Method for producing a three-dimensional molded article by layered material application

Description

[0001] The invention relates to a method for producing a three-dimensional shaped article by layered material application, wherein geometric data for the shaped article, a carrier part with a base surface for receiving the three-dimensional shaped article, a solidifiable liquid, flowable or powdery first material, a powdery second material, preferably comprising thermoplastic powder particles, and a solvent are provided in which the solidified first material is soluble.

[0002] In such a process known from practice, liquid polymers which can be solidified by exposure to ultraviolet radiation are used as the first and second materials. In the previously known process, a first material layer is first applied to the base surface of the carrier part by spraying droplet-shaped portions of the first and second materials onto different locations on the base surface using an inkjet printer. The locations at which the material droplets consisting of the different materials are applied to the base surface are selected depending on the provided geometric data for the molded article to be produced such that the regions of the material layer consisting of the second material form a bottom layer of the molded article to be produced.The first material serves as a support material, which is applied to the base surface at locations where no second material is applied and over which the molded article exhibits overhangs after the application of a further layer of the second material. These overhangs are to be supported by the support material until all material layers have solidified. The resulting bottom layer of material is then irradiated with ultraviolet radiation in a further step to solidify the polymers contained in the first and second materials by crosslinking.

[0003] After the bottom layer of material has been completed, further layers of material are applied and solidified in a similar manner until all layers of the molded article have been produced and solidified. The resulting stack of layers is then brought into contact with the solvent until the first material dissolves. The second material is insoluble in the solvent.

[0004] The previously known process allows for the comparatively cost-effective production of three-dimensional molded objects as prototypes or in small batches. The use of UV-curable polymers and the high printing resolution enable good surface quality. However, high-resolution 3D printing requires a very low viscosity of the polymers so that they can be applied through fine nozzles onto the base surface or a solidified material layer located thereon.

[0005] In inkjet printing, nozzles can typically handle a maximum viscosity of 25 mPa s. Higher viscosities are generally not jettable. Objects created from such materials have only minimal durability and can only serve as demonstration objects.

[0006] WO 2015 / 105047 A1 discloses a method for producing a three-dimensional molded object, in which the individual material layers are each made of at least three different materials. During the production of the individual material layers, an ink ejection step is first performed, in which a first and a different second material are applied by inkjet printing to a base surface or a solidified material layer located thereon. The first material serves to produce a solvent-soluble sacrificial layer, which is intended to support further layers to be applied thereon.

[0007] The second material is used to produce a portion of the molded article adjacent to the outer surface of the molded article and is insoluble in the solvent. The second material is applied to a base surface or a solidified material layer located thereon according to specified geometric data in such a way that the second material defines a cavity located in the inner volume of the molded article to be produced at a distance from its surface.

[0008] After the first and second materials have been applied to the base surface and the solidified material layer thereon, respectively, a curing step is performed in which the first and second materials are solidified. This produces a sacrificial layer and an outer layer of the molded article to be produced.

[0009] The cavity is then filled with a material composition containing a water-soluble resin and porous powder particles. If the material composition is in a solid state, it is heated to a flowable state before being filled into the cavity. The material composition can be applied to the cavity using a doctor blade, screen printing, or spin coating. The material composition filled into the cavity is planarized with the layer of the second material to create a material layer of uniform thickness.

[0010] A binder ink containing a curable resin that can match the first material is then added to the material composition in the cavity. The binder ink penetrates into the pores of the powder particles. The resin is then cured. This creates a bonded powder layer in which the cured resin is anchored in the pores of the powder particles. According to the published application, this enables a high mechanical dimensional stability of the bonded powder layer. Furthermore, the bonded powder layer is bonded by the resin to the material from the second

[0011] material existing outer layer of the molded article to be produced is combined into a uniform layer.

[0012] In the previously known process, the aforementioned steps are repeated to produce additional material layers in a corresponding manner. After all the material layers required for the molded article have been completed and solidified, the first material is dissolved in the solvent to remove the sacrificial layers.

[0013] Since the outer layer of the molded article is produced by applying droplets of material using an inkjet printing process, and only the interior of the molded article is made of powder that is then cured, the process enables a more refined design of the surface geometry of the molded article than a process in which the entire molded article is produced from powder layers that are then cured. According to the disclosure, the process also enables a precise color design of the surface of the molded article.

[0014] However, the process has the disadvantage of being relatively complex, because producing the outer surface layer of the molded article requires an additional material in addition to the material composition containing the powder, and this material must be applied in a structured manner. Furthermore, the process uses a liquid hardener that bonds with the powder particles. The internal volume of the molded article is therefore composed of various materials, which weakens the mechanical strength of the molded article.

[0015] The mechanical properties of the molded part produced using this process are also important to consider. This is because the part is not homogeneously made of a strong material, but consists of a weak layer (UV-curable material) and a stronger layer containing the powder. This shouldn't be critical for large molds. As parts become smaller, the ratio of part to protective layer decreases, and with it their properties, such as mechanical stability. Furthermore, the powder material is not a pure thermoplastic, but consists of a mixture and is therefore not as resilient as a pure thermoplastic.

[0016] US 9,423,756 B2 also discloses a method for producing a three-dimensional molded article by layer-by-layer material application, in which the individual material layers of the molded article to be produced can be applied to a base surface of a carrier roller and / or a solidified material layer located on the base surface using an electrophotographic printing device. The printing device has a photosensitive imaging roller that can be rotated about its roller axis in a first and a second direction of rotation by means of a motor. The imaging roller has a roller body coated on its outer surface with a light-sensitive coating, which is also referred to below as the active layer. The active layer consists of a material that is electrically insulating in the dark and electrically conductive when exposed to light.

[0017] To transfer an image to the active layer, the image drum cooperates with a first and a second charge generation device for electrically charging the active layer, an image converter, a first and a second electrostatic and magnetic development station, and a first and a second cleaning device. The first development station contains a first powdered material used to produce a support layer that is soluble in a solvent and is dissolved in the solvent after the molded article has been produced. The second development station contains a second material containing powder particles used to produce a molded article layer that is insoluble in the solvent.

[0018] The charge generation devices, the image converter, the development stations, and the cleaning devices are positioned on the circumference of the image roller such that, when the image roller rotates in the first direction of rotation, the outer surface of the active layer moves from the first charge generation device to the image converter, from there to the first development station, and then to the second cleaning device to coat the active layer with the first powdered material. When the image roller is rotated in the opposite second direction of rotation, the outer surface of the active layer moves from the second charge generation device to the image converter, from there to the second development station, and then to the first cleaning device to coat the active layer with the second material.

[0019] Using the charge generation device, electrical charges are first generated uniformly across the entire surface of the active layer in the dark. The active layer is then selectively exposed pixel by pixel to electromagnetic radiation using the image converter, based on geometric data for the molded object stored in a memory. The active layer becomes electrically conductive at the exposed areas, discharging the charges there into the roller body, thus electrically structuring the active layer.

[0020] In In the direction of rotation of the image drum behind the image converter, the surface of the active layer is moved past the first or second development station in such a way that the active layer is coated with the powdered material of the corresponding development station according to the charge distribution previously generated on its surface. In the development station, the powdered material is triboelectrically charged to an electrical potential that differs from the electrical potential of the active layer in such a way that the active layer is selectively coated with powdered material depending on its respective potential.

[0021] After the photosensitive imaging roller has been selectively coated with the first and second materials, the coating applied to the active layer is transferred from the active layer to the outer surface of a transfer roller, which is driven synchronously to the imaging roller by another motor in the opposite direction to the direction of rotation of the imaging roller. Here, too, the transfer of the powdered first or second material occurs due to a charge difference between the material and the outer surface of the transfer roller. If the synchronization of the imaging roller and transfer roller is not carried out with great precision, absolute positioning is lost. In a structure with thousands of layers, this creates a very irregular contour of the molded article and the optical homogeneity is impaired.

