Home' FLEXO Magazine : August 2016 Contents Vibration is inherent to the flexo process. As long as the plates have
printing and non printing areas, there will be impact at every turn.
But vibrations do not come only from the plate: When printing at
high speeds, any variations in accuracy or rotating parts throwing
things out of balance are magnified and can also lead to vibrations. All
vibrations negatively affect print quality and consistency directly, and
indirectly affect the above parameters.
Optimizing the performance of flexography’s many processes, such
as ink transfer, printing pressure and eliminating variables that may
cause bouncing, is the aim of all press manufacturers. The main goal
is to achieve consistent printing quality at high speeds.
Controlling the variables helps to eliminate defects during printing,
but as some bumps are inherent to the flexo process, a robust press is
the most important key to quality, repeatable printing.
STARTING ON SOLID GROUND
Starting with the foundations, the frames of some modern presses are
made in cast iron, designed to minimize vibrations. By minimizing
the number of separate pieces and maximizing the portions of the
press which are solid, manufacturers keep the machines robust, and
adhering to strict tolerances and precision. The combination of solid
frames with strict manufacturing tolerances is what, in the end, guar-
antees the maximum performance at higher speeds.
Still focusing on the stability and consistency of the press, it is import-
ant, during the machine’s design phase, to maximize deck robustness,
in order to be able to print the most difficult jobs. This is why bearing
clamps can be made from cast iron, heavily reinforced, with a very
solid articulation axis.
Carbon fiber mandrels are another inclusion, as they improve impact
absorption and provide better behavior against bouncing at high
speeds. A bigger diameter of the anilox and plate mandrels results in
a lower flexion level when printing at high speeds. Tests prove both
a recovery time against impacts and a flexion level 50 percent lower
than a conventional steel mandrel.
INK & BLADE
Continuing with the focus on manufacturing high end products that
allow for a high printing quality, one of the key factors is the stabil-
ity and consistency of the ink doctoring in the anilox. Ink must be
delivered constantly throughout the job’s running and in the correct
quantity to achieve the best printing quality.
One very important point on the topic of doctoring is the robustness
of the blade and its supports, and its adjustment against the anilox.
Some press manufacturers use low friction pistons that guarantee the
minimum pressure is applied from the blade to the anilox. This leads
to having better performance regarding bouncing and vibration, less
wear due to the synchronized movement of the doctor blade with the
anilox mandrel and the elimination of ink leakages.
Presses can come equipped with direct drive motors fixed on drum,
direct motors fixed to plate mandrels without mechanical transmis-
sion and absolute encoders fitted to shafts. Pressure adjustments are
made through servo motors.
There is still one last factor that must be managed to achieve
consistency and repetitive performance, job after job: Color. Color
adjustment is still often done directly on the machine during job
changeover. This introduces a lot of variation in the time and waste
required for doing the whole changeover, negatively affecting the
overall performance of the press.
Good practices “off machine” lead to avoiding process color adjust-
ments (CMYK) and to reducing to a minimum the adjustments in
spot colors. Manufacturers now offer matching tools which provide
the necessary rules to avoid making color corrections during job
changeover, to minimize machine downtime and to ensure repeatabil-
ity through process standardization. n
About the Author: Comexi is a press manufacturer based in Girona,
Spain. Technologies discussed in this article are offered on the company’s
presses. For more information, visit www.comexi.com.
AUGUST 2016 | FLEXO 107
“Color adjustment is still often done
directly on the machine during
job changeover. This introduces
a lot of variation in the time and
waste required for doing the whole
changeover, negatively affecting
the overall performance of the
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