www.kba.com
5
Issue 1/2008
PROCESSES | PRACTICES | PERSPECTIVES
Process technologies, consumables and applications for sheetfed offset printing on plastic substrates
Printing on plastics and
composites
Whether in advertising or magazine printing, in the
display sector or packaging, end customers and
agencies alike are constantly in search of that special
extra which will enable their product to stand out
above the crowds. In response, more and more
printers are looking beyond traditional papers and
board stocks and are discovering the possibilities for
printing on plastic films and synthetic papers, or
composites of paper, plastic film and aluminium
coating. Once domains of screen printers and narrow
web presses, these markets are today interesting
prospects for sheetfed offset, with its weighty
arguments of optimum quality and cost-effectiveness.
Koenig & Bauer and KBA-Metronic are long-standing
pioneers in the fields of UV and waterless offset
print, and are now able to play out their great knowhow lead to promote printing on non-absorbent
substrates such as plastic film and aluminium. In
cooperation with selected, and in some cases
exclusive partners, innovative solutions have been
developed for this booming market segment. The
plastics equipment package for KBA Rapida presses
comprises special components to
ensure smooth sheet travel, and
can be complemented with
unique options such
as a corona tower (as to be seen below on a Rapida
105) or substrate-friendly inert UV interdeck dryers.
Several Metronic solutions, furthermore, permit
direct printing on products such as plastic cards, CDs,
DVDs and Blu-ray Discs, even in non-standard shapes
and formats. KBA offers by far the broadest range of
presses and machines for offset printing on film
substrates and data storage media.
The term “plastics” covers a whole group of
individual materials with the most varied printability
and process properties. Only certain polymers are
properly suitable for any given application, for
example banners, signs, logos, lenticular images,
cards, in-mould labels or folding boxes and displays.
Against this background, this brochure is intended as
both inspiration and a decision aid for users
considering an investment in this exciting branch of
the print industry.
The authors include KBA partners with special
expertise in the fields of polymer films, UV inks and
coatings, in-mould labels, antistatic systems and
surface treatment. We have dispensed with detailed
articles on the more general aspects of waterless
offset, UV curing or photoinitiators, as they were
already topics in previous issues of KBA Process.
These earlier issues are unfortunately out of print,
but can be downloaded in five languages from the
KBA web site under News & Press\Press
Service\KBA Process. As in all previous
publications, KBA has done its best
to present an objective
overview of the processes,
their potential, quality
demands and possible
applications.
Contents
KBA
Editorial
2
Plastics
Modern substrates with great
potential: PVC, PE, PP, PET
3
The making of plastic webs: Rigid
PVC and its properties
5
Versatile polyester
8
In-mould labels based on PP film 10
Printability
Simple determination of surface
tension on plastic films
12
Raising surface tension with
a corona tower
14
Sheet travel
Antistatic systems
on sheetfed offset presses
16
Inks and coatings
Oil-based and UV-cured inks
for printing on plastics
18
Finishing of plastic films
with UV-cured coating systems
in sheetfed offset
21
Applications
KBA users hold the key to new
fields of business: Examples
23
Lenticular film: Special effects for
future-oriented niche markets 27
Glossary
Resources and partners
29
30
Contacts
31
Editorial
Dear customers and friends of KBA,
The issues of KBA Process to date have documented Koenig & Bauer’s
pioneering work in the most varied fields of offset printing: Direct sheetfed
offset on corrugated board, ecological waterless and keyless offset print,
product refinement with hybrid finishing and economical inline coating.
This latest issue of KBA Process is now to take a look at a rather less
widespread sheetfed offset application for which KBA again has plenty to
offer in the way of technology and experience: Printing on non-absorbent
substrates.
Ralf Sammeck, Executive Vice-President Sheetfed Sales, Koenig & Bauer AG
This is as always a topic with potential for the future. After all, the
extraordinary look, feel and utility value of plastics, composites and synthetic
papers expand the repertoire of innovative, open-minded print businesses
and represent an outstanding opportunity to break out from the often purely
price-driven standard market. “Plastics printing” offers interesting
possibilities to establish a regular base of discerning customers. And it is no
secret: If you can build up a reputation for high-quality speciality products
in a small, future-oriented market segment, then it is much easier to generate
comfortable margins. A well-prepared entry into the world of film and
plastics printing, whether with an individually tailored press configuration
or a dedicated system for direct printing on CDs, DVDs and plastic cards, is
an investment with a promising future.
also to those readers with no previous experience in this field. We would be
delighted if KBA Process No. 5 is able to provide a valuable tip here and
there, whether for your first steps in plastics printing or the further
expansion of existing activities; and when all's said and done, that is actually
the whole idea behind this series of publications from KBA.
KBA can point to numerous installations and excellent references for plastics
printing in all format classes. And we confidently bring the full weight of
our expertise to bear in championing the high productivity, quality and
format flexibility of sheetfed offset compared to conventional processes for
printing on plastics. No other press manufacturer is able to present such a
broad product range with so many innovations for this fast-growing segment.
It is already several years ago that KBA adapted two previous narrow-web
solutions for sheetfed applications, namely inline corona treatment and inert
UV interdeck drying. In both cases, our design engineers in Radebeul
mastered the challenge of achieving the desired effects despite the presence
of gripper systems. Such brilliant coups are of course only possible when
working hand in hand with exceptional partners. Many of these partners
have contributed to this issue of KBA Process, and all have earned our
boundless gratitude for their long-standing cooperation.
Yours,
Once more with the proven support of trade journalist Dieter Kleeberg, the
authors have, I believe, succeeded admirably in identifying the application
diversity of plastics printing, while at the same time presenting the unfamiliar
material properties and processes in a manner immediately understandable
2 Process 5 | 2008
Hoping that we can in this way contribute to your business success, we will
continue to do all we can to pinpoint attractive business ideas and to open
up new avenues for you, our customer. Because in the end, we all benefit
together from the strengthening of print in its countless facets.
Ralf Sammeck
Executive Vice-President Sheetfed Sales
Plastics | Substrates
Modern medium with great potential
Plastics – in modern common usage, that is the general term for a wide range of so-called polymers, i.e. organic
macromolecules composed from simpler hydrocarbon molecules (monomers). The chaining, branching or cross-linking
of these monomers determines the individual structure of the molecule group. Polymers are today used in many ways
as packaging and print substrates.
Slipcase printed with a floral design in sheetfed offset on PriPlak, a corona-treated polypropylene film produced by ArjoWiggins and
distributed by Papier Union
It is by no means the case that
polymers are always modern synthetic products. In fact we have
already been using naturally occurring biopolymers, such as asphalt
or tree resins, for many thousands
of years. When we speak of ‘plastics’, however, we usually mean
the range of synthetic polymers
encountered in practically every
sphere of daily life, e.g. PVC,
polypropylene, polyethylene or
polyester (see box).
Changed demands on the print and
packaging industry
New colourings, surfaces and
processing options have made
plastics an increasingly popular
medium for designers, and thus
also a relevant concern for the
print industry. Experts estimate
that the use of synthetic materials
rose by 10 to 15% between 2005
and 2006.
Where paper and board were once
the principal vehicles for informa-
tion, further industrial developments have in the meantime led to
an elementary shift in interests.
Even more specific demands are
being raised regarding the packaging, protection, transport and
presentation of goods. Consequently, the demands to be met
by the print substrate have also
gained in complexity:
• Labels are to be tear- and waterproof, but nevertheless simple
to print or write on.
• Reference works are to be more
durable and must not tear even
when subjected to heavy use.
• Transparent packaging is viewed
as necessary to enhance the
presentation of goods.
• Presentation possibilities at the
point of sale are to be
improved.
In such a situation, conventional
papers and boards soon reach the
limits of their performance capabilities – but the chemicals industry is on hand to save the day.
Plastics change the world
The discovery and further development of the most varied plastics
has changed the world like
practically no other technical
advance before. The spiral of
innovation is turning ever faster.
New plastics have inspired new
ideas for potential uses, new
printing inks, new processing
machines and techniques, and
new demands to be satisfied by
the material. And this in turn
triggers desires for new possibilities and thus new materials …
Whereas the packaging sector has
paid most attention to transparency and stability, the print
industry was naturally forced to
consider above all printability
issues. It is not long ago that
“flaming” was the only possibility
to enable printing on polypropylene. To activate the surface and to
improve ink adhesion, the sheet
was heated momentarily with a gas
flame, but without allowing the
plastic to melt. Not surprisingly,
many companies shied this complicated and expensive process.
Even so, polypropylene continued
to stimulate the imagination of
designers; after all, practically no
other synthetic material is as
versatile and – despite being a
plastic – as environment-friendly
as polypropylene. Consequently,
some manufacturers began to
treat the surface in a special
factory process to facilitate later
Synthetic polymers in daily life
Polyvinyl chloride (PVC) is the most widely used chlororganic plastic. According to Federal
Environment Office figures, approx. 1.5 million tonnes of PVC were being produced and
processed in Germany at the end of the 1990s. Some 10 to 20% of the PVC is used for
packaging, and a further 20 to 30% for a diversity of articles for daily use.
Polypropylene (PP) is the overall designation for a series of weldable thermoplastic
polymers which stand out by way of their great hardness, rigidity and heat resistance. PP is
processed, for example, in sheets, buckets and bottles, and its pollutant-free incineration
permits ecologically compatible disposal. According to Wikipedia, 30 million tonnes of PP
were produced worldwide in 2001.
Polyethylene (PE) is easily recognised by way of its soft, wax-like surface with pronounced
non-stick properties. It displays a low density, but at the same time high strength, hardness
and resistance to chemicals. PE is used, for example, for environment-friendly self-adhesive
foils and extremely tear-resistant sheet and roll materials, such as the fabric-like DuPont
Tyvek.
Polyethylene terephthalate (PET) is a thermoplastic polymer of the polyester family. Its
high tear strength makes PET an ideal material for film sheets of all thicknesses, from an
ultrathin 1 μm up to 500 μm. Applications range from aroma-tight food packaging to
coloured sun-protection films and test strips for the pharmaceuticals industry. It is today
almost impossible to imagine the soft drinks industry without PET bottles. Further uses are
to be found in textile fibres, e.g. for sportswear, and in many other spheres of daily life.
Process 5 | 2008 3
Plastics | Substrates
printing. In conjunction with special
inks and the corresponding technology, this so-called corona treatment
today permits relatively trouble-free
printing of this once “difficult”
material.
At the same time, other synthetic
print substrates – such as polystyrene,
rigid PVC and self-adhesive foils –
were developed further and are in the
meantime in daily use in many print
companies.
New materials, techniques and markets
Conference clipboard printed onto Lucprint rigid PVC
While plastics remained rigid materials, they were a safe domain for screen
printers. Only their machines were
able to handle such “unwieldy” media.
But then films and other flexible synthetics came onto the market. And
more and more companies began to
address a completely new challenge:
Offset printing on flexible plastics.
Plastics up to a thickness of 1 mm are
already no longer a problem for
specialised offset printers, and the
combination with UV-cured inks lifts
all previous restrictions on creativity.
Waterless offset and the hybrid
technology – each also thanks to the
pioneering work of KBA – have
similarly played an important role in
promoting the use of plastic
substrates.
A relatively new product class on the
market is that of digital flat-bed printing systems operating with solventbased or UV inks. With these systems,
the printing of synthetics can be
handled cost-effectively also for very
short runs.
The most interesting market segment
for plastics printing – and currently
the fastest-growing – is advertising.
There is no overlooking the colourful
packaging, signs, posters and displays
wherever we go. But plastics are also
finding their way increasingly into the
office sector. So-called permanent
paper can first be printed in a classic
offset process, and subsequently sent
through the office laser printer –
preprinting for synthetics.
Prospects
Food-safe Lucprint PVC films
are used, among other things, for
exclusive packaging
4 Process 5 | 2008
In future, too, there will still be countless fields of application for classic
board materials, especially where it
can be further refined by way of
coating, embossing and lamination,
etc. But the use of plastics for the
PowerJet Texpo banner of polyester fabric
Trevira CS B1, printed in a digital inkjet
process
most varied products will continue
to increase. Wholesalers such as
Papier Union have already reacted
to this trend by establishing independent sales departments with
specifically trained specialists for
the new synthetic materials.
It remains to be seen whether the
users of synthetic substrates will
in future have to or choose to rely
further on the “tried and trusted”
materials of the past. Heated
discussions are almost certain.
Most likely, however, is that new
developments will emerge, with
plastics on the basis of renewable
raw materials rather than the
limited resource mineral oil.
This development will require
new printing inks, presses and
techniques. And it will trigger
new desires. Service providers
hoping to gain a share of this
interesting market are advised not
to wait too long before jumping
on the bandwagon – because it is
already moving faster and faster.
Klaus Fischer (Papier Union GmbH),
Cornelia Lillelund
Plastics | Manufacturing process
The making of plastic webs
Plastic films are produced by completely different technologies to papers and boards. The example of unplasticised
or rigid PVC production at Klöckner Pentaplast illustrates how the later film properties are set on the high-temperature
calender machines.
1
Schematic representation of a calender machine
The production of film materials is
an established field of polymer
processing, as such films can be
used in an endless diversity of
applications. Whether as semi-finished or end products, their broad
range of modification possibilities
helps meet the prerequisites of
the most varied branches of industry. Several differing process technologies have been developed for
the production of plastic webs,
and together permit suitable films
to be made available economically
for a comprehensive spectrum of
uses. These technologies are
extrusion with slot-die or blow
forming, spreading, casting and
calendering.
Calendering of unplasticised PVC
films
Calendering is the process by
which high-viscosity polymer formulations are moulded into an
endless web under pressure and at
a defined processing temperature
in the gap between two or more
rolls. The set width of the gap
determines the thickness of the
resulting film. The arising gap
pressure is derived from the gap
geometry and the rheological
properties of the mass to be calen-
Fields of application for PVC
An analysis of product quantities and costs over the past few years illustrates how the
market development for PVC has been influenced by four principal factors: Economic
recessions, the introduction of restrictive packaging legislation, several anti-PVC campaigns
and improved substitute films (polypropylene, polyester or polystyrene). Contrary to the
forecasts of wide-scale replacement by the above-mentioned substitutes, PVC has actually
maintained a relatively constant market share, especially in the market segments
packaging and technical products. Reasons can be seen in the inexpensive production
and modification of PVC and in the generally good processability of the semi-finished
and end products.
