Digital BW, The Print

Robert wrote:

>Hydrocote is a polyurethane that is already polymerized!...
>that's why it is called "poly".  There are coatings which you
>add a cross-linker to but they are not available in
>water-based formula.

My understanding is that the water-based, single-component polyurethanes do
cross-link after application, whereas the acrylics do not.  Both are (I've
been told) soft "golf balls" in suspension.  While the best cross-linking is
with the 2-component, solvent-based polyurethanes, the single-component
water-borne version is said to be about half way between the acrylics and
the industrial-strength PURs.

As I understand it, the importance of the cross-linking is that without it
the coating is porous and cannot achieve as high hardness relative to
brittleness.  Many seem to recommend that a water-borne acrylic be coated
with a solvent-based polymer to seal it and reduce the "tackiness" of the
surface.  My hope with the PUR is to get a single-step coating procedure
that is tough enough to withstand some abuse.

For a tough, durable coating, the aliphatic PURs are the standard, as far as
I can tell.  The 2-component, solvent-borne versions just seem like they'd
be too much of a hassle to use.

One company has said it will send a formula to me/us that will make a
2-component water-based PUR.  This is the next step even for industrial
PURs, in part due to the pressure on VOCs.  This would probably be the
strongest water-based coating possible today, but I have yet to receive the
materials.

Paul
http://www.PaulRoark.com