Print head for an inkjet printer, in particular for coating print media

Abstract

A print head for an inkjet printer, wherein the print head has at least one ink supply channel and at least one nozzle with a nozzle channel and inflow opening, wherein ink from the ink supply channel can be pressed through the inflow opening into the nozzle channel and can be ejected therefrom, wherein the nozzle is arranged in a stationary manner on a side wall of the ink supply channel and the at least one nozzle is assigned a plunger, with a plunger end face located in the ink supply channel and located opposite the inflow opening and spaced apart therefrom, wherein the print head comprises first means for moving the plunger end face in the ink supply channel between a reversal point (U1) which is minimally spaced from the inflow opening of the nozzle and a reversal point (U2) which is maximally spaced from the inflow opening of the nozzle, wherein the first means limit the movement of a plunger end face to a movement between the reversal points (U1, U2) and second means are provided for acting upon the ink in the ink supply channel with a negative pressure relative to the ambient air pressure, wherein at least one set of said nozzles is present, which comprises the one nozzle and wherein a single common plunger is assigned to all nozzles of the one set of nozzles.

Description

[0001] Print head for an inkjet printer, in particular for coating printing media

[0002] The present invention relates to a print head for an inkjet printer according to the preamble of claim 1 and to a method for carrying out printing processes according to the preamble of claim 17.

[0003] Devices and methods for coating print media are typically used to apply at least one coating as uniformly as possible, which can fulfill specific functional and / or decorative purposes and is intended to improve the surface properties of the print media. Non-contact coating methods are preferred when relatively high coating speeds are required.

[0004] In contactless application processes and the devices underlying such processes, it is of great importance not only to deliver ink as evenly as possible over a specific delivery width of the print head, but also to apply the ink as evenly as possible over a specific application width of the printing medium to be covered.

[0005] To coat ceramic printing media, non-contact processes are typically used to refine their surfaces, usually using a glaze suspension.

[0006] A previously known print head for coating a printing medium is designed to apply ink to its surface by dispensing the ink in the form of drops from independently controllable nozzles of the print head onto the printing medium to be printed.

[0007] WO2013013983A1, for example, discloses such a printhead, which is designed as a drop-on-demand (DOD) printhead. This printhead has an ink supply channel and at least one nozzle with a nozzle channel and inlet opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inlet opening and ejected therefrom. A plunger with a plunger end located in the ink supply channel and spaced opposite the inlet opening is assigned to one nozzle. Multiple nozzles are present in the ink supply channel, with each nozzle being assigned a respective plunger. This prior art printhead comprises first means for moving the plunger end in the ink supply channel between a reversal point (U1) at a minimum distance from the nozzle inlet opening and a reversal point (U2) at a maximum distance from the nozzle inlet opening.

[0008] This previously known print head, operated by tappets, is suitable for the uniform dispensing and application of glaze suspension to printing media, especially when a relatively large amount of glaze suspension is to be dispensed per nozzle and time. However, due to its complex design, it requires a high level of manufacturing effort and is relatively prone to failure. Consequently, its acquisition and, in particular, maintenance are relatively expensive. In fact, print heads and processes operating with DOD are, by their very nature, actually designed to print not wide areas or solid surfaces, but rather every conceivable complex and fine pattern on printing media.

[0009] In addition, plunger-operated print heads in particular have a relatively high energy consumption per amount of ink dispensed per nozzle.

[0010] There is therefore a need to provide a plunger-operated drop-on-demand (DOD) printhead with multiple nozzles which enables efficient dispensing of ink from its nozzles by means of simple and cost-effective construction and which, in particular, has lower energy consumption per quantity of dispensed ink per nozzle.

[0011] The present invention is therefore based on the object of providing a plunger-operated drop-on-demand (DOD) print head with multiple nozzles, which enables efficient dispensing of ink from its nozzles by means of simple and cost-effective construction, and which in particular has a lower energy consumption per amount of dispensed ink per nozzle.

[0012] According to the invention, the object is achieved with a print head comprising the features of claim 1 and with a method comprising the features of claim 18. The respective subclaims relate to further advantageous and possibly additionally inventive embodiments.

[0013] The invention is based on the idea that all nozzles of a set of nozzles are assigned a single common plunger. The print head according to the present invention is a print head for an inkjet printer, wherein the print head has at least one ink supply channel and at least one nozzle with a nozzle channel and inlet opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inlet opening and ejected therefrom, wherein the nozzle is arranged in a fixed position on a side wall of the ink supply channel, and a plunger with a plunger end face located in the ink supply channel and spaced opposite the inlet opening is assigned to the at least one nozzle.wherein the print head comprises first means for moving the plunger end face in the ink supply channel between a reversal point (U1) at a minimum distance from the inlet opening of the nozzle and a reversal point (U2) at a maximum distance from the inlet opening of the nozzle, wherein the first means limit the movement of a plunger end face to a movement between the reversal points (U1, U2), and second means are provided for subjecting the ink in the ink supply channel to a negative pressure relative to the ambient air pressure, wherein at least one set of said nozzles is present, which comprises the one nozzle.

[0014] According to the invention, all nozzles of one set of nozzles are assigned a single common tappet.

[0015] A set of nozzles comprises a predetermined number of nozzles.

[0016] The negative pressure prevents ink from accidentally leaking from the ink supply channel and the nozzle channels. In this way, a closure body is not required. To eject the ink from all nozzles of the one set of nozzles, the plunger provided in the ink supply channel is used. The end face of the plunger is moved towards the nozzle channels of the one set of nozzles, whereby ink is pressed through the nozzle channels of the one set of nozzles and out of them. Preferably, a plunger / nozzle distance is maintained throughout the entire printing process, i.e. a plunger end face at a reversal point is at a distance from the inlet opening of greater than zero and the inlet openings of the nozzles of the one set of nozzles remain permanently open throughout the entire printing process. The plunger according to the invention therefore does not take on the function of a closure body.