20
%
15
19.6
900 000 t
15.0
10
8.4
5
0
8.4
3.7
1
2
3
4
5
9.3
8.4
8.4
4.7
3.7
2.8
6
7
4.7
2.8
8
9
10
11
12
13
The West European market for rigid PVC films accounts for a consumption of 900,000
tonnes. Of this, 60% is used for packaging (1 Foods, 2 Non-foods, 3 PVC composites, 4 Box
lids, 5 Pharmaceuticals, 6 Oriented films, 7 Others) and 40% in technical applications
(8 Adhesive tapes, 9 Office films, 10 Furniture and frames, 11 Offset/screen/digital printing,
12 Construction, 13 Others).
dered. A calender is thus to be
treated as a processing machine
purely for forming purposes.
The first calender-like machines
were already designed before
1800 for the smoothing of textile
surfaces. In 1836, the first
patents were granted for calender
machines for rubberising and for
the application of rubber to
textiles. Demands for higher
production speeds and closer
tolerances promoted further
development of the calender and
expansion of its range of applications to include the processing
of polyvinyl chloride (plasticised
and unplasticised PVC) in addition
to rubber. The first calender for
unplasticised PVC, introduced in
1937, was designed to be heated
to 220°C. Once highly active
stabilisers became available from
around 1960, it was possible to
supplement the previously used
low-temperature process (LT) with
a high-temperature process (HT)
based on modified recipes and
higher temperatures within the
calender.
The technical configurations and
implementations have remained
practically unchanged over the
past decades. The only real variation has been to widen the
calender rolls to increase output
or to facilitate avenues of specialisation in film production. The
established technology for the
production of unplasticised PVC
films is based on the HT process
and four- or five-roll calenders in
widths between 1,800 and
3,000 mm. The advantages of the
HT process are to be seen in the
broader options for modification
of the film properties and the
greater production output on
significantly wider machines. The
materials used are mainly S-PVC
and M-PVC with K values (degree
of polymerisation) around 58 to
63, which produce films with high
transparency, good deep-drawing
properties and appreciably greater
thickness.
Unplasticised PVC
In terms of production capacity
and consumption, PVC occupies
third place in the list of most commonly used standard polymers
with 28.6 million tonnes per year,
after polyethylene (57 million
tonnes) and polypropylene (35
million tonnes). The constantly
increasing consumption over the
past 60 years or so, from initially
around 10,000 tonnes to now
almost 30 million tonnes per year,
is indicative of the continued
industrial significance of PVC.
Thanks to its compatibility with a
whole range of auxiliaries and
media, PVC has built up and maintained a very broad range of applications, from window frames and
films to pastes and coatings.
In Germany and the rest of
Europe, the processing volume of
unplasticised PVC is around
double that of plasticised PVC.
Unplasticised PVC films account
for an approx. 15% share of the
total consumption of PVC. Packaging films make up some 60% of
the total film production. Further
important applications are technical films and films for printing.
20% of the unplasticised PVC is
calendered, with the most
important market segments
being packaging and technical
applications.
Vinyl chloride was first produced
by Henri Victor Regnault in 1835.
The first industrial-scale production began at IG Farben in
Germany in 1938, and at almost
the same time at Union Carbide
Process 5 | 2008 5
Plastics | Manufacturing process
and DuPont in the USA. Nowadays, it is produced by way of
a single- or two-stage reaction
involving chlorine and ethylene.
PVC, with a chlorine content of
57%, requires less mineral oil than
any other polymer and is produced
industrially by one of three
methods:
• Emulsion polymerisation (EPVC) – for pastes and film
applications;
• Suspension polymerisation (SPVC) – the main process, for all
applications;
• Mass polymerisation (M-PVC) –
primarily for rigid PVC
applications.
The choice of a particular PVC
type is governed by the demands
of further processing and the
purchasing price. S-PVC and MPVC are ver y versatile and
mutually exchangeable. M-PVC,
due to its purity, is preferred for
transparent products.
Film properties
PVC can be distinguished not only
by its production process, but also
by its material and processing
properties (Figs. 2 and 3). The
standard international designations are PVC-U (for unplasticised
or rigid PVC) and PVC-P (for plasticised PVC). Rigid PVC, as the
variant suitable for printable films,
Processing improvement
2 Comparison of material properties of
four different polymers: GB = Gas barrier,
WB = Water vapour barrier, Mi = Migration,
Mo = Modification, Tr = Transparency,
EM = Elastic modulus, HR = Heat resistance,
SpW = Specific weight
Surface properties for the printing
process
displays the following selected
properties:
• High mechanical strength, rigidity and hardness,
• Impact-sensitive at low temperature in unmodified form,
• Varying degrees of transparency,
• Good electrical properties in
the low-voltage and low-frequency ranges,
• High resistance to chemical
attack,
• Self-extinguishing upon removal
of the ignition source.
These properties are only to a
small degree attributable to the
production process. A greater
role is played by the additives
Film
recipe
Thermo-stabilisers
Application improvement
UV stabilisers
Internally and externally
effective slip agents
PVC S, M, E
Calendering aids
Impact strength enhancers
Pigments
Static eliminators
Anti-blocking, dulling,
flameproofing agents
High-temperature modifiers
SAN and ABS
4
Composition of a PVC-U recipe
Limit values for thickness deviation
Film thickness
Below 100 μm
Below 200 μm
Below 400 μm
Below 400 μm
6 Process 5 | 2008
3 Comparison of processing properties of
four different polymers: Pr = Printability,
Th = Thermoforming, Fo = Folding,
Se = Sealing, AS = Antistatic properties,
En = Process energy, Gl = Gluing, Sc =
Scratch resistance
elevations influences the optical
quality of the film. Flow lines are
caused by inhomogeneities in
the kneaded polymer melts fed
to the rolls, the reasons for which,
in turn, may lie in throughput
fluctuations or temperature
differences.
The current limit values for
thickness fluctuation for different
applications lie between 3 and
10% for rigid PVC films (see
table). Own research has demonstrated that thickness deviations
are rarely recipe-dependent.
Maximum thickness fluctuation for
packaging films
films for customer and credit cards
± 10%
± 7%
± 10%
± 5%
± 7%
± 3%
± 5%
± 3%
introduced
during
further
processing, such as stabilisers, slip
agents, pigments, fillers and static
eliminators (Fig. 4).
Film thickness and thickness
fluctuation
The film thickness is set by way of
the calender roll adjustment. For
packaging films, the thickness
normally lies within the range
from 100 to 800 μm. It is
measured radiometrically during
the production process, but
checked mechanically in the
laboratory between two gauge
surfaces subjected to a specified
pressure. Thickness deviations can
occur in both the lengthwise and
crosswise directions, as well as
diagonally.
Fluctuations in the crosswise
directions are essentially overcome by the compensation
systems of the calender. The
thickness profile can be improved
by measures such as crowning,
bending or skewing of the rolls,
with blower systems providing for
zonal thickness corrections.
Lengthwise
deviations
are
generally the result of excessive
play in the bearings of the
calender rolls, out-of-true running
or speed fluctuations after the
final calender roll. Fluctuating
loads in the roll gap are similarly
a possible cause.
Another source of annoyance is
the formation of so-called flow
lines oblique to the running direction. The varying light refraction
resulting from the approx. 10 μm
Rigid PVC films are produced with
a choice of glossy, matt and
embossed surfaces. The individual
film surface is achieved by way of
a corresponding matt or glossy roll
surface, or else with a separate
stamping module, dulling agents
in the recipe or temperature
control at the final calender rolls
and delivery.
For printing films, in particular,
the homogeneity of the surface is
a decisive factor, as the surface is
required to display specific
properties appropriate to the
subsequent print process. Glossy,
matt and embossed films are all
suitable for screen-printing and
UV offset. For conventional offset,
matt films are the most commonly
used substrates, while glossy
films are preferred for gravure
applications.
Film shrinkage
Shrinkage refers to the changes in
length and width of a film when
exposed to heat. Shrinkage can be
influenced by
• the temperature and speed
control after the calender,
• additives influencing the glass
transition temperature,
• additives
influencing
stretching,
• design measures to reduce
relaxation.
The cause for this shrinkage lies
in the expansion of the film above
the so-called glass transition
temperature, which marks the
relatively narrow transition range
between hardness and elasticity.
Plastics | Manufacturing process
100
%
75
160
˚C
120
50
80
25
40
0
1 2 3 4 5 6
7 8
0
1 2 3 4 5 6
7 8
5 Transparency (%) of different plastic
films, relative to PMMA (100%): 1 PP
random copolymer, 2 High-impact modified
PVC,
3 PETG, 4 Rigid PVC, 5 PC, 6 PS (Styrolux),
7 High-impact modified PMMA, 8 PMMA
6 Temperature stability of different
polymers on the basis of their Vicat
softening temperature (°C):
1 PP, 2 APET, 3 PETG, 4 High-impact modified
PVC, 5 Rigid PVC, 6 PS, 7 PMMA, 8 PC
The expansion leads to orientation
of the molecule chains, which are
then “frozen” in their new state
upon subsequent cooling. Later
reheating to a temperature above
the glass transition temperature
releases the frozen stresses and
the molecules return to their
original configuration. The arising
restoration forces reverse the
original deformation and produce
the shrinkage.
One important optical property of
a film is its transparency (Fig. 5),
i.e. the extent to which contours
behind the film, e.g. packaged
goods or lettering, remain visible
and accurately recognisable. The
transparency is influenced by the
recipe, the surfaces of the last
calender roll and the first delivery
roll, and the temperature control
at these two rolls.
Film defects affecting transparency
include, among others, the abovedescribed flow lines, whose
thickness fluctuations lead to
optical distortions.
flatness defects, with the result
that sheets refuse to lie flat and
reels deviate from their true
running direction when unwound.
Such temperature differences may
also be the cause of expansion
over the film width, in exactly the
same way as various expansion
problems arising from out-ofparallel roll settings or truerunning errors. Such defects are
noticeable above all at the edges
of the film web, and in extreme
cases may mean that these edges
are no longer suitable for further
processing.
Excessive dwell times due to
unfavourable flow processes in
the plasticiser or the first roll gap
also lead to variations in the
thermal loads acting on the film
and consequently to varying
thermal degradation. The resultant inhomogeneities in the
molecular structure are manifested as strength fluctuations
when the film is stretched or
flexed. This may lead, for
example, to tears or holes in the
film during crosswise stretching.
Film homogeneity and flatness
Impact strength and rigidity
Film homogeneity can be understood as the regularity of certain
optical and mechanical film properties which are of particular
importance for downstream
processes such as stretching,
printing or deep-drawing.
Temperature differences, whether
over the roll width or around the
roll circumference, cause thickness deviations in the form of
Films are often exposed to
mechanical impact stresses during
further processing or later use.
Their ability to withstand such
stresses is known as impact
strength, and is classified on a
scale from brittle to high impact
strength.
The impact strength can be
varied by way of suitable modifiers such as MBS, CPE, ABS or
Transparency
7
Oxygen and water vapour barrier properties of different plastics, relative to rigid PVC = 1
8 Permeation coefficients of polymers for oxygen permeation [cm3 μm m–2 d–1 bar –1] and
water vapour permeation [g μm m–2 d–1]
acrylate. Their effect is greater,
the higher the K value of the PVC
concerned. Optimum setting of
the plasticising and calendering
processes in respect of homogeneity and temperature control
is similarly significant for attainment of a particular impact
strength.
The rigidity of a film is dependent
on its modulus of elasticity and its
thickness. For example, a PP film
would have to be 1.3 times the
thickness of a PVC film to obtain
the same flexural rigidity.
Temperature stability (Vicat)
Where films are intended for
further processing or use in the
food and pharmaceuticals industries, one critical property is
temperature stability, e.g. to
permit heating in a microwave
oven or sterilisation process.
Figure 6 shows the so-called
Vicat softening temperatures of
various polymers. Polycarbonates
are excellently suited where such
demand profiles apply.
Barrier properties
The higher the barrier effect of a
film (Fig. 7), the lower its permeability for certain media. The
barrier properties are quantified
by the extent of permeation (Fig.
8) of a volume or amount of gas
(“gas permeation”) or vapour (e.g.
“water vapour permeation”)
through one square metre of a
film of a specified thickness at a
defined gas or vapour pressure
difference over the period of one
day.
Frank Waßmann (Klöckner Pentaplast
GmbH, Montabaur)
Process 5 | 2008 7
Plastics | Versatility
Polyester – The epitome
of versatility
The polyester family of plastics has gained a foothold in many areas of
packaging, advertising and CD/DVD printing in recent years. Contrary to the
most frequently used PVC and polypropylene substrates, polyester attracts
attention through the possibilities for modification and a very broad
suitability for different print and packaging applications – and even as a
substrate for electrically conducting inks.
The term “ester” derives from the
German “Essig-Äther” (literally:
vinegar ether), which is an old
name for ethyl acetate. Polyesters
are thermoplastic polymers with
the ester functional group
–[–CO–O–]– in their main chain.
“Thermoplastic” means that these
polymers can be formed at higher
temperatures and then maintain
their new form after cooling.
Polyesters are produced by various polycondensation processes,
depending on their chemical
composition.
Polyethylene terephthalate (PET, PETB)
The best-known and most
versatile polyester is PET, which is
obtained through the reaction of
the monomers terephthalic acid
and ethylene glycol. Semicrystalline PET molecules (CPET)
are linear chains without lateral
branches – ideal for crease-, tearand weather-resistant fabrics such
8 Process 5 | 2008
as Trevira or fleece, or equally for
tennis racquet strings. Colourlesstransparent amorphous PET
(APET) is processed into films in
thicknesses from 1 μm up to that
of cinematic film stock; PET is no
longer interesting as a material for
magnetic tapes. APET can also be
used to form injection- or stretchblown bottles, e.g. disposable
bottles for soft drinks, but is in
this field gradually being replaced
by polyethylene naphthalate
(PEN).
The high tensile strength,
athermanous properties, and gas
and water impermeability of even
thin films serve to identify APET
as an ideal barrier in composite
films for aroma-sealed food
packaging, which can then be
printed quite easily in a flexo
process. Biaxially oriented APET
films (boPET, DuPont Mylar) are
even used as insulation for space
suits.
