Continuous fluid recirculation and recirculation on-demand prior to firing for thermal ejection of fluid having concentration of solids

Fluid is continuously recirculated through a thermal fluid-ejection printhead. Prior to firing a thermal resistor of the printhead to thermally eject a drop of the fluid through a nozzle of the printhead, the fluid is recirculated on-demand through a chamber of the printhead between the nozzle and the thermal resistor. The thermal resistor is fired to thermally eject the drop of the fluid through the nozzle. The fluid has a concentration of solids greater than 12% by volume.

BACKGROUND

Printing devices, including standalone printers as well as all-in-one (AIO) printing devices that combine printing functionality with other functionality like scanning and copying, can use a variety of different printing techniques. One type of printing technology is thermal inkjet-printing technology, which is more generally a type of thermal fluid-ejection technology. A thermal fluid-ejection device, such as a printhead or a device having such a printhead, includes a number of thermal resistors and corresponding nozzles. Firing a thermal resistor can cause ejection of fluid, such as a drop thereof, from a corresponding nozzle.

DETAILED DESCRIPTION

As noted in the background, firing thermal resistors of a thermal fluid-ejection device causes ejection of fluid from nozzles of the device. Different types of thermal fluid-ejection devices, including different types of thermal inkjet-printing devices, can employ a variety of different types of fluid. For example, thermal inkjet-printing devices may use dye-based and/or pigmented inks. Dye-based inks include colorant that is fully dissolved in carrier liquid, whereas pigmented inks include a powder of solid colorant particles suspended in carrier liquid.

Inks and other fluids can vary in their concentration of solids.

Fluids like ink that have greater concentrations of solids are more likely to form viscous plugs at a fluid-ejection printhead's nozzles. A viscous plug forms when fluid sufficiently dries out at a nozzle, leaving behind a greater mass of solid particles that clog the nozzle in the form of a plug. Clogged nozzles can deleteriously affect image quality, by impeding or preventing fluid ejection through the nozzles, and/or by affecting the amount or trajectory of fluid ejected through the nozzles.

However, the desire to print with such more challenging inks has increased unimpeded. Thermal fluid-ejection devices are being called upon to eject fluids that have ever greater concentrations of solids, for instance.

Techniques described herein permit fluid-ejection devices to thermally eject fluids that have greater concentrations of solids than existing such devices, permitting thermal ejection of a wider variety of fluids. The described techniques can allow thermal fluid-ejection devices to eject types of fluid that heretofore otherwise necessitated the usage of different kinds of fluid-ejection devices, like those that employ piezoelectricity to eject fluid.

Specifically, in the techniques described herein, fluid is continuously recirculated through a thermal fluid-ejection printhead. The fluid may be continuously recirculated just through a chamber layer of the printhead, just through a device layer of the printhead, or just at a backside of the device layer. The fluid may instead be continuously recirculated both through the chamber layer and the device layer, or both through the chamber layer and at the backside of the device layer.

Furthermore, when a drop of fluid is to be ejected from the thermal fluid-ejection printhead, fluid is recirculated on-demand through a chamber prior to firing a thermal resistor to eject the fluid drop from the chamber through a nozzle. Such recirculation of fluid both continuously through the printhead and on-demand through a chamber prior to ejecting fluid from the chamber has been proven to expand the types of fluid that are thermally ejectable. For instance, fluid like ink having a concentration of solids greater than 12% by volume, and even greater than 30% by volume, is able to be thermally ejectable, which is believed to have not heretofore been possible.

FIGS.1A and1Brespectively show cross-sectional side and top views of an example thermal fluid-ejection printhead100. The cross-sectional side view ofFIG.1Adepicts the cross section of the printhead100at cross-sectional line101ofFIG.1B, and the cross-sectional top view ofFIG.1Bdepicts the cross-section of the printhead100at cross-sectional line103ofFIG.1A. The printhead100includes a device layer102, a chamber layer104, and a tophat layer106, as depicted inFIG.1A.