[0017] The print head according to the invention makes it possible to use inks with a wide viscosity range and / or particles. This is particularly true because the plunger does not have to function as a closure body, and the ink and / or particles that move between the plunger face and the inlet openings of the nozzle channels of the set of nozzles do not cause interference.

[0018] Accordingly, according to a preferred embodiment, at the minimum distanced reversal point (U1), the distance at any point between the tappet face and each inlet opening of each nozzle of the one set of nozzles is greater than zero.

[0019] This further development offers the advantage of preventing collisions between the plunger and the nozzles, thus increasing the service life of the plunger, the first means and the print head.

[0020] According to a further preferred embodiment, the first means comprise at least a first and a second actuator, wherein the plunger is operatively connected at a first section of the plunger via a first push rod to a first actuating element of the first actuator and at a second section of the plunger via a second push rod to a second actuating element of the second actuator, wherein the first and second sections are spaced apart from one another in particular in a direction vertical to the nozzle axis of one nozzle of the one set of nozzles.

[0021] This refinement offers the advantage of allowing a more space-saving design of the first means. Consequently, the smaller footprint of the first means enables a higher print resolution of the print head, which in turn can increase the print head's productivity, particularly in terms of the amount of ink ejected per unit of time.

[0022] Furthermore, it is possible for the one set of nozzles to comprise at least thirty nozzles, preferably at least fifty nozzles, particularly preferably at least seventy nozzles, which are very particularly preferably arranged in one or more rows.

[0023] Furthermore, it is of course possible for the one set of nozzles to comprise thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles, which are most preferably arranged in one or more rows.

[0024] If at least thirty nozzles are assigned to a single common plunger which is operatively connected to at least two actuators, the common plunger interacts synergistically with said nozzles in that when droplets of a given size are ejected from each of the plurality of nozzles, a total amount of energy is consumed which is far less than the sum of the energies which would be consumed when droplets of the same size are ejected if each nozzle were assigned a single plunger which is operatively connected to one of said actuators.

[0025] Accordingly, the print head according to the invention can be used to control a set of nozzles for ejecting ink in an energy-saving manner.

[0026] An actuator is a general term for a device that converts electrical signals into mechanical movement or other physical quantities. Actuators, as defined in the present invention, convert electrical signals into mechanical movement.

[0027] According to a preferred embodiment, it is possible for the first actuator to be designed to move one end of the first section of the plunger end face in the ink supply channel between the reversal point (U1) that is at a minimum distance from the inflow opening of one nozzle of the one set of nozzles and the reversal point (U2) that is at a maximum distance from the inflow opening of one nozzle of the one set of nozzles, and for the second actuator to be designed to move one end of the second section of the plunger end face in the ink supply channel between a reversal point (U3) that is at a minimum distance from the inflow opening of one nozzle of the one set of nozzles and a reversal point (U4) that is at a maximum distance from the inflow opening of one nozzle of the one set of nozzles.

[0028] Furthermore, it is possible for the second actuator to limit the movement of one end of the second section of the plunger face to a movement between the reversal points (U3, U4) and for the first actuator to limit the movement of one end of the first section of the plunger face to a movement between the reversal points (U1, U2).

[0029] The end of the first section may be a free end of the plunger face, wherein the end of the second section may be a free end of the plunger face opposite the first end of the first section.

[0030] Furthermore, it is possible that the distance between the end of the first section of the tappet end face and the inflow opening of one nozzle of the one set of nozzles at the maximum distanced reversal point (U2) and the distance between the end of the second section of the tappet end face and the inflow opening of one nozzle of the one set of nozzles at the maximum distanced reversal point (U4) can be adjusted by an arrangement for positioning the respective actuator.

[0031] This further development offers the advantage of allowing easy regulation of the ink ejection quantity across all nozzles in the set of nozzles.

[0032] Alternatively, it may also be possible for the distance between the end of the first section of the tappet end face and the inlet opening of one nozzle of the one set of nozzles at the minimum distanced reversal point (U1) and the distance between the end of the second section of the tappet end face and the inlet opening of one nozzle of the one set of nozzles at the minimum distanced reversal point (U3) to be adjustable by an arrangement for positioning the respective actuator.

[0033] Such an arrangement for positioning an actuator is disclosed, for example, in WO2019042586A1 of the same-named owner.

[0034] Furthermore, it is possible that the position of the reversal point (U2) as starting point and the subsequent reversal point (U1) as well as the position of the reversal point (U4) as starting point and the subsequent reversal point (U3) are selected such that a plunger stroke can eject a predetermined and preferably substantially identical amount of ink and thus droplet size from each nozzle of the one set of nozzles.

[0035] Inclined positions of the side wall of the ink supply channel, which often cannot be avoided due to the inherent manufacturing tolerances of all components of the arrangement, can lead to ink drops of different sizes being ejected from different nozzles of one set of nozzles.

[0036] These refinements thus offer the advantage that even if, for example, the side wall of the ink supply channel surrounding the nozzles has a corresponding inclination, a coating with a high degree of homogeneity can still be achieved across the width of the nozzles of a set of nozzles. Consequently, a coating of a printing medium with a more homogeneous ink thickness can be achieved.

