FORM 2

THE PATENTS ACT, 1970 (39 of 1970)

THE PATENTS RULES, 2003

COMPLETE SPECIFICATION [See section 10, Rule 13]

INKJET PRINT DEVICE WITH AIR INJECTOR, ASSOCIATED AIR INJECTOR AND WIDE FORMAT PRINT HEAD;

MARKEM-IMAJE, A CORPORATION
ORGANIZED AND EXISTING UNDER THE LAWS OF FRANCE, WHOSE ADDRESS IS 9, RUE GASPARD MONGE, F-26500 BOURG LES VALENCE, FRANCE

THE FOLLOWING SPECIFICATION

PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

DESCRIPTION

TECHNICAL FIELD

The invention relates to an improvement in
the print quality of inkjet printers, particularly socalled wide format printers.
More particularly, it deals with several
problems encountered in using a large number of jets in a print head.

PRIOR ART

Industrial inkjet printers can be used to
print character strings, logos or more highly
sophisticated graphic patterns on products being
manufactured or on packaging, starting from variable
digital data frequently under difficult environmental
conditions.
There are two main technological families
of printers of this type; one is composed of "drop on demand" printers and the other of "continuous jet" printers.
In all cases, at a given moment, the print
head projects a combination of drops aligned on a
segment of the surface to be printed in a very short
time. A new combination of drops is projected after
relative displacement of the head with respect to the
support, in the direction usually perpendicular to the
segments addressed by the head nozzles. Repetition of

this process with variable combinations of drops in the
segment and regular relative displacements of the head
with respect to the product, lead to printing of
patterns with a height equal to the height of the
segment and a length that is not limited by the print
process
"Drop on demand" printers directly and
specifically generate the drops necessary to make up
segments of the printed pattern. The print head for
this type of printer comprises a plurality of ink
ejection nozzles usually aligned along an axis. A
usually piezoelectric actuator, or possibly a thermal
actuator generates a pressure pulse in the ink on the
upstream side of the nozzle, locally causing an ink
drop to be expelled by the nozzle concerned, to
determine whether or not a drop is ejected depending on
the required combination at a given moment, for each
nozzle independently.
Continuous jet printers operate by the
electrically conducting ink being kept under pressure
escaping from a calibrated nozzle thus forming an
inkjet. The inkjet is broken down into regular time
intervals under the action of a periodic stimulation
device, at a precise location of the jet. This forced
fragmentation of the inkjet is usually induced at a so-
called jet "break" point by periodic vibrations of a
piezoelectric crystal, located in the ink on the input
side of the nozzle. Starting from the break point, the
continuous jet is transformed into a stream of
identical ink drops at a uniform spacing. A first group
of electrodes called "charge electrodes" is placed

close to the break point, the function of which is to
selectively transfer a predetermined quantity of
electric charge to each drop in the stream of drops.
All drops in the jet then pass through a second group
of electrodes called "deflection electrodes"; these
electrodes, to which very high voltages of the order of
several thousand volts are applied, generate an
electric field that will modify the trajectory of the charged drops.
In a first variant of continuous jet
printers called "deviated continuous jet" printers, a
single jet is capable of successively projecting drops
towards the different possible impact points of a
segment on the product to be printed. In this first
variant, the charge quantity transferred to the jet
drops is variable and each drop is deflected with an
amplitude proportional to the electric charge that it
received. The segment is scanned to successively
deposit the combination of drops onto a segment much
more quickly than the relative displacement of the head
with respect to the product to be printed, such that
the printed segment appears approximately perpendicular
to said displacement. Drops not deflected are recovered
in a gutter and are recycled into the ink circuit.
A second variant of continuous jet printers
called "binary continuous jet" printers is
differentiated from the previous variant mainly by the
fact that the trajectories of the ink drops may only
have two values: deflected or not deflected. In
general, the non-deflected trajectory is intended to
project a drop on the product to be printed and the

deflected trajectory directs the unprinted drop to a
recovery gutter. In this variant, a nozzle addresses a
point on the pattern to be printed on the product, and printing of characters or graphic patterns requires the use of a number of nozzles in the head corresponding to the segment height, for a given resolution.
Applications of industrial inkjet printers
can be broken down into two main domains. One of these
domains relates to coding, marking and customisation
(graphic) of printed products over small heights; this
involves print heads comprising one or several jets
based on the so-called "deviated continuous jet"
technology and several tens of jets using the "binary
continuous jet" or "drop on demand" technology.
The other application domain relates to
printing, mainly graphic, of flat products with large
surface areas for which the width may be very variable
depending on the applications and may be up to several
meters, the length of which is not limited by the
printing process itself. For example, this type of
application includes printing of monumental posters,
truck tarpaulins, strip textiles or floor or wall
coverings, and others.
These printers use print heads comprising a
large number of nozzles. These nozzles cooperate to
project combinations of drops at the ordered instants,
each combination addresses a straight segment on the
product.
Two configurations of inkjet printers are
normally used to print on large areas. The first
configuration can be used when the print rate is

relatively low. In this case, printing is done by the
print head scanning above the product. The head moves
transversely with respect to the advance direction of
the product that itself is parallel to the segment
addressed by nozzles in the head. This is the usual
operating mode of an inkjet office automation printer.
The product moves forward intermittently in steps with
a length equal to the height of the segment addressed
by the nozzles in the print head, or a sub-multiple of
this height, and stops during transverse displacement
of the print head. The productivity of the machine is
higher when the height of the segment addressed by the
head nozzles is high, but this height does not usually
exceed a fraction of the order of 1/10th to 1/5th of the
width of the product. The "drop on demand" technology
is preferred for this configuration, due to the low
weight of print heads that can be transported more
easily and the greater difficulty of making large print
heads using this technology, as is essential in the
second configuration. Furthermore, the intermittent
printing makes it easier to manage a constraint
inherent to this technology, which is that the head has
to be brought to a maintenance station periodically to
clean the nozzles.
The second configuration helps to obtain
the maximum productivity by making the product pass
forwards continuously at the maximum printing speed of
the head. In this case, the print head is fixed and its
width is the same order as the width of the product.
The segment addressed by the nozzles in the print head
is perpendicular to the direction of advance of the

6

E7SEP2009

product and the height is equal to at least the width
of the product. In this configuration, the product
advances continuously during printing as with existing
photogravure printing or silk screen printing
techniques using rotary frames but with the advantage
of digital printing that does not require the
production of expensive tools specific to the pattern
to be printed.
The development of wide format inkjet
printers, typically wider than 1 meter and particularly
between 1 meter and 2 meters wide, assumes that it is
possible to integrate a large number of nozzles into a
single print head. This large number is of the order of
100 to 200 for the "deviated continuous jet" technology
and several thousands for the "binary continuous jet"
and "drop on demand" technologies. The Burlington
patent US 4,841,306 describes a wide format print head
using the "binary continuous jet" technology in a
single piece for which the nozzle plate in particular
consists of a single part. The Imperial Chemical
Industries Inc. patent US 3,956,756 also describes a
wide format head using the "deviated continuous jet"
technology. Faced with the difficulty of making this
type of head, modular architectures have been developed
in which the print head is broken down into small
modules that can be made and controlled more easily,
and that are then assembled on a support beam. As can
be seen in patent EP 0 963 296 B1 or patent application
US 2006/0232644, this solution is suitable for "drop on
demand" printers. However, modules have to be stacked
and offset for size reasons, the connection to zones

7 L„7 SEP 2009

printed by the modules being made by the management of
print start times for each module. The "deviated
continuous jet" technology is particularly suitable for
modular architectures, and this technology enables a
space of several millimeters between jets, so that jets
and their functional constituents can be placed side by
side over large widths. This possibility of putting
jets side by side indefinitely can be transferred onto
modules of several jets as was used in patent
FR 2 681 010 granted to the applicant and entitled
"Module d'impression multi-jet et appareil d'impression
comportant plusieurs modules" (Multi-jet print module
and print device comprising several modules). This
patent FR 2 681 010 describes a wide format "deviated
continuous" multi-jet print head composed of the
assembly of print modules with m jets, typically 8
jets, placed side by side on a support beam, this support also performing functions to supply ink to the modules and to collect ink not used.
In all cases, in this type of industrial
application in which the environment is often severe,
drops and their trajectories before impact must be
protected as much as possible from external
disturbances (currents, dust, etc.) for which a random
nature prevents quality control of the printing. This is why drops usually travel between the nozzles and the exit from the head in a relatively confined cavity open to the outside mainly through the drop outlet orifice. This orifice is usually a slit, that should be kept as narrow as possible so that protection of the trajectories is as efficient as possible.

