Fluid reservoir and fluid supply method

Abstract

A fluid reservoir for a fluid supply system for a recirculating droplet ejection head, the fluid supply system comprising: a fluid supply pump having a fluid supply connection, fluidly connectable between the fluid reservoir and the droplet ejection head, for transferring fluid from the fluid reservoir to the droplet ejection head; and a fluid return pump having a fluid return connection, fluidly connectable between the droplet ejection head and the fluid reservoir, for transferring fluid from the droplet ejection head to the fluid reservoir, the fluid reservoir comprising a conical portion having a cross section on a plane perpendicular to a major axis, a fluid outlet through which fluid is supplied from the fluid reservoir to the droplet ejection head via the fluid supply pump, and a fluid return inlet through which fluid is received from the droplet ejection head to the fluid reservoir via the fluid return pump, the fluid return inlet having a central bore with a major axis. The fluid return inlet is located on the cone in cross section, and in the plane of the cross section, the angle between the major axis of the fluid return inlet hole and a tangent to the cross section is not equal to 90° at the point where the cross section intersects the major axis of the fluid return inlet hole, whereby, in use, a component of the direction of fluid flow entering the cone is tangential to the cross section and promotes fluid flow around the cone.

Description

[Technical Field]

[0001] The present invention relates to a fluid reservoir for a fluid supply system and device, a fluid supply system, and a method for supplying a fluid, and is particularly suited for applications in which a fluid with a high particle content is supplied to a droplet ejection head for ejection onto a medium. [Background technology]

[0002] Droplet ejection heads are now widely used in applications ranging from traditional ones such as inkjet printing to newer ones such as 3D printing. Droplet ejection heads have also been developed for industrial applications, such as direct printing on substrates such as ceramic tile and textiles. These industrial printing techniques using droplet ejection heads (e.g., piezoelectric inkjet printheads) have enabled short-run production runs, product customization, and even the printing of custom designs. It can be seen, therefore, that droplet ejection heads continue to evolve and become specialized to suit new and / or increasingly challenging applications.

[0003] In recent years, there has been growing interest in jetting fluids with high particle content (e.g., up to 40% v / v), such as highly pigmented inks and glass frits. These fluids consist of solid particles (ranging in size from a few nanometers to a few micrometers) that are maintained in suspension in a liquid medium, such as water or a solvent, with the aid of appropriate molecules adsorbed to the particle surface. High-particle-content fluids can be advantageously used to form three-dimensional shapes on a variety of substrates, including ceramic tiles, flooring, furniture, architectural glass (and other glass products for glass-on-glass decorative applications, such as bottles), windshields, and mobile device screens. They can also be used to form three-dimensional shapes, such as metal and plastic molds. Other applications include printing high-density, opaque images or base layers in a single pass. The use of high-particle-content fluids allows for a reduction in the thickness of the wet layer in any fluid jetting application, reducing the drying time, the number of passes required to achieve the desired opacity or color strength, and ultimately energy consumption. It also allows for fewer fluid jetting passes to achieve the desired three-dimensional shape. This contributes to reducing overall process times and costs, and also has a positive impact on the environment through reduced energy consumption, solvents, humectants, etc. Furthermore, the use of high particle content fluids in combination with fluid jetting technology allows for greater design flexibility and easier customization, as well as an improved color gamut.

[0004] Fluids with high particle content have a wide range of applications in many technology sectors, including textile printing, direct-to-shape (DTS) applications (such as printing swaths on bottles and other objects that exceed the width of a single droplet ejection head), wide-format graphics, coding and marking, and packaging.

[0005] In most applications, some type of fluid supply system is required to supply fluid to the droplet ejection head. The purpose of the fluid supply system may be limited to replenishing the fluid ejected by the droplet ejection head. In more complex systems, it may be necessary to control the flow rate of fluid through the droplet ejection head. This is because the fluid flow is used, for example, to improve printing reliability, control the fluid temperature, or cool the droplet ejection head.

