Static dissipative coating on Lexan

[knowlittle]

I have an application for acrylic sheet about 60 cm x 60 cm (2'x2'). But I need to control static charge buildup.

I have seen clear plastics with some kind of transparent coating that they claim to be static dissipative. What kind of coatings do they put on?

Other ways to mitigate static charge?

Thanks.

 

[btrueblood]

How long do you want the static dissipative characteristic to last? You can get spray-on coatings not much different than that used in dryer sheets and fabric softeners, that form a slightly waxy or oily film on the parts, and they wear off pretty quickly. Harder formulations (like a paint, dries hard) wear off more slowly. Then, there are products added to the parent resin prior to extruding/molding the sheet, and those tend to hold up the best...

 

[knowlittle]

Thanks for the quick reply. My apology for not giving boundary conditions.
1) Waxy or oily film cannot be used. Outgassing is a concern. It goes to space environment.
2) The harder formulation may work. What is available? conductive epoxy will not work. I have seen advertisements of some conductive layers that can be put on any plastic. What are they? Some are a few angstoms thick. They must be vapor deposits. some are microns thick. I have no idea what they might be.
3) Regarding the product that can be added to parent resin, this would be the ideal solution. Do they make acrylic sheets with this thing added so that I can buy a sheet off the shelf?

Thanks.

 

[knowlittle]

I realized I didn't answer your question: how long should static dissipation last? Answer: long term, I mean months. Ideally, permanent.

 

[dgowans]

knowlittle,

Do you need the material to be clear? LNP (part of Sabic, formerly GE) and RTP both make compounds that may meet your needs, but I don't know if they are available in clear.


Not much definitive information other than a couple places to ask, I realize. You can get sample plaques from LNP, if not both, if you need to do some testing.

 

[Demon3]

I just saw a presentation on that today at the Addcon conference in Barcelona. The contact person is names Constant Peek at SABIC for transparent PC with permanent antistatic. He is at SABIC Innovative Plastics BV in The Netherlands.

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

 

[Compositepro]

By the way Lexan is not acrylic. Anti-static additives generally migrate and require moisture to work. These are not suitable for space. Carbon black can work but not for transparent material. I think your only options are conductive coatings. Gold or aluminum can be applied so thin that the plastic is still mostly transparent. Tin oxide is transparent and conductive and is used on glass windows. I'm not sure if it can be applied to plastic but I thick it is used on aircraft cannopies.

Of course this only solves the charge separation between the plastic and the conductive structure. The charge is still on the spacecraft.

 

[patprimmer]

Stainless steel fibre as an additive is a permanent antistatic and can be used in such low add rates and the fibr is so fine, that the material retains clarity. DSM Engineering Plastics has PC clear permanent AS by this method. It may be workable in acrylic.

Contact DSM, Sabic and RTP. They are the main players in this field. You will then need to find someone to produce sheet or parts from the resin. This will be a very costly exercise. Alternatively you could ask the three compounders if they sell compound to a sheet producer

Regards

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[unclesyd]

Take a look at the PC350 on the SciCron site. If you material the also have an antistatic coating.

http://www.sctech.com/product_information_pc350.html

 

[unclesyd]

Here is another coating that you might want to look at.

http://www.hcstarck.de/index.php?page_id=961

 

[btrueblood]

Ugh. I was afraid you'd say you were in a vacuum, but space...that's the worst!

Outgassing, yes, and evaporation/oxidation of the gooey types of a-stats precludes those, and the salt-based and thiol-based resin coatings require atmoshperic moisture to stay conductive. The thin metallic coatings will work, but will usually be degraded over time by atomic oxygen at LEO - there is a NASA study/report on coatings, especially thin vapor and electro-deposits on various substrates, that is based on retrieval of a spacecraft that was purpose-built and launched to look at degradation, can't remember the name of it now...but it will give you a very good idea of the rate of degradation.

If you are operating higher up, e.g. GEO, the degradation is typically a lot slower. Ask some of the solar panel manufacturers what they use (e.g. entechsolar.com, or look at design details for the space station solar arrays, since that should be public-domain info.), static dissipation on solar arrays is a big issue, since arcing across the element contact grids due to static charge buildup is one of the main degradation mechanisms for those beasties. Last I'd heard, the predicted lifetime for a solar array in GEO was 15 years before output degraded to 50% of initial power.

A lot of work has been done on amorphous diamond coatings, which have some intrinsic conductivity. I think those coatings can be tweaked to increase the graphite composition, which can help make the coating more conductive. Dunno what the status (commercial availability) of the coatings is, it was a research project for a colleague back 10+ years ago, at a job I long since left behind...

The ss fiber that Pat mentions is one of the more bullet-proof additives to resins that I was thinking of, but even though the material is "clear", the optical properties of the part can be affected (e.g. may blur, distort or cause asterism in lenses).

 

[Demon3]

Carbon nanotubes work in such low amounts that it is still transparent. The SABIC guy I mentioned stated that his conductive PC needed no water vapor and works in a vacuum.

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

 

[knowlittle]

Wow, I love this place. From antistatic spray to amorphous diamond, all are covered in a span of a few days.

I think we will most likely take the approach of tin oxide coating that bonds chemically to polycarbonate substrate. It's available off the shelf.

By the way, my use of "space environment" was misleading. My apology. I didn't mean the vacuum space, but the space shuttle indoor environment. It doesn't see atomic oxygen or other high energy radiation.

It was a good learning process. Thank you all.