[0022] Finally, the powdered material is transferred from the outer surface of the transfer roller to the base surface or a top solidified layer of material located thereon, and then fixed by heat. The positioning accuracy of each of these layers is very critical, because the layer selectively created precisely on the image roller is not applied directly over the previous layer, but must first be transferred to a transfer roller and only then to the existing layer. The synchronization of these mechanical components, which are subject to expansion and temperature differences, is not precise enough. Furthermore, they are subject to wear, which over time leads to a deterioration in the accuracy of the superimposed layers.

[0023] The above steps are repeated until all material layers of the molded article are stacked on top of each other. The resulting layered arrangement is then dissolved in the solvent to remove the first material serving as the support material.

[0024] The following components are required to carry out the previously known procedure: An expensive and wear-prone, and therefore short-lived, photosensitive image drum, an expensive image converter, usually a laser scanner or LED scanner, complex and wear-prone, and therefore short-lived, charge generation devices, each with charge / discharge coronas for electrically charging the active layer, expensive and wear-prone, and therefore short-lived developer units.

[0025] All of these components are consumables with a relatively short lifespan and must be replaced frequently. The imaging drum, in particular, is subject to wear and tear on its photosensitive layer. The composition of the powdered materials is also very complex, as they must contain many components to make them charge-controllable, such as the building material for the molded article, additives to improve flowability, and additives to improve the electrical chargeability of the second material. The magnetic carrier particles must be precisely matched to the toner type, and the production of a functioning toner including carrier particles is complex.

[0026] In addition, the previously known method has the disadvantage that in the case of shaped articles in which a large number of material layers are printed on top of one another, the dimensional accuracy of the printed shaped article can only be maintained with difficulty because layer thickness tolerances of the material layer can occur.

[0027] The object of the invention is therefore to create a method of the type mentioned above that enables the simple and cost-effective production of a molded article with high mechanical stability and strength by means of layer-by-layer material application. In particular, the method should also enable high surface accuracy of the molded article and a molded article with long-term stability.

[0028] This problem is solved with the features of patent claim 1.

[0029] According to the invention, a hybrid process is provided in which materials with different properties are processed by means of different printing processes and are applied layer by layer to the base surface or a solidified material layer located thereon of the three-dimensional shaped object.

[0030] Particularly noteworthy is the precision in the construction of the layers of both the first and second materials. Both the negative mold is positioned by inkjet and the powder by coating roller without intermediate support. This allows for 100% control of the molds in every direction.

[0031] The first material can be very low-viscosity, i.e., thin-flowing, or highly fluid, because it serves only to create a negative mold for the second material. Due to the low viscosity or high flowability of the first material during application to the base surface or a solidified material layer located thereon, the mold can be printed using a digital printing process with high resolution and surface quality by applying a multitude of correspondingly small portions of the first material to the base surface or the solidified material layer located thereon of the three-dimensional molded object.

[0032] Only low demands are placed on the mechanical stability and strength of the material layer of the negative mold consisting of the first material, since the negative mold only has to carry the second material and support any forces exerted on the first material during the printing process intended for applying the second material. By solidifying the first material, it achieves sufficient strength to be able to serve as a mold for the second material. The mechanical strength of the first material in its solidified state has no influence on the mechanical stability of the molded article formed from the solidified layers of the second material, because the solidified first material is removed from the molded article by dissolving it in the solvent after all material layers have been applied. The solidified second material is insoluble in the solvent.

[0033] The powdered second material is the actual construction material for the molded object and can exhibit different properties, especially greater strength in the solidified state, than the first material. Thermoplastic powder particles are powdered particles that can be liquefied by applying energy.

[0034] Since the second material is geometrically shaped by molding the previously solidified negative mold precisely produced from the first material, the powdered second material can be easily applied to the carrier surface of the particle carrier over the entire surface or non-selectively. The particle carrier is then positioned on the cavity of the negative mold layer in such a way that the powdered second material is transferred from the carrier surface into the cavity and fills it completely. Since the second material is applied to the particle carrier over the entire surface, i.e. non-selectively, no structured regions of the second material located on the carrier surface need to be positioned relative to the cavity when positioning the particle carrier on the cavity. This enables simple implementation of the process.When molding the solidified negative mold, at least one boundary surface of the negative mold arranged transversely to the planes in which the material layers of the molded article extend is molded or transferred onto the second material.

[0035] The cavity floor formed by the base surface or the solidified material layer located thereon can be charged to the electrical or electrostatic potential of the first polarity by means of a charging corona and / or a charging plate. The charging plate is preferably arranged directly beneath the base surface and parallel to it, with an insulating layer provided between the base surface and the charging plate.

[0036] Because the individual molded article layers are each sintered by heat after being applied to the base surface or a solidified material layer located thereon, the molded body can be produced from a uniform material. During sintering, the powder particles contained in the powdered second material fuse together, forming a one-piece molded article. Through sintering, the at least one boundary surface of the solidified negative mold, arranged transversely to the planes in which the material layers of the molded article extend, is molded very precisely onto the molded article layer. This even makes it possible to produce three-dimensional molded bodies with a smooth or textured, mechanically stable surface. Solidifying the second material by sintering also enables a long-term stable molded article.Semi-crystalline and preferably amorphous thermoplastic powder particles are used as thermoplastic powder particles. Amorphous powder particles generally exhibit lower shrinkage during sintering than crystalline powder particles. Amorphous powder particles can be processed inside a printer at room temperature, meaning the second material or build material does not need to be heated to a temperature just below its melting point.

[0037] During sintering, the second material is preferably irradiated with thermal radiation, preferably generated using at least one flash lamp. Other energy sources that can deliver the energy very quickly can also be used. Using the flash lamp, the second material is quickly heated to the temperature required for sintering. After the flash is extinguished, the material cools down quickly. This ensures a sufficiently high energy input into the top material layer and the underlying material layer without unnecessarily heating the molded object or the base surface, but rather thermally bonding the two final layers.

[0038] The first and second materials are preferably selected such that the second material absorbs the thermal radiation generated during heat treatment more strongly than the first material. This can be achieved by making the second material more absorbent, e.g., darker, than the first material. In particular, the second material can be black and the first material white or transparent. This reduces the thermal load on the first material during heat treatment of the second material.

[0039] Since, in the method according to the invention, preferably after printing each individual material layer, regions of the solidified negative mold layer and / or the solidified molded article layer that project beyond a plane arranged at a predetermined distance from the base surface, preferably parallel to it, are removed by material removal to produce a flat surface, the individual layers of the molded article run exactly parallel or are arranged in a predetermined arrangement relative to one another and have a predetermined layer thickness. Furthermore, the material removal removes "contamination" that can occur on the surface of the uppermost solidified layer of the first material when the second material comes into contact with this surface when the cavities are filled with the second material.Removing the areas that protrude above the plane ensures that the mixed layer consisting of the solidified first and second materials always has the desired thickness and is free of solvent-insoluble second material on the surface of the first material. This enables very precise and distortion-free production of the molded article, even if the molded article has several thousand material layers.

[0040] In a preferred embodiment of the invention, the material portions of the first material are applied to the base surface and / or the solidified negative mold layer and / or a solidified molded article layer located thereon by means of a material application printing process, preferably an inkjet printing process. The first material is a material that can be solidified by the action of energy and is subjected to the energy to solidify the negative mold layer. The energy can be electromagnetic radiation, in particular ultraviolet radiation, by which a polymer and / or copolymer contained in the first material is solidified by crosslinking. In In this case, the first material preferably contains a photoinitiator. However, it is also possible to solidify the first material by irradiation with an electron beam. Furthermore, the first material can also be selectively applied to the base surface and / or a solidified material layer located thereon using an electrophotography process.