The device layer102is referred to as such to distinguish the layer102from the layers104and106, and is located between the layers104and106. The device layer102partially or completely defines slots108A and108B, which are collectively referred to as the slots108. The chamber layer104includes channels109, which can be of varying width and that fluidically connect the slots108. The chamber layer104is referred to as such because it further includes chambers110. The printhead100includes thermal resistors112disposed at bottoms of respective chambers110of the chamber layer104, as well as corresponding microfluidic pumps114disposed within the chamber layer104perFIG.1B.

The tophat layer106includes nozzles116, which can be of varying diameter, opposite respective thermal resistors112. The tophat layer106is referred to as such because it can be the topmost layer, above the layers102and104. Each nozzle116and its corresponding thermal resistor112are located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed at outward edges of the slots108, and there are no such components disposed between the slots108.

In the example ofFIGS.1A and1B, fluid continuously recirculates through the chamber layer104, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.1A, fluid travels inwards from the slot108A to the channels109per arrow118A, across the channels109per arrow118B, and outwards from the channels109to the slot108B per arrow118C. Likewise, inFIG.1B, fluid travels upwards into the slot108A per the tip of arrow118A, across the channels109per arrow118B, and downwards into the slot108B per the tail of arrow118C. Such continuous fluid recirculation can be referred to as macrofluidic recirculation, because it occurs throughout the entire thermal fluid-ejection printhead100.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Specifically, the fluid is recirculated from the slot108adjacent to the nozzle116, through the chamber110, and back to this same slot108, per arrow120. Such on-demand fluid recirculation can be referred to as microfluidic recirculation, because it occurs just within the chamber110from which fluid is to be ejected, and not through the entire printhead100. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired. Firing of the thermal resistor112causes ejection of fluid from the chamber110through the nozzle116.

FIGS.2A,2B, and2Crespectively show one cross-sectional side and two cross-sectional top views of another example of the thermal fluid-ejection printhead100. The cross-sectional side view ofFIG.2Adepicts the cross section of the printhead100at cross-sectional line101ofFIGS.2B and2C. The cross-sectional top view ofFIG.2Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.2A, and the cross-sectional top view ofFIG.2Cdepicts the cross section of the printhead100at cross-sectional line105ofFIG.2A.

The printhead100includes the device layer102, the chamber layer104, and the tophat layer106, as well as a chiclet layer202at a backside of the device layer102, as depicted inFIG.2A. A difference between the example ofFIGS.2A,2B, and2Cand the example ofFIGS.1A and1Bis that microfluidic recirculation occurs through the chiclet layer202at the backside of the device layer102inFIGS.2A,2B, and2C. By comparison, microfluidic recirculation occurs through the chamber layer104inFIGS.1A and1B.

The device layer102partially defines the slots108, and the chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114perFIG.2B. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chiclet layer202also partially defines the slots108, and includes channels204that fluidically connect the slots108, and which can be of varying width. The chiclet layer202is referred to as such to distinguish the layer202from the other layers102,104, and106. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed at both inward and outward edges of the slots108.

In the example ofFIGS.2A,2B, and2C, fluid continuously recirculates through the chiclet layer202, and thus at the backside of the device layer102, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.2A, fluid travels inwards from the slot108A to the channels204per arrow118A, across the channels204per arrow118B, and outwards from the channels204to the slot108B per arrow118C. Likewise, inFIG.2C, fluid travels upwards into the slot108A per the tip of arrow118A, across the channels204per arrow118B, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Specifically, inFIGS.2A and2B, the fluid is recirculated from the slot108adjacent to the nozzle116, through the chamber110, and back to this same slot108, per arrow120. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.3A,3B, and3Crespectively show one cross-sectional side and two cross-sectional top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.3Adepicts the cross section of the printhead100at cross-sectional line101ofFIGS.3B and3C. The cross-sectional top view ofFIG.3Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.3A, and the cross-sectional top view ofFIG.3Cdepicts the cross section of the printhead100at cross-sectional line105ofFIG.3A.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.3A. A difference between the example ofFIGS.3A,3B, and3Cand the example ofFIGS.2A,2B, and2Cis that macrofluidic recirculation occurs through the device layer102inFIGS.3A,3B, and3C. By comparison, macrofluidic recirculation occurs through the chiclet layer202and at the backside of the device layer102inFIGS.2A,2B, and2C.

