Printhead for printing high-viscosity printing substances, in particular pressure-sensitive adhesives

Abstract

The invention relates to a print head (10) of a 3D printing device for printing high-viscosity printing substances, comprising: i) an output unit (12) having an outlet opening (14) and a closing mechanism (16) arranged at the outlet opening (14), the closing mechanism (16) being designed to reversibly and non-destructively vary an outlet area of the outlet opening (14); and ii) a dosing unit (18) connected in a fluid-conducting manner to the output unit (12), comprising a housing (20) having a delivery element (22) rotatably arranged in the housing for delivering a printing substance and a drive mechanism (24) for driving the delivery element (22), in a first operating mode the printing substance is conveyed by the conveying element (22) in a first conveying direction to the discharge opening (14) of the output unit (12), and wherein in a second operating mode the dosing unit (18) is designed to convey the printing substance by the conveying element (22) in a second conveying direction opposite the first conveying direction.

Description

[0001] The present invention relates to a print head for a 3D printing device, a 3D printing device based on the print head, and a method for printing a high-viscosity printing material using a corresponding print head and / or a corresponding 3D printing device. In addition, the use of the corresponding print head and / or the corresponding 3D printing device in printing a high-viscosity printing material is disclosed.

[0002] In many different technical fields, such as medical and dental technology as well as automotive technology, additive manufacturing processes using 3D printing devices have become an integral part of the production chain in recent decades, both in series production and in the production of prototypes and models. The advantages of this 3D printing method derive in particular from the possibility of flexibly producing the desired target structure in a relatively time- and cost-effective manner (at least for one-off production). Additive manufacturing in particular also enables the efficient production of complex filamentary components with high precision, which is generally not possible using conventional production methods with considerable cost expenditure.

[0003] In this case, the person skilled in the art is aware of different 3D printing methods, among which so-called material extrusion methods, in particular so-called molten layer methods (English "Fused Deposition Modeling" (FDM) or "Fused Filament Fabrication" (FFF)) have proven to be particularly effective for many applications. In the molten layer, the target structure is built up layer by layer from one or more melts, such as polymer melts or metal melts. In the 3D printing device used here, the molding is usually carried out by applying layer by layer through an output unit (also called a print head), wherein the melt can be provided, for example, by an extruder or a similar quantitative addition unit (Dosiereinheit). For example, corresponding print heads are known from EP 3 117 982 A1.

[0004] However, in practice, for many 3D printing devices and methods, a challenge is that when applying the printing substance, in particular for high-viscosity printing substances such as pressure-sensitive adhesives, so-called stringing (Fadenzug) can occur, also known as "stringing". In the case of "stringing", after the required amount of printing substance has been applied, due to cohesive forces in the printing substance, there is still a material connection between the applied printing substance and the printing substance remaining in the output unit, which can be pulled into a string during the movement of the print head and solidify in this state.

[0005] Therefore, "stringing" leads to defects in the target structure to be printed, which are caused by excess material, and which lead to, for example, when the print head moves between different sub-regions of the sub-structure to be printed, these regions are connected to each other by stringing. In many cases, the effect of "stringing" leads to an increased post-processing effort in order to obtain the desired target structure with sufficient surface quality, wherein if the amount of material remaining locally due to stringing is greater than specified according to the printing input parameters (i.e. the printing instructions), the defects caused by "stringing" can also lead to irregularities in the generated target structure, wherein the defects generated here mainly continue to exist in the target structure by means of the layered structure and are usually even irreparable.

[0006] Although there is a wide range of established printing substances in 3D printing, the adaptability of techniques for applying adhesives, in particular pressure-sensitive adhesives, has recently returned to the spotlight, for example to form adhesive structures in the form of tapes. However, adhesives, in particular pressure-sensitive adhesives, generally have a particularly high cohesion. This inherently high cohesion makes the application of adhesives in 3D printing processes particularly susceptible to "stringing" in many cases. According to the inventor's assessment, many print heads and 3D printing devices known in the prior art that are sufficient for printing conventional printing substances are in many cases insufficient for applying printing substances that have a high viscosity due to the high cohesion. In addition, according to the inventor's assessment, in particular in the use of pressure-sensitive adhesives, the concept of avoiding "stringing" by adjusting the method procedures known in the prior art, i.e. by adjusting the printing input parameters, for example by the movement of the print head, has proven to be unsatisfactory in terms of reducing "stringing" alone.

[0007] The main object of the present invention is to eliminate or at least reduce the above-mentioned disadvantages of the prior art.

