think the area under the decal is not affected by the shrinkage caused by sunlight and UV rays. I think that over time the plastic shrinks and dries out leaving a "raised" portion under the decal but this raised portion was actually the original thickness of the fender when new. Just thinking out loud but I've seen this behavior in super-tough nylon which I believe to be close to what the plastic is made of.
I believe you are 100% correct. I have a 78 fender that I just peeled off a Gold belt decal from. Its a good 1/32 thicker under there if not more. Any of us old guys would know the logo as its so defined.
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SEEMEFIRST
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SEEMEFIRST 3/5/2020 6:08pm
3/5/2020 6:08pm
Yep!
Polyethylene has a lot of oil in it, and it "evaporates" over time.
I believe the first answer is the correct one.
special K
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special K 3/5/2020 6:28pm
3/5/2020 6:28pm
Appears that may be correct. It seemed more likely that the adhesive on the stickers swelled the plastic but after thinking about it and being in the printing business as I am, the adhesive on decals is not reactive in any way to anything.

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SEEMEFIRST
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SEEMEFIRST 3/5/2020 6:50pm
3/5/2020 6:50pm
special K wrote:
Appears that may be correct. It seemed more likely that the adhesive on the stickers swelled the plastic but after thinking about it and being in...
Appears that may be correct. It seemed more likely that the adhesive on the stickers swelled the plastic but after thinking about it and being in the printing business as I am, the adhesive on decals is not reactive in any way to anything.
UV does a number on plastic.

Was in the biz for quite a while. "If it ain't plastic, it ain't real" was our tagline.

But yeah, your stickers protected your plastic.
special K
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special K 3/5/2020 6:54pm
3/5/2020 6:54pm
I guess that would be why the boiled linseed oil and laquer thinner trick works to revive tired old plastic. Probably replenishes those oils.
SEEMEFIRST
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SEEMEFIRST 3/5/2020 7:00pm
3/5/2020 7:00pm
Yeah depending on the plastic being revitalized, and the severity of the degradation.

Here's a free tip for removing stuff off of plastic. You may know this, but charcoal lighter fluid is a good solvent that doesn't evaporate very rapidly.

Great adhesive solvent that won't kill a finish.
You can even get those gnarly 3M foam tapes off if you soak a paper towel and let it sit a while.
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SEEMEFIRST
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SEEMEFIRST 3/5/2020 7:03pm
3/5/2020 7:03pm
Oh, and a heat gun can reverse the "whiting" you get from bending or impacting plastic.

Sometimes you can revive it to new looking depending on the age of the plastic.
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