Digital BW, The Print

On 12/10/02 7:36 AM, "Paul Roark" <paul.roark@...> wrote:

> Ernst,
> 
>>> I am down to near the bottom of the quart can of Hydrocote I first
>>> purchased, and I think I've noticed a  viscosity increase.  ...
> 
>> Is there any chance the viscosity increase is actually 'Hydrocote
>> polymerised' or just solids sinking / solvents evaporating ? One would
>> expect polymerisation to happen on top of the liquid of course.
> 
> I think some polymerization is a distinct possibility.  I'd be most
> concerned if it occurred in clumps -- making a smooth application tough.
> 
> I'm wondering if we ought to stir the mix very well when first purchased and
> pour it into several smaller bottles.  The 4 oz./ 110 ml. ink bottles come
> to mind as possible candidates.
> 
Incidentally, don't put the polyshield in plastic...only glass or metal
cans...the cosolvent will absorb into the plastic and this could also cause
a viscosity change.  If you are also using syringes for application you may
experience a problem here as well...I believe that neoprene is what is used
for the black seals in syringes...and on the short run it is resistant to
N-methyl Pyrrolidinone (the cosolvent in Hydrocote Polyshield), but in the
long run it will swell.  Neoprene are the best regularly available gloves
for handling NMP (you can order them through a chemical supply company), but
they should be changed regularly for the same reason.  I believe it goes
right through latex.  Lastly, here is the warning from the safety sheet on
the cosolvent:  "Repeated or prolonged contact with skin may cause
dermatitis. Animal tests show that this substance possibly causes toxic
effects upon human reproduction".  When we used the solvent in the plant
(back in my chemistry days), operators were required to wear respirators,
gloves and full body jumpsuits because of the "sensitization hazard".
Hydrocote Polyshield uses NMP at 5-10% concentrations...but it is very
hydroscopic...so if you get the Hydrocote on your skin the NMP will be
immediately absorbed.  It also has a relatively high vapor pressure
(compared to water)...so it starts coming off the can as soon as you open
it.

Here's the safety sheet for NMP:

http://www.cdc.gov/NIOSH/ipcsneng/neng0513.html

And the MSDS for Hydrocote Polyshield:

http://www.hydrocote.com/msds.htm



Robert