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I want to cast items out of epoxy resin. They will be tools used to handle ESD sensitive devices, so they need to at dissipate static charge, or perhaps somewhat conduct. Resins used will vary depending on the part.

Unfortunately, resin suppliers seem to never give any data on electrical conductivity. I presume it's extremely low. So to have it conduct, am I right in saying I could mix in something like graphite to help conduction? I presume it would reduce strength, or at least change some physical properties, but that's fine.

I've previously experimented mixing graphite powder with non-conductive powders - No liquids or glue, and just compacted by hand in a glass tube. I found that the resistivity could not be controlled easily / effectively by varying the ratio; it seemed it either conducted quite well, or not at all, to the degree where fine tuning ratios would too unreliable.

Might that be the case with epoxy resin as well? How might I increase the conductivity of a resin? And how might it be tunable? Principles / formulas? I presume the geometry, size and other physical properties of the powder used is important, as well as, perhaps, the resin?

Jayy
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If you have to use a resin system like epoxy, it should be no problem to lower the volume resistivity of the finished parts by adding carbon black with a suitable coupling agent to make sure the carbon is evenly dispersed into the epoxy resin. The great loudspeaker designer Harold Beveridge used this epoxy/carbon mix to make the cast electrodes for his electrostatic loudspeakers. You can read how he did this in his US Patent # 3,668,335. To get the desired ESD time constants he mixed roughly 5% by weight of carbon into the epoxy resin to get a volume resistivity of about 10^10 ohms/sq. You can vary the amount to get your desired ESD time constants. Beveridge did not use a coupling agent in his formula but I recommend that you do so , materials science has come a long way since Mr.Beveridge was building his speakers (circa 1973) :-)

William Hird
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For non conductive samples in an electron microscope , silver paint was used to conduct away any charge. I would expect copper powder or small fibers may be available also. Caution , I tried mixing fine zinc powder into an epoxy and it immediately reacted with the liquid epoxy.

blacksmith37
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