Gas flush to eliminate residual bubbles

In a inkjet print cartridge ink flows from the reservoir around the edge of the silicon substrate before being ejected out of the nozzles. During operation, warm thermal boundary layers of ink form adjacent the substrate and dissolved gases in the thermal boundary layer of the ink form the bubbles. If the bubbles to grow larger than the diameter of subsequent ink passageways these bubbles choke the flow of ink to the vaporization chambers. This results in causing some of the nozzles of the printhead to become temporarily inoperable. The disclosure describes a method of avoiding such a malfunction in a liquid inkjet printing system by providing a method for reducing residual air bubbles in an inkjet print cartridge by flushing the empty cartridge by passing carbon dioxide through the fill port or the ink ejection nozzles prior to filling the print cartridge with ink and thereby eliminating residual air bubbles from the print cartridge when the print cartridge is filled with ink.

FIELD OF THE INVENTION 
The present invention generally relates to inkjet and other types of 
printers and, more particularly, to the ink flow to the printhead portion 
of an inkjet printer. 
BACKGROUND OF THE INVENTION 
An ink jet printer forms a printed image by printing a pattern of 
individual dots at particular locations of an array defined for the 
printing medium. The locations are conveniently visualized as being small 
dots in a rectilinear array. The locations are sometimes called "dot 
locations", "dot positions", or "pixels". Thus, the printing operation can 
be viewed as the filling of a pattern of dot locations with dots of ink. 
Thermal inkjet print cartridges operate by rapidly heating a small volume 
of ink to cause the ink to vaporize and be ejected through one of a 
plurality of orifices so as to print a dot of ink on a recording medium, 
such as a sheet of paper. Typically, the orifices are arranged in one or 
more linear arrays in a nozzle member. The properly sequenced ejection of 
ink from each orifice causes characters or other images to be printed upon 
the paper as the printhead is moved relative to the paper. The paper is 
typically shifted each time the printhead has moved across the paper. The 
thermal inkjet printer is fast and quiet, as only the ink strikes the 
paper. These printers produce high quality printing and can be made both 
compact and affordable. 
An inkjet printhead generally includes: (1) ink channels to supply ink from 
an ink reservoir to each vaporization chamber proximate to an orifice; (2) 
a metal orifice plate or nozzle member in which the orifices are formed in 
the required pattern; and (3) a silicon substrate containing a series of 
thin film resistors, one resistor per vaporization chamber. 
To print a single dot of ink, an electrical current from an external power 
supply is passed through a selected thin film resistor. The resistor is 
then heated, in turn superheating a thin layer of the adjacent ink within 
a vaporization chamber, causing explosive vaporization, and, consequently, 
causing a drop of ink to be ejected through an associated nozzle onto the 
paper. 
A concern with inkjet printing is the sufficiency of ink flow to the paper 
or other print media. Print quality is a function of ink flow through the 
printhead. Too little ink on the paper or other media to be printed upon 
produces faded and hard-to-read documents. 
In an inkjet printhead ink is fed from an ink reservoir integral to the 
printhead or an "off-axis" ink reservoir which feeds ink to the printhead 
via tubes connecting the printhead and reservoir. Ink is then fed to the 
various vaporization chambers either through an elongated hole formed in 
the center of the bottom of the substrate, "center feed", or around the 
outer edges of the substrate, "edge feed". In center feed the ink then 
flows through a central slot in the substrate into a central manifold area 
formed in a barrier layer between the substrate and a nozzle member, then 
into a plurality of ink channels, and finally into the various 
vaporization chambers. In edge feed ink from the ink reservoir flows 
around the outer edges of the substrate into the ink channels and finally 
into the vaporization chambers. In either center feed or edge feed, the 
flow path from the ink reservoir and the manifold inherently provides 
restrictions on ink flow to the firing chambers. 
Air and other gas bubbles can cause major problems in ink delivery systems. 
Ink delivery systems are capable of releasing gasses and generating 
bubbles, thereby causing systems to get clogged and degraded by bubbles. 