[0037] According to a preferred embodiment, the actuators are designed and controllable such that the movement of the tappet end face is effected by a synchronous movement of the first and second tappet rods. The tappet rods can each be firmly connected to the tappet, preferably via a positive connection and / or via a suitable material connection. The positive connection can be designed as a snap connection or a screw connection. The material connection can be designed as an adhesive connection. An adhesive connection includes the tappet rod as the first connection partner, the tappet as the second connection partner, and a suitable adhesive.

[0038] If the interlocking connection partners, i.e. the plunger and the plunger rod, are additionally glued together, a connection can be realized that does not allow any relative movement between the first connection partner and the second connection partner.

[0039] The plunger can be divided into a central and two opposite edge regions, preferably along a longitudinal axis of the plunger, wherein the first section lies in the first edge region and the second section lies in the second edge region opposite the first edge region, wherein the plunger is particularly preferably of an elongated design.

[0040] Each actuating element can be designed as a bending transducer, preferably as a piezoelectric bending transducer.

[0041] Furthermore, it is possible that at the minimum distanced reversal point (U1) and at the minimum distanced reversal point (U3), the distance at any point between the tappet face and each inlet opening of each nozzle of the one set of nozzles is greater than a particle size of the particles of a particle-containing ink.

[0042] Accordingly, the ink supply channel can be filled with an ink containing particles. The ink can be a glaze suspension.

[0043] Furthermore, it is possible for the distance at each point between the plunger end face and each inlet opening of each nozzle of the one set of nozzles to be greater than the volumetric diameter of the particle size d99(v), preferably greater than a factor of two of the volumetric diameter of the particle size d99(v), at the minimally spaced reversal point (U1) and at the minimally spaced reversal point (U3). The aforementioned developments offer the advantage that fragmentation of particles in the affected nozzle opening regions can be at least partially, preferably completely, prevented. Consequently, the service life of the plunger, the first means, and the print head can be increased.

[0044] Third means for pumping the ink through the ink supply channel may be provided, preferably permanently, and in particular at least in the area of ​​action of the plunger in one flow direction to prevent sedimentation of the ink in the ink supply channel.

[0045] Furthermore, it is possible that there are several sets of said nozzles, with each nozzle of the respective set of nozzles being assigned a single common tappet.

[0046] According to a preferred embodiment, no side wall is formed integrally with each nozzle of the set of nozzles, and an end face of the nozzles of the one set of nozzles surrounding each inlet opening is formed flush with an inner surface of a side wall of the ink supply channel that is in contact with the ink.

[0047] According to a further preferred embodiment, however, the side wall of the ink supply channel is formed integrally as a nozzle plate with at least each nozzle of the at least one set of nozzles.

[0048] These further developments offer the advantage that a print head with a higher print resolution can be specified.

[0049] According to a particularly preferred embodiment, an actuator is an actuator with a plunger comprising a base body and a plunger, wherein the base body comprises a base body and a cover element, wherein the base body comprises a bottom wall and a peripheral wall which together form a vessel enclosing a space which can be closed by means of the cover element and wherein a through-opening for the push rod operatively connected to the plunger is provided in the bottom wall, through which opening the push rod projects and the actuating element is provided in the base body, which is also operatively connected to the push rod, wherein the actuating element is designed as a bending transducer which can be divided into a central and an edge region and the bending transducer is arranged with at least part of its edge region on the base body, and the push rod is operatively connected to the bending transducer in the central region of the bending transducer.

[0050] An inkjet printer according to the invention comprises a plurality of printing heads according to the invention, wherein the inkjet printer comprises common second means for subjecting the ink in each ink supply channel of each printing head to a negative pressure relative to the ambient air pressure.

[0051] According to the invention, the object is also achieved by a method for carrying out printing processes according to claim 17.

[0052] The method according to the invention for carrying out printing processes comprises the following steps: a) providing a print head with an ink supply channel, a plunger and a nozzle with a nozzle channel and an inlet opening which forms the connection between the nozzle channel and the ink supply channel; b) filling the ink supply channel with ink; wherein, at least during the time intervals in which no printing is to take place, the ink supply channel is subjected to a negative pressure relative to the ambient air pressure, at least in the region of the inlet opening of the nozzle, thereby preventing ink from flowing out of the nozzle channel even without a closure body, wherein the ink supply channel is provided with at least one set of said nozzles, which set comprises the one nozzle.

[0053] According to the invention, the method is characterized in that a single common tappet is assigned to all nozzles of the one set of nozzles, wherein, in order to eject the ink, one end face of the tappet is moved from a starting point towards all inlet openings of the nozzles of the one set of nozzles.

[0054] According to a preferred embodiment of the method, one end face of the plunger is moved only up to a first reversal point (U1) toward the inlet opening of one nozzle of the set of nozzles, wherein at the first reversal point (U1), the distance at every point between the plunger end face and each inlet opening of each nozzle of the one set of nozzles is greater than zero. Furthermore, it is possible for the one set of nozzles to comprise at least thirty nozzles, preferably at least fifty nozzles, particularly preferably at least seventy nozzles, which are very particularly preferably arranged in one or more rows.

[0055] Furthermore, it is of course possible for the one set of nozzles to comprise thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles, which are most preferably arranged in one or more rows.

[0056] According to a further preferred embodiment of the method, after reaching the first reversal point (U1), the end face of the plunger is moved away from the inlet opening of one nozzle of the one set of nozzles to a second reversal point (U2), which forms the starting point for the subsequent printing cycle.

[0057] According to a particularly preferred embodiment of the method, the position of the starting point and the subsequent reversal point (U1) is selected such that the plunger stroke ejects a predetermined amount of ink and thus droplet size from each nozzle of the one set of nozzles.

[0058] Typically, the direction of the plunger changes at the reversal point (U1) and reversal point (U2) with a predetermined, preferably constant, frequency when a printing medium is to be coated.

