Inkjet print head for selective dropwise dosing of a liquid in a 3D printer

Abstract

Inkjet print head (1) for selectively dosing a liquid (F) dropwise in a 3D printer, the inkjet print head (1) comprising: - an inkjet printing module (100) for selectively dosing the liquid (F) dropwise, the inkjet printing module (100) comprising: ▪ a liquid inlet (110) for supplying the liquid (F) into the inkjet printing module (100); ▪ at least one nozzle (120) for dispensing a metered drop of the liquid (FT) in the 3D printer; ▪ and a liquid return (130) for returning a return medium (R) from the inkjet printing module (100), comprising at least one liquid return capillary (131) for returning the return medium (M) from the nozzle (120), wherein the return medium (R) comprises the liquid (F) and / or a disturbing medium (S), in particular air (L) and / or particles (P) taken up into the nozzle (120) from the 3D printer; - a liquid tank (200) for holding the liquid (F) and for supplying the liquid inlet (110) of the inkjet printing module (100) with the liquid (F), wherein the liquid tank (200) comprises: ▪ a liquid supply (210) for supplying liquid (F) to the liquid tank (200); ▪ a vacuum connection (230) for applying a vacuum (U), in particular at the liquid tank (200), wherein a meniscus equilibrium pressure (MGD) in the nozzle (120) can be set as a result of the vacuum (U), by means of which an uncontrolled escape of the liquid (F) from the nozzle (120) and / or an uncontrolled suction of the interfering medium (S) from the 3D printer into the nozzle (120) is prevented; ▪ and a return liquid supply (240) for returning liquid (F) from the inkjet printing module (100) via the liquid return (130) into the liquid tank (200); - and a return pump (300) for pumping the return medium (R) from the inkjet printing module (100) via the liquid return (130) into the return liquid supply (240); wherein a pulsation damper (400) is arranged between the return pump (300) and the liquid return (130).

Description

The invention relates to a pulsation damper, an inkjet print head for selective dropwise metering of a liquid in a 3D printer comprising the pulsation damper and a 3D printer comprising the inkjet print head according to the invention.Inkjet printing technology includes, among other things, drop-on-demand technology. "drop-on-demand" means that a nozzle selectively applies a liquid drop to the material to be printed.Drop-on-demand technology includes, among other things, continuous inkjet printheads, thermal printheads (also known as "bubble jet"), and piezoelectric printheads.The embodiments described in this disclosure relate, by way of example, to piezoelectric print heads. The invention further relates to all types of inkjet print heads, in particular all types of drop-on-demand print heads.The prior art discloses a 3D printer comprising a coater for applying particles layer by layer on a build area of the 3D printer, and an inkjet print head for selectively solidifying the particles applied layer by layer by selective dropwise metering of a liquid. The particles can be a powder, for example plastic powder or sand. The liquid can be binders which chemically solidify the particles with one another. Alternatively, the liquid may be, for example, a dye. The dye can be configured to absorb electromagnetic radiation, preferably infrared radiation, which heats the particles, as a result of which the particles (melt) melt and adhere to one another.The prior art discloses an inkjet print head for selective dropwise metering of a liquid in a corresponding 3D printer, comprising an inkjet print module for selective dropwise metering of the liquid.DE 10 2013 110 108 A1 discloses a printing system with a multi-part tank, in which a static first tank part takes over the ink storage and a moving second tank part supplies the printing ink.JP 2019-084772 A discloses a supply system which adjusts the liquid flow, compensates for pressure fluctuations by means of upstream and downstream pumps. The pressure is controlled by controlled inflow and return flow quantities, whereby uncontrolled escape of the ink or air intake is prevented.The inkjet printing module comprises a liquid inlet for supplying the liquid into the inkjet printing module.Furthermore, the inkjet printing module comprises at least one nozzle, preferably comprising a nozzle opening and a nozzle chamber, for dispensing a dosable drop of the liquid in the 3D printer. In a piezoelectric print head, the nozzle chamber can be deformable. Piezoelectric print heads utilize the property of a crystal (often lead zirconate, PZT in the case of inkjets) to expand under current and to contract again when it is switched off. This expansion causes a pumping effect in the nozzle chamber. Depending on the configuration of the crystal in the "bend" or "shear" mode, the two phases of expansion cause, for example, either the suction of the liquid with subsequent ejection through the nozzle, or acoustic pressure waves are built up, which have the same effect. In a thermal printhead, a component within the nozzle chamber is rapidly heated until the liquid evaporates and forms a gas bubble. This expands and presses a liquid drop out of the nozzle opening into the environment. In addition to these two inkjet printing technologies mentioned by way of example, the subject matter according to the invention is universally applicable to the further inkjet printing technologies.Furthermore, the inkjet printing module comprises a liquid return for returning a return medium from the inkjet printing module. The liquid return comprises at least one liquid return capillary for returning the return medium from the nozzle. The return medium comprises the liquid and / or a disturbing medium.An inkjet printing module with a liquid return comprising liquid return capillaries differs from inkjet print heads known from the prior art with a constant high liquid flow via a liquid inlet and a non-capillary liquid return (referred to below as "flow system"), inter alia in the dimensions of the return capillaries and the flow rate resulting therefrom. The liquid return capillaries can lead away individually from the nozzle chambers and join up to a liquid return outlet at which the return medium can be returned from the inkjet printing module. The liquid return capillaries preferably have a width in the order of magnitude of the nozzle opening or the nozzle chamber. The nozzle opening can have a diameter of 1 / 100 mm to 10 / 100 mm, preferably 5 / 100 mm. The nozzle chamber may have a diameter about 2 to 8 times as large as