Digital BW, The Print

Ernst,

You wrote:

>I think there are many good reasons ... applying Glop after printing. 
>... The first time glop was mentioned here I asked whether 
>it influenced bleed etc when applied at the same time with the inks. 

Sorry I missed that.  Yes, it does.  It can overload the coating and cause
serious roughness.  I recommend going to 2880 when printing with glop in the
mix.  This seems to control it best.

>Isn't the glop as used in the Epson R800 and its MIS clone not 
>basically the normal ink carrier without pigment but more resin added?

Yes, that is my understanding.  It looks like a slightly yellower UT base.
It does print with a bit of density, so it's more than just base. 

>... will act as a very fragile coating that can't be compared 
>to water based acrylic dispersions and polyurethane coatings 
>like Hydrocote's Polyshield. 

Exactly.  All it really does is counteract the bronzing.  I will probably
still spray or otherwise coat the important prints.  I may also not use the
glop when I'm going to spray the print -- unless my fade testing shows that
it offers more protection to the pigs, which it may.  If it doesn't I'm
going to suggest that MIS's supplier add some UV absorbing substances.

>Especially the last is something you wouldn't like to use in 
>inkjets as it can hardly be resolved after it dries, depends on 
>its hydrolyse grade of course.

By the way, there will be another entrant in the cross-linking,
non-yellowing, water-borne coating market, complete with a Wilhelm rating,
if they're lucky.  Something to protect these pigments from abraision, and
perhaps also UV, is almost certainly part of the best solution given current
materials. 

>What Epson writes is "the same high density resin as used in the 
>coating of the pigment particles". Sounds almost like a description 
>of polyethylene or polypropylene instead of acrylics. ...

I've heard that it is an acrylic, but they must have carefully balanced the
softness and stickiness with the need not to clog the heads too much.

On the other hand, I'll bet the "high density" may be about as misleading as
their description of the matte black's "solubility" layer.  There is no way
Epson would add a coating to a particle that had a higher specific gravity
than the dispersant base.

>The acrylic coating of the pigment (pellets) has more than just a 
>function in bonding.

Definitely.

> It delivers a better protection of the pigment itself

I'm not so sure of this.  Acrylic is not a particularly good oxygen barrier.
If one assumes that the total dimensions of the particles are, say, 0.1
micron, then the thickness of the coating may deliver less resistance to
oxidation than if there were that much more carbon or pigment.  The fact
that the Epson pigments seem to respond to the Print Shield protection more
than the MIS pigments suggests to me that the Epson coating probably does
not have significant UV blocking.  On the other hand, I'm suspicious the MIS
base does include some.

> and enhances the gloss quality of the ink.

That is near the top of the list and why it's going to be tough for an
uncoated pigment to match the high gloss look that the Epson pigments can
achieve.

I also think the acrylic can act as a bit of a floatation device.  In
general, the acrylic specific gravity is about the same as what I've
measured the base to be -- actually a bit less.  The pigments, on the other
hand, virtually all have higher specific gravities.

At any rate, neither Epson nor MIS's supplier is about to tell us exactly
what they are doing, unfortunately.  So, we'll just have to speculate.

Paul
www.PaulRoark.com