The device layer102partially defines the slots108, and includes channels304that fluidically connect the slots108, which can be of varying width. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114perFIG.3B. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed at both inward and outward edges of the slots108. The chiclet layer202also partially defines the slots108.

In the example ofFIGS.3A,3B, and3C, fluid continuously recirculates through the device layer102, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.3A, fluid travels inwards from the slot108A to the channels304per arrow118A, across the channels304per arrow118B, and outwards from the channels304to the slot108B per arrow118C. Likewise, inFIG.3C, fluid travels upwards into the slot108A per the tip of arrow118A, across the channels204per arrow118B, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Specifically, inFIGS.3A and3B, the fluid is recirculated from the slot108adjacent to the nozzle116, through the chamber110, and back to this same slot108, per arrow120. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.4A and4Brespectively show cross-sectional side and top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.4Adepicts the cross section of the printhead100at cross-sectional line101ofFIG.4B. The cross-sectional view ofFIG.4Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.4A.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.4A. A difference between the example ofFIGS.4A and4Band the example ofFIGS.1A and1Bis that the chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are located at inside edges of the slots108in the example ofFIGS.4A and4B. By comparison, the chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are located at outside edges of the slots108in the example ofFIGS.1A and1B.

The device layer102partially defines the slots108. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed between the slots108, with the chambers110, the thermal resistors112, and the nozzles116adjacent to the slot108B and the pumps114adjacent to the slot108A. The chiclet layer202also partially defines the slots108.

In the example ofFIGS.4A and4B, fluid continuously recirculates through the chamber layer104, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.4A, fluid travels inwards from the slot108A to chamber layer104per arrow118A, across the chambers110of the chamber layer104per arrow120, and outwards from the chamber layer104to the slot108B per arrow118C. Likewise, inFIG.4B, fluid travels upwards into the slot108A per the tip of arrow118A, across the chambers110per arrow120, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Such microfluidic recirculation through the chamber110is in addition to the macrofluidic recirculation through the chamber layer104as a whole, increasing fluidic flow through the specific chamber110from which fluid will be ejected. Specifically, the fluid is recirculated from the slot108A, through the chamber110, and to the slot108B, per arrow120. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.5A,5B, and5Crespectively show one cross-sectional side and two cross-sectional top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.5Adepicts the cross section of the printhead100at cross-sectional line101ofFIGS.5B and5C. The cross-sectional view ofFIG.5Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.5A, and the cross-sectional view ofFIG.5Cdepicts the cross section of the printhead100at cross-sectional line105ofFIG.5B.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.5A. A difference between the example ofFIGS.5A,5B, and5Cand the example ofFIGS.4A,4B, and4Cis that in the example ofFIGS.5A,5B, and5C, macrofluidic recirculation occurs through the chiclet layer202at the backside of the device layer102, in addition to through the chamber layer104. By comparison, in the example ofFIGS.4A,4B, and4C, macrofluidic recirculation occurs just through the chamber layer104.

The device layer102partially defines the slots108. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed between the slots108, with the chambers110, the thermal resistors112, and the nozzles116adjacent to the slot108B and the pumps114adjacent to the slot108A. The chiclet layer202also partially defines the slots108, and includes the channels204that fluidically connect the slots108, and which can be of varying width.