In the design of a good ink delivery system, it is important that 
techniques for eliminating or reducing bubble problems be considered. Most 
fluids exposed to the atmosphere contain dissolved gases in amounts 
varying with the temperature. The amount of gas that a liquid can hold 
depends on temperature and pressure, but also depends on the extent of 
mixing between the gas and liquid and the opportunities the gas has had to 
escape. 
Changes in atmospheric pressure normally can be neglected because 
atmospheric pressure stays fairly constant. However, temperature does 
change within an inkjet cartridge to make an appreciable difference in the 
amount of gas that can be contained in the ink. Bubbles have less tendency 
to originate at low temperatures, and their growth will also be slower. 
The colder a liquid, the less kinetic energy is available and the longer 
it takes to gather together the necessary energy at specific location 
where the bubble begins to form. 
Most fluids exposed to the atmosphere contain dissolved gases in amounts 
proportional to the temperature of the fluid itself. The colder the fluid, 
the greater the capacity to absorb gases. If a fluid saturated with gas is 
heated, the dissolved gases are no longer in equilibrium and tend to 
diffuse out of solution. If nucleation seed sites are present along the 
surface containing the fluid or within the fluid, bubbles will form, and 
as the fluid temperature rises further, these bubbles grow larger. 
Bubbles are not only made of air, but are also made of water vapor and 
vapors from other ink-vehicle constituents. However, the behavior of all 
liquids are similar, the hotter the liquid becomes, the less gas it can 
hold. Both gas release and vapor generation cause bubbles to start and 
grow as temperature rises. One can reasonably assume the gases inside the 
bubbles in a water-based ink are always saturated with water vapor. Thus, 
bubbles are made up both of gases, mostly air, and of ink vehicle vapor, 
mostly water. At room temperature, water vapor is an almost negligible 
part of the gas in a bubble. However, at 50.degree. C., the temperature at 
which an inkjet printhead might operate, water vapor adds importantly to 
the volume of a bubble. As the temperature rises, the water vapor content 
of the bubbles increases much more rapidly with temperature than does the 
air content. 
The best conditions for bubble generation are the simultaneous presence of 
(1) generating or "seed" sites, (2) ink flow and (3) bubble accumulators. 
These three mechanisms work together to produce large bubbles that clog 
and stop flow in ink delivery systems. When air comes back out of solution 
as bubbles, it does so at preferential locations, or generation or 
nucleation sites. Bubbles like to start at edges and corners or at surface 
scratches, roughness, or imperfections. Very small bubbles tend to stick 
to the surfaces and resist floating or being swept along in a current of 
ink. When the bubbles get larger, they are more apt to break loose and 
move along. However, if the bubbles form in a corner or other 
out-of-the-way location, it is almost impossible to dislodge them by ink 
currents. 
While bubbles may not start at gas generating sites when the ink is not 
flowing past those sites, when the ink is moving, the bubble generation 
site is exposed to a much larger volume of ink containing dissolved gas 
molecules. As ink flows past the gas generating site, gas molecules can be 
brought out of solution to form a bubble and grow; while if the ink was 
not flowing this would happen less rapidly. 
The third contributor to bubble generation is the accumulator or bubble 
trap, which can be defined as any expansion and subsequent narrowing along 
an ink passage. This configuration amounts to a chamber on the ink flow 
path with an entrance and an exit. The average ink flow rate, in terms of 
volume ink per cross section of area per second, is smaller within the 
chamber than at the entrance or at the exit. The entrance edge of the 
chamber will act as a gas generating site because of its sharpness and 
because of the discontinuity of ink flow over the edge. Bubbles will be 
generated at this site, and when they become large enough they get moved 
along toward the exit duct until the exit duct is blocked. Then, unless 
the system can generate enough pressure to push the bubble through, the 
ink delivery system will become clogged and ink delivery will be shut 
down. Thus, the chamber allows bubbles to grow larger than the diameter of 
subsequent ink passageways which may then become blocked. 
During the ink filling and priming process, bubbles are left behind in the 
print cartridge. They are left in the manifold region, between the filters 
92 and nozzles, where they can interfere with printhead reliability by 
causing intermittent nozzle problems and local or even global starvation. 
