Home' FLEXO Magazine : November 2014 Contents 38 FLEXO | NOVEMBER 2014
To be able to achieve consistent and repeatable results in your printing
process, the fingerprint must be run under normal conditions and
at production run speeds, i.e . 250 fpm. Virgin ink, along with clean
anilox rolls, must be used. Consistency is key for success. A spectro-
photometer is used to measure color and densities, as well as check
for even plate impression, which should be 3 percent or less between
operator and gear side. Watch for skips in the print or dirt on the
targets. This will cause the test results to be inaccurate.
After the fingerprint data is collected and extrapolated, the next step
will be to apply a curve to compensate for dot gain.
PROFILING FOR EG
After the fingerprint test, the next step in the expanded gamut cali-
bration process is profiling. A new set of plates with the curve applied
will be used to print the profile test target. One type of target used is
the IT8.7/4, which consists of 1,638 patches of different CMYK color
combinations for overprints.
There are several printruns for this test. The initial test is to print the
plates in the CMYK stations. Begin by moving the cyan plate to the
orange station and running the color combination of MykO. Then, re-
turn the cyan plate to the cyan station. Next, move the magenta plate
to the green station and print the color combination cGyk. After this,
move the magenta plate back to the magenta station. Lastly move the
yellow plate to the violet station and run the color combination cmVk.
With these four data set combinations the expanded gamut profile is
ready to be validated.
Once validation of the data is complete, conversion of screen builds
into spot colors can be accomplished through prepress software.
AUTOMATION EQUALS PROCESS CONTROL
The expanded gamut process requires a high level of registration and
web tension control to be successful. Building multiple spot colors out
of multiple screens requires registration tolerances of 0.001 or below.
CI presses always had an advantage of color to color registration, due
to the single impression roll and efficient web tension control between
decks. Traditional inline presses were constructed with line shaft de-
signs, gear boxes and gear driven transmissions that would contribute
to line shaft whip through speed ranges, gear backlash tolerances as
well as tension deviations due to multiple impression cylinders. These
variables were the main contributing factors to lineal registration
movement. If you could hold under 0.005, you were having a great day.
The current automation technology on narrow web inline presses
offers the ability to maintain the tightest register tolerances that allow
the expanded gamut process to succeed. On the more advanced nar-
row web inline equipment, there are no more line shafts, no more gear
boxes and no more gear transmissions that create all the unacceptable
accumulation of tolerances. Now we have the advantage of total auto-
mation. Multiple servo motors control all rotational axis of impression
rolls, anilox rolls and, at the highest level, gearless plate sleeves. This
level of automation eliminates line shaft whip or torsional twisting,
removes gear backlash and is reliable as a light bulb.
The end result is the same level of performance for the life of the servo
motor. We now have the precision of CI registration tolerances, along
with the optimum control of web transportation and tension control.
It has changed the way we go to press and the days of gear driven
machines are over.
There are many other advantages that automation has provided to bet-
ter control our printing process. Having the ability to save and recall
roll positioning is key to allowing the expanded gamut process to inte-
grate seamlessly with the flexo workflow—it improves performance by
only requiring a simple roll change by the operator. Recalling a saved
job will reset the entire process to its last known saved position. One
servo motor controls the rotational axis to reset lineal register; another
controls lateral register and yet others control print roll impressions.
A production run six months ago will be recalled and set up with no
waste, all while the press sits idle.
Now that the entire press is automated from the unwind to the
rewind, every servo motor position can be captured for total job
recall. The tension settings, dryer settings and all critical production
information is now captured, saved and stored for future recall with
minimal operator intervention. There are no longer manually adjusted
knobs all over the front of the press, requiring highly skilled operators
to reproduce past jobs.
A banded anilox (above) has multiple engraving bands across the
roll that have different screen counts with different bcm volume values;
below, a Nilpeter CLEANINKING chamber.
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