A selection of polycarbonate CDs and DVDs, printed in six-colour waterless UV offset on a
KBA-Metronic CD-Print
APET film sheets, in
some cases with different levels of glossiness for the top and
reverse surfaces, are
well suited for laser
and digital inkjet
printing, e.g. for projection foils and pointof-sale
advertising.
They are also in
increasing use in UV
offset (wet and waterless). APET, or better
still glycol-modified
PET (PETG), is furthermore the basis for
lenticular substrates.
In this case, the top
side is formed with
the
narrow
lens
stripes, while the
reverse accommodates
high-precision printing
Mini-movie on PET lenticular film, printed in waterless
in sheetfed offset with
sheetfed offset on a 74 Karat press from KBA
waterless, UV or
waterless UV inks.
The ability to print on
both smooth PET and lenticular Metronic Genius 52UV presses
films has enabled users of the to capture considerable market
KBA Rapida 74 UV and 105 UV, shares. For the booming producRapida 74 G, 74 Karat and KBA- tion of bank and customer loyalty
cards – a domain of the KBASoft drinks bottles and their labels are today Metronic presses – APET is used
often made from PET or PEN
for the lamination.
Plastics | Versatility
Polybutylene terephthalate (PBT)
AttoP-Check is a prefabricated PET tag which
is applied to transparent packaging films. The
nano-ink reacts with distinct discoloration as
soon as the underlying package contents
become even slightly discoloured. Paper
supplier Mondi produces and uses such tags –
calibrated for the correct paper moisture level
– to monitor larger batches.
(photos: Attophotonics.com)
Another field of application for
PETG is shrink labels. Oriented
PETG permits the full enveloping
of containers of any given form,
e.g. wine bottle necks or preserve
jars, with film labels printed on
the reverse in flexo (full body
sleeves, wrap-around labels,
shrink sleeves).
Like PVC and polypropylene,
APET or an APET composite with
polyethylene can also be used for
deep-drawn packaging components. The coextrusion sequence
PETG–APET–PETG
produces
GAG-PET, which forms the
blister cavities for press-out
packaging, e.g. for tablets or for
appropriately small products. The
lidding then comprises a 4/1printed Chromolux card finished
with a heat-sealing blister coating
on the front.
The coextrusion of APET with a
PET modified with isophthalic acid
(PETIP) achieves sealable films
which are then usually bonded
into metallised composites, e.g.
for aroma-safe coffee packaging.
PBT is used for injection-moulded
parts requiring high dimensional
stability and minimal abrasion
wear, e.g. operating elements for
vehicle interiors or electrical
components. Its heat-shock resistance renders PBT a material of
choice for coffee machines and
steam irons. In fibre form, we
come across PBT as the bristles of
toothbrushes or sheathing for
fibre-optic cables – and thus also
in cables for networking on
printing presses – and in
coextrusion with CPET as stretch
cord for trousers.
More recently, PBT has been used
as a nano-filler. In transparent
films which are to be stretched to
become opaque, the nanoparticles support the process of
cavitation. They fill the forming
voids and prevent these voids
leading to a loss of material
strength. Many an opaque film for
UV offset, therefore, contains
PBT. In injection-moulded parts,
the PBT nano-particles act as
flow enhancers for heated
thermoplastics, enabling more
intricate and pliable parts to be
processed.
Polycarbonate (PC)
PC is the most expensive
polyester. It is produced from
toxic carbonyl chloride (phosgene)
and a glycol. All CDs, DVDs and
Blu-ray discs are made from PC,
because this polyester is highly
transparent and also permits
error-free writing of the data layer
through the polymer.
It is not yet possible to print all components
of an RFID transponder
(photo: Infineon)
The fastest decoration method for
these discs is waterless UV offset,
which at the same time achieves a
photo-realistic image quality. With
its keyless machines CD-Print
(6,000 six-colour discs per hour)
and Premius (7,200 four-colour
discs per hour), KBA-Metronic
offers two optimum solutions for
this market. It is true that photorealistic results could also be
achieved by thermal retransfer
printing, but this process is too
slow. The screen and inkjet
processes, on the other hand, lag
behind waterless UV offset in
terms of both speed and quality.
Polycarbonate is well known in
prepress departments from the
transparent and coloured housings
of Apple computers. On account
of its perfect transparency, PC has
replaced the polymer polymethyl
methacrylate (PMMA, Plexiglas)
in many applications.
Printing with electrically conducting
polymers
Depending on the intended
purpose, polyesters – namely
flexible PET and PEN and rigid
PA – are alongside paper the
preferred substrates for another
fast-emerging technology: Industrial printing with electrically
conducting inks. These “printing
inks” are themselves actually
special polymers, whose partially
ionised structures provide for the
electron transport – hence the
usual terms “ionomers” or
“organic electronics”.
One such highly promising
copolymer is PEDOT:PSS, which
comprises the two ionomers
polyethylene dioxythiophene and
polystyrene sulfonate. PEDOT:PSS
currently appears to be the most
suitable choice for printing in
sheetfed or narrow web offset, as
it can be applied reliably and
correctly reproduces even fine
structures, despite the lower tack
than a pasty offset ink. Successful
tests have already been completed
with PEDOT:PSS added to the
dampening solution and the
inking units left unused. Here,
the aluminium oxide non-image
An HDTV flat-panel display from Samsung,
using not liquid crystal polymers but instead
active-matrix OLEDs on PET carriers – a
future prospect for sheetfed offset?
(photo: Aving.net)
areas of the printing plate
suddenly become the image areas,
whereafter the PEDOT:PSS is
transferred fully to the substrate
via a special blanket.
The general goal of printed electronics is a drastic cost reduction
compared to silicon wafers and
liquid crystal polymers. To date,
for example, it has been above all
the costs for production and
application which have prevented
the wide-scale introduction of
RFID tags (Radio Frequency IDentification). It is still the case that
only the trivial RFID components
– electrodes and bipolar antenna
– are printed. More complicated
electronic components, such as
transistors, diodes, capacitors,
oscillators, integrated circuits,
power sources and light-emitting
(OLED: Organic Light-Emitting
Diodes, e.g. for logos, lettering
or displays) or light-absorbing
structures (OPV: Organic PhotoVoltaics, i.e. photocells) need to
be built up in several layers when
printed.
Dieter Kleeberg
Process 5 | 2008 9
Plastics | Substrates
Polypropylene in-mould labels
in sheetfed offset
In-mould labels (IML) represent a cost-effective alternative for the decoration of packaging containers and lids. Unlike
self-adhesive labels, they are integrated inseparably into the surface of the product. In most cases, in-mould labels are
printed in sheetfed offset, ensuring maximum print quality also for this segment of the labels market. The production
process and selection criteria for IML films are here explained by supplier Treofan GmbH.
Most injection-moulded packaging for ice cream and salads is decorated with the IML film Treofan Decor EUH. The five-layer film with a density of a
mere 0.55 g/cm3 is corona-treated on both sides and displays very good antistatic properties. Its behaviour in connection with injection moulding
varies. The cellular core is embedded in two white OPP intermediate layers.
In-mould labelling is generally
understood as a process by which an
injection-moulded, blow-moulded
or thermoformed product is already
provided with its label in its final
mould. The special surface properties of the IML film cause it to bond
permanently with the product. It is
thus normally no longer removable.
Label printing
In-mould labels can be printed in
various processes:
• Sheetfed offset with oxidatively
drying or UV-cured inks,
• Gravure,
• Narrow web offset with UV inks,
• Flexo with UV inks,
• Letterpress with photopolymer
plates and oxidatively drying or UVcured inks.
The order of the list above corresponds more or less to the popularity of the individual processes.
Sheetfed offset is a frequent choice
on account of the possibilities to
combine various images on a single
sheet, as well as the excellent detail
reproduction in its photorealistic
printed images. Given the
favourable price of reel supplies, it is
also useful to configure a sheeter
unit ahead of the press feeder when
planning to work with IML films.
10 Process 5 | 2008
Gravure is preferred for high-volume production, e.g. labels for margarine tubs. Medium runs are often
entrusted to web offset printers.
Die-cutting is performed either
inline or offline, depending on the
print process.
Film manufacturing
The use of polypropylene films – or
to be more precise: OPP (oriented,
i.e. stretched PP) and CPP (cast PP)
films – for the decoration of injection-moulded packaging has seen
enormous growth over the past 15
years. The substrates used are
mostly OPP films, in some cases also
for particularly large labels, e.g. for
paint buckets.
To manufacture a CPP film, a singleor multilayer PP film is extruded
through a slit die. The film is then
trimmed and usually also pretreated
with a corona discharge ready for
printing. Finally, the film is wound
onto a reel and later cut to the width
requested by the customer. Typical
film thicknesses lie between 80 and
100 μm.
The manufacturing of an OPP film is
much more complex. First of all, in
the same way as for a CPP film, a
multilayer PP film is extruded. For
IML films, it is usual to coextrude
three to five layers. The different
melt flows are already combined in
the die and are deposited together
onto the chilling roller. After this socalled pre-film has cooled and set, it
is heated once more to a defined
temperature and stretched in its
lengthwise direction. The stretching
is accomplished by rollers rotating
with different surface speeds. The
normal procedure is to stretch the
film by a factor of four to five. The
film thickness is reduced correspondingly.
After lengthwise stretching, the film
is also stretched in its crosswise
direction. To this end, the film is
inserted into a so-called stenter,
where it is held along its two edges
by a chain of clips. The film is now
heated once more, and stretched
crosswise by a factor of eight to ten
once the defined constant temperature is reached. At Treofan, IML
films are usually produced in widths
up to seven metres.
After stretching, the film is stabilised to eliminate any stresses in
the material, and cooled, as it then
immediately comes into contact
with rollers.
To guarantee printability, the film
surface is treated with a corona discharge to raise the surface tension
to approx. 40 mN/m. To complete
Typical products sold in IML-decorated packaging
Forming method
Food products
Non-food products
Injection moulding
Margarine, butter, cheese, yoghurt,
ice cream, salads, desserts,
dried soups
Paints,
detergents,
garden products
Blow-moulding
—
Fabric softeners, cosmetics,
car care products
Thermoforming
Yoghurt, cheese (under development) —
Relevance of interactions of IML films and inks
Between film and forming
• Product application
• Form
• Cooling
Between film and printing
• Register
• Flatness
• Temperature
• Chemical compatibility
Between printing and forming
• Sheet/label separation
• Electrostatic charging
• Heat resistance
• Design
Plastics | Substrates
Treofan Decor IML film range for PP and PE injection-moulded packaging
These injection-moulded containers and lids for ice cream were decorated with the IML film
Treofan Decor ETR. The three-layer film with a density of 0.91 g/cm3 is corona-treated on both sides
and possesses a transparent OPP core.
the process, the film is wound onto
a machine reel and passed on for
cutting down to the widths required
for printing or sheeting.
Properties of films for IML
applications
OPP films for IML applications place
particular demands on the material
properties. Unlike the OPP films
used as packaging materials, IML
films are often required in trimmed
form (sheets) or even as single
labels. Consequently, IML films are
usually thicker than typical OPP
packaging films (57 to 90 μm). It is
furthermore important that the IML
sheets and labels can be separated
easily. This is normally achieved by
designing the IML film with a glossy
surface on one side and a matt surface on the other. The matt surface
enables air to penetrate better
between the sheets and facilitates
removal from the pile. In combination with special additives, the matt
layer is also able to reduce the electrostatic charging arising from separation of the two surfaces.
The demand for labels which lie as
flat as possible, i.e. with only minimal tendency to curl, calls for careful selection of the raw materials for
the various layers, as well as precise
matching of the individual layer
thicknesses. In this connection, it is
also necessary to ensure that the
print process and ink systems used
similarly exclude unwanted curling.
Choice of IML film
The selection of a suitable IML film
is to a large extent dependent on the
process used for moulding of the
final product.
In the case of injection-moulded
products, the essential influencing
factors are the required appearance
Composition of a five-layer IML film: The top surface (1) is responsible for the glossiness, the
antistatic properties and – following corona discharge treatment – for the bonding of the inks
and a possible metallising coating. The two intermediate layers (2, 4), together with the core
(3), determine the whiteness, opacity and density, and thus also the strength and flexural rigidity
of the film. The bottom layer (5) provides for bonding to the moulded product.
Product
Appearance
Film thickness
Weight
OPP films
EUH*
EWR
ETR
opaque/white, glossy/matt
white, glossy/matt
glossy, translucent
50 μm to 90 μm
57 μm
57 μm
27.5 to 49.5 g/m2
54.7 g/m2
54.7 g/m2
CPP films
CWD
CTD
white
transparent
80 μm and 100 μm
82 μm
74.2 and 92.8 g/m2
72.2 g/m2
of the label surface (glossy or matt)
and the product form. Products with
high-gloss labels can only be produced with a heavy OPP film (e.g.
EWR, ETR) or a CPP film (CWD,
CTD). One undesirable side-effect
manifested with OPP films, in particular, is a strong tendency to distortion after injection moulding when
applied to thin-walled, non-symmetrical products. This could be avoided
by choosing a film with a cellular
structure (EUH). The trade-off here,
however, is that it is not possible to
create high-gloss labels. For the marketing specialists, on the other
hand, it is a simple matter to turn
the necessity of a matt surface into
a virtue and to sell the orange-peel
effect as a “soft-touch” finish.
Cast PP films display practically no
influence with regard to distortion
of an injection-moulded product.
Due to their greater thickness and
thus greater weight, however, they
are more likely to be used for very
large items, such as 5 or 25-litre
paint buckets, than for food packages.
As the pressures involved are lower
when forming blow-moulded products, such as HDPE or PP bottles, the
materials used are mostly films with
a specific sealing coating. This sealing coating is furthermore applied
with a certain pattern to promote
the escaping of the air between the
product and the label. Tests aiming
to achieve this same effect with an
OPP or CPP film designed for injection moulding have not yet produced reliable solutions. With the
film type UND, however, Treofan
GmbH is developing an alternative
which permits the air to escape
through a permeable film. At the
same time, this film requires no
coating.
Thermoformed products are subject
to similar problems to those faced
when blow-moulding. In the past, it
proved very difficult to displace the
air from between the moulded product and the label surface. Earlier
tests sought a solution by perforating the labels. This approach, however, demanded an additional
process step, and also brought the
disadvantage that the perforation
remained visible later.