[0059] According to a preferred method, the first means are provided with at least a first and a second actuator, wherein the plunger is operatively connected at a first portion of the plunger via a first push rod to a first actuating element of the first actuator and at a second portion of the plunger via a second push rod to a second actuating element of the second actuator, wherein the first and second portions are spaced apart from one another in particular in a direction vertical to the nozzle axis.

[0060] This refinement offers the advantage of allowing for a more space-saving design of the first means. Consequently, the smaller footprint of the first means enables higher print resolution, which in turn increases productivity in terms of the amount of ink ejected per print head unit time.

[0061] It is possible for one end of the first section of the tappet end face to be moved toward the inlet opening of one nozzle of the set of nozzles by means of the first actuator only up to the first reversal point (U1) and for one end of the second section of the tappet end face to be moved toward the inlet opening of one nozzle of the set of nozzles by means of the second actuator only up to a third reversal point (U3).

[0062] Furthermore, it is possible that after reaching the first reversal point (U1) by one end of the first section of the plunger face, this is moved away from the inlet opening of one nozzle of the one set of nozzles by means of the first actuator to the second reversal point (U2), and after reaching the third reversal point (U3) by one end of the second section of the plunger face, it is moved away from the inlet opening of one nozzle of the one set of nozzles by means of the second actuator to the fourth reversal point (U4), wherein the reversal points (U2) and (U4) each form the starting point for the subsequent printing cycle.

[0063] Furthermore, it is possible that the position of the second reversal point (U2) and the subsequent first reversal point (U1) and the position of the fourth reversal point (U4) and the subsequent third reversal point (U3) are selected such that the plunger stroke ejects a predetermined and preferably substantially identical amount of ink and thus droplet size from each nozzle of the one set of nozzles.

[0064] These refinements offer the advantage that even if, for example, the side wall of the ink supply channel surrounding the nozzles has a corresponding inclination, a coating with a high degree of homogeneity can still be achieved across the width of the nozzles of a set of nozzles. Consequently, a coating of a printing medium with a more homogeneous ink thickness can be achieved.

[0065] A ram stroke between the respective reversal points, i.e. the distance traveled by the ram face between the respective reversal points, can have a value in the range between 30 pm and 90 pm, preferably between 40 pm and 80 pm, particularly preferably between 50 pm and 70 pm.

[0066] According to a preferred method, the movement of the tappet end face is effected by a synchronous movement of the first and second push rods by means of the at least first and second actuator.

[0067] The ink can be pumped through the ink supply channel, preferably permanently.

[0068] According to a preferred embodiment, the tappet / nozzle distance at the first reversal point (U1) and optionally at the third reversal point (U3) is between 80 pm and 400 pm, preferably between 200 gm and 280 gm, particularly preferably between 220 pm and

[0069] 260 gm.

[0070] According to a preferred embodiment, at the first reversal point (U1) and the third reversal point (U3), the distance at each point between the plunger face and each inlet opening of each nozzle of the one set of nozzles is greater than a particle size of the particles of a particle-containing ink. Accordingly, the ink supply channel can be filled with a particle-containing ink. The ink can be a glaze suspension.

[0071] Each actuating element can be designed as a bending transducer, preferably as a piezoelectric bending transducer.

[0072] Furthermore, when no voltage is applied to the bending transducer, the plunger face rests at a position that forms a starting point and lies between the respective reversal points (U1, U2) and, if applicable, (U3, U4). It is thus also possible for the distance between the plunger face and the inlet opening of one nozzle of the set of nozzles to be adjusted directly at the starting point by means of a respective arrangement for positioning the respective actuator.

[0073] According to a preferred embodiment of the method, the method comprises the steps:

[0074] - Transport of at least one printing medium along a transport direction in such a way that the printing medium is transported into and out of the effective area of ​​the print head;

[0075] - Coating the at least one printing medium by changing the direction of the plunger at the first reversal point (U1), or optionally changing the direction of one end of the first section of the plunger end face at the first reversal point (U1) and one end of the second section of the plunger end face at the third reversal point (U3), with a predetermined, preferably constant, frequency of preferably > 1 kHz, particularly preferably > 2 kHz.

[0076] According to a more general preferred embodiment of the method, the method comprises the steps:

[0077] - coating at least one printing medium with the print head by changing the direction of the plunger at the first reversal point (U1), or optionally changing the direction of one end of the first section of the plunger end face at the first reversal point (U1) and one end of the second section of the plunger end face at the third reversal point (U3), with a predetermined, preferably constant, frequency, preferably e 1 kHz, particularly preferably > 2 kHz,

[0078] - wherein during coating a continuous unidirectional relative movement occurs between the print head and the at least one printing medium.

[0079] According to a particularly preferred embodiment, the plunger end face is elongated with two opposite elongated longitudinal edges delimiting the plunger end face, wherein two plates are provided in the ink supply channel, each of which is arranged on one of its edges relative to the side wall of the ink supply channel, on which all nozzles of the one set of nozzles are arranged, and at a predetermined distance from the side wall such that the lateral surfaces fictitiously traveled in the ink by the movement of the elongated longitudinal edges are flanked at a predetermined distance by the inner side of the respective plates facing the respective elongated longitudinal edge, wherein the plates are dimensioned sufficiently large and the said distances are selected such that during the coating of a printing medium, a coating is produced on the printing medium,which has a higher homogeneity than a coating that can be produced under otherwise the same conditions but with different corresponding distances and smaller dimensioned plates.

