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Re: [TCML] Black printing can be *very* conductive!

That was also my conclusion.  The ink may contain lampblack or other
materials which can render it conductive or semiconductive.  I usually sand
off the exterior and then peel off the innermost layer on the interior.  2-3
coat soaking coats of AC-43 and they are ready to wind.

Dr. Resonance

On Mon, Mar 24, 2008 at 3:23 PM, <FIFTYGUY@xxxxxxx> wrote:

> Folks-
>    Well, I was sitting in my office today, and I  recalled our discussion
> about the conductivity of black printing on  Sonotube cardboard forms.
>    So I went to one corner, and picked up a  corrugated cardboard box with
> black printing on it and in the other corner  I got my megger.
>    My megohmmeter is a slightly older AEMC Model 1015,  but it's been just
> fine for my purposes. I used the 1000V setting.
>    The corrugated cardboard box had black printing on  the side. The part
> I
> tested had a black rectangle, 1" by 3", with an "unprinted"  5-digit
> number in
> the middle. Call it 60-70% black coverage in that  rectangle. And not the
> greatest printing job, as it wasn't as solid a color  as it could've been.
>    As I had posted earlier, I knew the black pigment  in the ink was
> basically soot, but I was astounded at how much a difference in
>  conductivity it made!
>    From one end of the rectangle to the other, I read  1 Meg of
> resistance.
> Enough that the 1mA of current sparked form the probe to  the surface of
> the
> box, and I could instantly, and strongly, smell burnt paper!  If I touched
> the
> probe down just a coupla millimeters to the side of the black  rectangle,
> the
> resistance read infinite - or at least over 1000 Megs, according  to my
> megger. Interestingly, the smallest reading I could attain was 300K, with
>  the
> probes 1/4" apart on the black rectangle. So it doesn't seem linear with
>  distance.
>    I was surprised that the basic cardboard box itself  was "infinite"
> resistance - the corrugated layers are held together with  water-based
> starch
> adhesive, and the paper layers themselves have some  moisture content.
>    So there you have it! Black printing on cardboard  can be *dangerously*
> conductive - enough to pass a few mA at a few thousand  volts, or enough
> to
> ignite the underlying cardboard! And this was a rather weak  print job.
> -Phil LaBudde
> Center for the Advanced Study of Ballistic  Improbabilities
> **************Create a Home Theater Like the Pros. Watch the video on AOL
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