the nozzle opening. The return capillary can have a diameter of, for example, 5 / 100 mm to 15 / 100 mm, preferably 10 / 100 mm. In these ranges of magnitude, capillary forces may occur in the liquid return capillaries. Consequently, small return flow rates result in the liquid return, preferably in a range between 1 and 20 ml / min, preferably in a range between 4 and 10 ml / min. The flow rates for capillary liquid returns fall in a similar order of magnitude to the amounts of liquid printed by the inkjet printing module. Depending on the liquid to be printed selectively, it is usually possible to print about 1 ml / min to 10 ml / min, in particular 1 to 4 ml / min, per inkjet printing module. The return flow rates can vary depending on the currently pressurized liquid quantity.Thus, inkjet printing modules with capillary liquid return differ substantially from flow systems in which the return flow rates exceed the printed liquid quantities by a multiple. Typically, flow systems maintain return flow rates in excess of 120 ml / min. Such return flow rates cannot be generated in capillary return systems due to capillary forces. In flow systems, therefore, the liquid is usually guided past the inlets of the nozzles at a constant high flow rate via lines whose width exceeds the dimensions of the nozzles by a multiple. Consequently, the high reflux flow rates can be realized. Only a fraction of the liquid flowing past the nozzle inlets reaches the nozzles and is printed through the nozzles into the environment.The perturbation medium may comprise air and / or particles received into the nozzle from the 3D printer. For example, the particulate material can be fluidized on the construction field of the 3D printer. Particles can thus pass via the nozzle opening into the nozzle and impede the latter when dispensing liquid droplets. Alternatively, air can pass from the 3D printer via the nozzle opening into the nozzle and impede the latter when discharging liquid droplets. In addition, other interfering media can pass from the environment into the nozzle, such as, for example, dirt.In addition, disturbing media can also be produced in the nozzle. For example, the liquid can chemically react with components of the inkjet printhead and / or can attack materials in the inkjet printhead that collect in the nozzle and impede the nozzle when dispensing liquid droplets. Furthermore, the liquid in the inkjet print head can change in its properties (e.g. viscosity) in an uncontrolled manner as a result of chemical and / or physical processes and can itself become a disturbance medium, which can impede the discharge of liquid droplets. Consequently, the system with liquid return capillaries is advantageous in order to return the return medium, comprising for example the liquid and / or the interfering medium, from the nozzle and thus maintain the functionality of the nozzle.The inkjet print head comprises a liquid tank for holding the liquid and for supplying the liquid inlet of the inkjet printing module with the liquid.The liquid tank comprises a liquid supply for tracking liquid to the liquid tank. In particular, liquid can be pumped from a storage tank outside the inkjet print head into the liquid tank. For this purpose, the 3D printer can comprise a pump, preferably outside the inkjet print head. Preferably, the liquid tank comprises a fill level sensor for monitoring the fill level of the liquid in the liquid tank. The 3D printer can be designed to track liquid into the liquid tank when a minimum fill level is undershot until a maximum fill level is reached.Furthermore, the liquid tank comprises a negative pressure connection for applying a negative pressure, in particular to the liquid tank, wherein as a result of the negative pressure a meniscus equilibrium pressure can be set in the nozzle, by means of which uncontrolled escape of the liquid from the nozzle and / or uncontrolled suction of the disturbance medium from the 3D printer into the nozzle is prevented. The negative pressure in the liquid tank can be adjusted in such a way that it counteracts the force of gravity of the liquid located in the liquid tank. Consequently, a force equilibrium is established in the nozzle, which prevents uncontrolled escape of the liquid from the nozzle and / or uncontrolled suction of the disturbance medium from the 3D printer into the nozzle. For example, negative pressures between -5 mbar and -125 mbar are suitable for this purpose, depending on the properties of the liquid (e.g. density, surface tension, viscosity, etc.) and the arrangement and / or configuration of the components of the inkjet print head (e.g. height difference between liquid tank and nozzle openings of the inkjet print module).This is a significant difference from continuous flow systems. In continuous flow systems, the meniscus equilibrium pressure is established via a pressure difference between the liquid inlet and the non-capillary liquid return. Due to the liquid constantly flowing past the nozzle inlets at flow rates which are many times higher than the pressurized liquid quantity, a negative pressure is established in the nozzles which counteracts the force of gravity of the liquid in the nozzle. Consequently, flow systems require constant measurement and readjustment of the prevailing pressures and / or flow rates at the liquid inlet and non-capillary liquid return.Furthermore, the liquid tank comprises a return liquid supply for returning liquid from the inkjet printing module via the liquid return into the liquid tank. The inkjet print head preferably further comprises a filter in order to filter out the interfering medium, in particular the particles, from the return medium. The inkjet print head preferably further comprises a degasser in order to filter out the interfering medium, in particular the air, from the return medium. The return medium flows through the filter and / or the degasser. In the flow direction downstream of the filter and / or the degasser, filtered liquid flows via the liquid return into the liquid tank. This is advantageous since liquid returned from the liquid return of the inkjet printing module can be collected in the liquid tank and further printed. This represents a further advantage over continuous flow systems. Due to the high flow rates to be achieved, in continuous flow systems the components required, in particular pumps and liquid tanks, are relatively large and therefore cannot be integrated into the movable inkjet print head. These components are arranged stationary in the 3D printer. Consequently, in continuous flow