Printhead for an inkjet printer, in particular for coating a print medium

Abstract

The invention relates to a print head for an inkjet printer, the print head having at least one ink supply channel and at least one nozzle having a nozzle channel and an inflow opening through which ink can be pressed from the ink supply channel into the nozzle channel and ejected from the nozzle channel, the at least one nozzle is arranged in a stationary manner on a side wall of the ink supply channel, and wherein the at least one nozzle is associated with a plunger having a plunger end side in the ink supply channel, which plunger end side is arranged opposite the inflow opening at a distance from the inflow opening, a first means for moving the plunger end side in the ink supply channel between a return point (U1) at a minimum distance from the nozzle inflow opening and a return point (U2) at a maximum distance from the nozzle inflow opening, a first means limiting the movement of the plunger end side to the movement between the return points (U1, U2), and a second means for limiting the movement of the plunger end side to the movement between the return points (U1, U2), and at least one nozzle for applying a negative pressure to the ink in the ink supply channel with respect to ambient air pressure, in which at least one set of said nozzles is present, including one nozzle, in which all nozzles in one set are associated with a single common plunger.

Description

Technical Field

[0001] The invention relates to a print head for an inkjet printer according to the preamble of claim 1 and a method for carrying out a printing process according to the preamble of claim 17 . Background Art

[0002] Devices and methods for coating print media are generally intended to provide the print media with at least one coating layer as evenly as possible, which layer fulfills a specific functional and / or decorative purpose and improves the surface properties of the print media. When processing at relatively high coating speeds is required, non-contact coating methods are preferably used.

[0003] In non-contact application methods and in devices based on this method, it is always crucial not only to apply the ink as evenly as possible over a certain output width of the print head, but also to apply the ink as evenly as possible over a certain application width of the print medium to be covered.

[0004] For coating ceramic printing media, contactless methods for modifying their surface are usually used, usually using glaze suspensions.

[0005] Previously known print heads for coating print media are configured to apply ink to the surface of the print media by outputting ink in the form of droplets from independently controllable print head nozzles onto the print media to be printed.

[0006] For example, WO2013013983A1 discloses a printhead of this type, which is configured as a drop-on-demand (DOD) printhead. The printhead comprises an ink supply channel and at least one nozzle having a nozzle channel and an inlet opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inlet opening and ejected from the nozzle channel, and the nozzle is associated with a plunger having a plunger end located in the ink supply channel and spaced opposite the inlet opening, wherein a plurality of nozzles are present in the ink supply channel, and each nozzle is associated with a plunger. The previously known printhead includes a first device for moving the plunger end in the ink supply channel between a turning point (U1) having the smallest distance from the nozzle inlet opening and a turning point (U2) having the largest distance from the nozzle inlet opening.

[0007] Such previously known printheads, which operate using a plunger, are suitable for uniformly dispensing and applying glaze suspension to the print medium, particularly when a relatively large amount of glaze suspension must be dispensed per nozzle and per unit time. However, due to their complex design, these printheads are expensive to manufacture and relatively prone to malfunction. Consequently, the purchase and, especially, maintenance costs of these printheads are relatively high. In fact, printheads and methods operating with DOD are generally not designed, by their very nature, to dispense glaze suspension onto wide or even entire surfaces, but rather to print any conceivable, complex, and detailed pattern on the print medium.

[0008] Furthermore, print heads operated with the aid of plungers have a relatively high energy consumption, in particular for the amount of ink delivered per nozzle.

[0009] Therefore, there is a need to provide a drop-on-demand (DOD) print head with multiple nozzles operated by means of a plunger, which print head can efficiently output ink from its nozzles using a simple and cost-effective device and has a lower energy consumption, in particular for each amount of ink output per nozzle. Summary of the Invention

[0010] The present invention is therefore based on the object of providing a plunger-operated drop-on-demand (DOD) print head having a plurality of nozzles, which enables efficient ink delivery from its nozzles using structurally simple and cost-effective components and which has, in particular, lower energy consumption per ink delivery quantity for each nozzle.

[0011] According to the invention, this object is achieved by a print head comprising the features of claim 1 and by a method comprising the features of claim 18. The corresponding dependent claims relate to further advantageous and possibly additionally inventive embodiments.

[0012] The invention is based on the idea that a single common plunger is associated with all nozzles of a group of nozzles.

[0013] 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 having a nozzle channel and an inflow opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inflow opening and ejected from the nozzle channel, wherein the nozzle position is fixedly arranged on the side wall of the ink supply channel, and the at least one nozzle is associated with a plunger, which has a plunger end side located in the ink supply channel, and the plunger end side is opposite to the inflow opening and spaced apart, wherein the print head includes a first device, which is used to move the plunger end side in the ink supply channel between a turning point (U1) with the smallest distance from the nozzle inflow opening and a turning point (U2) with the largest distance from the nozzle inflow opening, wherein the first device limits the movement of the plunger end side to the movement between the turning points (U1, U2), and a second device is provided, which is used to load the ink in the ink supply channel with a negative pressure relative to the ambient air pressure, wherein there is at least one group of said nozzles, which includes one nozzle.

[0014] According to the invention, all nozzles of a group of nozzles are associated with a single common plunger.

[0015] A group of nozzles includes a predetermined number of nozzles.