[0008] In particular, the purpose of the present invention is to provide a print head for a 3D printing device for printing high-viscosity printing materials and a 3D printing device based thereon. Compared with the prior art, when using the print head and the printing device to print high-viscosity printing materials, especially pressure-sensitive adhesives, the occurrence of wire drawing can be reduced and preferably even completely avoided, so that the print head is particularly suitable for printing high-viscosity printing materials.

[0009] Furthermore, the object of the present invention is to provide a method for printing a high-viscosity printing substance with a corresponding print head or a corresponding 3D printing device, by which method even complex target structures can be reliably generated from a high-viscosity printing substance due to the special suitability of the print head, the target structures having a small number of defects caused by "stringing".

[0010] It is therefore an object of the present invention to be able to reduce the amount of rework and repair work on the manufactured target structure by means of a method.

[0011] Likewise, the object of the invention is to provide a method which can be implemented in a more time- and cost-effective manner than the methods known from the prior art, wherein a simpler method sequence is desired, wherein idle phases provided to reduce "cross-talk" should be reduced as much as possible. In this respect, the method to be provided should also be able to apply relatively large amounts of printing material cleanly and without "cross-talk" in a short time.

[0012] A secondary object of the invention is to provide a use of a print head to be specified and / or a 3D printing device to be specified for avoiding stringing of applied printing substance.

[0013] The inventors of the present invention have now discovered that the above-mentioned object can be achieved in a surprising manner when a specific dosing unit with a conveying element is provided in a print head of a 3D printing device equipped for this purpose for printing a highly viscous printing substance, which, when combined with an output opening with a variable discharge area as defined in the claims, conveys the highly viscous printing substance both in the direction of the output opening and in the opposite direction. This makes it possible to advantageously print even highly viscous printing substances, in particular pressure-sensitive adhesives, with high precision and to control the material discharge particularly precisely here, so that undesired "stringing" can be reliably avoided.

[0014] The above objects are therefore achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention result from the dependent claims and the following embodiments.

[0015] Those embodiments referred to below as preferred are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Therefore, particularly preferred are combinations of two or more embodiments referred to below as particularly preferred. Also preferred are embodiments in which features of one embodiment referred to as preferred to a certain extent are combined with one or more other features of other embodiments referred to as preferred to a certain extent. Features of preferred 3D printing devices, methods and uses derive from features of preferred print heads.

[0016] The present invention relates to a print head of a 3D printing device for printing a high-viscosity printing material, in particular a pressure-sensitive adhesive, comprising:

[0017] i) an output unit having a discharge opening and a closing mechanism arranged at the discharge opening, wherein the closing mechanism is designed to reversibly and non-destructively change the discharge area of ​​the discharge opening, and

[0018] ii) a quantitative addition unit connected to the output unit in a fluid-conducting manner, comprising a housing, the quantitative addition unit having a conveying element rotatably arranged in the housing for conveying printing material and a driving mechanism for driving the conveying element,

[0019] wherein the quantitative addition unit is configured in a first operation mode to convey the printing material through the conveying element along a first conveying direction to a discharge opening of the output unit, and

[0020] The metering unit is configured in a second operating mode to transport the printing material via the transport element along a second transport direction opposite to the first transport direction.

[0021] The print head according to the invention is suitable for use in a 3D printing device. A person skilled in the art is in principle aware of various 3D printing devices in the prior art for printing printed matter, which rely on the use of a print head. However, according to the inventor's assessment, the print head according to the invention is particularly suitable for use in a material extrusion process, such as a melt coating process. Therefore, preferably, the print head according to the invention is as follows, wherein the 3D printing device is a melt coating device.

[0022] In particular, in the case of the above-mentioned melt coating method, the generation of the three-dimensional structure is carried out by discharging the printing material via the print head of the 3D printing device. In most cases, the printing material is initially supplied to the print head in a solid aggregate state, for example in the form of a filament (or filaments), wherein the print head converts the material into a flowable aggregate state by temperature control. In this state, the printing material can be output through the discharge opening of the output unit to produce the desired three-dimensional structure geometry and then restored to the solid aggregate state by cooling. The output of the printing material for generating the three-dimensional structure can be completed here, for example, on a receiving substrate provided for receiving the three-dimensional structure.

[0023] According to the invention, the print head comprises an output unit having a discharge opening. During the printing process, the printed material is discharged through the discharge opening. According to the invention, the output unit comprises a closing mechanism arranged at the discharge opening, by which the discharge area (i.e. the cross-sectional area) of the discharge opening can be reversibly and non-destructively changed. Therefore, the closing mechanism is arranged to open and close the discharge opening according to the printing requirements (i.e. the printing input parameters).

