Digital BW, The Print

On Tuesday, December 10, 2002, at 02:22  PM, Robert Morrison wrote:

> Paul,
>
> One thing to remember here...is that the technology that you are being
> handed from these companies is for coating wood...a rigid, hard 
> surface.
> The demands on a coating for a flexible, porous substrate like paper 
> are
> very different.  That's one reason why no artist's materials companies 
> use
> polyurethanes.
>
> Regardless of what you are being told about the aliphatic water-based
> polyurethanes...no significant crosslinking occurs after the original
> emulsion polymerization reaction...that's marketing hype.  The film 
> cure is
> very similar between the polyurethanes and the acrylics.  The 
> difference is
> that the polyurethane polymer is harder and more light sensitive than 
> some
> acrylics.  Because of the huge range of acrylics polymers, products 
> can be
> formulated with a considerable variance in hardness.
>
> The key in this application is to get something that is just hard 
> enough
> that there isn't a tack problem, but not as hard as polyurethane so 
> that
> there is still flexibility.  Of course this isn't an issue with wood.
>
> Robert
>
Some of the prints I coated with  AquaZar water based poly on Sunday 
curled quite badly while drying and today the coating started to crack. 
  Humidity was extremely low  during this period.  These were on 190 gsm 
eclipse satine.  Don't know if the AquaZar is  an aliphatic poly or not 
- label on the can says "non yellowing".  The dried coating was 
beautiful, but I won't be using this product again because of the 
cracking.  Any problems like this with the Hydrocote?