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Anyone know what is the protective plastic film on brass sheet made of?

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Rainbows20/11/2019 23:15:36
640 forum posts
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Title is the question really

Bought some brass sheet that comes with a translucent greeny-blue adhesive film for protecting the finish from scratches.

My thought is can I laser cut the film I can then use that as a stencil for acid etching text or symbols. However if it turns out to be vinyl the laser cutter is going to get wrecked by chlorine gas.

If it does turn out to be vinyl then I have some PP adhesive film as a backup but it would be convenient.

mark smith 2021/11/2019 00:11:22
619 forum posts
313 photos

I believe its usually LDPE (low density polyethylene)

Steve Skelton 122/11/2019 01:41:05
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Yes, it will be polyethylene.

Norman Billingham23/11/2019 13:22:40
27 forum posts

If you want to be sure, strip a bit of the film and put it in a flame. PVC will char and produce acrid fumes, PE will burn away smelling a bit like a candle and with almost no char. Incidentally the gas released from PVC is not chlorine, it's hydrochloric acid. You can double confirm by putting a bit of ammonia solution nearby - the acid released from PVC will produce clouds of white smoke - though you shouldn't need to do this - the difference is very obvious once seen.

Bandersnatch23/11/2019 17:08:40
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Others here are big enough and ugly enough to make their own decisions but personally I wouldn't touch that method with yours. Burning plastics is always a no-no in my book since some (notably vinyls) can produce hydrogen cyanide and most produce toxic/noxious fumes.

Neil Wyatt23/11/2019 17:32:30
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Posted by Bandersnatch on 23/11/2019 17:08:40:

Others here are big enough and ugly enough to make their own decisions but personally I wouldn't touch that method with yours. Burning plastics is always a no-no in my book since some (notably vinyls) can produce hydrogen cyanide and most produce toxic/noxious fumes.

If it's polyethylene it will only give off H2O and CO2, in approximately equal quantities.

Neil

Bandersnatch23/11/2019 18:28:24
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If you know up-front that it's polyethylene, doing the test is moot. If it isn't ...

John Haine23/11/2019 19:15:15
2697 forum posts
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If you mean peel the film off the brass then forget it. It stretches and loses its stick.

mark smith 2023/11/2019 19:27:03
619 forum posts
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Posted by Neil Wyatt on 23/11/2019 17:32:30:
Posted by Bandersnatch on 23/11/2019 17:08:40:

Others here are big enough and ugly enough to make their own decisions but personally I wouldn't touch that method with yours. Burning plastics is always a no-no in my book since some (notably vinyls) can produce hydrogen cyanide and most produce toxic/noxious fumes.

If it's polyethylene it will only give off H2O and CO2, in approximately equal quantities.

Neil

Hi Neil,

Sorry no.

Polyethlene when heated will produce an oily paraffin like stuff up to about 450 C ,above that black carbon deposits, various aldehydes, propane ,methylvinylketone and also several other things like acetic acid depending on temperature of course.

Also depending on how fast the temp. is reached which for a laser would be quite quickly.

not done it yet23/11/2019 20:34:58
3576 forum posts
15 photos

Has anyone read up on burning halogenated compounds? Not heard of dioxins? You just do not burn PVC - it has caused a huge amount of pollution from incinerators, in the past, and is likely the most toxic carcinogen produced by man.

CHARLES lipscombe23/11/2019 22:46:11
100 forum posts
8 photos

More realistically just put a piece of the film in water with a small amount of detergent. Only polythene and polypropylene have a density less than water and will float. All others will sink.

I would rate the chances of the film being PVC as virtually zero and the chances of harming yourself by burning a small piece of PVC also as virtually zero unless you do something moronically stupid, of course.

PVC is nowhere as common as it used to be, partly because it is a difficult material to recycle compared to PET and polythene. When it was widely used e.g. in transparent bottles I can't remember ever reading of any cases of people being poisoned by fumes of burning PVC unless the fire took place in a confined space e.g. an aircraft interior.

There is a definite place for personal safety in all we do but it is sensible also to beware of the hysterical over reaction so often promoted by the media.

Michael Gilligan23/11/2019 22:59:51
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Posted by not done it yet on 23/11/2019 20:34:58:

Has anyone read up on burning halogenated compounds? Not heard of dioxins? You just do not burn PVC - it has caused a huge amount of pollution from incinerators, in the past, and is likely the most toxic carcinogen produced by man.

.

Yes, I’ve just taken your hint and read these two documents:

**LINK**

http://www.seas.columbia.edu/earth/wtert/newwtert/Research/sofos/nawtec/nawtec08/nawtec08-0007.pdf

**LINK**

https://www.carlislesyntec.com/download.aspx?id=5534&fileID=6830

MichaelG.

Norman Billingham24/11/2019 09:58:38
27 forum posts

Oh dear - I do seem to have started a hare running here with an attempt to be helpful.

To be clear, I wasn't suggesting burning kilos of plastic, or tons in an incinerator. A piece of thin film about 2-3 mm square held on the point of a pin in a small flame is all that's needed and the risk from emissions is non-existent. Before IR spectroscopy became readily accessible, the flame test was a routine starting point for screening plastics. A version of it - the hot needle test is still sometimes used in heritage conservation, though largely superseded by spectroscopic methods for those who have access to them and can get suitable samples.

J Hancock24/11/2019 12:41:02
320 forum posts

Yes but...........that is the benefit from a forum like this which has some very informed people on it.

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