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Old 16th June 2005, 08:17 AM   #1
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Sy: you da guy to ask about chemical stuff. Was wondering if a diaphram coating (ESL) could be found on the shelf at the hardware store? Spray paint, lacquer etc that would bond to the mylar and be flexible enough. Wondered if a product with Aluminum oxide (used in white paints) or tin oxide or titanium oxide or tin oxide or even a carbon black might yield a surface resistivity high enough. There are also the hundreds of resistive inks formulated to be used on film packageing. Any ideas
Had another idea, what about useing a diaphragm with a ferrous magnetic coating (audio/video tape) would not the iron be attracted to the statore magnetically? Before anybody mentions weight Quads double sided nylon can not be light.
Another even stranger idea. They use bucking magnets to direct extra flux into the gap in dynamic speakers. So why not a static field bucking stator? If you wound your stators with a bifilar wire and did not attach them at the top of the panel but did at the bottom would that set up two parallel stator panels with the same polarity and would not those fields repel each other forceing some extra electrostatic field in toward the diaphragm? Just some late night ideas before I crash. Best regards Moray James.
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Old 16th June 2005, 12:49 PM   #2
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The pigment isn't the issue for adhesion and longevity.

Most metal oxides are dielectrics so probably unsuitable- tin oxide (SnO, not the SnO2 version) might be an exception. Tin oxide, though, is very difficult to find in extremely small particle sizes and is almost impossible to mill. It's most suitable if you can coat the diaphragm via sputtering or CVD, neither technique being easily accessible to amateurs. The CVD process for tin-indium oxide mixtures results in a clear yet conductive film, very attractive.

On balance, I still think that carbon black is the best all-around choice: it's easy to control resistivity, it blends well into carrier resins, it's relatively nontoxic, and it's stable.

I'm pretty familiar with the chemistry of resistive inks for printing on plastics, and most of the ones suitable for this sort of application are carbon-based. When they are used on most plastic substrates (like polyester), the substrate is first print-treated- and THAT is the major issue in home-making coated diaphragms.
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Old 16th June 2005, 05:12 PM   #3
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Just goes in circles I guess. I figured that there are all kinds of paints that are made to stick to fiberglass (polyester resin) so one would think that some of those would stick to Mylar film. If we could go down to the local "rent it all" shop and get a corona surface treater then the inks would be the best bet.
What about a carbon black solution with a little liquified phenol? Wouldn't the phenol bite into the Mylar surface and set the carbon black into the surface layer of the film? I guess that this horse is tired of its all to regular beatings. Thanks for your comments. Regards Moray James.
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Old 16th June 2005, 05:39 PM   #4
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I've just never had good luck sticking anything to non-treated Mylar. Yeah, a corona treater is optimal, but if you're brave and handy with chemicals, a chromic acid dip will work quite well. As I've cautioned in the past, it's DAMNED dangerous and toxic.

If you want to be adventurous, you might be able to rig up some sort of blown-flame system by blowing air through a heavy electrical arc.
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