Tube furnaces for sintering and / or debinding processes

Abstract

The present invention relates to the use of a tube furnace in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC). Further, the present invention relates to a tube furnace for use in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC). Furthermore, the present invention relates to the use of the tube furnace of the present invention in a process for the treatment of at least one three-dimensional green body (GB).

Description

[Technical Field]

[0001] The present invention relates to the use of a tube furnace in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC). Further, the present invention relates to a tube furnace for use in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC). Furthermore, the present invention relates to the use of the tube furnace of the present invention in a process for the treatment of at least one three-dimensional green body (GB). [Background technology]

[0002] A common problem encountered these days is the production of prototypes, spare parts, and models of metal or ceramic bodies, especially those with complex geometries. The production of prototypes, in particular, requires a rapid manufacturing process. There are many different processes known for this so-called "rapid prototyping." One of the most economical is the Fused Filament Fabrication process (FFF), also known as "Fused Deposition Modeling" (FDM).

[0003] Fused Filament Fabrication (FFF) is an additive manufacturing technology. Three-dimensional objects are produced by extruding a thermoplastic material through a nozzle and solidifying the thermoplastic material after extrusion to form layers. The nozzle is heated to heat the thermoplastic material above its melting temperature and / or glass transition temperature, and then the extrusion head deposits the thermoplastic material onto a base to form the three-dimensional object layer by layer. The thermoplastic material is typically selected and its temperature controlled to solidify substantially immediately upon extrusion or ejection onto a base, where multiple layers are built up to form the desired three-dimensional object.

[0004] To form each layer, a drive motor is provided to move the base and / or the extrusion nozzle (discharge head) relative to one another in a predetermined pattern along the X, Y, and Z axes. The FFF process was first described in U.S. Pat. No. 5,121,329.

[0005] Typical materials for producing three-dimensional objects are thermoplastics. The production of three-dimensional metal or ceramic objects by fused filament fabrication is only possible if the metal or ceramic material has a low melting point so that it can be heated and melted by the nozzle. If the metal or ceramic material has a high melting point, it must be fed into the extrusion nozzle in a binder composition. The binder composition typically contains a thermoplastic material. When a mixture of metal or ceramic material in a binder is deposited on a base, the resulting three-dimensional object is a so-called "green body" containing the metal or ceramic material in the binder. To obtain the desired metal or ceramic object, the binder must be removed and the object must finally be sintered. The three-dimensional object formed after binder removal is a so-called "brown body," and the three-dimensional object formed after sintering is a so-called "sintered body." Binder removal is also called "debinding."

[0006] Typically, the sintering and / or debinding process is carried out in a furnace.

[0007] There are various types of furnaces depending on their intended use. One of them is the so-called tube furnace. It has a tubular structure with a heating element on the outside of the tube. The tube can be closed at both ends, open at both ends, or closed at one end and open at the other. Gas-tight tubes and connectors to the tube allow for the creation of a controlled atmosphere inside the tube. Various types of gases at controlled pressure can be used for heating processes, such as sintering and / or debinding processes for printed 3D parts or metal injection molded parts.

[0008] There are a variety of materials available for manufacturing such tubes, and it is important that the tube withstands the process conditions without suffering damage, which may be caused by, for example, thermal or mechanical stress. For sintering and / or debinding processes of 3D printed or metal injection molded parts, it is further desirable for the tube to have an inner diameter greater than 90 mm and a heated length greater than 300 mm, while being capable of operating at temperatures exceeding 1250°C. The term "heated length" in the context of the present invention refers to the effective heated length, which is the section in which the temperature inside the tube deviates from the target temperature by -10 K to +10 K. This section is therefore the section in which a uniform temperature is achieved.

[0009] Nevertheless, the use of metal- or metal-alloy-based materials as tube materials allows for large internal diameters of up to 245 mm without introducing critical thermal stresses, but higher temperatures or negative pressures (vacuum) at higher temperatures lead to tube deformation. Furthermore, debinding processes are often carried out using acids, especially gaseous acids, which can lead to corrosion of tubes made of titanium or titanium alloys, for example. On the other hand, the use of ceramic- or glass-based materials allows for high temperatures above 1250 °C, but critical thermal stresses occur at internal diameters above 90 mm, causing tube damage.

[0010] Currently, no known tube material has an internal diameter of 90 mm or greater and a heated length of 300 mm or greater, and meets all of the desirable criteria, such as being non-corrosive in oxidizing and reducing atmospheres, acidic and alkaline media, being chemically inert, creep resistant, and fatigue resistant at temperatures above 1250°C.

[0011] International patent application WO 2016 / 184776 A1 states that 500W / m 2 A gas-tight multilayer composite tube is described having a heat transfer coefficient of greater than 1 / K and comprising at least two layers: a layer made from a non-porous monolithic oxide ceramic and a layer made from an oxide fiber composite ceramic.