In the example ofFIGS.5A,5B, and5C, fluid continuously recirculates through the chamber layer104and also through the chiclet layer202and thus at the backside of the device layer102, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.5A, fluid travels inward through the slot108A per arrow118A, across both the chamber layer104per arrow120and the channels204per arrow118B, and outwards through the slot108B per arrow118C. Likewise, inFIGS.5B and5C, fluid travels upwards into the slot108B per the tip of arrow118A, across the chambers110per arrow120inFIG.5Bas well as across the channels204per arrow118B inFIG.5C, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Such microfluidic recirculation through the chamber110is in addition to the macrofluidic recirculation through the chamber layer104as a whole, increasing fluidic flow through the specific chamber110from which fluid will be ejected. Specifically, the fluid is recirculated from the slot108A, through the chamber110, and to the slot108B, per arrow120inFIGS.5A and5B. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.6A and6Brespectively show one cross-sectional side and two cross-sectional top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.6Adepicts the cross section of the printhead100at cross-sectional line101ofFIGS.6B and6C. The cross-sectional view ofFIG.6Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.6A, and the cross-sectional view ofFIG.6Cdepicts the cross section of the printhead100at cross-sectional line105ofFIG.6A.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.6A. A difference between the example ofFIGS.6A,6B, and6C and the example ofFIGS.5A,5B, and5Cis that inFIGS.6A,6B, and6Cmacrofluidic recirculation occurs through the device layer102in addition to through the chamber layer104. By comparison, in the example ofFIGS.5A,5B, and5C, macrofluidic recirculation occurs through the chiclet layer202at the backside of the device layer104, in addition to through the chamber layer104.

The device layer102partially defines the slots108, and includes the channels304that fluidically connect the slots108, which can be of varying width. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed between the slots108, with the chambers110, the thermal resistors112, and the nozzles116adjacent to the slot108B and the pumps114adjacent to the slot108A. The chiclet layer202also partially defines the slots108.

In the example ofFIGS.6A,6B, and6C, fluid continuously recirculates through the chamber layer104and also through the device layer102, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.6A, fluid travels inward through the slot108A per arrow118A, across both the chamber layer104per arrow120and the channels304per arrow118B, and outwards through the slot108B per arrow118C. Likewise, inFIGS.6B and6C, fluid travels upwards into the slot108B per the tip of arrow118A, across the chambers110per arrow120inFIG.6Bas well as across the channels304per arrow118B inFIG.6C, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Such microfluidic recirculation through the chamber110is in addition to the macrofluidic recirculation through the chamber layer104as a whole, increasing fluidic flow through the specific chamber110from which fluid will be ejected. Specifically, the fluid is recirculated from the slot108A, through the chamber110, and to the slot108B, per arrow120inFIGS.6A and6B. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.7A and7Brespectively show cross-sectional side and top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.7Adepicts the cross section of the printhead100at cross-sectional line101ofFIG.7B. The cross-sectional view ofFIG.7Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.7A.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.7A. A difference between the example ofFIGS.7Aand7B and the example ofFIGS.1A and1Bis that inFIGS.7A and7Bthere are two slots108A and one slot108B. By comparison, inFIGS.1A and1B, there is one slot108A and one slot108B.

The device layer102partially defines two slots108A and the slot108B. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed between either slot108A and the slot108B, with the chambers110, the thermal resistors112, and the nozzles116adjacent to the slot108B and the pumps114adjacent to either slot108A. The chiclet layer202also partially defines the slots108.

In the example ofFIGS.7A and7B, fluid continuously recirculates through the chamber layer104, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.7A, fluid travels inwards from both slots108A to the chamber layer104per arrows118A, across the chambers110of the chamber layer104per arrow120, and outward from the chamber layer104to the slot108B per arrow118C. Likewise, inFIG.7B, fluid travels upwards into the slots108A per the tips of arrows118A, across the chambers110per arrow120, and downwards into the slot108B per the tail of arrow118C.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Such microfluidic recirculation through the chamber110is in addition to the macrofluidic recirculation through the chamber layer104as a whole, increasing fluidic flow through the specific chamber110from which fluid will be ejected. Specifically, the fluid is recirculated from the slot108A adjacent to the corresponding pump114, through the chamber110, and to the slot108B, per arrow120. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

FIGS.8A and8Brespectively show cross-sectional side and top views of another example of the thermal fluid-ejection printhead100. The cross-sectional view ofFIG.8Adepicts the cross section of the printhead100at cross-sectional line101ofFIG.8B. The cross-sectional view ofFIG.8Bdepicts the cross section of the printhead100at cross-sectional line103ofFIG.8A.