[0041] In a suitable embodiment of the invention, the first material has a working viscosity suitable for inkjet printing, which is less than 1000 mPa s, in particular less than 100 mPa s, optionally less than 30 mPa s, and preferably less than 20 mPa s, and is applied in the form of liquid droplets with a resolution of at least 180 dpi, in particular at least 360 dpi, and preferably at least 720 dpi or 1440 dpi to the base surface and / or the solidified material layer located thereon of the three-dimensional molded article. This enables a high surface quality of the negative mold and thus of the molded article.

[0042] It has proven advantageous if the areas of the solidified negative mold layer and / or the solidified molded article layer that extend beyond the plane mentioned in step g) of claim 1 are removed by chipping or particle-removing material removal, in particular by milling, grinding, lasering, cleaning, and / or polishing. This enables rapid work progress when leveling the individual material layers and the production of a material layer surface that is precisely flat and parallel to the base surface.

[0043] In a preferred embodiment of the invention, the powder particles are triboelectrically charged in step d) of claim 1. For this purpose, the powder particles are brought into contact with a material (carrier) that has a higher holding force than the powder particles, and then the powder particles are separated from the material by a potential difference. Preferably, the powder particles are rubbed against the material by mixing in a container so that the powder particles become triboelectrically charged.

[0044] The particle carrier expediently has an electrically conductive layer with an insulating layer thereon, wherein an electrical potential of the first polarity is applied to the electrically conductive layer in such a way that particles located on the carrier surface are electrostatically attracted to it through the insulating layer. The insulating layer is preferably made of ceramic or another abrasion-resistant material. The insulating layer enables a long service life and low wear of the particle carrier during printing. The surface of the particle carrier can be made of a material that is not photosensitive, i.e. the electrical properties of the surface are independent of whether it is in the dark or exposed to electromagnetic radiation, such as light. This enables the method to be carried out simply.

[0045] In another embodiment of the invention, the particle carrier has an electrically conductive layer with an active layer located thereon, the electrical conductivity of which can be changed by exposure to optical radiation, wherein the active layer is selectively structured by means of an electrophotography process with an electrical potential, wherein the active layer is then brought into contact with the powder particles of the second material such that they adhere to the active layer depending on the structuring of the active layer with the electrical potential, and wherein the active layer thus structured with the powder particles is positioned on the cavity in order to transfer the powder particles into the cavity. The surface of the particle carrier can therefore also be coated with the powder particles in an electrophotographically structured manner.This can reduce the amount of residual powder particles remaining on the particle carrier after filling the cavity of the negative layer.

[0046] Preferably, the powder particles in step d) of claim 1 are charged using a triboelectric charging device comprising a reservoir filled with the powder particles and a stirring tool in contact with the powder particles, which is configured and moved relative to the powder particles in such a way that they are electrically charged. The powder particles can thus be charged in a simple manner.

[0047] In an expedient embodiment of the invention, a coating roller is used as the particle carrier, the outer surface of which serves as a carrier surface for the powder particles, wherein the outer surface is brought into contact with the powder particles having the potential of the second polarity at a first location and the coating roller is rotated about the roller axis of the coating roller relative to the first location in order to coat the outer surface with the powder particles over the entire surface, and wherein the outer surface is facing the cavity at a second location coated with the powder particles, which second location is offset from the first location in the circumferential direction of the outer surface and is positioned so closely relative to the cavity that the powder particles are transferred from the outer surface into the cavity to form the molded article layer.With such a coating roller, the powdered material on the surface of the coating roller can be applied directly, continuously, and with great precision to the base surface or a solidified layer of material located thereon. The absence of intermediate supports allows for the highest positioning precision.

[0048] It is advantageous if powder particles adhering to a section of the coating roller's outer surface that lies behind the second location and in front of the first location in the direction of rotation are removed from the outer surface and transported back to the reservoir. The coating roller's outer surface is thus cleaned after passing the second location or after moving past the cavity before being repositioned at the first location. Cleaning the outer surface counteracts the accumulation of charge separating agents contained in the powder particles and / or applied to them as a coating on the outer surface.

[0049] In one embodiment of the invention, a cylindrical roller is used as the coating roller, wherein the carrier part having the base surface i) for applying a first layer of material, starting from a starting position, it is displaced in a forward transport direction relative to the coating roller, ii) then moved back to the starting position relative to the coating roller, iii) then for applying a second layer of material, it is displaced again relative to the coating roller in the forward transport direction, and wherein the carrier part is lowered relative to the coating roller during and / or between steps i) to iii). Thus, during the layer-by-layer production of the molded article, the base surface is moved back and forth relative to the cylinder axis of the cylindrical outer surface of the coating roller, for example, between two end positions. This embodiment of the method is preferably used when the geometric data for the molded article are available in a Cartesian coordinate system.

[0050] In a further development of the invention, the support part having the base surface is rotated relative to the coating roller during material application and, if appropriate, during the solidification of the materials about a rotational axis arranged transversely to the cylinder axis of the coating roller and, if appropriate, lowered relative to the coating roller during the rotational movement. The coating roller is designed as a conical roller whose cross-section decreases from its end remote from the rotational axis to its other end closer to the rotational axis. This design has the advantage that the base surface can be continuously rotated about the rotational axis throughout the entire manufacturing process of the molded article, enabling uninterrupted printing.Compared to a process in which the base surface is moved back and forth between two end positions during printing, the rotational movement of the base surface enables faster printing progress and less wear on the 3D printer used to carry out the process.

[0051] In the process known from US 9,423,756 B2, in which the coating roller is designed as an imaging roller with a photosensitive layer, a conical design of the imaging roller would not be practical because problems with the electrical charging of the outer surface would arise. The roller circumference must have a constant diameter along the corona in order to achieve a homogeneous potential on the outer surface of the imaging roller. Furthermore, the design of the developer unit would be complicated because the peripheral speeds of a commercially available developer unit would be different at the beginning and end of the magnetic roller. The discharging of the photo layer of the imaging roller via laser / LED beam would also occur with different energies at the ends of the roller - which would result in a different thickness of toner layer.

[0052] Thus, the method known from US 9 423 756 B2 can only be applied in a Cartesian coordinate system.

[0053] In an advantageous embodiment of the invention, a feed roller for the powder particles is provided, which is spaced from the coating roller's surface by a roller gap in which the carrier with the powder particles adhering thereto touches the coating roller's surface, wherein the feed roller has an electrically conductive feed roller layer on its surface with an insulation layer thereon, wherein an electrical potential of the second polarity is applied to the feed roller layer in such a way that particles located on the surface of the feed roller are electrostatically attracted thereto, wherein the surface of the feed roller is brought into contact with the powder particles at a point spaced from the roller gap and the feed roller is rotated about its axis in such a way that powder particles located on the surface of the feed roller reach the surface of the coating roller,and wherein the potential applied to the feed roller layer and the potential applied to the electrically conductive layer of the coating roller are selected such that the powder particles are transferred in the roller gap from the outer surface of the feed roller to the outer surface of the coating roller. This allows the powdered second material to be transferred to the outer surface of the coating roller with a defined layer thickness.

