Polycarbonate - sandblasting? painting?

[DrHoneydew]

Hi all,

I am in the process of having some parts vacuum-formed from clear polycarbonate.

The end result of the part needs to have a sort of 'frosted glass' look to it: translucent, not transparent, 'matte' finish, not glossy.

The top surface also needs to be scratch resistant and relatively UV protected.

Right now, I am looking into sandblasting the top/outer surface, and possibly applying a light coat of some kind of white-ish paint.

Does anyone have any advice on this? Can polycarbonate be adequately sandblasted? How long will that sandblast treatment last with people walking on the surface? What paint will be appropriate for polycarbonate?

Thanks to anyone who has a suggestion.

Cheers,
Bill

 

[Pud]

See if you can get sheet which looks like what you need. There are many, many effects out there (wherever you are).

Scratch resistance is by hard coating the surface with "paint". This involves high temp curing so you may get draw relaxation on your parts.

Cheers

Harry

 

[patprimmer]

Opal colour is available in PC and acrylic. Acrylic has better scratch, UV and wear resistance. If impact is not an issue, acrylic might be a better choice.

If you do paint the polycarbonate take great care in paint selection as many solvents used in many paints do cause stress cracking in polycarbonate. The manufacturer of the sheet should be able to advise on a suitable range of paint as the sheet is often used in back painted signs.

Regards

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[Demon3]

I would put an opacifier in the PC sheet and then apply a coat of polyurethane to give the wear resistance. All PVC flooring is coated with polyurethane to adjust friction level, gloss and give wear resistance. When I was working in that area one good PU manufacturer for that application was Lord Corporation Ltd, Manchester UK. As Pat said, if impact is not crucial I would go for acrylic instead. PC has terrible solvent resistance. One drop of acetone on that floor and it will crack.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[coatingengineer]

Hi.

Maybe this is 'way out there,' but have you considered:

1) Grit blasting surfaces of your thermoforming tool. Perhaps this will get you the "frosted" finish you need.

then,

2) Apply a siloxane to your plastic product. General Electric (others, too) manufacture what are called Silicone Hard Coats. They're engineered for polycarbonate, UV stable, and resist abrasion.

Just look at most automotive car exterior head-lamps or tail-lamps and you'll see what I mean. These coatings are comparatively thin film (nominal 0.0002 inch) and cross link by low heat and surface catalyst.

Good luck!

William Gunnar

http://www.IndustrialCoatingsWorld.com

 

[pierdesign]

Good information and advice William.

How are GE and others siloxane etc., applied and are such coatings applicable for different geometries including flat molded PC windows?

 

[patprimmer]

PC can be purchased opal colour with siloxane treatment already done. I think GE's trade name is Lexan MR for mar resist. There are other suppliers, including Bayer with their Makrolon range.

It will not conform well to a grit blasted surface due to extremely high viscosity and low pressure at the mould to sheet interface. To get good reproduction of mould surface in injection moulding, melt pressures of up to 20,000 psi are used.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.