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Individualized printed matter, personalization, increasingly smaller
volumes, a lower risk for the publisher when producing books – these are
the main competitive advantages of digital printing. Nevertheless digital
printing is just a print medium - with its benefits and disadvantages. The
advantage that printed products can be used everywhere without any
technical aid is counter-balanced by the supposed disadvantage that they
first have to be turned into a useable form. And
this "turning into a useable form" is the bookbinder's
task.
The digital process ends with the transfer of the
ink or toner onto the paper. But this does not mean that this is the end
of the problem. Just the opposite may be true, because ink, toner, paper,
the drying process and static charge can cause problems that are
completely different from post-press handling after offset printing.
Unexpected problems occur because during the introduction of digital
printing the focus is on data handling and the realization of the new
technology. Post-print
processing is often under-estimated or responsibility is delegated to the
bookbinder. But in many cases the bookbinder realizes too late that he
does not yet possess the know-how, experience and technology needed for
this job. Therefore digital printing also changes post-print processing.
While it is not a fundamental change - cutting, folding, stapling, gluing
and binding processes are still the same - a reorientation is necessary
because of special requirements and new processing steps.
The
traditional separation between printing and finishing is disappearing.
What has been printed in no time must also be delivered in no time.
In many cases there is not enough time to leave post-print
processing to other specialists. For this reason finishing equipment for
digital printing must satisfy special requirements:
- Simple
handling, because the operators are rarely skilled bookbinders
- Short
set-up and idle times, because low volumes mean frequent changes of
the set-up
- Minimum
waste, because there are no plus sheets as in offset printing
Because
of their high degree of automation and operator convenience,
computer-controlled folders from Mathias Bäuerle (MB Bäuerle) fully meet
the requirements of this market segment and now permit Folding on Demand
following Printing on Demand.
Computer-controlled folding means that vital
settings and adjustments no longer have to be made manually. Settings are
calculated and executed automatically by means of dedicated software. The
most important standard folds are programmed; all other folds are freely
programmable. Repeat fold jobs can be saved in memory and set up
automatically when needed. Computer
support is also used for fold roller setting.
Digital
printing has not only led to the design of book printing machines, but
special production lines have been created through clever combination of
single modules. This makes it possible to realize complex individual steps
as well as entire manufacturing processes of special products from
printing to finishing. Consequently each module must naturally be equipped
with the technical preconditions for online production. Since folding is
in most cases one of the production steps of these systems, MB Bäuerle
has also developed folders for online production.
Online-Fold
Systems
For
online applications MB Bäuerle offers the MB-System CAS 52 PoD. This
system is designed to connect directly to single sheet printers or, within
book assembly lines, for connection to cutters in a web-printing process.
The CAS 52 PoD system consists of mobile fold units which can be combined
according to the customer's needs.
The
transfer of the sheet from the printer to the cutter to the fold unit is
achieved by means of special register tables. These tables vary in size
and features. The largest register table (ART 52: corresponds to 52")
can align sheets up to a length of 132 cm and has been developed for book
production. The limited roll width of the printing systems calls for this
long sheet size to make it possible to produce a large number of sheets
per signature in spite of the limited roll width. It's possible to produce
signatures from 8 to 32 pages. Another possibility for sheet transfer is
the double alignment tables DAT 14 and DAT 24. They have been designed for
a sheet length of 14" and 24" and can be used for 2-up
production because of the left and right alignment rails which run
parallel into the folder. A turning station is also useful for this type
of production. In such a station, sheets can be turned 90° during
transport to change the direction without the use of a roller table.
Furthermore, digital printing permits the
creation of other products which so far could not be made online, for
instance, the production of brochures containing folded and unfolded
sheets or different types of folds (e.g. special charts or tables in
business reports, operator's manuals, and spare parts catalogues).
