Digital BW, The Print

koloshor wrote:


> But contaminated (even lightly contaminated) and all bets are off.
> 
> My parents house has what looks like 2 foot tall chunks of amber in front of it. My dad brought them home from work one day. They were the result of a tank of resin (he used to work at Rinchead-Mason, a big automotive paint manufacturer) that got contaminated and catalyzed into solid material in the tank.

Possible with 2 component inks (epoxy, polyester, polyurethane
etc), inks that solidify on oxidation (alkyds, linseed oil),
heat (infrared drying offset inks), UV curing resins, but not
likely to happen with dispersions with water, they still can
clogg the nozzles without getting solid though. Contamination
can disrupt the balance of the dispersion and coagulation or
settling may happen but that isn't a chemical reaction.


> I'd say, if it's kept clean, it should stay liquid for years. If you're mixing it with inks, that could be considered "contamination". Also if you're loading it into non-virgin carts.

Even our nice pigment inks settle without being contaminated.

> Grind something fine enough, and it can stay in colloidal suspension forever.

Would be very nice if it was that simple.

> 
> The water based versions use balls that are much bigger than the Epson ones. They won't stay in colloidal suspension, and form thixatropic slurrys.
> 
> To make something sprayable in a printer, the colloid has to be so fine that even under pressure, or local high differential velocities and shear, it stays a colloid. Thixatropy will clog the jets.
> 
> The solvent based coating don't have particles at all (except insoluble contaminants). The actual coating is fully in solution.

Pigment inkjet ink need a degree of thixotropy to have the
high viscosity for keeping the pigments from settling in the
carts while the viscosity has to get low for a better flow
when the ink is pumped through the nozzles, after that it is
nice when the ink gets the high viscosity again to keep
bleeding on the paper coating low. Even dye inks could use
that quality for the last aspect.

Ernst