[0006] To ensure reliable performance of a droplet ejection head, it is desirable to maintain a fluid meniscus within the droplet ejection head nozzle to prevent fluid from seeping into the nozzle plate. This is accomplished by maintaining a pressure within the droplet ejection head nozzle below atmospheric pressure (e.g., a negative pressure). This pressure is commonly referred to as back pressure, nozzle pressure, or meniscus pressure. It is also desirable to prevent air from being drawn into the droplet ejection head when the back pressure falls below a predetermined value, thereby preventing the meniscus from being drawn back into the droplet ejection head nozzle. This lower limit on back pressure may vary depending on the type of droplet ejection head and / or the fluid used. For example, it can be readily determined by experiment.

[0007] Therefore, the meniscus pressure must generally be maintained within a range determined by the following formula: 1) the meniscus pressure at which the fluid begins to ooze onto the nozzle plate, and / or 2) Meniscus pressure at which air is sucked through the nozzle.

[0008] Some droplet ejection heads are so-called through-flow or recirculating droplet ejection heads, which means that the fluid circulates through the droplet ejection head, some of it is drawn up through the nozzles and ejected, and the rest is expelled from the droplet ejection head and returned to the fluid source (e.g., a reservoir or pump).

[0009] When using fluids with high particle content, it is important that the fluid maintain sufficient homogeneity to minimize separation of suspended particles from the liquid medium. Particle separation can occur while the fluids described herein are held, for example, in a fluid reservoir, a component of a fluid delivery system. The fluid's residence time in the reservoir can be long enough for particles to begin to separate from the liquid medium, potentially adversely affecting the quality of the final decoration, product, or image. To mitigate particle separation, a mechanical stirrer can be installed in the fluid reservoir to constantly mix or agitate the fluid and keep the particles suspended. This solution is not ideal, especially when the fluid contains abrasive particles such as glass frit. Repeated contact between the particles and the stirrer can damage the stirrer, requiring frequent replacement, increasing maintenance and spare part costs. Furthermore, the use of a stirrer increases the energy consumption of the entire fluid delivery system.

[0010] The present invention has been devised in consideration of the above problems, and provides an improved fluid reservoir for a recirculating fluid supply system that is suitable for use with highly colored fluids and fluids with high particle content, such as glass frit, and that can reduce particle segregation without the use of mechanical stirrers or other additional components that wear out. Summary of the Invention

[0011] Aspects of the invention are set out in the accompanying independent claims, and details of particular embodiments of the invention are set out in the accompanying dependent claims.

[0012] According to a first aspect of the present invention, there is provided a fluid reservoir for a fluid supply system for a recirculating droplet ejection head. The fluid supply system includes a fluid supply pump fluidly connectable between the fluid reservoir and the droplet ejection head and having a fluid supply connection for transferring fluid from the fluid reservoir to the droplet ejection head, and a fluid return pump fluidly connectable between the droplet ejection head and the fluid reservoir and having a fluid return connection for transferring fluid from the droplet ejection head to the fluid reservoir. The fluid reservoir includes a conical portion having a cross section on a plane perpendicular to a major axis, a fluid outlet through which fluid is supplied from the fluid reservoir to the droplet ejection head via the fluid supply pump, and a fluid return inlet through which fluid is received from the droplet ejection head via the fluid return pump and introduced into the fluid reservoir, the fluid return inlet having a central bore with a major axis. The fluid return inlet is located on the cone in cross section, and in the plane of the cross section, the angle between the major axis of the fluid return inlet hole and a tangent to the cross section is not equal to 90° at the point where the cross section intersects the major axis of the fluid return inlet hole, whereby, in use, a component of the direction of fluid flow entering the cone is tangential to the cross section and promotes fluid flow around the cone.

[0013] According to a second aspect of the present invention, there is provided a fluid supply system including a fluid reservoir according to the first aspect of the present invention. According to a third aspect of the present invention, there is provided a method of supplying a fluid to a recirculating droplet ejection device via the fluid supply system of the second aspect, wherein the fluid comprises up to 40% v / v solid particles having a D90 value of 5 μm or less. [Brief explanation of the drawings]