[0016] Negative pressure prevents unintended ink leakage from the ink supply channel and the nozzle channel. This makes it possible to dispense with a closure. To eject ink from all nozzles in a nozzle group, a plunger arranged in the ink supply channel is used, the end face of which is moved toward the nozzle channels of the nozzle group, thereby squeezing the ink through the nozzle channels of the nozzle group and out of them. The plunger / nozzle spacing is preferably maintained throughout the entire printing process, i.e., the plunger end face at the turning point has a spacing greater than zero from the inlet opening, and the inlet opening of the nozzle group remains permanently open during the entire printing process. Consequently, the plunger according to the invention does not perform the function of a closure.

[0017] With the print head according to the invention, inks having a wide range of viscosities and / or containing particles can be used.

[0018] This is especially because the plunger does not have to work as a closing body and ink and / or particles moving between the plunger end side and the inlet opening of the nozzle channel of the nozzle group cannot cause interference.

[0019] Accordingly, in a preferred embodiment, at the smallest turning points (U1), the distance between the plunger end and each inflow opening of each nozzle in a group of nozzles is greater than zero at each location.

[0020] This improved solution provides the following advantages: it can prevent the plunger from colliding with the nozzle, thereby increasing the service life of the plunger, the first component and the print head.

[0021] According to another preferred embodiment, the first device includes at least one first actuator and a second actuator, wherein the plunger is operatively connected to a first adjusting element of the first actuator via a first push rod at a first section of the plunger and is operatively connected to a second adjusting element of the second actuator via a second push rod at a second section of the plunger, wherein the first section and the second section are spaced apart from each other in particular in a direction perpendicular to the nozzle axis of a nozzle in a group of nozzles.

[0022] This refinement offers the advantage that a more space-saving design of the first component can be achieved. Consequently, the smaller space requirement of the first component enables a higher printing resolution of the print head, which in turn can increase the productivity of the print head, particularly with respect to the amount of ink ejected per unit time.

[0023] Furthermore, it is possible that a group of nozzles comprises 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.

[0024] It is of course also possible that a group of nozzles comprises thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles, which are very particularly preferably arranged in one or more rows.

[0025] If at least thirty nozzles are associated with a single common plunger, which is operatively connected to at least two actuators, the common plunger acts in a coordinated manner with the nozzles to the extent that the total energy consumed when ejecting droplets of a preset size from each of the multiple nozzles is much lower than the total energy that would be consumed when ejecting droplets of the same size when each nozzle is associated with a separate plunger (each of the plungers is operatively connected to one of the actuators).

[0026] Thus, with the print head according to the invention, a group of nozzles can be actuated in an energy-saving manner for ejecting ink.

[0027] An actuator is a general name for a device that converts an electrical signal into a mechanical motion or other physical quantity. In the sense of the present invention, an actuator converts an electrical signal into a mechanical motion.

[0028] According to a preferred embodiment, it is feasible that the first actuator is configured to move the end of the first section on the plunger end side within the ink supply channel between a turning point (U1) at which the distance from the inflow opening of one of the nozzles in a group is minimum and a turning point (U2) at which the distance from the inflow opening of one of the nozzles in a group is maximum, and the second actuator is configured to move the end of the second section on the plunger end side within the ink supply channel between a turning point (U3) at which the distance from the inflow opening of one of the nozzles in a group is minimum and a turning point (U4) at which the distance from the inflow opening of one of the nozzles in a group is maximum.

[0029] It is also possible that the second actuator limits the movement of one end of the second section on the piston end side to movement between the turning points (U3, U4), while the first actuator limits the movement of one end of the first section on the piston end side to movement between the turning points (U1, U2).

[0030] The end of the first section may be a free end on the plunger end side, wherein the end of the second section may be a free end on the plunger end side opposite the free end of the first section.

[0031] It is also possible that the distance between the end of the first section on the piston end side at the turning point (U2) with the largest spacing and the inflow opening of one of the nozzles in a group of nozzles and the distance between the end of the second section on the piston end side at the turning point (U4) with the largest spacing and the inflow opening of one of the nozzles in a group of nozzles can be adjusted respectively by components for positioning the corresponding actuators.

[0032] This development offers the advantage that it allows a simple adjustment of the ink ejection quantity at all nozzles of a nozzle group.

[0033] However, it is also possible, alternatively, that the distance between the end of the first section on the plunger end side at the turning point (U1) with the smallest interval and the inflow opening of one of the nozzles in a group of nozzles and the distance between the end of the second section on the plunger end side at the turning point (U3) with the smallest interval and the inflow opening of one of the nozzles in a group of nozzles can be adjusted respectively by means of components for positioning the corresponding actuators.

[0034] For example, such an assembly for positioning an actuator is disclosed in WO 2019042586 A1 by the same owner.

[0035] It is also possible that the positions of the turning point (U2) as a starting point and of the subsequent turning point (U1) and the positions of the turning point (U4) as a starting point and of the subsequent turning point (U3) are selected so that the plunger stroke ejects a predetermined and preferably substantially identical amount of ink and thereby a predetermined and preferably substantially identical droplet size from each nozzle in a group of nozzles.

[0036] The angled position of the sidewalls of the ink supply channel, which are generally unavoidable due to naturally occurring manufacturing tolerances of all component parts of the assembly, may result in ink droplets of varying sizes being ejected from different nozzles within a group of nozzles.

[0037] These improvements therefore offer the advantage that even if, for example, the side walls of the ink supply channel containing the nozzles have a correspondingly inclined position, a highly uniform coating can still be achieved across the width of a group of nozzles. Consequently, a more uniform coating of the print medium with ink thickness can be achieved.

[0038] According to a preferred embodiment, the actuator is designed and can be controlled in such a way that a movement of the plunger end face is brought about by a synchronous movement of the first push rod and the second push rod.