Since 2006, new progress has been
made in this field. Through optimisation of the deep-drawing process,
use of a foil with a cellular structure
and modification of the sealing, it
has become possible to produce
bubble-free IML labels. The label
surface, on the other hand, is once
more a matt orange-peel finish. If a
breathable film such as Treofan
UND is used, however, it is also feasible to produce a gloss label in conjunction with suitable coatings.
Wilfrid Tews (Treofan GmbH,
Neunkirchen and Raunheim)
Process 5 | 2008 11
Plastics | Surface tension
Simple determination of
surface tension on plastic films
The printability of a plastic film is essentially dependent on its surface tension. To enable the ink to adhere, the
surface tension of the film must be higher than that of the ink. Simple methods permit fast checking of whether or
not the surface tension of a plastic substrate is sufficiently high.
remains adhered to the body. The
tensile force is gradually increased
until the film of liquid tears. The
surface tension can then be
calculated from the maximum
tensile force, the dimensions of
the immersed body and the
density of the liquid.
Measuring methods for solids
The cohesive forces between the molecules establish a state of energy
equilibrium in the bulk of a liquid, but not at the surface
(illustration: Schmid Rhyner)
Surface tension characterises the
behaviour of an interface between
a liquid (e.g. water) or solid (e.g.
film) and a gas (e.g. air), and is
thus also referred to as interfacial
tension. This phenomenon is manifested, for example, in the way a
liquid naturally seeks to minimise
its surface area. Consequently, a
droplet of liquid which is not
subject to external forces – in free
fall, for instance – will always
assume a near-spherical shape.
Molecular interactions
Neighbouring molecules are subject to attractive and repulsive
forces, so-called cohesive forces.
In the bulk of a liquid, these
forces are able to interact equally
in all directions. This is not true
for the molecules at the surface,
however, as they possess fewer
neighbours than the interior molecules. Within the liquid, the
motions of the individual molecules exist in state of energy equilibrium, whereas motion at the
surface requires energy to be
expended to break molecular
bonds.
If the surface of a liquid is to be
increased, therefore, a certain
12 Process 5 | 2008
Young’s equation permits the surface tension of a solid to be calculated
from the cosine of the contact angle
quantity of work must be done.
The work required to enlarge the
surface is dependent on the
surface tension of the liquid. The
ratio between the work done and
the resultant surface enlargement
is the surface tension (represented
by the symbol “sigma”)
σ = ΔW / ΔA
which is usually expressed in the
unit mN/m (millinewtons per
metre), corresponding to the SI
units 0.001 kg m/s2 or mJ/m2
(millijoules per square metre).
Water at 20°C displays a surface
tension of 72.8 mN/m, compared
to 484 mN/m for mercury or 21.7
mN/m for isopropanol.
Surface tension is temperaturedependent and generally decreases
as the temperature rises. Surfactant
substances, such as the tensides in
dampening solution additives,
reduce the surface tension of the
liquid to improve the wetting of an
offset printing plate.
work done to achieve this.
Examples are the ring method
developed by Pierre Lecomte du
Noüy, the Wilhelmy plate method
and the frame method after
Philipp Lenard.
In all three methods, a solid body
(ring, plate or frame) is immersed
in the liquid, and then drawn back
out such that a film of liquid
The surface tension of solids can
similarly only be measured indirectly. When using the contact
angle method, a solid is wetted
with two different liquids with a
known surface tension. The chosen liquids are frequently water
and diiodomethane. In Young’s
equation, to be seen alongside, the
indices S and L stand for “Solid”
and “Liquid”; the symbols σS and
σL describe the surface tension
components of the two phases;
YSL represents the interfacial tension between the two phases, and
θ stands for the contact angle, cor-
Measuring methods for liquids
In most cases, the surface tension
of a liquid is measured by
increasing the surface area of the
liquid in a defined manner and
then determining the quantity of
For an unformed liquid L to be able to spread and wet the formed surface of a solid S, the
surface tension of the solid must be greater than that of the liquid (bottom example), otherwise
it will be repelled in beads (top example)
(illustration: Weilburger Graphics)
Plastics | Surface tension
One commercially available camera contact angle measuring device is the pocket goniometer
PG-2 from Swedish manufacturer Fibro Systems
responding to the angle between
the vectors σL and YSL. To determine the surface energy, various
initial equations for YSL are combined with Young’s equation, with
cosθ representing a function of
the phase surface tensions. With
this system of equations, it is possible to calculate the surface tension of the solid.
The market offers a range of
instruments for the fast and
simple determination of contact
angles. Such goniometers comprise a system to inject a test
liquid and a camera to measure the
bead cross-section. This measurement is then used to calculate
the corresponding contact angle
values. A contact angle of 0°
results if the liquid spreads, i.e. if
the solid is completely wetted. A
contact angle between 0° and 90°
is considered to represent good
wetting, while a contact angle
between 90° and 180° is treated
as poor wetting. A contact angle of
180° means that the liquid is
repelled in the form of spherical
beads. This phenomenon is commonly referred to as the “lotus
effect”, after the corresponding
properties exhibited by leaves of
the lotus plant.
Another typical method to determine the surface tension of solids
is to use test inks. An ink with a
known surface tension is applied
to the material to be tested with a
brush. If the test ink wets the
surface, then the surface tension
of the material is equal to or
higher than that of the ink. On the
other hand, if the test ink retracts
into a bead within 3 seconds, then
the surface tension of the solid is
lower than that of the test ink.
Test inks ideal for plastics
The test ink method is based on
the knowledge that liquids achieve
good wetting of a solid if their
Test inks in use: On the left, the ink has spread, i.e. this full wetting shows that the surface
tension of the film is at least as high as the known surface tension of the test ink. On the right,
there is no wetting, i.e. the surface tension of the film is lower than the known surface tension
of the test ink
With a set of test inks, the surface tension of a film substrate can be determined iteratively
surface tension is lower than that
of the solid in question. This is
also why it is problematical to
print on substrates with a low
surface tension. To guarantee sufficient wetting of the substrate by
Surface tension of different plastic substrates
PC monitor image from the camera of a
goniometer. The contact angle is clearly
greater than 90°, indicating that the wetting
of the surface is poor
Source: Fraunhofer IGB
Material
Surface tension
PTFE (polytetrafluoroethylene, “Teflon”
22.5 mN/m
PE (polyethylene)
36.1 mN/m
PE (polyethylene) after corona treatment
38 … 44 mN/m
PVC (polyvinyl chloride)
38.4 mN/m
PS (polystyrene)
43.5 mN/m
PET (polyethylene terephthalate, “polyester”)
47.0 mN/m
PMMA (polymethyl methacrylate)
49.0 mN/m
PC (polycarbonate)
46.7 mN/m
the printing inks, it is necessary to
ensure that its surface tension is
higher than that of the inks, either
through appropriate selection or
pretreatment, etc. A set of test
inks is thus a very convenient
means to check the properties of
a particular plastic substrate.
Beatrix Genest (SID Sächsisches Institut
für die Druckindustrie GmbH, Leipzig)
Process 5 | 2008 13
Printability | Corona treatment
Raising surface tension
with a corona tower
Corona treatment is an effective method to raise the surface tension not only of plastic films and metallised substrates,
but also of non-absorbent paper and board surfaces. It is only above approx. 38 mN/m that the surface tension is
sufficient to enable an ink to bond. Since the corona effect on factory-treated films diminishes over the course of
storage, many plastics printers use inline corona systems. KBA’s partner in this field is Ahlbrandt System GmbH.
The keyless and waterless KBA Rapida 74 G in the customer demonstration centre at KBA in
Radebeul incorporates a corona tower ahead of the first printing unit (right-hand arrow) and direct
ozone extraction (left-hand arrow). In this particular configuration, it is already able to print
selected film types. The Rapida 74 G can also be supplied with UV equipment, in which case it is
able to process all types of plastic substrate.
How corona treatment functions
Corona treatment is the most
frequently used method to improve
the printability of film surfaces.
Raising the surface tension
provides for better bonding not
only for UV inks and coatings or
waterless offset inks, but also for
adhesives.
The Latin word ‘corona’ refers to a
crown or garland. If high voltage is
applied
to
an
electrode,
uncontrolled discharge produces a
bluish, luminous corona around
that electrode – the surrounding air
is “ionised”. More properly
speaking, the high-frequency
current is breaking down the
oxygen and nitrogen molecules in
View into the corona tower of a KBA Rapida 74:
The blue shine around the activated quartz
electrode can be seen behind the white sheet
guide rollers. The chrome-plated back cylinder
in the foreground is effectively a double-size
impression cylinder.
14 Process 5 | 2008
the air to form radicals. In the
corona treatment system, these
radicals are channelled from a
quartz electrode to a ceramiccoated back roller or – in the case
of the KBA Rapida – to the chromeplated impression cylinder. In the
process, they are accelerated along
the field lines and penetrate up to
0.1 nanometres into the film
surface, hurling hydrogen atoms
out of the polymer chains as they
do so. Atoms are also released in
similar fashion from the surface of
a metallised substrate. Within just
a few milliseconds, gaps are left in
the surface cross-linking structure;
this effect is also referred to as
“roughening”. The cylinder here
functions as the counter-electrode,
i.e. it dissipates the charge, and at
the same time provides for the
correct clearance between film and
corona electrode.
Adaptation for sheetfed offset
printing
KBA offers a corona option for
Rapida presses from a format
width of 74 cm. Its partner for such
installations is Ahlbrandt System
GmbH, based in Lauterbach/
Hessen, which supplies corona
systems specially adapted for
sheetfed offset printing exclusively
to KBA.
The AS Corona Star series was
originally developed for use on
flexo and narrow web presses and
for film manufacturers. In these
applications, the film passes the
quartz electrode at a clearance of
only 2 mm. On a sheetfed press,
however, it is impossible to work
with such a small clearance
because of the grippers. The
alternative of shifting the corona
discharge to the feed table is
similarly impracticable due to the
overlapping sheet stream and the
sheet deceleration.
Consequently, only one possibility
remains: The corona system must
be accommodated in a separate
tower ahead of the first printing
Printability | Corona treatment
unit. In such a corona tower, it is necessary
to increase the clearance between electrode
and film sheet to approx. 5 mm – and with it
also the discharge power. Depending on the
format width, and thus the available space in
the corona tower, up to three 15 kV electrodes are installed, each with a power rating
of 3 kW or more.
At full discharge power, the surface tension is
raised to the desired degree even at maximum
production speed. One important factor
contributing to uniform surface roughening is
the full-area contact between the film sheet
and the back cylinder, which thus takes the
form and dimensions of an impression
cylinder. There is no need to adjust the
electrode length for different film widths. The
ozone arising in the dielectric is extracted
directly.
Corona tower liberates the printer from
restrictions
The principal advantage of an inline corona
system is that printers are no longer
compelled to use up pretreated substrates
before the “expiry date” of the corona effect.
In fact, they can simply purchase untreated
materials as and when needed, and these
materials are naturally less expensive than
pretreated film. Or else they could build up a
stock of different substrates, so as to be able
to react flexibly to customer wishes, but
without having to worry about a loss of
printability over time.
Another point is that the corona effect on
factory-treated sheets may be quite literally
rubbed away during separation from the pile
and transport of the sheet stream on the feed
table. Even if a surface tension measurement
(with test inks) indicates that sufficient effect
remains, this does not necessarily mean that
this surface tension will actually survive
through to the printing units.
Printers working on a press with corona tower
must still always test the surface tension of
the untreated substrates. After all, they need
to know which discharge power is required to
work at the maximum possible production
speed. And furthermore, it is beneficial for
both profits and the environment not to
discharge energy unnecessarily and to keep
the amount of ozone produced to a minimum.
Alternative methods
Factory-treated substrates have not always
been processed in a corona discharge system.
But there are no cost advantages to be derived
from alternative treatment methods.
Film manufacturer Klöckner Pentaplast, for
example, has developed the so-called Dynox
process, which is used at least for rigid PVC
In the tower frame designed by KBA, the Ahlbrandt corona unit is mounted with optimum clearance to the back cylinder
(top photo). All three electrodes of this corona unit possess individual hoses for ozone extraction (bottom photo)
films. This treatment raises
the surface tension to over
45 mN/m. In contrast to
corona treatment, the surface
effect lasts for more than a
year, and is also not destroyed
on the feeder.
Another method is plasma
treatment. The desired effect is
here achieved by bombarding
the surface with ions. And once
again, the effect remains stable
for longer than with corona
discharge.
A third alternative is for the
film manufacturer to finish the
material with a special primer,
a so-called “top coat” which
preserves the corona effect.
The Ciba Prime IT technology
is a similar method.
Summary
less expensive untreated
materials. And if they do so,
they can at the same time be
sure that the printability of
the
chosen
sheets
is
absolutely reproducible.
Dieter Kleeberg
Matthias Lange (KBA Radebeul)
Printers working with plastic
substrates on a regular basis
can easily calculate whether it
makes sense to purchase an
inline corona unit and to use
Process 5 | 2008 15
Sheet travel | Static elimination
Antistatic systems on
sheetfed offset presses
The prevention of electrostatic charging is already of great general significance for smooth sheet travel through a sheetfed
offset press. But because the electrostatic tendency of plastic films is so incomparably greater than that of paper sheets,
it is here absolutely imperative to provide antistatic systems at the feeder and infeed.
Principle of electrostatic charging through electron transfer
Principle of electrostatic charging
(voltage U > 0) at sheet separation
What is static electricity?
All matter comprises individual
atoms. These atoms, in turn, each
comprise a positively charged
nucleus and orbiting negative electrons. Any single nucleus possesses
exactly as many negative electrons
as the number of positive charges
(protons) expressed by its atomic
number. Overall, therefore, the
charges cancel each other, and all
matter is thus in its original natural
state electrically neutral – we can
speak of “uncharged” matter.
This natural equilibrium of positive
and negative charges, however, can
be disturbed if objects are brought
into contact, pressed together or
rubbed against each other and then
separated once more. Negative particles (electrons) are effectively torn
out mechanically from the surface of
one object and passed by this friction to that of the other object. In
the resulting charge imbalance, one
object now possesses too few electrons to compensate all the positive
charges of its protons, and is thus
“positively charged”. The other
object, at the same time, now possesses too many electrons, and is
consequently “negatively charged”.