[0054] In a preferred embodiment of the invention, magnetically conductive and preferably triboelectrically chargeable carrier particles are provided and brought into contact with the powder particles of the second material in such a way that the powder particles remain releasably adhered to the carrier particles, that a magnetic feed roller is provided for the powder particles, which is spaced with its outer surface by a roller gap from the outer surface of the coating roller, that the magnetic carrier particles with the powder particles adhering thereto are brought into contact with the outer surface of the feed roller at a location spaced from the roller gap in such a way that the carrier particles remain magnetically adhered to the outer surface of the feed roller, that the feed roller is rotated about its axis in such a way,that carrier particles located on the outer surface of the feed roller, with the powder particles adhering thereto, are first moved past a stripping device to stiffen the carrier particles coated with powder particles and, after passing through the stripping device, enter the roller gap, and that the potential of the coating roller is selected to differ from the potential of the powder particles adhering to the carrier particles in such a way that the powder particles are detached from the carrier particles in the roller gap and transferred to the outer surface of the coating roller. The magnetically conductive carrier particles, in combination with the magnetic feed roller, enable a uniform application of the powdery second material to the coating roller with a defined layer thickness. After the powder particles have been detached from the carrier particles in the roller gap,The carrier particles can be recoated with powder particles and then reused. The powder particles adhere preferentially to the carrier particles via electrostatic forces.

[0055] In another preferred embodiment of the method, magnetically conductive carrier particles are provided and brought into contact with the powder particles of the second material in such a way that the powder particles remain releasably adhered to the carrier particles, that a coating roller is provided with a magnetic outer surface which is spaced by a transfer gap from the bottom of the cavity to be filled with the powder particles, that the magnetic carrier particles with the powder particles adhering thereto are brought into contact with the outer surface of the coating roller at a location spaced from the cavity in such a way that the carrier particles remain magnetically adhered to the outer surface of the coating roller, that the coating roller is rotated about its axis in such a way,that carrier particles located on the outer surface of the coating roller, with the powder particles adhering to them, are first moved past a stripping device to stiffen the carrier particles coated with powder particles and, after passing through the stripping device, reach the transfer gap. The potential of the cavity floor is selected to differ from the potential of the powder particles adhering to the carrier particles in such a way that the powder particles are detached from the carrier particles in the transfer gap and transferred to the cavity floor. The powder particles can therefore also be transferred directly from the developer's magnetic roller into the cavity of the negative mold. This eliminates the need for an additional coating roller and the return of the powder particles to the powder particle reservoir, so that the process can be carried out in a simple manner.

[0056] In a further development of the invention, an electrically conductive material is used as the first material and an electrically insulating material is used as the second material, wherein at least the solidified negative mold layer arranged closest to the carrier surface of the particle carrier is placed at an electrical potential which differs from the potential of the electrically conductive region of the particle carrier and from the electrical potential of the powder particles of the second material located on the particle carrier in such a way that when this negative mold layer is positioned on the carrier surface of the particle carrier, fewer, in particular 50% less, optionally 70% less and preferably 90% fewer powder particles per unit area are transferred to the negative mold layer than are transferred per unit area into at least one cavity of this negative mold layer when the cavity is positioned on the carrier surface of the particle carrier.The potentials of the electrically conductive region of the particle carrier, the negative mold layer, and the powder particles are thus selected to be different in such a way that the powdery second material is transferred from the carrier surface of the particle carrier essentially only into the cavity, but not to the surface of the uppermost negative mold layer. The material not transferred from the carrier surface of the particle carrier, which is coated with powder particles, or from the coating roller onto the negative mold layer can then, if necessary, be used to coat additional layers of the molded article. This correspondingly reduces the amount of second material required to produce the molded article.

[0057] In a further development of the invention, the powdered second material comprises a photoinitiator, wherein the thermoplastic powder particles comprise a polymer and / or copolymer, and wherein the photoinitiator is activated by irradiation with electromagnetic radiation after sintering to crosslink the polymer. This process can advantageously be used to produce a thermoset from thermoplastic particles. This increases the temperature resistance of the second material. In contrast, temperature resistance is problematic with pure thermoplastics.

[0058] In a particularly advantageous embodiment of the invention, the carrier part has at least two electrodes on the base surface, which are laterally offset from one another in a top view of the base surface and preferably interlock in a comb-like manner. An electrical voltage is applied to the electrodes in such a way that the electrical potential having the first polarity occurs at the bottom of the cavity. This allows the powder particles of the second material to be particularly effectively detached from the particle carrier at the cavity and fixed to the bottom of the cavity.

[0059] It is advantageous if the electrical voltage applied to the electrodes is increased at least once between the application of the first and the application of the last negative mold layer. This can counteract the decrease in the magnitude of the electrostatic potential at the bottom of the cavities of the negative mold layers that occurs with the increasing number of material layers applied to the base surface.

[0060] In a preferred embodiment of the invention, a measurement signal for the electrical potential at the level of the cavity floor is recorded and compared with a target value or a target value range. If a deviation occurs between the measurement signal and the target value or the target value range, the electrical voltage at the electrodes is adjusted to reduce the deviation. This allows the electrical potential at the cavity floor to be kept largely constant throughout the entire printing process.

[0061] The following is a detailed description of the embodiment of the invention. Fig. 1 is a schematic representation of a device in polar design for producing a three-dimensional shaped article by layer-by-layer material application, wherein the device has a first dispensing device for dispensing a liquid and a second dispensing device for dispensing a powdery material, Fig. 2A to 2F show a cross-section through a layer-by-layer produced shaped article during different process steps of its production, Fig. 3 is a partial plan view of the device in Fig. 1 shown device, wherein a cover arranged above the second dispensing device has been removed, Fig. 4 a conical coating roller, Fig. 5 a side view of a first embodiment of the second dispensing device during the application of a layer of the powdered material onto a solidified material layer, Fig. 6 a side view of a chipping and / or particle-removing leveling unit during the planar milling, grinding or polishing of a material layer, Fig. 7 a three-dimensional view of a layer stack consisting of the material layers of the first and second material, Fig. 8 a three-dimensional view of the molded article after the removal of the material layers of the first material with the aid of a solvent, Fig. 9 a cross-section through another molded article after the application of all material layers, Fig. 10 a cross-section through the in Fig. 9 shown molded article after removing the material layers of the first material, Fig. 11 a side view of a second embodiment of the second dispensing device during the application of a layer of the powdered material onto a solidified material layer, Fig. 12 a side view of a device in Cartesian design during the production of a three-dimensional molded article, Fig. 13 a cylindrical coating roller, Fig. 14 a plan view of the second dispensing device of the device from Fig. 12 , Fig. 15 a side view of another device in Cartesian design during the production of a three-dimensional shaped object, Fig. 16 a representation similar Fig. 15 , however, the powdered material is only applied to a material layer of the molded article in the region of a cavity, Figs. 17 and 19 show a longitudinal section of a device which has a charging plate for generating an electric field on a base surface onto which material layers are applied, Fig. 18 is a plan view of a carrier part designed as a charging plate, and Fig. 20 is a partial plan view of a device for producing a three-dimensional molded article, the device having a screw conveyor device by means of which powder particles can be transported from a cleaning device to a developer unit.

[0062] In a method for producing a three-dimensional molded object 1 by layer-by-layer material deposition, geometric data for the molded object 1 are provided by a control unit that communicates with a computer running software. Furthermore, a plate-shaped, electrically conductive carrier part 2 is provided with a base surface 3 arranged in a horizontal plane for receiving the molded object 1.

[0063] A first embodiment of the method is described with the aid of the Fig. 1 The device shown is used, in which the base surface 3 essentially has the shape of a circular disk. However, other configurations are also conceivable, in which the base surface 3 can, in particular, have the shape of a full circular disk or be rectangular.

[0064] In the first embodiment, a solidifiable liquid first material 4, a different powdery, solidifiable second material 5 comprising thermoplastic powder particles, and water as a solvent for the solidified first material 4 are provided. The solidified second material 5 is not soluble in the solvent. Due to the solid particles it contains, the second material 5 has a higher strength in the solidified state than the solidified first material 4. The first material 4 is a polymer containing a photoinitiator and is crosslinkable by irradiation with ultraviolet radiation.

