Method for the layered structuring of a three-dimensional object

Abstract

A method for the layered structuring of a three-dimensional object, comprising: (a) forming, on a substrate or preferably on a lower layer, a first mould layer with a first cutout, which corresponds to the negative of a first object layer, (b) filling the first cutout with object ink, in order to form the first object layer; (c) forming, on the first mould layer, a second mould layer with a second cutout, which corresponds to the negative of a second object layer, whereby an object and a supporting structure made up of or comprising sacrificial layers has been formed; (d) filling the second cutout with object ink, in order to form the second object layer; wherein each mould layer is formed by stacking a number of sacrificial layers one on top of the other, wherein the sacrificial layers are each formed with a layer thickness which is smaller than the layer thickness of each object layer at least by a factor of two in such a way that each sacrificial layer is formed by a first combination drop being applied to each pixel D1 in each row of a first printing raster imagined on the surface that is respectively to be printed, the first combination drop being made up in each case of K drops of the sacrificial ink each with a volume S, where K ϵ {0, 1, 2, 3,...}, and consequently an ink-application level KS is achieved for each pixel D1, and that each object layer is formed by a second combination drop being applied to each pixel D2 in each row of a second printing raster imagined on the surface that is respectively to be printed, the second combination drop being made up in each case of L drops of the object ink each with a volume T, where L ϵ {0, 1, 2, 3,... }, and consequently an ink-application level LT is achieved for each pixel D2, wherein the drop volume S of the respective K drops of the sacrificial ink is ≤100pl and the volume ratio (S:T) between the volume S of the respective K drops of the sacrificial ink and the volume T of the respective L drops of the object ink is in each case at least 1:15.

Description

[0001] Method for layer-by-layer structuring of a three-dimensional object

[0002] The present invention relates to a method for layer-by-layer structuring of a three-dimensional object, in particular by means of inkjet printing. Furthermore, the invention relates to a three-dimensional object obtainable by the method according to the invention.

[0003] Methods for layer-by-layer structuring of three-dimensional objects, especially ceramic objects, have been known for several years and are gaining increasing importance due to the general increase in interest, also due to the uncertain global supply chains.

[0004] To manufacture shaped objects with overhanging areas, it has become common practice in the industry to build up not only the overhanging areas to be formed on a support structure, but also the support structure itself layer by layer. The latter has the general task of supporting the individual object layers while the object is being structured layer by layer, maintaining their shape. However, in preferred cases, the support structure can also serve the same purpose during further shaping steps of the object, for example a firing step, provided its nature allows this. Depending on the chemical nature of the support structure and the composition of the manufactured object, one or more known methods can be used to remove it from the finished object without damaging the object.

[0005] A method is also known from the prior art in which a support structure is built up layer by layer in order to support not only overhanging areas but also lateral areas of the object in a shape-preserving manner.

[0006] Such a method is known from WO2018203331 A1, which comprises the following steps: (A) printing a first mold to define a first layer of the product; (B) filling the first mold with a casting material, thereby forming a first layer; (C) printing a second mold onto the first layer to define a second layer; and (D) filling the second mold with the casting material; to thereby form a molded layered product, wherein the respective molds are printed with an inkjet nozzle by ejecting drops of a first molding material comprising wax, and wherein the respective product layers are cast with a casting nozzle using the casting material comprising ceramic powder.

[0007] From the generic application WO2006078342A2, a method for forming an object is also known, comprising the steps of: (i) inkjet printing a first material to form a plurality of layers defining a support structure elevation having an inner surface; and (ii) extruding a second material to form a layer of the object, wherein the layer substantially corresponds to the inner surface of the support structure elevation and has a thickness greater than the thickness of each layer of the plurality of layers defining the support structure elevation. According to this application, the object resolution resulting from extrusion is generally about 130 micrometers, and the object resolution resulting from inkjet printing is generally about 50 micrometers.

[0008] These additive manufacturing processes are therefore analog-digital manufacturing processes.

[0009] From EP3659547A1, a method for producing a dental restoration made of ceramic is also known, in which (A) a slip containing not more than 5 wt.% of organic components, based on the total mass of the slip, is formed layer by layer to give the geometric shape of the desired dental restoration and the individual layers are dried after printing, and (B) the green compact thus obtained is subsequently dried, if necessary, and (C) the green compact is then sintered, wherein the layer-by-layer construction of the green compact in step (A) is carried out by a layer-by-layer inkjet printing process.

[0010] Compared to casting and extrusion, the printing speeds of inkjet printers are often significantly lower than those of, for example, casting printing devices and extruders. To increase printing speed, inkjet printers are often equipped with a large number of nozzles and / or inkjet print heads.

[0011] Inkjet printers (also called inkjet printing devices) have at least one inkjet print head with at least one row of adjacent nozzles through which ink can be applied to the surface to be printed. Printing occurs by ejecting ink droplets according to a predetermined, possibly variable, print frequency and droplet count.

[0012] During ejection, the inkjet print head performs a linear transverse movement, allowing one line to be printed. Alternatively, the substrate to be printed can perform a linear movement during ejection. This (transverse) movement determines the scanning direction. The method of printing line by line, which is known in the prior art, is therefore also called the scanning method. If one or more inkjet print heads extend across the entire width of the medium to be printed, as an alternative to the first embodiment mentioned above, only the substrate can be moved perpendicular to a row of nozzles, whereby the inkjet print head(s) are not moved. This method is also known as the single-pass method. If the print head only moves over the line once in the scanning method, this is referred to as the single-scan method. If the print head moves over the same line multiple times, this is referred to as the multi-scan method.The multi-scan process can lead to higher print quality in selected processes.

[0013] Once a line has been printed, the substrate to be printed can be moved one line perpendicular to the scan direction of the print head in one transport direction, and printing on the next line can begin. There are monodirectional processes, meaning the print head only prints in one direction during the transverse movement and returns to the beginning of the line without printing when the end of the line is reached. However, there are also bidirectional processes, in which the medium to be printed is shifted one line after the end of the line is reached, and the next line is printed when the print head returns to its starting position.

