Is it possible to achieve an optical mirror coating to a flexible plastic part?

If vacuum metalization is possible, would the reflective coating layer be durable enough to withstand the bending of a flexible plastic such as polyurethane or a thermoplastic elastomer, without cracking over time?

  • $\begingroup$ I think this is fine for here, honestly. Interesting question. $\endgroup$ – jonsca Jan 27 '13 at 17:42
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    $\begingroup$ read this: en.wikipedia.org/wiki/Metallised_film || I expect, that for some polymeres cooling of the plastic part may be an issue, but still. $\endgroup$ – permeakra Mar 11 '15 at 13:33

There are many techniques for metal-coated polymers, as linked by permeakra Generally, vacuum deposition is an issue because the metal is hot. Cold deposition techniques (e.g., sputtering, ink coating) often work better.

Common, commercially-available materials include:

As mentioned in other answers, adhesion is an issue, and to my knowledge, the processes to bind Pyralux and metabolized Mylar are proprietary.

Chemistry.About.com does mention vapor deposition of metals into Mylar, though.

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It might be possible to deposit a metallic film on a sheet of plastic. It is however, a problem with respect to the bonding of that layer. Depending on the plastic used, it might not have a strong bond with the metal, which would then over time develop defects.

On the other hand, it might be possible, when carefully manufacturing this, that the plastic has 'functional groups' (parts of the molecule with a specific function) that would bind a metal. Note however, that in this case, the functional groups might also react with other chemicals. Almost no functional group will only under go one reaction, especially not when metals are involved. Therefore, this would not be the most durable of options. Furthermore, because of the interface between, most likely, an amorphous solid (wikipedia, amorphous solids) and a metal structure is bound to create some defects.

A last option I can think of, is the use of conductive polymers. These polymers, because in many ways they mimic metals, also have a similar 'shininess' to them. However, I'm not sure about their really being a mirror.

Hope this helped.

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I would expect that gilding - classic manual gold plating using gold leaf - works.

(But as the frequency, amplitude and radius of flexing is not known, it's hard to tell)

It would be starting with the polished polymer surface.
That is coated with a special glue,
the gold leaf is just layed down on it,
and the gold surface is polished/burnished to create the mirror surface.

The difficult part may be finding the right glue substance, which depends on environment conditions. But a standard product should work.

So - why do I propose this ancient method?

I see the advantage in using an actual (microscopic) compact layer of sheet metal.
Gold leaf is just a thin gold foil.
But there is a special property in gold: it's very ductile. It's so ductile, that gold leaf can actually be produced roughly by taking a piece of gold and hammering it flat.

Now, I would think that the gold layer will not have much problems with the flexing polymer under it.
Another important property of gold here is the innertness of the metal, because we have the mirror layer directly exposed to air - not behind glass like in "consumer mirrors". With silver, that would be a problem

Gold makes a very good mirror for many wavelengths - you did not say which you are interested in. But if the yellow color tint of reflected visible light is a problem, one could try the same with other metals. No other metal has the level of ductility of gold, so they are possibly less suitable.

What makes me think that creating a sheet of metal first, and putting it on the surface in a second step is that any kind of metal plating where the metal is deposited on the surface will follow any roughness of the surface, which will cause irregular thickness and mechanical strength. On the other hand, the layer following the contours has a larger area, when looking closely, which shoud help with mechanical stretching. The typical thikness of deposited metas ist thinner than a foil. It can be made as thick for sure, but this could make coating expensive in terms of processing time.

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Yes, OCLI (optical coating labs inc) coated plastic film in 5' wide rolls that were 1000's feet long. This was done in the early 80's and I'm sure there is a lot of coating companies that do it now. One of my favorites was a nickle alloy film that we made into a recording tape. But they can coat both dielectric materials and metals. OCLI was bought up by JDS uniphase and later by somebody else.

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