[0065] The liquid first material 4 is arranged in a first reservoir 6, and the powdered second material 5 is arranged in a second reservoir 7. The first reservoir 6 is connected via a line to a first dispensing device 8 for the first material 4. The first reservoir 6 is designed as a substantially closed container, and the second reservoir 7 is designed as a trough.

[0066] The first dispensing device 8 comprises a first inkjet print head with a plurality of nozzles arranged in a row (not shown in detail in the drawing), which are directed to dispense portions of the first material 4 onto the base surface 3 or a solidified material layer of the first and / or second material 4, 5 located thereon. The row of nozzles is arranged parallel to the plane of the base surface 3 and extends transversely to the circumferential direction of the base surface 3, preferably substantially radially to its center.

[0067] The support part 2 and the first dispensing device 8 can be rotated relative to each other in the direction of arrow 10 and displaced parallel to the rotation axis 11 by means of a positioning device 9. Points located in the base surface 3 and spaced from the rotation axis 11 move along a helical or spiral trajectory.

[0068] The first dispensing device 8 and the first positioning device 9 are connected to a control device (not shown in detail in the drawing), which has a data memory for storing the geometric data of the molded article 1 to be produced. By means of the control device, the dispensing of the material portions of the first material 4 and the first positioning device 9 can be controlled depending on the geometric data such that negative mold layers 12 consisting of the flowable first material 4 can be applied to the base surface or a previously applied solidified material layer of the first and / or second material 4, 5 ( Fig. 2A ). The negative mold layers 12 each have at least one cavity 13, which contains a negative mold of a material layer of the molded article 1 to be produced. The cavities 13 each extend over the entire layer thickness of the respective negative mold layer 12 up to the base surface 3 or the solidified material layer located beneath the negative mold layer 12.

[0069] Arranged in the direction of arrow 10 behind the first dispensing device 8 is a solidifying device 14, by means of which the liquid first material 4 applied to the base surface 3 or a solidified material layer located thereon is solidified. For this purpose, the solidifying device 14 has a first UV radiation source (not shown in detail in the drawing), by means of which ultraviolet radiation can be emitted onto the material layer of the first material to be solidified in such a way that a photocrosslinker contained in the first material is activated and the polymers contained in the first material 4 are crosslinked.

[0070] In the direction of arrow 10 behind the solidification device 14, a second dispensing device 15 is arranged, by means of which the cavity(ies) 13 of the respective, previously solidified negative mold layer 12 are filled with the second material 5 in order to form a molded article layer 16 ( Fig. 2B ).

[0071] The second dispensing device 15 has a corona charging device 17, which is arranged behind the solidifying device 14 in the direction of arrow 10 and has a plurality of corona wires 18. A negative electrical potential is applied to the corona wires 18, which differs from the potential of a section of the base surface 3 positioned at the first dispensing device 8 and serves to electrically charge the bottom of the cavity 13 and, if applicable, the material layer of the first material 4 on its surface facing the corona wires 18. The electrical potential applied to the corona wires 18 ionizes the air in the space between the corona wires 18 and the surface region of the base surface 3 opposite them.When a layer of the first material 4 on the base surface 3 and / or on a solidified material layer located thereon is moved past the corona wires 18 in the direction of arrow 10, the bottom of the cavity 13 and, if applicable, the surface of the material layer consisting of the first material 4 facing the corona wires 18 are electrically charged to a positive first potential. The potential difference between the corona wires 18 and the potential of the carrier part 2 can be, for example, 5 kV.

[0072] As in Fig. 3 As can be seen, the second dispensing device 15 has a triboelectric charging device 19, which is only shown schematically in the drawing and is known per se, a conical feed roller 20A cooperating with this and a conical coating roller 21A.

[0073] The feed roller 20A and the coating roller 21A are each frustoconical and arranged such that the imaginary cone apex associated with their lateral surface lies on the rotation axis 11 of the support part 2. The feed roller 20A and the coating roller 21A are each arranged to rotate about their longitudinal central axis. In Fig. 3 It can be seen that the feed roller 20A and the coating roller 21A each have axle stubs at their axial ends, on which they are rotatably mounted on stationary bearings not shown in detail in the drawing. The axes of rotation 22, 23, about which the feed roller 20A and the coating roller 21A are each rotatably mounted, are arranged such that a roller gap 24 is formed between the outer surface of the feed roller 20A and the outer surface of the coating roller 21A, which has a constant gap width in a plane spanned between the axes of rotation 22, 23.

[0074] The feed roller 20A has an electrically conductive feed roller layer formed by its roller core, on which an electrical insulation layer is arranged, which forms the outer surface of the feed roller 20A. In Correspondingly, the coating roller 21A has an electrically conductive layer 43 formed by its roller core, which is coated on its outer surface with an electrical insulating layer 44.

[0075] In the Fig. 3 In the illustrated embodiment, the triboelectric charging device 19 has a rotationally driven stirring tool 25 arranged in the second reservoir 7, by means of which the powder particles of the second material 5 located in the second reservoir 7 are swirled in such a way that they rub intensively against each other, against the stirring tool 25 and against the walls of the second reservoir 7. In this process, the powder particles are triboelectrically charged to a positive second potential. The triboelectric charging device 19 of the Fig. 3 The device shown corresponds to the triboelectric charging device 19 of the device according to Fig. 5 .

[0076] In From the second reservoir 7, the electrically charged powder particles come into contact with the outer surface of the feed roller 20A at a contact point spaced from the roller gap 24. The electrically conductive roller core of the feed roller 20A is placed at a negative third potential that differs from the second potential and is selected such that the powder particles are electrostatically attracted to the outer surface of the feed roller 20A. The third electrical potential can be adjusted using a first adjusting element 26.

[0077] The feed roller 20A is rotated about its rotational axis 22, which lies on the roller axis, such that powder particles located on the outer surface of the feed roller 20A enter the roller gap 24. On their way to the roller gap 24, the powder particles are moved through a gap of a defined width. This determines the material thickness with which the outer surface of the feed roller 20A is coated with the second material 5. Excess material particles are stripped off at the gap by the feed roller 20A.

[0078] A fourth potential is applied to the electrically conductive layer 43 of the coating roller 21A, which is adapted to the third potential such that the powder particles are detached from the outer surface of the feed roller 20A in the roller gap 24 and transferred non-selectively to the outer surface of the coating roller 21A over the entire length of the roller gap 24. As a result, the outer surface of the coating roller 21A is coated non-selectively or continuously with the powder particles. The fourth electrical potential can be adjusted using a second adjusting element 27, preferably between a negative and a positive potential value, in particular from -1000 V to +1000 V.

[0079] Due to the rotational movement of the coating roller 21A about its axis of rotation 23 and the rotational movement of the base surface 3 about the axis of rotation 11, the powder particles located on the outer surface of the coating roller 21A reach a material discharge point, which is offset from the roller gap 24 in the circumferential direction of the outer surface and faces the cavity 13 in the material layer of the first material 4. The powder particles are positioned so closely relative to the cavity 13 that they are detached from the outer surface of the coating roller 21A by a force caused by the potential difference between the fourth and the first potential and are transferred into the cavity 13 to form the molded article layer 16. The cavity 13 is thereby completely filled with the second material 5.

