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Major breakthrough made in tackling HSWO ‘ghosting' and ‘vanishing dot' problems

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26/10/2007
Cross industry working group includes ContiTech, Kodak Communications Group,
MAN Roland, M-real and SunChemical 


A major breakthrough has been made in understanding and managing ‘ghosting' and
‘vanishing dot' phenomena that cause problems sometimes visible in the heatset
web offset (HSWO) printing process, especially in jobs with high quality layout
and photos.  Initial trials run by a working party, initiated by SunChemical
(inks & founts) with ContiTech (blankets), Kodak Communications Group (plates),
M-real (paper) and MAN Roland (printing presses), show that reductions in press
downtime and maculation can be achieved, and work is progressing towards
minimisation of the problems. 

To date, the only solution is to wash the blankets, causing press downtime and
maculation.  Register moving devices, such as auto-cycling systems, can prolong
the intervals between washing but do not cure the problem. 

As a result of trials run with major German printers to identify the root cause
of the phenomena, the working party has found that ghosting and vanishing dot
are both caused by depositions on the blanket.  These start from the dot's
edges and gradually eat into the dot as printing proceeds.  This way the
printed dot becomes smaller. 

As trials continued, improved combinations of paper, ink, fount, blanket and
plate were evaluated so that the optimum configuration to counter the problems
could be found.  In the most recent trial, use of the optimum configuration
resulted in no ‘ghost' appearing in the print run, and dot gain was
significantly improved.  Washing intervals could be minimised.  This was
compared to a control print run, using a standard configuration, where both
problems occurred. 

The working party, first established in 2005, includes 13 representatives from
SunChemical, ContiTech, Kodak Communication Group,  M-real, and MAN Roland. 
The full report may be obtained from M-real Publishing. 

Further customer trials are scheduled to verify the results and gather more
information about the role played by each component in the printing process. 
Updates are expected to be announced in early 2008. 

For additional information, please contact:
Miika Jokinen, AVP, Technical Services, M-real Publishing  +358 50 553 7531
miika.jokinen@m-real.com

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