Objects with like charges – irrespec-
16 Process 5 | 2008
tive of whether positive or negative
– repel each other, whereas differently charged objects are attracted
to each other.
Static electricity on sheetfed presses
This phenomenon also affects a
printing press in various ways. The
attraction forces between appropriately charged sheets can even bring
the whole production process to a
halt. At the feeder, for example, this
may be manifested in blocking of
the pile, poor separation, double
sheets and waviness on the feed
table, and crooked arrival at the
front lays. In the delivery, the sheets
are not straightened up properly
when dropped from the gripper carriages and thus form a disorderly
pile. That, in turn, restricts further
processing of the printed sheets. In
the case of very sensitive materials,
the ink application may also be
impaired.
The tendency of a material to build
up electrostatic charges is dependent not just on its physical properties, but also on its handling and the
ambient conditions in the press
room. While paper is subject to
charging at low humidities, it is
above all friction during transport
which is responsible for the charging of plastic films.
Factory-installed antistatic systems
To combat the problems of electrostatic charging, KBA sheetfed offset
presses can already be fitted with
various configurations of antistatic
equipment from KERSTEN Elektrostatik GmbH, Freiburg im Breisgau,
before they leave the factory. The
essential requirements for thin or
coated papers and boards are handled by a relatively simple basic
package. Corresponding upgrade
levels expand the range of potential
applications and cover also the significantly higher demands of plastic
substrates.
The fully plastics-capable equipment
package on the Rapida 106 press
installed in the KBA test print centre
enables us to identify the individual
components and to briefly describe
their purpose.
Antistatic systems on the feeder
All the antistatic systems at the pile
edges serve to support separation of
the sheets and are thus essential for
trouble-free functioning of the
feeder. Six antistatic heads are
installed across the rear width of the
feeder. The two central components
are DK 106 antistatic heads, which
are mounted on the KBA separating
air nozzles (1.1) and thus use the air
of the separation burst for static
elimination. Alongside, four DD 406
antistatic nozzles are used to blow a
variable volume of antistatic air into
the top of the pile as loosening air
(1.2 and 1.3). Two further static
eliminators are mounted at the pile
side edges. Here, too, the antistatic
heads are fitted to the KBA air nozzles.
On the feed table, a DE 206 electrode (4) is used to treat the top surface of the sheet, a DR 106-8 electrode array (5) takes care of the
underside, and a DR 206-6 array (7)
helps to lift the first sheet.
Antistatic systems in the delivery
The antistatic systems for the delivery are exclusively DE 206 electrodes, which eliminate the electrostatic charges over the full format
width. The underside of the sheet is
treated at the decurler (8.2) and
after the sheet brake (8.1), the top
surface at the powder sprayer (9.1)
and with three electrodes above the
pile (50.1 to 50.3). The objective of
these systems is to enable smooth
Sheet travel | Static elimination
The KERSTEN antistatic systems (depicted in yellow) on the feeder of the KBA Rapida 106 in the test print centre: Two DK 106 antistatic heads (photo top left, component 1.1, on the separating air
nozzles), one of four DD 406 antistatic nozzles (top right, components 1.2 and 1.3, as loosening blowers), and for the feed table a DE 206 antistatic electrode (bottom left, component 4, for the top
sheet surface) and a DR 206-6 array (top centre, component 7, to lift the first sheet). As can be recognised from the schematic drawing, the DR 106-8 array (component 5, for the underside of the sheet)
is not visible.
sheet transport, an even powder
application and precise pile formation.
Function principle
As already explained above, electrostatic charging is the expression of
an imbalance in the charges at
atomic or molecular level. To elimi-
50.1–3
nate the disturbing effect, this
imbalance must be neutralised, i.e.
the positive charges must be compensated with an appropriate number of negative inputs, and vice
versa. The result is then once more
a neutral charge distribution.
Antistatic systems draw the necessary compensating charges from the
molecules of the surrounding air. To
this end, a voltage of at least 2,500 V
is applied to needle-point electrodes, producing charged particles
(ions) in the immediate vicinity of
the needle points. These ions can
carry either a positive or negative
charge, depending on the polarity of
the applied voltage.
9.1
8.1
8.2
The KERSTEN DE 206 antistatic electrodes in the delivery of the KBA Rapida 106 in the test print centre: Static elimination for the underside at the
sheet decurler (component 8.2) and after the sheet brake (component 8.1), and for the top surface of the sheet at the powder sprayer (component 9.1)
and above the pile (components 50.1 to 50.3).
An antistatic system for a printing
press provides for a constant adequate supply of both negative and
positive ions. With the neXt® systems from KERSTEN, this is ensured
by using a stabilised bipolar DC voltage. Both polarities are present at
the electrodes at the same time.
Consequently, a maximum availability of both positive and negative
charge carriers can be maintained
constantly. This technology also produces significantly more ions than
the previously used AC systems.
An electrical field provides for
homogeneous distribution of the
ions over a wide surrounding area.
The relevant law of physics states
that opposite charges are always
attracted to each other. The charged
sheet thus “soaks up” precisely
those ions which are required to
neutralise its surface. If sufficient
ions are made available, the electrostatic charging of the sheet will be
eliminated completely. Any excess
ions are taken back by the antistatic
system itself.
Process 5 | 2008 17
Inks and coatings | Offset inks
Results and benefits for the user
With such antistatic systems, it is
possible to handle even difficult
print substrates without problems,
as the neutralisation is performed at
precisely those points on the press
where electrostatic charging is relevant. Given the high purchase prices
for plastic substrates, the investment in antistatic equipment is usually already returned after only a few
weeks.
The most important and above all
tangible effects for the user at a
glance:
• Improved sheet separation at the
feeder;
• Fewer double sheets and press
stoppages;
• Reduced non-productive times;
• More exact alignment at the
front lays;
• Enhanced productivity through
higher production speeds;
Function principle of the KERSTEN antistatic systems: An electrical field provides for homogeneous
distribution of the ions and full charge compensation (electrical charge Q = 0).
• Handling of substrates for which
static elimination is imperative (plastic films);
• Neutral delivery piles with tidy
pile edges;
• Better and faster further processing of the printed sheets;
• Fast return of investment;
• Greater operator satisfaction.
Operation and maintenance
Antistatic systems are easy to care
for and practically maintenancefree. From the electrical side, the
system is fully self-regulated, i.e. it
requires no special user settings.
The needle points of the electrodes
are the parts responsible for the production of the compensating ions.
To ensure the full static elimination
performance, therefore, they must
be cleaned at regular intervals as
demanded by the level of contamination (usually once a week).
A certain amount of experience is
also necessary for correct positioning and setting of the antistatic air
nozzles, particularly in respect of
the air blown into the feeder pile.
Wolfgang Zierhut
(KERSTEN Elektrostatik GmbH)
Oil-based and UV-curing Inks
for film and foil printing
In the past, offset printing on plastic film mainly used inks with mineral-oil
based binding vehicles. With printers, converters and end customers having
been demanding better performance systems over the past few years, the
conclusion has been reached that UV technology is the best alternative to oilbased inks. This article is to present in more detail the status and innovations
of the two ink systems—from the perspective of ink manufacturer Siegwerk.
Special requirements for printing on
film and foils
Synthetic substrates such as
plastic film and other nonabsorbent printing substrates are
becoming more and more frequent
in the printing sector, and particularly in offset printing.
18 Process 5 | 2008
The challenge to find a suitable
offset ink system for these applications include
• good printability,
• improved running characteristics on increasingly faster
presses,
1 The torque (y axis) of a rotation viscosimeter mapped against the water content (x axis) of
the ink permits conclusions on how the ink-water balance influences the printability of inks. The
more water an ink can absorb, the greater the margin for problem-free printing of films and
foils. Here a higher torque denotes a lower influence of the dampening ratio. Older types of UV
inks (1 and 2) did not absorb enough water. Latest-generation UV inks (3) exhibit an equally
suitable behaviour as oil-based inks (4)
Inks and coatings | Offset inks
Table 1: Criteria in film printing with oil-based inks
Criterion
Parameter
Level
Fount solution
pH value
IPA content
Water feed
>5*
3 … 12% **
As low as possible
Piling
Pile height
Pile temperature
restricted ***
< 40 °C ***
Powder
Powder quantity
specified
Waiting time ****
Period between printing
and post-press
< 48 h
*) Higher fount solution acidity slows drying down;
**) Up to 12% recommended for printing with smallest possible amount of fount solution;
***) To prevent blocking and set-off;
****) Do not over-ink, coating if scratch resistance is too low
• secure adhesion and scratch
resistance on non-absorbent
substrates.
In contrast to most paper and
carton substrates, the surface
structure of typical plastic film
does not allow the ink to set.
Drying and adhesion support by
filtration into the substrate is not
possible. Additionally, the presence of fount solution in oil-based
ink offset generally impairs the
drying process. Therefore, a good
ink-water balance is a key factor in
influencing the drying process.
Special oil-based inks have been
developed for synthetic substrates
to accommodate special technical
requirements concerning the
quality of the printed product.
However, a good compromise
between fast drying, safe piling,
adhesion and abrasion resistance
remains a difficult thing to achieve
with oil-based inks (see Table 1).
Here the advantages of UV curing
technology should be used,
including
• immediate hardening of the ink
layer,
• low influence of the amount of
fount solution, and
• fast readiness for further
processing.
Development of modified
radiation-curing printing inks
When UV ink systems were first
introduced in the printing
industry, they were criticised for
their
problematic
printing
behaviour in offset presses and for
adhesion
problems.
These
problematic characteristics have
been successfully overcome by
new raw materials and innovative
ink formulations.
Printability of UV inks
In non-absorbent substrates such
as plastic film, the
fount
solution
cannot filter into the
surface. The first
generation of UV
inks tended to build
up on rollers, plates
and/or blankets due
to excessive fount
solution absorption
and the resulting loss
of tack. Here, an
2 Ink-water balance profile in the production run. The wet
optimized ink-water
tack of the ink changes over time because of alternating
balance
improved
downtimes (make-ready, pile change, intermediate washing)
and optimum production speed. Recent UV inks (green)
printability. New ink
retain the set ink-water balance while former-generation UV
generations
with
inks get increasingly out of control
optimized absorption
and release of fount
solution exhibit a much greater
margin between over and underdamping.
For some years now, alcohol-free
printing has been on the increase.
Especially in film and foil printing,
however, the use of isopropanol has
proved to be the better choice,
with reduced surface tension of the
fount solution for optimal printing
and a good ink-water balance.
Instead of IPA, alcohol substitutes
might be used depending on press
configuration, plates etc.
especially of the UV coating, the
more volume is there to shrink.
One result is reduced adhesion.
Especially in the crosscut test, the
adhesive force of the adhesive
tape can exceed the bonding force
between the ink/coating and the
printing substrate, causing the inkcoating layer to lift off from the
substrate. Adhesion quality also
depends strongly on the use of
highly flexible ink/coating/binding
vehicle systems that reduce
shrinking.
Adhesion of UV inks
Curing of UV inks
In the past, UV inks showed
restricted adhesion on foils and
films, but these issues have been
overcome by newly developed
special ingredients and optimized
ink formulas.
An essential condition is, however,
that the substrate such as PVC does
not contain any plasticizers, static
inhibitors and other substances
that might diminish adhesion.
The recommended surface tension
for PVC is 35 mN/m. For substrates made of ABS, PP, PET, PE
and PS, a surface tension of over
40 mN/m is essential. These substrates should also be free of problematic additives like static
inhibitors, which might impede
uniform ink adhesion due to their
separating effects. The correct
surface tension in a synthetic substrate lies in the material formulation and thus with the
manufacturer of the substrate.
Manufacturers also sometimes use
so-called corona discharge technology to electrically treat the surface
of films. The surface tension might
fall during longer storage of the
substrate, and the corona pretreatment must be repeated
directly in the web or sheet-fed
press. This option is also advisable
if non pre-treated substrates are
used for economical reasons.
Moreover, the molecular structure
of the cured ink layer widely influences adhesive characteristics,
flexibility and scratch resistance.
Differing curing characteristics can
also influence the adhesion of the
ink/coating layer. If the ink does
not cure completely, adhesion
might be diminished by insufficient cross-linking of the ink/
coating layer. In rare cases, an
over-cured ink/coating layer might
shrink strongly and become
brittle, which results in lower flexibility and adhesion.
Flexibility of UV-cured layers
UV inks and coatings generally
tend to shrink during curing. The
thicker the layer of the ink, and
Versatility of UV inks
In the early days of UV technology,
it was rarely possible to use inks
specially formulated for film and
foil printing also for printing on
paper and carton due to the high
tackiness of the oligomers, which
ensure adhesion. Today, optimized
qualities allow the use of UV film
printing inks on paper-based substrates in many cases.
Requirements on UV systems
in film printing
The filming quality of UV inks can
be markedly improved by the use
of doped lamps or in a nitrogen
atmosphere (inert UV). So-called
cold UV systems reduce the
emitted heat and the pile
temperature, preventing dimensional changes in the films and
foils; however, it also slows down
the polymerization of the UV inks
and coatings. If the molecular
cross-linking process takes place
in the presence of nitrogen,
polymerization is faster, permitting
higher printing speeds. It is
essential to test the adhesion of
inks and coatings on the substrate
in all jobs. Unlike scratch
resistance, generally adhesion
Process 5 | 2008 19
Farben und Lacke | Offset inks
initiator systems, the use of ultrapure monomers and oligomers of
high molecular weights and
adapted formulations result in
very low migration and thus help
to meet new demands.
With all the high purity of
materials and sophisticated
manufacturing technology, users
still should check and coordinate
the qualities recommended by the
ink supplier with the technical
environment in the printing shop
(press, UV system, printing speed,
etc.) according to the legal
regulations. Apart from ink and
coating,
organoleptic
and
3 Characteristics of the UV offset ink series developed by Siegwerk for printing on plastics:
Pr = printability, Mi = low migration, Ad = adhesion, Ve = versatility, Od = low odour
does not improve any further after
12 hours from printing.
Sensory and migration properties
Printed films are used as wraps,
shrink film, cosmetics packaging,
labels and much more. Some of
these applications require particular specifications in UV inks and
coatings, such as
• low odour,
• no influence on the taste of the
packaged goods,
• no migration into the packaged
goods.
