EP1513669A1 - Granular material for 3d binder printing, production method and uses therefor - Google Patents

Granular material for 3d binder printing, production method and uses therefor

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Publication number
EP1513669A1
EP1513669A1 EP03740089A EP03740089A EP1513669A1 EP 1513669 A1 EP1513669 A1 EP 1513669A1 EP 03740089 A EP03740089 A EP 03740089A EP 03740089 A EP03740089 A EP 03740089A EP 1513669 A1 EP1513669 A1 EP 1513669A1
Authority
EP
European Patent Office
Prior art keywords
particles
granulate
surface layer
layer
binder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03740089A
Other languages
German (de)
French (fr)
Inventor
Rolf Pfeifer
Jialin Shen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Daimler AG
Original Assignee
DaimlerChrysler AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by DaimlerChrysler AG filed Critical DaimlerChrysler AG
Publication of EP1513669A1 publication Critical patent/EP1513669A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/28—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic using special binding agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/006—Coating of the granules without description of the process or the device by which the granules are obtained
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/165—Processes of additive manufacturing using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2029/00—Use of polyvinylalcohols, polyvinylethers, polyvinylaldehydes, polyvinylketones or polyvinylketals or derivatives thereof as moulding material
    • B29K2029/04—PVOH, i.e. polyvinyl alcohol
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/25—Solid
    • B29K2105/251—Particles, powder or granules
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
    • Y10T428/2991—Coated

Definitions

  • the invention relates to a granulate for 3D binder printing, a method for its production, a 3D binder printing method and an object that can be produced with the granulate or the printing method.
  • 3D binder printing processes are processes for the production of three-dimensional objects from a granulate, in which a layer of the granulate is applied to a base and then moistened with a binding liquid in predetermined areas, each of which corresponds to a layer of an object to be produced. These steps are repeated until a given three-dimensional object is completely built up from connected granulate particles. Then it removes excess granulate particles and removes the object.
  • the granulate particles in the moistened areas are dissolved on the surface by the binder liquid, and the subsequent evaporation of the binder liquid leads directly to the granulate particles adhering to one another in their edge areas, by melting them together.
  • a binder liquid which contains auxiliaries remaining in the moistened areas during drying, which enable the moistened granulate particles to be connected to one another by subsequent melting or sintering.
  • 3D binder printing processes in particular of the first type, are known from the European patents EP 0 644 809 B1, EP 0 686 067 B1 and the European patent application EP 1 099 534 A2.
  • Binder printing processes which cause the granulate particles to bond by dissolving them with the binder liquid have the disadvantage that the finished article has a significant shrinkage compared to the area of the granulate layer originally moistened with the binder liquid.
  • the reason for this is that touching dissolved particles move closer together under the influence of their surface tension, so that after the binder liquid has dried, the packing is denser than before.
  • This effect is not easily suppressed, it is also necessary to a certain extent in order to achieve a sufficiently firm cohesion of the particles in the finished article.
  • a serious disadvantageous consequence of this effect is, however, that in the case of an article produced using such a method which exceeds a certain maximum size, the shrinkage during the drying process leads to the formation of cracks.
  • binder printing processes have been developed in which the binder liquid contains additives which remain in the moistened areas of the layer after the liquid has dried and which make it possible to bond the particles in the moistened areas by including all of the processed powder mass of the non-humidified areas is heated so that the particles in the humidified areas sinter under the influence of the sintering aid, but the non-humidified particles do not.
  • sintering aids used are generally mineral in nature and at best dispersible in the binder liquid, but not are soluble and therefore cause considerable wear on the spray nozzles used to moisten the granules.
  • Another problem with the known binder printing processes is that, as a result of agglomeration of the granules used with them, objects produced with them tend to have an uneven, rough surface profile which does not exactly correspond to the profile of the moistened areas.
  • the object of the invention is to provide a granulate for 3D binder printing which avoids one or more of the disadvantages listed above, and to show a production process and applications of such a granulate.
  • the outside non-polar surface layer of these granules prevents or at least reduces the build-up of hydrogen bonds between granulate particles both directly and via water molecules adsorbed on the surface of the particles and thus significantly reduces agglomeration.
  • Objects with a smoother surface can be produced from the granules according to the invention than with conventional granules, or objects with finer, more detailed structures can be produced with the same particle size as with conventional granules.
  • the surface layer consists of a polymer material.
  • the advantageous effects of such a surface layer can be of two types.
  • a polymeric material composed of monomers with polar and non-polar groups is applied to a polar granule substrate, its polar groups tend to face the surface of the granule particles while the non-polar groups face outwards are swept. If the thickness of the polymer layer does not exceed a monolayer of the monomers, so that the non-polar groups facing outward form the outer surface of the surface layer, granules with a very low tendency to form hydrogen bonds or to accumulate water are obtained.
  • the surface layer is thicker, depending on the type of polymer material used, a highly non-polar, water-repellent surface can still be obtained, but there is also a second useful effect which is independent of the polarity of the surface layer. Due to the different chemical-physical properties of the surface layer and the underlying material, it is possible to limit the partial fusion of the particles required to produce a solid object from the granulate to the surface layer and thus depending on the ratio of the thickness of the surface layer to the underlying material limit the shrinkage of the granules.
  • Thicknesses of the surface layer in the range from 0.1 to 10% of the mean particle radius have proven to be suitable for this.
  • Polyvinyl butyrals in particular have proven to be suitable as polymer material for such a surface layer.
  • the surface layer of the granules consists of surfactant.
  • Surfactants are generally characterized in that they combine polar and non-polar groups in one molecule, so that they are able to mediate the dissolution of non-polar substances in polar solvents or vice versa, in that the polar group is attached to the polar substance and the non-polar group attached to the non-polar substance.
  • the thickness of the surfactant layer corresponds as exactly as possible to a monolayer, so that the positive Laral groups of the surfactant molecules are all directed towards the inside of the particles, if possible, but the non-polar to the outside, and thus form the non-polar outer surface of the granulate.
  • the surfactant layer could indeed be applied directly to a homogeneous core of the granulate particles, but it is preferred to apply it to an intermediate layer made of polymer material.
  • this intermediate layer should have a polar outer surface.
  • the surfactant and intermediate layer are expediently chosen such that a solvent exists in which the surfactant is soluble, but the intermediate layer does not. It is thus possible to apply the surfactant layer by bringing the particles provided with the intermediate layer into contact with a solution of the surfactant and drying them by evaporating the solvent.
  • Preferred materials for the intermediate layer are the polyvinyl pyrolidones.
  • the particles have a core made of metal, ceramic or polymer material.
  • a polymer material for the core should expediently be chosen such that a solvent exists which dissolves the surface layer - and, if present, the intermediate layer - but not the core.
  • a solvent can be used as a binder liquid in a subsequent 3D binder printing process.
  • This binder liquid dissolves the layers surrounding the core and thus enables the layers of adjacent particles to fuse, but since it does not attack the core itself, the shrinkage caused by the fusion is reduced to a proportion which is proportional to the ratio of the radius of the core to the Thickness of the surface layer and optionally the intermediate layer.
  • the object is further achieved by a production method with the features of claim 14.
  • the surface layer with a non-polar outer surface is preferably produced by bringing the particles of the granulate into contact with a solution which contains the material of the surface layer in a form dissolved in a first solvent, and drying the particles by evaporating the solvent.