[0014] [Figure 1] Figure 1A shows a fluid delivery system including a fluid reservoir according to one embodiment of the present invention, and Figure 1B shows a vertical cross section of a conical portion of a fluid reservoir according to one embodiment of the present invention. [Figure 2]Figure 2A shows a cross section of the conical portion of the fluid reservoir perpendicular to the major axis of the conical portion of Figure 1B at the point where the major axis of the fluid return inlet intersects the conical portion. Figure 2B shows a flow direction vector with a component tangential to the cross section of Figure 2A and a component along the radius of the cross section of Figure 2A. Figures 2C and 2D show details of the fluid return inlet at the point where it intersects the conical portion according to two different embodiments of the invention. [Figure 3] 3A and 3B show return inlets to a fluid reservoir according to two different embodiments of the present invention. [Figure 4] Figures 4A and 4B show a filling portion of a fluid reservoir according to one embodiment of the present invention. [Figure 5] 5A-5D show vertical cross sections of conical sections according to four different embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE INVENTION Embodiments and various implementations thereof will now be described with reference to the drawings, in which like reference numerals will be used to refer to like elements throughout the following description where appropriate.

[0016] 1A and 1B, there is shown a fluid supply system 100 including a fluid reservoir 101 according to one embodiment of the present invention. A fluid supply pump 103 has a fluid supply connection connectable between the fluid reservoir 101 and a droplet ejection head 107 via a fluid supply path 102. A fluid return pump 113 has a fluid return connection connectable between the droplet ejection head 107 and the fluid reservoir 101, and transfers fluid from the droplet ejection head 107 to the fluid reservoir 101 via a fluid return path 112.

[0017] The droplet ejection head 107 has a fluid inlet and a fluid outlet and is therefore a recirculating or "through-flow" device. The droplet ejection head 107 has a plurality of nozzles arranged in an array, e.g., one or more rows of nozzles extending in the array direction, and droplets of fluid are ejected from one or more nozzles when an actuator is activated by an electrical signal. Each of the one or more nozzles may be connected to an actuator that ejects fluid through the one or more nozzles.

[0018] A fluid supply pump 103 is fluidly connectable to the reservoir 101 and fluidly connectable to the droplet ejection head 107 to supply fluid to the droplet ejection head 107 .

[0019] 1A shows that fluid connection between fluid supply pump 103 and droplet ejection head 107, and between fluid supply pump 103 and fluid reservoir 101, is made via fluid supply path 102. Fluid supply path 102 includes fluid supply connection 105 connectable to an inlet of droplet ejection head 107. Fluid supply path 102 may include multiple sections and connectors to fluidly connect all components located between fluid reservoir 101 and droplet ejection head 107.

[0020] The fluid return path 112 can fluidly connect the droplet ejection head 107 to the fluid return pump 113, and between the fluid return pump 113 and the fluid reservoir 101. The fluid return path 112 includes a fluid return connection 115 connectable to an outlet of the droplet ejection head 107, thereby discharging fluid from the droplet ejection head 107. The fluid return path 112 can include multiple sections and connectors to properly fluidly connect all components between the droplet ejection head 107 and the fluid reservoir 101. It will be appreciated that the fluid supply connection 105 and the fluid return connection 115 can be simple push-fit connections to the droplet ejection head 107, or can be more complex connections, such as quick-release, self-sealing connectors. In some configurations, valves (not shown) can be provided to allow the droplet ejection head 107 to be removed without spilling liquid. Other connections required for the system are similarly considered.

[0021] The fluid delivery system 100 is configured to have an inlet pressure P S The sensor manifold 106 outputs the pressure PR=P1 near the outlet or return side of the droplet ejection head 107, and the differential pressure P is calculated using the following two equations: D and meniscus or nozzle or back pressure P M These calculations can be performed in a controller (not shown).

number

number

[0022] The fluid return pump 113 calculates the meniscus pressure P M , and the pressure at the nozzle is within an acceptable range of meniscus pressure (e.g., meniscus pressure window P M(WINDOW) This prevents air from being sucked in from the nozzles of the droplet ejection head 107 and prevents fluid from leaking out.

[0023] The conical portion 101a has a cross section (101a_s shown in FIG. 2A, cross section AA in FIG. 1A) in a plane perpendicular to its major axis 101a_a, a fluid outlet 101a_out that supplies fluid from the fluid reservoir 101 to the droplet ejection head 107 via a fluid supply pump 103, and a fluid return inlet 101a_in that receives fluid from the droplet ejection head 107 to the fluid reservoir 101 via a fluid return pump 113. The fluid return inlet 101a_in has a central hole with a major axis 20 (see FIGS. 2B to 2D). The fluid return inlet 101a_in is located on the cross section 101a_s of the conical portion 101a.