8 a7SEP2009

The use of wide format inkjet printers
creates some problems. The availability of such
printers is limited by the need for periodic
maintenance, in other words to periodically clean and dry the functional elements located in cavity in the head, the bottom of the head or the nozzle plate. Furthermore, the print quality cannot be controlled optimally regardless of the printed pattern, due to a mutual interaction between jets.

Three phenomena are involved:
1) The ink solvent evaporates from the
drops during their path. In the confined space of the
internal cavity in the head, the concentration of
solvent vapour is such that condensation conditions are
quickly reached and internal functional elements of the
cavity have to be dried periodically. Those skilled in
the art have already attempted to prevent condensation
either by heating the surfaces on which there is a
risk, but at the price of complex and expensive
solutions, or by drying these surfaces using an air
flow, possibly with hot air, but the efficiency of this
operation requires high air velocities, that causes
turbulence when projected onto the internal structure
of the cavity with a complex shape, that reduces the
stability of the drop trajectories and therefore the
print quality.
2) Splatter, that is the main cause of the
print head getting dirty and making periodic cleaning
necessary. This phenomenon, that is described in an
article "Splatter during ink jet printing" by J.L.

9 _..7 �tP° 1Tr14

Zable in the IBM Journal of Research, July 1977, is
created due to splatter of very small ink droplets
generated at the time of the impact of drops on the
support to be printed. These droplets have sufficient
kinetic energy so that they can be deposited under the
print head and droplets can even return into the head
against the current of drops. By accumulating on
functional elements inside the head, these droplets
eventually degrade operation of the print head. ITW's
US patent 6,890,053 proposes a solution to protect a
print head from dirt originating from outside by creating a barrier all around the head composed of an air stream blowing outwards. This solution does not deal with the problem of dirt created by the head itself in the protected containment.
3) Inside the internal cavity of the head,
the drops entrain air as studied in the "Boundary layer
around a liquid jet" article by H.C. Lee published in
the IBM Journal of Research, January 1977. This air
accompanies drops as far as their destination outside
the cavity. The air deficit created in the cavity is
compensated by an addition from the outside through the
head outlet slit or through other orifices such as the
lateral ends of the cavity located on each side of the
head. Drops exit from the head in variable numbers and
with a variable density depending on the printed
pattern, and obstruct the entry of air to rebalance the
internal pressure in the cavity. The result is the
formation of currents with a highly variable intensity
and direction that modify the drop flight time between
the nozzles and the support to be printed. It has been

9
10

7 SEP 2009

observed that the air deficit at the two ends of the
head is easily compensated by opening the cavity to
free air which creates a specific behaviour of air
currents around the edges of the head. In inkjet
technologies, the placement precision of drops on the
support and therefore the print quality depends very
much on the stability and control of the flight time of
these drops, therefore, it can be understood that the
phenomenon described prevents optimisation of the print
quality, regardless of what pattern is being printed at
a given instant.
Note that the nature of this phenomenon of
air entrainment by drops that induces a modification to
the behaviour of the jets at one location of the head
depending on the content of print jets at another
location of the head, is different from the nature of
aerodynamic interactions between drops in the same jet.
These interactions are reproducible for identical
situations in the same jet, and can be compensated by
acting on the usual print commands. Despite being
complicated to implement, many solutions for this
compensation have been proposed to attenuate the
incidence of the aerodynamic influence of one drop on
the trajectory of the next drop, the general concept
being to cancel the relative velocity between drops and
the surrounding air. For example, IBM's patent EP 0 025
493 and Creo Inc.'s patent US 2005/0190242 apply this
type of solution that requires air flows for which the
velocity must be very high (several meters or tens of
meters per second) and perfectly laminar to avoid
turbulence that could disturb drop trajectories. These

11 '

F7 SEP 2009

solutions require very high air flows in the framework
of a wide format multi-jet head, and sophisticated,
expensive and cumbersome means to guarantee a very stable and perfectly laminar air velocity.
The major disadvantages of using wide
format inkjet printers according to the state of the art can be summarised as follows:
1) Condensation of ink solvent vapours in
the head can cause functional problems if the inside of the head is not dried periodically.
2) Ink splatter due to the impact on the
substrate pollute the printed product, the bottom of the head and even the inside of the head, such that the head has to be cleaned periodically to prevent functional problems.
3) The print quality is not controlled due
to disturbances to drop trajectories related to air displacement effects in the head during printing.
Furthermore, as mentioned above, the two
transverse ends of the head are open, consequently a
specific behaviour of air drafts is created at the
edges, reducing the print quality at the ends of the
head because it is not homogeneous with the remainder of the head.

PRESENTATION OF THE INVENTION

The invention thus mitigates all or some of
the disadvantages mentioned above and discloses a print
device capable of improving the quality of the wide format print.

E7 SEP 2009
12

Thus, the solution according to the
invention consists of adding a unique air flow passing through the internal cavity in the print head.
To achieve this, a first embodiment of the
invention relates to a wide format print head composed of X inkjet print devices intended to print on a moving support in which:
- each device comprises:
- a body intended to extend along an axis
transverse to the direction of motion of the support,
- an ink ejector fixed to the body and
adapted to eject ink along an ejection plane parallel
to the axis,
- at least one part defining an output
orifice through which at least part of the ejected ink passes to print the moving support,
- a cavity delimited at least by the body,
the ejector and the part(s) defining the output orifice,
- an air injector adapted to blow air with
a flow approximately parallel to the ink ejection plane passing through the cavity, from a zone below the ejector a.; far as the output orifice;
-- the devices arein the form of adjacent
modules along the same transverse axis each comprising
a block of electrodes in which a single injector is common tca all modules, the injected air flow being uniform over the width of the head.
According to a second embodiment of the
invention, a wide format print head is composed of X

13

l SEP 2009

inkjet print devices intended to print a moving support in which:
- each device comprises
- a body intended to extend along an axis
transverse to the direction of motion of the support,
- an ink ejector fixed to the body and
adapted to eject ink along an ejection plane parallel to the axis,
- at least one part defining an output
orifice through which at least part of the ejected ink
passes to print the moving support,
- a cavity delimited by at least the body,
the ejector and the part(s) defining the output
orifice,
- an air injector adapted to blow air with
a flow approximately parallel to the ink ejection plane passing through the cavity, from a zone below the ejector as far as the output orifice;
- the print devices are in the form of adjacent
modules along the same transverse axis, each module
comprising a block of electrodes and an air injector,
the injected air flow being uniform over the width of
the head.
Thus, the direction of the flow is
approximately parallel to the jets to minimise components perpendicular to the jets that could degrade the print quality.
Preferably, air injected into the head is
dry to dry internal functional elements and is
advantageously clean to prevent pollution of these
elements.