[0039] The push rod can be firmly connected to the plunger, preferably via a form-fitting connection and / or via a suitable material-fitting connection. The form-fitting connection can be configured as a snap connection or a threaded connection. The material-fitting connection can be configured as an adhesive connection. The adhesive connection comprises a push rod as a first connection partner, a plunger as a second connection partner, and a suitable adhesive.

[0040] If the connecting partners that engage with one another, ie the plunger and the push rod, are additionally bonded to one another, a connection can be achieved that does not allow relative movements between the first and second connecting partners.

[0041] The plunger can be divided into a middle area and two opposite edge areas, preferably along the longitudinal axis of the plunger, wherein the first section is located in the first edge area and the second section is located in the second edge area opposite the first edge area, wherein the plunger is particularly preferably of elongated structural form.

[0042] Each adjusting element can be designed as a bending transducer, preferably as a piezoelectric bending transducer.

[0043] Furthermore, it is possible that at the turning point (U1) with the smallest spacing and at the turning point (U3) with the smallest spacing, the distance between the end side of the plunger and each inflow opening of each nozzle in a group of nozzles at each location is greater than the particle size of the particles in the particle-containing ink.

[0044] Accordingly, the ink supply channel can be filled with ink containing particles. The ink can be a glaze suspension.

[0045] It is also possible that at the turning point (U1) with the smallest spacing and at the turning point (U3) with the smallest spacing, the distance between the end side of the plunger and each inflow opening of each nozzle in a group of nozzles at each location can be greater than the particle size with a volume diameter of d99(v), preferably greater than twice the particle size with a volume diameter of d99(v).

[0046] The above-mentioned improvement offers the following advantages: the particles can be at least partially, preferably completely, prevented from breaking up in the region of the relevant nozzle opening. As a result, the service life of the plunger, the first component and the print head can be increased.

[0047] A third means may be provided for pumping ink through the ink supply channel, preferably permanently and in particular at least in the range of action of the plunger in the direction of flow, in order to prevent ink from settling in the ink supply channel.

[0048] Furthermore, it is possible that a plurality of groups of the nozzles are present, wherein a single common plunger is respectively associated with all nozzles in a respective group of nozzles.

[0049] According to a preferred embodiment, no side wall is implemented integrally with each nozzle in the group of nozzles, and the end side of the nozzles in a group of nozzles surrounding each inflow opening is configured to be flush with the inner surface of the side wall of the ink supply channel that contacts the ink.

[0050] According to another preferred embodiment, the side wall of the ink supply channel and at least each nozzle in at least one group of nozzles are integrally constructed as a nozzle plate.

[0051] These improvements offer the advantage that a print head with higher printing resolution can be provided.

[0052] According to a particularly preferred embodiment, the actuator is an actuator having a plunger, which comprises a base body and a push-top body, wherein the base body comprises a basic body and a cover element, wherein the basic body comprises a bottom wall and a peripheral wall, which together form a container enclosing a space and which can be closed by means of the cover element, and wherein a through-opening for a push rod operatively connected to the plunger is provided in the bottom wall, the push rod extends through the through-opening, and an adjusting element is provided in the base body, which is also operatively connected to the push rod, wherein the adjusting element is constructed as a bending converter, which can be divided into a middle area and an edge area, and the bending converter is arranged on the base body with at least a part of its edge area, and the push rod is operatively connected to it in the middle area of ​​the bending converter.

[0053] The inkjet printer according to the invention comprises a plurality of print heads according to the invention, wherein the inkjet printer comprises a common second device for applying a negative pressure relative to the ambient pressure to the ink in each ink supply channel of each print head.

[0054] According to the invention, this object is also achieved by a method for carrying out a printing process according to claim 17 .

[0055] The method for performing a printing process according to the present invention comprises the following steps:

[0056] a) providing a print head having an ink supply channel, a plunger and a nozzle, the nozzle having a nozzle channel and an inflow opening forming a connection of the nozzle channel to the ink supply channel;

[0057] b) filling the ink supply channel with ink;

[0058] In this case, at least during periods in which no printing takes place, the ink supply channel should be loaded with a negative pressure relative to the ambient air pressure at least in the region of the inlet opening of the nozzle, so as to prevent ink from flowing out of the nozzle channel even in the absence of a closure body, wherein the ink supply channel is provided with at least one group of said nozzles, which comprises one nozzle.

[0059] According to the invention, the method is characterized in that all nozzles of a nozzle group are assigned a single common plunger, wherein, for ejecting ink, the end face of the plunger is moved starting from a starting point towards all inflow openings of the nozzles of the nozzle group.

[0060] According to a preferred embodiment of the method, the end side of the plunger moves toward the inflow opening of a nozzle in a group of nozzles only up to a first turning point (U1), wherein, at the first turning point (U1), the distance between the end side of the plunger and each inflow opening of each nozzle in a group of nozzles at each location is greater than zero.

[0061] Furthermore, it is possible that a group of nozzles comprises 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.

[0062] Furthermore, it is of course possible for a group of nozzles to comprise thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles, which are very particularly preferably arranged in one or more rows.

[0063] According to another preferred embodiment of the method, after reaching the first turning point (U1), the end side of the piston moves away from the inflow opening of a nozzle in a group of nozzles to a second turning point (U2), which forms the starting point for the next printing cycle.

[0064] According to a particularly preferred embodiment of the method, the positions of the starting point and the subsequent turning point (U1) are selected such that the plunger stroke ejects a predetermined amount of ink and thus a predetermined droplet size from each nozzle of a group of nozzles.