systems, the recirculated liquid must be fed and recirculated to the inkjet print head via long fluid paths. These long fluid paths are associated with high pressure fluctuations, which require a complicated control for compensating the pressure fluctuations. In addition to pressure fluctuations resulting from the operation of the pumps, pressure fluctuations resulting from the travel movement of the inkjet print head over the construction field of the 3D printer can also arise in the long fluid paths (common-mode pressure fluctuations). The common-mode pressure fluctuations arise, for example, from the movement of the long fluid lines during the travel movement of the inkjet printing cop. By integrating the entire liquid recirculation into the inkjet printhead, such common mode pressure fluctuations in the inkjet printhead according to the disclosure can be minimized.The inkjet print head comprises a return pump for pumping the return medium out of the inkjet printing module via the liquid return into the return liquid supply of the liquid tank. The return pumps which are usually used have pressure fluctuations during operation which continue as far as the nozzle openings. In particular, pressure fluctuations of more than 5 mbar can arise, experience has shown that they are more than 15 mbar. Pressure fluctuations in this region lead to the meniscus equilibrium pressure not being able to be held in a working window in which uncontrolled escape of the liquid from the nozzle and / or uncontrolled suction of the disturbance medium from the 3D printer into the nozzle is prevented. Consequently, the functionality of the nozzle is impaired by the disturbance medium being sucked in and / or by uncontrolled leakage of the liquid from the nozzle into the 3D printer.Systems known from the prior art require a complicated control in order to counteract this problem. Such systems include sensors, for example for measuring variations in prevailing pressures and flow rates. Furthermore, in such systems it may be necessary to actively readjust the return pump and / or the negative pressure present at the liquid tank. Such control systems are associated with increased development, cost and maintenance effort. Furthermore, such control systems frequently fail, in particular in the event of system errors or failures and / or in the event of very high or / or very dynamically occurring pressure fluctuations.It is an object of the present application to provide an inkjet printhead and a 3D printer which overcomes the disadvantages of the prior art.The invention achieves this object with the features of the inkjet print head according to claim 1, with the features of the pulsation damper according to claim 25, and with the features of the 3D printer according to claim 26.The inkjet print head according to the invention has a pulsation damper. All features described below relating to the pulsation damper can relate both to the pulsation damper as a separate object according to claim 25 and to the inkjet print head comprising the pulsation damper according to claim 1.The pulsation damper is arranged between the return pump and the liquid return of the inkjet printing module. The pulsation damper is preferably designed to dampen pressure fluctuations of the return pump.The pulsation damper is preferably designed such that the pressure fluctuations resulting from the pressure fluctuations of the return pump are damped towards the nozzle in such a way that the meniscus equilibrium pressure is held in a working window in which uncontrolled escape of the liquid from the nozzle and / or uncontrolled suction of the disturbance medium from the 3D printer into the nozzle is prevented. In particular, the pressure fluctuations resulting from the pressure fluctuations of the return pump are attenuated toward the nozzle to an amplitude of at most 5 mBar, preferably to at most 1 mBar. Without pulsation dampers, the pressure fluctuations in the nozzle amount to more than 5 mbar, in particular more than 15 mbar. Such high pressure fluctuations can lead to air being sucked into the nozzle, for example, or to further interference media. Furthermore, such high pressure fluctuations can lead to liquid running out of the nozzle in an uncontrolled manner.The inkjet print head according to the disclosure thus does not require an active control, in particular no active control of the return pump and / or of the negative pressure present at the liquid tank. Consequently, only when the inkjet print head is put into operation in the 3D printer, the control of the return pump and / or the negative pressure applied to the liquid tank has to be set to a constant value once. During further operation of the inkjet print head, the meniscus equilibrium pressure remains in the required working window, in which uncontrolled escape of the liquid from the nozzle and / or uncontrolled suction of the disturbance medium from the 3D printer into the nozzle is prevented. This results in a device with components that are less susceptible to errors, such as sensors and control components. Consequently, the reliability and the life of the inkjet print head can be increased. The development, cost and maintenance effort can be reduced. Furthermore, a smaller space requirement results within the inkjet print head, which is why the pulsation damper can be integrated into the inkjet print head and / or which is why the inkjet print head can be made smaller overall. Consequently, the weight of the inkjet print head can be reduced. The inkjet print head can be moved more dynamically on the construction field of the 3D printer. In particular, common-mode printing fluctuations are minimized, which increase with increasingly dynamic travel movements in inkjet print heads known from the prior art.The aforementioned aspects can each be used alone or in combination to achieve the object. Additional advantageous embodiments of the inkjet print head according to the disclosure and in particular of the pulsation damper are disclosed in the further dependent claims.The disclosure is illustrated by way of example and schematically in the drawings. These show: FIG. 1 : shows a schematic functional structure of an inkjet print head according to the disclosure FIG. 2 : shows a pulsation damper according to an exemplary embodiment FIG. 3 : shows a pulsation damper according to an exemplary embodiment FIG. 4 : shows a pulsation damper according to an exemplary embodiment FIG. 5 : shows a schematic functional structure of an inkjet printing module with a nozzle and a liquid return capillary FIG. 6 : shows a schematic functional structure of an inkjet printing module with a plurality of nozzles and a plurality of liquid return capillariesFIG. 