Filaments for the thermoplastic 3D production of ceramic parts, metal parts or parts based on metal-ceramic composites or material composites

Abstract

A filament for thermoplastic 3D printing of ceramic or metal or metal ceramic composites or material composites by additive manufacturing, made of a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose, and ceramic powder, metal powder and / or metal ceramic powder, said binder system comprising 5-25% by weight of polyethylene, 0.5-4% by weight of stearic acid, 0.1-1.5% by weight of lignin sulfonate and 1-6% by weight of cellulose, based on the amount of filament.

Description

[Technical field]

[0001] The present invention relates to filaments for the thermoplastic 3D manufacturing of ceramic parts, metal parts or metal ceramic composites or material composites. [Background technology]

[0002] Such a method is known in particular as Fused Filament Fabrication, abbreviated as 3D FFF.

[0003] Typically, thermoplastic filaments are fed via an extruder to one or more heated nozzles. A binder or a polymer-based binder system is melted and deposited at the desired location. Thus, by cooling and hardening, layers with a thickness between 0.05 and several mm can be built up. This layer-building scheme can produce parts that are subsequently heat-treated. Usually, a thermal and / or chemical debinding follows first, and then a further heat treatment at higher temperatures for the purpose of sintering. After sintering, the parts acquire their final mechanical, thermomechanical, chemical and functional-technical properties.

[0004] Binders based on polyester, styrene-acrylic polymers, wax and / or polyethylene are common components in binder systems for 3D printer systems and are disclosed in CN104693637B (Patent Document 1), WO2018112263A1 (originally JP2020501941A) (Patent Document 2) or WO2017 / 182209A01 (Patent Document 3).

[0005] US9102114 B1 discloses a method for producing ceramic honeycomb structures, in which precursors containing TiO2 and Al2O3 are mixed with, among other things, a binder to form a paste, which is then extruded into a honeycomb shape, dried and sintered. Binder materials include cellulose, lignin- or lignosulfonate, polyethylene, and stearic acid can be added as a lubricant and plasticizer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] CN104693637B [Patent Document 2] WO2018112263A1(JP2020501941A) [Patent Document 3] WO2017 / 182209A01 [Patent Document 4] US9102114 B1 Summary of the Invention

[0007] The invention relates to a filament according to the independent claim 1, a method for its production and the use of the binder system, advantageous embodiments being contained in the dependent claims.

[0008] The invention comprises a binder system comprising polyethylene, stearic acid, lignin sulfonate and cellulose; and a filament for thermoplastic 3D printing of ceramic or metal or metal ceramic composites or material composites by additive manufacturing, made of ceramic powder, metal powder and / or metal ceramic powder, said binder system comprising 5-25 wt. % polyethylene, 0.5-4 wt. % stearic acid, 0.1-1.5 wt. % lignin sulfonate and 1-6 wt. % cellulose, based on the amount of filament.

[0009] In a preferred embodiment, the binder system additionally comprises 0.01 to 5 wt. % of fine ceramic powder having a d50 of less than 1 μm, based on the amount of filaments.

[0010] In a further preferred embodiment, titanium dioxide, silicon dioxide, iron oxide, lanthanum oxide, strontium oxide, gadolinium oxide, silicon carbide, boron carbide or mixtures thereof are used as finely divided ceramic powders.

[0011] The invention further comprises a method for producing the filaments of the invention, comprising granulating a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose together with ceramic powder, metal powder and / or metal-ceramic powder in a mixer and subsequently extruding at least once through a heatable extruder, followed by grinding the filaments and converting the resulting ground granules again through a heatable extruder to filaments.

[0012] The invention further comprises a method for producing 3D printed parts based on the filaments of the invention, which comprises synthesizing particles from metal and ceramic starting materials by pelletizing or 3D printing or coating processes, which are then converted into filaments in a heatable extruder together with the novel binder and subsequently thermoplastically printed.