[0014] In inkjet printing, resolution is determined by the spacing of the droplets deposited by the print. In two-dimensional printing, the resolution in a first dimension, for example, the x dimension, can differ from the resolution in the second dimension perpendicular to the first dimension, for example, the y dimension. For example, the resolution along the transverse movement of the print head is determined by the speed of the print head and the droplet ejection frequency, while the resolution in the transport direction is determined by the spacing of the nozzles in the nozzle row of the print head. It should be noted that this resolution can be increased by tilting the nozzle row.Alternatively, a higher resolution can also be achieved, for example, by arranging a row of nozzles of a first print head offset from a row of nozzles of a second print head on a print carriage in such a way that the resolution is doubled in the transport direction. In the case of three-dimensional printing, the resolution in the third dimension, for example, the z dimension, which is orthogonal to the xy plane, can differ from the resolution in the first and / or second dimension. For example, the z resolution is determined by the ink application level realized at each pixel.

[0015] An ink application level (0 to KS) of a sacrificial ink for forming a support structure or for forming inner edge regions of respective mold layers of a support structure is defined in the context such that the level KS, ie K*S, indicates the ink quantity KS of the sacrificial ink with which each pixel Di in each row of a first printing raster is applied and K is a drop or a multiple of a drop of the sacrificial ink emitted by one or more nozzles of at least one nozzle row, each individual drop of the sacrificial ink having substantially the same drop volume S.

[0016] An ink application level (0 to LT) of an object ink is defined in the context such that the level LT, i.e. L*T, indicates the ink quantity LT of the object ink with which each pixel D2 in each row of a second printing raster is applied and L is a drop or a multiple of a drop of the object ink emitted by one or more nozzles of at least one nozzle row, each individual drop of the object ink having substantially the same drop volume T.

[0017] Currently, methods for the additive manufacturing of three-dimensional objects are known which work with conventional inkjet print heads, such that both object layers and sacrificial layers for supporting overhanging areas of the object to be formed are formed at a high resolution, e.g. at a resolution of at least 300 dpi x 300 dpi.

[0018] WO2006078342A2 discloses, in a particularly preferred embodiment, the realization of object layers and structural layers by means of inkjet printing, which, as shown in Figure 9, each have the same layer thickness. This prior art does not disclose that different ink droplet sizes are used to create the structural layers or sacrificial layers and the object layers. In particular, it does not disclose that the droplet volume of the respective ink droplets for creating the structural layers or sacrificial layers is smaller than the respective droplet volume of the ink droplets for creating the object layers.

[0019] While the purely digital additive inkjet printing processes known to date represent a very good and flexible method for producing high-quality objects, they have so far only achieved a high degree of object reproduction accuracy at the expense of time. The analog-digital manufacturing processes for three-dimensional objects mentioned above also represent a very good method for producing high-quality outer surfaces of products. However, the time savings in forming the object layers can often only be achieved at the expense of an inhomogeneous top layer of the three-dimensional object.

[0020] There is therefore a need for a method for structuring three-dimensional objects that achieves high imaging accuracy over the entire surface of the object in a time-saving manner.

[0021] The present invention is therefore based on the object of specifying a method for structuring three-dimensional objects with which a high imaging accuracy over the entire surface of the object, ie also on its cover layer, is achieved in a time-saving manner.

[0022] According to the invention, this object is achieved by a method comprising the features of claim 1. The subclaims relate to further advantageous and, where appropriate, additionally inventive embodiments. The invention is based on the idea that different native drop volumes are used for the sacrificial ink and for the object ink to form each sacrificial layer of each mold layer of a support structure and to form each object layer. The drop volume of the respective drops of sacrificial ink is <1 00pl, with the volume ratio between the volume of the respective drops of sacrificial ink and the volume of the respective drops of object ink being at least 1:15.

[0023] Each mold layer for forming a support structure for the three-dimensional object is formed by stacking several sacrificial layers on top of each other, wherein the sacrificial layers are each formed with a layer thickness that is at least a factor of two smaller than the layer thickness of each object layer.

[0024] The sacrificial layers are formed in such a way that each sacrificial layer is formed by applying a first combination droplet to each pixel Di in each row of an imaginary first printing grid on the respective surface to be printed, each combination droplet being composed of K drops of the sacrificial ink each having a volume S, where K e {0, 1, 2, 3, ...} and thus an ink application level KS is realized at each pixel Di.

[0025] The formation of the object layers is again carried out in such a way that each object layer is formed by applying a second combination drop to each pixel D2 in each row of an imaginary second printing grid on the respective surface to be printed, which second combination drop is composed of E drops of the object ink each having a volume T, where L e {0, 1, 2, 3, ...} and thus an ink application level LT is realized at each pixel Ü2.

[0026] The method according to the invention comprises the following steps: (a) forming, on a substrate or preferably on a lower layer, a first mold layer with a first recess corresponding to the negative of a first object layer, (b) filling the first recess with object ink to form the first object layer; (c) forming, on the first mold layer, a second mold layer with a second recess corresponding to the negative of a second object layer, (d) filling the second recess with object ink to form the second object layer, whereby an object and a support structure made of or comprising sacrificial layers have been formed.

[0027] In this context, a first combination droplet can be understood as meaning those drops of the sacrificial ink printed with one nozzle or with several nozzles in succession, which essentially have the same drop volume S, which, when using grayscale-capable inkjet print heads, can combine in flight and at the latest before impacting the pixel Di to be printed, or which, alternatively, generally when using inkjet print heads, are combined at different times on a pixel position at which they were aimed, and which essentially have a multiple of the originally printed drop volume S of the sacrificial ink.

[0028] In this context, a second combination droplet can again be understood as meaning those drops of the object ink printed with one nozzle or with several nozzles in succession, which essentially have the same drop volume T, which can combine in flight when using grayscale-capable inkjet print heads and at the latest before hitting the pixel D2 to be printed, or which alternatively generally combine at different times on a pixel position at which they were aimed when using inkjet print heads, and which essentially have a multiple of the originally printed drop volume T of the object ink.

[0029] However, it should be explicitly noted that a combination drop can also consist of zero drops (K or L equals zero) or of one drop (K or L equals 1).