  • the particles are brought into contact with a solution containing material of an intermediate layer dissolved in a second solvent before the surface layer is deposited, and treated in the same manner as above.
  • the first solvent so that it does not dissolve the material of the intermediate layer, it is ensured that the intermediate layer remains intact when the surface layer is produced.
  • a 3D binder printing method is characterized in that the binder liquid used is chosen from liquids in which a surface layer of the particles of the granules used is soluble, but a core of the particles is not. If an intermediate layer is present, the binder liquid is preferably selected so that it dissolves it and the surface layer. Since an essentially solids-free binder liquid can be used, the service life of the nozzles used to apply the binder liquid to the granulate is increased.
  • FIG. 2 shows a schematic section through a layer of an object produced with the granulate from FIG. 1;
  • FIG. 3 shows a schematic section through a granulate particle according to a second embodiment of the invention
  • FIG. 4 shows a schematic section through a layer of an object produced from granulate particles according to FIG. 3.
  • the particle shows a granular particle according to a first embodiment of the invention in a schematic section.
  • the particle is shown as a sphere, but it goes without saying that it can also have a shape deviating from the spherical shape, for example ellipsoidal or irregular.
  • the particle has a core 1, e.g. made of metal, ceramic or an alcohol-resistant polymer material such as polymethyl methacrylate (PMMA), which is surrounded by a surface layer 2.
  • PMMA polymethyl methacrylate
  • a polyvinyl butyral is preferred as the material for the surface layer, since this material forms a highly water-repellent, non-polar outer surface. Suitable polyvinyl butyrals are sold under the name Pioloform by Wacker Polymer Systems; Pioloform BN18 is preferred.
  • the surface layer is produced by dissolving the pioloform in an alcohol such as ethanol, isopropanol, n-butanol etc. or an alcohol mixture, applying the solution to the particles of the granules and drying the particles.
  • granules are fluidized in a fluidized bed by a hot air stream and simultaneously sprayed with the solution. Drops of the solution that come into contact with granulate particles evaporate in this hot air stream, as a result of which the dissolved poliol form is deposited on them and forms the surface layer.
  • the resulting layer thickness can be controlled on the basis of the concentration of the solution used and the duration of the treatment.
  • a layer of such particles is applied to a base and sprayed from above with a binder liquid according to a predetermined pattern.
  • a device similar to a well-known ink jet printer can be used for spraying; devices of this type are described in the European patents mentioned at the outset and are not explained in more detail here.
  • the same alcohols that were used to separate the surface layer are suitable as the binder liquid.
  • To set a desired viscosity of the binding liquid e.g. Glycol can be added.
  • FIG. 2 schematically shows a section through a granulate layer after the binder liquid has been applied and dried.
  • the surface layers 2 ⁇ of the particles are fused to one another, so that the particles form a coherent body.
  • the particles are unchanged.
  • This thickness can e.g. 0.5 ⁇ m with an average radius of approx. 10 ⁇ m.
  • the non-polar nature of the outer surfaces of the particles prevents agglomeration of the particles before their surface layer is dissolved and thus ensures uniform gaps between the unconnected particles and accordingly also a uniform spreading of sprayed binder liquid.
  • the surfaces of the object obtained are therefore uniformly smooth and exactly follow the predetermined pattern of the distribution of the binder liquid.
  • FIG. 3 shows a schematic section through a particle of a granulate according to the invention in accordance with a second embodiment of the invention.
  • the particle in turn has a core 1 made of ceramic, metal or polymer material and a surface layer 2.
  • the surface layer 2 does not consist of a polymer material, but is a monolayer of a surfactant.
  • This surfactant can be any surfactant known from the field of washing, cleaning or personal care products, such as sodium lauryl sulfate, betaine or the like.
  • An intermediate layer 4 made of a polymer material is located between the surface layer 2 and the core 1.
  • this polymer material can be a polyvinyl butyral such as Pioloform, but there are also other classes of polymers such as polyvinylpyrrolidones, in particular the materials sold by BASF under the trade names Luviskol and Luvitec, and one by Belland AG acrylic polymer sold under the name Bellac.
  • polyvinylpyrrolidones in particular the materials sold by BASF under the trade names Luviskol and Luvitec, and one by Belland AG acrylic polymer sold under the name Bellac.
  • the intermediate layer 4 has a thickness in the order of 0.1 to 10% of the average radius of the particles, ie with an average particle diameter of approximately 20 ⁇ m, the layer thickness can expediently be 0.5 ⁇ m, for example.
  • the layer thickness can expediently be 0.5 ⁇ m, for example.
  • Such a layer is many times thicker than a monolayer, the extent of the polarity of the outer surface of the intermediate layer 4 is therefore not determined by the polarity or non-polarity of the material of the core 1, but by the intrinsic properties of the polymer used for the intermediate layer 4 itself
  • the extent of the polarity of the outside of the intermediate layer 4 is different for the different materials, but apparently even for polyvinyl butyral, the most water-repellent of the examined intermediate layer materials, is sufficient to reduce the tendency to agglomerate after the monomolecular surface layer has been attached To enable 1 on the intermediate layer 4.
  • the surfactant therefore reduces the tendency towards agglomeration in all the interlayer materials compared to granules without a surfactant layer.
  • the effect of the surfactant layer is most pronounced in the case of the superficial polar interlayer materials such as polyvinylpyrrolidone or Bellac; the tendency to agglomeration of a polyvinylbutyral surface is inherently so low that even without a surfactant layer, even with a structure according to the first exemplary embodiment, the tendency to agglomeration of the granules is sufficiently suppressed.
  • 3 can be made by fluidizing a starting powder of ceramic, metal, polymer or a mixture of these materials in a fluidized bed by a hot air stream and spraying for a time with a finely atomized solution of the interlayer material.
  • the solvent evaporates in the hot air stream in a very short time, so that drops that hit the particles of the starting material precipitate the dissolved intermediate layer material and form a closed film in the course of the treatment.
  • an alcohol or alcohol mixture is suitable as the solvent for polyvinyl butyral.
  • Polyvinylpyrrolidone and Bellac are soluble in basic aqueous media; a solution of ammonia in water is preferably used as the solvent, since this solution has the advantage over many other basic aqueous solutions that it can be evaporated without residue.
  • the surface layer of surfactant is produced in a manner analogous to the intermediate layer by spraying the fluidized particles in the fluidized bed with a second solution, which is an aqueous solution of the surfactant. Since polyvinyl butyral is not soluble in water, an intermediate layer 4 made of it is not attacked in this second coating process. If the intermediate layer consists of polyvinylpyrrolidone, which is soluble in weak acids and bases, then it must be ensured that the surfactant solution is pH neutral. In the case of an intermediate layer made from the basic soluble Bellac, the pH of the second solution must not exceed 9.5.
  • a liquid which dissolves the surface and intermediate layer that is to say an alcohol in the case of a polyvinyl butyral intermediate layer or a basic aqueous solution, is used as the binder liquid such as ammonia solution in the case of polyvinylpyrrolidone or Bellac interlayers.
  • FIG. 4 shows, analogously to FIG. 2, a section through a layer of the granulate according to the invention after application of the binder liquid to the area 3 in which the cores 1 of the granulate particles are again highlighted by hatching.
