Hi Len,
That was one of the best "Techno-Babble" posts on this subject yet!
It would appear as though you have a really good understanding of
the chemistry involved in this process that we are trying to achieve.
Based on your experience, what exactly do you think we should be
doing? So far, the MIS inks seem to be "on top" as being capable of
resisting the etching as well as being able to be used in the
commonly available printers.
As for board prep, from first hand experience, I know that not all
PCB copper is the same. I had some where toner transfer works
perfectly everytime, yet others where I can't get toner to stick to
it unless I pre-etch it.
As most of us here are not chemists, nor do we play one on TV, all
we can do is experiment and try different things.
As for the requirements of board prep and solvents in inks (being
water or otherwise) etc. I came to my "hunches" above based on
something similar in experience. We have all used Sharpie brand
markers as a resist. I have used it on every type of PCB material I
have purchased.
Oddly enough, I have never had to do ANY board prep work to get that
ink to adhere and work good. I don't believe it is water based (or
uses water as a solvent) and being that black is the standard color,
it also makes pretty good sense that black ink should also work in
ink jet printing. Now if we could extract the Sharpie ink out of the
pen, AND get it to pass through an ink jet printer, we would have
our solution that works very reliably. My hope is that the MIS inks
are similar enough in "chemsitry" that they will perform in an ink
jet printer as well as the sharpie pens :-)
Chris
--- In Homebrew_PCBs@yahoogroups.com, Len Warner <yahoo@...> wrote:
>
> Wed, 19 Apr 2006 19:48, lcdpublishing wrote:
> ><snip Tarn-X>
> >I have a hunch there are two key elements to this whole ink-jet
> >printing thing..
> >
> >1) The proper type of ink - solvent based as opposed to water
based
>
> But water _is_ a solvent, and a darned good one at that :-)
>
> However, it's a highly polar solvent, in contrast to the non-polar
> hydrocarbons and the non- or slightly-polar other organics.
>
> >and pigmented as opposed to dyes.
>
> But pigments aren't dissolved (it's what distinguishes them from
dyes.)
>
> So both your criteria are rather confusing.
>
> >2) Curing that ink so that it doesn't wash away.
>
> Agreed, but you are relying on the binder in the mix: the "solvent"
> is actually a carrier liquid, the pigment is the colour (which may
> be irrelevant to the resist properties) and the binder is the glue
> residue which holds the pigment particles onto the surface -
> or the pigment would be as durable as a dry-wipe marker
> on a smooth surface.
>
> Because these inks are designed for a high-gloss finish, there
> is a higher amount of binder as a lacquer to glaze the surface,
> otherwise the printing appears dull against a gloss paper.
> That's probably why we are having some success with this
> family of inks as etch resist.
>
> It may also explain why yellow is best - it is a very transparent
> colour which may contain little or no pigment, whereas black
> requires much. It's even possible that a heavy pigment load
> weakens or perforates the binder layer.
>
> Another approach would be to reinforce the ink: copperplate
> print etchers of old used to draw with a grease pencil then
> dust the image with "dragon's blood" (a resin powder) and
> fuse, repeating as necessary to produce a nitric acid resist.
> I wouldn't want to exercise that amount of skill but it might
> be made to work, perhaps even with toner powder. The old
> Kodak Diconix ink was very oily/sticky but the technology
> is likely too old to resurrect.
>
> A method AFAIK untried would be to coat the board with a raw
> resist coating such as gelatin, albumen, gum arabic or PVA
> and then jet-print with a tanning agent. Potassium dichromate
> followed by UV harden, alkaline develop and bake would
> probably work but I don't like to think what it might do to the
> print head. Tannic acid might work. Boiled oak-galls might.
> Eye of newt, etc. - wish we had a good chemist on the list. :-)
> It might be worth asking on sci.chem
>
> >The little bit of playing around I did with the durabrite ink
> >with "Bone stock" PCB material showed me that it not only adheres,
> >but it doesn't bead up or puddle like the other inks.
>
> Beading and puddling is a surface energy phenomenon, an effect
> mediated by the "wettability" of the surface by the liquid and
> the surface tension of the liquid, both being the manifestation
> of intermolecular attractions.
>
> So both surface preparation and liquid composition play a part.
>
> In respect of an aqueous liquid, the wettability of copper is
> decreased by oily contamination of the surface and
> increased by the presence of somewhat polar organics
> such as alcohols or detergents as surfactants.
>
> A "clean" copper surface is probably oxidized or carries
> some other copper compound as a chemical tarnish derived
> from its last bath - the wettability of this will be influenced
> by chemical reactions as well as surface affinity.
>
> So weak organic acids such as citric or acetic will probably
> increase wettability in many situations and ammonia water,
> which is alkaline and complexes copper, in others.
> Acetic acid and ammonia seem to have solvent activity too.
>
> Another possibility is a mild reducing agent
>
> (It's subtle influences like this, combined with pre-treatment
> of the surface, that makes litho printing possible.)
>
> >So, I wouldn't worry too much about the Tarnex at this time.
>
> I hold no brief for Tarn-X but it is worth considering what
> pre-treatment might leave a molecular film to improve
> the printing - it's easier than modifying the ink, because
> it doesn't affect the ink delivery. Even something as
> simple as buffing with a glycerin or hard-soap impregnated
> cloth might have an effect (I only say that as an example
> of technique, I don't know whether it would be beneficial.)
> Microfibre cloth seems a good candidate: no lint and
> a very fine fabric structure to dispense the agent.
>
> This reasoning also leads on to the conclusion that when
> a successful technique is found it will be necessary
> to copy it with scrupulous attention to detail.
>
> Regards, LenW
> --
> Wisdom, free to those with the capacity to receive it:
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>