' , =7 SEP 2009
14

The injected air flow is advantageously
greater than the volume necessary to renew air in the cavity at least once per second so as to efficiently expel solvent vapours from the ink towards the outside of the head.
The injected air flow is also
advantageously greater than the air flow corresponding to the maximum air quantity extracted by the print process per unit time, in the head.
The location at which air is injected into
the cavity is advantageously chosen to prevent the jet being disturbed at the exit from the nozzle.
The air velocity at the air injection is
preferably less than a value beyond which the generated
turbulence would destabilise the trajectory of the
drops and degrade the print quality. The velocity
profile at the exit from the injector is as uniform as
possible, in order to maximise the flow. The air
velocity also preferably remains sufficiently low
compared with the velocity of the drops to make the
behaviour of the jets relatively insensitive to dispersions and variations of the air velocity profile at the air injection.
The velocity of air expelled from each
print module through the outlet slit is high enough to
push droplets generated by splatter caused by the impact of drops onto the product being printed.
Preferably, the two lateral ends of the
cavity are closed to guarantee uniformity of the jet
behaviour over the width of a wide format print head.

JO SEP 2009
15

The print device may be associated with a
method to prevent droplets caused by splatter from
returning to the bottom of the head or the support to
be printed. This method consists of creating an air
draft under the print device parallel to the support to
be printed and moving along the direction of movement of the support. This air current entrains droplets originating from splatter to an extraction system. This air current is created either by blowing using blowing nozzle(s), or by suction through suction opening(s), or by combined blowing and suction.
Some aspects of the invention, that
improves the print quality and the availability of wide
format inkjet printers, are applicable to "drop on
demand" and "binary continuous jet" printers, but it is
particularly suitable for "deviated continuous jet"
printers in which all aspects of the invention can be
used. Therefore, the invention will be described in the
following in the context of this preferred type of
printers.
The invention also relates to the
arrangement of an air injector in a print module
composed of m jets that can be put side by side (in
other words ejecting a number equal to m inkjets).
It also relates to a wide format print head
using the "deviated continuous jet" technology equipped
with air flow generation means and an air flow
distribution system, and a plurality of m-jet print
modules according to the invention, placed adjacent on
a common support beam.

,-,7 SEP Z009

16

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the
invention will become clear after reading the detailed
description below given with reference to figures 1 to
11 as follows:
- Figures 1:
• 1A shows a wide format multi-jet print
head (T) according to the state of the art, with the
jets in operation but without printing the support (S) ,
• 1B is a sectional view along axis C-C
in figure 1A, showing a multi-jet print module (Mi)
integrated into the print head (T) according to the
state of the art, and operating according to the
preferred "deviated continuous jet" technology.
- Figures 2:
• 2A shows a partial view of the central
part of the wide format multi-jet print head according
to figure 1A, with the jets in operation printing a
full tone (APL1, APL2),
• 2B is a view of a portion of several
jets in figure 2A, of the result of printing on the
support (S) at the beginning of a full tone (APL1) with
density equal to 100% (called type A printing),
• 2C is a view on several jets in figure
2A, of the result of printing the support (S) , at the
beginning of a grey level full tone (APL2) (density
<100%), the connection between jets having been made on
a 100% full tone (APL1),

,7 SEP 2009

17

- Figures 3:
• 3A shows a wide format multi-jet print
head (T) according to the state of the art, with jets
in oPera tion bzat only some of them printing a full tone
(APL3) on a portion of its width and therefore of the
support (S) ,
• 3B is a view on several jets in figure
3A, of the beginning of a 100% full tone (APL3) (called
type B printing),
- Figure 4 shows a wide format multi-jet
print head (T) according to the state of the art, with
jets in operation printing a full tone (APL1, APL2-
APL3-APL4) over its entire width.
- Figure 5 shows a wide format multi-jet
print head (T) with lateral orifices closed by end
plates, according to the invention, printing a full
tone (APL1, APL2) over its entire width.
- Figures 6:
• 6A shows a wide format multi-jet print
head (T) , equipped with end plates and air injection
according to the invention, with jets in operation
according to the preferred "deviated continuous het"
technology and printing the support (S) over its entire
width,

• 6B is a sectional view along axis C-C
in figure 6A, of a multi-jet print module (Mi)
integrated into the print head (T) according to the
invention, and operating according to the preferred "deviated continuous jet" technology.

r r-7 SEP 2009
18

- Figures 7:
• 7A is a sectional view along axis C-C
in figure 6A, showing the air injector according to one
embodiment of the invention,
• 7B is a perspective view of the air
injector according to the invention,
• 7C is a sectional view along axis C-C
in figure 6A, showing the air injector according to
another embodiment of the invention.
- Figures 8:
• 8A shows a graphic view of the air
velocity profile at the exit from the air injector
according to figures 7A et 7B, 'transverse to its
output,

• 8B shows a graphic view of the air
velocity profile at the exit from the air injector
according to figures 7A et 7B, longitudinally to its
output and close to the maximum in dashed lines shown
in figure 8A.
- Figure 9 shows the principle diagram for
the supply of air to be injected in a printer
comprising several wide format print heads Tl,...,Tn
according to the invention.
Figures 10:
• 10A is a diagrammatic representation of
splatter generated by ink droplets that can occur close
to the wide format print head (T) according to the
invention, between the print head and the support (S)
to be printed while the support is moving under the
head,

19 El SEP 2009

• 10B is a diagrammatic representation of
a complementary means according to the invention enabling blowing of the droplets in figure 10A,
• 13C is a diagrammatic representation of
a complementary means according to the invention enabling suction of the droplets in figure 10A,
• 10D is a diagrammatic representation of
the combination of the complementary means according to
the invention as shown in figures lOB and 10C, enabling
both blowing and suction of the droplets in figure 10A.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

T h e preferred techno� ��y ivy p�i� iu�iTfg a
wide format inkjet printer is the "deviated continuous
jet
The use of a large number of simultaneous
jets in a print head at a constant spacing, addressing
connectable print zones on the support to be printed
and thus enabling printing over large widths, is
described in French patent FR 2 681 010 granted to the
applicant and entitled "Module d'impression multi-jet
et appareil d'impression comportant plusieurs modules"
(Multi-jet print module and print device comprising
several modules) In this patent mentioned above, a
wide format multi-jet print head (T) is composed of the
assembly of X print modules (Mi) each producing m jets,
typically 8 jets, and placed side by side on a support
beam, which also performs functions to supply ink to
the modules and to collect unused ink.
Thus, a wide format print head (T)
according to the state of trie art is composed

20 7 SEP 2009

identically of X print modules (Mi) and extends along
an axis A-A' transverse to the moving support (S) to be
printed (figure IA).
Each print module according to the
invention (Mi) is composed firstly of a body 1
supporting an ink ejector 2 with m jets 4 of drops 40
and integrating a set of m recovery gutters 10, and
also a block of retractable electrodes 3 supporting two
groups of electrodes necessary for the deflection of
some drops; a group of charge electrodes 30 and a group
of deflection electrodes 31 (figure 1B). More
precisely, the ink ejector 2 is adapted to eject ink in
the form of continuous jets 4, the break point of each
jet being placed close to the middle of the charge
electrodes 30 of the electrodes block 3. The jets 4 are
parallel in a vertical plane (E) and the drops 40
travel from the nozzles of the plate 20 fixed to the
ink ejector 2 towards the orifice of the corresponding
recovery gutter 10.
The electrodes block 3 can be lowered or
raised, by pivoting it about the axis 32. When it is in
the extreme down position, in other words in the
operating position, the electrodes 30, 31 are inserted
in the path of the drops 40 and control the charge and
deflection of some drops that escape from the gutter 10
and are deposited on the support to be printed (S)
When in the extreme down position, each
electrodes block 3 forms an internal cavity 5 with the
body 1 and the ink ejector 2. More precisely, the
internal cavity 5 is'limited at the back by the body 1,
at the front by the electrodes 30, 31, at the top by