[0080] In the context of the present invention, coating homogeneity is understood as the uniformity of an evaluable attribute of the coating, in particular banding effects, across the entire analyzed area of ​​the coating. Banding effects are known to be visible impairments in the quality of a coating and are characterized by abrupt or continuous transitions in coating attributes, such as gloss and / or layer height, being recognizable within the coating, particularly with the naked eye where transitions of this type are not desired.

[0081] This further development is advantageous because it ensures the production of coated printing media with less waste, regardless of the effective spatial dimensions of the ink supply channel.

[0082] Although the inventor does not wish to commit to a single explanation or theory, it is assumed that the inventive solution can reduce turbulent ink flows in the effective area of ​​the plunger face. There are various ways in which the skilled person can achieve suitable distances and sufficiently large dimensions of the plates. For example, in a first series of tests, they can carry out ink ejection runs with constant, but each time different, and in particular increasingly smaller, distances between the edges of the preselected plates and the said side wall at a preselected distance between the inside of the respective plates and the respective longitudinal edges of the plunger face, and thus check whether, and if so, at which distance(s) acceptable coating or application is possible.This or one of these distances is then set as the specified distance of the respective edge of the panels to the side wall.

[0083] If acceptable coating or application is not achieved, the respective preselected distance between the inside of the respective plates and the respective longitudinal edges of the ram face must be selected larger or smaller in a second test series until a corresponding repetition of the first test series with the newly preselected distance between the inside of the respective plates and the respective longitudinal edges of the ram face results in suitable distances and thus acceptable coating.

[0084] If acceptable coating or application is still not achieved, the size of the plates is increased in a third test series and the first test series and, if necessary, the second test series are repeated until the desired result is achieved.

[0085] A plate is preferably sufficiently large if its height, aligned parallel to the direction of the ram stroke, is at least 50 times the distance traveled by the ram stroke, and its length, aligned vertically to the height, corresponds at least to the length of an elongated longitudinal edge of the ram face. Preferably, the height of the plate is at least 150 times, and most preferably at least 500 times, the distance traveled by the ram stroke.

[0086] However, the specialist can also start the other way around and first carry out a test with constant, but varying distances between the inside of the plates and the respective long edges of the ram face, with a preselected distance between the edge of the preselected plates and the side wall, and check whether and, if so, at what distance or distances acceptable coating or application is possible. This distance or one of these distances is then set as the predetermined distance between the inside of the respective plates and the respective long edges. If acceptable coating or application is not achieved, at least one of the other two parameters is adjusted by carrying out a series of tests until an acceptable result is achieved.

[0087] According to a particularly preferred embodiment, the said plates are dimensioned so large and the said distances are selected such that a waste-free coating of a printing medium is ensured, wherein, in comparison to the respective distances, certain other corresponding distances and possibly smaller dimensioned plates would have led to a printing medium with waste.

[0088] This refinement is advantageous because it ensures the production of waste-free print media regardless of the effective spatial dimensions of the ink supply channel. This ensures that droplets of essentially identical size are ejected from all nozzles in a single set of nozzles.

[0089] The elongated plunger face preferably has a rectangular shape, with two opposite elongated longitudinal edges oriented parallel to each other and connected by two opposite shorter edges that are shorter than the longitudinal edges. A rectangular plunger face can, for example, have the profile of a rectangle or a parallelogram.

[0090] Furthermore, it is possible for the plates to each have a height such that they are in contact with that side wall of the ink supply channel which is opposite the side wall on which all nozzles of the one set of nozzles are arranged.

[0091] Typically, both the elongated plunger face and the two plates are aligned substantially parallel to the ink flow direction in the ink supply channel. In this preferred embodiment, it is further particularly preferred if the plates are arranged on the side wall of the ink supply channel such that the flow of ink between the two plates is not, or not significantly, impeded in the flow direction. The plates can also be directly connected to one another.

[0092] The respective distance between the edges of the plates and the side wall is preferably selected to be greater than the tappet / nozzle distance at the first reversal point (U1) and optionally at the third reversal point (U3), thereby further increasing the reliability of forming a homogeneous coating. Furthermore, it is possible to provide a printer with at least two print heads, each print head applying a print stripe of ink with a print width, the first and second print heads being arranged relative to one another such that the width of the print stripes essentially corresponds to the sum of the stripe widths of the two print heads.

[0093] According to a preferred embodiment, the method is characterized in that for producing a relief-like decoration with areas to be understood as depressions and with areas to be understood as elevations on the printing medium, the method comprises the steps:

[0094] - Applying a water-based ink-repellent liquid composition to the areas to be regarded as depressions on the printing medium with a first dissolution, followed by

[0095] - printing the water-based ink with the print head at a second resolution either exclusively on the areas to be regarded as elevations or exclusively on the areas to be regarded as elevations and on the edge areas of the areas to be regarded as depressions, wherein the first resolution is at least four times, preferably at least eight times higher than the second resolution.

[0096] This further development offers the advantage that relief-like decorations can be achieved with a high level of reproduction accuracy, and moreover, areas that can be regarded as depressions can be created in the relief-like decoration and are always free of ink, thereby achieving a high level of print quality. This advantageous technical effect is particularly noticeable after the firing of a ceramic printing medium. Furthermore, this advantageous effect is guaranteed even if the respective areas that can be regarded as depressions are so large that otherwise, i.e. even if the ink is printed on the respective central areas of the areas that can be regarded as depressions, the effect that emanates from the water-based ink-repellent liquid composition, namely pushing the water-based ink out of the areas that can be regarded as depressions towards the edge, can no longer be guaranteed.

