Re: Adhesion

From: MARTINM ^lt;martinm@SoftHome.net>
Date: 02/13/05-05:25:32 AM Z
Message-id: <001c01c511be$bfb907c0$b79f4854@MUMBOSATO>

> 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?

Yes, I expect "silane" to work in such a case. Note there is a large
variety of different kinds of "silanes". Take a look at:
http://www.powerchemical.net/index.htm
You may pay special attention on "silane coupling agents".

"Silane coupling agents belong to a class of organosilane compounds having
at least two reactive groups of different types bonded to the silicon atom
in a molecule. One of the reactive groups of different types (ex. methoxy,
ethoxy and silanolic hydroxy groups) is reactive with various inorganic
materials such as glass, metals, silica sand and the like to form a chemical
bond with the surface of the inorganic material while the other of the
reactive groups (ex, vinyl, epoxy, methacryl, amino and mercapto groups) is
reactive with various kinds of organic materials or synthetic resins to form
a chemical bond.
As a result of possessing these two types of reactive groups, silane
coupling agents are capable of providing chemical bonding between an organic
material and an inorganic
material."(http://www.micchem.com/products/SilaneCouplingAgents.htm)

I am not sure whether the 3-aminopropyltriethoxysilane is the best silane to
use when dealing with gum arabic solutions. 3-aminopropyltriethoxysilane
used to be the standard agent to promote gelatin (silver-halide emulsions)
adhesion on glass.
Prior to the introduction of silanes, glass subbing had also been done with
sodium/potassium silicate (water glass). By the way, temperature was said to
play a crucial part when coating gelatin on glass. 50C was considered about
the upper limit.

Martin

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, February 12, 2005 10:17 AM
Subject: Adhesion

> 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 Sun Feb 13 05:25:19 2005

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