Against the background of
constantly increasing demands by
consumers, legislation and better
analyses, ink manufacturers must
satisfy new requirements every
day. Ink qualities are formulated
4 For the testing of printing inks, a liquid chromatograph/mass
spectrometer (LC/MS) system may be used to measure impurities,
which might migrate in very small amounts
migration data can be influenced
by many other parameters beyond
the influence of the ink
manufacturer. This applies in
particular to suitable cleaners and
dampening additives. Printing
substrates also might develop an
with special materials that
minimize the organoleptic effects,
e.g. the excitation of sensitive
receptors such as olfactory and
gustatory nerves in the mucous
membranes, and reduce molecular migration. Optimized photo
Table 2: UV litho printing inks of Siegwerk Druckfarben AG for film printing
Substrates
Non-absorbent
Printing ink series
Sicura Plast SP Sicura Plast LO Sicura Plast LM Sicura Litho
Paper/Board
Sicura LM
Folding boxes for primary food packagings
X
X
***
X
***
Folding boxes for secondary food packagings
**
***
**
**
***
Folding boxes for cosmetics, pharmaceuticals, tobacco
***
**
*
***
*
Folding boxes for chemicals
***
*
*
***
*
Labels & tags
***
**
*
***
*
IML
X
*
***
X
***
Display
***
*
*
***
*
Brochures, leaflets
***
*
*
***
*
Metal Dec 3P
***
***
*
X
X
*) Not fit to purpose but can be used; **) Recommended; ***) Highly recommended; X) No possible use
20 Process 5 | 2008
inherent odour after UV radiation.
Careful handling and storage of
the printed run is another
important factor. For questions
or special jobs, especially in the
sensitive area of food packaging,
it is always advisable to contact
the local representative of the ink
and coating manufacturer in order
to receive the best possible
technical support and advice.
Resume
Printing on increasingly demanding substrates with impenetrable
surfaces – from plastic films to
metalized substrates or even sheet
metal – requires ink
manufacturers to constantly develop their
products. Increasing press speeds
and the resulting shorter drying
times present a particular challenge.
Due to their absence of shrinking,
oil-based systems continue to be
used for special applications.
However, UV technology will
continue to occupy an ever
increasing place in the graphic
industr y,
with
constantly
improving ink formulations and
manufacture (in particular with
regard to organoleptic qualities),
tonal value control in pre-press
and physical properties of
radiation equipment.
Peter Psotta and Walter J. Bolliger
(Siegwerk Backnang GmbH),
Marc Larvor and Olivier Deage
(Siegwerk France S.A.)
Printability | UV coating
Finishing of plastic films
with UV-cured coating systems
in sheetfed offset
Apart from the fact that UV gloss coatings require a certain time to spread before the UV radiation is applied, the curing
mechanisms for UV inks and UV coatings are basically identical. The point calling for attention is the different behaviour
of a plastic substrate compared to paper or board stocks. This contribution from coating supplier ACTEGA Terra describes
some of the special considerations.
UV-coated plastic labels
Chemical curing by way of UV radiation is one of the most innovative
technologies used in the print
industry for the drying of inks and
coatings. With the aid of the UV
technology, it is also possible to
print on a diversity of nonabsorbent substrates. The first
applications in the early 1970s
already exploited the same process
benefits as remain valid today
(Table 1). In the narrow-web sector,
Photo: ACTEGA Terra
UV curing has in the meantime
secured a share of over 90%. UV systems are also gaining in popularity
among packaging printers, where
sheetfed offset is increasingly the
process of choice for printing and
coating.
Intensive research and development
concerning both raw materials on
the one hand, and the inks and coatings on the other, has promoted ever
more widespread use of the technol-
Table 1: Benefits of UV coating
ogy in many areas of the modern
print industry – also for the printing
of plastic films. When compared to
paper and board applications, however, there are various special points
to be taken into account when
applying coatings to plastic films
(Table 2).
Heat sensitivity of the film
UV lamps always release also a certain amount of IR radiation, i.e. heat.
This heat is by all means welcome to
support the curing process, but can
easily lead to curling of the sheets if
too intense. The resultant problems
are reduced register accuracy and
undesirably high pile temperatures.
It is thus important to use only as
much UV radiation as is actually
required to cure the inks and coating
applied. Adaptation of the process
parameters can help to eliminate
unnecessary heat input.
Normally, UV curing takes place
under the influence of the ambient
air. However, as the oxygen molecules in the air also strive to react
with constituents of the ink or coating, this competitive reaction must
be compensated by raising the lamp
power, which naturally also places
unwanted heat loads on the substrate. With the inert UV technology,
a long-established technology in
webfed applications, a solution is also
on hand for sheetfed offset. The
space between the UV lamp and the
substrate is rendered inert by flushing with nitrogen to displace the parasitic oxygen. The competitive reaction with the atmospheric oxygen is
prevented, with the result that the
lamp power can be reduced significantly, and thus less heat is introduced into the substrate. A further
advantage is that the necessary
photoinitiator content of the UV inks
and coatings is lower, as a prerequisite for low-odour UV systems.
Table 2: Special considerations when coating on plastic films
Criterion
Quality
Properties
Consequences
VOC emissions
None (solvent-free)
Shrinking, swelling or curling of the film
Content of solid matter
100%
Heat sensitivity of the film
(thermoplasticity)
Productivity
Immediate further processing
Polymerisation shrinking of the coating
Curling of the film
Gloss
Very high (up to 100 points)
Surface tension of the film
Chemical resistance
High
Bonding of the coating to smooth,
non-absorbent film surfaces
Mechanical resistance
High
Electrostatic charging of the film
Repulsion of the coating, glass plate effect
Cleaning
Simple (does not dry)
Smoothness of the film or coating
Glass plate effect
Process 5 | 2008 21
Printability | UV coating
Table 3: Phases of coating on plastic films
Application phase
The coating is applied to the
plastic film
Spreading phase
The liquid coating spreads to form
an homogeneous surface
Bonding of the coating
to the substrate
Numerous factors determine the
bonding to a plastic substrate. As
this bonding is actually always a
process of mechanical adhesion, surface tension plays an important role.
To achieve good bonding of the ink
or coating, the surface tension of
polyolefin
substrates,
e.g.
polypropylene (PP) and polyethylene
(PE) films, should be at least 38
mN/m, and preferably 40 mN/m. In
most cases, the surface of the film is
already corona-treated by the individual supplier.
It is nevertheless recommended to
check the surface tension before
use, as the positive effects of pretreatment diminish over time and
are lost after at most six months,
and often significantly earlier (for
details of test methods, see the article on surface tension). If the measured surface tension is too low, it
can be raised once more by corona
treatment immediately prior to
printing. Particularly for PP and PE,
this has been shown to be a very
expedient provision. With PVC, PET
and PS substrates, on the other
hand, corona treatment is not usu-
Curing phase and possible results thereafter
Bonding problems
Curling/shrinking
Optimum result
Excessive shrinking within the
coating prevents proper bonding
to the substrate
The bonding is good, but the
coating contracts due to
polymerisation shrinking and
causes the plastic film to curl
A matched coating with the
correct polarity and reduced
polymerisation shrinking provides
for optimum bonding without
curling
ally necessary, but may still prove
useful if adhesion problems are
encountered. KBA offers corona
modules for inline pre-treatment
ahead of the first printing unit.
The heat input is not the only factor
which can lead to curling of the substrate. The same effect is produced
by so-called polymerisation shrinking. The curing of the UV inks and
coatings reduces their volume by 2
to 10%, depending on the quality of
the individual product. This also
causes the surface area of the ink or
coating film to contract, resulting in
curling of the plastic film.
The effect can be reduced or at least
influenced significantly by selecting
a non-shrinking UV coating. It is similarly important to ensure that the
coating application is not unnecessarily thick.
sheets, this leads to problems with
separation at the press feeder and
during downstream further processing. Besides installation of antistatic
systems on the presses and finishing
machines (see the article on antistatic systems by Kersten), correct storage is also able to reduce charging.
To permit proper acclimatisation,
the films should be kept at temperatures between 20 and 22°C and a
relative humidity of 55% for three
days before printing.
Especially in the case of very thin
films, poor separation of the printed
film is almost to be expected. For
this reason, it may be useful to use
a coating with a static eliminator
component to avoid the so-called
“glass plate effect”, where the
mutual attraction of the sheets is
further enhanced by the air being
forced out from between the sheets
and by the very smooth film and
coating surfaces.
Electrostatic charging
and glass plate effect
Coatings for plastic films
in sheetfed offset
All plastic films – irrespective of
whether in web or sheet form – are
in general highly susceptible to electrostatic charging. In the case of
To obtain optimum results, the raw
material formulation of UV coatings
for plastic films differs from that of
UV coatings for paper and board. UV
Curling of the substrate
after printing and coating
Table 4: Formulation differences between UV coatings for paper/board and for plastic films
Component
UV coating for paper/board
UV coating for plastic films
Binder
(high-viscosity pre-polymers)
Epoxyacrylates:
Hard, brittle, high gloss,
average bonding
Modified epoxyacrylates: Flexibilised,
good gloss, improved bonding properties;
Urethane acrylates: Flexible, good bonding
Reactive thinner,
monomers/polyether
(low to medium viscosity)
Di-tetrafunctional, average bonding,
medium to high
polymerisation shrinking
Mono- to trifunctional, good bonding,
low polymerisation shrinking
Photoinitators
Diverse
Diverse; no significant differences
Additives
Flow-control agent, foam inhibitor, stabilisers
Flow-control agent, foam inhibitor, stabilisers,
static eliminator
22 Process 5 | 2008
film coatings thus possess very good
binding properties, and the flexibility of the final coating on the sheet
is enhanced.
In addition to the standard highgloss and matt coating types, various
gold and silver effects, pearlescent
finishes and opaque white grades
are similarly available for use on
plastic film. UV film coatings can
also be tailored to provide individual
functions, such as chemical resistance to the most varied solvents,
acids and alkalis. Special formulations, furthermore, are able to influence the mechanical properties of
the result. High rub resistance and
friction values across the whole
range from antislip to instant release
effect are possible. Further options
are heat-resistant UV coatings for inmould labels or low-odour and lowmigration UV systems for food packaging.
The printing and coating of plastic
substrates
places
particular
demands on all those contributing to
the process: the press manufacturer,
the film, ink and coating suppliers,
and not least the printer at the end
of the chain. It is thus indispensable
for the user to maintain intensive
dialogue with all partners, as only in
this way is it truly feasible to
become a successful player in this
interesting and innovative market
segment.
Mark Fregin (ACTEGA Terra GmbH, Lehrte)
Applications | Examples
KBA users hold the key
to new fields of business
No other manufacturer is able to match KBA’s comprehensive portfolio of press configurations for plastics printing, waterless and UV equipment, and special machines for printing on films, cards and data storage media. KBA users can be sure of
a tailored solution as the key to new fields of business. That also becomes clearly evident from the following cross-section
of recent application examples.
KBA-Metronic: Direct printing on
cards and data storage media
KBA-Metronic AG has already been
highly successful on these two specialist markets for many years. In the
data media segment, the Blu-ray
Disc is set to ensure order continuity when CDs and DVDs approach
the ends of their product life cycles.
KBA-Metronic OC200 for direct printing
on ISO-format plastic cards
The discs can be printed in optimum
waterless offset quality with the
machines CD-Print and Premius.
The latter also handles mini-discs
and digital business cards of deviating sizes and shapes.
The KBA-Metronic OC200 is the
world’s most widely used machine
for direct printing on ISO-format
plastic cards (both with and
without cavities to accommodate a chip). A turning
facility at the end of the
print section permits immediate printing of the card
reverse. Subsequently, it is
possible to personalise the
cards in an inkjet process on
the KBA-Metronic universys,
or to add scratch-off patches
or labels. As an alternative
minimalist solution, the
scratch-off
module
UDA150-S can be combined
with up to two alphaJET C inkjet
printing heads.
KBA Rapida 74 and 74G:
Strong with plastics
The Rapida 74 has built up a significant share of the market for the
printing of plastics. Rudolf Berle, the
owner of berle:druck in KaarstBüttgen, invested in a five-colour
coater press with UV equipment in
2004. He prints above all lenticular
film, the same specialisation as family printers Staffner in St. Johann in
Film and plastics printing package
for KBA sheetfed offset presses
Applications: Non-absorbent surfaces
(glossy coated board, films/composites
with board-like flexural rigidity)
Infeed/feeder*: Antistatic systems, coatings (e.g. chrome), timed guide shaft
with rollers, rollers above front lays,
timed sheet guide with rollers, blower
air support
Printing units/coating units*: Sheet guiding with mechanical board guides and
blower air support, sheet travel sensors,
modified grippers, antistatic systems,
preparations for UV (ink agitators,
rollers, washing systems, UV interdeck
drying, coating supply)
Delivery*: Sheet guide plates with controlled air, switching between suction
and blowing, sheet brake, antistatic
systems, extraction system, extended
delivery with UV final dryers
*) The available features vary according to
press type and format, and are matched
to individual customer requirements.