Bubbles left behind downstream of the filters 92 can be shocked through 
the filters 92 and into the manifold. 
Previous solutions included eliminating bubble traps in the manifold and 
filling and priming slowly. Unfortunately, design and manufacturing 
constraints make eliminating bubble traps prohibitively difficult. Filling 
and priming slowly enough to assure no bubble trapping would tend to 
adversely affect manufacturing cycle time. In addition, effectiveness of 
the slow fill and prime is negated by the bubble traps. 
Accordingly, there is a need for a process to eliminate the residual air 
left in the print cartridge after the ink filling and priming process. 
SUMMARY OF THE INVENTION 
In a inkjet print cartridge ink flows from the ink reservoir through 
filters, through a standpipe, through or around the silicon substrate, 
through ink channels and into vaporization chambers for ejection out of 
the nozzles. During operation, warm thermal boundary layers of ink form 
adjacent the substrate and dissolved gases in the thermal boundary layer 
of the ink form the bubbles. Also, bubbles tend to form at the corners and 
edges of the walls along the ink flow path. If the bubbles grow larger 
than the diameter of subsequent ink passageways these bubbles choke the 
flow of ink to the vaporization chambers. This results in causing some of 
the nozzles of the printhead to become temporarily inoperable. 
The present invention provides a method of avoiding such a malfunction in a 
liquid inkjet printing system by providing a method for reducing residual 
air bubbles in an inkjet print cartridge by flushing the empty cartridge 
by passing carbon dioxide through the fill port or the ink ejection 
nozzles prior to filling the print cartridge with ink and thereby 
eliminating residual air bubbles from the print cartridge when the print 
cartridge is filled with ink.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, reference numeral 10 generally indicates an inkjet 
print cartridge for mounting in the carriage of an inkjet printer. The 
inkjet print cartridge 10 includes a printhead 14 and an ink reservoir 12, 
which may be a "integral" reservoir, "snap-on" reservoir, or a "reservoir" 
for receiving an ink from an off-axis ink reservoir. Print cartridge 10 
includes snout 11 which contains an internal standpipe 51 (shown in FIG. 
8) for transporting ink to the printhead from the reservoir 12. The 
printhead 14 includes a nozzle member 16 comprising nozzles or orifices 17 
formed in a circuit 18. The circuit 18 includes conductive traces (not 
shown) which are connected to the substrate electrodes at windows 22, 24 
and which are terminated by contact pads 20 designed to interconnect with 
printer providing externally generated energization signals to the 
printhead for firing resistors to eject ink drops. Printhead 14 has 
affixed to the back of the circuit 18 a silicon substrate 28 (not shown) 
containing a plurality of individually energizable thin film resistors. 
Each resistor is located generally behind a single orifice 17 and acts as 
an ohmic heater when selectively energized by one or more pulses applied 
sequentially or simultaneously to one or more of the contact pads 20. 
FIG. 2 shows the print cartridge 10 of FIG. 1 with the printhead 14 removed 
to reveal the headland pattern 50 used in providing a seal between the 
printhead 14 and the print cartridge body 15. FIG. 3 shows the headland 
area in an enlarged top plan view. Shown in FIGS. 2 and 3 is a manifold 52 
in the print cartridge 10 for allowing ink from the ink reservoir 12 to 
flow to a chamber adjacent the back surface of the printhead 14. The 
headland pattern 50 formed on the print cartridge 10 is configured so that 
a bead of epoxy adhesive (not shown) dispensed on the inner raised walls 
54 and across the wall openings 55 and 56 will form an ink seal between 
the body 15 of the print cartridge 10 and the back of the printhead 14 
when the printhead 14 is pressed into place against the headland pattern 
50. 
