Inkjet Inks and Paper
An entire book could easily be written
about inkjet papers and inks (and many already have been).
The following is in no way intended to be comprehensive,
but rather to give you a starting point, a vocabulary, to
help you ask questions. Your printer will guide you through
the rest.
First of all, if you’re printing
display signage for a trade show or any other large-format
single image, you will want a printer with digital imaging
capabilities. Not all offset printers have such equipment
and knowledge. Vendors tend to specialize in either offset
or digital work, although you may be pleasantly surprised
to find out that your old tried-and-true printer has sprung
for some new equipment.
After you find your printer and tell
him about your job, you may first want to explore the various
surfaces on which you can print with an inkjet printer.
They run a wide gamut. You can print on paper, plastic,
and glass. You can create faux art prints on canvas. Everyone
has seen the back-lit displays in the subway, essentially
inkjet ink sprayed on transparent plastic and then lit from
behind. You can even print on food (with the proper non-toxic
inks). For example, photographs can be printed on birthday
cakes.
Second, consider the physical qualities
of your intended surface. When printing on a non-porous
surface such as glass or plastic, you would use solvent-based
inks. The solvent in these inks will be flashed off (caused
to quickly evaporate through the application of heat), leaving
only the ink colorant on the printed surface. Water-based
inks, on the other hand, could not be used on plastic or
glass, since they will not sit up on top of the printed
surface. Water-based inks need something to soak into (e.g.,
paper). Paper is porous; glass is not.
Next, you need to consider whether
the large-format ink-jet image will be used inside or outside.
The kind of ink your vendor chooses will depend on your
answer. Dye-based inks are used indoors only; pigment-based
inks are used indoors and outdoors. What’s the difference?
Pigmented ink-jet inks are composed of colorant (usually
a metal or mineral) molecules suspended between the molecules
of the ink vehicle (water or solvent: the liquid that makes
the ink fluid). In dye-based inks, the colorants have already
been absorbed into the vehicle (usually water), creating
one homogeneous solution. Outdoors, because your large-format
print will need to withstand the sun (UV radiation) and
rain, you need to use pigmented inks--normally pigmented
inks suspended in solvent. This kind of ink is generally
toxic and more expensive, but it is necessary for most outdoor
signage. Also, remember that these inks will let you print
on non-porous surfaces.
Finally, consider color accuracy (called
color fidelity). Many ink-jet printers (all of which start
with a four-color process ink set just like an offset printing
press) have added two or more additional colors, usually
light magenta and light cyan. Some also add even another
black ink. Why? Because not all colors (some PMS colors
in particular) can be approximated with only four inks.
Adding the extra colors to the ink-set expands an ink-jet
printer’s color gamut to more closely approximate
a wider range of PMS colors. Discuss this with your printer
to ensure a satisfactory result.
Armed with this information, you have
a starting point from which to choose a vendor and begin
asking questions. Using this common language, you will be
able to describe the results you are looking for and the
concerns you may have.
One final note: a good way to start
your search for a vendor with large-format ink-jet capabilities
is to ask your offset printer (whom you trust) to suggest
a vendor that focuses on “signage” or point-of-purchase
displays (i.e., the plastic or cardboard pop-up displays
in retail stores). The Internet is another good resource
for finding these printers.
What is a Freesheet?
A freesheet, which your printer will
distinguish from a groundwood sheet, includes no more than
10 percent mechanical wood pulp. Mechanical wood pulp exists
only in the two lowest grades of paper stock.
Why does this matter to you?
The impurities in a groundwood sheet
will cause the paper to age and yellow more quickly. This
may not matter if your publication is designed to be read
once and then discarded, like a newspaper. If, on the other
hand, you are printing an annual report that will (hopefully)
be kept and reread, you might choose a freesheet.
Also keep in mind that a freesheet
will be brighter than a groundwood sheet--an added plus
for a high-profile publication. Not surprisingly, freesheet
paper stock is incrementally more costly, depending on the
quality of the paper stock you choose.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]