  • the surface layers can no longer be made out, and the intermediate layers 4 are fused at the points of contact between the particles.
  • surface layer 2 persists and prevents agglomeration with neighboring particles, so that a finished article with precisely shaped, smooth surfaces is obtained.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Optics & Photonics (AREA)
  • Powder Metallurgy (AREA)

Abstract

The invention relates to a granular material for 3D binder printing, said granular material consisting of particles provided with an externally non-polar surface layer (2). The invention also relates to a method for producing a granular material for 3D binder printing, whereby a surface layer (2) having a non-polar outer side is applied to initial particles (1), and to a method for producing an object consisting of the inventive granular material, according to which a layer of the inventive granular material is applied to a base, and pre-determined regions (3) of said layer are moistened with a binding fluid, said binding fluid being selected from fluids in which a surface layer of the particles of the granular material is soluble. The invention further relates to objects consisting of interconnected particles of the inventive granular material. The invention enables a very precise printing process.

Description

Granulat für 3D-Binderdruck, Herstellungsverfahren und Anwendungen dafür Granules for 3D binder printing, manufacturing processes and applications therefor
Die Erfindung betrifft ein Granulat für 3D-Binderdruck, ein Verfahren zu dessen Herstellung, ein 3D-Binderdruckverfahren sowie einen mit dem Granulat oder dem Druckverfahren herstellbaren Gegenstand.The invention relates to a granulate for 3D binder printing, a method for its production, a 3D binder printing method and an object that can be produced with the granulate or the printing method.
3D-Binderdruckverfahren sind Verfahren zur Herstellung von dreidimensionalen Gegenständen aus einem Granulat, bei denen eine Schicht des Granulats auf einer Unterlage ausgebracht und dann in vorgegebenen Bereichen, die jeweils einer Schicht eines zu erzeugenden Gegenstands entsprechen, mit einer Bin- derflüssigkeit befeuchtet wird. Diese Schritte werden so oft wiederholt, bis ein vorgegebener dreidimensionaler Gegenstand vollständig aus verbundenen Granulatpartikeln aufgebaut ist. Danach wird er Überschuss an Granulatpartikeln entfernt und er Gegenstand entnommen. Bei einem ersten Typ dieser Verfah- ren werden die Granulatpartikel in den befeuchteten Bereichen von der Binderflüssigkeit oberflächlich angelöst, und das anschließende Verdampfen der Binderflüssigkeit führt unmittelbar zu einem Aneinanderhaften der Granulatpartikel in ihren Randbereichen, indem diese miteinander verschmelzen. Bei ei- nem zweiten Typ dieser Verfahren wird eine Binderflüssigkeit eingesetzt, die beim Trocknen in den befeuchteten Bereichen zurückbleibende Hilfsstoffe enthält, die ein Verbinden der befeuchteten Granulatpartikel miteinander durch anschließendes Anschmelzen oder Sintern ermöglichen. 3D-Binderdruckverfahren insbesondere des ersten Typs sind aus den europäischen Patenten EP 0 644 809 Bl, EP 0 686 067 Bl sowie der europäischen Patentanmeldung EP 1 099 534 A2 bekannt .3D binder printing processes are processes for the production of three-dimensional objects from a granulate, in which a layer of the granulate is applied to a base and then moistened with a binding liquid in predetermined areas, each of which corresponds to a layer of an object to be produced. These steps are repeated until a given three-dimensional object is completely built up from connected granulate particles. Then it removes excess granulate particles and removes the object. In a first type of these processes, the granulate particles in the moistened areas are dissolved on the surface by the binder liquid, and the subsequent evaporation of the binder liquid leads directly to the granulate particles adhering to one another in their edge areas, by melting them together. In a second type of this method, a binder liquid is used which contains auxiliaries remaining in the moistened areas during drying, which enable the moistened granulate particles to be connected to one another by subsequent melting or sintering. 3D binder printing processes, in particular of the first type, are known from the European patents EP 0 644 809 B1, EP 0 686 067 B1 and the European patent application EP 1 099 534 A2.
Binderdruckverfahren, die eine Verbindung der Granulatpartikel durch Anlösen mit der Binderflüssigkeit bewirken, haben den Nachteil, dass der fertige Gegenstand eine deutliche Schrumpfung gegenüber dem ursprünglich mit der Binderflüssig- keit befeuchteten Bereich der Granulatschicht aufweist. Der Grund hierfür ist, dass einander berührende angelöste Partikel unter dem Einfluss ihrer Oberflächenspannung enger zusammenrücken, so dass nach dem Trocknen der Binderflüssigkeit eine dichtere Packung als zuvor vorliegt. Dieser Effekt ist nicht ohne weiteres zu unterdrücken, er ist auch in gewissem Umfang notwendig, um einen hinreichend festen Zusammenhalt der Partikel im fertigen Gegenstand zu erzielen. Eine schwerwiegende nachteilige Folge dieses Effekts ist jedoch, dass bei einem mit einem solchen Verfahren hergestellten Gegens- tand, der eine bestimmte maximale Größe überschreitet, die Schrumpfung während des Trocknungsprozesses zur Rissbildung führt .Binder printing processes which cause the granulate particles to bond by dissolving them with the binder liquid have the disadvantage that the finished article has a significant shrinkage compared to the area of the granulate layer originally moistened with the binder liquid. The reason for this is that touching dissolved particles move closer together under the influence of their surface tension, so that after the binder liquid has dried, the packing is denser than before. This effect is not easily suppressed, it is also necessary to a certain extent in order to achieve a sufficiently firm cohesion of the particles in the finished article. A serious disadvantageous consequence of this effect is, however, that in the case of an article produced using such a method which exceeds a certain maximum size, the shrinkage during the drying process leads to the formation of cracks.
Um dieses Problem zu bekämpfen, sind Binderdruckverfahren entwickelt worden, bei denen die Binderflüssigkeit Zusätze enthält, die in den befeuchteten Bereichen der Schicht nach Trocknen der Flüssigkeit zurückbleiben und die es ermöglichen, die Partikel in den befeuchteten Bereichen zu verbinden, indem die gesamte bearbeitete Pulvermasse einschließlich der nicht befeuchteten Bereiche so erhitzt wird, dass die Partikel in den befeuchteten Bereichen unter dem Einfluss des Sinterhilfsmittels sintern, die unbefeuchtet gebliebenen Partikel jedoch nicht.To combat this problem, binder printing processes have been developed in which the binder liquid contains additives which remain in the moistened areas of the layer after the liquid has dried and which make it possible to bond the particles in the moistened areas by including all of the processed powder mass of the non-humidified areas is heated so that the particles in the humidified areas sinter under the influence of the sintering aid, but the non-humidified particles do not.
Ein Problem dieser Technik ist, dass die verwendeten Sinterhilfsmittel im allgemeinen mineralischer Natur sind und in der Binderflüssigkeit allenfalls dispergierbar, aber nicht löslich sind und daher einen erheblichen Verschleiß der zum Befeuchten des Granulats eingesetzten Spritzdüsen verursachen.A problem with this technique is that the sintering aids used are generally mineral in nature and at best dispersible in the binder liquid, but not are soluble and therefore cause considerable wear on the spray nozzles used to moisten the granules.
