EP0709212A1

EP0709212A1 - Pen-based degassing scheme for ink jet pens

Info

Publication number: EP0709212A1
Application number: EP95305643A
Authority: EP
Inventors: Christopher S. Magirl
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1994-10-31
Filing date: 1995-08-14
Publication date: 1996-05-01
Also published as: JPH08207312A

Abstract

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 primary ink reservoir, transporting ink from the primary reservoir to the vaporization chamber, while passing the liquid ink past a degassing station. A printhead mounted on a carriage is disclosed having a nozzle array and providing an ink vaporization chamber with an activation element therein for expelling a drop of ink from a nozzle. The vaporization chamber is filled with the ink after the ink has passed the degassing station.

Description

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 fitting 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 to a 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. The flow path from the ink reservoir and the manifold inherently provide some restriction 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. Under ordinary circumstances, all liquids, including ink, contain dissolved air and sometimes other dissolved gasses. 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 of 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 reasonable 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° 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 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 comers 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 could not happen.
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.
One solution is to degas the ink immediately before fitting the ink cartridge; however, some intrinsic difficulties arise when taking this approach. The most obvious problem is that the print cartridge body itself is not impervious to the diffusion of gases. Given enough time, the ink in the print cartridge will eventually gain back most, if not all, of the dissolved gases removed before ink fill. Ideally, the ink degassing process would occur immediately before firing ink from the substrate, in other words, inside the print cartridge itself.

SUMMARY OF THE INVENTION

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 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 primary ink reservoir, mounting a printhead having a nozzle array on a carriage, providing an ink vaporization chamber with an activation element therein for expelling a drop of ink from a nozzle in the nozzle array, transporting ink from the primary reservoir to the vaporization chamber, said transporting step including passing the liquid ink past a degassing station, and filling the vaporization chamber with the ink, said filling step occurring after said passing step.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be further understood by reference to the following description and attached drawings which illustrate the preferred embodiment.
Fig. 1 is a perspective view of an inkjet print cartridge.
Fig. 2 is a perspective view of the headland area of the inkjet print cartridge of Fig. 1.
Fig. 3 is a top plan view of the headland area of the inkjet print cartridge of Fig. 7.
Fig. 4 is a top perspective view, partially cut away, of a portion of the printhead assembly showing the relationship of an orifice with respect to a vaporization chamber, a heater resistor, and an edge of the substrate.
Fig. 5 is a schematic cross-sectional view of a printhead assembly and the print cartridge as well as the ink flow path around the edges of the substrate.
Fig. 6 is a top plan view of a magnified portion of the printhead assembly showing the relationship of ink channels, vaporization chambers, heater resistors, the barrier layer and an edge of the substrate.
Fig. 7 is a magnified, partially cut away view in perspective of the portion of the circuit or nozzle member after the nozzle member has been properly positioned over the substrate structure to form a printhead.
Fig. 8 is a schematic diagram showing an print cartridge-based degassing mechanism shown immediately upstream of the printhead.
Fig. 9 is a schematic diagram showing an an off-axis ink supply system.
Fig. 10 is a perspective view of an inkjet print cartridge for use with an off-axis ink supply system.

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 15 (shown in Fig. 8) for transporting ink to the printhead from the reservoir 12. The printhead 14 includes a nozzle member 16 comprising holes 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 printhead body. Fig. 3 shows the headland area in an enlarged top plan view. Shown in Figs. 1 and 2 is a central slot 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 and wall openings 55, 56, surrounding the substrate 28 and showing the substrate 28 being adhesively secured to a central portion of the circuit 18 by the thin adhesive layer 84 on the top surface of the barrier layer 30 containing the ink channels and vaporization chambers 72. A portion of the plastic body 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 central slot 52 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 102.
Ink flows from the reservoir 12 through filters (not shown) through the standpipe (shown in Fig. 8) in the snout 11, the slot 52 and around the edge 86 of the silicon substrate 28 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 the bubbles 89. This results in causing some of the nozzles 17 temporarily becoming 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 through the standpipe (shown in Fig. 8), the slot 52 and across the substrate 28 over the lifetime of the print cartridge 10. If all, or even some, of the dissolved gases contained within the ink reservoir 12 outgas, substantial bubbles would form. Also, to a lesser extent, bubbles 91 tend to form at the corners and edges of the walls 55 along the ink flow path 88 in the central slot 52. In addition, the region between the slot 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 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 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.