[0030] Accordingly, the method according to the invention is a method for layer-by-layer structuring of a three-dimensional object, comprising:

[0031] (a) forming, on a substrate or preferably on a lower layer, a first mold layer with a first recess corresponding to the negative of a first object layer,

[0032] (b) filling the first recess with object ink to form the first object layer;

[0033] (c) forming, on the first mold layer, a second mold layer with a second recess which corresponds to the negative of a second object layer,

[0034] (d) Filling the second recess with object ink to form the second object layer.

[0035] According to the invention, each mold layer is formed by stacking several sacrificial layers on top of each other, wherein the sacrificial layers are each formed with a layer thickness that is at least two times smaller than the layer thickness of each object layer, such that each sacrificial layer is formed by applying a first combination droplet to each pixel Di in each row of an imaginary first printing grid on the respective surface to be printed, which first combination droplet is composed of K drops of the sacrificial ink each having a volume S, where K e {0, 1, 2, 3, ...} and thus an ink application level KS is realized at each pixel Di, and that each object layer is formed by applying a second combination drop to each pixel D2 in each row of an imaginary second printing grid on the respective surface to be printed, said second combination drop being composed of E drops of the object ink each having a volume T, where L e {0, 1, 2, 3, ...} and thus an ink application level LT is realized at each pixel D2, where the drop volume S of the respective K drops of the sacrificial ink is <100pl and the volume ratio (S:T) between the volume S of the respective K drops of the sacrificial ink and the volume T of the respective L drops of the object ink is at least 1:15, preferably at least 1:20.

[0036] In the context of this description, a layer refers to a continuous layer. Accordingly, in the method according to the invention, the drops of sacrificial ink and the drops of object ink are applied in such a way that the edge regions of first combination drops of sacrificial ink applied to adjacent pixels D1 merge into one another, and the edge regions of second combination drops of object ink applied to adjacent pixels D2 also merge into one another. Accordingly, the method according to the invention is also designed such that the drops of sacrificial ink and the object ink are applied in such a way that the XY screen rulings in the x- and y-dimensions of the first printing screen are each selected to be smaller than the respective XY screen rulings in the x- and y-dimensions of the second printing screen.The neighboring pixels are typically directly adjacent pixels that were actually exposed to a combination droplet. However, it is also possible that the neighboring pixels are indirectly adjacent pixels, where, for example, only every second pixel in the x and y directions was actually exposed to a combination droplet.

[0037] In the context of this description, a mold layer is understood to mean a mold layer which consists of a side wall enclosing a recess, which side wall comprises several sacrificial layers stacked one above the other.

[0038] According to a preferred embodiment of the method, the drop volume S of the respective K drops of sacrificial ink is in each case < 100 pl, preferably 100 pl < S < 80 pl, particularly preferably 20 pl < S < 45 pl, wherein the volume ratio (S:T) between the volume S of the respective K drops of sacrificial ink and the volume T of the respective L drops of object ink is in each case at least 1:50, preferably at least 1:150, particularly preferably at least 1:300, and very particularly preferably up to 1:1500. These developments offer the advantage that the time saved in the formation of the object layer can be increased and a high imaging accuracy is also achieved over the entire surface of the object.

[0039] Accordingly, the sacrificial layers can, for example, each be formed with a layer thickness that is at least a factor of four smaller, preferably at least a factor of eight smaller, than the layer thickness of each object layer. In a preferred embodiment, each formed object layer is dried and / or cured before a further object layer is formed thereon. The respective object layers are typically not completely dried. This results in improved adhesion between the layers.

[0040] In a particularly preferred embodiment, each formed object layer is dried by removing the water, preferably substantially only the water, from each formed object layer before a further object layer is formed thereon.

[0041] According to a preferred embodiment, the object ink contains as components (a) water, (b) an organic binder and (c) an organic dispersant or (z) an organic dispersant-effective binder instead of components (b) and (c), and (d) ceramic particles and / or metallic particles dispersed in the water, the method further comprising the step of firing the object to obtain a fired ceramic and / or metallic object.

[0042] The organic binder (component (b)) is designed in such a way that it has the task of temporarily holding the ceramic and / or metallic particles of the respective object layers formed in place after the water has been removed by drying the respective object layers and until the particles are bonded together by sintering during the firing step.

[0043] The dispersant (component (c)), which is distinct from the organic binder, promotes the wetting and stabilization of the ceramic and / or metallic particles in the object ink, thus preventing floating and settling of the particles present, thereby maintaining the homogeneity of the suspension over a longer period of time. The organic dispersant is designed accordingly.

[0044] The organic binder can also be designed to fulfill the function of an organic dispersant. Such a binder is referred to in this description as an organic dispersant binder (component (z)).

[0045] Corresponding organic binders, organic dispersants and organic dispersing binders are known from the prior art.

[0046] Suitable organic binders (components (b)) are, for example, first polymers. Such polymers are known to the person skilled in the art. Suitable organic dispersants (components (c)) are, for example, second polymers. Such polymers are also known to the person skilled in the art.

[0047] Suitable organic dispersing binders (component (z)) are preferably third polymers, for example methylcellulose. Such polymers are also well known to the person skilled in the art.

[0048] In a particularly preferred embodiment, the object ink comprises the following components:

[0049] 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a); and

[0050] 0.3 wt% - 5 wt%, preferably 0.5 wt% - 1.5 wt%, component (b); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (c); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d), or

[0051] 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (z); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d), wherein the organic component content of the object ink is in total < 6 wt%, preferably < 5 wt%, particularly preferably < 3 wt%, and wherein the respective percentages relate to the total weight of the object ink.

[0052] Typically, the object ink comprises, as additional component (e), at least one additional additive, for example, an organic slip and / or flow additive, which serves to reduce the surface tension of the object ink. According to some embodiments of the present invention, the amount of slip and / or flow additive in the ink is between 0.2 wt% and 3 wt%, preferably between 0.5 wt% and 1 wt%, based on the total weight of the object ink.