[0097] An edge region of an area to be understood as a depression is to be understood as an edge region which is defined by a fictitious edge of the area to be understood as a depression, which edge region is spaced from the actual edge and which is preferably spaced from the actual edge by up to 1.5 cm, particularly preferably up to 1.0 cm, very particularly preferably up to 0.5 cm, wherein the said edge region thereby defines and encloses a corresponding central region of the area to be understood as a depression but does not overlap with it.

[0098] The person skilled in the art is familiar with the corresponding water-based ink-repellent liquid compositions from the prior art.

[0099] The ink-repellent composition can be applied using an inkjet print head with nozzles, where each individual nozzle can be controlled separately.

[0100] A liquid composition that repels a water-based ink is typically hydrophobic.

[0101] A ceramic printing medium can be provided as the printing medium.

[0102] The ink can be a suspension, preferably a glaze suspension, in particular a water-based glaze suspension, which is particularly preferably a non-Newtonian fluid. The ink can also be a water-based ink, as stated above.

[0103] Furthermore, it is possible to fire the ceramic printing medium with its relief-like decoration in order to create a fired relief-like decoration on the surface of the printing medium, provided that a glaze suspension is used as ink.

[0104] According to a preferred embodiment, after the water-based ink and the liquid composition repellent to the water-based ink have dried on the printing medium, a motif is applied to the areas to be regarded as depressions and / or to the areas to be regarded as elevations by means of at least one inkjet print head with nozzles, in which each individual nozzle can be controlled separately.

[0105] This further development has the advantage that the correspondence between certain relief features and the printed motif leads to a high-quality motif, in particular a natural impression of a motif to be depicted, such as certain stone motifs or wood motifs.

[0106] The method can be used to coat at least one ceramic printing medium with a glaze, engobe, or smaltobe as ink, each in the form of a suspension, by applying it to the at least one ceramic printing medium and then at least partially concentrating it. Layer-by-layer slip application methods for producing a three-dimensional object are known from the prior art.For example, a corresponding method for building up a three-dimensional green body layer by layer is previously known, comprising the steps of: (i) providing an elongated pouring nozzle; (ii) applying a slurry to a surface to form a slurry layer by moving the pouring nozzle back and forth between two opposite positions, during which slurry is poured from the elongated opening of the pouring nozzle, followed by drying the layer to form a powder layer; and (iii) consolidating the powder of the powder layer at the locations corresponding to the cross-section of the green body; and (iv) repeating steps ii) and iii) until the green body has been produced.

[0107] One problem causing the high material consumption is the fact that the currently known layer-by-layer slip application processes for producing three-dimensional objects only implement the manufacturing method described above. There are three-dimensional objects in which almost every layer has relatively small powder areas to be consolidated and correspondingly relatively large powder areas not to be consolidated (free areas). If a pouring nozzle is moved over a free area of ​​a row, it still pours slip over the entire width of the build area. The resulting layer build-up is accompanied by high slip consumption, since the dried form is currently not recyclable or can only be recycled with considerable effort. This is particularly relevant when a constant build area width is relatively large and only very small areas in a large number of layers are to form part of the green body.

[0108] It would therefore be desirable to have a layer-by-layer slip application process that can keep material consumption low regardless of the size of the object.

[0109] The present invention is therefore also based on the object of providing a method for the layer-by-layer production of a green body with which the material consumption can be kept low, thereby providing a more sustainable method.

[0110] The problem is solved by the method according to claim 32.

[0111] Accordingly, according to a preferred embodiment, the method is characterized in that it comprises the steps of producing a three-dimensional green body, comprising the steps of: c) filling the ink supply channel with ink which is a ceramic and / or metallic slurry; d) printing the slurry on a specific surface to form a layer of a green body with the print head by ejecting the slurry from all nozzles of the one set of nozzles at a predetermined, preferably constant frequency, and drying the layer to form a powder layer; e) consolidating the powder of the powder layer at the locations corresponding to the cross-section of the green body; f) repeating steps d) and e) until the green body has been completely produced.

[0112] As a result, with each ejection of the slurry, drops of slurry are ejected from all nozzles of the one set of nozzles. As described above, the ejection of the slurry occurs by moving the end face of the plunger from a starting point towards all inlet openings of the nozzles of the one set of nozzles of the print head. Accordingly, during the corresponding printing, a change of direction of the plunger preferably occurs at the first reversal point (U1), or optionally a change of direction of one end of the first section of the plunger end face at the first reversal point (U1) and of one end of the second section of the plunger end face at the third reversal point (U3), with a predetermined, preferably constant frequency.

[0113] Typically, the green body is dissolved from the unconsolidated powder before firing it into a sintered three-dimensional object.

[0114] According to a preferred embodiment, consolidation is carried out by applying drops of a fixing liquid to the locations corresponding to the cross-section of the green body using an inkjet print head with nozzles, in which each individual nozzle can be controlled separately.

[0115] Furthermore, it is possible that the fixing liquid comprises or consists of an organic binder.

[0116] The fixing liquid, in particular the organic binder, has the property of holding the consolidated ceramic and / or metallic particles and layers together in a form-fitting manner, in particular of gluing them together.

[0117] Typically, the ceramic and / or metallic slip comprises one or more additives, for example at least one dispersant and / or at least one organic binder, which particularly preferably differs from the organic binder of the fixing liquid.

[0118] According to a preferred embodiment, the inkjet print head with nozzles, in which each individual nozzle can be controlled separately, is designed to eject drops of the fixing liquid with a drop volume of <100 pl each, preferably of > 10 pl and < 80 pl each, particularly preferably > 20 pl and < 45 pl each.

