Over the years, the printing industry has
seen major revolutions that have completely altered the prerequisites for
the entire industry. Desktop publishing totally eliminated the
typesetting profession some fifteen years ago. Now, the rapid growth of digital
printing and the convergence of digital and offset printing tend to make new
demands on the finances of the printing industry.
This rapid growth is a result of
technological developments. Only a few years ago, offset printing and rotogravure were
unchallenged when high demands were placed on print quality and
speed. Today, both ink-jet printing and electroencephalographic printing
are capable of high speeds and high print quality. This means that the
areas in which the various printing processes are financially feasible are
beginning to overlap, and it is not obvious whether a certain print job should
be run on offset or on one of the available digital printing processes. The
possibility of making every copy unique makes digital printing more flexible
than conventional printing techniques.
In the near future, rapid growth is
foreseen for digital printing. However, it is believed that a fast technical
development in the digital printing processes will have to be matched by a
corresponding development in the printing paper. Today,
the volumes of paper being used in elector photographic printing are much
greater than the volumes of paper used in high-speed ink-jet printing.
However, several reports predict a very rapid growth for high speed ink-jet paper grades . This can also be expected for packaging materials. These
predictions justify efforts to study the physics and chemistry involved in the
extremely fast ink-jet processes that are forecast to prevail in the future
and to design an optimized substrate accordingly.
Ink-jet printing technology is based on
microscopic ink drops emitted under pressure from a jet onto a substrate. Ink-jet printing raises new demands on the properties of
printing paper. An optimum uncoated surface is said to consist of a
mat of fibers with an evenly distributed gradient of sizing, additives
and fillers. When the sizing and fillers are distributed unevenly on the
surface, aqueous inks tend to wick along the exposed paper fibers,
significantly degrading the quality of the ink-jet print.
A coating provides a
homogeneous surface for ink penetration, overcoming the difficulties of winking, and
also provides a bright surface and yields a high print contrast .
The surface of inkjet papers-should further be engineered to be a highly
absorbent interface that at the same time exhibits micro-capillarity on a
defined scale .
The influence of the paper structure on the
ink-jet drop impact and spreading must be considered (Oliver 1984). New
paper making technologies regarding internal sizing and surface sizing systems
will make it possible to enhance the color gamut volume and the print sharpness
on the paper. In order to achieve a high
print sharpness, care should
further be taken not to have too high a
liquid penetration rate in the paper
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