[0024] As used herein, a "conical section" refers to a section having a substantially inverted cone shape, i.e., a hollow body that tapers from a circular or nearly circular (e.g., elliptical) base to a tip (or apex). It is understood that a conical section can have any shape that can be described as an inverted tapered body of revolution (shown in cross section in Figures 5A-5D, but not limited to such), and that the taper can have any suitable shape, including linear, or concave, convex, or segmented. It is further understood that a conical section can have a truncated shape, such as a frustum shape.

[0025] The cross section 101a_s can have any suitable shape, as long as it is a closed curve. In some embodiments, the cross section 101a_s is substantially circular.

[0026] As used herein, the "major cone axis" refers to the vertical axis passing through the apex of the cone (or the virtual apex in the case of a truncated shape, i.e., the apex of the corresponding non-truncated shape).

[0027] As used herein, the "major axis of the central bore" is the axis parallel to the direction of fluid flow in the fluid return channel.

[0028] 2A to 2D show in detail the arrangement of the fluid return inlet 101a_in at cross section AA. Cross section AA is shown in FIG. 1A. As already mentioned, the fluid return inlet 101a_in has a central bore having a major axis 20. The main direction of flow 20_f along the central bore may be parallel to the major axis 20. At the point where the fluid exits the bore into the conical portion 101a, the main direction of flow 20_f may be approximately parallel to the major axis 20. The fluid return inlet 101a_in is arranged on the conical portion 101a at cross section 101a_s to supply fluid to the conical portion 101a, and is arranged such that in the plane of the cross section 101a_s, the major axis 20 of the fluid return inlet bore 101a_in forms an angle μ with respect to the tangent 101a_s_tan of the cross section 101a_s. Here, the angle μ is not 90° at the point where the cross section 101a_s intersects with the fluid return inlet hole major axis 20. Thus, in use, the component 20_f_tan of the fluid flow direction 20_f entering the conical section 101a is tangential to the cross section 101a_s, promoting fluid flow around the conical section 101a. This is because the component 20_f_tan of the fluid flow direction 20_f is different from zero (non-zero). The larger the magnitude (also referred to as the coefficient) of the component 20_f_tan, the faster the fluid flows around the conical section 101a. As mentioned above, the component 20_f_tan may form an angle μ with respect to the fluid return inlet hole major axis 20 (e.g., the centerline of the fluid return inlet 101a), where μ may be between 30° and 50°, preferably between 35° and 45°, more preferably between 37° and 41°, and most preferably 39°.

[0029] In a preferred embodiment, at least a portion of the outer hole edge 101'a_in of the fluid return inlet 101a_in is tangential to the cross section 101a_s. Furthermore, in a preferred embodiment, the major axis 20 of the fluid return inlet hole may be parallel to the outer edge 101'a, as shown in Figure 2D. This may be beneficial in allowing fluid entering the conical section 101a from the fluid return inlet 101a_in to remain attached to the convex surface (the Coanda effect), which may help to maximize the magnitude of the component 20_f_tan.

[0030] In another preferred embodiment (not shown), at least a portion of the inner edge of the fluid return inlet 101a_in hole is tangent to the cross section 101a_s, and the major axis 20 of the fluid return inlet hole is parallel to the inner edge.

[0031] The cross-section of the return inlet 101a_in hole is not particularly limited. In some embodiments, the cross-section of the return inlet 101a_in hole may be substantially circular, while in other embodiments, some or all of the hole may be rectangular or slit-shaped, with a dimension along the conical axis 101a_a greater than a dimension perpendicular to the conical axis 101a_a, thereby increasing the proportion of fluid entering the conical portion 101a from the fluid return inlet 101a_in that comes into direct contact with the inner surface of the conical portion 101a. Additionally, the cross-sectional size and / or shape of the return inlet 101a may vary along the hole. For example, the hole may taper along its length and / or the hole may change from a circular cross-section away from the conical portion 101a to a slit-like shape adjacent to the conical portion 101a.

[0032] The vertical component of the fluid flow also serves to remove any air bubbles that may be present and send them to the surface of the fluid in the fluid reservoir 101, removing air from vents, if present.

[0033] The component 20_f_rad of the fluid flow direction 20_f, perpendicular to the component 20_f_tan, may also be different from zero.

