Years ago (maybe 40) I read about a technique that mentioned taking
standard 2-part epoxy and loading it with graphite (the typical powered
graphite for injecting into locks to make them smooth.) I also seem to
remember from trying it that you had to add it to the catalyst/hardner,
not the the epoxy as the graphite would cause the epoxy to "go off."
It will not be a terrific conductor, but it should become conductive.
Conductive epoxies depend on the fact that they are heavily loaded with
a conductive material such as nickel, copper, silver, gold, or
graphite. As the epoxy cures, it slightly contracts causing the
particles to be forced into contact. The devil is in the details.
Copper and silver in particular are subject to oxidation, so with time
the material may not work so well.
Once you have loaded the epoxy with enough material it gets pretty thick
(actually should be a paste) -- not liquid pencil material. However,
you can take epoxies that are already mixed with catalyst (but you need
a slow working one such as a 1 hour cure or more) and dilute it with a
solvent such as MEK. The trick here is that you have to apply it thin
enough and allow enough time for the solvent to evaporate before it
hardens and traps the solvent (yielding bubbles.) The MEK will also
slow down the curing process somewhat but the real problem is that when
applied to the substrate, most (but not all) the MEK will evaporate
quickly so the epoxy thickens up and "goes off" at pretty much its
normal cure time. Your other problem here is that MEK is a very
aggressive solvent, so if the pen is a typical plastic, kiss the pen
goodbye. I can't think of good answer right now for that problem other
than use an old fashioned bow pen (like a miniature tweezers with a
thumb screw adjustment) that was used in drafting with India ink (you
know -- in prehistoric times before CAD programs). The bow.was made of
steel and wouldn't be bothered by MEK. And it still may not work
because of the low surface tension of MEK may not let you hold the
"liquid pencil" blob within the bow, although I know I have used
tweezers to pickup a bit of MEK to transfer it to the point where I
wanted to dissolve something. So it will meniscus in a tweezers.
Anyway another thing you might want to try.
Regards,
Charles R. Patton
On 7/27/2011 11:16 AM, Donald H Locker wrote:
>
> I used a mechanical pencil lead once as an electrode in an etching
> experiment; worked quite well, which is why I thought maybe one of
> these might. Oh well, thanks for the update.
>
> Donald.
> --
> *Plain Text* email -- it's an accessibility issue
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>
> ----- Original Message -----
> > From: "David Mitchell" <gossiphog@...
> <mailto:gossiphog%40gmail.com>>
> > To: "Homebrew PCBs" <Homebrew_PCBs@yahoogroups.com
> <mailto:Homebrew_PCBs%40yahoogroups.com>>
> > Sent: Wednesday, July 27, 2011 2:14:13 PM
> > Subject: Re: [Homebrew_PCBs] liquid pencil
> > Never mind. I tried it and the lines are not at all conductive. I'll
> > try and
> > think to check again in 24 hours after its cured or whatever. Actual
> > pencil
> > lines im still interested in trying to plate though. Some day!
> >
> > On Tue, Jul 26, 2011 at 9:52 PM, Donald H Locker
> > <dhlocker@... <mailto:dhlocker%40comcast.net>>wrote:
> >
> > > **
> > >
> > >
> > > Thanks for the link; now to find a local retailer or such.
> > >
> > >
> > >
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > ------------------------------------
> >
> > Be sure to visit the group home and check for new Links, Files, and
> > Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
>
>
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