1 shows, by way of example, a schematic functional structure of an inkjet print head ( 1) according to the disclosure for the selective dropwise metering of a liquid (F) in a 3D printer.The inkjet print head (1) comprises an inkjet printing module (100) for selective dropwise dosing of the liquid (F). The inkjet printhead (1) may comprise one or more inkjet printing modules (100). Furthermore, the term inkjet print head (1) can comprise a unit of a plurality of inkjet print heads (1). The plurality of inkjet print heads ( 1) can be moved synchronously within the 3D printer, for example.The inkjet printing module (100) comprises a liquid inlet (110) for supplying the liquid (F) into the inkjet printing module (100), at least one nozzle (120), preferably comprising a nozzle opening (121) and a nozzle chamber (122) for dispensing a dosable drop of the liquid (FT) in the 3D printer, and a liquid return (130) for returning a return medium (R) from the inkjet printing module (100), comprising at least one liquid return capillary (131) for returning the return medium (M) from the nozzle (120), wherein the return medium (R) comprises the liquid (F) and / or a disturbing medium (S), wherein the disturbance medium (S) from the 3D printer may comprise air (L) and / or particles (P) received in the nozzle (120).FIG. 5 shows, by way of example, a schematic functional structure of the inkjet printing module ( 100) according to the disclosure, having a liquid inlet ( 110), a nozzle ( 120) and a liquid return capillary ( 131). In FIG. 5, a sectional plane (SE) is shown along the longitudinal axis of the liquid return capillary ( 131). FIG. 6 shows, by way of example, a schematic functional structure of an inkjet printing module ( 100) having a plurality of nozzle openings ( 121) and a plurality of liquid return capillaries ( 131) along the sectional plane (SE) in FIG. 5.As shown in FIG. 5, the liquid (F) can be supplied to the nozzle ( 120) via a liquid inlet ( 110). The liquid (F) can enter the nozzle chamber (122), for example by a pressure resulting from the intrinsic weight of the liquid (F). The nozzle chamber (122) is formed by a plurality of nozzle chamber walls (123), for example. The nozzle chamber wall ( 123) can be deformable in a piezo print head. The nozzle opening ( 121) can have a smaller axial diameter than the nozzle chamber ( 122). The nozzle ( 120), in particular the nozzle opening ( 121), can be cylindrical. For returning the return medium (R) from the nozzle (120), the liquid return capillary (131) can lead away from the nozzle chamber (122).As shown in FIG. 6, the liquid return capillary (131) can lead to a discharge channel (133). The return medium (R) can be returned from the inkjet printing module (100) via the summation channel (133). The reaction channels ( 133) can unite and guide the return medium (R) to a liquid return outlet ( 132) of the inkjet printing module ( 100), at which the return medium (R) leaves the inkjet printing module ( 100) (see FIG. 1 ). As shown in FIG. 6, the liquid return capillaries (131) may have, for example, a V-shaped path arrangement.As shown in FIG. 1, the inkjet print head (1) comprises a liquid tank (200) for holding the liquid (F) in place and for supplying the liquid (F) to the liquid inlet (110) of the inkjet print module (100). The liquid tank (200) comprises a liquid supply (210) for tracking liquid (F) to the liquid tank (200), a negative pressure connection (230) for applying a negative pressure (U), in particular to the liquid tank (200), wherein as a result of the negative pressure (U) a meniscus equilibrium pressure (MGD) in the nozzle (120) is adjustable, by means of which uncontrolled escape of the liquid (F) from the nozzle (120) and / or uncontrolled suction in of the disturbance medium (S) from the 3D printer into the nozzle (120) is prevented, and a return liquid supply (240) for returning liquid (F) from the inkjet printing module (100) via the liquid return (130) into the liquid tank (200). The liquid tank (200) may further comprise a level sensor (220) for monitoring the level of the liquid (F) in the liquid tank (200).As shown in FIG. 1, the inkjet print head (1) comprises a return pump (300) for pumping the return medium (R) out of the inkjet print module (100) via the liquid return (130) into the return liquid supply (240) of the liquid tank (200). In a system with a plurality of inkjet printing modules (100), one or more return pumps (300) can be connected to each inkjet printing module (100). Alternatively, one or more return pumps (300) may be connected to a plurality of inkjet printing modules (100) simultaneously. The return pump (300) can be integrated into the inkjet print head (1) or arranged on the latter. Furthermore, in the case of a unit of a plurality of inkjet print heads (1), one or more return pumps (300) can be connected to a plurality of inkjet print heads (1). These aspects may be advantageous individually or in combination in order to reduce the number of return pumps (300) required and thus the space requirement in and / or on the inkjet print head (1).As shown in FIG. 1, the inkjet print head ( 1) can comprise a filter ( 500) and / or a degasser ( 600), in order to filter out the interfering medium (S), in particular particles (P) and / or air (L), from the return medium (R). In a system having a plurality of inkjet printing modules (100), one or more filters (500) and / or one or more degassers (600) can be connected to each inkjet printing module (100). Alternatively, one or more filters (500) and / or one or more degassers (600) may be connected to a plurality of inkjet printing modules (100) simultaneously. The filter ( 500) and / or the degasser ( 600) can be integrated into the inkjet printhead ( 1) or arranged thereon. Furthermore, in the case of a unit of a plurality of inkjet print heads (1), one or more filters (500) and / or one or more degassers (600) can be connected to a plurality of inkjet print heads (1). These aspects may be advantageous individually or in combination in order to reduce the number of filters (500) and / or degassers (600) required and thus the space requirement in and / or on the inkjet printhead (1).In an embodiment not shown in the figures, the inkjet print head (1) can comprise a device for tempering liquid (F) and / or the return medium (R). Consequently, the liquid (F) to be printed can be kept in a temperature window in which the inkjet print head (1)I, in particular