[0012] European Patent Application EP 3 835 639 A1 describes a laminated laminated laminated with at least two layers and a thermal conductivity of 500 W / m 2 A gas-tight multilayer composite tube of greater than 1 / K is described, which has, across the cross section of the wall of the composite tube, an inner layer of non-open porous monolithic oxide ceramic surrounded by an outer layer of oxide fiber composite ceramic, and an electrically conductive system embedded in the wall of the composite tube.

[0013] International Patent Application WO 2019 / 201654 A1 describes a device for sealingly connecting two tubular elements (10, 20), in which an end face of a first tubular element is sealingly connected to an end face of a second tubular element. Each tubular element has a radially outwardly extending collar (12, 22). The second tubular element (20) is made of a ceramic material and its connecting end is at least partially provided with a circumferential support layer. A sleeve made of a ceramic material surrounds and is rigidly connected to the support layer as the collar (22), and a connecting element (30) is connected to the outside of the sleeve. The support layer is made of an oxide ceramic fiber composite material.

[0014] International patent application WO 2020 / 187607 A1 states that the heat transfer coefficient is 500 W / m 2 A gas-tight multilayer composite pipe of more than / K is described, the structure of which has as an inner layer on the cross section of the wall of the composite pipe a non-porous monolithic oxide ceramic, which is surrounded by an outer layer of an oxide fiber composite ceramic, which outer layer has an open porosity of 5%<ε<50%, and the inner surface of the composite pipe has a plurality of recesses facing the outer wall of the composite pipe.

[0015] A drawback of current technology is that oxide ceramic composite reinforcements are only permanently resistant up to approximately 1200°C. Furthermore, oxide ceramic composites lose beneficial mechanical properties such as strength and quasi-ductility. As a result, in this temperature range, oxide ceramic composites become brittle and sensitive to thermal shock. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] WO 2016 / 184776 A1 [Patent Document 2] EP 3 835 639 A1 [Patent Document 3] WO 2019 / 201654 A1 [Patent Document 4] WO 2020 / 187607 A1 Summary of the Invention [Problem to be solved by the invention]

[0017] The object underlying the present invention is therefore to provide an improved tube furnace that can be used in sintering and / or debinding processes and that does not have the above-mentioned drawbacks of the prior art, or only to a significantly reduced extent. [Means for solving the problem]

[0018] This object is solved by a method for the use of a tube furnace in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC).

[0019] Another object of the present invention is a tube furnace for use in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC).

[0020] A further object of the present invention is the use of a tubular furnace according to the invention in a process for the treatment of at least one three-dimensional green body (GB), wherein this process comprises at least the following steps: a) providing at least one three-dimensional green body (GB), wherein the at least one three-dimensional green body (GB) comprises an inorganic powder (IP) and a binder (B); b) providing an acid; c) treating at least one three-dimensional green body (GB) with acid in a tube furnace to obtain at least one three-dimensional Brownian body (BB); and, optionally d) sintering the at least one three-dimensional Brownian body (BB) obtained in step c) in a tubular furnace to obtain at least one three-dimensional sintered body (SB). Includes:

[0021] Surprisingly, it has been found that this is achieved by the use of a tube furnace in a sintering and / or debinding process, wherein the tube furnace comprises a tube (T) comprising an oxide ceramic matrix composite (OCMC), wherein inner diameters of the tube are in the range of 50 mm to 500 mm, more preferably in the range of 90 mm to 400 mm, particularly preferably in the range of 90 mm to 300 mm, and most preferably in the range of 120 mm to 280 mm, and wherein the tube (T) can be heated to achieve a homogeneous temperature in the range of 1250°C to 1500°C over a length of at least 100 mm, preferably over a length of at least 300 mm, without damage and / or corrosion of the tube, while end zones of the tube outside the furnace are at a lower temperature.

[0022] Furthermore, it has surprisingly been found that the tubular furnace of the present invention can also be used in a process for treating at least one three-dimensional green body (GB) with an acid, in particular a gaseous acid, without corrosion of the tubular furnace occurring. The process for treating a three-dimensional green body (GB) with a gaseous acid is also called a catalytic debinding process.

[0023] It is also possible for the debinding process, in particular the catalytic debinding process, and the sintering process to be carried out sequentially or in parallel without equipment exchange or interaction, which allows for a very fast and robust workflow. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows an inner tube (IT) comprising a wall (W) having an inner surface (IS) and an outer surface (OS). [Figure 2]FIG. 2 shows a cross section of an inner tube (IT) including an inner surface (IS) and an outer surface (OS) and a wall (W) having a wall thickness (WT). [Figure 3] FIG. 3 shows a cross section of a tube (T) comprising an inner tube (IT) and an outer layer (OL). DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will now be described in more detail.

[0026] tube furnace A first object of the present invention is the use of a tubular furnace in a sintering and / or debinding process, wherein the tubular furnace comprises a tube (T).

[0027] Tube (T) In a preferred embodiment, the tube (T) comprises an inner tube (IT) and an outer layer (OL), wherein the outer layer (OL) is attached to the inner tube (IT), the inner tube (IT) comprises a non-porous monolithic oxide ceramic, and the outer layer (OL) comprises an oxide ceramic matrix composite (OCMC).