Ein weiteres Problem der bekannten Binderdruckverfahren ist, dass infolge von Agglomeration der verwendeten Granulate mit ihnen hergestellte Gegenstände dazu neigen, einen ungleichmäßigen, rauhen Oberflächenverlauf aufzuweisen, der dem Verlauf der befeuchteten Bereiche nicht exakt entspricht.Another problem with the known binder printing processes is that, as a result of agglomeration of the granules used with them, objects produced with them tend to have an uneven, rough surface profile which does not exactly correspond to the profile of the moistened areas.
Aufgabe der Erfindung ist, ein Granulat für den 3D-Binder- druck anzugeben, das einen oder mehrere der oben aufgeführten Nachteile vermeidet, sowie ein Herstellungsverfahren und Anwendungen eines solchen Granulats aufzuzeigen.The object of the invention is to provide a granulate for 3D binder printing which avoids one or more of the disadvantages listed above, and to show a production process and applications of such a granulate.
Die Aufgabe wird zum einen gelöst durch ein Granulat mit den Merkmalen des Anspruchs 1.The object is achieved on the one hand by a granulate with the features of claim 1.
Die außen unpolare Oberflachenschicht dieses Granulats ver- hindert oder reduziert zumindest den Aufbau von Wasserstoffbrückenbindungen zwischen Granulatpartikeln sowohl unmittelbar als auch über an der Oberfläche der Partikel adsorbierte Wassermoleküle und reduziert so deutlich die Agglomeration. So können aus dem erfindungsgemäßen Granulat Gegenstände mit glatterer Oberfläche als mit einem herkömmlichen Granulat hergestellt werden, oder bei gleicher Partikelgröße wie bei einem herkömmlichen Granulat können Gegenstände mit feineren, detailreicheren Strukturen hergestellt werden.The outside non-polar surface layer of these granules prevents or at least reduces the build-up of hydrogen bonds between granulate particles both directly and via water molecules adsorbed on the surface of the particles and thus significantly reduces agglomeration. Objects with a smoother surface can be produced from the granules according to the invention than with conventional granules, or objects with finer, more detailed structures can be produced with the same particle size as with conventional granules.
Einer ersten bevorzugten Ausgestaltung zufolge besteht die 0- berflächenschicht aus einem Polymermaterial. Die vorteilhaften Wirkungen einer solchen Oberflachenschicht können von zweierlei Art sein. Wenn ein solches Polymermaterial, das aus Monomeren mit polaren und unpolaren Gruppen aufgebaut ist, auf einem polaren Granulatsubstrat aufgebracht wird, neigen dessen polare Gruppen dazu, sich der Oberfläche der Granulatteilchen zuzuwenden, während die unpolaren Gruppen nach außen gekehrt sind. Wenn die Dicke der Polymerschicht eine Monolage der Monomeren nicht überschreitet, so dass die nach außen gekehrten unpolaren Gruppen die Außenfläche der Oberflachenschicht bilden, wird ein Granulat mit sehr geringer Neigung zur Ausbildung von Wasserstoffbrückenbildung bzw. zur Anlagerung von Wasser erhalten.According to a first preferred embodiment, the surface layer consists of a polymer material. The advantageous effects of such a surface layer can be of two types. When such a polymeric material composed of monomers with polar and non-polar groups is applied to a polar granule substrate, its polar groups tend to face the surface of the granule particles while the non-polar groups face outwards are swept. If the thickness of the polymer layer does not exceed a monolayer of the monomers, so that the non-polar groups facing outward form the outer surface of the surface layer, granules with a very low tendency to form hydrogen bonds or to accumulate water are obtained.
Wenn die Oberflachenschicht dicker ist, kann je nach Art des verwendeten Polymermaterials immer noch eine hochgradig unpo- lare, wasserabweisende Oberfläche erhalten werden, doch kommt hier noch eine zweite, von der Polarität der Oberflachenschicht unabhängige Nutzwirkung hinzu. Aufgrund unterschiedlicher chemisch-physikalischer Eigenschaften der Oberflachenschicht und des darunter liegenden Materials ist es nämlich möglich, die zum Herstellen eines festen Gegenstandes aus dem Granulat erforderliche teilweise Verschmelzung der Partikel auf die Oberflachenschicht zu beschränken und so in Abhängigkeit vom Verhältnis der Dicke der Oberflachenschicht zum darunterliegenden Material die Schrumpfung des Granulats zu be- grenzen.If the surface layer is thicker, depending on the type of polymer material used, a highly non-polar, water-repellent surface can still be obtained, but there is also a second useful effect which is independent of the polarity of the surface layer. Due to the different chemical-physical properties of the surface layer and the underlying material, it is possible to limit the partial fusion of the particles required to produce a solid object from the granulate to the surface layer and thus depending on the ratio of the thickness of the surface layer to the underlying material limit the shrinkage of the granules.
Hierfür haben sich Dicken der Oberflachenschicht im Bereich von 0,1 bis 10 % des mittleren Partikelradius als geeignet erwiesen.Thicknesses of the surface layer in the range from 0.1 to 10% of the mean particle radius have proven to be suitable for this.
Als Polymermaterial für eine solche Oberflachenschicht haben sich insbesondere Polyvinylbutyrale als geeignet erwiesen.Polyvinyl butyrals in particular have proven to be suitable as polymer material for such a surface layer.
Einer zweiten Ausgestaltung zufolge besteht die Oberflächen- schicht des Granulats aus Tensid. Tenside sind allgemein dadurch gekennzeichnet, dass sie polare und unpolare Gruppen in einem Molekül vereinen, so dass sie in der Lage sind, die Lösung von unpolaren Substanzen in polaren Lösungsmitteln oder umgekehrt zu vermitteln, indem jeweils die polare Gruppe sich an der polaren Substanz und die unpolare Gruppe an der unpolaren Substanz anlagert. Auch hier entspricht die Dicke der Tensidschicht möglichst genau einer Monolage, so dass die po- laren Gruppen der Tensidmoleküle möglichst sämtliche zum Innern der Partikel gerichtet sind, die unpolaren aber nach außen, und so die unpolare Außenfläche des Granulats bilden.According to a second embodiment, the surface layer of the granules consists of surfactant. Surfactants are generally characterized in that they combine polar and non-polar groups in one molecule, so that they are able to mediate the dissolution of non-polar substances in polar solvents or vice versa, in that the polar group is attached to the polar substance and the non-polar group attached to the non-polar substance. Here too, the thickness of the surfactant layer corresponds as exactly as possible to a monolayer, so that the positive Laral groups of the surfactant molecules are all directed towards the inside of the particles, if possible, but the non-polar to the outside, and thus form the non-polar outer surface of the granulate.
Die Tensidschicht könnte zwar unmittelbar auf einem homogenen Kern der Granulatpartikel aufgebracht sein, bevorzugt ist jedoch, sie auf einer Zwischenschicht aus Polymermaterial aufzubringen. Selbstverständlich sollte diese Zwischenschicht eine polare Außenfläche aufweisen.The surfactant layer could indeed be applied directly to a homogeneous core of the granulate particles, but it is preferred to apply it to an intermediate layer made of polymer material. Of course, this intermediate layer should have a polar outer surface.
