Sign Africa Journal November / December 2018 | Page 36

FEATURE
PULP
FACT,
NOT FICTION
BY JOHN CORRALL, MANAGING DIRECTOR OF INDUSTRIAL INKJET
The world of packaging is changing. The hedonistic
throw away culture of years gone by, where plastic
was king, is already a fading memory. The future sees
a rejection of the practices that poison our oceans and
contaminate our land for generations, instead favouring
the recyclable and the sustainable.
Leading the way in this revolution is pulp. This product is made from recycled
cellulose, sugar cane or even grass. It has a multitude of potential uses, from
internal packaging for electronics to egg boxes, disposable plates to fruit
punnets, it can be used for salad boxes or even detergent packs. It can be light
but strong and can even be made grease-proof.
The next question is how to decorate these new packages. Nothing looks more
drab on a shelf than endless grey or brown packages, so they need to look
brightly-coloured and appealing. However, any decoration has to de-ink easily
for recycling. For long production runs, flexo is currently used, but for short runs
or runs with a lot of variation (for example different types of fruit in the same
size punnet) this can mean that more pulp cartons are used for setup than in
production (hardly a green solution). Using labels is then the logical alternative,
but these can cost more than the pulp carton itself, potentially ruining the
commercial viability. So what if an alternative was possible?
Print direct to the pulp carton using economic and safe water-based inks in vivid
colours? Surely that would be the perfect solution? And in order to achieve this
goal, what are the technical challenges to be overcome?
The Right Ink
As with most inkjet projects, the printing hardware has to be right, but the ink is
the key. Without the right ink, no project will ever succeed. In the case of pulp
packaging, the demands on the ink are widespread:
Bright colours: it’s obvious that bright or strong colours will be needed – but
they need to remain bright on what is often a very absorbent material. The
water content of the ink may be absorbed quickly, but the pigment needs to stay
on or near the pulp surface. Also the carton material itself may be an off-white
colour or may be pre-coloured (grass-based pulp packaging is – not surprisingly
– green in colour).
Regulatory Requirements: if the carton will be used to hold food then the
relevant regulation is EC1935/2004. For the printing ink most customers expect
compliance with Swiss Ordinance SR 817.023.21. This regulation defines the
materials that may be used in a printing ink for ‘non-direct food contact’. There
are tests to check what will migrate out of the ink and into any food contained.
We need to worry not just about ink that penetrates through the carton wall
36
Inkjet-decorated pulp cartons (lid top and sides).
from the outside to the inside, but also any cross-contamination between the
ink on the outside of a carton and the inside of the carton below it when they
are stacked together.
Cost: as ever, the economics will make or break the project. Inkjet ink is always
going to be more expensive per-litre than flexo ink but this is compensated
for by the lack of setup time (and therefore setup cost) and the lack of waste
during setup. The economics will obviously change a lot depending on the
extent of the decoration required. For example, the cost of printing a small
picture of a strawberry or a plum, plus some text and a barcode, might be only
10% of the cost of decorating the entire top and sides of the carton.
Pulp Media Type: ‘Normal’ water-based inks usually work well on regular pulp
cartons. The problem comes with grease-proof cartons that have had the
pulp material treated with a hydrophobic coating. The ink simply sits on the
surface of the carton and can easily be ‘smudged’ with a finger. With this kind
of material, we can use a pre-treatment such as a primer to help fix the ink. Or
we can use an alternative ink such as a water-based polymeric ink that will ‘fix’
to the pulp surface when heated. In either case, there is an additional cost to be
considered.
Inkjet System
As with any inkjet hardware to be used in-line in a production environment,
the system will need to be very reliable. After that there are several aspects to
decorating pulp cartons that are a little unusual:
Orientation: high-quality colour inkjet print in an industrial environment usually
uses piezo drop-on-demand technology. These inkjet print heads have open
nozzle holes and the ink is prevented from falling out by careful application
of a small vacuum to the ink supply system. This works fine when printing
downwards (for example onto the carton lid) because all of the nozzles in the
inkjet print head are at the same height and see the same pressure.
However, when printing cartons such as fruit punnets, we need to print both
sides of the punnet at more or less the same time. The inkjet print heads are
ISSUE 98 NOV/DEC 2018 | www.SignAfrica.com