[0024] In the method according to the invention, the closing mechanism has two tasks in particular. On the one hand, the adjustable discharge area of ​​the discharge opening allows a flexible adaptation to the material flow provided by the dosing unit, so that the discharge of highly viscous printing substances can be carried out essentially at a constant pressure, thereby achieving a particularly uniform material discharge. On the other hand, the closing mechanism is used to "squeeze out (or clamp off)" the material bundle after the required amount of printing substance has been applied. In this case, the material bundle is at least partially cut off by the closed discharge opening or more precisely by the closing mechanism, i.e., the diameter is reduced by mechanical deformation, wherein in particular in the case of a substantially complete "clamping off" in combination with the process control of the dosing unit disclosed below, particularly good results are achieved, and this is also true even in the case of the application of pressure-sensitive adhesives.

[0025] The necessary partial, preferably complete closability of the discharge opening can be conveniently achieved by a closure element arranged at the discharge opening, which is movable, i.e. reversibly and non-destructively movable, wherein, according to the inventors' assessment, the use of two or more closure elements allows the discharge opening to be closed (closed) more evenly from all sides, which has a favorable effect on the print quality. For most applications, therefore, it is relevant to have a print head according to the invention in which the closure mechanism comprises one or more, preferably two or more, closure elements and is arranged to change the discharge area of ​​the discharge opening by a relative movement of the closure elements.

[0026] The possibility of closing the discharge area of ​​the discharge opening as much as possible is advantageous for both aspects mentioned above, since it allows the material flow to be adapted within a wide range of parameters and to be "clamped off" as much as possible, and furthermore allows the discharge opening to be closed as much as possible to prevent unwanted material from escaping. Therefore, preference is given to a print head according to the invention in which the closing mechanism is arranged to reversibly and non-destructively change the discharge area of ​​the discharge opening between the widest and the smallest opening by 50% or more, preferably 70% or more, particularly preferably 90% or more, very particularly preferably substantially 100%.

[0027] In order to design the step of partial cutting of the material beam in the method according to the invention as effectively as possible, the inventors propose to design the closing element in such a way that the separation process of the material beam is conveyed during closing, for example by designing the part of the closing element facing the center of the discharge opening as a cutting edge. Therefore, the following print head according to the invention is preferred, in which the closing mechanism comprises one or more cutting and / or separating elements as closing elements, which at least partially taper in the direction of the discharge opening, wherein the cutting and / or separating element preferably has a cutting edge.

[0028] The output unit or the discharge opening can be formed, for example, as a nozzle, such as a circular nozzle. In most cases, the geometry of the discharge opening of the nozzle determines the width and height of the discharged printed material. The inventors have recognized that when using a print head according to the present invention, it is even advantageous to use a wide slot nozzle without the adverse effect of "threading" on the 3D printing process. The use of a wide slot nozzle, i.e. a nozzle whose length range in one direction is significantly greater than the length range in another direction, has the following advantages: a large area of ​​discharge can be achieved at the same time with a low discharge height, thereby achieving a higher printing speed. However, at the same time, the use of a wide slot nozzle in a conventional print head can even increase the tendency of unwanted "threading", which is a disadvantage in conventional print heads, especially when applying pressure-sensitive adhesives. Therefore, a print head according to the present invention is preferred as follows, in which the discharge opening of the output unit is a wide slot nozzle.

[0029] As described above, in the method according to the invention, particularly good results can be achieved with regard to highly time-efficient flat coating and at the same time low discharge heights using in particular wide slot nozzles. However, according to the inventors' assessment, the general use of polygonal discharge openings and in particular the use of wide slot nozzles in many cases requires that the output unit be designed to be rotatable in order to be able to accurately map complex or particularly fine structural areas of the three-dimensional target structure to be printed. For an output unit that is implemented in a non-rotatable manner, the width of the wide slot nozzle will limit the resolution of the target structure in at least one dimension, unless the print head itself can alternatively be designed to be rotatable, for example by a rotatable arrangement in a motion unit of a 3D printing device. Therefore, a print head according to the invention is preferred as follows, in which the discharge opening of the output unit is polygonal, preferably square, particularly preferably rectangular, very particularly preferably a wide slot nozzle, wherein the output unit has a rotation mechanism, by which the orientation of the discharge opening can be changed, in particular by rotation about an axial direction, preferably by a control device, particularly preferably depending on the printing input parameters.