[0080] Powder particles that are not detached from the outer surface of the coating roller 21A at the material discharge point are removed from the outer surface of the coating roller 21A by means of a cleaning device 39. The cleaning device 39 has a scraper 40 acting on the outer surface of the coating roller 21A and a cleaning roller 41 that is driven to rotate about an axis arranged parallel to the axis of rotation of the coating roller 21A, counter to the direction of rotation of the coating roller 21A. The scraper 40 and the cleaning roller 41 are arranged behind the material discharge point and in front of the feed roller 20A in the direction of rotation of the coating roller 21A. To remove material particles, the cleaning roller 41 comes into contact with the outer surface of the coating roller 21A at its outer circumference.The scraper 40 and the cleaning roller 41 are arranged in a collecting container into which the material particles removed from the outer surface of the coating roller 21A are discharged. At the bottom of the collecting container is a conveyor screw 42, by means of which the powder particles can be transported from the cleaning device 39 back to the second reservoir 7 for reuse (Fig. Fig. 5 , 11 , 12 . 17 and 19 ).

[0081] A heat treatment station 28, which may include, for example, an infrared radiator and / or a flash lamp, is arranged in the direction of arrow 10 behind the material discharge point where the cavity 13 was filled with the second material 5. Upon passing through the heat treatment station 28, the second material 5 previously filled into the cavity 13 is thermally sintered, with the powder particles contained therein fusing with one another and, if appropriate, with a layer of the second material 5 located underneath.

[0082] If required, a crosslinking device 29 can be arranged in the direction of arrow 10 behind the heat treatment station 28, at which a polymer and / or copolymer contained in the second material 5 is crosslinked to form a thermoset by irradiation with ultraviolet radiation and / or by irradiation with an electron beam.

[0083] Thereafter, in a further method step, areas of the solidified negative mold layer 12 and / or the solidified molded article layer 16 and / or solidified second material 5 arranged on the negative mold layer are removed by means of a chip-removing or particle-removing milling, grinding or polishing device 30 ( Fig. 2C , 6 ). In this process, areas of the solidified first and / or second material 4, 5 that protrude beyond a plane arranged parallel to the base surface at a predetermined distance therefrom are removed by machining and subsequently vacuumed away using a suction nozzle 31. If necessary, a surface cleaning device 32 can be arranged behind the suction nozzle 31. This can comprise a rotating brush for brushing off the last applied material layer of the molded article.

[0084] Now, in a corresponding manner, another negative mold layer 12 ( Fig. 2D ) and a further shaped article layer 16 is applied ( Fig. 2E, 2F ) are applied. These steps are repeated until all the molded article layers 16 of the molded article to be produced have been produced ( Fig. 7 and 8 ).

[0085] In a further process step, the negative mold layers 12 are brought into contact with the solvent 33 in such a way that the solidified first material 4 dissolves completely in the solvent. This can be achieved, for example, by immersing the layer stack consisting of the negative mold layers 12 and the molded article layers 16 for a predetermined period of time in the solvent 33 located in a container 34 and, if necessary, treating it with ultrasound. Thereafter, the finished molded article ( Fig. 8 ) from solvent 33 and dried.

[0086] As in Fig. 9 und 10 As can be seen, the method according to the invention can also be used to produce shaped articles with overhangs 35 and cavities 36.

[0087] In a second embodiment, a magnetic toner is used instead of the non-magnetic toner. The method is carried out with a device that differs from the one described in Fig. 1 and 3 shown device, which instead of the one shown in Fig. 5 shown triboelectric charging device 19 which is in Fig. 11 The triboelectric charging device 19' shown in FIG. 1 is used, and instead of the conical feed roller 20A, a corresponding conical feed roller is used, which is magnetic on its outer surface. The magnetic field is generated by means of stationary permanent magnets arranged inside the feed roller 20A. Otherwise, the device used for the second embodiment corresponds to the device according to FIGS. Fig. 1 and 3 In this respect, the description of the first embodiment applies accordingly to the second embodiment.

[0088] In the second embodiment, magnetically conductive carrier particles are provided and brought into contact with the powder particles of the second material 5 in the second reservoir 7 in such a way that the powder particles remain releasably adhered to the carrier particles. The magnetically conductive carrier particles, with the adhering powder particles, are brought into contact with the outer surface of the feed roller at a location spaced from the roller gap in such a way that the carrier particles remain magnetically adhered to the conical outer surface of the feed roller.

[0089] As the feed roller rotates around its axis, the carrier particles located on the outer surface of the feed roller, along with the powder particles adhering to them, are first moved past a stripping device 37, where carrier particles coated with powder particles are removed from the conical outer surface of the feed roller. As shown in Fig. 11 As can be seen, the outer surface behind the stripping device 37 is coated with a layer of a defined thickness comprising the carrier particles and the powder particles located thereon. After passing through the stripping device 37, the carrier particles coated with the powder particles enter the roller gap formed between the conical feed roller and the conical coating roller 21A.

[0090] An electrical potential different from the potential of the powder particles adhering to the carrier particles is applied to the electrically conductive roller core of the coating roller 21A. This electrical potential is selected such that the powder particles are detached from the carrier particles in the roller gap and transferred to the outer surface of the coating roller 21A. The carrier particles remain on the outer surface of the feed roller and, due to its rotational movement, return to the effective area of ​​the stirring tool 25, where they are again coated with powder particles (toner) of the second material.

[0091] For the implementation of a third embodiment, the Fig. 12 The device shown in FIG. 1 is used, in which the individual processing stations, namely the first discharge device 8, the hardening device 14, the second discharge device 15, the heat treatment station 28, optionally the cross-linking device 29, the chip-removing or particle-removing milling, grinding or polishing device 30 and optionally the surface cleaning device 32 are arranged in a straight line one behind the other. Fig. 12 In the device shown, both the feed roller 20B and the coating roller 21B are each cylindrical ( Fig. 13 ). The coating roller 21B has an electrically conductive layer 43 (roller core) which is coated on its outer surface with an electrically insulating layer 44.

[0092] In contrast to the first and second embodiments, in the third embodiment the carrier part 2 having the base surface 3 is not rotated but is used to apply a layer of material a) moved from an initial position in a transport direction 38 to an end position and b) then - if a further layer of material is to be applied - moved from the end position against the transport direction 38 back to the initial position.

[0093] Furthermore, the carrier part 2 is lowered relative to the coating roller during and / or between steps a) and b). The above steps are repeated with each application of a material layer until all material layers of the molded article 1 are stacked.

[0094] Otherwise, the third embodiment corresponds to the first embodiment. The description for the first embodiment therefore applies accordingly to the third embodiment.

[0095] In a fourth embodiment, a magnetic toner is used instead of the non-magnetic toner. The method is carried out with a device that differs from the one described in Fig. 12 The difference from the device shown is that instead of the Fig. 12 illustrated triboelectric charging device 19 a triboelectric charging device 19' similar Fig. 11 which has a cylindrical feed roller and a cylindrical coating roller. The cylindrical feed roller is magnetic on its outer surface. Otherwise, the device used for the fourth embodiment corresponds to the device according to Fig. 12 In this respect, the description of the third embodiment applies accordingly to the fourth embodiment. Regarding the description of the charging device 19', reference is made to the description of the second embodiment.

[0096] In the first to fourth embodiments and in the Fig. 15 In the fifth exemplary embodiment shown, the powdered second material 5 is introduced into the cavity 13 with the aid of the coating roller 21B, both over its entire surface and also applied to the surface of the negative mold layer 12 facing the coating roller 21B. After solidification, the second material 5 applied to the negative mold layer 12 is completely removed with the aid of the chip-removing or particle-removing milling, grinding, or polishing device 30. At the same time, material that was applied in the region of the cavity and protrudes beyond a plane arranged at a predetermined distance from the base surface is removed in order to achieve a precisely flat surface that extends continuously over the cavity 13 and the negative mold layer 12.

[0097] In a Fig. 16 In the sixth embodiment shown, the powdered second material 5 is applied by means of the coating roller 21B, which is coated with it over its entire surface, only where the cavity 13 is located. The surface of the negative mold layer 12, however, is not coated with the second material 5. This reduces the material consumption of the second material 5 accordingly.