[0065] Typically, when the printing medium is to be coated, the plunger undergoes a direction change at the turning point (U1) and the turning point (U2) at a predetermined, preferably constant frequency.

[0066] According to a preferred method, a first device having at least one first actuator and a second actuator is provided, wherein the plunger is operatively connected to a first adjusting element of the first actuator via a first push rod at a first section of the plunger and is operatively connected to a second adjusting element of the second actuator via a second push rod at a second section of the plunger, wherein the first section and the second section are spaced apart from each other in particular in a direction perpendicular to the nozzle axis.

[0067] This improvement offers the advantage that a more space-saving design of the first component can be achieved. The smaller space requirement of the first component thus enables a higher printing resolution of the print head, which in turn increases the productivity of the print head in terms of the amount of ink ejected per unit time.

[0068] It is possible here to move the end of a first section on the piston end side toward the inflow opening of a nozzle in a group of nozzles only as far as a first turning point (U1) by means of a first actuator, and to move the end of a second section on the piston end side toward the inflow opening of a nozzle in a group of nozzles only as far as a third turning point (U3) by means of a second actuator.

[0069] It is also possible that after one end of the first section of the piston end side reaches the first turning point (U1), the first section of the piston end side is moved away from the inflow opening of one of the nozzles in a group of nozzles toward the second turning point (U2) by means of a first actuator, and after one end of the second section of the piston end side reaches the third turning point (U3), the second section of the piston end side is moved away from the inflow opening of one of the nozzles in a group of nozzles toward the fourth turning point (U4) by means of a second actuator, wherein the turning points (U2) and (U4) respectively form the starting points for the next printing cycle.

[0070] It is also possible to select the positions of the second turning point (U2) and the subsequent first turning point (U1) and the positions of the fourth turning point (U4) and the subsequent third turning point (U3) in such a way that the plunger stroke ejects a predetermined and preferably substantially identical amount of ink and, thereby, a predetermined and preferably substantially identical droplet size from each nozzle in a group of nozzles.

[0071] These improvements offer the advantage that even if, for example, the side walls of the ink supply channel containing the nozzles have a correspondingly inclined position, a highly uniform coating can still be achieved across the width of a group of nozzles. Thus, a more uniform coating of the print medium with ink thickness can be achieved.

[0072] The plunger stroke between the corresponding turning points, i.e. the length of travel of the plunger end side between the corresponding turning points, can be in the range of 30 μm to 90 μm, preferably in the range of 40 μm to 80 μm, particularly preferably in the range of 50 μm to 70 μm.

[0073] According to a preferred method, the movement of the plunger end side is achieved by synchronously moving the first push rod and the second push rod by means of at least a first actuator and a second actuator.

[0074] Ink can be pumped through the ink supply channel, preferably permanently.

[0075] According to a preferred embodiment, the plunger / nozzle distance at the first turning point (U1) and optionally at the third turning point (U3) is between 80 μm and 400 μm, preferably between 200 μm and 280 μm, particularly preferably between 220 μm and 260 μm.

[0076] According to a preferred embodiment, at the first turning point (U1) and at the third turning point (U3), the distance between the plunger end and each inlet opening of each nozzle in the set of nozzles at each location is greater than the particle size of the particles in the particle-containing ink. Therefore, the ink supply channel can be filled with the particle-containing ink. The ink can be a glaze suspension.

[0077] Each adjustment element can be designed as a bending transducer, preferably as a piezoelectric bending transducer.

[0078] Furthermore, it is possible that, when no voltage is applied to the bending converter, the plunger end face can rest in a position which forms the starting point and which lies between the respective turning points (U1, U2) and, if appropriate, between the turning points (U3, U4). It is also possible that the distance between the plunger end face and the inlet opening of one of the nozzles of a group can be adjusted directly at the starting point by means of an assembly for positioning the respective actuator.

[0079] According to a preferred embodiment of the method, the method comprises the following steps:

[0080] - conveying at least one printing medium along a conveying direction such that the printing medium is conveyed into the range of action of the print head and conveyed out of the range of action of the print head again;

[0081] - The at least one printing medium is coated by causing the plunger to change direction at a first turning point (U1), or if possible, causing one end of a first section of the plunger end side to change direction at the first turning point (U1) and one end of a second section of the plunger end side to change direction at a third turning point (U3), the direction change being performed at a preset, preferably constant frequency, preferably ≥1kHz, particularly preferably ≥2kHz.

[0082] According to a more general preferred embodiment of the method, the method comprises the following steps:

[0083] - coating the at least one printing medium with the aid of a print head by causing the plunger to change direction at a first turning point (U1) or, if appropriate, at the first turning point (U1) at one end of a first section of the plunger end and at a third turning point (U3) at one end of a second section of the plunger end, the direction change taking place at a predetermined, preferably constant frequency, preferably ≥1 kHz, particularly preferably ≥2 kHz;

[0084] - wherein during lamination a continuous unidirectional relative movement takes place between the print head and the at least one print medium.

[0085] According to a particularly preferred embodiment, the plunger end side is configured as an elongated shape with two opposing elongated long sides that delimit the plunger end side, wherein two plates are provided in the ink supply channel, wherein the plates are respectively upright with one side relative to a side wall of the ink supply channel (all nozzles of a group of nozzles are arranged at the side wall) and are arranged at a preset distance from the side wall so that the inner sides of the corresponding plates facing the corresponding elongated long sides are located at a preset distance on both sides of the circumference that is virtually swept by the movement of the elongated long sides in the ink, wherein the size of the plates is sufficiently large and the above-mentioned distance is selected so that during coating of the printing medium, a coating applied to the printing medium is generated that has a higher uniformity than a coating that can be generated under otherwise identical conditions but with different corresponding distances and smaller plate sizes.