[0034] In some embodiments, the major axis 20 of the central bore of the fluid return inlet 101a_in forms an angle β substantially equal to 90° (β=90°) with the major axis 101a_a of the conical section 101a, which is the arrangement shown in FIGS. 1A-1B and 2A-2D. In some embodiments, the major axis 101a_a of the conical section 101a is substantially vertical, and the major axis 20 of the central bore of the fluid return inlet 101a_in is substantially horizontal. In this context, it will be understood that orientations that are very close to "vertical" or "horizontal" but still achieve the intended purpose are encompassed by the term "substantially."

[0035] In other embodiments, the major axis 20 of the central bore of the fluid return inlet 101 a_in forms an angle other than 90° with the major axis 101 a_a of the conical portion 101 a. In some embodiments, the major axis 101 a_a of the conical portion 101 a is substantially vertical and the major axis 20 of the central bore of the fluid return inlet 101 a_in is inclined with respect to the horizontal plane.

[0036] It will be appreciated that by controlling the flow of fluid through the return inlet 101a_in, a flow can be established within the conical portion 101a that is at least partially tangential to the inner surface of the conical portion 101a and toward the bottom of the conical portion 101a. This can be thought of as a downward spiral path. This particular motion helps to keep particles suspended in the liquid component of the fluid, minimizes particle deposition at the bottom of the reservoir 101, and does not significantly alter the properties of the fluid. As will be appreciated by those skilled in the art, "sufficiently does not alter" as used herein means that the resulting droplet ejection performance and image or product quality are acceptable for a particular application.

[0037] It will be appreciated that the appropriate velocity of the fluid entering the conical portion 101a through the return fluid path 112 will be set based on fluid properties such as fluid viscosity, meniscus pressure, differential pressure, etc., and system requirements, as well as the particular application.

[0038] It will be further appreciated that the velocity of the fluid within the conical section 101a can be modified or optimized as needed by tilting the fluid return inlet 101a_in of the conical section 101a toward the top or bottom of the fluid reservoir 101, as shown in Figures 3A and 3B. The angle of the major axis 20 relative to the major axis 101a_a of the conical section 101a is indicated by angle β in Figures 3A and 3B. As shown in Figure 3A, tilting the fluid return inlet 101a_in toward the wider region of the conical section 101a so that the angle β between the major axis 20 of the central hole of the fluid return inlet 101a_in and the conical section major axis 101a_a is greater than 90° (angle β > 90°) can reduce the velocity of the fluid toward the bottom, i.e., narrower, region of the conical section 101a. 3B, slanting the fluid return inlet 101a_in toward the narrow region of the fluid reservoir 101 such that the angle β is less than 90° (angle β<90°) can increase the velocity of the fluid toward the bottom of the conical section 101a. An angle β=90° is, for example, the arrangement shown in FIG. 1A, where the major axis 20 is perpendicular to the major axis 101a_a.

[0039] As will be appreciated by those skilled in the art, the angle of inclination of the fluid return inlet 101a_in can be selected depending on one or more of the viscosity of the ink used in the system, the flow rate, and the particle concentration in the ink used in the system. For example, depending on the operating conditions, the values ​​of the angle β and the angle μ can be selected to determine the direction in which fluid flows from the fluid return inlet 101a_in into the conical portion 101a.

[0040] The fluid return inlet 101a_in is located in a region of the conical portion 101a having a larger cross-sectional area 101a_s than the cross-sectional area of ​​the region in which the fluid outlet 101a_out is located. Preferably, the fluid return inlet 101a_in is located in the wider half of the conical portion 101a. Also, preferably, the fluid outlet 101a_out is located in the narrower half of the conical portion 101a. In this manner, a spiral fluid path is formed, minimizing separation of suspended particles from the liquid components of the fluid and sufficiently preventing the overall properties of the fluid from changing as it is discharged from the conical portion 101a through the fluid outlet 101a_out and into the supply path 102, allowing it to be supplied to the droplet ejection head 107.

[0041] More preferably, the fluid outlet 101a_out is located in a region of the conical portion 101a where the cross-sectional area is substantially smallest. This minimizes "dead spots" or corners in the conical portion 101a below the fluid outlet 101a_out, which may cause airborne particles to separate from the liquid component of the fluid. Furthermore, during operation, the supply pump 103 draws fluid away from areas where particles tend to accumulate.