[0098] This is achieved by using an electrically conductive material as the first material 4 and an electrically insulating material as the second material 5, and by applying an electrical potential to the negative mold layer 12 which differs from the electrical potential of the powder particles of the second material located on the outer surface of the coating roller 21B and from the potential of the electrically conductive layer 43 of the coating roller 21B in such a way that when the negative mold layer 12 is positioned on the outer surface of the coating roller 21B, practically no powder particles are transferred from the outer surface to the negative mold layer 12. In the embodiment in Fig. 16 the negative mold layer 12 is placed at ground potential, the electrically conductive layer 43 of the coating roller 21B is placed at a negative potential and the powder particles of the second material 5 are charged to a positive potential.

[0099] In a Fig. 17 In the seventh embodiment shown, the electrical potential at the base surface 3 is generated with the aid of a carrier part 2 designed as a charging plate, which has electrodes 47A, 47B integrated into the carrier part 2 below the coating roller. This eliminates the need for a charging corona, or it can be optionally added.

[0100] As in Fig. 18 As can be seen, the electrodes 47A, 47B are each comb-shaped. Each electrode 47A, 47B has a longitudinal web 48A, 48B, on which several parallel transverse webs 49A, 49B are arranged. The electrodes 47A, 47B run parallel to the base surface 3 and directly border it or are closely adjacent to it. An electrical insulating material, for example, potting compound or glass, is arranged between and / or below the electrodes 47A, 47B.

[0101] A constant electrical voltage is applied between the electrodes 47A, 47B, which can be adjusted by means of a fourth adjusting element 51, preferably to a value between 0 and -45 kV. One electrode 48B is at ground potential. The electric field generated by the voltage penetrates the negative mold layers 12 and the molded article layers 16. The first material 4 and the second material 5 each contain dipoles that align in the electric field approximately parallel to its field lines. As a result, powder particles located on the outer surface of the coating roller 21B that enter the transfer gap 47 are electrostatically attracted to the bottom of the cavity 13 in such a way that they detach from the outer surface of the coating roller 21B and settle on the bottom of the cavity 13.

[0102] If necessary, the electrical potential at the bottom of the cavity 13 can be measured, for example using a probe not shown in detail in the drawing, and compared with a target value. If a deviation between the measured value and the target value is detected, the potential applied to the electrodes 47A, 47B of the carrier part 2 is changed to reduce the deviation. The potential at the bottom of the cavity 13 can therefore be regulated to the target value. This prevents the potential at the bottom of the cavity 13 from decreasing in magnitude with an increasing number of material or negative mold layers applied to the base surface 3 when the distance between the bottom of the cavity 13 and the electrodes 47A, 47B increases.

[0103] Otherwise, the seventh embodiment essentially corresponds to the embodiment according to Fig. 11 The description of the second embodiment applies accordingly to the seventh embodiment. The coating roller and the feed roller can be conical or cylindrical in the seventh embodiment.

[0104] In a Fig. 19 In the eighth embodiment shown, magnetically conductive carrier particles are provided in a reservoir 7 and brought into contact with the powder particles of the second material 5 by means of a stirring tool 25 located in the reservoir 7 such that the powder particles releasably adhere to the carrier particles. A coating roller 21B with a magnetic outer surface is provided, which is spaced from the bottom of the cavity 13 to be filled with the powder particles by a transfer gap 47.

[0105] The magnetic carrier particles with the powder particles adhering thereto are brought into contact with the outer surface of the coating roller 21B at a location spaced from the cavity 13 in such a way that the carrier particles coated with the powder particles remain magnetically adhered to the outer surface of the coating roller 21B.

[0106] The coating roller 21B is rotated about its axis of rotation 22 such that carrier particles located on the outer surface of the coating roller 21B, with the powder particles adhering thereto, are first moved past a stripping device 37' to stiffen the carrier particles coated with powder particles and, after passing through the stripping device 37', reach the transfer gap 47. Due to the electric field applied between the electrodes 47A, 47B, the powder particles located on the carrier particles, which reach the transfer gap 47 on the outer surface of the coating roller, are electrostatically attracted to the bottom of the cavity 13 such that they detach from the carrier particles and settle on the bottom of the cavity 13.

[0107] Otherwise, the eighth embodiment essentially corresponds to the seventh embodiment. In this respect, the description of the seventh embodiment applies accordingly to the eighth embodiment.

Claims

1. A process for preparing a three-dimensional molded article (1) by means of a layerwise application of material, wherein geometric data for said molded article (1), a support part (2) having a base surface (3) for receiving the three-dimensional molded article (1), a solidifiable liquid, free-flowing or powdery first material (4), a powdery second material (5) comprising thermoplastic powder particles. and a solvent in which said solidified first material (4) is soluble are provided, a) wherein, for forming a negative mold layer (12), material portions of said free-flowable, liquid or powdery first material (4) are applied to the base surface (3), and / or a solidified layer of material covering it, in accordance with the geometric data in such a manner that said negative mold layer (12) has at least one cavity (13) at its surface facing away from said base surface (3), which cavity has a negative shape of a layer of material to be prepared of said molded article (16), b) wherein said negative mold layer (12) is solidified, c) wherein at least the bottom of the cavity (13) formed by the base surface (3) or a solidified material layer located thereon is charged to an electrical potential of a first polarity, d) wherein powder particles of the second material are charged to an electrical potential with a second polarity opposite to the first polarity and are applied flatly to a support surface of a particle support, e) wherein the support surface with the powder particles located thereon faces the at least one cavity (13) and is positioned relative to the cavity (13) in such a way that the powder particles are transferred from the support surface into the cavity (13) and form therein a molded article layer (16) with a positive shape matching the negative mold, f) wherein the thus obtained molded article layer (16) is sintered and solidified by the action of heat, g) wherein regions of the solidified negative mold layer (12) and / or of the solidified molded article layer (16) that project over a plane provided at a predetermined distance to the base surface (3) are removed by material ablation in such a way that a planar surface is formed that extends over the negative mold layer (12) and the molded article layer (16), h) wherein steps a) to g) are repeated at least once, and i) wherein thereafter said negative mold layers (12) are contacted with the solvent in such a way that said solidified first material (4) dissolves in the solvent.

2. The process according to claim 1, characterized in that the material portions of the first material (4) are applied to the base surface and / or the solidified negative mold layer (12) covering it and / or a solidified molded article layer (16) by a material deposition printing method, preferably inkjet printing method, and said first material (4) is a material that can be solidified by exposure to energy, and is exposed to such energy for solidifying the negative mold layer (12).

3. The process according to claim 2, characterized in that said first material (4) has a working viscosity suitable for ink jet printing, which is lower than 1000 mPa·s, especially lower than 100 mPa·s, optionally lower than 30 mPa·s, and preferably lower than 20 mPa·s, and is applied to said base surface and / or the solidified layer of material covering it, of said three-dimensional molded article (1) in the form of liquid droplets with a resolution of at least 180 dpi, especially at least 360 dpi, and preferably at least 720 dpi or 1440 dpi.

4. The process according to any of claims 1 to 3, characterized in that in step g) of claim 1, the regions of the solidified negative mold layer (12) and / or the solidified molded object layer (16) projecting beyond the plane are removed by machining or particle-ablating material removal, especially by milling, grinding, lasering and cleaning and / or polishing.

5. The process according to any of claims 1 to 4, characterized in that the powder particles in step d) of claim 1 are charged triboelectrically.

6. The process according to any of claims 1 to 5, characterized in that the particle support has an electrically conductive layer (43) with an insulating layer (44) thereon, and that an electrical potential of the first polarity is applied to the electrically conductive layer (43) in such a way that particles located on the support surface are electrostatically attracted to it through the insulating layer (44).

