New technologies
of the inkjet textile printing system
Nassenger-V
Mitsuhashi, Taku*
Takeuchi, Hiroshi* Fujii, Yozo*
Table 1
Characteristics of Nassenger-V
Ink Disperse dye
ink, Reactive dye ink
Mode Resolution
Disperse dye
ink
Reactive dye
ink
Printing speed
High speed 540dpi
x 360dpi 60 m2/h 48 m2/h
Normal 540dpi x
540dpi 40 m2/h 32 m2/h
High quality
540dpi x 720dpi 30 m2/h 24 m2/h
Maximum density
900dpi x 540dpi 27 m2/h 21 m2/h
Maximum printing
width 1650 mm
Fabric size
width: 330 mm to 1650 mm, thickness: 15 mm
Operating
conditions temperature: 15°C to 30°C, humidity: 40% to 70%
Dimensions,
weight W4200 mm x D1600 mm x H1545 mm, 440kg
Abstract
A new inkjet
textile printing system, Nassenger-V,
was developed.
Reliability, productivity, and print
quality were
highly improved in order to meet the
requirements as
an actual production machine. A
newly designed
inkjet print head, an ink drop
detection system,
and a fabric belt feed system
developed
specifically for this printer are discussed.
1. Introduction
The inkjet
textile printing technology has been
rapidly getting
accepted in the past few years.
The history of
applying inkjet to textile printing is
rather long, as
an alternative convenient method to
conventional
printing technology. It was expected to
be suitable for
quick delivery, short-run production
and photographic
print with multi-level tone
reproduction,
which is difficult to achieve with
existing analog
technology. Some advanced users
have already used
inkjet for years to manufacture a
wide variety of
products, mainly for short-run
production or
sample-making. Recently, however,
improved
reliability of inkjet printers, along with the
introduction of
digital technology in design process
has made this
technology a realistic option to be
utilized for
mass-production. Market expectation for
more productive
inkjet textile printer has also
contributed to
this new trend.
With the aim of
meeting performance requirements
as a production
machine, we have developed the
Fig. 1
Nassenger-V
inkjet textile
printing system, Nassenger-V, reliability,
productivity and
quality of which are remarkably
improved (Fig.
1).
The basic
performance parameters of Nassenger-V
are summarized in
Table 1. In order to achieve
these
specifications, technologies such as, (1) a
newly designed
print head customized for this
printer, (2) a
fabric belt feed system and (3) an ink
drop detection
system to detect miss-firing of
droplet have been
introduced. These newly applied
technologies are
explained in the following sections.
2. Newly
developed inkjet head
Image quality
requirements for inkjet textile printing
systems include
graininess, sharpness, tone
reproduction,
wide color gamut and high solid
density. We have
reported that a resolution of 540
dpi is sufficient
for obtaining practically acceptable
Konica Minolta
Technology Center Inc.
Inkjet Technology
R&D Center
image qualities
in inkjet textile printing systems.*1
In Nassenger-V,
the standard mode was decided to
be 540 dpi
accordingly. In order for this mode to
achieve printing
speed of 40m2/h, two 256 nozzles
heads were
combined for each of 8 different color
inks, totaling 16
heads. Table 2 shows a summary
of
characteristics of the print head used for this
printer.
Table 2.
Characteristics of the inkjet
print head
Technology shear
mode piezo,
drop on-demand
Number of nozzles
256 (128×2 lines)
Nozzle density
180 dpi (90 dpi×2lines)
Operating
frequency
18.2 kHz
(disperse dye ink)
14.9 kHz
(reactive dye ink)
Drop weight 18 ng
(disperse dye ink)
20 ng (reactive
dye ink)
Dimensions W59.5
x D18.3 x H67mm
Weight 50g
Though the ejection
principle of this head is the
same shear mode
piezo drop on-demand as the
previous model of
Nassenger II, newly developed
high-precision
process technology and actuator
lamination
technology have made it possible to
provide180 dpi,
256 nozzle print head comprising
two 90 dpi, 128
nozzle actuators.
Ejection
frequency was determined from print
speed, print
resolution, number of nozzles, and
structurally
caused non-printing time.
The volume of
ejected ink droplet was
experimentally determined
to optimize image quality
and performance.