The waterless Rapida 74 at Roldán Gráficas prints PVC, PETG and PS cards
Personalisation, labelling and scratch-off patches for plastic cards on the KBA-Metronic universys
Standard discs, mini-discs and digital business cards printed on the KBA-Metronic Premius
Process 5 | 2008 23
Applications | Examples
All KBA presses and machines on which films and plastic substrates can be printed (subject to further changes)
Model
Max. format
Possibilities for plastics printing
Inks
Finishing options
Corona option
KBA-Metronic CD-Print
CD, DVD, Blu-ray
Special machine for rigid data storage media
Waterless UV
no
KBA-Metronic Premius
CD, DVD, Blu-ray
Special machine for rigid data storage media
Waterless UV
KBA-Metronic OC100/200
8.6 x 5.4 cm x2
KBA-Metronic universys
8.6 x 5.4 cm
ABS, PC, PET, PS, PVC cards up to 1.2 mm,
Waterless UV
with cavity
Personalisation of ABS, PC, PET, PS,
Inkjet inks
PVC cards up to 0.8 mm
Personalisation of ABS, PC, PET, PS,
Inkjet inks
PVC cards up to 0.8 mm
Approx. 0.1 to 0.8 mm, depending on polymer Waterless UV
Films from 0.05 to 0.6 mm
UV
Option for films up to 1.0 mm
UV, waterless UV
Option for ABS, PC, PET, PS, PVC films
Waterless (Zeller+
up to 1.0 mm
Gmelin Toracard TF)
Option for films up to 1.0 mm
Waterless UV
Option for films up to 1.0 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
Option for films up to 1.2 mm
UV, waterless UV
UV screen-printing or
flexo primer
UV screen-printing primer,
UV coating
UV primer, UV coating
KBA-Metronic UDA150-S “Scratch-off” 8.6 x 5.4 cm
KBA-Metronic Genius 52UV
KBA Performa 74 UV
KBA Rapida 74 UV
KBA Rapida 74G
36 x 52 cm
52 x 74 cm
52 x 74 cm
52 x 74 cm
KBA Rapida 74G UV
NEW: KBA Rapida 75 UV
KBA Rapida 105
NEW: KBA Rapida105 (previously universal)
NEW: KBA Rapida106
KBA Rapida 130
KBA Rapida 130a
KBA Rapida 142
KBA Rapida 162
KBA Rapida 162a
KBA Rapida 185
KBA Rapida 205
52 x 74 cm
52/60.5 x 75 cm
74 x 105 cm
74 x 105 cm
74 x 106 cm
91 x 130 cm
96.5 x 130 cm
102 x 142 cm
112 x 162 cm
120 x 162 cm
130 x 185 cm
151 x 205 cm
Tirol (Austria), whose five-colour
Rapida 74 with coater, extended
delivery, hybrid and UV equipment
and plastics package was started up
at the beginning of 2008.
The first waterless Rapida 74 in
Spain was delivered to Roldán Gráficas, a member of the European
Waterless Printing Association based
in Terrasa near Barcelona, in 2007.
It is equipped with four UV interdeck modules and UV final drying,
and handles above all PVC, PETG
and PS cards.
At Güse Verlag GmbH in Karben
near Frankfurt am Main, the first
Rapida 74G installed in Germany
has been in use since November
2005. The waterless offset press
with its keyless Gravuflow inking
units is configured for alternating
production with oxidatively dried
and UV-cured inks. Specialities of
the company are plastic markers,
labels and tags for plant and gardening suppliers.
Rudolf Berle, berle:druck, with a lenticular sheet from his Rapida 74 UV
24 Process 5 | 2008
Scratch-off hot-foil stamping,
labelling
Scratch-off hot-foil stamping,
labelling
UV coating
UV coating
UV coating
Dispersion coating
(Tippl Tipadur P-1203 B3)
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
UV coating
no
no
no
no
no
no
realised
realised
possible
possible
realised
realised
possible
upon request
upon request
upon request
upon request
upon request
upon request
upon request
At Güse in Karben near Frankfurt, the Rapida 74 G is used to print plastic markers and tags
for gardening suppliers in waterless UV
Markus Staffner prints primarily lenticular substrates on this raised-pile Rapida 74
Applications | Examples
The world’s first inline corona tower for sheetfed offset at Etna in Nantua (France)
The first sheetfed offset press with
an inline corona tower went into
production at Etna in Nantua
(France) in April 2003. The sixcolour Rapida 74 is also able to pretreat films for later printing on other
presses without corona facilities.
KBA Rapida 105:
Also with Inert dryers
A corona tower also belongs to the
configuration of the 15-unit Rapida
105 at Graf-Poz in Poznan (Poland) –
at 30 metres the longest Rapida in
Europe. Already ahead of the seven
printing units, the film surface is
roughened with a corona discharge
and primed with a metallic coating
or opaque white. This primer is then
dried in the two subsequent intermediate dryer towers. At the end of
the press, which is also equipped
with special board-handling features, a double-coating configuration allows for the application of
The first unit of the 30-metre Rapida 105 at Graf-Poz in Poznan (Poland) is a corona tower
One of the two inert UV interdeck dryers on the six-colour Rapida 105 at Crea
Crea Printing Industries recently received an
RTE Award for Innovation in the category
Printing & Packaging for a biodegradable
lenticular presentation box. Further product
examples from the company:
1 Advertising displays with flip-image effect;
2 Floor graphics; 3 PET presentation box for
bottles; 4 Transparent inserts for books and
magazines; 5 School utensils with advertising
designs; 6 PET packaging for underwear;
7 Medical info posters; 8 Table-talkers;
9 Ring folders; 10 Place mats
high-gloss or effect coatings.
The company Serigraph in West
Bend, Illinois, is one of the largest
film printing specialists in the USA.
The screen printing activities which
lent the company its name were
already complemented with offset
capabilities some years ago. Serigraph has owned a six-colour KBA
Rapida 105 UV coater press since
2000.
Crea Printing Industries in Roeselare near Bruges (Belgium) was in
2002 the first user in the world to
install the inert UV technology in
sheetfed offset. Two of the dryer
modules developed by SID Leipzig
in cooperation with Eltosch are provided as interdeck units on the sixcolour KBA Rapida 105 with coater.
Crea is thus able to print also thin
PVC films without curling, because
the heat input can be significantly
reduced.
Process 5 | 2008 25
Applications | Examples
Capital Print, London, uses a Rapida 205 for
large-format plastic advertising materials
KBA Rapida 205:
Plastics in superlarge format
Capital Print, London, installed a
four-colour Rapida 205 with coater,
dryer and the special equipment
packages for board handling and
plastics in 2005. In addition to the
printing of mass articles, the intention is to produce also large-format
advertising materials much more
cost-effectively than in screen printing.
KBA-Metronic Genius 52UV:
Versatility in B3 format
What the big Rapidas can do, that is
also no problem for the small-format
Product examples from Serigraph in West Bend, Illinois (USA): 1 Ceiling hanger printed on both sides; 2 Vacuum-formed company logo as badging;
3 Lenticular film as wrapping band; 4 Shelf wobbler with lenticular effects; 5 Lenticular inlay for DVD packaging; 6 Wall display; 7 Vacuum-formed wall
display; 8 Place-mat for restaurant chain with “Micromotion” effect (Serigraph technology producing a flash effect as the viewing angle changes);
9 Micromotion adhesive label for a film packaging; 10 Floor graphics; 11+15 Vacuum-formed retail displays; 13 Treadmill control panel;
14 In-mould labels on golf clubs; 16 Vacuum-formed elements for a plastic shelf display
waterless UV press Genius 52UV.
The most prominent user is the
Swedish Inplastor Group, where
bank cards are printed and laminated under strict security precautions. The press installed in
Strängnäs possesses a separate
coater and an extended delivery.
Mercurius in Zaanstad prints films in four and five colours on the Genius 52UV
26 Process 5 | 2008
Ultimate quality is also the image of
Kunstdrukkerij Mercurius in
Zaanstad (Netherlands), who
received a five-colour Genius 52UV
at the end of 2006. The press is used
primarily for printing on plastics.
The fifth unit is required for coatings and varnishes. A separate UV
coater with UV dryer and extended
delivery is also available.
The KBA-Metronic Genius 52UV at Inplastor is used to print bank cards
Applications | Lenticular images
Special effects for
future-oriented niche markets
Flip images and mini-movies, 3D, zoom and morphing effects – these extremely attractive eye-catchers are still far from
commonplace. This profitable application for plastics printers is based on the use of lenticular film. But precise and
reliable press technology is equally imperative. One of the presses of the KBA product range which offers the necessary
prerequisites is the KBA-Metronic Genius 52UV.
Figure 1
The lenticular sheet comprises an
array of parallel cylindrical lens and is printed
on the reverse (here underneath)
Many of us remember them from
our childhood days: Images of figures which appeared to wave a
hand or blink an eye. It was usually
just a simple image change (flip)
which suggested the motion or
action. In the past few years, however, the technology of lenticular
printing has been revolutionised.
The amazing multi-stage images can
in the meantime comprise up to 16
phases. They trick the human eye
perfectly and convey the impression of a film sequence or diorama.
There are three factors which have
made the recent progress possible
and which are decisive for the quality of modern lenticular printing:
• The finely structured lens sheet
• Exact preparation of the digital
image data with the aid of special
software
Flip images printed
on a Genius 52UV
in sheet format 36 x 52 cm
• A printing press capable of delivering a brilliant, highly precise image
with perfect registration.
How lenticular printing functions
The lenticular technology makes use
of the laws of optics. “Lenticula” is
of Latin origin and means “small
lens”. A lenticular sheet comprises a
multitude of very fine cylindrical
lens arranged side by side across the
sheet (Figure 1) and formed such
that their focal plane lies exactly at
the rear surface of the film. Typical
lenticular films possess between 40
and 130 lens lines per inch (15 to 50
lines per centimetre).
In simplified terms, the light beams
emanating from any particular point
on the focal plane are refracted by
the shape of the lens and formed
into a more or less parallel bundle.
Consequently, the observer sees
only one small section of the image
behind the lens – for example, as
shown schematically in Figure 2,
only the blue stripes and thus
overall only the blue image portion. If the observer changes his
viewing angle, however, the blue
image disappears and is replaced by
the green image, and so on.
This effect can be exploited to place
several different images or image
versions behind the individual
lenses. To achieve an image
sequence with four separate elements (Figure 3, line A), for
instance, each element must be
divided into stripes with exactly the
same width as a single lens (Figure
3, line B). It is here important that
each original image is divided into as
many stripes as there are lenses in
the array. This newly composed
“striped” image is naturally four
times wider than the actual sheet
format. Consequently, it must be
compressed to a quarter of its width,
so that the each set of stripes fits
exactly under one and the same lens
(Figure 3, line C). All in all, this is a
highly complex process, whose
implementation has only become
properly feasible with modern software, and furthermore demands the
trained eye of an experienced
printer.
A case for the Genius 52UV
With the Genius 52UV, KBAMetronic supplies a flexible and efficient press to handle the special
demands of printing on innovative
substrates such as lenticular film.
Holger Volpert, director of KBAMetronic AG, sees the press as a
high-performance tool for niche
markets with high development
potential:
“The Genius 52UV is ideally
matched to the demand profile of
print companies wanting to handle
creative short to medium-run work
in brilliant quality and at favourable
cost. Its efficiency and particular
reliability also guarantee unrivalled
competitiveness for niche applications such as lenticular film.”
Once the final lenticular image has
been calculated, it is printed onto
the reverse of the transparent film.
Holger Volpert, formerly sales director for print technology, understands the user's concerns in every-
Figure 2
Behind each cylindrical lens of width m, n image stripes are printed at the focal
plane (sheet reverse). The example here is a lenticular image comprising n = 4 phases or elements.
Depending on the viewing angle, the observer sees only the light beams depicting one of the
image stripe sets 1 (here red), 2 (blue), 3 (green) or 4 (yellow) – demonstrated above for a switch
between the blue and green phases
Process 5 | 2008 27
Applications | Lenticular images
footprint of just 12 m2, promises costeffective waterless offset printing
with UV-cured inks, for outstanding
print quality on the most varied nonabsorbent substrates in thicknesses
from 0.1 to 0.8 mm.
Attractive new markets
Figure 3
For an image sequence with four elements (line A; here, as in Figure 2, coloured
red, blue, green and yellow to aid understanding), each element is divided into stripes which
are exactly the width of a single lens (line B). There must be exactly the same number of
stripes as there are lenses in the array. As our sequence comprises four elements, the combined image is now four times the width of the lens array. Consequently, the overall image
must be compressed to a quarter of its original width (line C), so that one stripe of each image
element fits under each lens.
All figures © KBA-Metronic AG/Peter Schmitt
day practice: “For lenticular printing, absolute precision is decisive.
As there are no ink keys in the inking units of the Genius 52UV, the
inking is consistently stable. On top
of that, the register system guaran-
tees exact automatic plate mounting. As a result, the start-up waste
is minimal. And that is an important
argument when using expensive
materials such as lenticular film.”
As runs are often particularly short
in the small-format sector, low consumption and fast makeready are
imperative. On the Genius 52UV, a
single operator can complete a job
changeover in only seven minutes.
The compact Genius 52UV, with a
Lenticular printing lends images
depth and motion. In this way, printed
products using lenticular film achieve
something which is becoming ever
more valuable nowadays: They grab
the attention. Whether for advertising, fairs or merchandising – the list of
possible applications is sheer endless.
Lenticular images are particularly
effective for labels, displays,
brochures, packaging, decoration and
many other products, drawing positive reactions from the most varied
target groups with their eye-catching
special effects. But such dynamic
images are more than just vehicles for
decorative impressions – it is also possible to fit multiple information, function descriptions, detail views, etc.
into a lenticular image.
Holger Volpert is convinced: “Technology made in Germany has enjoyed an
excellent standing over many
decades, but this position must now
be consolidated in a globalised market. This will only be successful if we
remain permanently and closely in
touch with the demands of the market, and if we employ our innovative
strengths to develop sustainable
potential – ideas and visionary strategies are what we need. With the
Genius 52UV, we open up a broad
spectrum of opportunities and further
strengthen the reputation of KBAMetronic as a strong and committed
partner to the print industry.”
Birgit Grosse, Dipl.-Phys. Peter Schmidt
(Innovations & Patents Dept.,
KBA-Metronic AG, Veitshöchheim)
With its waterless and keyless offset process, the Genius 52UV from KBA-Metronic sets new standards in respect of quality and cost-effectiveness
for the printing of flexible and rigid films (e.g. PVC, PET, ABS) in substrate-dependent thicknesses between 0.1 and 0.8 mm
28 Process 5 | 2008
Glossary
The most important plastics
at a glance
In the plastics industry, the long names of the individual chemical compounds have thankfully been reduced to manageable proportions in the form of internationally standard abbreviations. This glossary provides an overview of the abbreviations and common names for the most important polymers, including all those compounds mentioned in the articles of
this brochure.
ABS:
Acrylonitrile-butadiene
styrene; films suitable for printing
with UV-cured and waterless offset
inks
Acrylic glass: see PMMA
APET, A-PET, PET-A: Amorphous
PET; for highly transparent, highly
glossy printable PET films and thin
plastic card laminations
BOPET: Biaxially oriented APET
film (i.e. stretched in both lengthwise and crosswise directions), e.g.