[0053] In contrast to the object inks according to the invention, conventional object inks with ceramic and / or metallic particles for producing corresponding objects contain a significantly higher weight fraction, i.e., a weight fraction of over 15 wt%, usually even over 30 wt%, of organic components relative to the total weight of the object ink. This includes, in particular, an organic humectant to prevent drying and / or agglomeration of the ceramic and / or metallic particles in the nozzles of conventional inkjet print heads with a nozzle diameter of up to 60 μm. This successfully minimized nozzle clogging, thus achieving high printing reliability with these print heads.

[0054] An object produced from the ceramic and / or metallic object ink according to the invention behaves in such a way that—even if no significant organic component was removed from its layers during the respective drying process—a fired ceramic and / or metallic object can be produced from it in a significantly shorter time compared to the aforementioned conventional object inks without defects. In this context, the object behaves in particular in such a way that, by means of a temperature ramp, it can be heated from room temperature to a temperature at which it begins to sinter within a significantly shorter heating time without defects occurring in the object.

[0055] As a result, the layered object behaves in such a way that even if, for example, <20 wt.%, preferably <10 wt.% of the organic components of the object ink were removed from each layer of the object during the respective drying process, a fired ceramic and / or metal object can be produced from it in a significantly shorter time compared to the conventional object inks mentioned above without defects.

[0056] A defect-free object is one that is produced after the firing process without cracking and / or bursting of individual object layers.

[0057] Until now, ceramic and / or metal objects fired with the above-mentioned conventional object inks could only be produced defect-free by a lengthy thermal debinding step prior to the firing step, i.e., the sintering step. This step typically lasted several days and was usually carried out at an average temperature of over 150°C. For the purposes of this description, the debinding step is defined in such a way that, in contrast to the firing step, even partial sintering of the inorganic particles of the object ink, i.e., the ceramic and / or metal particles, does not occur in this step.

[0058] With the method according to the invention, using the object inks according to the invention, objects with a significantly greater wall thickness can be produced without defects, which could not be produced until now using conventional methods and object inks, even if the thermal debinding process is extended.

[0059] Interestingly, the inventors have observed that the inventive object inks, which are low in organic components, when formulated as inkjet printing inks and processed with nozzles of an inkjet print head each with an inner diameter in the range of 100 μm to 400 μm, enable surprisingly high printing reliability of the inkjet print head. Despite the low organic component content of < 6 wt%, preferably < 5 wt%, particularly preferably < 3 wt%, the risk of drying and / or agglomeration of the ceramic and / or metal particles could be drastically reduced, thus correspondingly minimizing the risk of nozzle clogging.

[0060] The reduction of the organic component content in the object ink also makes the process more environmentally friendly than the corresponding conventional processes.

[0061] The object ink can comprise an object ink A and an object ink B, each comprising components (a), (b), (c), and (d) or components (a), (z), and (d), but in different and predetermined weight proportions and compositions, and which are applied to the pixels D2 of the second printing grid according to a predetermined printing pattern to form an object layer. This enables the formation of objects with very different chemical and / or physical properties. For example, object ink A can comprise ceramic particles made of aluminum oxide and object ink B can comprise ceramic particles made of zirconium oxide. If both object inks are used to form the respective object layers according to selected and known printing schemes, the fracture toughness and strength of the individual object layers and thus also that of the object itself can be significantly increased.

[0062] Furthermore, it is possible that the object ink and the sacrificial ink are each formed as inkjet inks and that the K drops of the sacrificial ink are dispensed from at least one first inkjet print head with a plurality of nozzles, and that the E drops of the object ink are dispensed from at least one second inkjet print head, each with a plurality of nozzles, wherein during the formation of each sacrificial layer a linear relative movement takes place at least between the first inkjet print head and the substrate and wherein during the formation of each object layer a linear relative movement takes place at least between the second inkjet print head and the substrate.

[0063] Furthermore, it is possible for the plurality of nozzles of the second inkjet print head to each have an inner diameter in a range from 100 pm to 400 pm, preferably in a range from 150 pm to 350 pm, particularly preferably in a range from 150 pm to 250 pm, and for the plurality of nozzles of the first inkjet print head to each have an inner diameter of up to 60 pm, preferably in a range from 20 pm to 45 pm.

[0064] According to a preferred embodiment, a plunger-driven inkjet print head is provided as the second inkjet print head. The plunger-driven inkjet print head may include a circulation pump provided outside the print head for pumping the object ink through an ink supply channel of the print head.

[0065] Examples of such inkjet printheads include the plunger-operated inkjet printheads for inkjet printers disclosed in the descriptions of WO 2013 / 013983 A1, WO 2019 / 042586 A1, and WO 2019 / 042585 A1, each by the applicant of the same name. Due to the large inner diameter of the nozzles, between 250 pm and 350 pm, such printheads can print, for example, suspensions with larger particles than with the otherwise typical piezoelectrically operated inkjet printing devices of the prior art, which typically have nozzles with an inner diameter of only up to 60 pm.

[0066] According to a further preferred embodiment, at least 95%, preferably at least 99%, of the pixels D2 of the object layer actually to be printed are exposed to one and the same second combination droplet, which is composed of L drops of the object ink, where L e {1, 2, 3}, preferably L e {1}, and thus the same ink application level IT, 2T, or 3T, preferably IT, is realized for each of these pixels D2. These developments offer the advantage that the imaging accuracy of each object layer as an intermediate layer can be further increased, so that overall a more homogeneous cover layer of the three-dimensional object is achieved.

[0067] According to another preferred embodiment, at least 95%, preferably at least 99%, of the pixels Di of the sacrificial layer actually to be printed are exposed to one and the same first combination droplet, which is composed of K drops of sacrificial ink, where K e is {1, 2, 3}, preferably K e {1}, and thus the same ink application level IS, 2S, 3S, preferably IS, is realized for each of these pixels Di. These developments offer the advantage of further increasing the imaging accuracy of a base layer of the object.

[0068] According to a particularly preferred embodiment, at least 95%, preferably at least 99% of the pixels Di actually to be printed, either of a region near the edge of the recess of the sacrificial layer or of an inner edge region of a mold layer, if a recess is present, or of the entire region of the respective sacrificial layer, are exposed to one and the same first combination droplet.