the inkjet print module (100), is operated under ideal conditions. In particular, under ideal conditions, it can be assumed that the actual quantity of liquid (F) printed corresponds to the desired quantity to be printed corresponding to the control pulses output.In an embodiment not shown in the figures, the inkjet printhead (1) may comprise a device for feeding an additive liquid (A) into the liquid circuit of the liquid (F) and / or the return medium (R). The addition of the additive liquid (A) can contribute to a targeted change in the properties of the liquid (F) and / or of the reflux medium (R). For example, by adding the additive liquid (A), an unwanted viscosity change of the liquid (F) and / or of the return medium (R) can be corrected. Alternatively, the addition of the additive liquid (A) can prevent unwanted clump formation of particles (P) in the inkjet print head (1), in particular in the nozzles (120) of the inkjet print module (100). Consequently, clogging of the nozzles (120) can be prevented.In an embodiment not shown in the figures, the inkjet print head (1) can comprise a device for flushing the liquid return (130). Consequently, blockages present in the liquid return (130), in particular in the liquid return capillaries (131), can be dissolved or flushed out. For example, particles (P) adhering in the liquid return capillaries (131) can be flushed out.As shown in FIG. 1, a pulsation damper (400) is arranged between the return pump (300) and the liquid return (130) of the inkjet printing module (100). All the features described with respect to the pulsation damper (400) can relate both to the pulsation damper (400) as a separate object according to claim 25 and to the inkjet print head (1) comprising the pulsation damper (400) according to claim 1.The pulsation damper (400) is preferably designed to dampen pressure fluctuations of the return pump (300). The pulsation damper (400) can be configured such that the pressure fluctuations resulting from the pressure fluctuations of the return pump (300) are damped towards the nozzle (120) in such a way that the meniscus equilibrium pressure (MGD) is held in a working window in which uncontrolled escape of the liquid (F) from the nozzle (120) and / or uncontrolled suction of the disturbance medium (S) from the 3D printer into the nozzle (120) is prevented. The pressure fluctuations resulting from the pressure fluctuations of the return pump (300) towards the nozzle (120) are preferably attenuated to an amplitude of at most 5 mBar, preferably to at most 1 mBar. In a system with a plurality of inkjet printing modules (100), one or more pulsation dampers (400) can be connected to each inkjet printing module (100). Alternatively, one or more pulsation dampers (400) may be connected to a plurality of inkjet printing modules (100) simultaneously. The pulsation damper (400) can be integrated into the inkjet print head (1) or arranged on the latter. Furthermore, in the case of a unit of a plurality of inkjet print heads (1), one or more pulsation dampers (400) can be connected to a plurality of inkjet print heads (1). These aspects can be advantageous individually or in combination in order to reduce the number of pulsation dampers (400) required and thus the space requirement in and / or on the inkjet print head (1).FIGS. 2 to 4 show, by way of example, an embodiment of a pulsation damper ( 400). The pulsation damper (400) comprises a pump connection (420) for connecting to the return pump (300) and a module connection (430) for connecting to the liquid return (130) of the inkjet printing module (100).Furthermore, FIGS. 2 to 4 show, by way of example, the return pump ( 300). The return pump (300) may include a return pump inlet (310) for connecting to the pulsation damper (400) and a return pump outlet (320) for connecting to the liquid tank (200). As shown in FIG. 4, the return pump outlet (320) may pass through a portion of the pulsation damper (400).The return pump (300) may comprise, for example, a Brushless motor for conveying the return medium (R). Furthermore, the return pump (300) comprises a control system, at which the pump output is adjustable. Preferably, the pump power is set to a constant value when the inkjet printhead ( 1) is put into operation.The liquid return (130) may include a liquid return outlet (132) for connection to the pulsation damper (400).The pulsation damper (400), the pump connection (420), the module connection (430), the return pump inlet (310) and / or the liquid return outlet (132) can be formed rigidly. Pressure fluctuations arising within these components are preferably minimized, in particular pressure fluctuations resulting from uncontrolled oscillations, resonances and / or damping of these components. In this context, rigid means that these components have no or little elasticity. Consequently, changing flow rates and / or pressures do not lead to any oscillation of these materials, as a result of which the already prevailing pressure fluctuations of the return pump ( 300) are not amplified, changed or attenuated in an uncontrolled manner. This is advantageous since, in addition to the pressure fluctuations resulting from the operation of the return pump ( 300), the generation of additional pressure fluctuations is thus minimized. Furthermore, a defined damping of pressure fluctuations takes place exclusively in the pulsation damper ( 400). Unpredictable attenuations or resonances in other components, for example depending on the flow rate of the liquids, are minimized. This results in a system having high operating stability under constant operating conditions.Furthermore, the pump connection ( 420), the module connection ( 430), the return pump inlet ( 310) of the return pump ( 300) and / or the liquid return outlet ( 130) of the inkjet printing module ( 100) can be short. Pressure fluctuations arising within these components are preferably minimized, in particular pressure fluctuations resulting from uncontrolled oscillations, resonances and / or damping of these components. In this context, short means in particular that these components are shorter than 15 cm, preferably shorter than 10 cm, more preferably shorter than 5 cm. This is a significant difference from flow systems in which the pumps and the liquid tank are often not integrated into the print head, since the components required for generating the high flow rates are designed to be comparatively large and consequently cannot be integrated into such print heads.As shown in FIGS. 2 to 4, the pulsation damper ( 400) is preferably arranged directly in front