[0028] Preferably, the inner tube (IT) comprises a wall (W) having an inner surface (IS) and an outer surface (OS), wherein an outer layer (OL) is preferably attached to the outer surface (OS) of the wall (W) of the inner tube (IT). The outer layer (OL) may cover the outer surface (OS) of the wall (W) of the inner tube (IT) over the entire length of the inner tube (IT) or over a portion of the axis of the inner tube (IT).

[0029] Figure 1 shows an inner tube (IT) comprising a wall (W) having an inner surface (IS) and an outer surface (OS). Figure 3 shows a cross section of a tube (T) comprising an inner tube (IT) and an outer layer (OL), where the outer layer (OL) is attached to the outer surface (OS) of the wall (W) of the inner tube (IT).

[0030] If the outer layer (OL) covers only the outer surface (OS) of the wall (W) of the inner tube (IT), i.e., over part of the axis of the inner tube (IT), the advantages are that the cost of the tube (T) is lower and heat transfer in the high temperature region in the center of the tube (T) is improved.

[0031] The wall (W) of the inner tube (IT) typically has a wall thickness (WT). The inner tube (IT) can have any desired wall thickness (WT). Preferably, the wall thickness (WT) of the inner tube (IT) is in the range of 0.5 to 45 mm, more preferably in the range of 1 to 25 mm, and most preferably in the range of 3 to 15 mm.

[0032] FIG. 2 shows a cross section of an inner tube (IT) including an inner surface (IS) and an outer surface (OS) and a wall (W) having a wall thickness (WT).

[0033] The outer layer (OL) can also have any desired thickness, preferably in the range of 0.5 to 5 mm, more preferably in the range of 0.5 to 4 mm.

[0034] The total thickness of the wall thickness (WT) of the inner tube (IT) and the outer layer (OL) can also be in any desired range, and is preferably in the range of 1 to 50 mm, more preferably in the range of 1.5 to 29 mm, and most preferably in the range of 3.5 to 19 mm.

[0035] Preferably, the tubular furnace is equipped with a heating element on the outside of the tube (T). The tubular furnace can include any desired heating element. Preferably, the tubular furnace includes a metallic heating element.

[0036] The tube (T) preferably comprises two ends, where the tube (T) is closed at both ends, open at both ends, or one closed end and the other open end.

[0037] The inner diameter of the inner tube (IT) can have any desired range, and is preferably in the range of 50 mm to 500 mm, more preferably in the range of 90 mm to 400 mm, particularly preferably in the range of 90 mm to 300 mm, and most preferably in the range of 120 mm to 280 mm.

[0038] In a preferred embodiment, the tube (T) is heated over a length of 100 mm to 1000 mm, preferably 300 mm to 600 mm.

[0039] As defined above, the term "heated length" in the context of the present invention means the effective heated length, which is the section of the tube (T) where the temperature inside the tube (T) deviates from the target set temperature by -10 K to +10 K. This section is therefore the section where a uniform temperature is achieved.

[0040] The tube (T) can be heated to any desired temperature, preferably to a temperature in the range of 15°C to 1500°C, more preferably to a temperature in the range of 100°C to 1500°C, and most preferably to a temperature in the range of 1250°C to 1500°C.

[0041] The tube (T) preferably comprises an inner tube (IT) and an outer layer (OL).

[0042] Inner tube (IT) The inner tube (IT) comprises a non-porous monolithic oxide ceramic. Preferably, the inner tube (IT) consists of a non-porous monolithic oxide ceramic.

[0043] Non-porous monolithic oxide ceramic The non-porous monolithic oxide ceramic may be any non-porous monolithic oxide ceramic known to those skilled in the art.

[0044] In the context of the present invention, the term "non-porous" means that the porosity of the oxide ceramic is preferably <10%, more preferably <4%, where porosity is defined as the ratio of the void volume of the oxide ceramic to the total volume of the oxide ceramic x 100%.

[0045] In the context of the present invention, the term "monolithic" means that the inner tube (IT) comprising the non-porous oxide ceramic is preferably prepared as one continuous piece from the non-porous oxide ceramic. The manufacturing process of monolithic ceramics is known in the art and is described, for example, in Informationzentrum Technische Keramik, IZTK (Hrsg.) (1999). Brevier Technische Keramik.

[0046] The non-porous monolithic oxide ceramic preferably comprises at least 90 wt. %, more preferably at least 95 wt. %, and most preferably at least 97 wt. % aluminum oxide (Al2O3) and mullite (Al2O3), based on the total weight of the non-porous monolithic oxide ceramic. 4+2x Si 2-2x O 10-x ; x≈0.4). As non-porous monolithic oxide ceramics it is possible to use, in particular, Haldenwanger Pythagoras 1800Z™, Pythagoras 1800 (mullite), Alsint 99.7™, Kyocera Degussit® AL23 or Degussit® AL24 (aluminum oxide).