ci SEP ZOOS
21

the nozzle plate 20 and at the bottom by the projection
11 of the body integrating the gutter 10 and the toe 33
of the electrodes block 3. The space between the
projection 11 and the toe 33 of the electrodes block 3
defines an output orifice 6 forming a slit through
which drops 40 can pass for printing (figure 1B) This
slit 6 is as narrow as possible to assure confinement
of the cavity 5. Such a confinement can protect the
drops currently being deflected from external
disturbances, such as air currents or ink projections,
dust or other, for which the random nature prevents
control over the print quality.
When all electrode blocks 3i of the head
(T) are in their extreme down position, the internal
space Si of each module (Mi) forms a single elongated
cavity 5 for which the section is approximately
identical over the entire width of the head.
The phenomena described above in a general
manner exist in this print head according to the state
of the art (figures lA and 1B):
1) The condensation phenomenon mainly
affects high voltage deflection electrodes 31 and the
insulating parts that support them. These parts are dry
so as to guarantee sufficient insulation level between
the plates raised to a potential difference of several
thousand volts and to prevent any current consumption
in the electronic (generating) device creating the high
voltage. These conditions guarantee good deflection
stability and eliminate risks of the high voltage

generator from tripping,

which can occur at

NOV%

7IS F^ i
22

indeterminate instants and cause a sudden stop of the deflection of the drops.
2) Splashes are generated at the time of
the impact of the drops 40 on the support (S) In the
"deviated continuous jet" technology, the relatively large size of the drops 40 and their high impact
velocity contribute to resending droplets with a high
kinetic energy towards the head. They are also
disturbed by turbulent.air currents present between the
head (T) and the moving support (S) Furthermore, these
droplets are electrically charged because the printed
drops themselves are charged to be deflected. Under
these conditions, the droplets can be redeposited on
the bottom of the head (T) and on the support (S) , but
they can also pass through the output slit 6 of the
drops in the reverse direction and return to the cavity
S.. They are then electrostatically attracted by the
deflection electrodes 32 that become dirty, with the
same consequences as in the case of condensation.
3) During the use of a print head (T) based
on the principle of a deviated continuous jet, it is
found that the deflection amplitude of drops 40 of jets
4 located at a given location on the head is influenced
by the printing of other jets 4i, these jets 4i
possibly being relatively far from the jets 4. These
"interjet" phenomena are demonstrated by considering
the printout of a particular pattern over the width of
the head, comprising a sequence of 100% full tones
(maximum drop density, all printable positions
occupied) and 0% (no printed drops), for all jets 4i on
the head (T) at the same time. The jets are previously

23

"connected",, in other words the electronic adjustments
have been applied to the jet deflection control devices
such that the printable zone addressed by each jet 4i
is perfectly adjacent to those of the neighbouring jets
(figure 2B) . This process is described in the patent
application FR2801836 entitled "Imprimante a
fabrication simplifiee et procede de realisation"
(Printer with a simplified manufacturing and production
process) filed by the applicant. Printing the above
pattern shows that at the beginning of a 100% full tone
(APL1), the deflection of the jets is smaller than the
connection deflection, and it then progressively
increases during a certain time until it reaches the
nominal connection deflection at the end of a few
millimeters (about fifteen) (figure 2B).
The other parameters that influence the
deflection having been satisfied, it is found that this behaviour is due to a variation in the flight time of the drops.
For all inkjet technologies, this result
creates an inaccuracy in the impact time, and therefore the position of the drop 40 on the support to be
printed in the direction of motion f of the support.
For the "deviated continuous jet"
technology, this also causes a modification in the
presence time of charged drops 40 in the field created
by the deflection electrodes 31; the deflection
increases when the drops slow down and vice versa. When
few or no drops 40 are printed, which is the situation
present before the start of printing, the drops follow
a trajectory one behind the other in the nozzle as far

E7SF2
24

as the recovery gutter 10 (figure 1B) Inside the
internal cavity 5 of the head (T) , the drops 40 entrain
air in contact with the jet. This air entrainment
phenomenon has been studied by H.C. Lee in the
"Boundary layer around a liquid jet" article published
in the IBM Journal of Research, January 1977. The drops
40 and the entrained air are sucked in by the gutters
10; the air deficit in the cavity 5 can easily be
compensated by an input from the outside of the head
(T) , mainly through the outlet slit 6 of the drops 40
and lateral openings of the cavity 5. In equilibrium, a
fairly low but regular air flow circulates between the
outside and the inside of the cavity 5. Figure 1A
illustrates this situation for a head with X=32
identical modules (Mi), schematically shown in section
in a vertical plane (E) passing through the middle of
the cavity 5 and the outlet slit 6 of drops 40. The
cavity 5 is limited at the top by the level of nozzle
plates 20i and at the bottom by the level of the
gutters 10. In this figure lA, the small black arrows
distributed under the head (T) diagrammatically show
the incoming air flow through the outlet slit 6 of the
drops; the size of the arrows being proportional to the
intensity of the flow.
The first drops 40 of a 100% full tone
(APL1) are emitted outside the head under these
aerodynamic conditions in the head, as shown
diagrammatically in figure 2A. It is known that due to
the aerodynamic effect, a drop 40 that penetrates in
air creates a positive pressure in front of it and a
pressure pressure behind it. If another drop follows

25 E7 SEP 2009

it, the other drop is drawn in by the pressure pressure
preceding it and its velocity increases. When printing
a 100% full tone (APL1) (figure 2B), the expected
behaviour in free air is that the drops 40 at the
beginning of the full tone that deviate from the trajectory carrying them to the gutters 10, penetrate
into the air at a given velocity and progressively the
velocity of the following drops increases until an
equilibrium is found. The consequence should result in
a transient behaviour of the deflection of the jets 4
that should reduce between the first front of drops in
the full tone and when the equilibrium condition is set
up. But as described above, the opposite effect is
observed. The inventor has shown that a high pressure
pressure is created inside the cavity 5, which
counteracts the aerodynamic effects described above.
This pressure pressure is generated:
- firstly by the drops 40 output from the
head (T) in large quantities (shown diagrammatically by
white arrows in figure 2A), that entrain a large air
volume towards the outside,
- secondly, by suction of the gutters 10
which, having much less ink 4 to be recycled, take up
more air.
This pressure pressure can only be
compensated by an incoming air flow (shown
diagrammatically by the black arrows in figure 2A),
particularly through the counter current slit 6 of the
drops 40. However, the effective (or real) width of the
slit 6 through which air can enter is very much reduced
by the front of outgoing drops (white arrows figure

26 ,7SEP2009

2A), which increases the incoming air circulation
velocity. These effects slow down the drops 40 which
increases their deflection because they stay within the
deflection electrodes 31 for a longer period. The time
to set up this condition, starting from the beginning
of printing a 100% full tone (APL1) 100 %, then
creation of the pressure pressure until an equilibrium
has been set up, is of the order of 2 to 3 seconds,
which corresponds to a transient disturbance of the
deflection that disturbs printing over about 3 to 4
times the width of a jet 4 as shown in figure 2B. This
figure 2B shows the start of printing a 100% full tone
(APL1) over several jets, which after a given set up
time (corresponding to a given distance d shown in
figure 2B), has a correct jet connection; the full tone
background (APL1) shown in figure 2B is continuous over
the entire width. This type of behaviour is called Type A printing.
As illustrated in figure 2C, the inventor
has demonstrated that the amplitude of the effect on
the deflection depends on the density of printed drops,
in other words the deflection amplitude at the
beginning of the full tone does not depend on the
density of drops printed in the full tone; but the
amplitude reached under steady conditions is
correspondingly smaller when the density of printed
drops is low. This creates a problem with the stability
of the connection of printable zones in each jet. If
the connection was optimised over a 100% full tone
(APL1), the printable zones will no longer be quite
adjacent if a full tone with a lower density (APL2) is

j,7 SEP Z009
27

printed (figure 2C) . In the case in which an arbitrary
pattern composed of zones with variable drop densities
is printed, printing cannot be optimum everywhere at
the same time (Figure 2C).
In figure 3A, a single portion (M12 to M15)
of the head (T) prints a 100% full tone (APL3). It is
seen that the deflection variation of jets does not
appear and the jet printing zones, previously connected
over a 100% full tone (APLI) printed over the entire
width of the head, have a constant width but are no
longer adjacent (figure 3B). This type of behaviour is
called type B printing. In this case, the pressure
pressure created in the cavity 5 at the portion (M12 to
M15) of the head (T) printing the full tone (APL3) is
easily compensated by air incoming through the outlet
slit 6 in zones in which the density of the printed
drops is zero or low. Under these conditions, air
circulation does not hinder circulation of the drops 40
in the cavity 5 and through the outlet slit 6; their
velocity and therefore their deflection remain
unchanged.
In addition to the phenomena 1) , 2) and 3)
mentioned above, it is found that in the case of a wide
format printer (T) according to the state of the art
and according to the principle of the deviated
continuous inkjet as described in patent FR 2 681 010
mentioned above, the jets 4 located on the extreme
lateral edges (Ml and M32) are not affected by the
widening of the frame, even when printing a 100% full
tone over the entire width of the head (T) This effect
attenuates progressively from the edges (Ml and M32)