Referring to FIG. 4, shown is an enlarged view of a single vaporization 
chamber 72, thin film resistor 70, and frustum shaped orifice 17 after the 
substrate is secured to the back of the circuit 18 via the thin adhesive 
layer 84. Silicon substrate 28 has formed on it thin film resistors 70 
formed in the barrier layer 30. Also formed on the substrate 28 are 
electrodes (not shown) for connection to the conductive traces (not shown) 
on the circuit 18. Also formed on the surface of the substrate 28 is the 
barrier layer 30 in which is formed the vaporization chambers 72 and ink 
channels 80. A side edge of the substrate 28 is shown as edge 86. In 
operation, ink flows from the ink reservoir 12 around the side edge 86 of 
the substrate 28, and into the ink channel 80 and associated vaporization 
chamber 72, as shown by the arrow 88. Upon energization of the thin film 
resistor 70, a thin layer of the adjacent ink is superheated, causing 
explosive vaporization and, consequently, causing a droplet of ink to be 
ejected through the orifice 17. The vaporization chamber 72 is then 
refilled by capillary action. 
Shown in FIG. 5 is a side elevational cross-sectional view showing a 
portion of the adhesive seal 90, applied to the inner raised wall 54 
portion of the print cartridge body 15 surrounding the substrate 28 and 
showing the substrate 28 being bonded to a central portion of the circuit 
18 on the top surface 84 of the barrier layer 30 containing the ink 
channels and vaporization chambers 72. A portion of the plastic body 15 of 
the printhead cartridge 10, including raised walls 54 is also shown. 
FIG. 5 also illustrates how ink 88 from the ink reservoir 12 flows through 
the standpipe 51 formed in the print cartridge 10 and flows around the 
edges 86 of the substrate 28 through ink channels 80 into the vaporization 
chambers 72. Thin film resistors 70 are shown within the vaporization 
chambers 72. When the resistors 70 are energized, the ink within the 
vaporization chambers 72 are ejected, as illustrated by the emitted drops 
of ink 101, 102. 
In FIG. 6, vaporization chambers 72 and ink channels 80 are shown formed in 
barrier layer 30. Ink channels 80 provide an ink path between the source 
of ink and the vaporization chambers 72. The flow of ink into the ink 
channels 80 and into the vaporization chambers 72 is around the long side 
edges 86 of the substrate 28 and into the ink channels 80. The relatively 
narrow constriction points or pinch point gaps 145 created by the pinch 
points 146 in the ink channels 80 provide viscous damping during refill of 
the vaporization chambers 72 after firing. The pinch points 146 help 
control ink blow-back and bubble collapse after firing to improve the 
uniformity of ink drop ejection. The addition of "peninsulas" 149 
extending from the barrier body out to the edge of the substrate provided 
fluidic isolation of the vaporization chambers 72 from each other. The 
definition of the various printhead dimensions are provided in Table I. 
TABLE I 
______________________________________ 
DEFINITION OF INK CHAMBER DEFINITIONS 
Dimension Definition 
______________________________________ 
A Substrate Thickness 
B Barrier Thickness 
C Nozzle Member Thickness 
D Orifice/Resistor Pitch 
E Resistor/Orifice Offset 
F Resistor Length 
G Resistor Width 
H Nozzle Entrance Diameter 
I Nozzle Exit Diameter 
J Chamber Length 
K Chamber Width 
L Chamber Gap 
M Channel Length 
N Channel Width 
O Barrier Width 
U Shelf Length 
______________________________________ 
The frequency limit of a thermal inkjet print cartridge is limited by 
resistance in the flow of ink to the nozzle. However, some resistance in 
ink flow is necessary to damp meniscus oscillation. Ink flow resistance is 
intentionally controlled by the pinch point gap 145 gap adjacent the 
resistor. An additional component to the fluid impedance is the entrance 
to the firing chamber. The entrance comprises a thin region between the 
nozzle member 16 and the substrate 28 and its height is essentially a 
function of the thickness of the barrier layer 30. This region has high 
fluid impedance, since its height is small. The dimensions of the various 
elements formed in the barrier layer 30 shown in FIG. 6 are identified in 
Table II below. 