[0047] However, it is also possible that the non-porous monolithic oxide ceramic is at least one compound selected from the group consisting of ZrO2, YO3 and MgO. Furthermore, it is also possible that the non-porous monolithic oxide ceramic contains a significant amount of a non-oxidizing compound, such as a carbide or nitride, for example, SiC, Si3N4, AlN.

[0048] The density of the non-porous monolithic oxide ceramic is preferably greater than the density of the oxide ceramic matrix composite (OCMC). The density of the non-porous monolithic oxide ceramic is preferably 1000 to 7000 kg / m 3 range, more preferably 2000 to 5000 kg / m 3 For example, in the case of mullite, it is in the range of 2800 kg / m 3 , and 3700 kg / m for aluminum oxide (Al2O3). 3 and the purity is over 99.7%.

[0049] Outer layer (OL) The outer layer (OL) comprises an oxide ceramic matrix composite (OCMC), and preferably consists of an oxide ceramic matrix composite (OCMC).

[0050] Oxide Ceramic Matrix Composites (OCMC) The oxide ceramic matrix composite (OCMC) preferably comprises: a matrix (M) containing ceramic oxide particles (P), and - Fiber (F) Including, Here, fibers (F) are embedded between ceramic oxide particles (P) in a matrix (M) in the form of wires, sheets, or a three-dimensional woven structure.

[0051] The ceramic oxide particles (P) are usually present in the form of a sintered body, which means that they exist as a solid block.

[0052] In a more preferred embodiment, the oxide ceramic matrix composite (OCMC) comprises: a matrix (M) containing ceramic oxide particles (P), and - Fiber (F) Made up of Here, fibers (F) are embedded between ceramic oxide particles (P) in a matrix (M) in the form of wires, sheets, or a three-dimensional woven structure.

[0053] The density of the oxide ceramic matrix composite (OCMC) is preferably 500 to 3,000 kg / m 3 The range is.

[0054] Matrix (M) The matrix (M) contains ceramic oxide particles (P), and preferably consists of ceramic oxide particles (P).

[0055] The ceramic oxide particles (P) can in principle comprise any desired ceramic oxide, and are preferably particles comprising an oxide of at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te, or a mixture of these oxides.

[0056] In the context of the present invention, the term "oxide of at least one element" means that the oxide is selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te. or that the oxide contains two or more elements from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te. An example of an oxide comprising two or more elements from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te is Al2SiO5.

[0057] The oxide ceramic particles (P) are more preferably particles containing an oxide of at least one element selected from the group consisting of Ti, Zr, Hf, Cr, Fe, Al, Si, Na, and K, and most preferably particles containing an oxide of at least one element selected from the group consisting of Zr, Al, and Si.

[0058] In a particularly preferred embodiment, the oxide ceramic particles (P) are particles comprising an oxide of at least one element selected from the group consisting of Zr, Al, Si.

[0059] In a most preferred embodiment, the ceramic oxide particles (P) comprise a mixture of aluminum oxide and silicon oxide, preferably the ceramic oxide particles (P) consist of a mixture of aluminum oxide and silicon oxide.

[0060] Fiber (F) The oxide ceramic matrix composite (OCMC) preferably comprises fibers (F).

[0061] As fibers (F), in principle, all known fibers can be used. Preferably, the fibers (F) are ceramic fibers (F), more preferably non-oxidized and / or oxidized ceramic fibers (F), most preferably oxidized ceramic fibers (F).

[0062] The oxidized ceramic fibers (F) preferably comprise an oxide of at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te, or a mixture of these oxides.

[0063] In a more preferred embodiment, the oxidized ceramic fibers (F) comprise a compound selected from the group consisting of alumina, such as NEXTEL 610 or OxCeFi A99, mullite, a mixture of alumina and mullite, such as NEXTEL 720 or OxCeFi M75, zirconia-toughened alumina (ZTA) and zirconia-toughened mullite (ZTM), and more preferably, the oxidized ceramic fibers (F) consist of a compound selected from the group consisting of alumina, mullite, a mixture of alumina and mullite, zirconia-toughened alumina (ZTA) and zirconia-toughened mullite (ZTM).

[0064] The non-oxidized fibers (F) preferably contain at least one compound selected from the group consisting of boron nitride, tungsten carbide, aluminum nitride, barium titanate, lead zirconate titanate, and boron carbide.

[0065] Of course, the fibers (F) can also contain an oxide of at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earth elements, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se, and Te, or a mixture of these oxides, and / or at least one compound selected from the group consisting of boron nitride, tungsten carbide, aluminum nitride, barium titanate, lead zirconate titanate, and boron carbide. In this case, the fibers (F) have a non-oxidized ceramic portion and an oxidized ceramic portion.

[0066] The fibers (F) can have any desired diameter, preferably in the range of 5 to 15 μm, more preferably in the range of 10 to 12 μm.