[0030] According to the present invention, the print head includes a quantitative addition unit connected to the output unit in a fluid conduction mode as a second component, and the quantitative addition unit is used to supply the printed substance to the output unit or the discharge opening. The quantitative addition unit includes a conveying element driven by a driving mechanism and rotatably arranged in the housing. Here, taking the following print head according to the present invention as an example, wherein the housing of the output unit and / or the quantitative addition unit is at least partially formed by a material selected from plastics and metals such as steel or aluminum.

[0031] The conveying element rotatably arranged in the housing is used to convey the printed material, wherein the conveying movement is realized by a suitable drive mechanism. Here, the following print head according to the present invention is taken as an example, wherein the drive mechanism includes a motor. Additionally or alternatively, the following print head according to the present invention is preferred, wherein the conveying element is a conveying screw.

[0032] In most cases, the dosing unit also has the task of making the initial printing substance present in a solid aggregate state (e.g. as filaments or particles) in a printable (i.e. flowable) state by temperature control, and thereby producing the actual printing substance or the application (or application) state of the printing substance. Therefore, for most cases, the following print head according to the invention is relevant, wherein the dosing unit is configured to convert the print output substance entering the dosing unit as a solid into a high-viscosity printing substance by the action of temperature, preferably temperature and mechanical load. The following print head according to the invention is also preferred, wherein the dosing unit comprises one or more temperature control units, which are used to temperature-control the printing substance entering the dosing unit.

[0033] According to the inventors' assessment, such a dosing unit is particularly suitable for a print head according to the invention which is designed according to the type of extruder. Therefore, a print head according to the invention is particularly preferred in which the dosing unit comprises an extruder.

[0034] According to the invention, the dosing unit is configured to convey the printing substance in a first operating mode via a conveying element along a first conveying direction to a discharge opening of the output unit. In the first operating mode, the printing substance is accordingly conveyed from the dosing unit to the output unit, for example by rotation of a screw-shaped conveying element, and is output there as a substance beam, thereby providing a first operating mode for applying the printing substance.

[0035] According to the invention, the dosing unit is configured to convey the printing substance via the conveying element in a second operating mode in a second conveying direction opposite to the first conveying direction, which can be achieved in most cases, especially when using a screw-shaped conveying element, in particular by reversing the direction of rotation. Conveying the printing substance in the second conveying direction therefore means conveying the printing substance in the opposite direction of its application direction and withdrawing it from the discharge opening accordingly. Therefore, a print head according to the invention is advantageous in which the drive mechanism is configured to rotate the conveying element in the opposite direction in the first operating mode and in the second operating mode.

[0036] Those skilled in the art will appreciate that the present invention also relates to a 3D printing device for printing a high-viscosity printing material, comprising:

[0037] u) at least one print head according to the invention,

[0038] v) a moving unit connected to the print head for changing the position of said print head,

[0039] w) a control device, which is used to control the 3D printing device,

[0040] The control device is configured to change the discharge area of ​​the discharge opening and / or switch the quantitative addition unit between the first operation mode and the second operation mode according to printing input parameters.

[0041] According to the present invention, the 3D printing device comprises at least one print head according to the present invention, so that the above advantages also apply to the 3D printing device.

[0042] The print head is movably arranged in the 3D printing device by a moving unit and can be controlled by a control device like the moving unit, wherein, in particular, the opening and closing of the discharge opening and the change of the operation mode of the quantitative addition unit can be changed according to the printing input parameters (i.e., the printing plan) to prevent undesired "cross-talk". Therefore, the control device according to the present invention is configured to change the discharge area of ​​the discharge opening according to the printing input parameters and / or switch the quantitative addition unit between the first operation mode and the second operation mode.

[0043] The printing input parameters required for printing in the corresponding 3D printing device include, for example, information about the temperature required to convert the printed output substance into a flowable aggregate state, the printing path to be driven, the speed of the output unit on this printing path and the output volume of the printed substance varying over time, in particular instructions for changing the discharge area of ​​the discharge opening and / or changing the operating mode of the quantitative addition unit depending on other printing input parameters.

[0044] Due to the precise controllability and a high degree of automation, preference is given to a 3D printing device according to the invention in which the movement unit comprises at least one robot arm and / or at least one linear axis system.

[0045] Basically, a 3D printing device can apply the three-dimensional target structure to be generated on any surface. However, in most cases, the 3D printing device will include a receiving substrate, such as a base plate, to receive the target structure. Therefore, it is typical that the 3D printing device according to the present invention is as follows, wherein the 3D printing device includes a receiving substrate, which is configured to generate a three-dimensional structure on its surface by the 3D printing device.

