What’s coming in industrial inkjet for display graphics?
Digital technologies have made possible the production of
low-volume print jobs at prices that screenprinting could not
approach. Chris Lynn, VP sales & marketing, Xaar Americas,
discusses the use of digital printing in the display graphics industry.
The wide-format graphics
industry has been
transformed through the
emergence over the past dozen
years of digital inkjet printing
technology. Digital technologies
have made possible the production
of low-volume print jobs at prices
that screenprinting could not
approach – but this has not so much
eaten into the screen market as
taken away its growth, according to
researchers at Web Consulting.
Screenprinting still rules where high
volumes or quality requirements
allow the cost of pre-press to be
recovered in the total price. Digital
printing for outdoor graphics has
moved from aqueous to solventbased
inks, from paper to vinyl, and
from 100dpi to 360dpi or more.
But the market is now starting to
look almost mature, and new points
of differentiation are being found:
UV inks for better durability
without lamination, flatbed printers
for direct printing onto rigid
materials, and 6-colour ink sets. I
am referring to the use of additional
colours like violet, orange and
green, that actually make for a more
colour-accurate reproduction.
As this illustration shows, the
spectrum of colours that can be
reproduced with a six-colour ink
set is significantly broader than with
conventional CMYK alone, resulting
in punchier graphics.
At up to six times the price of
solvent inks, the cost of UV inkjet
inks has been much-criticized, and
they are certainly expensive on a
per-litre basis. But there are a lot
of positives to UV-cured inks: the
fact that the ink sits on the surface
of the substrate instead of being
absorbed means that less ink is used
to achieve full coverage; the
potential to avoid the entire process
of lamination to ensure durability
helps to provide a cost advantage;
the fact that – unlike solvent inks -
UV inks cannot cure in the
printhead, improving printhead life
and reducing the need for
maintenance; and the avoidance of
VOC-handling, with its attendant
OSHA- and EPA-compliance
requirements. Taken together,
these benefits lead many printers
to conclude that the use of UV
makes a lot of sense.
Another development that drive
quality expectations to yet higher
levels: the use of grayscale
printheads. ‘Grayscale’ refers to
the ability of an inkjet printhead to
deliver drops of ink of varying sizes.
Conventional inkjet printheads are
‘binary’ – they either eject a drop
of ink or they do not – and the drop
size is typically between 20 and 80
picolitres.
Grayscale heads eject even smaller
drops – typically in the range of 3-8
picolitres – but they do so in groups
at a much faster rate. A group of
small drops join together to make
a larger single drop by the time it
lands on the substrate, a millimeter
or so from the nozzle. The volume
of the resulting larger drop is a
multiple of the volume of each of
the smaller drops, up to the number
of ‘gray levels’ supported by the
printhead. e.g. 8, 16, 24, 32, or 40
picolitres for a 6-level head with an
8 picolitre sub-drop volume (zero
counts as one level).
What’s the point of this? Image
quality. By varying the size of the
dots made on the substrate,
grayscale heads simulate a much
higher resolution than their
physical nozzle spacing and firing
frequency allow. The apparent
resolution is roughly equal to the
real resolution multiplied by the
square root of the number of gray
levels. For example, Xaar’s
OmniDot 760GS8 printhead
has a native resolution of 360dpi,
and is capable of printing variable
drops from 8 to 40 picolitres in
size i.e. 6 gray levels. So the
apparent resolution of the head
is 360 x 6 = 882dpi. This is
approaching the quality of a
photographic print made on your
desktop photo-printer – and
exceeds the 720 x 720dpi
mode on a typical wide-format
printer such as Epson’s SP9800 –
while providing the ability to
print several hundred square feet
per hour.
Do you need photo-quality on a
billboard? Clearly not, if the viewing
distance is too great to tell the
difference from conventional 100-
200dpi prints. But with a wideformat
or grand-format machine
that prints grayscale, you can offer
clients the ability to print the same
quality of image for all their display
graphics – and do it without needing
to buy separate machines for
smaller format, photo-quality work
and for wider format, highproductivity
use. Alternatively, you
can simply use the extra resolution
to buy productivity: scale back the
resolution in the print direction
to 180dpi, knowing that the
variable dot size will make it
look like 440dpi, and print at twice
the speed.
Who makes grayscale printheads
for solvent and UV inks and where
are they used? Xaar has its
OmniDot range, and has licensed
its technology to Toshiba TEC,
which offers two 8-level grayscale
models, and to Konica-Minolta
which has two 4-level grayscale
models. Spectra too has discussed
a grayscale head, though this has
not yet appeared in the product
line-up. Because the technology is
relatively new, few printer
manufacturers have gone public
with machines based on grayscale
to date. Agfa announced the
introduction of its UPH-head
Annapurna 100, a 100 inch UV rollto-
roll/flatbed machine capable of
printing up to 1,000 sqft/hour. The
UPH head is Agfa’s version of
Xaar’s OmniDot 760, with up to
16 gray levels. The same heads –
64 of them – feature in Agfa’s MPress,
a digital press that integrates
with Thieme’s 5000XL series
screenprinting modules to form a
hybrid press.
The use of digital printing in the
display graphics industry is well
enough established to encourage
talk of market maturity, but the
rate of innovation in the field
has not diminished. Continued
developments in inks and
substrates, print quality, and
machine productivity and reliability
will drive digital printing deeper
into analog territory.
(For more info, contact: Neeraj
Thappa, field applications engineer,
Xaar India, B&B1, Enkay Towers,
Udyog Vihar – V, Gurgaon – 122016,
Ph: 0124 4109227, 0124 4109223,
fax: 0124 4109225, mobile:
9810249227.)
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