28 �: 7 SEP 2009

towards the middle of the head (T) over a distance of a
few modules. As shown in figure 4, printing is of type
B towards the edges (firstly M1 tp M4 and secondly M28
to M32) of the head (T) , type A in the central part
(M12 to M21), of the head (T) , and intermediate APL4
between the two (firstly M4 to Ml� and secondly M21 to
M28). The pressure pressure is compensated by external
air benefiting from a local access to the cavity 5. The
jets 40 concerned benefit from air incoming through the
lateral openings of the cavity 5 located on each side
of the head (right side of Ml and left side of M32).
The black arrows and the curves shown diagrammatically
in figure 4 illustrate this phenomenon.
The phenomena described imply that the
connection valid for large full tones is no longer valid for small patterns, and more generally the jets deflection amplitude depends on the printed pattern near to several tens of centimeters on each side of the jets considered.
During any printing, the two effects
illustrated in figures 2A to 4 are all present at the
same time and with variable intensities over the width
of the head, depending on the nature of the printout at
a given instant. This situation means that compromises
have to be made to minimise the result that degrades
the print quality, depending on the printout, which in
any case cannot be perfect.
The solution according to the invention
shown in figures 5 to 10D can give a better print
quality, independently of the print type.

29 C- 7 SEP Z00V

Firstly, in order to reduce non-homogeneity
in the behaviour of the print along the head (T) ,
according to the invention the openings (right side of
Ml and left side of M32) of the cavity 5 opening up on
each side of the head (T) are closed using the end
plates 70, 71 (figure 5) The deflection behaviour of
the drops then becomes practically identical over the
width of the print head as shown in figure 5. The
printout is then type A everywhere under the head (T)
(the white arrows indicating the output front of the
drops 40)
Figure 6A shows the diagram of a print
head {T) according to the invention, equipped with
closing end plates 70, 71 of the lateral openings
(right side of Ml, left side of 4 132) of the cavity 5
and a blower device 8, distributed over the width of
the head, which creates an air inlet for which the flow
shown by the longest black arrows 50 passes through the
cavity 5 from the top towards the bottom and prolongs
by an outgoing flow, represented by the shorter black
arrows 51 towards the outside of the head (T) through
the continuous outlet slit 6 of the drops 40. Air
transported by the drops 40 or drawn in by the droplets
10 no longer has any effect on the drop velocity, which
behave as if they were moving ih free air; this is
shown by the white arrows 52 in figure 6A longer than
the white arrows in figure 5. Furthermore, the presence
of the end plates 70, 71 homogenises the behaviour over
the entire head, which is shown in figure 6A, by arrows
with equal length over the entirh width of the head.
Printing of a full tone over the head width is then of

z7SEP2009
30

type B everywhere under the head. Therefore the
connection made on a 100% full tone (APL1) remains
valid for grey levels (APL2) and for arbitrary patterns
(APL3, APL4).
Figure 6B contains a section along C-C
showing a preferred arrangement of the blower device 8
according to the invention at one of the modules (Mi)
of a modular "deviated continuous jet" wide format
print head. In this case, the blower device 8 comprises
an air injector 9 adapted to generate an air flow using
the solution described above with reference to figure 6A.
Preferred arrangement of a blower device or
an air injector:
The layout of an air injector 9 according
to the invention in each print module (Mi) forming the
head (T) is intended such that air is injected into the
internal cavity 5 of the head (T) , below the charge
electrodes 30 but above the deflection electrodes 31
(figure 6B) This air injection zone in the cavity 5
prevents moving air from disturbing breaking of jets 4
according to the "continuous jet" technology. In this
technology, stability at the time of the break can be
used to control the charge of the drops 40 and
therefore the print quality by means of the stability
of deflection of the drops 40. This injection zone also
enables air to reach the zone located between the
deflection electrodes 31 so as to dry these electrodes,
without sending the flow directly onto the drops 40 in
flight. The exit from the injector placed between the
jets 4 and the internal wall 14 of the body 1, directs
air approximately parallel to the jets 4. These jets

E7 SEP 2009
31

are thus only concerned by air circulating at the edge
of the air stream output from the injector 9. The air
movement at this location is weakened and is parallel
to the jets 4. This thus minimises components of the
air velocity perpendicular to the jets 4 that, when
they exceed a certain threshold, cause destabilisation
of the trajectories of the drops 40. In the very broken
environment of the cavity 5 in which many elements such
as the electrodes 30, 31 interfere with the air flow,
the air velocity is preferably limited so as to avoid
the creation of turbulence at uneven points. Beyond a
certain threshold, this turbulence also destabilises
drop trajectories which also degrades the print
quality. The position of the air injector 9 as
illustrated in figure 6B, distributes the air flow
optimally in the cavity 5. Firstly, the air velocity
remains supportable for the drops and approximately collinear with the jets 4 in the broken zone in the
cavity in which the drops travel, and secondly the air
velocity is greater between the jets and the internal
wall 14 of the body 1 to provide a maximum air flow.
In this preferred embodiment of the blower
device 8 in a modular head (T), composed of a plurality
X of m-jet modules adjacent to each other on a support
beam, this device 8 comprises the juxtaposition of air
injectors 9i implanted in the modules (Mi) with one air
injector 9 for each module (figures 6B, 7B). Another
interesting mode to be considered consists of
implanting a single air injector for all X modules, the
width 1 of this single injector being equal
approximately to the large width of the print head.

32 El SEP Z009

Preferred embodiment of the air injector:
The function of the air injector 9 is to
distribute air supplied to it in the cavity 5 without
turbulence, uniformly over its width 1 and along a
direction parallel to the jets 4.
Figures 7A and 7B respectively show a
preferred structure of the air injector 9 and an
advantageous layout variant in the body 1. According to
this advantageous layout variant, the injector 9 is an
add-on part in a groove 13 machined in the body 1 of
each print module (Mi) Its air supply takes place
through the rear, in other words through an inlet duct
12 also formed through the body 1. In this case, air is
advantageously distributed to the different modules
(Mi) through the support beam (P) like ink used for
printing.
Functionally, the air injector 9 according
to figure 7A comprises a volume 90 in its upper part
forming an air expansion and turbulence damping
chamber. In this case, the volume of this chamber 90 is
of the order of 0.7 cm3 per injection module Mi, namely
22.4 cm3 for a head (T) of X=32 modules. This chamber
90 is supplied directly through the air duct 12
outputting the necessary flow for a given module (Mi)
ejecting m jets or for the corresponding portion of
cavity 5. This air inlet duct 12, a single duct in this
case but that can be composed of multiple channels,
typically has a diameter of 2 mm and injects highly
turbulent air at high velocity into the chamber 90. The
chamber opens onto a narrow vertical slit 91 (typically
300 dam wide) and long (typically 2 mm) compared with
E7 SEP Z009
33