[0067] The fibers (F) are embedded between the ceramic oxide particles (P) of the matrix (M) in the form of wires, sheets, or a three-dimensional woven structure, preferably embedded between the ceramic oxide particles (P) of the matrix (M) in the form of sheets or a three-dimensional woven structure.

[0068] An example of a linear woven structure is a fiber bundle, which is a combination of many fibers (F). Such a fiber bundle can be wound onto a bobbin (roving).

[0069] Examples of sheet-like textile structures include woven fabrics, knitted fabrics, braided fabrics, and nonwoven fabrics processed from fibers (F), for example, linear fiber structures such as fiber bundles.

[0070] An example of a three-dimensional textile structure (main body structure) is a fiber hose which is also fabricated from fibers (F), for example linear fiber structures such as fiber bundles.

[0071] Suitable rovings are NEXTEL 610 1500 denier, NEXTEL 610 4500 denier, NEXTEL 610 10000 denier, NEXTEL 610 20000 denier, NEXTEL 720 1500 denier and 10000 denier.

[0072] Suitable sheet-like or three-dimensional woven structures are NEXTEL 610 DF11, DF-13-4500, DF19, NEXTEL 720 EF11 and EF19.

[0073] Fiber (F) is i) the same composition as the ceramic oxide particles (P), or ii) Components different from oxide ceramic particles (P) may include:

[0074] The tube (T) preferably undergoes at least the following steps i) and ii) i) providing an inner tube (IT) comprising a non-porous monolithic oxide ceramic; and ii) attaching the outer layer (OL) to the inner tube (IT), preferably by lamination techniques; It is prepared by a process comprising:

[0075] Preferably, step i) comprises at least the following steps: i-1) preparing non-porous monolithic oxide ceramic particles; i-2) preparing a three-dimensional green body from the particles prepared in step i-1), for example by molding, extrusion or isostatic pressing, preferably by extrusion or isostatic pressing; i-3) Sintering the three-dimensional green body obtained in step i-2) to obtain an inner tube (IT). Includes:

[0076] The attachment of the outer layer (OL) to the inner tube (IT) according to step ii) preferably comprises the following steps: ii-1) providing fibers (F), wherein the fibers (F) are in the form of a line, a sheet, or a three-dimensional woven structure, preferably a sheet or a three-dimensional woven structure; ii-2) infiltrating the fibers (F) with a slurry to obtain infiltrated fibers (IF), the slurry comprising water, ceramic oxide particles (P) and a binder (B1); ii-3) laminating the inner tube (IT) with the infiltrated fiber (IF) obtained in step ii-2) to obtain a laminated inner tube (LIT); ii-4) drying the laminated inner tube (LIT) obtained in step ii-3) at a temperature in the range of 40 to 150°C, preferably at a temperature in the range of 60 to 100°C, to remove at least a part of the water, thereby obtaining a dried laminated inner tube (DLIT); ii-5) sintering the dried laminated inner tube (DLIT) obtained in step ii-4) at a temperature in the range of 1100 to 1300°C, preferably in the range of 1150 to 1250°C, to completely remove the binder (B1) and water, thereby obtaining a tube (T), wherein the tube (T) comprises an inner tube (IT) and an outer layer (OL), the outer layer (OL) is attached to the inner tube (IT), the inner tube (IT) comprises a non-porous monolithic oxide ceramic, and the outer layer (OL) comprises an oxide ceramic matrix composite (OCMC). This is done by lamination techniques including:

[0077] Steps ii-1) to ii-5) can be repeated until a desired thickness of the outer layer (OL) is obtained.

[0078] The binder (B1) is preferably at least one compound selected from the group consisting of ZrO2, Al2O3 and SiO2.

[0079] The infiltration in step ii-2) is preferably carried out by dipping or knife coating, more preferably by knife coating.

[0080] Another object of the invention is also a tube furnace for use in sintering and / or debinding processes, wherein the tube furnace comprises a tube (T) containing an oxide ceramic matrix composite (OCMC).

[0081] For the tube furnaces, the above-mentioned embodiments and preferences regarding the use of at least one tube furnace in the sintering and / or debinding process apply analogously.

[0082] The tube furnace is used in a sintering and / or debinding process, preferably in a debinding process of at least one three-dimensional green body (GB) to obtain at least one three-dimensional Brownian body (BB) and / or in a sintering process of at least one three-dimensional Brownian body (BB) to obtain at least one three-dimensional sintered body (SB).

[0083] Use of a tube furnace in the processing of at least one three-dimensional green body (GB) Therefore, another object of the present invention is the use of a tube furnace according to the invention in a process for treating at least one three-dimensional green body (GB), which process comprises at least the following steps: a) providing at least one three-dimensional green body (GB), wherein the at least one three-dimensional green body (GB) comprises an inorganic powder (IP) and a binder (B); b) providing an acid; c) treating at least one three-dimensional green body (GB) with acid in a tube furnace to obtain at least one three-dimensional Brownian body (BB); and, optionally d) sintering the at least one three-dimensional Brownian body (BB) obtained in step c) in a tubular furnace to obtain at least one three-dimensional sintered body (SB). Includes:

[0084] The process for treating at least one three-dimensional green body (GB) according to the present invention comprises at least steps a) to c) and optionally step d).