[0042] The inclination angle α of the conical portion 101a (see FIG. 1B) can be selected depending on one or more of the viscosity, flow rate, and particle concentration of the fluid used in the fluid supply system 100. For example, α can be in the range of 15° to 45°, preferably in the range of 25° to 35°. The angle α may be 30°.

[0043] The fluid reservoir 101 may be provided with a filling unit 110 for supplying fresh fluid to the fluid reservoir 101. The filling unit 110 may include a fresh fluid inlet, e.g., a fresh fluid inlet pipe 111, connectable to an external fluid tank 201 to supply fresh fluid to the fluid reservoir 101. FIGS. 4A and 4B show two different arrangements of the fluid tank 201. In some embodiments, as shown in FIG. 4A, the fresh fluid inlet pipe 111 may be directly connected to the external fluid tank 201. In some cases, the fluid reservoir 101 may further be provided with a vent, e.g., a vent pipe 116. In some embodiments, the filling unit 110 may be arranged to supply fresh fluid to the fluid reservoir 101 by gravity. First, fluid is added to the fluid reservoir 101 from the tank 201 via the fresh fluid inlet pipe 111. As long as the vent pipe 116 is not in contact with the fluid in the reservoir 101, fluid will flow from the tank 201 to the reservoir 101 via the fresh fluid inlet pipe 111 and air will be released from the fluid reservoir 101 to the tank 201 via the vent pipe 116. As soon as the fluid level reaches and blocks the opening of the vent pipe 116, the flow of air from the fluid reservoir 101 to the tank 201 will stop and the flow of fluid from the tank 201 to the reservoir 101 will also stop.

[0044] When the fluid supply system 100 is in use, fluid flows to the droplet ejection head 107, where a portion of the fluid is ejected, and the remainder flows from the droplet ejection head 107 back to the fluid reservoir 101, gradually draining the fluid from the fluid reservoir 101 over time. As liquid is ejected from the droplet ejection head 107 and consumed, fresh liquid from the external tank 201 replenishes the liquid, maintaining a constant level of liquid in the liquid reservoir 101. The fresh liquid entering the liquid reservoir 101 immediately mixes with the liquid already present in the liquid reservoir 101. In this way, the state of the liquid in the liquid tank 101 remains substantially constant, ensuring reliable ejection of liquid droplets from the nozzles of the droplet ejection head 107. The liquid ejected from the droplet ejection head 107 returns to the conical portion 101a of the liquid reservoir 101, where it mixes with the ink (already mixed with fresh liquid) in the ink reservoir 101. In this way, the volume of ejected fluid is easily replaced with fresh fluid, and mixing of the fresh fluid with the fluid already present in the fluid reservoir 101 ensures that the properties of the fluid do not change significantly over the period of use.

[0045] 4B, the fresh fluid inlet can be connected to a fill pump 202, which can be connected to a tank 201. In some embodiments, the fill pump 201 can be part of the fluid supply system 100. In other embodiments, the fill pump 202 can be an external device.

[0046] Of course, other suitable configurations known in the art may be used to replenish the fluid reservoir 101 with fresh fluid.

[0047] Preferably, the fluid reservoir 101 is also provided with a level sensor 117 to alert the user when the fluid reservoir 101 has stopped being refilled with new fluid because the tank 201 has become empty.

[0048] As will be appreciated by those skilled in the art, fluid reservoir 101 may be a disposable fluid reservoir that is not intended to be refilled and is convenient for very short applications or relatively unstable fluid compositions.

[0049] The fluid reservoir 101 may further include a drain 123 including a drain port for draining fluid from the fluid reservoir 101. This prevents stagnation of fluid within the fluid reservoir 101 when the fluid delivery system is not in use, avoiding the separation of particles present in the fluid that may occur if the fluid is stationary. Fluid drained from the fluid reservoir 101 may be collected in a drain container 124 (shown in FIG. 1A) and reused. The drain bottle and / or external tank 201 may be stored in a suitable agitation device between successive uses to avoid the separation of particles.

