Heatset Vs. Non-Heatset Web Presses
Web presses fall into two categories:
heatset and non-heatset (also referred to as coldset webs).
These presses print on paper rolls fed into the printing
equipment instead of on stacks of paper.
Heatset web presses
have more components than non-heatset webs. They feature
ovens at the delivery end of the press. These ovens flash
off the solvent in the ink, effectively drying the ink film
on the paper’s surface as the paper runs through the
press. Upon leaving the oven, the paper then passes through
chill rollers. Many web presses include finishing equipment,
such as in-line folders, which allow the final product delivered
by the press to be a complete signature ready for binding.
Non-heatset web presses
differ from heatset presses in one major way. They do not
have ovens or chill rollers. Ink laid down by these presses
must be absorbed into the paper to dry (or the solvent must
evaporate into the surrounding air).
The distinction between these
two types of presses determines the kind of work
for which each is best suited. Since intense heat quickly
dries the ink printed by a heatset web, the ink can be printed
on a coated sheet. The halftone dots and solid ink film
will sit up on top of the sheet, and the images will be
crisp. Such a press is ideally suited for long-run, high-quality,
four-color work. Some presses even have eight units (or
more), allowing both sides of the uncut ribbon of paper
moving through the press at from 300 fpm (feet per minute)
to 3,000 fpm to accept four or more colors of ink at once.
Keep in mind that in most cases paper
travels through a web press once. It is a ribbon of paper
running from the rolls at the infeed section of the press
all the way through the inking units, oven, and chill rollers
to the delivery end of the press, where it is cut into sheets
(or folded and cut). A sheetfed press, on the other hand,
allows the operator to bring back the printed sheets to
the infeed section of the press and either print the opposite
side of the sheet or add more ink colors or varnish to the
first side of the sheet. In contrast, on a web press, all
ink colors and varnishes must be printed in a single pass
through the press.
Non-heatset webs are ideal for jobs
on uncoated paper or the cheap, throw-away newspaper inserts
you get on the weekend. For this type of press, quality
issues are not paramount. Area screens and halftones printed
on such a press (particularly large screens) must be printed
with somewhat coarse line-rulings (150 to 175 lpi), because
mottling or uneven printing can occur.
If you are cost conscious, web presses
are best suited for very long press runs,
while sheetfed presses should be used for shorter press
runs. For instance, you might produce 5,000 brochures on
a sheetfed press, but it would not be economical in most
cases to print fewer than 50,000 press sheets of brochures
(with perhaps four brochures per sheet, for a total of 200,000
brochures) on a web press.
Another way of looking at this is that
15,000 copies of an 80-page magazine printed on a sheetfed
press might be of higher quality (crisper, more vibrant
photos, for instance) than the same magazine printed on
a heatset web press. However, the magazine printed on the
web press might cost several thousand dollars (or even as
much as ten thousand dollars) less than the same magazine
printed on a sheetfed press. How much is the better quality
worth to you?
Regarding quality, though, web presses
have improved significantly, and the quality of a four-color
printed piece in many cases is comparable to the quality
of a sheetfed printed product for pleasing color. However,
showcase color, like what you would need for a coffee-table
art book, still would require a sheetfed press. Look at
a selection of samples from your print providers to help
your make your decision.
What is Flying Paster?
A flying paster is a
piece of equipment attached to the infeed section of a web
press that pastes a new roll of printing paper
onto an almost exhausted roll of paper while the press is
running. It’s a wonderful invention because rolls
of paper at the infeed section of a web press eventually
run out, and stopping a web press to reload paper is highly
uneconomical, wasting both paper and time. Therefore, this
device was invented to allow a new roll of paper to be spliced
onto a roll of paper that’s just finishing up without
slowing down the press.
[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.]