[0085] Steps a) and b) can be performed simultaneously, but it is also possible for step a) to be performed before step b), or for step b) to be performed before step a). Step c) is preferably performed after steps a) and b), and optional step d) is preferably performed after step c), more preferably directly after step c).

[0086] Process a) In step a), at least one three-dimensional green body (GB) is provided.

[0087] The term "at least one three-dimensional green body" according to the present invention means precisely one three-dimensional green body as well as a mixture of two or more three-dimensional green bodies.

[0088] At least one three-dimensional green body (GB) comprises an inorganic powder (IP) and a binder (B), wherein the binder (B) is (b1) Contains at least one polyoxymethylene (POM).

[0089] Preferably, the at least one three-dimensional green body (GB) comprises 30-70 vol. % of inorganic powder (IP) and 30-70 vol. % of binder (B), based on the total volume of the at least one three-dimensional green body (GB), where the sum of the vol. % of inorganic powder (IP) and binder (B) is generally 100%.

[0090] More preferably, the at least one three-dimensional green body (GB) comprises 45-65 vol. % of inorganic powder (IP) and 35-55 vol. % of binder (B), based on the total volume of the at least one three-dimensional green body (GB), where the sum of the vol. % of inorganic powder (IP) and binder (B) is generally 100%.

[0091] Particularly preferably, the at least one three-dimensional green body (GB) comprises 48 to 60 vol. % of inorganic powder (IP) and 40 to 52 vol. % of binder (B), based on the total volume of the at least one three-dimensional green body (GB), where the sum of the vol. % of inorganic powder (IP) and binder (B) is generally 100%.

[0092] In one embodiment of the present invention, at least one three-dimensional green body (GB) comprises at least one dispersant. Preferably, at least one three-dimensional green body (GB) comprises 0.1 to 5% by volume of at least one dispersant, particularly preferably 0.2 to 4% by volume of at least one dispersant, and most preferably 0.5 to 2% by volume of at least one dispersant, based on the total volume of the at least one three-dimensional green body (GB).

[0093] It is clear to those skilled in the art that when at least one three-dimensional green body (GB) comprises at least one dispersant, the sum of the volume percentages of inorganic powder (IP), binder (B) and at least one dispersant is generally 100%.

[0094] "At least one dispersant" according to the present invention means exactly one dispersant, but also a mixture of two or more dispersants.

[0095] Examples of suitable dispersants include oligomeric polyethylene oxides with low molecular weights of 200 to 600 g / mol, stearic acid, stearamide, hydroxystearic acid, fatty alcohols, fatty acid esters, sulfonates, and block copolymers of ethylene oxide and propylene oxide, and also particularly preferably polyisobutylene.

[0096] The components of at least one three-dimensional green body (GB) are described in detail below.

[0097] Inorganic powder (IP) At least one three-dimensional green body (GB) comprises an inorganic powder (IP).

[0098] As the inorganic powder (IP), a known inorganic powder (IP) can be used. Preferably, a sinterable inorganic powder (IP) is used. More preferably, the inorganic powder (IP) is a powder of at least one inorganic material selected from the group consisting of a metal, a metal alloy, and a ceramic material. Most preferably, the inorganic powder (IP) is a metal or a metal alloy, and particularly preferably, the inorganic powder (IP) is a metal.

[0099] The term "inorganic powder (IP)" refers not only to one type of inorganic powder (IP) but also to a mixture of two or more types of inorganic powders (IP). The same applies to the term "inorganic material." The term "inorganic material" refers to both exactly one type of inorganic material and a mixture of two or more types of inorganic materials. The term "metal" refers to both exactly one type of metal and a mixture of two or more metals. The metal in the present invention can be selected from any metal in the periodic table that is stable under the conditions of the fused filament fabrication process and capable of forming a three-dimensional object. Preferably, the metal is selected from the group consisting of aluminum, yttrium, titanium, zirconium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, carbonyl iron powder (CIP), cobalt, nickel, copper, silver, zinc, magnesium, tin, and cadmium. More preferably, the metal is selected from the group consisting of titanium, niobium, chromium, molybdenum, tungsten, manganese, iron, carbonyl iron powder (CIP), nickel, and copper. Particularly preferably, the metal is selected from the group consisting of titanium, iron and carbonyl iron powder (CIP).

[0100] Carbonyl iron powder (CIP) is a high-purity iron powder prepared by chemical decomposition of refined iron pentcarbide.

