Digital Prints

The reason I say “in most cases” is that, in terms of longevity, certain dye-based inks and
media combinations are definitely getting better. As already explained in the last chapter,
HP has carefully matched its newest “durable dye” inks with specific HP media and
swellable coatings in order to come up with combinations that rival the permanence predictions
of popular pigment-ink solutions. The way this works is that the dyes interact
with ingredients in the coated paper to gain the permanence. Print those same dyes on a
different paper, and the projected permanence is significantly reduced.
Third-party ink suppliers have also gotten on board by producing improved dye-based
color inksets. Futures Wales, Ltd., for example, released Futures Ink Wide Gamut dyebased
inkset in mid-2004 claiming that it provided a wider color gamut than other dye
inks, and that it was as durable as the leading pigments.
Pigment Inks
Unlike dyes, a pigment is a solid material comprised of many colorant molecules tightly
bound together and “stacked up” in a particular order into a single particle. These
“super-molecules” (actually crystalline solids) are more complex and are much larger
than their dye counterparts. While a dye molecule might be 1.5 to 4 nanometers in size
(a nanometer is 1/1,000th of a micrometer or a micron, which is 1/1,000th of a millimeter),
pigment particles are typically in the .05–.2 micron range or 50–200 nanometers.
Even though this might seem large in relation to dye molecules, these pigment
particles, which have been carefully ground down to microfine sizes, are easily small
enough to flow through the smallest 10-micron inkjet nozzle orifice that is 50–100 times
as large (see Figure 7.2).
Because pigment particles are insoluble in water, pigments remain in a solid state dispersed
throughout the liquid vehicle that will deliver them to the paper. One goal of a good pigment
ink is to keep the particles suspended for a long period of time. Epson uses microencapsulation
with pigment particles encased in a polymer resin medium to help with this.
(Not all of Epson’s pigment inks are microencapsulated. The Matte Black in the UltraChrome
inkset, for example, is not, which makes it problematic for use on glossy or semiglossy papers
where there can be “rub off” of the ink without a top coating of some kind.)
Chapter 7 ■ Choosing Your Consumables 215
Figure 7.2 A relatively large pigment
particle (left) is still very small
compared to an inkjet nozzle orifice. As
ink researcher David Matz likes to
explain it: Think of a golf ball falling
into a six-foot-diameter cup.
Recreated from diagrams of Dr. Ray
Work (left) and Dr. David Matz