Thermopolymer that will noticeably change color when vacuum-formed 1

[abates]

Gentlemen,

Can anyone tell me if a thermopolymer exists that will noticeably and cleanly change color when vacuum formed? Perhaps more information about what I'm trying to do is in order.

I need to take a piece of this dark colored thermopolymer (for example, black) and vacuum form it over a die that has text. I need the raised text to be as white as possible for readability after the vacuum-forming process is completed. The trick is, I need the raised lettering to contrast as much as possible, so a slight color change really won't work.

If anyone can point me in the right direction, that would be great. If this doesn't sound like it would be to difficult to have specially made, please tell me who I can talk to perhaps with the possibility of developing this material.

 

[patprimmer]

Sounds impossible to me. It will be possible to change the surface reflectivity due to orientation of coloured fillers, but not to get a good contrast.

You might be able to back-paint clear plastic after thermoforming, by painting the high spots only white, say with a roller or by masking, the painting it black so it shows white on a black background.

Regards

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[abates]

Thank you for your reply! That's what I had feared and your suggestion was my follow up plan..that is, to thermo-form a clear applique and sandwich it to a colored base with the lettering on the base in white letters. Possibly via a silkscreened process for large runs, digital printer for small runs.

My follow-up question is this..what thermoplastic gives good forming results and is crystal clear so that the background color/graphic shows through with minimal color distortion? I will also need to try and find this with a matte (not shiny) finish. So, I expect to lose a little of the color contrast through the matte finish.

 

[patprimmer]

Acrylic also known as PMMA, poly methyl methacrylate, Perspex, Oroglass, Plexiglass.

It is extensively used in the outdoor sign industry, being back painted with lights behind the it.

Regards

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[Demon3]

You can thermoform with PMMA as Pat said. Polystyrene will work well and so will other more expensive polymers. It depends what mechanical properties you need. Usually you go for the cheapest polymer that satisfies the demands of the application.

There are thermochromic pigments for polymers that change colour with temperature but this effect is usually reversible. On top of that there are pigments that change colour when exposed to UV light. Some of those change irreversibly. That means you could irradiate your text with UV and get the colour contrast you wanted. These pigments are commercially available, a Google search should work.

These ones are reversible but I know there are ones that change colour irreversibly with UV as well.

http://www.matsui-color.com/photopia/

 

[abates]

That's very interesting stuff Demon3, thanks a bunch for posting. The thermochromic pigmentation sounds like the right solution. I'll do some research via google and perhaps follow up with a message on how I made out.

We use large format UV screen printers at our shop now. Perhaps I'll get a sample of this material and try it out.

 

[abates]

Whoops, I meant the UV ink, NOT the thermochromic..

 

[Demon3]

Another thing to mention is that some polymers start dark and become white when deformed. This is because the polymer stress whitens when deformed. The most common example is PVC filled with calcium carbonate. See for instance Dymo labels (

http://global.dymo.com/enUS/Products/Organizer_Xpress.html).

Maybe this effect could be used to generate what you want cheaply. So you thermoform a sheet of filled plastic and it goes white where deformed.

 

[abates]

Demon3, that is EXACTLY the type of contrast I'm looking for, albeit via the thermoform process. You certainly described what I needed better than I did. Cheaply is the key of course. Are there any brand-names that come to mind I should try to acquire samples of for testing?

Thank You

 

[patprimmer]

Polypropylene also stress whitens, but the key word is stress. It will not stress whiten if thermoformed at normal moulding temperature. It must be loaded when cold enough to stress.

Regards

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[abates]

hmmm, the effect is exactly what I'm looking for, but I really need to cheaply thermoform the part AND get this stress whitening effect. What I need is an easily stressed thermoplastic.

 

[abates]

Anyone have any ideas as to a particular type or brand-name of thermopolymer that would exhibit the qualities as noted above? I liked Demon3's example of the PVC/calcium carbonate example. Would this be attainable when vacuu-formed in addition to stress formed?

 

[patprimmer]

Use your local yellow pages to find a plastic sheet supplier or thermoformer. The thermoformer will have his own source of suppliers.

If you thermoform to shape, then place over a second core with the contrast areas cut into it, then cold form by using a punch to stretch the sheet into the recess in the core you should get a result.

You may need to experiment with the depth of the punching action and the shape of the nose of the punch so as to avoid white outline, but no whitening of the centre of the lettering lines.



Regards

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