[0086] Within the scope of the present invention, the homogeneity of a coating is understood to mean the uniformity of the evaluable properties of the coating, in particular the banding effect, over the entire analysis area. As is known, banding is a visible defect in the quality of the coating and is characterized by abrupt or continuous changes in coating properties (such as gloss and / or layer thickness) that are visible in the coating, especially visible to the naked eye, where such a change is not expected.

[0087] This refinement is advantageous because, regardless of the effective spatial dimensions of the ink supply channel, it is ensured that a printed medium having a coating layer containing less waste material is produced.

[0088] Although the inventors do not wish to be bound by a single explanation or theory, it is assumed that the solution according to the invention reduces the turbulent flow of ink in the area of ​​action on the plunger end side.

[0089] There are various possible approaches for achieving a suitable spacing and a sufficiently large plate size. For example, in a first test sequence, a person skilled in the art can perform a plurality of ink ejection runs with a preselected constant but varying (especially decreasing) spacing between the plate edge and the side wall, and with a preselected spacing between the inner side of the respective plate and the respective long side of the plunger end, and thereby check whether, and if so, at which spacing or spacings, an acceptable coating or application is achieved. This spacing or one of these spacings can then be determined as the predetermined spacing between the respective plate edge and the side wall.

[0090] If an acceptable coating or application is not achieved, the corresponding preselected spacing of the inner side of the corresponding plate and the corresponding long side of the plunger end side is selected to be larger or smaller in the second test sequence, so that when the first test sequence is repeated accordingly, an appropriate spacing and therefore an acceptable coating is achieved with the re-preselected spacing of the inner side of the corresponding plate and the corresponding long side of the plunger end side.

[0091] If an acceptable coating or application is still not achieved, the panel size is increased in a third test sequence and the first and, if applicable, second test sequences are repeated until the desired result is achieved.

[0092] The plate is preferably sufficiently large if its height, oriented parallel to the direction of the plunger stroke, is at least 50 times the distance traveled by the plunger stroke, and its length, oriented perpendicular to the height, corresponds at least to the length of the long side of the long shape of the plunger end face. The plate height is more preferably at least 150 times the distance traveled by the plunger stroke, and very particularly preferably at least 500 times the distance traveled by the plunger stroke.

[0093] However, a person skilled in the art can also start in a different way and first perform tests with a preselected spacing between the respective plate edge and the side wall, with a constant but varying spacing between the inner side of the plate and the respective long side of the plunger end, and check whether and, if so, at which spacing or spacings an acceptable coating or application is achieved. This spacing or one of these spacings is determined as the preset spacing between the inner side of the respective plate and the side wall. If an acceptable coating or application is not achieved, at least one of the other two parameters is adjusted by performing multiple test sequences until an acceptable result is achieved.

[0094] According to a particularly preferred embodiment, the plates are dimensioned so large and the spacings are selected so as to ensure a waste-free coating of the print medium, wherein other corresponding spacings determined and possibly smaller plates than the corresponding spacings would result in wasteful print medium.

[0095] This improvement is advantageous because no matter how the effective space size of the ink supply channel is, it is ensured that a waste-free print medium is produced.Thus, all nozzles in a group of nozzles eject droplets of substantially the same size.

[0096] The elongated plunger end preferably has a rectangular shape, with its two opposite elongated long sides oriented parallel to each other and connected by two opposite shorter sides (which are shorter than the long sides). The rectangular plunger end can for example have a rectangular or parallelogram profile.

[0097] Furthermore, it is possible that the plates each have such a height that they are in contact with that side wall of the ink supply channel which is opposite to the side wall in which all nozzles of a nozzle group are arranged.

[0098] Typically, both the elongated plunger end and the two plates are oriented substantially parallel to the direction of ink flow in the ink supply channel. In this preferred embodiment, it is particularly preferred that the plates are arranged on the side walls of the ink supply channel such that the flow of ink between the two plates in the direction of flow is not impeded or not significantly impeded. Furthermore, the plates can be directly connected to one another.

[0099] The respective distance between the edge of the plate and the side wall is preferably selected to be greater than the plunger / nozzle distance at the first folding point (U1) and, if appropriate, at the third folding point (U3), thereby further increasing the reliability of forming a uniform coating.

[0100] Furthermore, a printer having at least two print heads can be provided, wherein a print strip consisting of ink having a print width is applied with each print head, wherein the first print head and the second print head are arranged relative to each other such that the width of the print strip substantially corresponds to the sum of the strip widths of the two print heads.

[0101] According to a preferred embodiment, the method is characterized in that it is used to produce a relief-like decoration on a printing medium having areas to be interpreted as recessed portions and areas to be interpreted as raised portions, wherein the method comprises the following steps:

[0102] - applying a liquid composition that repels water-based ink at a first resolution to the areas of the print medium that are to be interpreted as depressions, and then

[0103] - Using a print head, water-based ink is printed at a second resolution either only on areas that should be interpreted as raised portions or only on areas that should be interpreted as raised portions and on edge areas of areas that should be interpreted as recessed portions, wherein the first resolution is at least four times higher than the second resolution, preferably at least eight times higher.

