Digital BW, The Print

"Greg" <dfaprinting@...> wrote:

...
> Paul, does it settle in the ink lines or just in the carts? 

I'm not sure, but I think it's the wide format printer carts where 
the problem is.  From what I can tell once the 7500 starts to print 
the dampers and lines get agitated enough to take care of whatever 
problems may have been there.  Also, the dilute Eboni positions in 
the 7500 virtually never show a bad nozzle check even after 
relatively long periods of non-use.  (The 100% Eboni will sometimes 
need a cleaning cycle.)

> If it is stable in the lines then you could probably make a 
> vibrating mechanism that keeps the carts agitated enough 
> to keep it in suspension. ...

You're probably right.  What I do now is just roll the cart end of 
the 7500 back and forth occassionally -- vigorously.  It's actually 
very simple.  

But if I didn't have very clear warnings about this problem in my PDF 
and here there would be too many people who would put the inkset into 
wide format type printers (including 3800) and then complain loudly 
that the inkset is a dog.  Likewise the 1800 sponge-
containing "spongeless" MIS carts that cause a tone change with Eboni-
6.  These types of problems really blow up for MIS and I if the 
issues are not very clearly disclosed when found and avoided whenever 
possible.

I might add that the old sepia and other blended inks in MIS mixes 
also have these problems, as discussed at page 4 of 
http://www.paulroark.com/BW-Info/4K+.pdf

This tone shifting problem was first noticed by a wide format user 
who did not use a stand.  Those of us who regularly printed with a 
stand found that the rocking of the stand did the job -- as long as 
the printer was used often.  But if no stand is used -- as in many 
3800, 4000, etc. installations -- these problems can (will) show up 
even with regular use.  

One of the interesting issues with the HP neutral pigments is whether 
HP's pigment and stabilization advances will avoid this even when the 
inks are diluted.  The HP neutral greys and PK are blends of 
different types of pigments from what I can tell, and the literature 
on pigment stabilization is consistent with what I've seen -- blends 
tend to separate.  Particularly with electrostatically stabilized 
matrices, the particles that are dissimilar just don't fit in as 
well, so the fall out of the matrix.  The trick appears to be to very 
closely match the pigment characteristics that affect the 
stabilization.  So far, the tone changes I'm seeing with the HP 
pigments in the centrifuge tests -- diluted or not -- are minor.

Paul
www.PaulRoark.com