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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
>
>
>
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