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LABELS&LABELING |45
of highlight details allows consistent,
pin-sharp halftones with minimal dot
gain. This produces good flesh tones
and vignettes of the type associated
with labels for the cosmetics, toiletries,
healthcare, spirits and wine sectors.
The best of flexo, or indeed high-end
digital printing, can approximate these
effects, but offset achieves them more
easily and more quickly. Furthermore,
as its name suggest, offset printing is an
indirect process using precision-made
rubber blankets to transfer the image to
the substrate. This allows a wide choice
of printable substrates, ranging from
thin unsupported films to textured or
uncoated paper grades.
Similar quality criteria apply to shortto-medium
run flexible packaging
applications. As is happening with flexo,
wider and more versatile presses are
opening up opportunities for producing
shrink sleeves, sachets, pouches,
wraparounds, tube laminates, as well
as small folding cartons. Production
flexibility is essential, which helps explain
the increased interest in offset-based
combination/platform presses. So while
the process colors are offset printed,
typical press lines may include one or
more UV flexo and rotary screen units
for printing large solids, varnishes
and opaque white backgrounds. Other
options include gravure units with forced
air drying for printing metallic inks, heavy
solids and some coatings, as well as hot/
cold foiling with embossing, and inkjet for
variable data.
Offset units normally have two-cylinder
inserts (plate and blanket cylinders),
with a fixed impression cylinder, to
allow variable size changes without web
breaks. Sleeve technology takes this
a stage further when changing plates
and blankets. The sleeve carriers are
easy to handle and store being made
from lightweight materials, such as
polycarbonates and similar synthetics.
Gallus and Nilpeter both use aluminum
carriers, which are said to retain their
dimensional stability over a machine's
service life and are ideal in situations
requiring heavy impression pressures.
The actual wrap-around offset plates
are conventional metal types offering
good offset quality with minimal dot
gain. Working practices must take into
account a non-printing gap, usually of
two to three millimeters, which rules
out wallpaper-type designs. Blankets
sleeves can improve the inking/damping
performance even at high press speeds.
Even when sleeve cylinders replace
costly conventional cylinder cassettes,
offset combination/platform presses
still cost about half as much again as
comparable UV flexo presses. Offset
requires more complex inking trains
with several forme rollers to transfer the
higher viscosity inks to the blanket and,
except with waterless offset, must include
alcohol dampening systems to achieve
a good ink/water balance. The counter
argument is that over the longer-term, as
a quality-driven process, offset is more
economic and offers good productivity
benefits. Industry-standard color
management tools allow users to create
certain Pantone colors from the process
color set. What may require six units on
a flexo press is achievable with four on
an offset press. Furthermore, automatic
controls over the main functions ensure
that operators can quickly achieve good
quality and maintain it with minimal
attention. Importantly, pre-press costs
are far lower than with flexo. The plates
are not only cheaper, they are durable
over long runs and take less time to
make using in-house computer-to-plate
systems. Benefits like these appeal to
printers of wet-glue and in-mold labels
wishing to augment their sheet-fed offset
presses with variable size offset presses.
Where feasible, this introduces the
efficiencies of reel-to-reel or reel-to-sheet
printing and converting, backed by
existing pre-press facilities.
TECHNOLOGY HIGHLIGHTS
Offset combination technology began
with Nilpeter, when in 1994 it introduced
the 330-mm wide M-3300 with the help of
OEM suppliers. Despite initial skepticism,
the company has since sold hundreds
of offset-based presses all over the
world. The current fourth-generation
MO-4 platform press appeared in 2007.
Designed for short-to-long runs, it uses
aluminum-based sleeve technology
and has a web width of 406mm. At
Labelexpo, Nilpeter introduced the Press
Management Center (PMC). Its three
17-inch touch screens allow operators
to control UV-curing rates, electronic
registration and remote inking. Other
features include error diagnostics
backed by an online service function, job
management data and online customer
information. The PMC's functions are
compatible with the international CIP3
operating standard.
MPS's new EXL 410 Sleeve-Offset
combination press has roots in the EO
(Effective Offset) series, also from 2007.
The patented, bearer-less sleeves for
the plate and blanket cylinders give
variable repeat sizes of 18-25 inches. An
overhead rail allows the free positioning
of a compact flexo unit. Short runs are
facilitated by MPS's Automatic Print
Control (APC) system. It covers the
inter-related settings governing forme
rollers, plate sleeve, blanket sleeve and
impression cylinder, including print gap
control, for storage and retrieval from the
job memory function. The EXL-Packaging
is a UV flexo version with webs up to
660mm wide and a top print speed of 300
m/min.
As an OEM supplier, Goebel
manufactures the ink/water system for
the EXL 410. The Darmstadt-based group
also has links with DG press ServiceS
(sic), which in 2009 emerged from the
wreckage of Drent-Goebel as a spares
and service provider. Drent-Goebel's
Vision series of web-offset presses
featured the VSOP (Variable Sleeve
Offset Printing) system, developed by
rotec Hülsensysteme (now with the Flint
Group). DG press ServiceS recently
launched the Vision SP, based on the
520-mm wide Vision, with interchangeable
plate and blanket sleeve cylinders.
The servo-driven impression cylinders
are separately driven from the plate and
blanket cylinders, while the web tension
system is arranged in such a way to print
thin aluminum foils in perfect register, as
JANUARY 2012 | L&L