[0050] The outlet 123 may comprise, for example, a valve, preferably a solenoid valve. As will be appreciated by those skilled in the art, any flow control device other than a valve, or combination of devices known in the art, may be used to drain fluid from the fluid reservoir 101. In other embodiments, the outlet 123 is simply an outlet and may be connected to a suitable fluid drainage device provided as part of the fluid delivery system 100. While the figures show the outlet 123 located at the bottom of the fluid reservoir 101, this is by no means limiting.

[0051] The fluid supply system 100 of the present invention comprises the fluid reservoir 101 described above.

[0052] The fluid supply system 100 may further include a damping system 108 to equalize pressure fluctuations in the fluid path (the supply pump and / or the return pump), thereby improving ejection performance. The supply pump 103 and / or the return pump 113 may have a fluid damper 108 adjacent thereto. It will be appreciated that a damping system or damper is not necessary in all situations and will depend on factors such as the required ejection quality, the type of pump used, the performance of the selected pump, and the configuration of the fluid supply system. It will also be appreciated that as long as pressure pulsations are sufficiently damped (typically less than ±2 mbar), the fluid supply pump 103 and / or the fluid return pump 113 do not need to be located adjacent to the droplet ejection head 107, which may be advantageous in some applications for weight considerations.

[0053] In some embodiments, the fluid supply system 100 includes one or more restrictors 121 in addition to or instead of the damping system 108 to further improve control of pressure pulses in the fluid path (supply and / or return).

[0054] The fluid delivery system 100 may further include a sensor manifold 106, as described above.

[0055] The sensor manifold 106 may further include temperature sensors for measuring the temperature near the inlet or supply side (temperature T1) of the droplet ejecting head 107 and the temperature near the outlet or return side (temperature T2) of the droplet ejecting head 107. These temperature measurements are used to ensure control of the temperature (and therefore viscosity) of the fluid, such as ink.

[0056] One or more conditioning devices (not shown) may be provided in the fluid supply system 100. Examples of conditioning devices include one or more fluid conditioning devices such as a temperature control device (e.g., heater, cooler), a degasser, etc.

[0057] A temperature sensor in the sensor manifold 106 (if present) can be used to provide feedback to a temperature control loop in a controller (not shown). Such a temperature control loop can include a temperature control device, such as a heater or cooler. A change in the temperature of a fluid typically changes its viscosity, which in turn changes the differential pressure within the system. Using a temperature control loop and a temperature control device, the temperature of the ink can be controlled, eliminating the need to adjust the performance of one or more pumps to accommodate temperature changes.

[0058] A further control loop can use the average (T2+T1) / 2 of the inlet and outlet temperatures across the droplet ejection head 107 to adjust the printing duty cycle, such as reducing the duty cycle if the temperature rise is too great.

[0059] Fluid delivery system 100 may also include a filter 117 to block unwanted foreign matter or particle collections from reaching droplet ejection head 107 and potentially causing clogging and poor ejection performance.

[0060] The droplet ejection head 107 is suitable for use in any recirculating droplet ejection device, and the fluid delivery system 100 of the present invention can reliably deliver to the recirculating droplet ejection device a fluid containing up to 40% v / v of solid particles with a particle size distribution D90 value of 5 μm or less, meaning that 90% of the particles dispersed in the fluid have a particle size of 5 μm or less.

[0061] The fluid supply system 100 of the present invention may supply fluid to one or more droplet ejection heads 107, or may supply multiple droplet ejection heads 107, the number of droplet ejection heads 107 depending on the recirculation rate of the fluid and the flow rate achievable by the pump for a given fluid.

[0062] The above-described embodiments and variations thereof may be used alone or in combination depending on the requirements of a particular application.

Claims

1. 1. A fluid reservoir in a fluid supply system for a recirculating droplet ejection head, comprising: the fluid supply system comprising: a fluid supply pump having a fluid supply connection fluidly connectable between the fluid reservoir and the droplet ejection head for transferring fluid from the fluid reservoir to the droplet ejection head; a fluid return pump having a fluid return connection fluidly connectable between the droplet ejection head and the fluid reservoir for transferring fluid from the droplet ejection head to the fluid reservoir; the fluid reservoir: a) a conical portion having a cross section in a plane perpendicular to the major axis; b) a fluid outlet through which fluid is supplied from the fluid reservoir to the droplet ejection head via the fluid supply pump; c) a fluid return inlet through which fluid is received from the droplet ejection head into the fluid reservoir via the fluid return pump, the fluid return inlet having a central bore with a major axis; the fluid return inlet is located on the cone at the cross section, and the angle formed in the plane of the cross section between a major axis of the fluid return inlet aperture and a tangent to the cross section at the point where the major axis of the fluid return inlet aperture intersects the cross section is other than 90 degrees, whereby, in use, a component of the direction of fluid flow entering the cone is tangential to the cross section to promote fluid flow around the cone; Fluid reservoir.

