Re: gloy for tricolor on yupo?

From: Loris Medici <mail@loris.medici.name>
Subject: RE: gloy for tricolor on yupo?
Date: Fri, 31 Mar 2006 10:44:50 +0300

> But what makes you think: the PVA which adheres perfectly to the
> substrate before exposure should (or may) loose that property when
> hardened? We know that colloids hardened in different ways such as
> gelatine + formaldeyhde / glutaraldeyhde / alum... (silver gelatine) /
> dichromate (carbon + oil) , egg + dichromate (temperaprint), gum +
> dichromate (gum dichromate)... somehow manage to stay on the substrate
> they were applied. Is there any example denying this fact?

Crosslinking of macromolecules doesn't have to be dense, and indeed, a
small number of crosslinking (in relation to the number of
macromolecules or crosslinkable sites) is sufficient to insolubilize
the binder in water.

Unless PVA (or gum or whatever) is hugely excessively crosslinked,
there is little reason to suspect that the adhesion itself is
significantly affected by crosslinking.

What I think is the most significant reason why chromium-hardened PVA
(or gum) slips off some surface is lateral swelling and force due to
this lateral expansion. To prevent it, you want to use polymer with
less swelling in water.

In the case of dichromated PVA on yupo, there are two contradicting
requirements for this goal, and seeking an optimal solution may be
tricky. I think the best solution is to sub the surface with something
a bit more hydrophilic (such as gelatin), but this is also not very
easy.

In above list of crosslinked colloids, they are usually coated on
paper or something more hydrophilic. In most cases, the substrate also
swells in water and the distortion caused by the lateral swelling is
at least partially alleviated. But if you use nonswellable substrate
like polypropylene (yupo), polyester (PET films), or glass, the story
is a bit different.
Received on Fri Mar 31 01:59:31 2006