In the past years there have been
several improvements in the flexo printing plates manufacturing,
such as better mounting devices, improved plate quality with
higher resolution and high quality negatives.
The only thing
which has not been greatly improved in the conventional plate
manufacturing is the exposure process.
In retrospect, bank
exposure (tube exposure) has been used since the beginning
of plate production in 1974.
Initially, with very little UV-A
output and in the course of time with a higher UV output;
however, the system was not changed.
This means a large number
of tubes and a matt vacuum foil is still needed.
This also means in spite of the improvements of the flexo
plate material an improvement of the quality can only be achieved
to a certain extent.
One of the reasons that no improvements
have been achieved with tube exposure units is the irregular
UV output. Furthermore, the extreme scattered light caused
by the close arrangement of tubes and the vacuum foil is also
a disadvantage of the bank exposure units.
In addition, the
temperature variations during the exposure have had a negative
impact on the quality. These limitations could not be eliminated,
although modern tube technology, cooling and control systems
have been applied.
Point light was introduced in the 90`s. Unfortunately, this
kind of light source which originated from offset led into the
wrong direction.
Due to the three-dimensional plate structure,
it was not possible to achieve a solid shoulder by use of a
point light source. The further away the lines were from the
exposing center, the more unstable they were, with the tendency
to topple over. Even the use of a diffusion sheet which is inserted before
the exposure between the plate and light led to no improvements.
A cooperation of the companies Theimer,
F-TH and InnoFlex
has led to the new concept, QualyDOT
Scan-Light-Source.
A high-tech light source moves across the flexo plate. The
great advantage of a scan light source is obvious: The complete
plate format is evenly exposed.
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Because of the high UV output the exposure
time is reduced. An efficient cooling system HEAT-EX
prevents the flexo plate from receiving too much heat.
An even UV output allows a concentrated exposure, which means
it is not necessary to over expose as a result of uneven amounts
of UV delivered to the plate.
Another important point is the
drastic reduction of scattered light and therefore deep reverses,
steep flank angles and exact transfer of the screen dots from
the negative.
The sensor-controlled even UV output leads to
repeatable good results each time.
The construction of the QualyDOT has additional advantages
over the bank exposure. A newly designed vacuum bed guaranties
a rapid and excellent vacuum build-up.
By means of a handle the semi-automatic vacuum foil dispenser
is evenly rolled over the plate without creating bubbles and
wrinkles. The dispenser can be arrested at various positions
in order to remove dust or other particles.
The working area is accessible from three sides at an operator-friendly
height.
The design of the QualyDOT is simple and safe, which
rules out any operating errors. The change of the vacuum foil
and the UV tubes can be carried out very easily, thus longer
production interruptions can be avoided.
The following formats are available:
650 x 900 mm (25 x 35 in.),
950 x 1350 mm (37 x 53 in.).
With the technology of the QualyDOT the conventional plate
exposure meets the high quality standards of the existing
flexo plates.
In summary, the QualyDOTScan-Light-Source exposure sets
new standards in analogous plate exposure, as well as in connection
with CTP in an economical way.
written by Udo Möller
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