Adhesion

From: Katharine Thayer ^lt;[email protected]>
Date: 02/12/05-03:17:37 AM Z
Message-id: <420DC98B.87B@pacifier.com>

I've explained this before, but on reflection I think perhaps it would
be helpful to explain it again:

There are two places where adhesion is an issue in gum printing. The
first is when the wet coating is brushed onto the substrate. While I
consider that a rather trivial issue, and it's certainly not what I've
been talking about in this discussion, it occurs to me in hindsight that
this is the issue that most people have been talking about when
addressing the issue of gum sticking to glass. To me it's a rather
uninteresting issue, because I never have any problem with gum sticking
to glass, mylar, or whatever, when brushing the wet coating on. At any
rate, when I refer to a problem with gum sticking to slick surfaces, I'm
not referring to a problem with the wet coating sticking to the surface.
The issue I'm talking about, and concerned with, is what happens to the
hardened gum after it's printed and it goes into the water.

The gum coat will brush on easily and stick well, in my experience, even
to very hard slick surfaces, and will dry easily and print well. But
good adhesion of the wet coating to a slick surface bears no correlation
whatever to whether the gum once hardened will stick to the surface. The
hardening process involves the gum crosslinking to itself, not to the
substrate, and only if there is some tooth present-- some paper fiber,
some roughened surface, any bit of stuff that is attached to the surface
and that can be enclosed within the crosslinked gum as it hardens, does
the gum stick to the surface. But if there's just slickness with nothing
to grab onto, then the crosslinked gum washes away in the water. I can't
prove this, but all the experience I've had printing gum says that this
is a valid principle, and I've done very well printing gum on hard slick
surfaces by proceeding as though it were true.

But I'm still interested in the question of whether adhesion (of the
hardened gum, not the wet emulsion) to glass can be improved by
chemistry, as Ryuji suggests. I'm skeptical, obviously, but I'm
interested. Unfortunately it seems like what's been suggested is not
readily available, so I don't know how I'll find out.

I'm interested because I decided that I want to present the gum on glass
by turning it around so the image will be viewed through the glass and
through the gum from the underneath, rather than presenting the gum on
the front of the glass where it could be scratched or otherwise damaged.
I've found that while my added-tooth solution works well for adhering
the hardened gum to the glass, and while from most angles the gum image
views well through the glass from the back, once in a while you get an
angle of view where all you see is the fine grit I used for tooth, and
you get white-out. So if there is a way to make a completely transparent
gum image that will adhere to glass without added tooth, I'd be
interested.

It seems to me that silane, for example, would help stick the wet
coating to the glass if that were the problem, but would it really help
with the more important problem of keeping the crosslinked gum on the
surface?. Is silane something that a person can get a small amount of,
and has anyone actually used this to print gum on glass or other hard
surfaces?

Katharine Thayer
Received on Sat Feb 12 11:12:58 2005

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