Home' FLEXO Magazine : June 2017 Contents tube age and quality, tube temperature, bed temperature, ballast con-
figuration and many other factors.
Getting consistent light exposure throughout the plate from a frame is
difficult to do. Bank lights are not consistent over their lives, degrad-
ing in output quality continuously until they reach the end of their
500 to 700 hour lifetime. To compensate, operators have to adjust
exposure times quite often. And, when new bulbs are inserted in a
light frame, they should be “burned in” for eight hours. Unfortunately,
extending the exposure time does not completely compensate for the
loss of light intensity. The degradation is also different for each indi-
vidual lamp, as research has found there is approximately 10 percent
variation in output intensity with new bulbs.
The product that came from these needs was developed over many
years. Twelve years ago, Esko introduced Inline UV technology to
deliver excellent consistency, while maintaining the round top dot
geometry considered standard at that time. In 2012, it evolved into
Full HD Flexo, with Inline UV2 technology that used UV LED diodes
inside the CDI, expanding capabilities to include flat top dots.
This led Esko to develop the XPS Crystal, ultimately part of a com-
pletely automated plate making system. It is a digitally controlled UV
LED exposure unit, providing both main and back exposures, sup-
porting all photopolymer flexo plates. Plates are placed onto the glass
surface, where very accurate back and main exposures—by patented
UV LED light technology that, unlike light bulbs, allows very precise
control—are conducted simultaneously. Plate consistency is one of
the keys to achieving and maintaining optimal print quality. One of
the main factors influencing plate stability is the plate’s UV exposure.
Unlike UV frames using light bulbs fluctuating in output, the XPS
Crystal uses UV LEDs that don’t need warmup time and always emit
The consistent light source and nearly concurrent back and main
exposure deliver unmatched relief and image consistency combined
with perfectly formed flat top dots. As a result, these plates deliver the
highest level of consistency and quality on press.
STRONGER, CONSISTENT DOTS & FLOOR
Using UV LEDs for back exposure delivers precise, consistent relief
within each plate and from plate to plate over a long period of time.
The operator no longer needs to worry about warming up bulbs before
exposure or adjusting exposure times as tubes degrade.
While light frames are inconsistent from one area of the plate to
another—and one day to the next—the XPS Crystal utilizes very con-
sistent diode light. It never changes. For example, the optimal relief of
a 0.067-in. plate according to Flexographic Image Reproduction Specifi-
cations & Tolerances (FIRST) is 0.020-in with a tolerance of ±0.002-in.
Light frames typically cannot accomplish this, with ±0.004 tolerance
common. This is due to the temperature of the frame, the inconsistent
light and other variables.
With the XPS Crystal, customers have reported ±0.001 floor toler-
ance. Research has proven that consistent relief leads to consistent
dots, which leads to consistent print on press. With less plate consis-
tency, it takes more time to get the press on color.
More important, the XPS Crystal exposes a plate, both back and front,
at virtually the same time—perhaps a couple of seconds apart. A
simultaneous and optimally controlled UV main and back exposure
produces highly consistent digital flexo plates—for every digital flexo
plate type at every time of the production day. This is simply not
possible with a light frame. When using a light frame, a table might
be back exposed, then carried to a digital imager, and then main
exposed. This could certainly take a few minutes—and perhaps even
longer if the operator is required to spend some time on another task.
Esko learned that “dwell effect”—the amount of time between main
exposure and back exposure—has a tremendous influence on the
The optimal relief on a 0.067-in. plate, according to FIRST, is 0.02-in. with a tolerance of ±0.002-in. Light frames typically cannot accomplish this, with a
±0.004-in. tolerance being the norm. With Esko’s XPS Crystal 5080, customers have reported ±0.001-in. floor tolerance. Research has proven that consistent
relief leads to consistent dots, which leads to consistent print on press.
Images courtesy of Esko.
JUNE 2017 | FLEXO 37
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