Sack handbook - Billerud AB

Printability and appearance
Most paper sacks are printed on the
outer ply. The main reason for printing
industrial sacks is to identify the content,
but there is an increasing demand for
more information and improved appearance.
For consumer sacks a high quality
finish is an important commercial factor.
The dominant printing method in the sack industry is
flexography. For simple 1-3 colour prints, sack paper
may be printed in-line in the tubers, or more often
nowadays, in separate pre-printers. Print quality as
well as productivity is improved with pre-printing.
The print quality depends on the right combination
of the artwork, printing press, plates, anilox rollers,
colours and paper surface. The skill of the printing
operators is of course also very important. Most
industrial sacks are printed in 1-4 colours. For more
demanding applications, such as consumer sacks,
process pre-printing is mostly used.
Flexographic Printing Machines
Flexography is the fastest growing printing method.
For modern flexo presses the technology, efficiency
and capacity is very much improved. For process printing
the anilox rollers, colour application system, web
video control, and the cleaning and drying system are
all very important. New presses may be equipped with
8-10 colour stations. Older flexo presses can still give
good print quality if the machines are well maintained
and the anilox rollers regularly changed.
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