More specifically, the droplet
volume has to be
determined according to the print
resolution. If
the volume is larger than the optimum
amount, not only
are graininess and sharpness
deteriorated but
also is image quality degraded due
to blur. On the
other hand, if it is smaller, it becomes
difficult to
obtain required color gamut and/or solid
density. In the
worse case, white lines appear
where sufficient
ink amount was not delivered,
resulting in
considerable deterioration of image
quality. In 540
dpi print mode, the optimum ink
droplet volume of
disperse ink for polyester was 18
ng, while that of
reactive ink for cotton and silk was
20 ng.
The structure of
a head that meets above
performance
specifications was designed by highly
advanced computer
simulation. Basic head
performance can
be calculated from dimensions of
channel, actuator
and nozzle shape, physical
characteristics
of piezo element, structure material,
adhesive
chemicals, and driving waveform to drive
the actuator. All
these parameters and ink
characteristics
determine the total inkjet head
performance*2.
The head dimension parameters
such as channel
length and nozzle shape were
optimized to meet
required printer specifications,
taking into
account easiness of exhausting air
bubbles in the
channel to ensure stable ink ejection.
The driving
waveform was also improved to achieve
stable ejection
at a higher operating frequency.
The head housing
was re-designed to cope with
increased heat
generation associated with the
increased number
of nozzles and raised frequency
so that quick
heat release is assured. The head
mount mechanism
was also improved to ensure
easy head
replacement by the user, which leads to
easy maintenance.
Because of the compact design
of the print
head, the carriage size where heads are
mounted was
greatly reduced from the previous
printer, despite
the fact that the total number of
nozzles used is
four times that of the previous
printer. Fig. 2
shows appearance of the newly
developed inkjet
print head.
Fig. 2 Inkjet
print head
3. Fabric belt
feed system
Feed length of
the previous printer, which adopted
a feed roller
system, varied by fabrics according to
their thickness
and friction behavior. It was
necessary
therefore to adjust the feed length for
each fabric to be
used, costing laborious work.
This feed system
also had difficulty in handling thin
or elastic fabric
accurately due to stretch or bent of
the fabric.
Moreover, in the case of thin fabric
printing, ink
having passed through the fabric on to
the feed roll
caused image stain of the successive
print area.
In order to cope
with these problems, a fabric belt
feed system with
electrostatic adsorption
mechanism was
introduced (Fig. 3). This system
enabled feeding
fabrics at a predetermined length
regardless of the
fabric characteristics such as
thickness, since
the feed length is determined only
by combination of
drive roller and feed belt.
In order to
achieve higher image quality, print
resolution of
feed direction should be raised from
300 dpi to 540 or
720 dpi. Feed length accuracy of
the previous
printer, comprising worm gears and a
timing belt, was
found to be insufficient in
preventing
overlaps or jumps of each main-scan
print swath.
To improve this
accuracy, a new driving system
Driving roller
Belt Weight roller
Driven roller
Electorostatic
chuck system
Fabric
Driving roller
Belt Weight roller
Driven roller
Electorostatic
chuck system
Fabric
Fig.3 Schematic
diagram of the belt feed
comprising a DC
servomotor and a harmonic drive
was introduced.
PID control of it was also optimized.
Results are shown
in Fig. 4. Feed length for each
scan is plotted
on Y axis. The graph shows that
fluctuation of
feed length was reduced to
approximately 25%
of that of previous system.
Fig.4 Fluctuation
of belt motion
1 6 11 16 21 26
31 36 41 46 51 56 61
Number of carrige
scan
Amount of feed
Nassenger-V(belt
feed) Nassenger-II (roller feed)
Belt
Cleaning roller
Squeeze roller
Permeate print
image
Weight roller
Remaining ink
Fig.5 Schematic
diagram of the belt cleaning
system
With this belt
feed system, when the fabric being
printed is thin
enough for the ink to get through to
the backside and
to reach the surface of the belt, or
when the user
intentionally deliver too much ink
onto the fabric
to let the ink reach the back side, the
belt becomes wet
with this ink. Therefore the belt
should be cleaned
to prevent it from staining
successive print
area at the next belt turn. A belt
cleaning roller
made of porous medium was
therefore
installed to touch the belt surface in the
lower part of the
machine to remove residual inks
on the belt
surface (Fig. 5).
Fig. 6 shows a
relationship of the cleaning roller
pressure to the
belt and cleaning performance.