[0046] The control device can advantageously be configured to convert a computer-generated image of a desired three-dimensional target structure into movement of a print head via a 3D printing device in a CAM method, preferably a CAD / CAM method, and to control the movement as a function of printing input parameters derived from the image, thereby reducing undesired "cross-talk", as will also be disclosed subsequently for the method according to the invention.

[0047] In particular, the present invention also relates to a method for printing a high-viscosity printing substance using a print head according to the present invention and / or a 3D printing device according to the present invention, comprising the following method steps:

[0048] a) producing or supplying printing substance in a dosing unit of a print head, and

[0049] b) conveying the printing substance along the first conveying direction by the quantitative adding unit and outputting the printing substance as a substance beam through the discharge opening of the output unit to apply a predetermined amount of printing substance,

[0050] And the following method steps after applying the predetermined amount of printing substance:

[0051] c) reducing the discharge area of ​​the discharge opening in order to at least partially cut off the substance beam and / or to switch the operating mode of the dosing unit between the first operating mode and the second operating mode.

[0052] The method according to the invention can be implemented using a print head according to the invention or a 3D printing device according to the invention to print highly viscous printing substances, such as adhesives, preferably pressure-sensitive adhesives.

[0053] The method according to the invention comprises in a first step the manufacture or provision of a printed substance in a dosing unit of a print head. As mentioned above, the advantages of the method according to the invention are particularly shown in the case of high-viscosity printed substances, in particular pressure-sensitive adhesives, which are particularly susceptible to the effects of stringing due to their high cohesion. Therefore, according to the inventor's assessment, it is also particularly advantageous to use the method according to the invention for such pressure-sensitive adhesives. Therefore, the following method according to the invention is preferred, wherein the high-viscosity printed substance is a pressure-sensitive adhesive, which is preferred for substantially all embodiments.

[0054] At this, according to the understanding of the technician, pressure-sensitive adhesive is understood to refer to an adhesive with pressure-sensitive adhesive properties, that is, even under relatively weak applied pressure, the ability to form a permanent connection with the adhesion substrate. The corresponding pressure-sensitive adhesive layer can typically be separated (peeled off) again from the adhesion substrate substantially without residue after use, and generally, even at room temperature, there is permanent inherent viscosity, which means that they have a certain viscosity and touch viscosity (contact viscosity), so that they can wet the surface of the substrate even under low applied pressure. Do not wish to be bound by this theory, often assume that pressure-sensitive adhesive can be regarded as a fluid with an extremely high viscosity of an elastic component (component), which correspondingly has the characteristic viscoelastic properties that cause the above-mentioned permanent inherent viscosity and pressure-sensitive adhesive ability. Assume that in the case of the corresponding pressure-sensitive adhesive, when mechanically deformed, there is a viscous flow process, and there is the formation of elastic restoring force. Proportional (at a certain proportion) viscous flow is used to realize adhesion here, and for realizing cohesion, a proportional (at a certain proportion) elastic restoring force is particularly required. The relationship between rheology and pressure-sensitive adhesive properties is known in the prior art and is described, for example, in Satas, "Handbook of Pressure Sensitive Adhesives Technology", 3rd edition (1999), pages 153 to 203. To characterize the extent of the elastic and viscous components, the storage modulus (G') and the loss modulus (G") are usually employed, which can be determined by dynamic mechanical analysis (DMA), for example using a rheometer as disclosed, for example, in WO 2015 / 189323. Within the scope of the present invention, when heated at a temperature of 23°C for 10 0 Up to 10 1 rad / s, G′ and G″ are each at least partially located within the range of 10 3 Up to 10 7 Pa, the adhesive is preferably understood to be pressure-sensitively adhesive and is therefore a pressure-sensitive adhesive.

[0055] In pressure-sensitive adhesives, excellent printing results and significantly reduced "stringing" can be achieved by using the method according to the invention, in particular using synthetic rubber adhesives and acrylate adhesives. Therefore, the following method according to the invention is preferred, wherein the printing substance is a pressure-sensitive adhesive and comprises one or more (co)polymers selected from (meth)acrylate polymers and synthetic rubbers, preferably synthetic rubbers. Both (meth)acrylate polymers and synthetic rubbers, such as styrene block copolymers, are very familiar to those skilled in the art of adhesive technology and belong to the group of larger (co)polymers that are often used in adhesives. For those skilled in the art, suitable (co)polymers and adhesives based thereon are commercially available from various manufacturers, wherein the skilled person selects a suitable pressure-sensitive adhesive according to the specific physicochemical properties required for the printing process.