[0069] When, in the context of this description, reference is made to "a region of the recess of the sacrificial layers close to the edge", this means an edge region which is defined both by the actual edge of the recess of the sacrificial layer and by a fictitious edge which surrounds the recess of the object layer at a distance and runs within the sacrificial layer, wherein the distance between the actual edge and the fictitious edge is up to 5 cm, preferably up to 1 cm.

[0070] The method typically includes an additional step of removing the support structure formed from or comprising sacrificial layers from the object, preferably by mechanical removal, evaporation of volatile components, melting, dissolving, or incineration of the support structure. This allows the object to be preserved as such during one and the same process. The support structure serves to support lateral and / or overhanging areas of the object.

[0071] Furthermore, it is possible to form one or more sacrificial layers on the substrate prior to step (a) by stacking them one on top of the other. This development is advantageous because it reduces the effort required to remove the object from the substrate.

[0072] Furthermore, it is possible for step (a) to also comprise the formation, on the substrate or on a lower layer, of a first core layer within the respective recess, such that a ring-like recess is formed; and for step (c) to also comprise the formation, on the lower layer, of a second core layer, such that a ring-like recess is formed. This allows the variety of shapes of the three-dimensional objects to be expanded.

[0073] According to a further preferred embodiment, in step (c) the formation of a second mold layer also takes place on the first object layer.

[0074] Furthermore, it is typically possible for each sacrificial layer to be solidified or dried and / or cured before a further sacrificial layer, or preferably an object layer and a further sacrificial layer, is formed thereon.

[0075] According to a preferred embodiment, the sacrificial ink comprises a wax, or the sacrificial ink consists of a wax that has a melting temperature (smp) of >40°C, preferably an smp of >60°C, particularly preferably an smp of >90°C, and that has been preliminarily heated to a temperature higher than its melting temperature for applying the pixels Di of the first printing grid. The wax can solidify by passive or active cooling of the substrate at a temperature lower than the melting temperature of the wax.

[0076] According to another preferred embodiment, the sacrificial ink comprises a liquid carrier, a dispersant, a photoinitiator that forms radicals through UV radiation, and a polymer that is radically curable and dispersed in the liquid carrier by the dispersant. The drying of each sacrificial layer can be achieved by exposing the sacrificial ink to thermal energy, for example, IR or NIR radiation, and the UV curing of each sacrificial layer can be achieved by exposing the sacrificial ink to UV radiation.

[0077] Furthermore, it is possible that when filling an n-th recess of an n-th mold layer with object ink to form an n-th object layer, the not yet dried and / or not yet hardened n-th object layer is formed with a layer thickness that is less than or equal to the layer thickness of the solidified or dried and / or hardened n-th mold layer, which corresponds to the negative of the n-th object layer.

[0078] The letter n of an (n)-th form layer corresponds to the number of form layers formed so far, and the letter n of an (n)-th object layer corresponds to the number of object layers formed so far.

[0079] The xy screen rulings, ie the screen rulings in a dimension x and in a dimension y of the first printing screen aligned vertically to the dimension x, can each correspond to an ink drop density of > 300 dpi, preferably > 600 dpi, particularly preferably > 1200 dpi, and the screen rulings in the dimension x and in the dimension y of the second printing screen can each correspond to an ink drop density of < 150 dpi, preferably from 50 dpi to 100 dpi each.

[0080] It is clear that the method according to the invention may comprise further printing cycles of the so-called first type, if necessary to completely produce the desired object, wherein a printing cycle of the first type comprises:

[0081] Forming, on the (n)th mold layer, and preferably on the (n)th object layer, an (n+l)th mold layer with a predetermined recess corresponding to the negative of the (n+l)th object layer;

[0082] Filling the specified cavity with object ink to form the (n+l)th object layer; where n is increased by 1 after each printing cycle of the first type.

[0083] The method according to the invention may also comprise one or more printing cycles of the so-called second type until the desired object has been completely formed, wherein a printing cycle of the second type comprises:

[0084] Forming, on the (n)th mold layer and on the (n)th object layer, an (n+l)th object layer, wherein n is increased by the number 1 after each printing cycle of the second type. In this case, preferably the (n)th mold layer, to which an (n+l)th object layer is to be applied, is formed exclusively by stacking the plurality of sacrificial layers one on top of the other.

[0085] Each object layer can be leveled with a mechanical means for leveling its surface, preferably with a suitable roller or squeegee, before another object layer is formed on top. This can increase the imaging accuracy of the object's top layer.

[0086] Each sacrificial layer can also be leveled with a mechanical means for leveling its surface, preferably with a suitable roller or doctor blade, before another sacrificial layer is formed on top of it. This can increase the imaging accuracy of the surface layer of the object and, if necessary, increase the imaging accuracy of the bottom layer of the object.

[0087] According to a first, particularly preferred embodiment, the object is formed with at least one desired color gradient by forming the respective undried and / or uncured object layers in such a way that they are optionally printed with drops, each with a volume of <50 pl, of one or more color inks containing inorganic or organic color particles according to a predetermined print pattern using at least one third inkjet print head, such that the layer thickness of each undried and / or uncured object layer does not increase significantly, preferably by no more than 3%, particularly preferably by no more than 1.5%. This makes it possible, for example, to recreate realistic color gradients of a dental crown.

[0088] According to a second, particularly preferred embodiment, ceramic and metallic object layers are formed alternately, such that insulating and conductive object layers are formed alternately. This allows, for example, electronic components to be manufactured.

[0089] Furthermore, it is possible for the sacrificial ink to comprise particles, wherein the particles of the sacrificial ink have a volumetric diameter of 0.001 pm < d50 < 2.0 pm, preferably 0.1 pm < d50 < 1 pm, wherein the particles of the sacrificial ink particularly preferably make up 3 wt% to 50 wt%, very particularly preferably 3 wt% to 30 wt%, of the total weight of the sacrificial ink. Furthermore, it is possible for the ceramic particles and / or metallic particles of the object ink to have a volumetric diameter of 0.1 pm < d50(v) < 10 pm, preferably 0.35 pm < d50(v) < 6 pm, particularly preferably 0.5 pm < d50(v) < 4 pm.Inks comprising particles with a volumetric diameter of 0.35 pm < d50(v) < 6 pm, preferably 0.5 pm < d50(v) < 4 pm, behave in such a way that an inkjet print head printing such inks can operate at a noticeably higher droplet ejection frequency than would be the case with comparison inks comprising particles with a volumetric diameter of d50(v) < 0.25 pm, especially since the former can be provided with a significantly lower viscosity than the latter. Consequently, these inks according to the invention may enable an increase in productivity compared to the comparison inks. Moreover, the production of inks with particles with 0.35 pm < d50(v) < 6 pm, preferably 0.5 pm < d50(v) < 4 pm, is significantly less cost-intensive than is the case with the said comparison inks, especially since the grinding effort is lower.