TABLE 2 
______________________________________ 
INK CHAMBER DIMENSIONS IN MICRONS 
Dimension 
Minimum Nominal Maximum 
______________________________________ 
A 600 625 650 
B 19 25 32 
C 25 50 75 
D 84.7 
E 1 1.73 2 
F 30 35 40 
G 30 35 40 
I 20 28 40 
J 45 51 75 
K 45 51 55 
L 0 8 10 
M 20 25 50 
N 15 30 55 
O 10 25 40 
U 0 90-130 270 
______________________________________ 
The nozzle member 16 in circuit 18 is positioned over the substrate 
structure 28 and barrier layer 30 to form a printhead 14. The nozzles 17 
are aligned over the vaporization chambers 72. Preferred dimensions A, B, 
and C (not shown in FIG. 6) are defined as follows: dimension A is the 
thickness of the substrate 28, dimension B is the thickness of the barrier 
layer 30, and dimension C is the thickness of the nozzle member 16. 
Further details of the printhead architecture are provided in U.S. 
application Ser. No. 08/319,893, filed Oct. 6, 1994, entitled "Barrier 
Architecture for Inkjet Printhead;" which is herein incorporated by 
reference. 
From Table II it can be seen that the nominal channel width of 30 microns 
and nominal channel height of 25 microns, allows for channel blockage by 
very small bubble diameters. 
FIG. 7 shows how ink containing dissolved gases flows from the ink 
reservoir 12 of the ink cartridge 10 through filters 92 along ink flow 
path 88 through standpipe 51 in the snout 11, into manifold 52, around the 
edge 86 of substrate 28, along ink channels 80 and into vaporization 
chambers 72 before being ejected out of the nozzles 17. During operation, 
warm thermal boundary layers of ink 88 form adjacent the substrate 28. 
Therefore, dissolved gases in the thermal boundary layer of the ink 88 
behind the substrate 28 tend to form and diffuse into the bubbles 89. 
Also, bubbles 91 tend to form at the corners and edges of the walls 55 
along the ink flow path 88. In addition, the region between the manifold 
52 and substrate 28 acts as an accumulator or bubble trap. This 
configuration amounts to a chamber on the ink flow path 88 with an 
entrance and an exit. The average ink flow rate, in terms of volume ink 
per cross section of area per second, is smaller within the chamber than 
at the entrance or at the exit. The entrance edge of the vaporization 
chamber 72 will act as a gas generating site because of its sharpness and 
because of the discontinuity of ink flow over the edge. Bubbles will be 
generated in this chamber and when they become large enough they get moved 
along toward the ink chamber. If the chamber allows bubbles to grow larger 
than the diameter of subsequent ink passageways which may then become 
blocked. These bubbles choke the flow of ink to the vaporization chambers 
72, especially at high firing frequencies, i. e., greater than 8 kHz. This 
results in causing some of the nozzles 17 to temporarily become 
inoperable. Although the total amount of dissolved gases contained within 
the fluid volume of the boundary layer is small, in reality, all of the 
ink in the reservoir 12 will eventually flow along ink path 88 over the 
lifetime of the print cartridge 10. If all, or even some, of the dissolved 
gas contained within the ink reservoir 12 outgasses, substantial bubbles 
will form. When the bubbles become large enough they get moved along 
toward the ink chamber. If the bubbles grow larger than the diameter of 
subsequent ink passageways, the passageways may become blocked and choke 
the flow of ink to the vaporization chambers 72. This results in causing 
some of the nozzles 17 to temporarily become inoperable. 
Bubbles in the ink near the printhead 14 of an inkjet print cartridge 10 is 
one of the most critical problems that impairs the performance of the 
print cartridge. Bubbles arise from several causes: (1) bubbles are 
trapped in the ink feed channels during filling and priming of the print 
cartridge and (2) bubbles are formed at bubble "seed sites" in the fibrous 
carbon-filled material of walls 57, 58 of the print cartridge body 15 
during operation. As the ink is heated during printing, dissolved air 
outgasses from the ink and is accreted onto these trapped bubbles and seed 
sites, resulting in bubbles that grow over time. The bubbles block the 
nozzles 17 from ejecting ink and if the blockage is large enough it can 
cause the entire printhead 14 to suffer "global starvation." Bubbles have 
been a problem in the past, but they are a much more serious problem in a 
600 dot per inch ("dpi") printhead. This is due primarily to the reduced 
size of the ink flow channels 80 and nozzles 17 diameter as set forth in 
the above description with respect to FIG. 6 and accompanying Table II. 