Tensid und Zwischenschicht sind zweckmäßigerweise so gewählt, dass ein Lösungsmittel existiert, in welchem das Tensid löslich ist, die Zwischenschicht jedoch nicht. So ist es möglich, die Tensidschicht aufzubringen, indem die mit der Zwi~ schenschicht versehenen Partikel mit einer Lösung des Tensids in Kontakt gebracht werden und durch Verdampfen des Lösungsmittels getrocknet werden.The surfactant and intermediate layer are expediently chosen such that a solvent exists in which the surfactant is soluble, but the intermediate layer does not. It is thus possible to apply the surfactant layer by bringing the particles provided with the intermediate layer into contact with a solution of the surfactant and drying them by evaporating the solvent.
Bevorzugte Materialien für die Zwischenschicht sind die Poly- vinylpyrolidone .Preferred materials for the intermediate layer are the polyvinyl pyrolidones.
Bei beiden oben erläuterten Ausgestaltungen ist bevorzugt, dass die Partikel einen Kern aus Metall, Keramik oder Polymermaterial aufweisen. Ein Polymermaterial für den Kern soll- te zweckmäßigerweise so gewählt sein, dass ein Lösungsmittel existiert, welches die Oberflachenschicht - und, sofern vorhanden, die Zwischenschicht - löst, nicht aber den Kern. Ein solches Lösungsmittel kann in einem anschließenden 3D- Binderdruckverfahren als Binderflüssigkeit verwendet werden. Diese Binderflüssigkeit löst zwar die den Kern umgebenden Schichten an und ermöglicht so ein Verschmelzen der Schichten benachbarter Partikel, da sie aber den Kern selbst nicht angreift, ist die durch die Verschmelzung verursachte Schrumpfung auf ein Maß reduziert, das proportional zum Verhältnis des Radius des Kerns zur Dicke der Oberflachenschicht und gegebenenfalls der Zwischenschicht ist. Die Aufgabe wird ferner gelöst durch ein Herstellungsverfahren mit den Merkmalen des Anspruchs 14.In both configurations explained above, it is preferred that the particles have a core made of metal, ceramic or polymer material. A polymer material for the core should expediently be chosen such that a solvent exists which dissolves the surface layer - and, if present, the intermediate layer - but not the core. Such a solvent can be used as a binder liquid in a subsequent 3D binder printing process. This binder liquid dissolves the layers surrounding the core and thus enables the layers of adjacent particles to fuse, but since it does not attack the core itself, the shrinkage caused by the fusion is reduced to a proportion which is proportional to the ratio of the radius of the core to the Thickness of the surface layer and optionally the intermediate layer. The object is further achieved by a production method with the features of claim 14.
Die Oberflachenschicht mit unpolarer Außenfläche wird vor- zugsweise hergestellt, indem die Partikel des Granulats mit einer Lösung in Kontakt gebracht werden, die das Material der Oberflachenschicht in einem ersten Lösungsmittel gelöster Form enthält, und die Partikel durch Verdampfen des Lösungsmittels getrocknet werden.The surface layer with a non-polar outer surface is preferably produced by bringing the particles of the granulate into contact with a solution which contains the material of the surface layer in a form dissolved in a first solvent, and drying the particles by evaporating the solvent.
Wenn eine Zwischenschicht erzeugt werden soll, werden die Partikel noch vor Abscheiden der Oberflachenschicht mit einer Lösung in Kontakt gebracht, die Material einer Zwischenschicht in einem zweiten Lösungsmittel gelöster Form enthält, und in gleicher Weise wie oben behandelt.If an intermediate layer is to be produced, the particles are brought into contact with a solution containing material of an intermediate layer dissolved in a second solvent before the surface layer is deposited, and treated in the same manner as above.
Indem das erste Lösungsmittel so gewählt wird, dass es das Material der Zwischenschicht nicht löst, wird gewährleistet, dass die Zwischenschicht beim Erzeugen der Oberflachenschicht unversehrt bleibt.By choosing the first solvent so that it does not dissolve the material of the intermediate layer, it is ensured that the intermediate layer remains intact when the surface layer is produced.
Ein 3D-Binderdruckverfahren gemäß der vorliegenden Erfindung ist dadurch gekennzeichnet, dass die verwendete Binderflüssigkeit unter Flüssigkeiten gewählt wird, in denen eine Ober- flächenschicht der Partikel des verwendeten Granulats löslich ist, ein Kern der Partikel jedoch nicht. Wenn eine Zwischenschicht vorhanden ist, ist die Binderflüssigkeit vorzugsweise so gewählt, dass sie diese und die Oberflachenschicht löst. Da eine im wesentlichen feststofffreie Binderflüssigkeit ver- wendet werden kann, wird die Lebensdauer der zum Aufbringen der Binderflüssigkeit auf das Granulat verwendeten Düsen erhöht.A 3D binder printing method according to the present invention is characterized in that the binder liquid used is chosen from liquids in which a surface layer of the particles of the granules used is soluble, but a core of the particles is not. If an intermediate layer is present, the binder liquid is preferably selected so that it dissolves it and the surface layer. Since an essentially solids-free binder liquid can be used, the service life of the nozzles used to apply the binder liquid to the granulate is increased.
Weitere Merkmale und Vorteile der vorliegenden Erfindung er- geben sich aus der nachfolgenden Beschreibung von Ausführungsbeispielen mit Bezug auf die beigefügten Figuren. Es zeigen: Fig. 1 einen schematischen Schnitt durch einen Granulatpartikel gemäß einer ersten Ausgestaltung der Erfindung;Further features and advantages of the present invention result from the following description of exemplary embodiments with reference to the attached figures. Show it: 1 shows a schematic section through a granulate particle according to a first embodiment of the invention;
Fig. 2 einen schematischen Schnitt durch eine Schicht eines mit dem Granulat aus Fig. 1 hergestellten Gegenstands;FIG. 2 shows a schematic section through a layer of an object produced with the granulate from FIG. 1;
Fig. 3 einen schematischen Schnitt durch einen Granulatpartikel gemäß einer zweiten Ausgestaltung der Erfindung; und Fig. 4 einen schematischen Schnitt durch eine Schicht eines aus Granulatpartikeln gemäß Fig. 3 hergestellten Gegenstands .3 shows a schematic section through a granulate particle according to a second embodiment of the invention; and FIG. 4 shows a schematic section through a layer of an object produced from granulate particles according to FIG. 3.
Fig. 1 zeigt einen Granulatpartikel gemäß einer ersten Ausgestaltung der Erfindung in einem schematischen Schnitt. Der Partikel ist als Kugel dargestellt, es versteht sich jedoch, dass er auch von der Kugelform abweichende Gestalt, etwa el- lipsoidisch oder unregelmäßig, haben kann. Der Partikel hat einen Kern 1, z.B. aus Metall, Keramik oder einem alkoholbeständigen Polymermaterial wie etwa Polymethylmethacrylat (PMMA) , der von einer Oberflachenschicht 2 umgeben ist. Als Material für die Oberflachenschicht ist ein Polyvinylbutyral bevorzugt, da dieses Material eine stark wasserabweisende, unpolare Außenfläche ausbildet. Geeignete Polyvinylbutyrale werden unter der Bezeichnung Pioloform von der Fa. Wacker Po- lymer Systems vertrieben; bevorzugt ist Pioloform BN18.1 shows a granular particle according to a first embodiment of the invention in a schematic section. The particle is shown as a sphere, but it goes without saying that it can also have a shape deviating from the spherical shape, for example ellipsoidal or irregular. The particle has a core 1, e.g. made of metal, ceramic or an alcohol-resistant polymer material such as polymethyl methacrylate (PMMA), which is surrounded by a surface layer 2. A polyvinyl butyral is preferred as the material for the surface layer, since this material forms a highly water-repellent, non-polar outer surface. Suitable polyvinyl butyrals are sold under the name Pioloform by Wacker Polymer Systems; Pioloform BN18 is preferred.