DuPont Mylar
BOPP: Biaxially oriented polypropylene film
CA: Cellulose acetate; highly transparent, highly glossy and highly rigid
natural polymer
CAP: Cellulose acetopropionate
COC: Cyclic olefin copolymer,
Topas
Coextruded film: Film composite
produced by extruding melts of two
identical or different polymers
Composites: Print substrates and
packing materials in which several
identical or different material layers
are bonded or welded together.
CPET, C-PET: Semi-crystalline PET
CPO: Cyclic polyolefins
Extruder
EVOH, EVAL: Ethylene vinyl alcohol
Extrusion: Manufacturing process
in which a plastic film is produced by
forcing one or more polymer melts
through nozzles (dies)
GAG-PET: Coextruded PET composite (PETG–APET–PETG); for blister and deep-drawn packaging components
GPPS: General-purpose polystyrene
HDPE: High-density polyethylene
HIPS, PS-I: High-impact polystyrene
HTR, PHEMA: Hard tissue replacement, polyhydroxylethylmethacrylate; extremely tear- and UV-resistant films for flexo and offset printing; good deep-drawing and
lamination properties
IML: In-mould label; usually oriented multilayer PP films, integrated
into the surface of a plastic package
as pre-printed labels during the
moulding process
LDPE: Low-density polyethylene
Lenticular film: Plastic film comprising a fine array of parallel, cylindrical lenses
LLDPE: Isotactically linear LDPE
Monofilm: Plastic film produced
from a single polymer; compare:
Coextruded film.
Mylar: Trademark of DuPont; synonym for oriented PET films
OLED: Organic light-emitting
diode; printable, electrically conducting polymer which emits light
when a voltage is applied
OPET-A: Oriented (i.e. stretched)
PET-A film; high transparency, high
glossiness, high rigidity
OPP: Oriented (i.e. stretched)
polypropylene
OPV: Organic photovoltaic; photocell comprising a printable, electrically conducting polymer
OPVC-P: Oriented (i.e. stretched)
plasticised PVC film
PA: Polyamide; condensation polymer with low transparency, but good
glossiness and rigidity; thermoplastic whose rigid variant is also
processed into films for offset printing; often found in composites with
PE for food bags; as PA 6.6 fibres for
synthetic papers
PAN: Polyacrylonitrile; highly transparent, highly glossy and highly rigid
polymer
PBN: Polybutylene naphthalate
PBT: Polybutylene terephthalate;
polyester for heat- and wear-resistant injection-moulded parts, sheathings and nano-fillers
PC: Polycarbonate; the most expensive polyester; highly transparent,
highly glossy and highly rigid condensation polymer used for CDs,
DVDs, Blu-ray Discs and transparent
device housings
PE: Polyethylene, polythene; polyolefin polymer with average to good
transparency, wax-like, low gloss,
average rigidity
PEDOT:PSS: Copolymer of polyethylene dioxythiophene and polystyrene sulfonate; printable, electrically conducting copolymer
PEEK: Polyetheretherketone
PEN: Polyethylene naphthalate;
condensation polymer with good
transparency and high glossiness
and rigidity; replacement for PET in
many applications
PET, PETB: Polyethylene terephthalate; most important polyester material; highly crease-resistant condensation polymer
PET-A: APET, amorphous PET
PETB: PET
PETG, PET-G: Glycol-modified PET;
rigid film with good transparency as
base carrier for lenticular films and
shrink-sleeve labels
PETIP: Coextrusion of APET with a
PET modified with isophthalic acid;
for sealable films in metallised composites
PHEMA:
Polyhydroxylethylmethacrylate; see HTR
PK: Polyketone
PLA: Polylactic acid; degradable
“bio-polyester” produced from
renewable raw materials; can also
be printed in offset as a rigid film
with high gloss and high strength
Plastic: Trivial designation for synthetic and semi-synthetic polymers;
distinction is made between thermoplastics (can be formed when
heated, e.g. PVC, PP), thermoset
plastics (cannot be re-formed, e.g.
PUR, hardened epoxides) and elastomers (all cold-formed rubbers);
generally speaking, only films produced from thermoplastics are suitable for printing; also processed into
blow-moulded packing materials.
Plastic films: Polymer webs produced by way of injection moulding
or extrusion, processed into substrates and composites with thicknesses between 20 and 150 μm
(typically 50 to 100 μm) and sold in
sheet or reel form; available in cleartransparent to opaque white and
coloured grades, with glossy, semimatt and matt surfaces, or alternatively structured with patterns or as
lenticular film; effectively any plastic
film can be printed using UV-cured
inks; conventional and waterless
inks can also be used in sheetfed
offset, or solvent- and water-based
inks in flexo and gravure applications; processed for use as folding
boxes, flexible packaging, cards and
advertising materials
Plexiglas: PMMA
PMMA: Polymethyl methacrylate,
Process 5 | 2008 29
Glossary | Resources and partners
polymethacrylate; known as Plexiglas or acrylic glass, usually only
processed in screen printing
Polyester: Ethyl acetate; polymers
with the ester functional group, e.g.
PET, PEN, PC
Polymer: Organic macromolecule
on the basis of simple hydrocarbon
molecules (monomers), whose high
strength and other properties are
determined by the chaining, branching or cross-linking of these
monomers; homopolymers (comprising a single monomer type): PE,
PP, PVC; copolymers (comprising different monomers): ABS
POM: Polyoxymethylene, polyacetal
resin, polyformaldehyde
PP: Polypropylene, polypropene;
average to good transparency, glossy,
wax-like, rigid
PS: Polystyrene; clear-transparent,
rigid; can be foamed (then no longer
suitable for printing)
Resources and partners
At this point we would like to thank all cooperation partners whose products, solutions and
equipment enable our customers to print on plastic substrates on KBA sheetfed offset
presses.
Advice, certification
Berufsgenossenschaft Druck und Papierverarbeitung, Wiesbaden (www.bgdp.de)
Druck & Beratung D. Braun, Mülheim/Ruhr (www.wluv.de)
fogra Forschungsgesellschaft Druck e.V., Munich (www.fogra.org)
PSU: Polysulphone
PTT: Polytrimethylene naphthalate
PUR: Polyurethane; basis for
moulded parts and adhesives
PVC: Polyvinyl chloride; average to
good transparency, rigid
PVC-P: Plasticised PVC
PVC-U: Unplasticised PVC
PVDC: Polyvinylidene chloride, a
polyolefin polymer
PVOH: Polyvinyl alcohol; antistatic,
weldable, water-soluble, bio-degrad-
able, high-strength barrier film
Tacticity: Preferred alignment of
polymer molecules; isotactic polymers (i.e. polymers with identically
aligned molecules, e.g. PP) are particularly easy to stretch
TPE: Thermoplastic elastomers
Dieter Kleeberg
Dryer systems
Adphos Vertriebs GmbH, Hamburg (www.adphos.de, www.eltosch.de)
Grafix GmbH Zerstäubungstechnik, Stuttgart (www.grafix-online.de)
Heraeus Noblelight GmbH, Hanau (www.heraeus-noblelight.com)
Kühnast Strahlungstechnik GmbH, Wächtersbach (www.uv-technology.de)
Dr. Hönle AG UV Technology, Gräfelfing (www.hoenle.de)
IST Metz GmbH, Nürtingen (www.ist-uv.com)
RadTech Europe, Den Haag/Netherlands (www.radtech-europe.com)
Sächsisches Institut für die Druckindustrie (SID), Leipzig (www.sidleipzig.de)
Inks, coatings, additives and cleaning solvents
ACTEGA Terra Lacke GmbH, Lehrte (www.actega.com/terra/)
DS Druckerei Service, Reutlingen (www.dsgroup.de, www.fujihunt.com)
Eckart GmbH & Co. KG, Fürth (www.eckart.de)
Epple Druckfarben AG, Neusäß (www.epple-druckfarben.de)
Flint Group Germany GmbH, Stuttgart; Day International GmbH/Varn Products GmbH,
Reutlingen (www.flintgrp.com, www.dayintl.com)
Huber Group, Munich; Hostmann-Steinberg GmbH, Celle (www.mhm.de,
www.hostmann-steinberg.de)
Jänecke+Schneemann Druckfarben GmbH, Hannover (www.js-druckfarben.de)
Merck KGaA, Darmstadt (www.merck-pigments.com)
SunChemical Hartmann Druckfarben GmbH, Frankfurt am Main (www.sunchemical.com)
Schmid Rhyner AG Print Finishing, Adliswil/Switzerland (www.schmid-rhyner.ch)
Siegwerk Group, Siegburg, Backnang, Annemasse/France (www.siegwerk-group.com,
www.sicpa.com)
Dipl.Ing. Werner Tippl, Vienna/Austria (tippl@xpoint.at)
VEGRA GmbH, Aschau am Inn (www.vegra.de)
Weilburger Graphics GmbH, Gerhardshofen (www.weilburger-graphics.de)
Zeller+Gmelin GmbH & Co. KG, Eislingen (www.zeller-gmelin.de)
30 Process 5 | 2008
Corona and antistatic systems
Ahlbrandt System GmbH, Lauterbach/Hessen (www.ahlbrandt.de)
KERSTEN Elektrostatik GmbH, Freiburg im Breisgau (www.kersten.de)
Plastic films, metal foils, lenticular sheets
DPLenticular Ltd, Dublin (www.dplenticular.com, www.lenticular-folien.com)
Folienwerk Wolfen GmbH, Wolfen-Thalheim (www.folienwerk-wolfen.de)
Klöckner Pentaplast GmbH & Co. KG, Montabaur (www.kpfilms.com)
Leonhard Kurz Stiftung & CO. KG, Fürth (www.kurz.de)
Papier Union GmbH, Hamburg (www.papierunion.de)
Priplak SAS, Neuilly-en-Thelle/France (www.priplak.com, www.arjowiggins.com)
Schneidersöhne Unternehmensgruppe, Ettlingen (www.schneidersoehne.de)
Treofan Germany GmbH & Co KG, Neunkirchen, Raunheim (www.treofan.com)
3D software
Digi-Art Neue Visuelle Medien Elmar Spreer, Apen (www.lenticularsoftware.de)
HumanEyes Technologies Ltd, The Hebrew University, Jerusalem (www.humaneyes.com,
www.dispro.at)
KBA Process 5
Koenig & Bauer AG
Würzburg Facility
Friedrich-Koenig-Str. 4
97080 Würzburg
Germany
Tel.: +49 931 909-0
Fax: +49 931 909-4101
Web: www.kba.com
E-mail: kba-wuerzburg@kba.com
Koenig & Bauer AG
Radebeul Facility
Friedrich-List-Str. 47
01445 Radebeul
Germany
Tel.: +49 351 833-0
Fax: +49 351 833-1001
Web: www.kba.com
E-mail: kba-radebeul@kba.com
KBA-Metronic AG
Benzstr. 11
97209 Veitshöchheim
Germany
Tel.: +49 931 9085-0
Fax: +49 931 9085-100
Web: www.kba-metronic.com
E-mail: info@kba-metronic.com
If you wish to receive our free
customer magazine “KBA-Report”,
but are not yet a subscriber, please
contact Anja Enders in our marketing department:
E-mail: anja.enders@kba.com
Tel.: +49 931 909-4518
Fax: +49 931 909-6015
KBA Process
is a technically oriented publication created to facilitate strategic investment
planning by providing detailed, practical information on the current status
and future prospects of new technologies and advances.
Publications to date:
KBA Process No. 1 “Focus: Direct Offset Printing on Corrugated Board”
(2002)
KBA Process No. 2 “Waterless and Keyless” (2005)
KBA Process No. 3 “Quality Enhancement with Hybrid Production”
(2006)
KBA Process No. 4 “Inline Coating” (2007)
Publisher:
Koenig & Bauer Group (www.kba.com)
Editors:
Jürgen Veil
Klaus Schmidt
Dieter Kleeberg
KBA, head of sheetfed offset marketing, responsible
for the content, juergen.veil@kba.com
KBA, marketing director, klaus.schmidt@kba.com
Trade journalist/PR service provider to the print
industry, dieter.kleeberg@t-online.de
Authors and contributors:
Walter J.Bolliger
Siegwerk Backnang GmbH, Backnang
Martin Dähnhardt KBA Radebeul
Olivier Deage
Siegwerk France S.A., Annemasse
Klaus Fischer
Papier Union GmbH, Hamburg
Mark Fregin
ACTEGA Terra GmbH, Lehrte
Beatrix Genest
SID Sächsisches Institut für die Druckindustrie
GmbH, Leipzig
Anne-Kathrin Gerlach KBA Radebeul
Birgit Grosse
KBA-Metronic AG, Veitshöchheim
Dieter Kleeberg
Dipl.-Ing. D. Kleeberg, Nidderau
Izabella Kwiatkowska European Media Group, Poznan
Matthias Lange
KBA Radebeul
Marc Lavor
Siegwerk France S.A., Annemasse
Cornelia Lillelund
Freelance journalist (for Papier Union)
Peter Psotta
Siegwerk Backnang GmbH, Backnang
Peter Schmidt
KBA-Metronic AG, Veitshöchheim
Wilfrid Tews
Treofan GmbH, Neunkirchen and Raunheim
Jürgen Veil
KBA Radebeul
Frank Waßmann
Klöckner Pentaplast GmbH, Montabaur
Wolfgang Zierhut
KERSTEN Elektrostatik GmbH, Freiburg im Breisgau
Layout:
Katrin Jeroch
KBA Radebeul
Product specifications and features may be changed without prior notice.
No part of this publication may be reproduced in any way without the publisher’s permission and without source data. Although registered trademarks
and copyrighted or patented products are not specified as such, this does
not mean that they are or may be treated as public domain.
Printed in the Federal Republic of Germany
Process 5 | 2008 31
KBA Sheetfed Offset
KBA Rapida 106
Your innovative makeready champion
KBA.P.616.e
Ever since Drupa 2004 our high-tech Rapida 105 has been defining the
benchmarks for medium-format offset in terms of automation, performance,
flexibility and innovation. At Drupa 2008 our new Rapida 106 took makeready efficiency, quality management, ease of operation, waste reduction
and cost-effective printing one step further. The new-generation Rapida
106: all you'll ever need, all you've ever wanted, and all in one press. Come
and see for yourself.
Koenig & Bauer AG, Sheetfed Offset Presses, Radebeul
phone: +49 351 833-0, kba-radebeul@kba.com, www.kba.com