Digital BW, The Print

Tony Sleep <TonySleep@...> wrote:

> On 24/01/2009 pr_roark wrote: ...
> > The most surprising result of the test is that the HP 
> > Grey settled significantly more than my dilutions of the HP PK.
 
> HP claim their electrostatic encapsulation of pigment 
> maintains dispersion and prevents settling.

All inkjet pigments have some form of stabilization coating, even if 
just an un-attached surfactant.  These stop 
flocculation/agglomeration, but the carbon-based pigments are still 
heavier than water or the base/medium that is likely used.  Brownian 
motion will help and may be enough to keep the very smallest 
particles from settling, but from what I can tell, all of our 
pigmented inks have particles that will ultimately settle or separate 
if not agitated.  The higher the viscosity of the medium or dilutant, 
the slower they settle.  Specific gravity of the medium is also a 
factor.  However, the bottom line is that even with an outstanding 
stabilization coating, our pigments are still subject to settlement 
or stratification (particularly multi-pigment mixes) in the medium if 
left still for long enough.

So, while I think HP has an excellent stabilization system, I doubt 
that by itself is enough.  My tests indicate their grey ink likely 
settles with time.  It appears, however, that HP has taken steps to 
deal with that issue.  I certainly would not worry about it if you 
have or are considering buying an HP printer.

> This may be overwhelmed by a centrifuge, giving a 
> result that does not reflect real life.

My real world sample comparisons are not that many, but to the extent 
I've been able to compare long term settlement in bottles to the 
results of the centrifuge, they do correlate rather well.  The 
centrifuge is basically just subjecting the samples to 6000 G's and 
thus accelerating whatever gravity would do.  If anything, I suspect 
it under estimates problems because the longer time in a bottle would 
allow more flocculation/agglomeration if it were going to occur, and 
the centrifuge has some vibration which probably tends to mix the 
samples a bit.

Keep in mind that when I say the HP grey pigs settled much more than 
some of the latest dilutions I'd mixed, I'm still looking at only 
about a 5% change over what is probably equivalent to 4 months of 
being still in a bottle.  This is not a major problem.  But I'm 
looking at less that a 0.2% change in some of the HP dilutions I'm 
testing.  With this new tool and the best input pigments, I hope to 
make some mixes that are very stable even in wide format printers -- 
which has been a problem in the past.  We should not have to agitate 
our carts regularly.

Paul
www.PaulRoark.com