[0104] This refinement offers the following advantages: a relief-like decoration can be achieved with high imaging accuracy. Furthermore, within the relief-like decoration, areas that should be interpreted as depressions can be created, which are always free of ink, thereby achieving high print quality. This advantageous technical effect is particularly noticeable after the ceramic printing medium has been fired. Furthermore, the advantageous effect is ensured even if the corresponding areas that should be interpreted as depressions are so large that the effect of repelling the liquid composition of the water-based ink, i.e., the water-based ink is displaced from the areas that should be interpreted as depressions toward the edges, is no longer ensured, even if ink were to be printed onto the corresponding central areas of the areas that should be interpreted as depressions.

[0105] The edge area of ​​the area to be interpreted as a recess is to be understood as an edge area which is defined by a virtual edge which is spaced apart from the actual edge of the area to be interpreted as a recess, the virtual edge preferably being spaced apart from the actual edge by at most 1.5 cm, particularly preferably at most 1.0 cm, quite particularly preferably at most 0.5 cm, wherein the edge area thereby defines and surrounds a corresponding central area of ​​the area to be interpreted as a recess, but does not overlap with the central area.

[0106] The person skilled in the art is familiar with corresponding liquid compositions that repel water-based inks from the prior art.

[0107] The application of the ink-repellent composition can be performed using an inkjet print head having nozzles, wherein each individual nozzle can be individually controlled.

[0108] Liquid compositions that repel water-based inks are generally hydrophobic.

[0109] A ceramic printing medium may be provided as the printing medium.

[0110] The ink may be a suspension, preferably a glaze suspension, in particular a water-based glaze suspension, which is particularly preferably a non-Newtonian fluid. The ink may also be a water-based ink as described above.

[0111] Furthermore, it is possible to fire the ceramic printing medium with its relief decoration in order to produce a fired relief decoration on the surface of the printing medium if a glaze suspension is used as ink.

[0112] According to a preferred embodiment, after the water-based ink and the liquid composition that repels water-based ink have dried on the printing medium, a pattern is applied to the areas that should be interpreted as recessed portions and / or to the areas that should be interpreted as raised portions by means of at least one inkjet print head having nozzles, wherein each individual nozzle can be individually controlled.

[0113] This development has the advantage that the equality between the specific relief features and the printed pattern leads to a high-quality pattern, in particular a natural impression of the pattern to be imaged, for example a specific stone pattern or wood pattern.

[0114] The method can be used to coat at least one ceramic printing medium with a glaze or engobes or a glass mosaic 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 compressing it.

[0115] Layer-by-layer slurry application methods for producing three-dimensional objects are known in the prior art. For example, a corresponding method for constructing a three-dimensional green body layer by layer is previously known, comprising the following steps: (i) providing an elongated casting nozzle; (ii) applying slurry to a surface by moving the casting nozzle back and forth between two relative positions, during which the slurry is cast from the elongated opening of the casting nozzle to form a slurry layer, which is then dried to form a powder layer; and (iii) consolidating powder in the powder layer at a location corresponding to the cross-section of the green body; and (iv) repeating steps ii) and iii) until the green body is produced.

[0116] One problem that contributes to the high material consumption is the fact that only the above-described production method is possible in the layer-by-layer slurry application methods known today for producing three-dimensional objects. There are three-dimensional objects in which almost every layer has a relatively small powder area to be consolidated and a correspondingly relatively large powder area that cannot be consolidated (free area). If the casting nozzle is guided over a row of open areas, it will still pour the slurry over the width of the structure area. The resulting layer construction is associated with a high consumption of slurry, since its dry form cannot currently be recycled or can only be recycled at considerable expense. This is particularly relevant when the non-variable structure area width is relatively large and only very small areas of a large number of layers are to form part of the green body.

[0117] It would therefore be desirable to provide a layer-by-layer slurry application method with which the material consumption can be kept low independently of the size of the object.

[0118] 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.

[0119] This object is achieved by a method according to claim 32 .

[0120] Accordingly, according to a preferred embodiment, the method is characterized in that, in order to produce a three-dimensional green body, the method comprises the following steps:

[0121] c) filling the ink supply channel with ink, wherein the ink is a ceramic and / or metal slurry;

[0122] d) imprinting the slurry on a defined surface by ejecting the slurry from all nozzles of a group of nozzles at a predetermined, preferably constant frequency, with the aid of the print head to form a layer of a green body, and drying the layer to form a powder layer;

[0123] e) consolidating powder of the powder layer at a location corresponding to the cross section of the green body;

[0124] f) Repeating steps d) and e) until the green body is completed.

[0125] Thus, with each ejection of the slurry, droplets of the slurry are ejected from all nozzles in the nozzle group. As described above, the slurry is ejected by moving the end side of the plunger from the starting point toward all inflow openings of the nozzles in the nozzle group of the print head. Therefore, during the corresponding printing, the direction of the plunger is preferably changed at the first turning point (U1), or, if possible, one end of the first section of the plunger end side is changed at the first turning point (U1) and one end of the second section of the plunger end side is changed at the third turning point (U3), and the direction change is performed at a predetermined, preferably constant frequency.

[0126] Typically, the green body is dissolved from the unconsolidated powder before firing the green body to form a sintered three-dimensional object.

[0127] According to a preferred embodiment, the consolidation is achieved by applying droplets of the fixing liquid at locations corresponding to the cross section of the green body using an inkjet print head having nozzles, in which each individual nozzle can be individually controlled.

[0128] Furthermore, it is possible that the fixing liquid comprises or consists of an organic binder.

[0129] The fixing liquid, in particular an organic binder, has the property of holding the ceramic and / or metal particles and layers consolidated thereby together in a form-fitting manner, in particular of gluing them together.