[0013] The present invention further comprises the use of a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose for the production of said binder system and filaments made of ceramic powders, metal powders and / or metal ceramic powders for thermoplastic 3D printing of ceramic or metal or metal ceramic composites or material composites by additive manufacturing, said binder system comprising 5 to 25% by weight of polyethylene, 0.5 to 4% by weight of stearic acid, 0.1 to 1.5% by weight of lignin sulfonate and 1 to 6% by weight of cellulose, based on the amount of filament.

[0014] In a preferred embodiment, the binder system used further comprises a d of less than 1 μm, based on the amount of filament. 50 The ceramic powder has a molecular weight of 0.01 to 5% by weight.

[0015] In a further preferred embodiment, titanium dioxide, silicon dioxide, iron oxide, lanthanum oxide, strontium oxide, gadolinium oxide, silicon carbide, boron carbide or mixtures thereof are used as finely divided ceramic powders.

[0016] In embodiments, the binder system for filaments or granular metal for thermoplastic 3D printing of ceramic or metal or metal-ceramic composites or material composites by additive manufacturing consists of polyethylene, stearic acid, lignin sulfonate and cellulose.

[0017] In a further embodiment, the binder system for filaments or granular metals for thermoplastic 3D printing of ceramics or metals or metal-ceramic composites or material composites by additive manufacturing has a d of less than 1 μm when the sintering temperature of the metal is lower than the sintering temperature of the ceramic. 50 The composite material is made of polyethylene, stearic acid, lignin sulfonate and cellulose, together with an additive based on a ceramic powder having the formula:

[0018] In embodiments, advantageously, binder systems are disclosed which, on the one hand, have a high structural stability after debinding or, if possible, a low residual carbon content, and, on the other hand, the sintering temperature, especially in the case of composites made of metal and ceramic, is kept as low as possible without melting the metal or the ceramic (e.g. in the case of the use of refractory metals). As a result, in the case of metal-ceramic composites, the risk of in situ carbide formation is reduced, and, on the other hand, the structural stability of the parts during sintering is maintained, since the use of fine ceramic powders below 1 μm usually reduces the sintering temperature of the ceramic. For structural stability after debinding, in embodiments, the deliberate addition and combination of stearic acid, cellulose and especially lignin sulfonate is utilized in the disclosed binder systems. Advantageously, the novel binder systems are suitable for thermal debinding below 400-500 ° C.

[0019] In embodiments, the binder system comprises 1-6 wt% cellulose, 0.1-1.5 wt% lignin sulfonate, 0.5-4 wt% stearic acid, and 5-25 wt% polyethylene. If the sintering temperature of the metal is lower than the sintering temperature of the ceramic, in embodiments, the thermoplastic binder has a d of less than 1 μm. 50 The composition is made up of polyethylene, stearic acid, lignin sulfonate and cellulose, together with an additive based on a fine ceramic powder having the formula:

[0020] In a further embodiment, the binder system consists of 1-6 wt.% cellulose, 0.1-1.5 wt.% lignin sulfonate, 0.5-4 wt.% stearic acid, 5-25 wt.% polyethylene, and 0.01-5 wt.% fine ceramic powder.

[0021] In embodiments, for example, titanium dioxide, silicon dioxide, iron oxide, lanthanum oxide, silicon carbide, strontium oxide, gadolinium oxide, boron carbide, or mixtures thereof are used as the fine ceramic powder.

[0022] In embodiments, the novel binders can be advantageously used to print both fine-grained (grains less than 100 μm) and coarse-grained (grains 100 μm or greater) parts / components made of ferrous and non-ferrous metals, refractory metals or mixtures thereof, made from ceramic synthetic or natural sources.

[0023] In embodiments, particles can be synthesized from metal and ceramic starting materials, for example by pelletizing granulation or 3D printing or coating processes, which are subsequently converted into filaments, for example in an extruder, together with the novel binder; and subsequently thermoplastically printed, for example using a 3D filament printer.