The printhead100includes the device layer102, the chamber layer104, the tophat layer106, and the chiclet layer202at the backside of the device layer102, as depicted inFIG.8A. A difference between the example ofFIGS.8A and8Band the example ofFIGS.7A and7Bis that inFIGS.8A and8Bthe slots108A are fluidic inlet slots and the slot108B is a fluidic outlet slot. By comparison, in the example ofFIGS.7A and7B, the slots108A are fluidic outlet slots and the slot108B is a fluidic inlet slot.

The device layer102partially defines the two slots108A and the slot108B. The chamber layer104includes the chambers110, at the bottoms of which are disposed respective thermal resistors112, and which have corresponding microfluidic pumps114. The tophat layer106includes the nozzles116, which can be of varying diameter, opposite respective thermal resistors112, with each nozzle116and its corresponding resistor112located at opposite ends of a corresponding chamber110. The chambers110, the thermal resistors112, the microfluidic pumps114, and the nozzles116are disposed between either slot108A and the slot108B, with the chambers110, the thermal resistors112, and the nozzles116adjacent to either slot108A and the pumps114adjacent to the slot108B. The chiclet layer202also partially defines the slots108.

In the example ofFIGS.8A and8B, fluid continuously recirculates through the chamber layer104, regardless of whether fluid is being ejected from any nozzle116. Specifically, inFIG.8A, fluid travels inwards from the slot108B to the chamber layer104per arrow118C, across the chambers110of the chamber layer104per arrow120, and outward from the chamber layer104to the slots108A per arrows118A. Likewise, inFIG.8B, fluid travels upwards into the slot108B per the tip of arrow118C, across the chambers110per arrow120, and downwards into the slots108A per the tails of arrows118A.

When fluid is to be ejected from a nozzle116, a corresponding microfluidic pump114is actuated to also recirculate fluid on-demand through the chamber110at which the nozzle116is located, per arrow120. Such microfluidic recirculation through the chamber110is in addition to the macrofluidic recirculation through the chamber layer104as a whole, increasing fluidic flow through the specific chamber110from which fluid will be ejected. Specifically, the fluid is recirculated from the slot108B, through the chamber110, and to the slot108A adjacent to the chamber110, per arrow120. After the on-demand fluid recirculation has occurred, the thermal resistor112corresponding to the nozzle116is fired, causing ejection of fluid from the chamber110through the nozzle116.

The examples of the thermal fluid-ejection printhead100that have described can be variously combined and modified. That is, the examples are not discretely separate implementations. The thermal fluid-ejection printhead100permits thermal ejection of a wider variety of fluid, like ink, as compared to other types of thermal fluid-ejection printheads, including those in which fluid recirculation occurs just continuously or just on-demand.

FIGS.9A and9Bare graphs depicting an example space900of fluid that the thermal fluid-ejection printhead100can eject, as compared to other types of thermal fluid-ejection printheads and piezoelectric fluid-ejection printheads. The fluid space900is three-dimensionally defined over an x-axis902, a y-axis904, and a z-axis906.FIG.9Ashows the two-dimensional plane907defined by the x-axis902and the y-axis904of the fluid space900, andFIG.9Bshows the two-dimensional plane917defined by the x-axis902and the z-axis906of the fluid space900. The x-axis902denotes concentration of solids by volume, as the percentage of the total volume within the fluid that the solids occupy. The y-axis904denotes viscosity of the fluid in centipoise (cP). The z-axis906denotes drop volume in picoliters (pl).

The fluid space900includes three regions908,910, and912. The region908specifies fluids that may be able to be ejected by thermal fluid-ejection printheads in which no fluid recirculation occurs. The region908encompasses fluids having concentrations of solids no greater than 12% by volume, viscosities no greater than 5 cP perFIG.9A, and drop volumes no less than 12 pl perFIG.9B(smaller drop volumes are more difficult to eject than larger drop volumes). The region910specifies fluids that may be able to be ejected by thermal fluid-ejection printheads in which through-chamber recirculation on demand occurs but in which no continuous fluid recirculation occurs. The region910is inclusive of the region908, and encompasses fluids having concentrations of solids no greater than 30% by volume, viscosities no greater than 15 cP perFIG.9A, and drop volumes no less than 12 pl perFIG.9B.