When the pressure
is high enough, the residual ink
is completely
removed from the feed belt.
Fig.6 Relation
between pressure of the
cleaning roller
and remaining ink
amount on belt
0
10
20
30
40
50
60
Amount of contact
of belt and belt cleaning roller
Remaining ink
amount on conveyerbelt(mg/. )
To feed the
fabric accurately with this belt system, it
is necessary to
assure the fabric adhered firmly to
the belt. Without
enough adhesive force, feed
length of the
fabric will be affected by its self weight
and friction
force. Hence ensuring stable feed
performance
regardless of the kind of fabrics
becomes
difficult. The electrostatic adhesion
system was
adopted to fix the fabric onto the belt.
The system is
illustrated in Fig. 7. High DC voltage
is applied to
electrodes embedded in an insulation
layer,
alternately charged positive and negative,
thus generating
positive and negative charge
between the belt
and fabric. Table 3 shows the
adhesion force of
typical fabrics to the belt.
Adhesion force
here refers to tensile force
necessary to
start moving a 100 mm x 100 mm
piece of fabric
adhered on the feed belt. Fig. 8
shows fluctuation
of feed length for polyester. The
use of the
electrostatic adhesion system clearly
increased the
adhesive force between them.
Fig.7 Cross
section of adhesion system+-+-
Adsorption layer
Insulation layer
Belt
Fabric
Electrode
Table.3 Adhesion
force for fabric
Type of fabric
Adhesion
system
Without
adhesion
system
Polyester 775 39
Cotton 470 29
Polyester knit
794 29
Satin 775 29
Table.3 Adhesion
force for fabric
Type of fabric
Adhesion
system
Without
adhesion
system
Polyester 775 39
Cotton 470 29
Polyester knit
794 29
Satin 775 29
(x 10-3N)
Fig.8 Deviation
of fabric motion
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
1 3 5 7 9 11 13
15 17 19 21 23 25 27 29 31Fabric feed(m)
Deviation of
feeding amount(%)
4. Detection of
ink drops
The number of
nozzles in one print head has been
gradually increased
in line with market demands for
higher image
quality at higher print speed, resulting
in development of
printers having more than 4,000
nozzles with 16
colors. Ideally all these nozzles
should be kept in
good condition, but in reality,
some of them may
fail in ejecting ink. If printing is
continued with
these faulty nozzles, image quality
deteriorates
considerably with bandings. If ink drops
can be detected,
it becomes possible to clean the
nozzles only when
miss-firing occurred, instead of
regularly
cleaning all the nozzles even when they
function
properly. This leads to reduced ink
consumption,
shorter print loss time and remarkably
improved
reliability of the system by substituting
faulty nozzles
with other good nozzles.
Fig. 9
illustrates a schematic diagram of the layout
for an ink
droplet detector, inkjet heads and a
spittoon. A light
detector and a detection circuit
are placed in a
shielded case, placed opposite to a
light source.
Fig. 10 shows the mechanism of this
system. A row of
nozzles are arranged in parallel to
an optical path
consisting of the light source and the
detector. Ink
drops are ejected one by one from a
nozzle at one end
to the nozzle at the other end of
the optical path.
Shadow of ink drops thus ejected
is checked by the
light detector to identify the flying
of the ink drops
for every nozzle. Nozzles which do
not eject ink
drops are judged to be faulty.
Fig.9 Schematic
diagram of ink drop detection system
Light
source Light
detector
light beam
Spittoon
Carrige
scaning
direction
Ink
jethead
Head
Optical
path
Ink drop
Light source
Light detector
Signal
corresponding to
Signal
corresponding
normal nozzle.
to clogged nozzle.
Light is not
blocked.
Light is blocked
by ink drop
Fig.10 Mechanism
of drop detection system
5. Conclusions
In the
development of Nassenger-V, intensive
improvement in
the printer, including the newly
designed head,
belt feed system and ink drop
detection system,
has successfully contributed to
greatly enhanced
productivity, along with user
friendly
operation by sophisticated software and
offering of post
processing options. Nassenger-V is
expected to be
used as a very efficient inkjet textile
printing system.
• References
1) MITSUHASHI,
Taku, and KATO, Takayuki:
Journal of
Society of Photography Science and
Technology of
Japan, 41, 67 (2002).
2) TAKEUCHI,
Yoshio: Konica Technical Report, 15,
31 (2020).