[0056] As mentioned above, the printout substance is advantageously converted into a flowable state by the dosing unit. Therefore, of high practical relevance is the method according to the invention in which the printout substance is produced by melting the printout substance, wherein the printout substance preferably enters the dosing unit in solid form, particularly preferably in filament form.

[0057] According to the knowledge of those skilled in the art, in most cases, the manufacture of the printed substance or the generation of the application state of the printed substance requires temperature control of the printed output substance used to convert it from a solid aggregate state into a sufficiently flowable aggregate state before output. Those skilled in the art understand that the properties of the printed substance used in the 3D printing process are subject to certain requirements in practice when applied. In some cases, a printed substance with too high a temperature, i.e. a printed substance with a correspondingly low viscosity, may not be able to fully maintain the desired shape after extrusion before cooling. A printed substance with too low a temperature, i.e. a material with a very high viscosity, may clog the output unit and / or can only be applied at an insufficient speed. In this regard, the inventors have proposed favorable viscosity and temperature ranges, using which good results can be achieved in the method according to the invention, especially in the processing of pressure-sensitive adhesives. In particular, the method according to the invention is preferred in which the printed substance has a DMA melt viscosity at 9.42 Hz in the range of 100 to 1000 Pa s, preferably in the range of 150 to 800 Pa s, particularly preferably in the range of 200 to 500 Pa s at 160° C. and / or the printed substance has a DMA melt viscosity at 9.42 Hz in the range of 1000 to 7000 Pa s, preferably in the range of 1500 to 4500 Pa s, particularly preferably in the range of 2000 to 4000 Pa s at 100° C. Likewise preferred is the method according to the invention in which the printed substance has a temperature in the range of 100 to 260° C., preferably in the range of 110 to 200° C., particularly preferably in the range of 120 to 160° C. when it is discharged from the discharge opening.

[0058] The method according to the invention also comprises in another step accordingly conveying the printable printing substance with the dosing unit along the first conveying direction, ie along the discharge opening direction. This leads to the desired output of the printing substance through the discharge opening, wherein a substance beam is obtained.

[0059] In the sense of the method according to the invention, a predetermined amount of printing substance is hereby understood to mean a volume of printing substance specified, for example, in the printing input parameters, which volume is intended to be applied in a sub-step of the printing method, before the printing process is interrupted during this time, for example by moving the print head to another position of the printing path. The moment when the predetermined amount of printing substance has been applied is therefore a moment when the printing process is particularly susceptible to undesired "cross-talk".

[0060] In this case, the special suitability of the print head according to the invention is utilized to avoid undesired "cross-talk". In method step c), the material bundle is "clamped off", i.e. the discharge area of ​​the discharge opening is reduced to at least partially cut off the material bundle, and the printing substance is additionally or alternatively withdrawn from the discharge opening, i.e. the operating mode of the metering unit is switched, for example by reversing the direction of rotation of the conveying element.

[0061] In this case, it is particularly advantageous to withdraw the printed matter and to "clamp off" the printed matter, wherein these two steps are preferably performed simultaneously. Therefore, the following method according to the invention is particularly preferred, wherein method step c) comprises:

[0062] c) reducing the discharge area of ​​the discharge opening to at least partially cut off the substance beam and switching the operating mode of the dosing unit between the first operating mode and the second operating mode, wherein the reduction of the discharge area and the switching of the operating mode are preferably carried out directly successively or essentially simultaneously, particularly preferably essentially simultaneously.

[0063] Many other functional principles of the method and preferred embodiments according to the invention have been discussed above for the print head and the 3D printing device according to the invention.

[0064] Therefore, a method according to the invention is preferred, wherein the method is controlled by a control device of the 3D printing device, preferably according to printing input parameters. In particular, a method according to the invention is preferred, wherein the printing input parameters comprise printing instructions for printing the desired target structure from the printing substance.

[0065] In this respect, additionally or alternatively, the following method according to the invention is also preferred, wherein the control device is arranged to control the print head via the mobile unit according to the print input parameters. Additionally or alternatively, the following method according to the invention is also preferred, wherein the control device is arranged to change the discharge area of ​​the discharge opening according to the print input parameters and switch the quantitative addition unit between the first operating mode and the second operating mode.

[0066] The following method according to the invention is preferred, in which in method step c) the discharge area of ​​the discharge opening is greatly reduced, so that the material beam is cut off by 50% or more, preferably 70% or more, particularly preferably 90% or more, very particularly preferably essentially 100%.