The region912specifies fluids that can be ejected by the examples of the thermal fluid-ejection printhead100that have been described, in which both on-demand and continuous fluid recirculation occurs. The region912further specifies fluids that may be able to be ejected by piezoelectric fluid-ejection printheads. The region912is inclusive of the regions908and910, and encompasses fluids having concentrations of solids greater than 30% by volume, viscosities greater than 15 cP perFIG.9A, and drop volumes as low as 2 pl perFIG.9B. The region912potentially encompasses fluids having concentrations of solids exceeding 40% by volume, viscosities exceeding 40 cP, and/or drop volumes less than 2 pl, which is why the respective bounds of the region912are indicated by dotted lines inFIGS.9A and9B.

FIGS.9A and9Bthus show that the examples of the thermal fluid-ejection printhead100that have been described greatly expand the space900of fluids that are thermally ejectable as compared to thermal fluid-ejection printheads in which both continuous and on-demand fluid recirculation do not occur. Furthermore,FIGS.9A and9Bshow that the space900of fluids that the thermal fluid-ejection printhead100can eject rivals if not exceeds that of fluids which piezoelectric fluid-ejection printheads may be able to eject. In such instances, fluid-ejection devices using thermal fluid ejection may be substituted for devices that employ piezoelectric fluid ejection, with resulting potential benefits in cost, performance, and reliability.

Examples of fluids that the thermal fluid-ejection printhead100can successfully eject include water-based ultraviolet (WBUV)-curable ink, white ink, and clear varnish. Such WBUV-curable ink may include polyurethane dispersion (PUD) particles. Such white ink may include titanium dioxide particles or other types of white pigment particles, and may also include binders like PUD particles and latex particles. Such clear varnish may include concentrations of water-dispersible monomers or other types of water-dispersible solids. Other examples of fluids that the thermal fluid-ejection printhead100can successfully eject into color inks, such as cyan, magenta, yellow, and black inks, having high concentrations (e.g., 16% or 24% by volume) of binders like PUD particles and latex particles.

FIG.10shows an example method1000for ejecting fluid using the thermal fluid-ejection printhead100that has been described. The fluid may have a concentration of solids greater than 12%. The method1000includes continuously recirculating fluid through the thermal fluid-ejection printhead100(1002). The method1000includes, prior to firing a thermal resistor112of the printhead100to thermally eject a drop of the fluid through a nozzle116, recirculating the fluid on-demand through a chamber110between the nozzle116and the resistor112. The method1000includes then firing the thermal resistor112to thermally eject the drop of the fluid through the nozzle116(1006).

FIG.11shows an example fluid-ejection device1100. The device100may be a thermal inkjet-printing device, for example. The fluid-ejection device100includes a device layer102and a chamber layer104fluidically connected to the device layer102. The device100includes a thermal resistor112that is fired to eject fluid through a nozzle116, and a microfluidic pump114at the chamber layer104to recirculate the fluid on-demand prior to firing of the resistor112.

The fluid-ejection device100includes another, macrofluidic pump1102to continuously recirculate the fluid. The macrofluidic pump1102may continuously recirculate the fluid through the chamber layer104, through the device layer102, at a backside of the device layer102, through both the chamber layer104and the device layer102, or both through the chamber layer104and at the backside of the device layer102. The fluid may have a concentration of solids greater than 12% by volume.

The techniques that have been described herein permit an expanded space of fluids that can be thermally ejected. In accordance these techniques, fluid is continuously recirculated throughout a thermal fluid-ejection printhead. The fluid is also recirculated on-demand within a chamber between a thermal resistor and a nozzle, prior to firing the thermal resistor to eject a drop of the fluid through the nozzle.