[0119] According to a preferred embodiment, the print head is designed to eject drops of the slip with a drop volume which each has at least 15 times the volume, preferably at least 50 times the volume, particularly preferably at least 150 times the volume, very particularly preferably at least 300 times the volume of the drops of the fixing liquid of the inkjet print head with nozzles, in which each individual nozzle can be controlled separately.

[0120] According to a preferred embodiment, all nozzles of the at least one set of nozzles each have an inner nozzle diameter of between 100 pm and 400 pm, preferably between 100 pm and 250 pm, whereby with such print heads, for example, suspensions with larger particles can be printed than with the otherwise typical piezoelectrically operated inkjet printing devices from the prior art, which typically comprise nozzles with an inner diameter of only up to 60 pm.

[0121] According to a particularly preferred embodiment of the method, an inkjet printer for producing a three-dimensional object comprising a plurality of printing heads according to the invention is provided, wherein the inkjet printer comprises common second means for subjecting the ink in each ink supply channel of each printing head to a negative pressure relative to the ambient air pressure, wherein the inkjet printer is also provided with a plurality of inkjet printing heads with nozzles in which each individual nozzle can be controlled separately.

Claims

Claims:

1. Print head for an inkjet printer, wherein the print head has at least one ink supply channel and at least one nozzle with a nozzle channel and inlet opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inlet opening and can be ejected from the latter, wherein the nozzle is arranged in a stationary manner on a side wall of the ink supply channel and a plunger with a plunger end face located in the ink supply channel and spaced opposite the inlet opening is assigned to the at least one nozzle, wherein the print head comprises first means for moving the plunger end face in the ink supply channel between a reversal point (U1) at a minimum distance from the inlet opening of the nozzle and a reversal point (U2) at a maximum distance from the inlet opening of the nozzle, wherein the first means limit the movement of a plunger end face to a movement between the reversal points (U1,U2) and second means are provided for subjecting the ink in the ink supply channel to a negative pressure relative to the ambient air pressure, wherein at least one set of said nozzles is present, which comprises the one nozzle, characterized in that all nozzles of the one set of nozzles are assigned a single common tappet.

2. Print head according to claim 1, characterized in that at the minimum distanced reversal point (U1) the distance at any point between the plunger end face and each inlet opening of each nozzle of the one set of nozzles is greater than zero.

3. Print head according to claim 1 or 2, characterized in that the one set of nozzles comprises at least thirty nozzles, preferably at least fifty nozzles, particularly preferably at least seventy nozzles.

4. Print head according to at least one of the preceding claims 1 to 3, characterized in that the first means comprise at least a first and a second actuator, wherein the plunger is operatively connected at a first section of the plunger via a first plunger rod to a first actuating element of the first actuator and at a second section of the plunger via a second plunger rod to a second actuating element of the second actuator, wherein the first and second sections are spaced apart from one another in particular in a direction vertical to the nozzle axis of one nozzle of the one set of nozzles.

5. Print head according to claim 4, characterized in that the first actuator is designed to move one end of the first section of the plunger end face in the Ink supply channel between the reversal point (U1) which is at a minimum distance from the inlet opening of one nozzle of one set of nozzles and the reversal point (U2) which is at a maximum distance from the inlet opening of one nozzle of one set of nozzles, and the second actuator is designed to move one end of the second section of the plunger end face in the ink supply channel between a reversal point (U3) which is at a minimum distance from the inlet opening of one nozzle of one set of nozzles and a reversal point (U4) which is at a maximum distance from the inlet opening of one nozzle of one set of nozzles.

6. Print head according to claim 5, characterized in that the second actuator limits the movement of one end of the second section of the plunger end face to a movement between the reversal points (U3, U4) and the first actuator limits the movement of one end of the first section of the plunger end face to a movement between the reversal points (U1, U2).

7. Print head according to claim 5 or 6, characterized in that the position of the reversal point (U2) as starting point and of the subsequent reversal point (U1) as well as the position of the reversal point (U4) as starting point and of the subsequent reversal point (U3) are selected such that one plunger stroke can eject a predetermined and preferably substantially identical amount of ink and thus droplet size from each nozzle of the one set of nozzles.

8. Print head according to at least one of claims 4 to 7, characterized in that the actuators are designed and controllable in such a way that the movement of the plunger end face is effected by a synchronous movement of the first and second plunger rods.

9. Print head according to at least one of claims 4 to 8, characterized in that the push rods are each firmly connected to the push rod, preferably via a positive connection and / or via a material connection.

10. Print head according to at least one of claims 4 to 9, characterized in that the plunger can be divided into a central and two opposite edge regions, preferably along a longitudinal axis of the plunger, wherein the first section lies in the first edge region and the second section lies in the second edge region opposite the first edge region, wherein the plunger is particularly preferably of an elongated design. 1 1. Print head according to at least one of claims 4 to 10, characterized in that each actuating element is designed as a bending transducer, preferably as a piezoelectric bending transducer.

12. Print head according to at least one of the preceding claims 5 to 11, characterized in that at the minimum distanced reversal point (U1) and at the minimum distanced reversal point (U3), the distance at each point between the plunger end face and each inlet opening of each nozzle of the one set of nozzles is greater than a particle size of the particles of a particle-containing ink.

13. Print head according to at least one of the preceding claims, characterized in that third means are provided for pumping the ink through the ink supply channel of the print head, preferably permanently, in particular at least in the effective area of ​​the plunger in one flow direction.

14. Print head according to at least one of the preceding claims, characterized in that there are several sets of said nozzles, wherein all nozzles of the respective set of nozzles are assigned a single common plunger.

15. Print head according to at least one of the preceding claims, characterized in that the side wall of the ink supply channel is formed integrally as a nozzle plate with at least each nozzle of the at least one set of nozzles.