[0130] Typically, the ceramic and / or metal slurry comprises one or more additives, for example at least one dispersant and / or at least one organic binder, which is particularly preferably different from the organic binder of the fixing liquid.

[0131] According to a preferred embodiment, an inkjet print head having nozzles, wherein each individual nozzle can be individually controlled, is configured to eject droplets of a fixed liquid with a drop volume of corresponding ≤100pl, preferably corresponding ≥10pl and ≤80pl, particularly preferably corresponding ≥20pl and ≤45pl.

[0132] According to a preferred embodiment, the print head is configured to eject slurry droplets having a droplet volume, wherein the droplet volume is at least 15 times, preferably at least 50 times, particularly preferably at least 150 times, and most particularly preferably at least 300 times the volume of a fixed liquid droplet of an inkjet print head with nozzles; wherein each individual nozzle can be individually controlled.

[0133] According to a preferred embodiment, all nozzles of the at least one group of nozzles each have a nozzle inner diameter of between 100 μm and 400 μm, preferably between 100 μm and 250 μm, whereby, compared to other typical piezoelectrically operated inkjet printing devices in the prior art, which usually include nozzles with an inner diameter of only up to 60 μm, such a print head can, for example, print suspensions with larger particles.

[0134] According to a particularly preferred embodiment of the method, an inkjet printer for producing three-dimensional objects is provided, which comprises a plurality of print heads according to the invention, wherein the inkjet printer comprises a common second device for loading the ink in each ink supply channel of each print head with a negative pressure relative to the ambient air pressure, wherein the inkjet printer is also provided as having a plurality of inkjet print heads with nozzles, wherein each individual nozzle can be individually controlled.

Claims

1. A print head for an inkjet printer, wherein: The print head has at least one ink supply channel and at least one nozzle having a nozzle channel and an inflow opening, wherein ink can be pressed from the ink supply channel into the nozzle channel through the inflow opening and ejected from the nozzle channel, wherein the nozzle is arranged in a fixed position on the side wall of the ink supply channel, and the at least one nozzle is associated with a plunger, which has a plunger end side located in the ink supply channel and is located opposite the inflow opening at a distance, wherein the print head includes a first device for moving the plunger end side in the ink supply channel between a turning point (U1) with a minimum distance from the inflow opening of the nozzle and a turning point (U2) with a maximum distance from the inflow opening of the nozzle, wherein the first device limits the movement of the plunger end side to a movement between the turning points (U1, U2), and a second device is provided for applying a negative pressure relative to the ambient pressure to the ink in the ink supply channel, wherein there is at least one group of nozzles, which includes one nozzle, characterized in that all nozzles in the group of nozzles are associated with a single common plunger.

2. The print head according to claim 1, wherein At the smallest-spaced turning points (U1), the distance between the plunger end face and each inflow opening of each nozzle of the group of nozzles is greater than zero at each location.

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

4. The print head according to claim 1 , wherein: The first device includes at least a first actuator and a second actuator, wherein the plunger is operatively connected to a first adjusting element of the first actuator via a first push rod at a first section of the plunger and is operatively connected to a second adjusting element of the second actuator via a second push rod at a second section of the plunger, wherein the first section and the second section are spaced apart from each other in particular in a direction perpendicular to a nozzle axis of a nozzle of the group of nozzles.

5. The print head according to claim 4, wherein: The first actuator is configured to move the end of the first section of the plunger end side within the ink supply channel between a turning point (U1) having the smallest spacing from the inflow opening of one of the nozzles in the group of nozzles and a turning point (U2) having the largest spacing from the inflow opening of one of the nozzles in the group of nozzles, and the second actuator is configured to move the end of the second section of the plunger end side within the ink supply channel between a turning point (U3) having the smallest spacing from the inflow opening of one of the nozzles in the group of nozzles and a turning point (U4) having the largest spacing from the inflow opening of one of the nozzles in the group of nozzles.

6. The print head according to claim 5, wherein: The second actuator limits the movement of one end of the second section of the plunger end side to movement between the folding points (U3, U4), while the first actuator limits the movement of one end of the first section of the plunger end side to movement between the folding points (U1, U2).

7. The print head according to claim 5 or 6, characterized in that: The positions of the turning point (U2) as a starting point and the subsequent turning point (U1) and the positions of the turning point (U4) as a starting point and the subsequent turning point (U3) are selected so that the plunger stroke can eject a predetermined and preferably substantially identical amount of ink and thereby a predetermined and preferably substantially identical droplet size from each nozzle in the group of nozzles.

8. The print head according to claim 4, wherein The actuator is designed and can be controlled in such a way that a movement of the plunger end face is brought about by a synchronous movement of the first push rod and the second push rod.

9. The print head according to claim 4, wherein The push rods are each operatively connected firmly to the plunger, preferably via a form-fitting connection and / or via a material-fitting connection.

10. The print head according to claim 4, wherein The plunger can be divided into a middle area and two opposite edge areas, preferably along the longitudinal axis of the plunger, wherein the first section is located in the first edge area and the second section is located in a second edge area opposite the first edge area, wherein the plunger is particularly preferably of elongated structural form.

11. The print head according to claim 4, wherein Each adjustment element is designed as a bending transducer, preferably as a piezoelectric bending transducer.

12. The print head according to claim 5, wherein At the turning point (U1) with the smallest spacing and at the turning point (U3) with the smallest spacing, the distance between the end side of the plunger and each inflow opening of each nozzle in the group of nozzles at each location is greater than the particle size of the particles in the ink containing the particles.