[0101] The term "metal alloy" refers to both precisely one metal alloy and a mixture of two or more metal alloys. In the context of the present invention, the term "metal alloy" refers to a solid solution or partial solid solution that exhibits metallic properties and contains a metal and other elements. As mentioned above, "metal" refers to precisely one metal and a mixture of two or more metals. The same applies to "another element." "Another element" refers to precisely one other element and a mixture of two or more other elements. A solid-solution metal alloy exhibits a microstructure with a single solid phase, while a partial-solution metal alloy exhibits two or more solid phases. These two or more solid phases may be homogeneously distributed in the metal alloy or may be heterogeneously distributed in the metal alloy. Metal alloys can be prepared according to any process known to those skilled in the art. For example, a metal can be melted and other elements can be added to the molten metal. However, inorganic powders (IPs) can also contain a metal and other elements without the prior preparation of a metal alloy. Metal alloys can be formed during the process of preparing a three-dimensional object.

[0102] The above-described embodiments and preferences apply for the metal. The other element can be selected from the above-described metals, provided that the other element is different from the metal contained in the metal alloy. The other element can be selected from any element of the periodic table that forms a stable metal alloy under the conditions of the fused filament production process, or that is stable under the conditions of the fused filament production process or forms a stable alloy with the metal. In preferred embodiments of the present invention, the other element is selected from the group consisting of the aforementioned metals, boron, carbon, silicon, phosphorus, sulfur, selenium, and tellurium. Particularly preferably, at least one other element is selected from the group consisting of the aforementioned metals, boron, carbon, silicon, phosphorus, and sulfur. Preferably, the metal alloy according to the present invention comprises steel.

[0103] "Ceramic material" refers to exactly one ceramic material and to mixtures of two or more ceramic materials. In the context of the present invention, the term "ceramic material" refers to a non-metallic compound of a metal or a first metalloid and a non-metal or a second metalloid.

[0104] "Metal" means exactly one metal and a mixture of two or more metals. The same applies to "nonmetal," "first metalloid," and "second metalloid." "Nonmetal" means exactly one nonmetal and a mixture of two or more nonmetals. "First metalloid" means exactly one first metalloid and a mixture of two or more first metalloids. "Second metalloid" means exactly one second metalloid and a mixture of two or more second metalloids.

[0105] Non-metals are known per se to those skilled in the art. The non-metal according to the present invention can be selected from any non-metal of the periodic table. Preferably, at least one non-metal is selected from the group consisting of carbon, nitrogen, oxygen, phosphorus and sulfur.

[0106] Metalloids are well known to those skilled in the art. The first metalloid and the second metalloid can be selected from any metalloid in the periodic table. Preferably, the first metalloid and / or the second metalloid is selected from the group consisting of boron and silicon. It will be clear that the first metalloid and the second metalloid are different from each other. For example, if the first metalloid is boron, the second metalloid is selected from other metalloids in the periodic table of elements other than boron.

[0107] In one embodiment of the present invention, the ceramic material is selected from the group consisting of oxides, carbides, borides, nitrides and silicides. In a preferred embodiment, the ceramic material is selected from the group consisting of MgO, CaO, SiO2, Na2O, Al2O3, ZrO2, YO3, SiC, Si3N4, TiB and AlN. Particularly preferably, the ceramic material is selected from the group consisting of Al2O3, ZrO2 and YO3.

[0108] To prepare inorganic powders (IPs), inorganic materials must be pulverized. Any method known to those skilled in the art can be used to pulverize the inorganic materials. For example, the inorganic materials can be pulverized. For example, pulverization can be performed using a classifier mill, a hammer mill, or a ball mill.

[0109] Carbonyl iron powder (CIP) is prepared by chemical decomposition of purified pentavalent carbonyl iron.

[0110] The particle size of the inorganic powder (IP) used is preferably 0.1 to 80 μm, particularly preferably 0.5 to 50 μm, and more preferably 0.1 to 30 μm, as measured by laser diffraction.

[0111] Binder (B) The at least one three-dimensional green body (GB) also comprises a binder (B), wherein the binder (B) is preferably (b1) at least one polyoxymethylene (POM) Includes:

[0112] In a preferred embodiment, the binder (B) is (b1) 50 to 96% by weight of at least one polyoxymethylene (POM), based on the total weight of the binder (B); (b2) 2 to 35% by weight of at least one polyolefin (PO), based on the total weight of the binder (B); (b3) 2 to 40% by weight of at least one further polymer (FP), based on the total weight of the binder (B). wherein the sum of the weight percent of components (b1), (b2) and (b3) is generally 100%.

[0113] In a more preferred embodiment, the binder (B) comprises: As component (b1), 60 to 90% by mass of at least one polyoxymethylene (POM), As component (b2), 3 to 20% by mass of at least one polyolefin (PO), and as component (b3), 5 to 30% by weight of at least one further polymer (FP), wherein the sum of the mass % of components (b1), (b2) and (b3) is typically 100%.

[0114] Particularly preferably, the binder (B) is, based on the total weight of the binder (B), as component (b1), 70 to 85% by weight of at least one polyoxymethylene (POM); As component (b2), 4 to 15% by mass of at least one polyolefin (PO), and as component (b3), 10 to 26% by weight of at least one further polymer (FP), wherein the sum of the weight percent of components (b1), (b2) and (b3) is 100%.