7. The process according to any of claims 1 to 5, characterized in that the particle support has an electrically conductive layer with an active layer on top, the electrical conductivity of which can be changed by exposure to optical radiation, that the active layer is selectively structured by means of an electrophotography process with an electrical potential, that the active layer is then brought into contact with the powder particles of the second material in such a way that these adhere to the active layer with the electrical potential depending on the structuring of the active layer, and that the active layer thus structured with the powder particles is positioned on the cavity (13) in order to transfer the powder particles into the cavity (13).

8. The process according to any of claims 1 to 7, characterized in that the powder particles in step d) of claim 1 are charged by means of a triboelectric charging means (19), which has a reservoir (7) filled with the powder particles and a stirring tool (25) in contact with the powder particles, which is designed and moved relative to the powder particles in such a way that the latter become electrically charged.

9. The process according to any of claims 1 to 8, characterized in that a coating roller (21A, 21B) the lateral surface of which serves as a support surface for the powder particles is used as the particle support, that the lateral surface is brought into contact with the powder particles having the potential of the second polarity at a first location and the coating roller (21A, 21B) is rotated about the roller axis of the coating roller (21A, 21B) relative to the first location for the surface coating of the active lateral surface with the powder particles, and that the lateral surface is positioned at a second location coated with the powder particles, which is offset from the first location in the circumferential direction of the lateral surface, facing the cavity (13) and is positioned so close relative to the cavity (13) that the powder particles are transferred from the lateral surface into the cavity (13) to form the molded article layer (16).

10. The process according to claim 9, characterized in that powder particles adhering to a portion of the lateral surface of the coating roller (21A, 21B) which lies behind the second location and in front of the first location in the direction of rotation are removed from the lateral surface and transported back into the reservoir (7).

11. The process according to claim 9 or 10, characterized in that a cylindrical roller is used as said coating roller (21B), that the support part (2) having the base surface (3) i) for applying a first layer of material, is displaced in a forward transport direction relative to the coating roller (21B) starting from a starting position, ii) thereafter moved back into the starting position relative to the coating roller (21B), iii) then is again displaced relative to the coating roller (21B) in the forward transport direction to apply a second layer of material, and that the support part (2) is lowered relative to the coating roller (21B) during and / or between steps i) to iii).

12. The process according to claim 9 or 10, characterized in that the support part (2) having the base surface (3) is rotated relative to the coating roller (21A) about a rotation axis (11) arranged transversely to the cylinder axis of the coating roller (21A) during the material application and optionally during the solidification of the materials (4, 5), and is optionally lowered relative to the coating roller (21A) during the rotational movement, and that the coating roller (21A) is designed as a conical roller, whose roller cross-section decreases from its end remote from the rotation axis (11) to its other end closer to the rotation axis (11).

13. The process according to any of claims 9 to 12, characterized in that a feed roller (20A) for the powder particles is provided, which is spaced with its lateral surface by a roller gap (24) from the lateral surface of the coating roller (21A, 21B), that the feed roller (20A) has on its lateral surface an electrically conductive feed roller layer with an insulating layer thereon, that an electrical potential of the first polarity is applied to the electrically conductive layer in such a way that particles located on the lateral surface of the feed roller (20A) are electrostatically attracted to it, that the lateral surface of the feed roller (20A) is brought into contact with the powder particles at a point spaced from the roller gap (24) and the feed roller (20A) is rotated about its axis in such a way that powder particles located on the lateral surface of the feed roller (20A) arrive in the roller gap (24), and that the potential applied to the feed roller layer and the potential applied to the electrically conductive layer (43) of the coating roller (21A, 21B) are selected such that the powder particles in the roller gap (24) are transferred from the lateral surface of the feed roller (20A) to the lateral surface of the coating roller (21A, 21B).

14. The process according to any of claims 9 to 13, characterized in that magnetically conductive support particles are provided and thus brought into contact with the powder particles of the second material (5), that the powder particles adhere releasably to the support particles, that a magnetic feed roller for the powder particles is provided which is spaced with its lateral surface by a roller gap (24) from the lateral surface of the coating roller (21A, 21B), that the magnetic support particles with the powder particles adhering thereto are brought into contact with the lateral surface of the feed roller (20B) at a location spaced from the roller gap (24), that the support particles adhere magnetically to the surface of the feed roller (20B), that the feed roller (20B) is rotated about its axis in such a way that support particles located on the lateral surface of the feed roller (20B) with the powder particles adhering thereto are first moved past a stripping device (37) for stripping off support particles coated with powder particles, and after passing through the stripping device (37), arrive in the roller gap (24), and that the potential of the coating roller (21A, 21B) is selected to deviate from the potential of the powder particles adhering to the support particles in such a way that the powder particles in the roller gap (24) are detached from the support particles and transferred to the lateral surface of the coating roller (21A, 21B).

15. The process according to any of claims 9 to 12, characterized in that magnetically conductive support particles are provided and thus brought into contact with the powder particles of the second material (5), that the powder particles adhere releasably to the support particles, that a coating roller (21B) with a magnetic lateral surface is provided, which is spaced from the bottom of the cavity (13) to be filled with the powder particles by a transfer gap (47), that the magnetic support particles with the powder particles adhering thereto are brought into contact with the lateral surface of the coating roller (21B) at a location spaced from the cavity (13), that the support particles adhere magnetically to the lateral surface of the coating roller (21B), that the coating roller (21B) is rotated about its axis in such a way that support particles located on the lateral surface of the coating roller (21B) with the powder particles adhering thereto are first moved past a stripping device (37) for stripping off support particles coated with powder particles, and after passing through the stripping device (37), arrive in the transfer gap (46), and that the potential of the bottom of the cavity (13) is selected to deviate from the potential of the powder particles adhering to the support particles in such a way that the powder particles in said transfer gap are detached from the support particles and transferred to the bottom of the cavity (13).

16. The process according to any of claims 1 to 15, characterized in that a preferably electrically conductive material is used as the first material and a preferably electrically insulating material is used as the second material, that at least the solidified negative mold layer (12) arranged closest to the support surface of the particle support is placed at an electrical potential that differs from the potential of the electrically conductive region of the particle support and from the electrical potential of the powder particles of the second material located on the particle support in such a way that when positioning this negative mold layer on the support surface of the particle support (12), fewer, in particular 50% fewer, optionally 70% fewer and preferably 90% fewer powder particles per unit area are transferred to the negative mold layer (12) than are transferred per unit area into at least one cavity (13) of this negative mold layer (12), when the cavity (13) is positioned on the support surface of the particle support (12).

17. The process according to any of claims 1 to 16, characterized in that the powdery second material (5) comprises a photoinitiator, that the thermoplastic powder particles comprise a polymer and / or copolymer, and that the photoinitiator is activated after sintering to crosslink the polymer by irradiation with electromagnetic radiation.

18. The process according to any of claims 1 to 17, characterized in that the support part (2) has at least two electrodes (47A, 47B) on the base surface (3) which are laterally offset from one another in the plan view of the base surface (3), preferably intermeshing in a comb-like manner, and that an electrical voltage is applied to the electrodes (47A, 47B) in such a way that the electrical potential having the first polarity occurs at the bottom of the cavity (13).

19. The process according to claim 18, characterized in that the electrical voltage applied to the electrodes is increased in magnitude at least once between the application of the first and the application of the last negative mold layer (12).

20. The process according to claim 18 or 19, characterized in that a measuring signal for the electrical potential at the level of the bottom of the cavity (13) is acquired and compared with a target value or a target value range, and that if a deviation occurs between the measurement signal and the target value or the target range, the electrical voltage at the electrodes (47A, 47B) is changed to reduce the deviation.