13. The print head according to claim 1, characterized in that A third means is provided for pumping the ink through the ink supply channel of the print head, preferably permanently, in particular in the flow direction at least within the range of action of the plunger.

14. The print head according to claim 1, characterized in that There are a plurality of groups of said nozzles, wherein a single common plunger is respectively associated with all of the respective nozzles.

15. The print head according to at least one of the preceding claims, characterized in that The sidewall of the ink supply channel is integrally constructed with each nozzle of the at least one group of nozzles to form a nozzle plate.

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

17. A method for performing a printing process, the method comprising the steps of: a) providing a print head having an ink supply channel, a plunger, and a nozzle, the nozzle having a nozzle channel and an inflow opening, the inflow opening forming a connection of the nozzle channel to the ink supply channel; b) filling the ink supply channel with ink; In which, at least during time periods in which no printing takes place, the ink supply channel should be loaded with a negative pressure relative to the ambient air pressure, at least in the region of the inlet openings of the nozzles, so as to prevent ink from flowing out of the nozzle channel even in the absence of a closure body, wherein the ink supply channel is provided with at least one group of nozzles, comprising a nozzle, characterized in that all nozzles of the group of nozzles are associated with a single common plunger, wherein, in order to eject ink, the end side of the plunger moves from a starting point towards all inlet openings of the nozzles of the group of nozzles.

18. The method according to claim 17, characterized in that The end side of the plunger moves toward the inflow opening of a nozzle in the group of nozzles only up to a first turning point (U1), wherein, at the first turning point (U1), the distance between the end side of the plunger and each inflow opening of each nozzle in the group of nozzles is greater than zero at each location.

19. The method according to claim 17 or 18, characterized in that The group of nozzles comprises thirty nozzles, preferably fifty nozzles, particularly preferably seventy nozzles.

20. The method according to at least one of claims 17 to 19, characterized in that After reaching the first turning point (U1), the end side of the plunger moves away from the inflow opening of one of the nozzles in the group of nozzles towards the second turning point (U2), which forms the starting point for the next printing cycle.

21. The method according to claim 20, characterized in that The positions of the starting point and the subsequent turning point (U1) are selected so that the plunger stroke ejects a predetermined amount of ink and thus a predetermined droplet size from each nozzle of the group of nozzles.

22. Method according to at least one of the preceding claims 17 to 21, characterized in that A first device is provided having at least a first actuator and a second actuator, wherein the plunger is operatively connected to a first adjusting element of the first actuator via a first push rod at a first section of the plunger and is operatively connected to a second adjusting element of the second actuator via a second push rod at a second section of the plunger, wherein the first section and the second section are spaced apart from each other in particular in a direction perpendicular to the nozzle axis.

23. The method according to claim 22, characterized in that With the aid of the first actuator, the end of the first section of the plunger end side is moved toward the inflow opening of one of the nozzles in the group only up to the first turning point (U1), and with the aid of the second actuator, one end of the second section of the plunger end side is moved toward the inflow opening of one of the nozzles in the group only up to the third turning point (U3).

24. The method according to claim 23, wherein After one end of the first section of the plunger end side reaches the first turning point (U1), the first section of the plunger end side is moved away from the inflow opening of one of the nozzles in the group toward the second turning point (U2) by means of the first actuator, and after one end of the second section of the plunger end side reaches the third turning point (U3), the second section of the plunger end side is moved away from the inflow opening of one of the nozzles in the group toward the fourth turning point (U4) by means of the second actuator, wherein the turning points (U2) and (U4) respectively form starting points for the next printing cycle.

25. The method according to claim 24, characterized in that The positions of the second turning point (U2) and the subsequent first turning point (U1) and the positions of the fourth turning point (U4) and the subsequent third turning point (U3) are selected so that the plunger stroke ejects a predetermined and preferably substantially identical amount of ink and thereby a predetermined and preferably substantially identical droplet size from each nozzle in the group of nozzles.

26. Method according to at least one of claims 22 to 25, characterized in that The movement of the plunger end side is caused by synchronously moving the first push rod and the second push rod by means of at least the first actuator and the second actuator.

27. The method according to at least one of claims 17 to 26, characterized in that 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 turning point (U1) and at the third turning point (U3), the distance between the plunger end side and each inflow opening of each nozzle in the group of nozzles at each location is greater than the particle size of the particles in the ink containing particles.

29. The method according to at least one of claims 17 to 28, characterized by the following steps: - conveying at least one printing medium along a conveying direction such that the printing medium is conveyed into the range of action of the print head and conveyed out of the range of action of the print head again; - The at least one printing medium is coated by causing the plunger to change direction at the first turning point (U1), or if possible, causing one end of the first section of the plunger end side to change direction at the first turning point (U1) and one end of the second section of the plunger end side to change direction at the third turning point (U3), the direction change being performed at a preset, preferably constant frequency.

30. The 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. The 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. The method according to at least one of claims 1 to 31, characterized in that To produce a three-dimensional green body, the method comprises the following steps: c) filling the ink supply channel with ink, wherein the ink is ceramic and / or metal slurry; d) imprinting the slurry into a layer of green body on a defined surface by ejecting the slurry from all nozzles in the set of nozzles at a preset, preferably constant frequency using the print head, and drying the layer into a powder layer; e) consolidating powder of the powder layer at a location corresponding to a cross section of the green body; f) Repeating steps d) and e) until the green body is produced.

33. The method according to claim 32, characterized in that The consolidation is achieved by applying droplets of a fixing liquid at locations corresponding to the cross section of the green body using an inkjet print head having nozzles, in which each individual nozzle can be individually controlled.

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