its width. The slit 91 is preferably made over the
entire width 1 of the injector 9 (figure 7B) This slit
91 connects the upper chamber 90 to an outlet passage
92 typically with a developed length of 8 mm
(approximately equal to 4 times the height of the slit
91) The profile of the passage 92 is divergent and it
is identical over the entire width 1 of the injector 9
(figure 7B). The volume of the chamber 90 and the high
Pressure loss created by the slit 91 are such that air
expands; the air flows through the slit 91 uniformly
over the width 1 of the slit. Iz) this case, the air
velocity in the slit 91 is of the order of 5 m/s for a
typl cal fl ow 3t the of tl et 93 of the order of 3 litres
Per minute for a module (Mi) The Reynolds number
calculated over the section of the slit 91 in this case
is equal to about 100, therefore the air flow arrives
at the inlet to the passage 92 With an approximately
laminar flow with minimum turbulence. In this case the
outlet passage 92 is S-shaped so as to carry the air
flow from the slit 91 to the irijection zone in the
cavity 5, orienting the output flow parallel to the
jets 4. The passage 92 is divergent to reduce the air
velocity and distribute the flow 1n the section of the
cavity 5, while keeping the initial flow. The passage
divergence half-angle S is preferably less than 10°, so
as to avoid separation of the air streams in the
Passage. This could create undesirable turbulence at
the exit 93 from the passage 9a. The shape of the
different recesses forming the chamber 90, the slit 91
and the passage 92 from the injector 9 is
advantageously intended such that. there is no liquid

7 SEP 2009
34

retention zone. Thus, a liquid that somehow
accidentally penetrates into the passage 92, the slit
91 or even the chamber 90, for example during cleaning
of the cavity 5, will naturally be expelled outside the
injector 9 by circulation of air brought in through the
duct 12.
It is preferable to close the injector
laterally by the end plates 94, 95 (figure 7B), so as
to avoid air leaks between two adjacent modules
(Mi/Mi+l) that would disorganise the injected air flow.
Advantageously, the end plates 94, 95 of the injector
do not completely close off the passage 92 in its part
93 opening up into the cavity 5 (figure 7B); this
minimises the flow disturbance created by the end
plates 94, 95.
As indicated above, a preferred embodiment
of the blower device 8 at a print module (Mi) consists
of creating a rectangular section groove 13 in the body
1 and inserting the air injector 9 into it as shown in
Figure 7A. This embodiment is made possible through the
use of the bottom wall of the groove 13 in the body 1
as the functional surface for the injector; this bottom
wall closes off the expansion chamber 90 of the
injector 9 at the back, so that the air inlet duct 12
can open into it directly. Furthermore, this bottom
wall forms one face of the slit 91 that enables the
pressure loss of the inlet air flow. The section of the
inlet air flow is perfectly defined by the fact that
the bottom wall of the groove 13 acts as a reference
stop on which the back of the injector 9 applies
pressure.
M7 SEP 2009
35

is observed at which the characteristic dimensions, the
uneven environment of the cavity 5 and the
characteristics of the air injection cause the
occurrence of turbulence with a level such that the
effect on the print quality becomes perceptible. For
some types of pattern to be printed, the air velocity
may be increased up to twice this limiting value, while
keeping an acceptable print quality.
In practice, the inventor has observed that
the flow should be as high as possible for a limiting
air velocity before tolerable destabilisation
(corresponding to 0.7 m/s for the curve shown in figure
8A) and at an arbitrary location at the outlet of the
tip 93 from the air injector 9. The inventor has also
observed that the jets 4 located close to the lateral
position at which this velocity is maximum are the
first to destabilise when the flow (or air velocity) is
increased. Thus in practice, for a given air injector 9
configuration, the maximum possible flow will be higher
if the air velocity profile is uniform over the entire
width of the injector, but as long as the maximum
tolerable value is not reached, the air velocity may
have an arbitrary amplitude without disturbing the print quality.
Figure BA is a curve showing the transverse
air velocity profile at the outlet of the tip 93 from
the injector 9, for a flow of 2.5 1/min per module (Mi)
and measured close to the middle of the injector. This
figure 8A shows that the maximum of this transverse
profile is offset slightly towards the jets 4, which

36 E ` SEP 2009

Another embodiment of the injector 9 shown
in figure 7C is particularly interesting; this may be
machined directly in the bulk of a single piece part 1,
for example using wire cutting by spark machining. It
is thus possible to keep the cutting tool perpendicular
to the sides of the module (Mi), cutting being done
along the trajectory shown in dashed lines in figure 7C
that represents the profile of the section of the
injector 9. With this embodiment, the shape of the
section of the injector 9 may easily be adapted to
optimise the determined air outlet function. According
to this embodiment, the end plates 94, 95 may be added
onto and fixed to the sides of the single-piece body 1,
for example by any means known to those skilled in the
art.
Preferred dimension of the air flow:
The compensation of the air deficit related
to aerodynamic effects and air suction through the
gutter 10 preferably requires an inlet air flow of
between 2 and 6 litres per minute and per module (or
for 8 jets) (in other words a volume per minute equal
to 150 to 450 times the volume of the cavity 5 for a
module (Mi)) into the chamber(s) 90. This flow should
preferably be increased by the flow necessary to create
an output air flow intended to push back droplets
generated by splatter under the head (T) Furthermore,
the limiting air velocity at the exit from the injector
9 at which the inventor observed initial
destabilisation of the trajectory of the drops 40, is
about 0.7 m/s (namely 1/2 5th times the velocity of the
inkjet 4) This limiting value before destabilisation

7SEP2009
37

tends to bring air at low velocity between the
deflection electrodes 30.
Figure 8B shows the longitudinal profile of
the air velocity measured at the outlet 93 from the
injector 9, over a trajectory passing through the
maximum of the transverse profile shown in dashed lines
in figure 8A. The measurement is made on a print module
(Mi) with width 1 inserted between two other adjacent
modules (Mi+l and Mi-1), slightly projecting on each
side. This figure SB shows that the longitudinal
profile is approximately uniform over the central 2/3
of the injector 9 and the air velocity reductions
observed on the edges correspond to the flow being
sheltered by the side plates 94,95 of the injector 9.
As explained above, these velocity drops have no
incidence on operation of the system. The low asymmetry
between the left and right parts of the profile are
explained by the position of the air inlet orifice 12
as it enters the expansion chamber 90 of the injector
9, offset by construction.

Preferred air supply device on the input
side of air injectors 9:
Each air injector 9 generates an air flow
independently. The required flow uniformity at each
print module (Mi) in this case is extended to the head
(T) To achieve this, the air supply characteristics to
each injector are identical. The main air flow is
unique for a given head (T) , the distribution to
injectors 9 advantageously being made with balanced
pressure losses. In the preferred embodiment, the

7 S E P 2009
38

tolerable flow unbalance between modules is of the
order of 0.1 1/min. Therefore, the flow adjustment may
be made at the source, globally for a module support
beam (Mi) The input side air treatment preferably
provides perfectly dry air to replace air saturated
with solvent vapour in the cavity 5 and to dry the
electrodes 30,31 and the walls of the cavity. The air
is also preferably filtered to prevent pollution of the
internal elements 10, 20, 30,31 in the cavity and also
ink 40 that returns to the ink circuit because a large
quantity of air is drawn in by the gutters 10 at the
same time as the ink not used for printing that returns
to the ink circuit.
Figure 9 shows a diagram of the air supply
device for a printer with at lEast one wide format
print head (T)
The blower compressor 80 supplies de-oiled
air to an air dryer 81 followed by a particle filter
82. Air at the exit from the filter 82 has the required
quality to supply injectors 9 to each module (Mi) with
a general flow adjustment for each print head (T) This
is followed by the distributor 83 with balanced
pressure losses, and for each module (Mi), the air
injector 9 comprises an expansion and turbulence
damping chamber 90, a slit 91 and the divergent passage
92 leading to the outlet 93.
Figures 10A to 10D illustrate the means
according to the invention used to extract droplets
generated by splatter due to the impact of the drops 40
onto the support (S) from below the wide format print
head (T)
7 SE P 2009
3y

