Pigment coatings
2015-03-05 by roark.paul@...
Regarding format, I think we might be better off starting different threads for some of these discussions that could get interesting.
Coatings on the pigment particles are what I would like to focus on here. They are important and a variable that is subject to technological advance. All commonly used pigments are coated. The issues are the nature, purposes and effects of those coatings.
Carbon pigment inks have been coated for over a thousand years. Gum Arabic was one that was used for a very long time (and even recently -- but probably not for long -- for carbon nanotube research). It served as both a dispersant (what I think of as holding the individual particles apart at near distances), and it also served as a binder to glue the particles to the paper/substrate. (I tested gum Arabic and found it had way too many drawbacks relative to modern dispersants.)
Gum Arabic simply attaches itself to the pigment in a non-ionic fashion, like many surfactants will do. It used what is called a “steric” method of holding the other particles away. Today, most manufacturers appear to use an electrostatic repulsion approach to keeping the particles separated. The coatings are usually ionically attached to, for example, the edge of a carbon particle. (My carbon chemist brother indicated that the “edge effect” of carbon – what you can bond onto the relatively open carbon bonds at the edges – is a chemistry sub-specialty all by itself; it’s a big field.)
HP managed to combine the “steric” and “electrostatic” coatings with its Vivera pigments. See http://www.paulroark.com/BW-Info/HP-Vivera-Notes.pdf
In the Canon line, you see an advance in the Lucia EX from the older Lucia. Mark’s testing verified the advantages in fade testing.
The new Epson P600 may be another example of a new, advanced coating being used. Hopefully this will not only improve the yellow performance but also lower the various glossy artifacts.
The new Eboni v. 1.1 (from STS) is probably different due to a new, state of the art dispersant. The ink performs better in a number of respects, but at a cost of 1 Lab B unit, on average, more warmth.
All of the popular OEM pigment inksets use coatings on the color, LK/LLK and PK pigments that serve, among other things, to hold them onto the slick glossy surfaces that are very popular, particularly for un-glazed prints. Everyone also uses an MK that does not have this glossy-compatible coating.
For matte B&W printing, I tend to think that using the same type of pigment throughout the print can be an advantage. I also think mixing-up and hiding the cross-overs can be significant. The issue that relates to both of these is that you can often see the transitions from one density to another and from one pigment type to another. In fact, that may be one reason to have a blend even at the 100% spot. If the pigments are different types, like having different types of coatings, one can mask that. If I combine Epson MK (for ultimate longevity) and Eboni v.1.1 MK (for ultimate dmax), that may be what I’ll have to do at the 100% spot, even if it lowers the dmax a bit from what it would be with 100% Eboni/STS MK by itself.
Paul
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