2. The fluid reservoir of claim 1 , wherein the cross section of the cone is substantially circular.

3. 3. The fluid reservoir of claim 1, wherein the major axis of the central bore of the fluid return inlet forms an angle substantially equal to 90 degrees with the major axis of the conical portion.

4. The fluid reservoir of claim 3 , wherein the major axis of the conical portion is substantially vertical and the major axis of the central bore of the fluid return inlet is substantially horizontal.

5. 3. The fluid reservoir of claim 1, wherein the major axis of the central bore of the fluid return inlet forms an angle other than 90 degrees with respect to the major axis of the conical portion.

6. The fluid reservoir of claim 5 , wherein the major axis of the conical portion is substantially vertical and the major axis of the central bore of the fluid return inlet is inclined relative to a horizontal plane.

7. The inclination angle of the fluid return inlet is a) the viscosity of the ink used in the system; and b) flow rate; and c) the concentration of particles in the fluid used in the system; and selected according to one or more of The fluid reservoir of claim 6 .

8. 8. A fluid reservoir according to any one of claims 1 to 7, wherein the fluid return inlet is located in the wider half of the cone.

9. 9. The fluid reservoir of claim 1, wherein the fluid outlet is located in the narrow half of the cone.

10. 10. A fluid reservoir according to any one of claims 1 to 9, wherein the fluid outlet is located on the conical portion in a region where the cross section of the conical portion is substantially smallest.

11. 11. A fluid reservoir according to any one of claims 1 to 10, further comprising a new fluid inlet connectable to an external fluid tank for supplying new fluid to the fluid reservoir.

12. The fluid reservoir of claim 1 , further comprising a vent.

13. 13. The fluid reservoir of claim 1, further comprising a fluid level sensor.

14. 14. The fluid reservoir of claim 1, further comprising a drain for draining fluid from the fluid reservoir.

15. 15. A fluid reservoir according to claim 14, wherein the outlet comprises a valve, preferably a solenoid valve.

16. The inclination angle of the conical portion is a) the viscosity of the fluid used in the fluid supply system; and b) flow rate; and c) the concentration of particles in the fluid used in the fluid delivery system; and selected according to one or more of 16. A fluid reservoir according to any one of claims 1 to 15.

17. 17. The fluid reservoir of claim 16, wherein the cone has an angle of inclination in the range of 15 to 45 degrees.

18. 1. A fluid supply system for a recirculating droplet ejection head, comprising: A fluid reservoir according to any one of claims 1 to 17; a fluid supply pump having a fluid supply connection fluidly connectable between the fluid reservoir and the droplet ejection head for transferring fluid from the fluid reservoir to the droplet ejection head; a fluid return pump having a fluid return connection fluidly connectable between the droplet ejection head and the fluid reservoir for transferring fluid from the droplet ejection head to the fluid reservoir; Fluid supply system.

19. The fluid delivery system of claim 18 further comprising a damping system.

20. 20. The fluid delivery system of claim 18 or 19, further comprising a restrictor.

21. 21. A fluid supply system according to any one of claims 18 to 20, comprising a fluid temperature control device.

22. 22. The fluid delivery system of any one of claims 18 to 21, further comprising a sensor manifold.

23. 23. A fluid delivery system according to any one of claims 18 to 22, further comprising a filter.

24. 24. A fluid supply system according to any one of claims 18 to 23, comprising a fill pump connectable between the fluid reservoir and the external fluid tank to supply fresh fluid to the fluid reservoir from an external fluid tank.

25. 25. A method of supplying a fluid to a recirculating printing device via a fluid supply system according to any one of claims 18 to 24, wherein the fluid comprises up to 40% by volume of solid particles having a D90 value of 5 μm or less.

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