[0024] In a further embodiment, the filaments are produced with a binder system by granulating said binder system together with ceramic powders, metal powders and / or metal-ceramic powders in a mixer and subsequently extruding at least once through a heatable extruder, subsequently grinding the filaments and converting the resulting ground granules again through a heatable extruder to filaments.

[0025] In a further embodiment, particles are synthesized from metal and ceramic starting materials through a pelletizing or 3D printing process or coating process, then converted into filaments together with said novel binder in a heatable extruder, and subsequently thermoplastically printed to produce 3D printed parts based on filaments containing the binder system.

[0026] In embodiments, debinding is carried out below 500°C and sintering is carried out above 1000°C.

[0027] In a further embodiment, the thermal debinding is carried out according to the following regime: 10 K min -1 up to 370 °C, 30 min at 370 °C, 1 K min -1 up to 50°C.

[0028] In embodiments, the ceramic powders combined with the novel binder for the production of the filaments may be, for example, Al2O3, ZrO2, MgAl2O4, TiO2, CaZrO3, BaZrO3, BaTiO3La2O3, MgO SiO2, SiO2, MgO, Cr2O3, LaCrO3, SiC, Si3N4, BN, B4C, TiB2, TiN, AlN, etc., or mixtures thereof.

[0029] In embodiments, metal powders that are combined with the novel binders for the production of filaments include, for example, iron, steel, steel alloys, Al, Mg, Ti, Ni, Nb, W, Ta, Pt, Si, Cu, Zn, Mn, Sr, La, Co, Cr, and the like. EXAMPLES

[0030] An example is given below.

[0031] [Table 1]

[0032] [Table 2]

[0033] In Tables 1 and 2, binder systems based on polyethylene (Rowalit H150, Rowalit H70 Rowak, Kreitgau-Griessen), stearic acid (≥98%, Carl Roth, Karlsruhe), lignin sulfonate (C12C, Otto Dille, Norderstedt), cellulose powder (Fluka Analytical, Sigma-Aldrich, Taufkirchen), and titanium dioxide (TiO2, d50 Examples are given of mixtures of aluminium oxide-rich magnesium aluminate-spinel (0-20 μm, AR 78, Almatis, Ludwigshafen) with or without steel powder 316L (0-60 μm, Deutche Edelstahl Werke, Witten) and aluminium oxide-rich magnesium aluminate-spinel (0-20 μm, AR 78, Almatis, Ludwigshafen) with or without steel powder 316L (0-60 μm, Deutche Edelstahl Werke, Witten). Advantageously, the combination of TiO2 with composites made of 316L and magnesium aluminate-spinel allows the production of dense (porosity-free) parts even at sintering temperatures up to 1400 ° C under argon protective gas atmosphere.

[0034] For the production of the filaments, a twin-screw extruder (Brabender GmbH, Duisburg) was used. The extruder was equipped with six heating elements, each with an associated thermoelement along the length of the screw. These ensured a very precise control of the extrudate behavior and opened up the possibility of detailed adjustment of the temperature gradient within the extruder for a perfectly homogeneous, application-specific polymerization of the binder material of the 3D printing filament. The extrusion process can be subdivided into four phases: I) powder feeding, II) preheating and premixing, III) melting and polymerization, IV) squeezing and extrusion. In each phase, the temperature of the heating elements was regulated individually. Acquisition of the optimal temperature and speed during extrusion is crucial for successful process stability.

[0035] For the printing process, it is necessary that the 3D printing filament has a certain degree of flexibility and at the same time a sufficient dimensional stability. This depends greatly on the porosity and surface structure of the filament. A perfect homogeneity of the extrudate is required to reduce the porosity of the filament. For this, a uniform distribution of the solid and binder materials as well as a uniform structure of the binder are required. The distribution of the solid and binder materials could be significantly improved by a preceding granulation process. The granulation process was performed in two steps (premixing and granulation) in a laboratory mixer Eirich EL1 (Maschinenfabrik Gustav Eirich, Hartheim, Germany) for up to 700 g of powder material each. The parameters of the granulation process are summarized in Table 3.