[0067] In particular when using print heads with polygonal output units, preferably wide slot nozzles, the following method according to the invention is preferred, wherein the method comprises further method steps before, during or after method step b):

[0068] d) Rotating the discharge opening of the output unit about an axial direction, preferably according to the printing input parameters.

[0069] With regard to the conversion of the computer-generated image of the desired three-dimensional target structure into a printed product, the following method according to the invention is preferred, wherein the method is a CAM method, preferably a CAD / CAM method.

[0070] Finally, the use of a print head according to the invention and / or a 3D printing device according to the invention for printing a high-viscosity printing substance is disclosed, which is used to avoid stringing of the applied printing substance, preferably in a method according to the invention, wherein after applying a predetermined amount of printing substance, the discharge area of ​​the discharge opening is reduced and / or the operating mode of the quantitative addition unit is switched from a first operating mode to a second operating mode. Preferably, both the discharge area of ​​the discharge opening is reduced and the operating mode of the quantitative addition unit is switched.

[0071] In the following, preferred embodiments of the present invention will be explained and described in more detail with reference to the accompanying drawings. Here, it is shown:

[0072] Figure 1 A schematic cross-sectional view of a print head according to the invention in a preferred embodiment in a first operating mode; and

[0073] Figure 2 Figure 1 Schematic cross-sectional view of a print head according to the invention in a second operating mode.

[0074] Figure 1 A print head 10 according to the invention for a 3D printing device is shown, which is used, by way of example, for printing a high-viscosity printing substance in a melt coating method according to the invention, which is implemented, for example, as a CAD / CAM method, whereby printing input parameters are derived from a computer model of the target structure to be printed.

[0075] The print head 10 comprises in the lower region an output unit 12 with an outlet opening 14 and a closing mechanism 16 with two separating elements, which can reversibly and non-destructively change the outlet area of ​​the outlet opening 14 between the widest and the smallest opening (i.e. completely closed) by relative movement of the separating elements. The separating elements taper in the central direction of the outlet opening 14 and each have a cutting edge at the tip of the wedge, so that they can particularly effectively separate a material bundle of the printing substance discharged through the outlet opening 14 or can reliably prevent further overflow of the printing substance from the outlet opening 14 in the completely closed state.

[0076] In this example, the output unit 16 is a wide slot nozzle rotatably implemented via a rotating mechanism 26 so that the orientation of the corresponding rectangular discharge opening 14 can be changed by rotating about the axial direction of the print head 10 to enable efficient printing of even complex target structures.

[0077] The print head 10 according to the invention also comprises a metering unit 18 connected to the output unit 12 in a fluid-conducting manner, which has a housing (20) made of steel in the illustrated embodiment; and a conveying element 22 rotatably arranged in the housing 20 for conveying the printing substance entering the print head 10. The conveying element 22 is formed as a conveying screw in the illustrated embodiment, so that the metering unit 18 is generally designed according to the type of extruder. Particularly suitable as the metering unit 18 are conveying units that work according to the so-called continuous piston principle and belong to the group of rotary positive displacement pumps, wherein the shape of the inner wall of the housing 20 is adapted to the shape of the conveying element 22.

[0078] In an exemplary method according to the present invention, a printing output material as a pressure-sensitive adhesive based on synthetic rubber is supplied to a quantitative addition unit 18 in the form of a solid (e.g., filament) on the side facing away from the output unit 12 and is converted into a highly viscous printing material by the action of temperature and mechanical load, wherein the quantitative addition unit 18 includes a plurality of temperature control units (not shown) for this purpose.

[0079] For the rotation of the screw-shaped conveying element 22 , the dosing unit 18 in the embodiment shown comprises a drive mechanism 24 with an electric motor which can drive the conveying element 22 in opposite directions of rotation depending on the set operating mode.

[0080] The closing mechanism 16 and the drive mechanism 24 are here also controlled by a control device of the 3D printing device including the print head 10 as well as a movement unit and other components of the 3D printing device, ie in particular as a function of the printing input parameters.

[0081] exist Figure 1 , the print head 10 is schematically shown in a first operating mode, in which a high-viscosity pressure-sensitive adhesive is conveyed by a conveying element 22 in a first conveying direction to the discharge opening 14 of the discharge unit 12. The resulting rotation of the conveying element 22 is indicated by a dashed arrow. In the first operating mode, with the closing mechanism 16 open, a material stream of the printing material can be discharged through the discharge opening 14 until a predetermined amount for a sub-step of the printing process has been discharged. Advantageously, by adapting the opening cross section to the material flow provided by the metering unit 18, a constant output print and thus a particularly uniform material discharge can be achieved.