However, this is also due to the higher firing frequencies and consequent 
flow rates of ink ejection. Because the venturi forces that pull bubbles 
toward the firing chambers are now higher, the tendency for bubbles to 
interfere with nozzle operation is greater. 
Several methods of controlling bubbles in inkjet print cartridges 10 have 
been employed including: (1) making the ink feed channel more 
"bubble-tolerant" by deepening the headland area 50 behind the printhead 
14 to make room for bubbles to float up and away from the nozzles 17, and 
(2) flushing the empty cartridge with carbon dioxide prior to fill. 
The printhead was redesigned to be more tolerant of existing bubbles. The 
most critical areas for the design is the area around the filters, the 
standpipe, and the headland. The goals are to minimize dead spaces, 
streamline the geometry for fluid flow and allow bubbles to easily escape 
from the printhead area. Since the pen prints with the nozzles downward, 
the ink manifold behind the printhead substrate was redesigned. The 
manifold was made deeper, to allow a space for bubbles to drift upward and 
away from the nozzles. See U.S. patent application Ser. No. 08/550,143, 
filed Oct. 30, 1995, entitled "Bubble Tolerant Manifold Design for Inkjet 
Cartridge". 
The continued presence of trapped bubbles despite the above efforts, 
resulted in several other attempted solutions. It was discovered that by 
incorporating a carbon dioxide flush of the print cartridge 10, trapped 
bubbles were further eliminated. The print cartridge is first filled with 
carbon dioxide gas, and then filled with ink. By flushing the print 
cartridge 10 with carbon dioxide prior to ink filling and priming, the 
residual bubbles are carbon dioxide gas, rather than air, which have a 
much higher solubility in the ink than bubbles composed of air (oxygen and 
nitrogen) and the bubbles quickly dissolve and disappear. 
This elimination of residual bubbles by carbon dioxide gas flush turned out 
to be effective for both anionic inks, which were able to dissolve up to 
220 percent of their volume in carbon dioxide gas and cationic inks which 
were able to dissolve 73 percent of their volume in carbon dioxide gas. 
Since the total gas trapped in a print cartridge during the filling and 
priming process is approximately 1 to 2 cc in volume versus approximately 
50 cc of ink, total absorption of carbon dioxide gas is easily possible. 
Further experiments showed that carbon dioxide flush is very effective; 
entrapped bubbles were virtually eliminated within an hour of filling and 
priming and had disappeared entirely within 24 hours. 
Shown in FIG. 8 is a schematic diagram showing the carbon dioxide gas 
flushing apparatus. The carbon dioxide source can be located off-line. The 
flushing apparatus is very compact and can be located on the print 
cartridge assembly line immediately before the ink fill station. The 
carbon dioxide gas is provided from carbon dioxide source 202 and passes 
through pressure reducer 204, carbon dioxide warmer 205, and then into 
supply tubes 206 and 208, and then passes through pressure and flow 
controllers 210 and 212, respectively. Supply tube 206 provides carbon 
dioxide under control of valve 210 to headland slide mechanism 214 and 
supply tube 208 provides carbon dioxide under control of valve 212 to fill 
port slide mechanism 216. The pressure of the carbon dioxide gas at the 
headland slide 214 is approximately 25 to 40 psi and the pressure at the 
fill port slide 216 is approximately 15 to 30 psi, respectively. 
Headland slide mechanism 214 lowers to engage the print cartridge printhead 
or headland area 220. Headland slide 214 has a means of tolerance 
compliance designed into it so it will locate off of features on the print 
cartridge 10 as it comes down to address the print cartridge 10 on the 
pallet 222. The headland slide 214 has a boot 218 that seals onto the 
nozzles 17 in headland area 220 of the print cartridge 10 to allow carbon 
dioxide to be passed into the print cartridge through nozzles 17. The 
headland slide 214 can alternatively be plumbed to apply a vacuum to 
nozzles 17 via a valve to headland area 220 in accordance with an 
alternative procedure set forth below. 