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 dimensions of the various elements shown in Figs. 6 and 7 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 II

INK CHAMBER DIMENSIONS IN MICRONS
Dimension	Minimum	Nominal	Maximum
E	1	1.73	2
F	30	35	40
G	30	35	40
I	23	26	34
J	45	50	55
K	45	50	55
L	0	8	10
M	20	35	50
N	15	30	55
O	10	25	40
P	30	40	50
U	75	155-190	270

Fig. 7 is a magnified, partially cut away view in perspective of the portion of the circuit or nozzle member 18 after the nozzle member 18 has been properly positioned over the substrate structure 28 to form a printhead 14. As shown in Fig. 7, the nozzles 17 are aligned over the vaporization chambers 72. Fig. 7 also illustrates the ink flow 88 from an ink reservoir 12 generally situated below the substrate 28 as the ink flows over an edge 86 of the substrate 28 and enters ink channels 80.
Preferred dimensions A, B, and C in Fig. 7 are provided in Table III below, where dimension C is the thickness of the nozzle member 18, dimension B is the thickness of the barrier layer 30, and dimension A is the thickness of the substrate 28. Table III

SUBSTRATE, INK CHANNEL AND NOZZLE MEMBER DIMENSIONS IN MICRONS

Dimension Minimum Nominal Maximum

A 600 625 650

B 19 25 32

C 25 50 75

D 84.7

H 40 55 70

T 50 100 150
From Tables II and III above, 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.
The above described of outgassing inks and bubble formation could be eliminated t by degassing the ink before it reaches the thermal boundary layer behind the substrate. Fig. 8 shows how ink containing dissolved gases flows from the ink reservoir 12 of the ink cartridge 10 through standpipe 15 and across the degassing heater element 93 separating air and other vapors 91 from the flow of ink 88. Heater element 93 is connected to electrical contacts 95 which can connect to the printer for example through contacts 20. The procedure removes the gases 91 in the standpipe 15 region of the ink cartridge 10 where the presence of bubbles 91 is not damaging to the operation of the printhead. The degassed ink then flows over the substrate 28 to the printhead 14 while the removed gases 91 flow upward from the standpipe 15 into the reservoir 12 where no blockage to the printhead can occur. Alternatively, the gases 91 can be bled from the system through a bleed valve (not shown).
Fig. 9 shows the heater element 91 as a resistive coil inserted within the ink passageway, or standpipe 15 of the snout 11 portion of print cartridge 10. In an alternative embodiment of the present invention, the heating element 93 comprises a tubular duct with a roughened internal surface inserted within standpipe 15 which is heated by applying heat externally to the duct to provide not only a thermal boundary layer, but also numerous bubble generation or nucleation sites in order to promote bubble formation and growth. In a further alternative embodiment of the present invention, heater element 93 comprises a second silicon substrate inserted in the standpipe 15 upstream of the firing substrate 28. This heater element substrate has multiple resistors, such as resistors 70, etched onto it and operates solely in a pulse warming mode, i. e., heating, but not vaporizing the surrounding ink. This pulse warming can be accomplished by utilizing a narrower pulse width than required for firing pulses. One skilled in the art will appreciate that the ultimate heater 93 would be optimized to meet the design and space constraints of the print cartridge 10.
During degassing, the ink is not boiled, but rather the heater element 93 warms the ink to a temperature slightly higher than the highest temperature the ink will be exposed to at the thermal boundary layer adjacent the substrate 28 of the printhead (e.g., approximately 70 C). Although not all gas 91 may not be removed from the ink during degassing, unless the temperature of the ink rises above the substrate temperature 28, no more bubbles will form. A significant advantage in using heat as the degassing mechanism is that the ink is only exposed to what normally occurs when the ink is brought in contact with the heated substrate 28 and ink chambers 72. The degassing is simply being moved upstream to a more acceptable region of the ink cartridge 10 where the gases can be removed form the area of the printhead.
The present invention has been described above as having the degassing operation performed within a print cartridge having either a "integral" reservoir or "snap-on" reservoir because this is the embodiment which is the most difficult to implement. Shown in Fig. 9 is a schematic diagram showing an off-axis ink supply system. The system has a print cartridge 10 which is mounted on the carriage of an inkjet printer (not shown). The print cartridge is connected to an off-axis ink supply bag 19 by a flexible supply tube 13. Off-axis implies that the ink supply bag 19 is preferably mounted on the printer body (not shown) and not on the carriage with the print cartridge 10. The degassing station may be located at either at 93C on the carriage or at 93P on the printer. However, it is generally best to locate the degassing as close to the print cartridge as feasible. It should be appreciated that the degassing could still be performed on the print cartridge itself even in an off-axis ink supply system. It will be appreciated by one skilled in the art that the same mechanisms for degassing may be used in this off-axis system.
Shown in Fig. 10 is a perspective view of an inkjet print cartridge for use with an off-axis ink supply system. The inkjet print cartridge 10' includes a printhead 14' and an optional on-board ink reservoir ink reservoir 12' of low capacity. The inkjet print cartridge 10 receives ink from an off-axis ink supply through supply tube 13. The other features of print cartridge 10' denominated 14', 16', 17', 18', 20', 22', 24', and 36' are the same as for print cartridge 10 in Fig. 1. The features of print cartridge 10 shown in Fig. 2 through Fig. 7 apply to print cartridge 10'.
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.