[0082] exist Figure 2 In the figure, it is schematically shown Figure 1 The print head 10 is in a second operating mode, in which the printing material is conveyed in the opposite direction by the conveying element 22, which now rotates in a second conveying direction opposite to the first conveying direction, whereby the printing material is conveyed away from the discharge opening and thus withdrawn from the discharge opening. The resulting rotation of the conveying element 22 is again indicated by a dashed arrow.

[0083] also, Figure 2 , that is, substantially simultaneously with the change in conveying direction, the discharge opening 14 is completely closed by the separation element of the closing mechanism 16, so that the material beam previously output through the discharge opening 14 is completely cut off. In conjunction with the change in conveying direction, the separation element ensures that the material beam still in the discharge opening 14 is cleanly separated. Therefore, Figure 2 A preferred embodiment of the method according to the invention is schematically shown, in which undesired stringing can be avoided in an advantageous manner even in the case of pressure-sensitive adhesives with an inherently high cohesion.

[0084] Reference numerals list

[0085] 10 Print head

[0086] 12 Output Units

[0087] 14 Discharge opening

[0088] 16 Closing of institutions

[0089] 18 quantitative addition unit

[0090] 20 Shell

[0091] 22 Conveying elements

[0092] 24 Driving mechanism

[0093] 26 Rotating mechanism

Claims

1. A print head (10) of a 3D printing device for printing a high-viscosity printing material, comprising: i) an output unit (12) having a discharge opening (14) and a closing mechanism (16) arranged at the discharge opening (14), wherein the closing mechanism (16) is designed to reversibly and non-destructively change the discharge area of ​​the discharge opening (14), and ii) a dosing unit (18) connected to the output unit (12) in a fluid-conducting manner, comprising a housing (20), the dosing unit having a conveying element (22) rotatably arranged in the housing for conveying printing material and a drive mechanism (24) for driving the conveying element (22), The quantitative addition unit (18) is configured in a first operating mode to convey the printing material through the conveying element (22) along a first conveying direction to the discharge opening (14) of the output unit (12), and The metering unit (18) is configured in a second operating mode to transport the printing material via the transport element (22) along a second transport direction opposite to the first transport direction.

2. The print head (10) according to claim 1, wherein the discharge opening (14) of the output unit (12) is polygonal, wherein the output unit (12) has a rotation mechanism (26) by which the orientation of the discharge opening (14) can be changed.

3. A print head (10) according to claim 1 or 2, wherein the closing mechanism (16) is arranged to reversibly and non-destructively change the discharge area of ​​the discharge opening (14) between the widest and smallest openings by 50% or more.

4. The print head (10) according to claim 1, wherein the closing mechanism (16) comprises one or more cutting and / or separating elements as closing elements, which taper at least partially in the direction of the outlet opening (14).

5. A 3D printing device for printing a high-viscosity printing material, comprising: u) at least one print head (10) according to one of claims 1 to 4, v) a moving unit connected to the print head (10) for changing the position of the print head (10), w) a control device, which is used to control the 3D printing device, The control device is configured to change the discharge area of ​​the discharge opening (14) and / or switch the quantitative addition unit (18) between the first operation mode and the second operation mode according to printing input parameters.

6. A method for printing a high-viscosity printing material using a print head (10) according to any one of claims 1 to 4 and / or a 3D printing device according to claim 5, comprising the following method steps: a) producing or supplying printing substance in a dosing unit (18) of a print head (10), and b) conveying the printing substance along the first conveying direction by the quantitative addition unit (18), and outputting the printing substance as a substance beam through the discharge opening (14) of the output unit (12) to apply a predetermined amount of printing substance, And the following method steps after applying the predetermined amount of printing substance: c) reducing the discharge area of ​​the discharge opening (14) to at least partially cut off the substance beam and / or switching the operating mode of the dosing unit (18) between the first operating mode and the second operating mode. The method according to claim 6 , wherein the high-viscosity printing substance is a pressure-sensitive adhesive.

8. The method according to claim 6 or 7, wherein the printing substance comprises one or more (co)polymers selected from (meth)acrylate polymers and synthetic rubbers.

9. The method according to any one of claims 6 to 8, wherein the method is controlled by a control device of a 3D printing device.

10. The method according to any one of claims 6 to 9, wherein step c) comprises: c) reducing the discharge area of ​​the discharge opening (14) to at least partially cut off the substance beam and switching the operating mode of the dosing unit (18) between the first operating mode and the second operating mode.

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