Fill port slide mechanism 216 engages the ink fill port 224 of print 
cartridge 10. The fill port slide 216 can be retracted as the fill port 
slide comes down and is used for alignment while the needle comes down, 
and also as a means to plug the port. The fill needle 228 is mounted to 
the fill port slide 216, which aligns off the headland slide 214. In a 
first position, the fill port slide 216 is lowered so that fill needle 228 
passes through fill port 224 and the end of fill needle 228 is located 
toward the bottom of cartridge 10. In this first position, an annular ring 
exists between fill needle 228 and fill port 224 to allow air and carbon 
dioxide to escape from the cartridge 10 through fill port 224. Fill port 
slide 216 is further lowered to a second position, so that tapered top 
section 226 of the fill port needle 228 seals with the ink fill port 224 
to plug the print cartridge fill port 224 of print cartridge 10. 
Referring to FIG. 9, in the preferred embodiment, the process is as 
follows. In step 301, begin carbon dioxide pressure at headland slide 214. 
In step 302, lower headland slide 214 to engage boot 218 to the nozzles 17 
in headland 220 of print cartridge 10 and begin carbon dioxide fill at 
headland 220. In step 303, lower fill port slide 216 to its first position 
so that fill needle 228 passes through fill port 224 and the end of fill 
needle 228 is located toward the bottom of cartridge 10. The carbon 
dioxide film needle 228 engages the fill port 224 leaving an annular ring 
at the top open. In step 304, carbon dioxide pressure is begun at the fill 
needle 228 and the carbon dioxide begins to purge the print cartridge of 
air. The air in the print cartridge mostly exits through the annular ring 
at the top of the fill port. In step 305, continue carbon dioxide purge 
for approximately 2 to 6 seconds. In step 306, discontinue carbon dioxide 
pressure at headland slide. In step 307, discontinue carbon dioxide purge 
at fill needle 228. In step 308, lower fill port slide 216 to its second 
position so that tapered end 226 seals fill port 224. 
The boot 218 of headland slide 214 continues to seal the headland area 220 
and tapered end 226 continues to seal fill port 224 until the print 
cartridge is ready to be filled. 
Referring to FIG. 10, in an alternative embodiment, the process is as 
follows. In step 401, begin pulling a vacuum at headland slide 214. In 
step 402, lower headland slide 214 to engage boot 218 to headland 220 of 
print cartridge 10 and begin vacuum at headland 220. In step 403, lower 
fill port slide 216 to its first position so that fill needle 228 passes 
through fill port 224 and the end of fill needle 228 is located toward the 
bottom of cartridge 10. The carbon dioxide fill needle 228 engages the 
fill port 224 leaving an annular ring at the top open. In step 404, carbon 
dioxide pressure is begun at the fill needle 228 and the carbon dioxide 
begins to purge the print cartridge of air. The air in the print cartridge 
mostly exits through the annular ring at the top of the fill port. In step 
405, continue carbon dioxide purge for approximately 2 to 6 seconds. In 
step 406, lower fill port slide 216 to its second position so that tapered 
end 226 seals fill port 224. In step 407, discontinue vacuum at headland 
slide. In step 408, Discontinue carbon dioxide purge at fill needle 228. 
The boot 218 of headland slide 214 continues to seal the headland area 220 
and tapered end 226 continues to seal fill port 224 until the print 
cartridge is ready to be filled. 
The carbon dioxide flush apparatus can hold a carbon dioxide flushed print 
cartridge sealed for up to 15 minutes without loss of the positive effects 
of the flush; whereas a flushed, unsealed at the fill port 224 print 
cartridge 10 would lose the benefits of carbon dioxide flush after only 10 
seconds. Carbon dioxide, being denser than air, tends to escape out the 
ink fill hole and "slump" down out of the manifold area, thus leaving air, 
not carbon dioxide, to be trapped as bubbles upon print cartridge priming. 
Prior to the use of carbon dioxide flush, residual bubbles remained in the 
print cartridges. Eliminating the residual bubbles has had a dramatic 
impact on long term print cartridge reliability. 
It will be understood that the foregoing disclosure is intended to be 
merely exemplary, and not to limit the scope of the invention, which is to 
be determined by reference to the appended claims.