16. An inkjet printer comprising a plurality of print heads according to at least one of the preceding claims, wherein the inkjet printer comprises common second means for subjecting the ink in each ink supply channel of each print head to a negative pressure relative to the ambient air pressure.

17. Method for carrying out printing processes with the following steps: a) Providing a print head with ink supply channel, plunger and nozzle with nozzle channel and inlet opening which forms the connection of the nozzle channel to the ink supply channel, b) Filling the ink supply channel with ink, whereby at least during the time intervals in which no printing is to take place, the ink supply channel is filled at least in the area of ​​the inlet opening of the nozzle with a Negative pressure relative to the ambient air pressure is applied, whereby an outflow of the ink from the nozzle channel is prevented even without a closure body, wherein the ink supply channel is provided with at least one set of said nozzles, which comprises the one nozzle, characterized in that all nozzles of the one set of nozzles are assigned a single common tappet, wherein in order to eject the ink, an end face of the tappet is moved from a starting point towards all inflow openings of the nozzles of the one set of nozzles.

18. Method according to claim 17, characterized in that one end face of the tappet is moved only up to a first reversal point (U1) towards the inlet opening of one nozzle of the set of nozzles, wherein at the first reversal point (U1) the distance at every point between the tappet end face and each inlet opening of each nozzle of the one set of nozzles is greater than zero.

19. Method according to claim 17 or 18, characterized in that the one set of nozzles comprises thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles.

20. Method according to at least one of claims 17 to 19, characterized in that after reaching the first reversal point (U1), the end face of the plunger is moved away from the inlet opening of one nozzle of the one set of nozzles to a second reversal point (U2), which forms the starting point for the subsequent printing cycle.

21. Method according to claim 20, characterized in that the position of the starting point and the subsequent reversal point (U1) is selected such that the plunger stroke ejects a predetermined amount of ink and thus droplet size from each nozzle of the one set of nozzles.

22. Method according to at least one of the preceding claims 17 to 21, characterized in that the first means are provided with at least a first and a second actuator, wherein the plunger is operatively connected at a first section of the plunger via a first push rod to a first actuating element of the first actuator and at a second section of the plunger via a second push rod to a second actuating element of the second actuator, wherein the first and second sections are spaced apart from one another in particular in a direction vertical to the nozzle axis.

23. Method according to claim 22, characterized in that one end of the first section of the tappet end face is moved by means of the first actuator only up to the first reversal point (U1) towards the inlet opening of one nozzle of the set of nozzles and one end of the second section of the tappet end face is moved by means of the second actuator only up to a third reversal point (U3) towards the inlet opening of one nozzle of the set of nozzles.

24. Method according to claim 23, characterized in that after reaching the first reversal point (U1) by one end of the first section of the plunger end face, said plunger end face is moved away from the inlet opening of one nozzle of the one set of nozzles by means of the first actuator to the second reversal point (U2), and after reaching the third reversal point (U3) by one end of the second section of the plunger end face, said plunger end face is moved away from the inlet opening of one nozzle of the one set of nozzles by means of the second actuator to the fourth reversal point (U4), wherein the reversal points (U2) and (U4) each form the starting point for the subsequent printing cycle.

25. Method according to claim 24, characterized in that the position of the second reversal point (U2) and the subsequent first reversal point (U1) and the position of the fourth reversal point (U4) and the subsequent third reversal point (U3) are selected such that the plunger stroke ejects a predetermined and preferably substantially identical amount of ink and thus droplet size from each nozzle of the one set of nozzles.

26. Method according to at least one of claims 22 to 25, characterized in that the movement of the plunger end face is effected by a synchronous movement of the first and second push rods with the aid of the at least first and second actuator.

27. Method according to one of claims 17 to 26, characterized in that the ink is pumped through the ink supply channel, preferably permanently.

28. Method according to at least one of claims 17 to 27, characterized in that at the first reversal point (U1) and at the third reversal point (U3) the distance at each point between the plunger end face and each inlet opening of each nozzle of the one set of nozzles is greater than a particle size of the particles of a particle-containing ink.

29. Method according to at least one of claims 17 to 28, characterized by the following steps: - Transport of at least one printing medium along a transport direction such that the printing medium is transported into and out of the effective area of ​​the print head; - Coating the at least one printing medium by changing the direction of the plunger at the first reversal point (U1), or optionally changing the direction of one end of the first section of the plunger end face at the first reversal point (U1) and one end of the second section of the plunger end face at the third reversal point (U3), with a predetermined, preferably constant, frequency.

30. Method according to at least one of claims 17 to 29, characterized in that the ink is a suspension, preferably a glaze suspension, which is particularly preferably a non-Newtonian fluid.

31. Method according to at least one of claims 17 to 30, characterized in that a ceramic printing medium is provided as the at least one printing medium.

32. Method according to at least one of claims 1 to 31, characterized in that it is used for producing a three-dimensional green body, comprising the steps of: c) filling the ink supply channel with ink which is a ceramic and / or metallic slurry; d) printing the slurry on a specific surface to form a layer of a green body with the print head by ejecting the slurry from all nozzles of the one set of nozzles at a predetermined, preferably constant frequency, and drying the layer to form a powder layer; e) consolidating the powder of the powder layer at the locations corresponding to the cross-section of the green body; f) repeating steps d) and e) until the green body has been produced.

33. Method according to claim 32, characterized in that the consolidation is carried out by applying drops of a fixing liquid to the locations corresponding to the cross-section of the green body using an inkjet print head with nozzles, in which each individual nozzle can be controlled separately.

34. A method according to claim 32 or 33, characterized in that the fixing liquid comprises or consists of an organic binder.

Images