[0036] [Table 3]

[0037] During extrusion, at higher temperatures, a reaction occurs between the binder additive and the polyethylene, which in turn results in the formation of a new composite polymer. One objective was to maintain this polymer formation throughout the extrudate to achieve a uniform structure. It was found that the extrusion process had to be carried out four times for each material. In the first step, the granulated powder was extruded, completely melted and homogenized. The product of the first extrusion was then manually crushed and prepared for the second extrusion.

[0038] Mixtures of polyethylene and stearic acid first show signs of softening at temperatures between 110 and 140 °C, depending on the addition of additives. During the growth of the filaments, in particular lignin sulfonates as polymer plasticizers and cellulose nanofibers as structural stabilizers proved to be advantageous additives. These ensured the excellent stability of the filaments and at the same time the retention of flexibility, which is essential for the success of the 3D printing process. These filaments do not show any loss of structural stability after the initial softening at 110-140 °C.

[0039] In FIG. 1, filaments from said binder system are shown at the very front and immediately after them, deformed filaments with, inter alia, wax addition and heat treatment according to the following regime: 10 K min -1 up to 370 °C, 30 min at 370 °C, 1 K min -1 up to 50 °C. The stability of the new filaments makes them suitable for subsequent 3D printing with high requirements for tolerance compliance.

Claims

1. a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose; Ceramic powder, metal powder and / or metal ceramic powder; A filament for thermoplastic 3D printing of ceramic or metal or metal-ceramic composites or material composites by additive manufacturing, comprising The binder system comprises, based on the amount of filaments, 5 to 25% by weight of polyethylene, 0.5 to 4% by weight of stearic acid, 0.1 to 1.5% by weight of lignin sulfonate, and 1 to 6% by weight of cellulose; The filament.

2. The binder system further comprises a d ５０ 2. The filament according to claim 1, characterized in that it contains 0.01 to 5% by weight of a fine ceramic powder having the formula:

3. 3. The filament according to claim 2, characterized in that as fine ceramic powder titanium dioxide, silicon dioxide, iron oxide, lanthanum oxide, strontium oxide, gadolinium oxide, silicon carbide, boron carbide or mixtures thereof are used.

4. 4. A method for producing the filaments according to claim 1, characterized in that a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose is granulated in a mixer together with ceramic powder, metal powder and / or metal-ceramic powder and subsequently extruded at least once through a heatable extruder, followed by grinding the filaments and converting the resulting ground granules again through a heatable extruder to filaments.

5. A method for producing 3D printed parts based on the filaments according to any one of claims 1 to 3, characterized in that particles are synthesized from metal and ceramic starting materials by a pelletizing or 3D printing process or a coating process and then converted into filaments together with the novel binder in a heatable extruder and subsequently printed thermoplastically.

6. 1. Use of a binder system containing polyethylene, stearic acid, lignin sulfonate and cellulose for thermoplastic 3D printing of ceramic or metal or metal ceramic composites or material composites by additive manufacturing and for the production of filaments made of ceramic powders, metal powders and / or metal ceramic powders, wherein the binder system comprises 5-25 wt.-% polyethylene, 0.5-4 wt.-% stearic acid, 0.1-1.5 wt.-% lignin sulfonate and 1-6 wt.-% cellulose, based on the amount of filament.

7. The binder system further comprises a d ５０ 7. The method according to claim 6, characterized in that it contains 0.01 to 5% by weight of a fine ceramic powder having the formula:

8. 8. Use according to claim 7, characterized in that as fine ceramic powder titanium dioxide, silicon dioxide, iron oxide, lanthanum oxide, strontium oxide, gadolinium oxide, silicon carbide, boron carbide or mixtures thereof are used.

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