[0090] According to a preferred second variant of the method according to the invention, at least one mold layer can be divided into an outer edge region and an inner edge region, wherein the inner surface of the inner edge region of the mold layer defines the corresponding recess of the mold layer, wherein the inner edge region of at least the first and second mold layers is formed by stacking the plurality of sacrificial layers on top of one another, and the respective outer edge region of at least the first and second mold layers is produced with an outer structure-forming ink, such that the respective outer edge region is formed by applying a third combination droplet to each pixel D3 in each row of an imaginary third printing grid on the respective surface to be printed, each droplet being composed of M drops of the outer structure-forming ink, each with a volume U, where M e {0, 1, 2, 3, ...}} and thus an ink application level MU is realized at each pixel D3, whereby the volume ratio (S:U) between the volume S of the respective K drops of the sacrificial ink and the volume U of the respective M drops of the ink forming the outer structure is at least 1:15.

[0091] This resulted in the formation of an object made up of object layers and a support structure made up of sacrificial layers and outer structural layers.

[0092] The inner edge region of each mold layer can be formed according to said method by stacking the plurality of sacrificial layers on top of each other, and the outer edge region of each mold layer can be formed according to said method with the outer structure forming ink.

[0093] The third printing grid can correspond to the first printing grid.

[0094] These developments offer the advantage that the object can be created quickly and effectively and, at the same time, a high level of imaging accuracy can be achieved on the outer surface of the object. An ink application level (0 to MU) of an external structure-forming ink for forming the outer edge regions of the respective mold layers of a support structure is defined in the context such that the level MU, i.e. M*U, indicates the ink quantity MU of the external structure-forming ink with which each pixel D3 in each row of a third printing raster is applied and M is a drop or a multiple of a drop of the external structure-forming ink emitted by one or more nozzles of at least one nozzle row, wherein each individual drop of the external structure-forming ink has substantially the same drop volume U.

[0095] In this context, a third combination droplet can again be understood as meaning those drops of the ink forming the outer structure which are printed with one nozzle or with several nozzles in succession and which essentially have the same drop volume U, which can combine in flight when using grayscale-capable inkjet print heads and at the latest before hitting the pixel D3 to be printed, or which alternatively generally combine at different times on a pixel position to which they were aimed when using inkjet print heads, and which essentially have a multiple of the originally printed drop volume U of the object ink.

[0096] However, it should be explicitly noted that a combination drop can also consist of zero drops (M equals zero) or of one drop (M equals 1).

[0097] According to a preferred embodiment of the method, the drop volume S of the respective K drops of the sacrificial ink is in each case < 100 pl, preferably 100 pl < S < 80 pl, particularly preferably 20 pl < S < 45 pl, wherein the volume ratio (S:U) between the volume S of the respective K drops of the sacrificial ink and the volume U of the respective M drops of the ink forming the outer structure is in each case at least 1:50, preferably at least 1:150, particularly preferably at least 1:300.

[0098] The inner edge region of a molding layer can have a width of 20 pm to 5000 pm, preferably of 100 pm to 2000 pm, particularly preferably of 100 pm to 500 pm, and the outer edge region of a molding layer can have a width of greater than 500 pm, preferably greater than 1000 pm, particularly preferably greater than 2000 pm.

[0099] According to a preferred embodiment of the second variant, each mold layer is formed with an inner and outer edge region by first forming the inner edge region of the mold layer and preferably solidifying or drying and / or hardening it before the outer edge region of one and the same mold layer is formed and preferably solidifying or drying and / or hardening it.

[0100] The drop volume T of the respective L drops of the object ink can be essentially identical to the drop volume U of the respective M drops of the ink forming the outer structure.

[0101] Furthermore, it is possible that the ink forming the outer structure is formed as inkjet ink and that the M drops of the ink forming the outer structure are dispensed from at least one third inkjet print head with a plurality of nozzles, wherein preferably the first and the third inkjet print head are the same inkjet print head.

[0102] Furthermore, it is possible for the plurality of nozzles of the third inkjet print head to each have an inner diameter in a range from 100 pm to 400 pm, preferably in a range from 150 pm to 350 pm, particularly preferably in a range from 150 pm to 250 pm.

[0103] According to a preferred embodiment, a plunger-driven inkjet print head is provided as the third inkjet print head. The plunger-driven inkjet print head may include a circulation pump provided outside the print head for pumping the ink forming the external structure through an ink supply channel of the print head.

[0104] According to a particularly preferred embodiment of the second variant, the outer structure-forming ink for producing an outer edge region of a mold layer contains as components (a) water, (b2) a second organic binder and (c2) a second organic dispersant or (c2) a second organic dispersant binder instead of components (b2) and (c2), and (d2) second ceramic particles and / or second metallic particles dispersed in the water, wherein the sacrificial ink has been selected and formed with respect to both the object ink and the outer structure-forming ink such that an inner edge region of a respective mold layer formed by the sacrificial ink resists the bonding of the outer edge region of one and the same mold layer to the object during sintering.

[0105] The person skilled in the art is familiar with corresponding sacrificial inks from the state of the art.

[0106] A corresponding sacrificial ink according to the invention may comprise wax and non-sinterable particles.

[0107] Non-sinterable particles of the sacrificial ink are, for example, particles that have a first sintering temperature that is higher than the second sintering temperature of the particles of the object ink and also higher than the third sintering temperature of the particles of the ink forming the external structure. In this preferred embodiment, the object is fired at a firing temperature that is higher than the second sintering temperature of the particles of the object ink and also higher than the third sintering temperature of the particles of the ink forming the external structure, but lower than the first sintering temperature of the particles of the sacrificial ink.

