Re: Adhesion

Sorry to send this message once more - I already sent it yesterday but it
didn't seem to have been posted to alt.photo...

> The gum process requires that the gum that's not exposed, that's still
> soluble, must be free to leave. I'm sure you must know this, so I take
> it you're saying that this close chemical bond between the silane, the
> glass, and (theoretically) the gum would be loose enough to allow the
> soluble gum to be released while at the same time it would hold the
> crosslinked gum tight to the glass?

Just a guess but I assume the situation of a silane/gum coated glass will
not greatly differ from that of a gum coated paper.
Maybe we ought to consider a photo layer (say, a "normal" silver halide
layer, dichromated gum, photopolymer etc.) as a three-dimensional
structure -
even if it's a few um thick only. Its surface is likely to behave
differently from those parts closest to the substrate.
If that particular silane ( 3-aminopropyltriethoxysilane) really behaved the
way I believe, the only relevant region would be where gelatin/gum gets in
contact with the glass. I assume this to take place on a "sub"-nano level
AND NOT throughout the whole layer thickness.
But as you already pointed out, unless someone tried... Well, at least with
gelatin it works.

Martin

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, February 18, 2005 7:20 AM
Subject: Re: Adhesion

> MARTINM wrote:
> >
> > I'd guess the silane doesn't care whether the gum is crosslinked or not
and,
> > it won't have any effect on the crosslinking.
> > It simply adheres to both glass and gelatin (or gum, hopefully), making
a
> > close bond between the two.
>
> I think maybe we're talking past each other, Martin. Maybe we're saying
> the same thing but not understanding each other. Let me give another
> stab at what I'm trying to say, and see if we can get any closer.
>
> The gum process requires that the gum that's not exposed, that's still
> soluble, must be free to leave. I'm sure you must know this, so I take
> it you're saying that this close chemical bond between the silane, the
> glass, and (theoretically) the gum would be loose enough to allow the
> soluble gum to be released while at the same time it would hold the
> crosslinked gum tight to the glass?
>
> There's only one way to determine whether silane works for gum, of
> course, but since there are about 27 different silanes and I don't know
> which would be a good one for gum (although I concur with you in
> wondering whether the ones that work best with gelatin would work well
> with gum, since the groups available for bonding are different in the
> two cases) and since I'm dealing with only two things right now: (1)
> pain and (2) these two group shows coming up, this will have to be
> tabled for later, unless some gum printer other than myself is willing
> to take it on as a project. Since I do know how to adhere a gum image to
> glass using the principle of tooth, I will continue on that path for the
> time being.
>
> In my opinion the quality of getting dissolved
> > by water has nothing to do with adhesion. That mainly depends on the
degree
> > of crosslinking.
>
> I agree, to an extent, that the quality of being water soluble has
> nothing to do with adhesion. Using the distinction I made earlier
> between the adhesion of the wet gum coating to glass and the adhesion of
> the crosslinked gum to glass: the wet gum coating adheres well to glass,
> in my experience, even though the coating when dry is completely and
> highly water soluble. And the fact that the soluble gum adheres well to
> glass has no relation at all to whether the crosslinked gum will adhere
> well to the glass. As I keep saying, if there's tooth, the crosslinked
> gum will stay; if there's not, off it goes. So certainly, adhesion is
> not related to solubility.
>
> But still, there's this problem that the gum has to stick only where the
> image is, and has to not stick where the image isn't, and that's the
> problem that I have with the idea of the adhesion of gum to substrate
> being a question of chemical bonding. It seems to me that either it
> would bond the gum to the glass entirely, in which case you would get no
> image because the entire glass would be covered with pigmented gum, or
> it wouldn't bond the gum to the glass at all, in which case you wouldn't
> get an image for a different reason.
>
> If it can be demonstrated that the silane somehow provides that physical
> "tooth" or even a chemical tooth which will allow the crosslinked gum to
> hang on but the uncrosslinked gum to let go, in the same way that paper
> fibers and grit and roughed-up plastic keep the crosslinked gum and
> release the soluble gum, then certainly I'd have to be convinced, but
> I'd have to see it to believe it, and I'd still want to understand the
> mechanism of how it would work.
>
> > Consider the situation when dealing with a silane subbed glass plate.
The
> > tiny silane layer firmly adheres to glass (actually, it's very difficult
to
> > remove it again). At the same time it provides (what you previously
> > called )"teeth" for the gelatin (gum)...
>
>
> Actually, I have not stopped calling "teeth" "teeth." Anyone who thought
> he had convinced me that "tooth" is not a useful construct to describe
> the "adhesion" of crosslinked gum to a substrate would be quite
> mistaken. As I've explained several times, what I've seen demonstrated
> again and again in my own practice and experimentation, is that tooth is
> everything when it comes to affixing a crosslinked gum image to its
> substrate, "tooth" being any physical structure (paper fiber, grit, any
> surface roughness, perhaps a crystalline structure (although that last
> part so far is pure speculation on my part) that the gum can
> incorporate into itself as it hardens and by that physical handle hold
> itself to the surface.
>
> Katharine
Received on Mon Feb 21 12:17:28 2005