of the return pump ( 300) in the flow direction of the return medium (R). The pump connection ( 420) and / or the return pump inlet ( 310) are preferably short. Pressure fluctuations arising within the return pump are preferably attenuated after a short fluid path has been passed through in the pulsation damper ( 400). In this context, a fluid path of less than 15 cm can be used, preferably less than 10 cm, more preferably less than 5 cm or 2 cm. Consequently, the pressure fluctuations arising in the return pump ( 300) cannot spread effectively in the direction of the inkjet printing module ( 100). Preferably, the pump connection ( 420) and / or the return pump inlet ( 310) together have an overall length of less than 15 cm, in particular of less than 10 cm, more preferably of less than 5 cm or 2 cm. For example, as shown in FIGS. 2-4, the return pump inlet (310) may be penetrable into the pump connection (420), for example, via a port penetrating an opening.The pulsation damper (400) can be interchangeably connectable to the return pump (300) and / or to the inkjet printing module (100). Consequently, the pulsation damper (400) can be easily replaced in maintenance work. For this purpose, the pump connection (420), the module connection (430), the return pump inlet (310) of the return pump (300) and / or the liquid return outlet (130) of the inkjet printing module (100) can comprise, for example, interchangeably connectable plug and / or screw connections. Since the pulsation damper (400) is easily replaceable, the damping properties of the inkjet print head (1) can be quickly adjusted with little maintenance effort. This is particularly advantageous if the inkjet print head ( 1) is converted, for example, to operation with another liquid (F) having different (oscillation) properties. Another pulsation damper ( 400), for example with different dimensions or different materials and thus different damping properties, can easily be installed without having to adapt further components of the inkjet printhead ( 1).As shown in FIGS. 1, 2 and 3, the pulsation damper (400) may include a diaphragm (410) for damping the pressure fluctuations of the return pump (300). The membrane ( 410) is preferably designed to be elastic. Preferably, the membrane ( 410) has a high elasticity and / or a low Shore hardness. Preferably, the membrane (410) is made of a material resistant to the liquid (F). For example, the membrane ( 410) can consist of a plastic, preferably of an elastomer such as EPDM.FIGS. 2 and 3 show an embodiment of a pulsation damper ( 400) according to the disclosure. All the features described with respect to the pulsation damper (400) can relate both to the pulsation damper (400) as a separate object according to claim 25 and to the inkjet print head (1) comprising the pulsation damper (400) according to claim 1.The pulsation damper (400) can comprise a line body (440), which forms a line volume (441), through which the return medium (R) flows. Furthermore, the pulsation damper (400) can comprise a damping body (450) which forms a damping volume (451).The membrane (410) can be attachable, in particular clampable, between the line body (440) and the damping body (450), so that the membrane (410) and the line body (440) form a closed line volume (441), through which the return medium (R) flows, wherein the return medium (R) flows past the membrane (410). Furthermore, the membrane ( 410) and the damping body ( 450) can form a closed damping volume ( 451), through which no return medium (R) flows. Preferably, the line volume ( 441) and / or the damping volume ( 451) are larger than the further fluid line volume between the inkjet printing module ( 100) and the return pump ( 300). The line volume ( 441) and / or the damping volume ( 451) form an intermediate reservoir compared to the further fluid line volume between the inkjet printing module ( 100) and the return pump ( 300). Consequently, effective damping can be effected in the intermediate reservoir. The pressure fluctuations of the return pump ( 300) can be attenuated in a defined manner in the intermediate reservoir. The pressure fluctuations can be effectively attenuated at the relatively large diaphragm ( 410) between the relatively large line body ( 440) and the relatively large attenuation body ( 450) with a small amplitude deflection of the diaphragm ( 410). In particular, the line volume ( 441) and / or the damping volume ( 451) are at least 10 times greater than the further line volume between the inkjet printing module ( 100) and the return pump ( 300). Furthermore, the effective surface of the membrane (410) past which the return medium (R) flows is greater than the diameter of the fluid lines of the inkjet print head (1), in particular greater than the diameter of the pump connection (420), of the module connection (430), of the return pump inlet (310), of the return pump outlet (320) and / or of the components of the liquid return (130). The pressure fluctuations can be effectively attenuated at the relatively large effective surface of the diaphragm ( 410) with a small amplitude deflection of the diaphragm ( 410). In an embodiment not shown, the membrane (410) may be arranged on an adapter. The adapter may be formed of a rigid material. The adapter may include an opening. The adapter can be designed (for example via the opening) to preset the effective surface of the diaphragm ( 410), within which the diaphragm ( 410) can vibrate and dampen the pressure fluctuations. The adapter can be arranged interchangeably. During maintenance, the adapter can be replaced, for example, by another adapter which specifies a different effective surface for the diaphragm ( 410). Consequently, the size and / or the shape of the effective surface of the membrane ( 410) can be varied. As a result, for example, the damping properties of the pulsation damper ( 400) can be adapted.The damping body ( 450) can be fillable with a damping medium (D), in particular with the liquid (F), for example via a damping body opening ( 452). Alternatively, another damping medium (D) may be used that has certain desired damping characteristics. For example, the damping medium (M) can comprise air (L), or any desired gaseous medium. The damping medium (D) is preferably filled exclusively during installation or maintenance work. For the operation of the inkjet print head ( 1), the damping body ( 450) can be closed in a fluid-tight manner, for example with a shut-off valve ( 700). In addition, the pulsation damper (400) can comprise a device for tempering the damping medium (D). By changing the