Die Oberflachenschicht wird erzeugt durch Lösen des Pioloform in einem Alkohol wie Ethanol, Isopropanol, n-Butanol usw. o- der einem Alkoholgemisch, Aufbringen der Lösung auf die Par- tikel des Granulats und Trocknen der Partikel. Zu diesem Zweck wird Granulat in einem Wirbelbett durch einen Heißluftstrom fluidisiert und gleichzeitig mit der Lösung besprüht. Tropfen der Lösung, die auf Granulatpartikel stoßen, verdunsten in diesem Heißluftstrom, wodurch sich das gelöste Pioloform an ihnen niederschlägt und die Oberflachenschicht bildet. Die resultierende Schichtdicke ist anhand der Konzentra- tion der verwendeten Lösung und Dauer der Behandlung steuerbar.The surface layer is produced by dissolving the pioloform in an alcohol such as ethanol, isopropanol, n-butanol etc. or an alcohol mixture, applying the solution to the particles of the granules and drying the particles. For this purpose, granules are fluidized in a fluidized bed by a hot air stream and simultaneously sprayed with the solution. Drops of the solution that come into contact with granulate particles evaporate in this hot air stream, as a result of which the dissolved poliol form is deposited on them and forms the surface layer. The resulting layer thickness can be controlled on the basis of the concentration of the solution used and the duration of the treatment.
Zum Erzeugen eines Gegenstandes aus Partikeln des in Fig. 1 gezeigten Typs wird eine Schicht aus derartigen Partikeln auf einer Unterlage ausgebracht und von oben mit einer Binderflüssigkeit gemäß einem vorgegebenen Muster besprüht. Zum Besprühen kann ein Gerät ähnlich einem allgemein bekannten Tintenstrahldrucker eingesetzt werden; derartige Geräte sind in den eingangs genannten europäischen Patentschriften beschrie- ben und werden hier nicht näher erläutert.To produce an object from particles of the type shown in FIG. 1, a layer of such particles is applied to a base and sprayed from above with a binder liquid according to a predetermined pattern. A device similar to a well-known ink jet printer can be used for spraying; devices of this type are described in the European patents mentioned at the outset and are not explained in more detail here.
Als Binderflüssigkeit sind die gleichen Alkohole geeignet, die auch zum Abscheiden der Oberflachenschicht eingesetzt wurden. Zum Einstellen einer gewünschten Viskosität der Bin- derflüssigkeit kann z.B. Glykol zugesetzt werden.The same alcohols that were used to separate the surface layer are suitable as the binder liquid. To set a desired viscosity of the binding liquid, e.g. Glycol can be added.
Durch Besprühen von Teilen der Granulatschicht mit der Binderflüssigkeit wird die Oberflachenschicht 2 angelöst, nicht aber der davon eingeschlossene Kern 1. Das Ergebnis ist in Fig. 2 gezeigt, die schematisch einen Schnitt durch eine Granulatschicht nach Aufbringen und Trocknen der Binderflüssigkeit zeigt. In einem Bereich 3 der Schicht, in welchem die Kerne 1Λ der Granulatpartikel durch Schraffur hervorgehoben sind, sind die Oberflächenschichten 2 Λ der Partikel unterein- ander verschmolzen, so dass die Partikel einen zusammenhängenden Körper bilden. In der nicht von der Binderflüssigkeit getroffenen Umgebung des Bereichs 3 sind die Partikel unverändert .By spraying parts of the granulate layer with the binder liquid, the surface layer 2 is dissolved, but not the core 1 enclosed by it. The result is shown in FIG. 2, which schematically shows a section through a granulate layer after the binder liquid has been applied and dried. In an area 3 of the layer in which the cores 1 Λ of the granulate particles are highlighted by hatching, the surface layers 2 Λ of the particles are fused to one another, so that the particles form a coherent body. In the area of area 3 not affected by the binder liquid, the particles are unchanged.
Durch wiederholtes Aufbringen einer Schicht frischen Granulats auf die in Fig. 2 gezeigte Schicht und Befeuchten von Bereichen der neuen Schichten mit Binderflüssigkeit nach ei- nem vorgegebenen Muster, das von Schicht zu Schicht unterschiedlich sein kann, wird schließlich ein zusammenhängender Körper aus verschmolzenen Granulatpartikeln erhalten, der nur noch von den umgebenden, unverschmolzen gebliebenen Partikeln befreit werden muss.By repeatedly applying a layer of fresh granules to the layer shown in FIG. 2 and moistening areas of the new layers with binder liquid after a In a given pattern, which can vary from layer to layer, a coherent body of fused granulate particles is finally obtained, which only has to be freed from the surrounding, unmelted particles.
Da der als Binderflüssigkeit verwendete Alkohol die Kerne der Partikel nicht löst, bleibt deren ursprüngliche Gestalt im fertigen Gegenstand unverändert erhalten, so dass die Schrumpfung des fertigen Gegenstandes nicht stärker sein kann als das Verhältnis der Dicke der Oberflachenschicht 2 zu einem mittleren Radius der Kerne der Partikel. Diese Dicke kann z.B. 0,5 μm bei einem mittleren Radius von ca. 10 μm betragen.Since the alcohol used as the binder liquid does not dissolve the cores of the particles, their original shape remains unchanged in the finished article, so that the shrinkage of the finished article cannot be greater than the ratio of the thickness of the surface layer 2 to an average radius of the cores of the particles , This thickness can e.g. 0.5 μm with an average radius of approx. 10 μm.
Die unpolare Natur der Außenflächen der Partikel verhindert eine Agglomeration der Partikel vor dem Anlösen ihrer Oberflachenschicht und gewährleistet so gleichmäßige Zwischenräume zwischen den unverbundenen Partikeln und entsprechend auch eine gleichmäßige Ausbreitung von aufgespritzter Binderflüssigkeit. Die Oberflächen des erhaltenen Gegenstandes sind daher gleichmäßig glatt und folgen genau dem vorgegebenen Muster der Verteilung der Binderflüssigkeit.The non-polar nature of the outer surfaces of the particles prevents agglomeration of the particles before their surface layer is dissolved and thus ensures uniform gaps between the unconnected particles and accordingly also a uniform spreading of sprayed binder liquid. The surfaces of the object obtained are therefore uniformly smooth and exactly follow the predetermined pattern of the distribution of the binder liquid.