The air flow output from the head (T)
through the outlet slit 6 prevents most of the droplets
generated by splatter from returning inside the head
(T) , in other words in the cavity 5 of each module.
However, since the air flow outlet from the head must
be limited for the reasons mentioned above, the output
air flow may not be sufficiently effective in some
cases in which the dirt appears on the internal edges
of the slit.
The air stream output from the head strikes
the moving support to be printed (S) and creates
turbulence (represented by the spiral lines shown in
figure IDA) that combine with air displaced by the
support (S) The air moves under the head (T) from
electrode blocks 3 to the support beam (P) The
consequence is that the disturbarice of the air under
the head (T) causes redeposition of the droplets
projecting them onto the nearby surfaces and rather on
the output side of the impact point of the drops 40,
namely below the back 1,P of the head and on the
support to be printed, as shown by the arrows shown in
dashed lines in figure 10A. Note that if the support
velocity is low, the air flow output perpendicularly
from the head is preponderant and splatter can be
distributed in all directions, including on the input
side of the head. Thus, firstly the print quality is
degraded, and secondly it becomes necessary to
regularly clean the bottom 1, P of the head (T) and
possibly the inside of the outlet slit, which limits
the availability of the wideformat printer. The
inventor had the idea of extracting the droplets from
El SEP 2009
40

the bottom 1, P of the head (T) before they are
redeposited, to overcome these disadvantages.
Two methods are used for this purpose.
The first method consists of blowing air
through a blower nozzle (BS) between the head (T) and
the support (S) along a direction parallel to the
support and in the direction of its displacement (from
the input side to the output side), as shown in figure
10B. This air flow is combined with the air flow
perpendicular to the support through the outlet slit 6
of the head (T) to create a laminar air current that
forces the turbulence and droplets to move in the downstream direction, outside the print zone. The droplets thus expelled into the environment around the printer are retrieved by the general air extraction system of the wide format printer.
The second method shown diagrammatically in
figure 10C consists of placing suction openings (Basp)
between the head (T) and the support (S) on the
downstream side of the outlet slit 6 for the drops 40.
The suction generates an air flow parallel to the
support that, combined with the air stream output
perpendicular to the slit 6, creates an air current
that causes turbulence and droplets in the suction
openings (Gasp)
Obviously, the two methods can be combined
as shown diagrammatically in figure 10D. Those skilled
in the art will take care to create a specific
adjustment for the blowing or suction intensity so that
it is effective against turbulence and transport of
droplets, without destabilising the end of the

41 7 SEP 2009

trajectory of the print drops 40. This adjustment
depends on the flow and velocity of air output from the
head (T)
The different aspects of the invention that
have just been described apply to (A, B, C) :
A) closing of the ends of the print head
(T) by end plates 70, 71; closing of the orifices that
enable a point or local air inlet in the cavity 5 of
the head, particularly the lateral ends 94, 95 of the
cavity 5.
B) injection of an air flow passing through
the cavity 5 from generation of the inkjet 4 to the
exit of the drops 40, while remaining homogeneous over
the width of the head (T) and circulating approximately
parallel to the jets 4 to prevent the transverse
components from disturbing the trajectory of the drops
40 and degrading the printout.
This air flow has the following
advantageous characteristics:
- it may be dry, and possibly hot, to dry
the inside of the head,
- it may be clean, to prevent pollution of
the cavity 5 and the ink 4, for example by oil and
particles,
- it is preferably injected below the
sensitive zone in which the drops form, to avoid disturbing the charge on the drops 40,
- it is preferably injected above the
deflection plates 31, such that dry air dries them
while circulating,

' h 7 SEP 2009
42

- its flow is preferably greater than 50
times the volume of the cavity per minute to expel
moist air and/or solvent vapours outside the head,
- its flow is sufficient to cancel out the
aerodynamic effects between jets 4 by neutralising the
pressure pressure created inside the cavity 5 of the
head. This flow includes air entrained by the drops
towards the outside of the head, the air drawn in
through the gutters 10 and the additional air creating
an output flow through the slits 6 distributed along
the head (T) In the preferred embodiment of the
invention, this flow is between 50 and 500 times the
camp � o�c ' min te,
its air velocity in the cavity 5 is lower
than the level at which turbulence becomes sufficiently
high to destabilise the trajectory of the drops 40 and
degrade printing. This air velocity in the cavity 5 is
advantageous and must enable it to accept dispersions,
fluctuations and local level of the air flow
generation. In the preferred embodiment of the
invention, this limiting velocity before the drop
trajectories are destabilised is between 1/10 and 1/50
of the velocity of the jet 4,
- its air velocity in the outlet slit 6 of
the head (T) is sufficient to oppose the kinetic,
aerodynamic and electrostatic forces that carry
droplets output from splatter to the inside 5 of the
head. In the preferred embodiment, the velocity is

between 0.05 and 0.5

meters per second.

L7 SEP 2009

43

According to one example, this air flow in
the wide format print head (T) may be generated by a
device comprising the following preferred means:
- a blower compressor 80 generating the
necessary air flow (up to 500 times the volume of the
cavities 5 per minute, namely 6.5 1/min/module) and
capable of supplying one or several print heads (T) ,
- an air dryer 81 on the downstream side of
the compressor 80 so as to obtain a low hygrometry
appropriate for use, possibly adjustable as a function
of the conditions occurring within the cavity 5,
- a filter 82, on the downstream side of
the compressor 80 used to purify air,
- a global air flow adjustment device for a
given print head (T) ,
- a distributor 83 distributing air to each
module (Mi) in the head with a flow for which the
unbalance between modules is less than 0.1 1/min,
- an air injector 9 located in each module
(Mi) and with the same width as the module. Putting
modules (Mi) adjacent to each other within the
framework of a modular wide format ink jet printer,
provides a means of building a blower device 8
distributed homogeneously over the width of the head
(T)
The air injector 9 is preferably composed
of the following means:
- an expansion and turbulence damping
chamber 90, for which one of the dimensions is equal to
the width of the injector 9 and for which the unit
volume is typically of the order of 0.7 cm3,

44

F-7 SEP 2009

- a slit 91 opens up with a pressure loss
function, in which the chamber 90 and the slit 91 is
formed over the entire width of the chamber, and its
cross section has a length/thickness ratio (thickness
corresponding to the cross-section of the slit passage)
of the order of 7. The width/thickness ratio is of the
order of 17,
- a divergent air diffusion passage 92 for
which the divergence half-angle 0 is less than 10°, for
which the length is typically four times greater than
the slit 91; the entry into the passage corresponding
to the outlet from the slit 91 and the outlet 93 opens
up into the cavTity 5 of the head fT),
- two end plates 94,95 laterally closing
the chamber 90, the slit 91 and a part of the passage 92.
C) the displacement of the splatter
droplets present between the print head (T) and the
printed support (S) , by the creation of an air current
under the head, parallel to the movement of the
support, and in the direction of this movement f. This
air current may advantageously be produced by:
- blowing from the nozzle(s) (Bs) located
on the upstream side of the head (T) ,
- suction through the opening(s) located on
the downstream side of the head (T) ,
- a combination of blowing on the upstream
side and suction on the downstream side.
Although the inventioi has been described
with reference to a wide format print head according to
the deviated continuous jet technology, it is equally
applicable to an inkjet technology based on binary
45 E7 SEP 2009

continuous jet or drop on demand. Thus while in the
deviated jet technology only part of the ejected ink
exits from the outlet orifice according to the
invention and is used to print the moving support, in
the drop on demand technology, all ejected ink exits 'from the orifice according to the invention and is used to print the moving support.
The invention can also be applied to a wide
format print head moved over a support either
perpendicular to the direction of the strip or parallel
to it.
The invention can also be applied to so-
called scanning heads
Similarly, the invention can be applied to
!r wide format heads made in a single piece, in other
words in this case, the value X according to the
invention is equal to 1 and a given wide format head
comprises a single print device and a single injector.
The air velocity at the injector outlet is
advantageously less than 1/10th of the velocity of the
jets or the drops.
The air velocity injected into the print
device (Mi) is advantageously equal to at least 1/25th
of the ink ejection velocity.