[0108] A corresponding wax can have a melting temperature (Smp) of >40°C, preferably an Smp of >60°C, particularly preferably an Smp of >90°C, and which has been brought in advance to a temperature higher than its melting temperature in order to apply the pixels Di of the first printing grid.

[0109] Such sacrificial inks with wax and non-sinterable particles facilitate the mechanical removal of the outer edge area of ​​the support structure from the object after the firing process.

[0110] At least one of the components b2, c2, d2, and z2 may be different from its corresponding letter component b, c, d, and z. Alternatively, each component b2, c2, d2, and z2 may be identical to all of its corresponding letter components b, c, d, and z.

[0111] Furthermore, in a particularly preferred embodiment, the ink forming the outer structure may comprise the following components:

[0112] 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a2); and 0.3 wt% - 5 wt%, preferably 0.5 wt% - 1.5 wt%, component (b2); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (c2); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d2), or

[0113] 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, of component (a2); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, of component (z2); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, of component (d2), wherein the organic component content of the ink forming the outer structure is in total < 6 wt%, preferably < 5 wt%, particularly preferably < 3 wt%, and wherein the respective percentages relate to the total weight of the ink forming the outer structure. Furthermore, it is possible for the ceramic particles and / or metallic particles of the ink forming the outer structure to have a volumetric diameter of 0.1 pm < d50(v) < 1 pm. preferably 0.35 pm < d50(v) < 6 pm, particularly preferably 0.5 pm < d50(v) < 4 pm.

[0114] Furthermore, it is possible for the ceramic particles and / or metallic particles of the object ink and / or the second ceramic particles and / or second metallic particles of the ink forming the external structure to each contain at least two particle size populations which differ from one another, the first population (PI) having a volumetric diameter of the particle size of 0.1 pm < d50(v) < 4 pm and the second population (P2) having a volumetric diameter of the particle size of 0.8 pm < d50(v) < 12 pm, the ratio between the d50(v) value of the population PI and the d50(v) value of the population P2 being in a range from 1:8 to 1:3.

[0115] This allows for denser packing of particles and thus denser objects to be created.

[0116] The object mentioned at the outset is also achieved by a three-dimensional object according to the invention, preferably a ceramic and / or metallic object, which is obtainable by at least one method according to the invention.

Claims

Claims:

1. Method for structuring a three-dimensional object layer by layer, comprising: (a) Forming, on a substrate or preferably on a lower layer, a first form layer with a first recess corresponding to the negative of a first object layer, (b) Filling the first recess with object ink to form the first object layer; (c) Forming, on the first mold layer, a second mold layer with a second recess corresponding to the negative of a second object layer, (d) Filling the second recess with object ink to form the second object layer; characterized in that each form layer is formed by stacking several sacrificial layers on top of each other, the sacrificial layers each having a layer thickness that is at least twice as small as the layer thickness of each object layer, such that each sacrificial layer is formed by striking each pixel Di in each row of a first printing grid imagined on the surface to be printed with a first combination droplet, each droplet being composed of K drops of sacrificial ink, each with a volume S, where K e {0, 1, 2, 3, ...} and thus an ink application level KS is realized at each pixel Di, and that each object layer is formed by applying a second combination droplet to each pixel D2 in each row of a second printing grid imagined on the surface to be printed, each droplet being composed of L droplets of the object ink, each with a volume T, where L e {0, 1, 2, 3, ...} and thus an ink application level LT is realized at each pixel D2, where the droplet volume S of the respective K droplets of the sacrificial ink is < 10 ...

2. Method according to claim 1 characterized in that the drop volume S of the respective K drops of the sacrificial ink is each < 1000, preferably 1000 < S < 8000, particularly preferably 2000 < S < 4500, wherein the volume ratio (S:T) between the volume S of the respective K drops of the sacrificial ink and the volume T of the respective L drops of the object ink is each at least 1:50, preferably at least 1:150, particularly preferably at least 1:

300.

3. Method according to claim 1 or 2 characterized in that each formed object layer is dried and / or hardened before a further object layer is formed on it.

4. Method according to at least one of the preceding claims, characterized in that the object ink comprises as components (a) water, (b) an organic binder and (c) an organic dispersing agent or (z) an organic dispersing binder instead of Components (b) and (c), and (d) ceramic particles and / or metallic particles dispersed in water, the process further comprising the step of firing the object to obtain a fired ceramic and / or metallic object.

5. Method according to claim 4 relating to claim 3, characterized in that each formed object layer is dried by removing the water, preferably substantially only the water, from each formed object layer before a further object layer is formed on it.

6. Method according to claim 4 or 5 characterized in that the object ink comprises the following components: 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a); and 0.3 wt% - 5 wt%, preferably 0.5 wt% - 1.5 wt%, component (b); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (c); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d), or 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (z); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d), wherein the total organic component content of the object ink is < 6 wt%, preferably < 5 wt%, particularly preferably < 3 wt%, and wherein the respective percentages refer to the total weight of the object ink.

7. Method according to at least one of claims 4 to 6 characterized in that the object ink comprises an object ink A and an object ink B, each comprising components (a), (b), (c) and (d) or components (a), (z) and (d), but in different and predetermined weight proportions and compositions, and which are applied to the pixels D2 of the second printing grid according to a predetermined printing pattern in order to form an object layer.