Fig. 3 zeigt einen schematischen Schnitt durch einen Partikel eines erfindungsgemäßen Granulats gemäß einer zweiten Ausgestaltung der Erfindung. Der Partikel verfügt wiederum über einen Kern 1 aus Keramik, Metall oder Polymermaterial und eine Oberflachenschicht 2. Die Oberflachenschicht 2 besteht, an- ders als beim Partikel der Fig. 1, nicht aus einem Polymermaterial, sondern es handelt sich um eine Monolage eines Tensids. Bei diesem Tensid kann es sich um ein beliebiges aus dem Gebiet der Wasch-, Reinigungs- oder Körperpflegemittel bekanntes Tensid wie etwa Natriumlaurylsulfat, ein Betain o- der dergleichen handeln. Zwischen der Oberflachenschicht 2 und dem Kern 1 befindet sich eine Zwischenschicht 4 aus einem Polymermaterial. Dieses Polymermaterial kann wie beim ersten Ausführungsbeispiel ein Polyvinylbutyral wie Pioloform sein, es kommen jedoch auch andere Klassen von Polymeren wie etwa Polyvinylpyrrolidone, insbesondere die von der Fa. BASF unter den Handelsnamen Lu- viskol und Luvitec vertriebenen Materialien, sowie ein von der Belland AG unter der Bezeichnung Bellac vertriebenes Ac- rylpolymer in Betracht.3 shows a schematic section through a particle of a granulate according to the invention in accordance with a second embodiment of the invention. The particle in turn has a core 1 made of ceramic, metal or polymer material and a surface layer 2. Unlike the particle in FIG. 1, the surface layer 2 does not consist of a polymer material, but is a monolayer of a surfactant. This surfactant can be any surfactant known from the field of washing, cleaning or personal care products, such as sodium lauryl sulfate, betaine or the like. An intermediate layer 4 made of a polymer material is located between the surface layer 2 and the core 1. As in the first exemplary embodiment, this polymer material can be a polyvinyl butyral such as Pioloform, but there are also other classes of polymers such as polyvinylpyrrolidones, in particular the materials sold by BASF under the trade names Luviskol and Luvitec, and one by Belland AG acrylic polymer sold under the name Bellac.
Die Zwischenschicht 4 hat eine Dicke in der Größenordnung von 0,1 bis 10 % des mittleren Radius der Partikel, d.h. bei einem mittleren Partikeldurchmesser von ca. 20 μm kann die Schichtdicke z.B. zweckmäßig 0,5 μm betragen. Eine solche Schicht ist um ein Vielfaches dicker als eine Monolage, das Ausmaß der Polarität der Außenfläche der Zwischenschicht 4 ist daher nicht durch Polarität oder Unpolarität des Materials des Kerns 1 bestimmt, sondern durch die intrinsischen Eigenschaften des für die Zwischenschicht 4 verwendeten Poly- mers selbst. Das Ausmaß der Polarität der Außenseite der Zwischenschicht 4 ist für die verschiedenen Materialien unterschiedlich, ist aber offenbar selbst für Polyvinylbutyral, das am stärksten wasserabweisende der untersuchten Zwischenschichtmaterialien, ausreichend, um eine Verringerung der Ag- glomerationsneigung nach Anlagerung der monomolekularen Ten- sid-Oberflächenschicht 1 auf der Zwischenschicht 4 zu ermöglichen. Das Tensid bewirkt daher bei allen untersuchten Zwischenschichtmaterialien eine Verringerung der Agglomerationsneigung im Vergleich zu einem Granulat ohne Tensidschicht. Die Wirkung der Tensidschicht ist allerdings am ausgeprägtesten bei den oberflächlich polaren Zwischenschichtmaterialien wie Polyvinylpyrrolidon oder Bellac; die Agglomerationsneigung einer Polyvinylbutyral-Oberflache ist von sich aus bereits so gering, dass auch ohne Tensidschicht, bereits mit einer Struktur gemäß dem ersten Ausführungsbeispiel, die Agglomerationsneigung des Granulats ausreichend unterdrückt wird. Ein Granulat mit Partikeln der in Fig. 3 gezeigten Struktur kann hergestellt werden, indem ein Ausgangspulver aus Keramik, Metall, Polymer oder einem Gemisch dieser Materialien in einem Wirbelbett durch einen Heißluftstrom fluidisiert und eine Zeitlang mit einer fein zerstäubten Lösung des Zwischenschichtmaterials besprüht wird. Das Lösungsmittel verdunstet in dem Heißluftstrom in kürzester Zeit, so dass sich aus Tropfen, die auf die Partikel des Ausgangsmaterials treffen, das gelöste Zwischenschichtmaterial niederschlägt und im Laufe der Behandlung einen geschlossenen Film bildet. Als Lösungsmittel für Polyvinylbutyral kommt, wie oben angegeben ein Alkohol oder Alkoholgemisch in Betracht. Polyvinylpyrro- lidon und Bellac sind in basischen wässrigen Medien löslich, vorzugsweise wird hier als Lösungsmittel eine Lösung von Ammoniak in Wasser verwendet, da diese Lösung gegenüber vielen anderen basischen wässrigen Lösungen den Vorteil hat, rückstandsfrei zu verdampfen.The intermediate layer 4 has a thickness in the order of 0.1 to 10% of the average radius of the particles, ie with an average particle diameter of approximately 20 μm, the layer thickness can expediently be 0.5 μm, for example. Such a layer is many times thicker than a monolayer, the extent of the polarity of the outer surface of the intermediate layer 4 is therefore not determined by the polarity or non-polarity of the material of the core 1, but by the intrinsic properties of the polymer used for the intermediate layer 4 itself The extent of the polarity of the outside of the intermediate layer 4 is different for the different materials, but apparently even for polyvinyl butyral, the most water-repellent of the examined intermediate layer materials, is sufficient to reduce the tendency to agglomerate after the monomolecular surface layer has been attached To enable 1 on the intermediate layer 4. The surfactant therefore reduces the tendency towards agglomeration in all the interlayer materials compared to granules without a surfactant layer. However, the effect of the surfactant layer is most pronounced in the case of the superficial polar interlayer materials such as polyvinylpyrrolidone or Bellac; the tendency to agglomeration of a polyvinylbutyral surface is inherently so low that even without a surfactant layer, even with a structure according to the first exemplary embodiment, the tendency to agglomeration of the granules is sufficiently suppressed. Granules with particles of the structure shown in Fig. 3 can be made by fluidizing a starting powder of ceramic, metal, polymer or a mixture of these materials in a fluidized bed by a hot air stream and spraying for a time with a finely atomized solution of the interlayer material. The solvent evaporates in the hot air stream in a very short time, so that drops that hit the particles of the starting material precipitate the dissolved intermediate layer material and form a closed film in the course of the treatment. As the solvent for polyvinyl butyral, as mentioned above, an alcohol or alcohol mixture is suitable. Polyvinylpyrrolidone and Bellac are soluble in basic aqueous media; a solution of ammonia in water is preferably used as the solvent, since this solution has the advantage over many other basic aqueous solutions that it can be evaporated without residue.