46 El SEP 2009

WE CLAIM :

1. Wide format multi-jet print head (T),
wider than 1 meter, composed of several X inkjet print
devices (Mi) intended to print on a moving support (S)
In which:
each device comprises:
a body ( 1) intended to extend along an
axis (A-A' ) transverse to the direction of motion (f)
of the support,
- an ink ejector ( 2) fixed to the body ( 1)
dnd adapted to eject ink along an ejection plane (E)
caraf'e' to the axis
- at least one part ( 3,33 ; 1,11) defining
,,n output orifice ( 6) through which at least part of
the ejected ink ( 40) passes to print the moving
Support,
- a cavity ( 5) delimited at least by the
body ( 1) , the ejector ( 2) and the part(s) ( 3,33 ; 1,11)
defining the output orifice,
- an air injector ( 9) adapted to blow air
with a flow approximately parallel to the ink ejection
( 4) plane (E) passing through the cavity ( 5) , from a
Zone below the ejector ( 2) as far as the output orifice
r61
- the devices are in the form of adjacent
i nodules (Mi) along the same transverse axis (A-A') and
Each module producing several m jets ( 4) and comprising
2 block of electrodes ( 3) , in which a single injector
( 9) is common to all modules (M1-I x) , the injected air
:low being uniform over the width of the head (T)

L7 SEP 2009
47

2. Wide format multi-jet print head (T) ,
wider than 1 meter, composed of several X inkjet print
devices (Mi) intended to print a moving support (S) in
which:
- each device comprises:
- a body ( 1) intended to extend along an
axis (A-A' ) transverse to the direction of motion (f)
of the support,
- an ink ejector ( 2) fixed to the body ( 1)
and adapted to eject ink along an ejection plane (E)
parallel to the axis (A-A'),
- at least one part ( 3,33 ; 1,11) defining
an output orifice (6) through which at least part of
the ejected ink (40) passes to print the moving
support,
- a cavity ( 5) delimited by at least the
body ( 1) , the ejector (2) and the part(s) ( 3,33 ; 1, 11)
defining the output orifice,
- an air injector ( 9) adapted to blow air
with a flow approximately parallel to the ejection
plane (E) of the ink ( 4) passing through the cavity
( 5) , from a zone below the ejector (2) as far as the
output orifice ( 6) ;
- the print devices are in the form of adjacent
modules (Mi) along the same transverse axis (A-A') ,
each module (Mi) producing several m jets ( 4) and
comprising a block of electrodes ( 3i) and an air
injector ( 9i), the injected air flow being uniform over
the width of the head (T) , namely the air flow
difference ZI between two injectors ( 9i) is less than or
equal to 0.1 1/min.

C7 SEP 2009
4-8

3. Wide format multi--jet print head (T)
according to claim 2, in which the air inlet is common
to X air injectors ( 9i)

4. Wide format multi-jet print head (T)
according to one of claims 1 to 3, in which an end
plate ( 70, 71) is arranged at transverse ends of the
head (T) so as to transversally close the cavities ( 5)
of the two devices (Ml, Mx) the furthest away from each
other.

5. Wide format multi-jet print head (T)

according to one of claims 1 to
print device, two parts ( 1, 11
output orifice forming a slit (
formed by part of the body (1)
formed by a part forming a toe

4, in which, for each
; 3, 33) define the
6) , one (1, 11) being
and the other being
(33) of the block of

electrodes ( 3) , the block of electrodes ( 3) having an

Operating position such that at least one input side

part (30, 31) is located in the ejection plane (E) and

such that the spacing between the output side toe (33)

and the body defines the width of the output slit (6);

the volume delimited by the body ( 1) , the ejector ( 2)

and the block of electrodes ( 3) in operating position

defining the cavity (5) opening up on the output slit

( 6)

6. Wide format multi-jet print head (T)

according to one of claims 1 to 5, in which, for each

print device, the block of electrodes ( 3) is pivoting

about the ink ejector ( 2) between its operating

L-7SEPZ009
49 1

position and an extreme raised position to enable
maintenance of the ink ejector ( 2) and/or the block of
electrodes ( 3) and/or the air injector ( 9)

7. Wide format multi-jet print head (T)
according to one of claims 1 to 6, in which, for each
print device, the ink ejector ( 2) is adapted to eject
ink in the form of continuous jets ( 4) , the break point
of each jet being placed close to the middle of charge
electrodes ( 30) of the electrodes block ( 3) and in
which the air injector ( 9) is positioned so as to blow
air below the charge electrodes ( 30) and above the
deflection electrodes ( 31) of the block ( 3)

8. Wide format multi-jet print head (T)
according to one of claims 1 to 7, in which, for each
print device, the air injector (9) is positioned so as
to blow air between the ejection plane (E) of the ink
jets and the body ( 1)

9. Wide format multi-jet print head (T)
according to one of claims 1 to 8, in which, for each
print device, the air velocity at the injector outlet
( 9) is less than 1/10th of the velocity of the ink jets
( 4, 40) or the ink drops.

10. Wide format multi-jet print head (T)
according to one of claims 1 to 9, in which for each
print device, the blown air is dry air.

30 7 SEP 2009

11. Wide format multi-jet print head (T)
according to one of the previous claims, in which for
each print device, the blown air is filtered air.

12. Wide format multi-jet print head (T)
according to one of the previous claims, in which for
each print device, the air injector ( 9) is fixed to the
body ( 1)

13. Wide format multi-jet print head (T)
according to claim 12, in which, for each print device,
the air injector ( 9) is inserted into a groove ( 13)
formed in the body ( 1)

14. Wide format multi-jet print head (T)
according to one of claims 1 to 11, in which for each
print device, the air injector ( 9) forms an integral
part of the body ( 1)

15. Wide format multi-jet print head (T)
according to one of claims 1 to 14, in which, for each
pri rt devllee, the air flora from the air injector is
between 50 and 500 times the cavity volume per minute.

16. Wide format multi-jet print head (T)
according to one of claims 1 to 15, in which, for each
print device, the air velocity injected is equal to at
least 1/25th of the ink ejection velocity.

17. Wide format multi-jet print head (T)
according to one of claims 1 to 16, in which, for each

.7 SEP 2009

print device, the air injector ( 9) comprises an inner
chamber (90) adapted to be directly connected to an air
inlet duct ( 12) and to expand air and to damp
turbulence of incoming air.

18. Wide format multi-jet print head (T)
according to 17, in which the air injector ( 9)
comprises an inner channel ( 92) on the output side of
the inner chamber ( 90), forming a passage a profile
identical over its entire length (1) but diverging in
cross section of the injector, as far as the injector
output ( 93) in the cavity ( 5)

19. Wide format multi-jet print head (T)
according to claim 18, in which the divergence half-
angle 8 passage ( 92) is less than 10°.

20. Wide format multi-jet print head (T)
according to claim 18 or 19, in which the air injector
comprises a slit ( 91) connecting the inner chamber ( 90)
to the passage ( 92) and making the air originating from
the chamber approximately laminar.

7 SEP 2009
52

21. Wide format multi-jet print head (T) according
to claim 20, in which two end plates (94, 95) laterally
closed the chamber (90), the slit (91) and a part of the
passage (92) of the injector (9)