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Web offset printing using electron beam (EB) drying is believed to provide an efficient
alternative to heat-set web offset using thermal drying. Some of the potential advantages of
that non conventional printing/drying technology are
- the use of solventless, 100 % reactive printing inks,
- the dramatic reduction of the emission of volatile organic compounds (VOC's),
- the extremely low amount of extractables in the cured layer,
- the good rub resistance of the cured printing inks,
- the exactly controllable drying process,
- instantaneous drying of the printing inks even at high running speeds of the press and
- practically no paper temperature rise during the curing process.
The worldwide about 50 EB dryers on web offset presses / 1 / are still a small quantity if
compared to thermal drying installations. The introduction of the efficient and environmentally
friendly EB printing/drying technology presently suffers from disadvantages in respect to
total printing costs and printing quality. Radiation curable printing inks are usually twice as
expensive as heat-set inks. At comparable capital costs the lower operational costs for EB
printing/curing can only partially compensate for the ink costs. Avoiding waste offers one
way to make EB drying competitive. An other important task is the improvement of the
printing quality. The development work which is needed to overcome the present obstacles
should be carried out using advanced pilot units or industrial web offset presses. In this paper
we report on EB drying trials performed on a 4co!or web offset printing press "zirkon forta.
660". The printing quality obtained was characterized in respect to gloss, ink coverage,
contrast and tone value. Additionally, micro roughness studies were performed using an
atomic force microscope.
An further promising future application of EB drying is believed to be in the field of flexo
printing. High quality flexo printing seems to be able to compete with web offset printing
especially in the field of package printing. UV drying is already used in flexo printing. Several
central cylinder machines are equipped with UV lamps between the printing units. Due to the
complicated geometry of flexo machines, EB drying after each printing unit seems to be no
realistic alternative to UV drying. But final EB curing of the printed product can offer the
advantage of controlled through curing. A minimum of extractables is achieved using final EB
curing and even the unreacted photoinitiator concentration is decreased.
Here we report on the characterization of the printing quality of EB and UV flexo printing inks
and the determination of extractables.