Printing a variety of formats in the correct sequence is no problem for
the printing system, but folding different paper sizes in an arbitrary
sequence cannot be done with a conventional folder. For this special
application, MB Bäuerle has created a solution, namely "Selective
Folding". The technical basis for this application is a device for
measuring the length of the sheet and special fold plates. The system
measures the length of each incoming sheet and recognizes for which sheet
the fold plates have to close or open in order to produce the correct
fold. 8- or 16-page signatures and folded or unfolded sheets can thus be
produced in any required sequence.
Offline-Fold
Systems
Contrary to online-fold systems, offline-fold systems are not
dependent on preceding and following modules. Their applications are
therefore more versatile, and permit a large variety of folds because of
their flexibility. They are also capable of handling the most diverse
types of paper and cover a large range of formats.
MB Bäuerle offers computer-controlled folders for offline-operation for
paper widths of 35 cm, 38 cm and 52 cm. For digital printing, machines of
the multimaster CAS 52 folder line are predominantly used. Unfolded paper
sizes range from 10 x 12 cm to 52 x 85 cm. The smallest fold length is 3.5
cm, or 1.8 cm using an additional add-on fold unit. The range of
applications can be increased by means of gate fold plates, gluing
devices, a variety of perforating and slitting tools as well as pulsed
cutting and perforating heads.
Special
technology facilitates the folding process
Because
of the particular characteristics of digital printing, problems related to
paper flow, handling and fold quality may occur during the folding
process. Remedies are available in the form of a variety of special
attachments and features with these applications in mind.
Problems
& Solutions of Folding Digital Prints
Problem:
Disruptions in the paper flow and adverse effects on the operators by
static charge
Digitally printed products
often tend to accumulate static charges, caused by high temperatures
during the fixing process and the resulting loss of humidity. This may
lead to disruptions in the paper flow and an increased workload for the
operators.
Solution:
Antistatic devices
Antistatic devices in the
infeed section, the fold unit and the delivery section considerably reduce
static charge. MB Bäuerle offers suitable retrofit kits for the different
types of machines.
Problem: Inferior quality caused by marks and streaks
Depending on the paper quality,
marks may develop on the suction drum or in the fold plates.
Solution: Coated suction drum
A coated suction drum
considerably reduces marks.
Solution:
Fold plates with coated paper guide elements
A special coating reduces the
friction coefficient at all paper guide elements in the fold plate so that
marks can be reduced.
Problem: Loss of quality through damage to the printed surface
A typical phenomenon when
folding digital prints is toner break-up along the fold line. The reason
for this is not the fold process per se, but the physical behaviour of
toner and paper.
Solution:
Special scoring tool for digital printing
Depending on the properties of
paper and toner, the problem can be visibly reduced or completely avoided
by scoring along the fold line. However, the traditional scoring tools are
often unsuitable for this purpose. A notable improvement is achieved with
special scoring tools that produce the score line by means of a
non-metallic scoring ring. The use of this scoring tool is therefore
highly recommended.
Problem: Scoring as a separate work cycle
There
are numerous devices and machines for scoring before folding, but their
application entails an additional operating step.
Solution:
Scoring in the folder
In
order to avoid this additional step and to be able to score and fold in
one pass, the infeed width of the folder should be wide enough to allow
the sheet to be fed landscape. This makes it possible to score in the
first fold unit and to fold in the second fold unit.
Thanks to its versatility, digital printing is opening up new
markets for printed products. These breed new product ideas and require
new technical solutions for the creation of the printed image, but also
for the development of finishing equipment tailored to the efficient
production of these special products. From the very start of this
development, MB Bäuerle has been an important contributor to the
automation of the folding process and will continue to be active in this
field.
The
author, Otto Siegel, is Marketing Manager for Mathias Bäuerle, manufacturer of the
Multimaster CAS computer-controlled folder line and GBR Systems
Corporation's parent company. GBR
is the U.S. distributor of the Multimaster CAS computer-controlled folder
line.
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