Die Oberflachenschicht aus Tensid wird in analoger Weise wie die Zwischenschicht durch Besprühen der im Wirbelbett fluidi- sierten Partikel mit einer zweiten Lösung erzeugt, die eine wässrige Lösung des Tensids ist. Da Polyvinylbutyral in Wasser nicht löslich ist, wird eine daraus bestehende Zwischen- schicht 4 in diesem zweiten Beschichtungsvorgang nicht angegriffen. Wenn die Zwischenschicht aus Polyvinylpyrrolidon besteht, das in schwachen Säuren und Basen löslich ist, so ist darauf zu achten, dass die Tensidlösung pH-neutral ist. Bei einer Zwischenschicht aus dem basisch löslichen Bellac darf der pH der zweiten Lösung 9,5 nicht überschreiten.The surface layer of surfactant is produced in a manner analogous to the intermediate layer by spraying the fluidized particles in the fluidized bed with a second solution, which is an aqueous solution of the surfactant. Since polyvinyl butyral is not soluble in water, an intermediate layer 4 made of it is not attacked in this second coating process. If the intermediate layer consists of polyvinylpyrrolidone, which is soluble in weak acids and bases, then it must be ensured that the surfactant solution is pH neutral. In the case of an intermediate layer made from the basic soluble Bellac, the pH of the second solution must not exceed 9.5.
Die Herstellung eines Gegenstandes aus dem so erhaltenen Material läuft im wesentlichen in gleicher Weise ab, wie oben mit Bezug auf Fig. 2 beschrieben; als Binderflüssigkeit wird jeweils eine Flüssigkeit verwendet, die Oberflächen- und Zwischenschicht löst, also ein Alkohol im Fall einer Polyvinyl- butyral-Zwischenschicht oder eine basische wässrige Lösung wie etwa Ammoniaklösung im Falle von Zwischenschichten aus Polyvinylpyrrolidon oder Bellac.The manufacture of an article from the material thus obtained proceeds essentially in the same way as described above with reference to FIG. 2; a liquid which dissolves the surface and intermediate layer, that is to say an alcohol in the case of a polyvinyl butyral intermediate layer or a basic aqueous solution, is used as the binder liquid such as ammonia solution in the case of polyvinylpyrrolidone or Bellac interlayers.
Fig. 4 zeigt analog der Fig. 2 einen Schnitt durch eine Schicht des erfindungsgemäßen Granulats nach Aufbringen der Binderflüssigkeit auf den Bereich 3, in dem die Kerne 1 der Granulatpartikel wieder durch Schraffur hervorgehoben sind. Im Innern des Bereichs 3, wo durch durch die Binderflüssigkeit Oberflächen- und Zwischenschichten der Partikel angelöst worden sind, sind die Oberflächenschichten nicht mehr auszumachen, und die Zwischenschichten 4 sind an den Berührungspunkten zwischen den Partikeln verschmolzen. Am Rand des Bereichs 3, dort, wo keine Binderflüssigkeit hingelangt ist, besteht die Oberflachenschicht 2 fort und verhindert eine Ag- glomeration mit benachbarten Partikeln, so dass ein fertiger Gegenstand mit präzise geformten, glatten Oberflächen erhalten wird. FIG. 4 shows, analogously to FIG. 2, a section through a layer of the granulate according to the invention after application of the binder liquid to the area 3 in which the cores 1 of the granulate particles are again highlighted by hatching. In the interior of area 3, where surface and intermediate layers of the particles have been dissolved by the binder liquid, the surface layers can no longer be made out, and the intermediate layers 4 are fused at the points of contact between the particles. At the edge of area 3, where no binder liquid has reached, surface layer 2 persists and prevents agglomeration with neighboring particles, so that a finished article with precisely shaped, smooth surfaces is obtained.

Claims

Patentansprüche claims
1. Granulat für 3D-Binderdruck, welches aus mit einer Oberflachenschicht (2) versehenen Partikeln besteht, d a d u r c h g e k e n n z e i c h n e t , dass die Oberflachenschicht (2) aus einem Polyvinylbuty- ral besteht und eine unpolare Außenfläche aufweist.1. Granules for 3D binder printing, which consists of particles provided with a surface layer (2), so that the surface layer (2) consists of a polyvinylbuteralal and has a non-polar outer surface.
2. Granulat nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass die Dicke der Oberflachenschicht etwa einer Monolage der Monomere entspricht.2. Granules according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the thickness of the surface layer corresponds approximately to a monolayer of the monomers.
3. Granulat nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass die Dicke der Oberflachenschicht etwa 0,1 bis 10 % des mittleren Radius der Partikel beträgt.3. Granules according to claim 1, so that the thickness of the surface layer is approximately 0.1 to 10% of the average radius of the particles.
4. Verfahren zur Herstellung eines Granulats für SD-Binderdruck, d a d u r c h g e k e n n z e i c h n e t , dass auf Ausgangspartikel (1) eine Oberflachenschicht (2) aus einem Polyvinylbutyral aufgebracht wird.4. Process for the production of a granulate for SD binder printing, so that a surface layer (2) made of a polyvinyl butyral is applied to the starting particles (1).
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass die Ausgangspartikel (1) mit einer Lösung in Kontakt ge- bracht werden, die das Material der Oberflachenschicht (2) in gelöster Form enthält, und durch Verdampfen des Lösungsmittels getrocknet werden.5. The method according to claim 4, characterized in that the starting particles (1) are brought into contact with a solution which is the material of the surface layer (2) in dissolved form, and dried by evaporation of the solvent.
6. 3D-Binderdruck-Verfahren zum Herstellen eines Gegenstandes aus einem Granulat, welches aus mit einer Oberflachenschicht (2) versehenen Partikeln besteht, mit den Schritten:6. 3D binder printing process for producing an object from a granulate which consists of particles provided with a surface layer (2), with the steps:
Ausbringen einer Schicht des Granulats auf eine Un- terlage,Spreading a layer of the granulate on a base,
Befeuchten vorgegebener Bereiche (3) der Schicht mit einer Binderflüssigkeit,Moistening predetermined areas (3) of the layer with a binder liquid,
Wiederholen dieser Schritte bis der Gegenstand gebildet ist, d a d u r c h g e k e n n z e i c h n e t , dass ein Granulat mit unpolarer Oberfläche verwendet wird und dass die Binderflüssigkeit unter Flüssigkeiten gewählt wird, in denen die Oberflachenschicht (2) der Partikel des Granulats löslich ist.Repeat these steps until the object is formed, that is, that a granulate with a non-polar surface is used and that the binder liquid is chosen from liquids in which the surface layer (2) of the particles of the granulate is soluble.
7. 3D-Binderdruck-Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass ein Granulat gemäß einem der Ansprüche 1 bis 3 ver- wendet wird.7. 3D binder printing method according to claim 6, characterized in that a granulate according to one of claims 1 to 3 is used.
8. 3D-Binderdruck-Verfahren nach Anspruch 6 oder 7, dadurch gekennzeichnet, daß die Binderflüssigkeit in Ihrer Viskosität, insbeson- dere durch Zugabe von höherwertigen Alkoholen, einstellbar gewählt wird.8. 3D binder printing method according to claim 6 or 7, characterized in that the binder liquid in its viscosity, in particular by adding higher-quality alcohols, is chosen to be adjustable.
9. Gegenstand aus miteinander verbundenen Granulatpartikeln, dadurch gekennzeichnet, dass er aus einem Granulat nach einem der Ansprüche 1 bis 3 oder in einem Verfahren nach einem der Ansprüche 6 bis 8 erhalten ist. 9. An article made of interconnected granulate particles, characterized in that it is obtained from a granulate according to one of claims 1 to 3 or in a process according to one of claims 6 to 8.
EP03740089A 2002-06-18 2003-06-16 Granular material for 3d binder printing, production method and uses therefor Withdrawn EP1513669A1 (en)

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