Claims

A method of avoiding a malfunction in a liquid inkjet printing system comprising:
providing an ink reservoir;
providing a fluid channel;
mounting a printhead on a printer carriage;
providing an ink vaporization chamber with an activation element therein for expelling a drop of ink from a nozzle in a nozzle array on the printhead;
transporting ink from the reservoir through the fluid channel to the vaporization chamber, said transporting step including passing the liquid ink past a degassing station in the fluid channel; and
filling the vaporization chamber with the ink, said filling step occurring after said passing step.
A method according to claim 1 wherein said passing step occurs in close proximity to the vaporization chamber.
A method according to claim 1 wherein said passing step occurs adjacent to the ink reservoir.
A method according to claim 1 wherein said passing step occurs in the fluid channel upstream from the printhead.
A method according to claim 1 wherein said passing step occurs on the printer carriage.
A method according to any of the preceding claims wherein in said passing step the degassing station includes a heating element which heats the ink.
A method according to any of the preceding claims wherein in said passing step the degassing station includes venting to the atmosphere.
A method according to any of the preceding claims wherein in said passing step includes warming the ink to lower the solubility of the ink to dissolved gases.
A liquid inkjet printing system comprising:
a substrate having a top surface and an opposing bottom surface;
a nozzle member having a plurality of ink orifices formed therein, said nozzle member being positioned to overlie said top surface of said substrate;
a plurality of ink vaporization chambers formed on said top surface of said substrate, each of said ink vaporization chambers being located proximate to an associated one of said orifices for causing a portion of ink to be expelled from said associated orifice;
a fluid channel, communicating with an ink reservoir, leading to each of said orifices and said ink vaporization chambers, said fluid channel allowing ink to flow from said ink reservoir to said top surface of said substrate so as to be proximate to said orifices and said ink vaporization chambers; and
a degassing station located in said fluid channel.
A system according to claim 9, wherein the fluid channel comprises:
a first fluid channel, communicating with a primary ink reservoir leading to a secondary ink reservoir, said first fluid channel allowing ink to flow from said primary ink reservoir to said secondary ink reservoir; and
a second fluid channel, communicating with the secondary ink reservoir, leading to each of said orifices and said ink vaporization chambers, said second fluid channel allowing ink to flow from said secondary ink reservoir to said top surface of said substrate so as to be proximate to said orifices and said ink vaporization chambers;
and wherein the degassing station is located in the first fluid channel.
A system according to claim 9 or 10 wherein said degassing station is in close proximity to the vaporization chamber.
A system according to claim 9 or 10 wherein said degassing station is adjacent to the ink reservoir.
A system according to claim 9 or 10 wherein said degassing station is located in a standpipe portion of said fluid channel.
A system according to any of claims 9 to 13 wherein in said degassing station includes a heating element.
A system according to any of claims 9 to 14 wherein in said degassing station includes a vent to the atmosphere.
A system according to any of claims 9 to 15 wherein the degassing station includes a means to warm the ink to lower the solubility of the ink to dissolved gases.