temperature of the damping medium (D), its damping properties can be varied in a targeted manner.The membrane ( 410) can oscillate between the line volume ( 441) and the damping volume ( 451) as the return medium (R) flows past. The inherent elasticity of the membrane ( 410) and / or the fluid properties of the return medium (R) in the line volume ( 441) and / or of the damping medium (D) in the damping volume ( 451) can in this case damp the pressure fluctuations from the return pump ( 300) in a defined manner. The damping properties of the pulsation damper ( 400) can be varied, inter alia, via the elasticity and / or the size and / or the shape of the effective surface of the membrane ( 410). Furthermore, the damping properties of the pulsation damper ( 400) can be varied, for example, via the type of damping medium (D) and the size of the damping volume ( 451). Furthermore, the damping properties can be varied over the size of the line volume ( 441).For example, the line body ( 440) and the damping body ( 450) can be detachably connected, in particular via one or more bores and screws. Consequently, the diaphragm ( 410) and / or the damping body ( 450) and / or the line body ( 440) and / or the adapter can be easily replaced without having to perform further adaptations to the inkjet printhead ( 1).In an alternative embodiment, the filter ( 500) and / or the degasser ( 600) can be integrated into the pulsation damper ( 400). Consequently, all components of the inkjet printhead (1) that must be regularly maintained are integrated in an easily replaceable device. This ensures simplified serviceability of the inkjet print head ( 1).In an embodiment not shown in the figures, the disclosure further comprises a 3D printer, a coater for applying particles (P) layer by layer on a construction field of the 3D printer, and an inkjet print head (1) according to the disclosure for selectively solidifying the particles (P) applied layer by selective dropwise metering of the liquid (F).The 3D printer preferably comprises a supply printing line, via which the 3D printer is supplied with a supply printing air. The supply printing air can be supplied to the 3D printer with a minimum overprint, preferably of over 2.5 bar.The 3D printer may comprise a Venturi valve, at which the negative pressure (U) is generated via the supply of the supply pressurized air. Alternatively, the negative pressure (U) can be generated via a pump.Experience has shown that the reduced pressure (U) only breaks from a pressure of the supply compressed air which is significantly below the minimum excess pressure, for example at 1 bar.The 3D printer can be configured such that all shut-off valves, in particular the shut-off valves ( 700) at the liquid inlet ( 110) and / or at the liquid return ( 130), automatically shut off the fluid flow within these lines. For this purpose, the shut-off valves can be self-closing pneumatic shut-off valves which automatically close when the minimum overpressure is undershot. Alternatively, the shut-off valves can be electrically connected and automatically close when the minimum overpressure is undershot. This is advantageous since the shut-off valves close even before the vacuum (U) applied to the inkjet print head ( 1) is broken off. Uncontrolled leakage of the liquid (F) from the printing module (100) is prevented even before the negative pressure (U) breaks off and no longer counteracts the force of gravity of the liquid (F) in the inkjet printing module (100). Control systems can be saved. This represents a substantial advantage over continuous flow systems in which the pressures and / or flow rates present at the inlets and outlets of the pressure modules must be continuously measured and readjusted in order to prevent uncontrolled leakage of the liquid (F) from the pressure module.Modifications of the invention are possible in various ways. The features shown, described or claimed for the respective exemplary embodiments can be combined with one another in any desired manner, replaced, supplemented or omitted.Reference numerals denote reference numerals1 Inkjet print head 100 Inkjet print module 110 Liquid inlet 120 Nozzle 121 Nozzle opening 122 Nozzle chamber 123 Nozzle chamber wall 130 Liquid return 131 Liquid return capillary 132 Liquid return outlet 133 Filling channel 200 Liquid tank 210 Liquid supply 220 Fill level sensor 230 Negative pressure connection 240 Return liquid supply 300 Return pump 310 Return pump inlet 320 Return pump outlet 400 Pulsation damper 410 Membrane 420 Pump connection 430 Module connection 440 Line body 441 Line volume 450 Damping body 451 Damping volume 452 Damping body opening 500 Filter 600 Degasser 700 Shut-off valve U Negative pressure MGD Meniscus equilibrium pressure F Liquid FT Liquid drop R Return medium S Disturbance medium L Air P Particle D Damping medium SE Sectional planeReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2013 110 108 A1

[0007] JP 2019-084772 A

[0008]

Claims

An inkjet printhead (1) for selectively metering liquid (F) dropwise in a 3D printer, the inkjet printhead (1) comprising: - an inkjet printing module (100) for selectively metering liquid (F) dropwise, the inkjet printing module (100) comprising: ▪ a liquid inlet (110) for supplying the liquid (F) into the inkjet printing module (100); ▪ at least one nozzle (120) for dispensing a meterable drop of the liquid (FT) in the 3D printer; ▪ and a liquid return (130) for returning a return medium (R) from the inkjet printing module (100), comprising at least one liquid return capillary (131) for returning the return medium (M) from the nozzle (120), wherein the return medium (R) comprises the liquid (F) and / or a disturbance medium (S), in particular air (L) and / or particles (P) taken into the nozzle (120) from the 3D printer; a liquid tank (200) for holding the liquid (F) in hand and for supplying the liquid inlet (110) of the inkjet printing module (100) with the liquid (F), wherein the liquid tank (200) comprises: ▪ a liquid supply (210) for tracking liquid (F) to the liquid tank (200); ▪ a negative pressure connection (230) for applying a negative pressure (U), in particular to the liquid tank (200), wherein as a result of the negative pressure (U) a meniscus equilibrium pressure (MGD) can be set in the nozzle (120), by means of which uncontrolled escape of the liquid (F) from the nozzle (120) and / or uncontrolled suction of the disturbance medium (S) from the 3D printer into the nozzle (120) is prevented; ▪ and a return liquid supply (240) for returning liquid (F) from the inkjet printing module (100) via the liquid return (130) into the liquid tank (200); - and a return pump (300) for pumping out the return medium (R) from the inkjet printing module (100) via the liquid return (130) into the return liquid supply (240); wherein a pulsation damper (400) is arranged between the return pump (300) and the liquid return (130).The inkjet printhead (1) according to claim 1, wherein the pulsation damper (400) is configured to attenuate pressure fluctuations of the return pump (300)Inkjet print head (1) according to one of the preceding claims, wherein the pulsation damper (400) is designed such that the pressure fluctuations resulting from the pressure fluctuations of the return pump (300) are damped towards the nozzle (120) in such a way that the meniscus equilibrium pressure (MGD) is held in a working window in which uncontrolled escape of the liquid (F) from the nozzle (120) and / or uncontrolled suction of the disturbance medium (S) from the 3D printer into the nozzle (120) is prevented.Inkjet print head (1) according to one of the preceding claims, wherein the pressure fluctuations resulting from the pressure fluctuations of the return pump (300) towards the nozzle (120) are attenuated to an amplitude of at most 5 mBar, preferably to at most 1 mBar.The inkjet printhead (1) of any preceding claim, wherein the liquid return (130) comprises a liquid return outlet (132) for connection to the pulsation damper (400).The inkjet printhead (1) of any preceding claim, wherein the return pump (300) comprises a return pump inlet (310) for connection to the pulsation damper (400) and a return pump outlet (320) for connection to the liquid tank (200).The inkjet printhead (1) according to any of the preceding claims, wherein the pulsation damper (400) comprises a pump connection (420) for connection to the return pump (300) and a module connection (430) for connection to the liquid return (130) of the inkjet printing module (100).The inkjet printhead (1) according to any one of the preceding claims, wherein the pulsation damper (400), the pump connection (420), the module connection (430), the return pump inlet (310) and / or the liquid return outlet (132) are formed rigidly.Inkjet print head (1) according to one of the preceding claims, wherein the pump connection (420), the module connection (430), the return pump inlet (310) of the return pump (300) and / or the liquid return outlet (130) of the inkjet print module (100) are short, in particular shorter than 15 cm, preferably shorter than 10 cm.Inkjet print head (1) according to one of the preceding claims, wherein the pulsation damper (400) is arranged directly in front of the return pump (300) in the flow direction of the return medium (R), wherein in particular the pump connection (420) and / or the return pump inlet (310) are formed short, in particular shorter than 15 cm, preferably shorter than 10 cm.The inkjet print head (1) according to any one of the preceding claims, wherein the pulsation damper (400) is interchangeably connectable to the return pump (300) and / or to the inkjet printing module (100).The inkjet printhead (1) according to any of the preceding claims, wherein the pulsation damper (400) comprises a membrane (410) for damping the pressure fluctuations of the return pump (300).Inkjet print head (1) according to one of the preceding claims, wherein the membrane (410) is formed to be elastic.Inkjet print head (1) according to one of the preceding claims, wherein the pulsation damper (400) is designed such that the return medium (R) can flow past the membrane (410).Inkjet printhead (1) according to any of the preceding claims, wherein the pulsation damper (400) comprises a conduit body (440) forming a conduit volume (441) through which the return medium (R) flows.The inkjet printhead (1) according to any of the preceding claims, wherein the pulsation damper (400) comprises a damping body (450) forming a damping volume (451).The inkjet printhead (1) according to any of the preceding claims, wherein the membrane (410) is attachable between the conduit body (440) and the damping body (450).Inkjet print head (1) according to one of the preceding claims, wherein the membrane (410) can be clamped between the line body (440) and the damping body (450).Inkjet print head (1) according to one of the preceding claims, wherein the membrane (410) can be attached between the line body (440) and the damping body (450) in such a way that the membrane (410) and the line body (440) form a closed line volume (441), through which the return medium (R) flows, wherein the return medium (R) flows past the membrane (410).Inkjet print head (1) according to one of the preceding claims, wherein the membrane (410) can be attached between the line body (440) and the damping body (450) in such a way that the membrane (410) and the damping body (450) form a closed damping volume (451), through which no return medium (R) flows.Inkjet print head (1) according to one of the preceding claims, wherein the line body (440) and the damping body (450) can be detachably connected, in particular via one or more bores and screws.Inkjet print head (1) according to one of the preceding claims, wherein the damping body (450), in particular via a damping body opening (452), can be filled with a damping medium (D), in particular with the liquid (F).The inkjet printhead (1) according to any of the preceding claims, wherein the liquid tank (200) comprises a level sensor (220) for monitoring the level of the liquid (F) in the liquid tank (200).The inkjet print head (1) according to any one of the preceding claims, wherein the inkjet print head (1) comprises a shut-off valve (700), wherein the shut-off valve (700) is arranged at the liquid inlet (110), at the liquid return (130), and / or at the damping body opening (452).Pulsation damper (400) for damping pressure fluctuations, wherein the pulsation damper (400) comprises: - a membrane (410) for damping the pressure fluctuations, - a line body (440) which forms a line volume (441) through which a return medium (R) flows, and - a damping body (450) which forms a damping volume (451); wherein the pulsation damper (400) is designed such that the return medium (R) can flow past the membrane (410).A 3D printer comprising: - a coater for applying particles (P) layer by layer on a construction field of the 3D printer, and - an inkjet print head (1) according to one of the preceding claims, for selectively solidifying the particles (P) applied layer by layer by selectively metering the liquid (F) dropwise.

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