8. Method according to at least one of the preceding claims, characterized in that the object ink and the sacrificial ink are each designed as inkjet inks and that the K droplets of the sacrificial ink are dispensed from at least one first inkjet printhead with multiple nozzles, and that the L droplets of the object ink are dispensed from at least one second inkjet printhead with each The method of printing is characterized in that the multiple nozzles of the second inkjet printhead each have an inner diameter in the range of 100 pm to 400 pm, preferably in the range of 150 pm to 350 pm, and particularly preferably in the range of 150 pm to 250 pm, and that the multiple nozzles of the first inkjet printhead each have an inner diameter of up to 60 pm, preferably in the range of 20 pm to 45 pm. The method of claim 8 or 9 is characterized in that a plunger-operated inkjet printhead is provided as the second inkjet printhead.A method according to at least one of the preceding claims, further characterized by the step of removing the support structure, which is formed from or comprises sacrificial layers, from the object, preferably by mechanical removal, evaporation of volatile components, melting, dissolving, or burning of the support structure. A method according to at least one of the preceding claims, characterized in that, prior to step (a), a sacrificial layer or several sacrificial layers are formed on the substrate by stacking them one above the other. A method according to at least one of the preceding claims, characterized in that each sacrificial layer is solidified or dried and / or hardened before a further sacrificial layer, or preferably an object layer and a further sacrificial layer, is formed on it.The method of claim 13, characterized in that the sacrificial ink comprises a liquid carrier, a dispersing agent, a photoinitiator that forms radicals upon UV radiation, and a polymer which is radically curable and is dispersed in the liquid carrier by the dispersing agent. The method of at least one of the preceding claims, characterized in that when filling an nth recess of an nth mold layer with object ink, in order to create an nth recess, the sacrificial ink is formed by the formation of a new, free-floating, and free-floating, inert, inert, and free-floating, inert, inert, and free-floating, inert, inert, and free-floating, inert, sacrificial, free-floating, and free-floating, inert, sacrificial ... to form an object layer, the nth object layer which is not yet dried and / or not yet hardened, with a layer thickness that is less than or equal to the layer thickness of the solidified or dried and / or hardened nth mold layer, which corresponds to the negative of the nth object layer.A method according to at least one of the preceding claims, characterized in that the object is formed with at least one desired color gradient by forming the respective undried and / or uncured object layers such that they are optionally printed with droplets, each with a volume of <30 pl, of one or more color inks with inorganic or organic color particles according to a predetermined print pattern using at least one third inkjet printhead, such that the layer thickness of each undried and / or uncured object layer does not increase significantly, preferably by no more than 3%, particularly preferably by no more than 1.5%. A method according to at least one of the preceding claims, characterized in that ceramic and metallic object layers are formed alternately, such that insulating and conductive object layers are formed alternately.A method according to at least one of the preceding claims, claim 4, or according to at least one of claims 5 to 17 relating to claim 4, characterized in that the sacrificial ink comprises particles, wherein the particles of the sacrificial ink have a volumetric diameter of preferably 0.001 pm < d50 < 2.0 pm, more preferably 0.1 pm < d50 < 1 pm. A method according to claim 4 or according to at least one of claims 5 to 18, wherein the ceramic particles and / or metallic particles of the object ink have a volumetric diameter of 0.1 pm < d50(v) < 10 pm, more preferably 0.35 pm < d50(v) < 6 pm, more preferably 0.5 pm < d50(v) < 4 pm.A method according to at least one of the preceding claims 1 to 19, characterized in that at least one mold layer can be subdivided into an outer edge region and an inner edge region, wherein the inner surface of the inner edge region of the mold layer defines the corresponding recess of the mold layer, wherein the inner edge region of at least the first and second mold layers is formed by stacking the several sacrificial layers on top of each other, and the respective outer edge region of at least the first and second mold layers is produced with an ink forming an outer structure, such that the respective outer edge region is formed by applying a third combination droplet to each pixel D3 in each row of a third printing grid imagined on the surface to be printed, which is each composed of M droplets of the outer structure-forming ink, each with a volume U, wherein M e {0, 1, 2, 3, ...} and thus D3 is generated at every pixel. The ink application level MU is realized, wherein the volume ratio (S:U) between the volume S of the respective K drops of the sacrificial ink and the volume U of the respective M drops of the ink forming the outer structure is at least 1:

15.

21. Method according to claim 20 characterized in that the drop volume S of the respective K drops of the sacrificial ink is each < 100pl, preferably 100pl < S < 80pl, particularly preferably 20pl < S < 45pl, wherein the volume ratio (S:U) between the volume S of the respective K drops of the sacrificial ink and the volume U of the respective M drops of the ink forming the outer structure is each at least 1:50, preferably at least 1:150, particularly preferably at least 1:

300.

22. Method according to claim 21 characterized in that each mold layer with inner and outer edge region is formed by first forming the inner edge region of the mold layer and preferably solidifying or drying and / or hardening it, before forming the outer edge region of one and the same mold layer and preferably solidifying or drying and / or hardening it.

23. A method according to claim 20 or 22, each relating to claim 4, characterized in that the outer structure-forming ink for producing an outer edge region of a mold layer comprises as components (a) water, (b2) a second organic binder and (c2) a second organic dispersing agent or (z2) a second organic dispersing binder instead of components (b2) and (c2), and (d2) second ceramic particles and / or second metallic particles dispersed in the water, wherein the sacrificial ink is selected and configured with respect to both the object ink and the outer structure-forming ink such that an inner edge region of a respective mold layer formed by the sacrificial ink resists the bonding of the outer edge region of one and the same mold layer to the object during sintering.

24. The method according to claim 23, characterized in that: 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a2); and 0.3 wt% - 5 wt%, preferably 0.5 wt% - 1.5 wt%, component (b2); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (c2); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d2), or 10 wt% - 40 wt%, preferably 15 wt% - 25 wt%, component (a2); and 0.01 wt% - 5 wt%, preferably 0.2 wt% - 2 wt%, component (z2); and 50 wt% - 85 wt%, preferably 70 wt% - 80 wt%, component (d2), wherein the total organic component content of the ink forming the outer structure is < 6 wt%, preferably < 5 wt%, particularly preferably < 3 wt%, and wherein the respective percentages refer to the total weight of the ink forming the outer structure.

25. A method according to at least one of claims 20 to 24 relating to claim 18, characterized in that the ceramic particles and / or metallic particles of the ink forming the outer structure have a volumetric diameter of 0.1 pm < d50(v) < 1000 pm, preferably 0.35 pm < d50(v) < 6 pm, and particularly preferably 0.5 pm < d50(v) < 4 pm. A three-dimensional object, preferably a ceramic and / or metallic object, obtainable by a method according to at least one of claims 1 to 25.