ESL Diaphragm coating

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.
 
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??
 
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
 
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.
 
wolf_moses said:
Does anyone know anything about the Shackman coating mentioned here?

http://shackman-electrostatic-loudspeakers.reromanus.net/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 = *******
 
I received a funny answer mentioning some 'bi-activated' mechanism of course 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 !!!!!!!!!!!

Agreed, pretty suspicious. I've done a fair amount of work for the past 30 years or so on conductive coatings and ICPs (have a dozen or so patents on them, quite a few published papers, and run programs for top aerospace companies), and these are terms I've never heard of.

A decent coating can be made very inexpensively, but as I've said again and again and again (seemingly to no effect), the coating is no trick, it's the surface preparation of the film which is the key.
 
SY said:


A decent coating can be made very inexpensively, but as I've said again and again and again (seemingly to no effect), the coating is no trick, it's the surface preparation of the film which is the key.

Chemicals can do the job as well (not always ofcourse).
Surface preparation is not that practical as the effect decreases with time. It also breaks covalent bondings of the surface.
 
The treatment only needs to last as long as it takes you to paint the surface and dry it. That's pretty much a non-issue. Yes, it breaks covalent bonds (there aren't any other kinds in plastic film) on the surface- that's the whole point of it.

Chemical treatments can work, but the only effective ones are HIGHLY dangerous and toxic, so I won't make any recommendations.
 
SY said:
The treatment only needs to last as long as it takes you to paint the surface and dry it. That's pretty much a non-issue. Yes, it breaks covalent bonds (there aren't any other kinds in plastic film) on the surface- that's the whole point of it.

Chemical treatments can work, but the only effective ones are HIGHLY dangerous and toxic, so I won't make any recommendations.


There is a whole world of modern glue and paint technology without using pretreatment, it is not a must. These paints and glues are not awfully toxic. No you can't eat or drink them but they won't burn off your skin.

I received a lot of feedback from DIY of all kind of products with their problems and their +. Adhesion problems are rarely mentioned as a problem, except in case of metalised Myar which is obsolete now anyway.
 
Hi,

I have been using a waterbased schoolglue from Velpon (without solvents) for some time now.
I spray it on in some layers with an airbrushpistol.

The good thing is that it sticks excellent to the mylar and holds for years, without any problem as I have experienced.
I can only clean it of the membrane , if I should want to, rubbing it with pure ammonia .
It is completely clear an feels dry and not sticky, ones dried out

The bad thing is that it's working as a conductive coating is based on the hygroscopic principle and so it's surfance resistance can get to high ,depending on weather conditions, also as I have experienced.
Anyway I want to have the surface resistance around 1Gohm, without changing to 20 or more Gohms.

I have been thinking if it could be an idea to mix a conductive substance (graphite based or other) with this glue, to get a substance that sticks well ( should not be a problem because this glue simply works) but also becomes better conductive and less dependant from air humidity (self conductive)

Any chemist who can help or give some tips?
I am shure willing to do some tests , measure, and publish here.
I use a Megger for high tension purposes to measure the surface resistance.

Geert
 
Hi,

@Nevod
I wouldn´t regard the charge on the diaphragm as capacitor.
But if so Teflon would be the wrong conclusion.
Teflon is not stable against Ozone (which is nearly always created in an ESL in small doses).
Its dielectrectic constant is very low and its resistance values extremely high.
It is nearly impossible to get something to stick to Teflon, especially not a flexible and vibrating material.

A solution could be to use 2 very thin diaphragms of Mylar/Hostaphan and the coating between (as kind of a glue to both membranes)
This could reduce the problems of hygroscopic coatings and ageing and would even raise the flashover treshold a bit (~100-300V).

The waterbased glue, doped with ink (which works stable for Years now) is probabely the ideal DIY-option, since its cheap, easy to handle (brush, paint or spray), absolutely non-toxic, very thin and light and the parameters can be easily taylored to Your needs (a charging time of a few seconds is ok, 5min way too much).

As I am told(!) Gold as well as some other metallic compounds seem to be not stable in this application. Kind of ´cracks´ seem to develop over time and under HV-conditions leading to a creation of little ´isles´ of coating that loose more and more contact to each other till the coating fails to conduct. Same seems to apply to the ITO-coatings (which afaik ML used for a while). ITO coatings come as standard off the role 12µm thick material for TFT-displays is quite low in resistivity and could only be useful for smaller hybrid ESL panels.

jauu
Calvin
 
Hi Calvin,

What kind of ink do you use to dope the glue? and in which quantities.
Did you measure the surface resistance?

This weekend I coated a membrane with a mixture of waterbased glue and black waterbased airbrushpaint.
Once dry,te surface resistance measured around 4Gohm.
The recoated ESL is playing perfectly, but I really would like to find a way to get the surface resistance to around 500Mohm - 1,5 Gohm


The bizar thing is that in the past ( years ago) I measured resistances around 1,5Gohm... with a mixture of that shoolglue with some drops of blue airbrushink.

I wonder if mixing the glue with graphite particles or for example with contact chemie graphit33 could work?
Or is there another waterbased well conducting liquid, wich can be mixed with te glue?

Another thing.
Has anyone on the forum ever tried Contact chemie antistatic 100.
I think it may be a bit to good conducting and I don't know how it will stick on a moving membrane in time?

Geert