ESL Diaphragm coating

[SY]

MJ, as I said, graphite is not a good choice here- it has too low of a structure factor. You want particles that are branched, hairy, dendritic, not laminar or spherical. The Cabot Vulcan XC are a nice place to start (BTW, Cabot has all kinds of great technical info on their website).

For Mylar films, I'd load some phenoxy resin in a BCA solvent, maybe start with one part carbon black, seven or eight parts resin, then thin with DBE or carbitol acetate to a thin enough consistency to get the right coating thickness. Forced heated air will be needed for drying and, as I said, you want the surface to be freshly treated and running 45 dynes or higher.

[arend-jan]

SY,

interesting point you make about the surface energy. Do you know of a way to DIY treat the surface like that?

[SY]

You can use a Tesla coil; the sort generally used for vacuum leak testing seems to work fine. I made a wire electrode for it and treated some Clysar sheets to 50+.

[AuroraB]

Just out of curiosity...there are conductive paints on the market, for ESD protection, both latex and polyurethane based. resitivity is spec'd E5 or E6, but I don't know how that is measured. Also some antistatic floor finishes.....
What if thinned and sprayed.. adhesion problems?

What's the active stuff in these spraycan antistat products??

[Calvin]

Hi,

as Sy pointed out earlier, getting some material with the right resistivity is no problem. The problems ly in the bonding capabilities of this material to a PET-diaphragm. A further problem arises out of the thickness of the dried coating and such out of its mass. The afore mentioned Licron for example adds considerable mass, because it forms a rather thick layer (besides its nearly impossible to get an really 100% even coating because of this xxxx spray nozzle cans).
The less mass the diaphragm/coating sandwich has, the better resolution and sparkle exhibits the panel (these are very small differences, but still detectable in a good setup)

One of the smart features of the conductive polymeres is that they dry out to an extremely thin film that doesn´t add too much mass (less than 1µm possible, whereas a ´normal´ laquer adds >25µm and as such becomes the major part of the moving mass and the mechanical parameters of the panel)

jauu
CAlvin

[Nevod]

One man from a Russian forum has developed a (at least realtively) efficient double-layer coating, consisting of a graphite layer overlaid with layer of nylon, dissolved in phenol-isopropyl mixture. The coating is fast-charging, stable, and allows for pretty good sensitivity. Nylon layer is, by design, only an protection for graphite, holding it in place.

My own thougths on coating have led me to several key points:
1. Coating must be resistive enough for constant charge operation, and to transfer as little charge af possible in case of diaphragm hitting stators.
2. At once, resistivity must be low enough to allow charging in under 5 minutes.
3. Coating must exhibit mechanical stability not to fall off, electrical stability not to be damaged by hitting stators and thus discharging, hygroscopically stable to resist weather changes, and so on.
4. It should be thin - to be light.
5. And that is the questionable one. Let's look at powered, but idling ESL, with stators at 0V, but fully charged diaphragm. It may be viewed as a series of capacitors, first one with dielectric layer of diaphragm coating, second one of air, and third - of stator coating. Voltage is distributed between them as between series resistors. And the force driving the diaphragm is, essentially, E*Q, with E ~being polarisation voltage, and Q being the charge on diaphragm. Then, as diaphragm with its coating can be viewed as a capacitor, then it's charge is proportional to Vad*Cd, where Vad is voltage across diaphragm's coating, and Cd is capacitance of coating, depending on it's material's dielectric coefficient, surface of coating and it's thickness. That creates such requirements on the coating, as high resistance, high dielectric coefficient, and thinness (although increase in Cd made by thinness is negated by equal-magnitude drop of Vad). That essentially made me think that, probably, one of best possible coatings is a double-layer coating of graphite overlaid with thin teflon coating. (and, some commercial ESL, such as Sound Lab's, do seem to use teflon coating).

However, that theory is highly questionable and i definitely need criticism and correction, at least on 5th statement.

[dazzdax]

Hi, I've always tought some well known electrostatic speaker manufacturers use a very thin coating of gold compound? What do Martin Logan and Sound Lab use?

Chris

[wolf_moses]

Does anyone know anything about the Shackman coating mentioned here?

http://shackman-electrostatic-loudsp.../Refurbish.htm

How good is it?

[MJ Dijkstra]

Originally posted by wolf_moses
Does anyone know anything about the Shackman coating mentioned here?

http://shackman-electrostatic-loudsp.../Refurbish.htm

How good is it?

I asked the shackman guys about the properties of their coating. I received a funny answer mentioning some 'bi-activated' mechanism, ofcourse this means nothing. (bi what?, activated what?) They didn't explain. Yes, the price of their coating is surely bi or tri or giga activated. 59 euro for 20 cc !!!!!!!!!!!

The site of shackmann also shows the coating fluid in some glasswork which is only used for quantitative analysis, not for production. Obviously this picture is there to impress the customer but it makes me laugh as I have seen a laboratory from the inside.

Their ridiculous price, their unwillingness to provide even the basic properties, their funny picture, can make only one conclusion to me:

Shackman = *******

[daanve]

Here an entry in ebay on this. ebay item

"Nearly shortcut-safe, adjustable to your needs by new ICP polymere conductivity."

"Special coating liquid on the basis of intrinsic conductive organic substances (ICP). that means without adding anorganic substrats."

etc..