[0115] According to the present invention, component (b1) is different from component (b2), component (b2) is different from component (b3), and component (b3) is different from component (b1). However, components (b1), (b2) and (b3) may contain the same building blocks, e.g., different further building blocks and / or different molecular weights.

[0116] Components (b1), (b2) and (b3) of the binder (B) are described in detail below.

[0117] Component (b1) / Polyoxymethylene (POM) For the purposes of the present invention, the terms "component (b1)" and "at least one polyoxymethylene (POM)" are synonymous and are used interchangeably throughout the present invention.

[0118] Preferably, the binder (B) comprises 50 to 96% by mass, more preferably 60 to 90% by mass, and most preferably 70 to 85% by mass of at least one polyoxymethylene (POM), based on the total mass of the binder (B).

[0119] "At least one polyoxymethylene (POM)" in the present invention means exactly one type of polyoxymethylene (POM) and a mixture of two or more types of polyoxymethylene (POM). For the purposes of the present invention, the term "polyoxymethylene (POM)" encompasses both polyoxymethylene (POM) itself, i.e., polyoxymethylene (POM) homopolymer, as well as polyoxymethylene (POM) copolymers and polyoxymethylene (POM) terpolymers. Polyoxymethylene (POM) homopolymers are usually prepared by polymerization of monomers selected from the formaldehyde source (b1a). The term "formaldehyde source (b1a)" refers to a substance capable of releasing formaldehyde under the reaction conditions for the preparation of polyoxymethylene (POM). The formaldehyde source (b1a) is preferably selected from the group of cyclic or linear formals, in particular from the group consisting of formaldehyde and 1,3,5-trioxane. 1,3,5-trioxane is particularly preferred.

[0120] Polyoxymethylene (POM) copolymers are known per se and commercially available. They are usually prepared by polymerization of trioxane as the main monomer. In addition, comonomers are used in combination. The main monomers are preferably selected from trioxane and other cyclic or linear formals or other formaldehyde sources (b1a). The expression "main monomers" is intended to indicate that the proportion of these monomers in the total amount of monomers, i.e., the sum of the main monomers and the comonomers, is greater than the proportion of the comonomers in the total amount of monomers. Very generally, the polyoxymethylene (POM) according to the invention has at least 50 mol % of -CHO- repeating units in the main polymer chain. Suitable polyoxymethylene (POM) copolymers are in particular those containing the repeating unit -CHO- and 0.01 to 20 mol %, in particular 0.1 to 10 mol %, very particularly preferably 0.5 to 6 mol % of repeating units of formula (I):

[0121] [ka]

[0122] (In the formula, R 1 ~R 4 are each independently selected from the group consisting of H, C1-C4-alkyl, and halogen-substituted C1-C4-alkyl; R 5 is a chemical bond, (-CR 5a R 5b -) group, and (-CR 5a R 5b O-) groups, where R 5a and R 5b are each independently selected from the group consisting of H and unsubstituted or at least monosubstituted C1-C4-alkyl, the substituents are selected from the group consisting of F, Cl, Br, OH and C1-C4-alkyl; where n is 0, 1, 2 or 3).

[0123] If n is 0, R 5 is the chemical bond between adjacent carbon and oxygen atoms. 5 (-CR 5a R 5b -) group, (-CR 5a R 5b The oxygen atom (O) of the (O-) group is bonded to another carbon atom (C) of formula (I), not to the oxygen atom (O) of formula (I). In other words, formula (I) does not include peroxide compounds. The same applies to formula (II).

[0124] In the context of the present invention, the definition of C1-C4-alkyl refers, for example, to the radical R 1 ~R 4As defined above, means that the substituent (radical) is an alkyl radical having from 1 to 4 carbon atoms. The alkyl radical may be straight-chained or branched, and optionally cyclic. Alkyl radicals having both cyclic and straight-chain components fall within this definition as well. Examples of alkyl radicals include methyl, ethyl, n-propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0125] In the context of the present invention, the definition of halogen-substituted C1-C4-alkyl is used, for example, in the radical R 1 ~R 4 means that the C1-C4-alkyl, as defined above, is substituted with at least one halogen. Halogen is F (fluorine), Cl (chlorine), Br (bromine) and I (iodine).

[0126] The repeating units of formula (I) can be advantageously introduced into polyoxymethylene (POM) copolymers by ring-opening of cyclic ethers as first comonomers (b1b). First comonomers (b1b) of general formula (II) are preferred:

[0127] [ka]

[0128] where R 1 ~R 5 and n has the meaning defined above for general formula (I).

[0129] Examples of first comonomers (b1b) include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepane (=butanediol formal, BUFO), as cyclic ethers, and linear oligoformals or polyformals, such as polydioxolanes or polydioxepanes. 1,3-Dioxolanes and 1,3-dioxepanes are particularly preferred first comonomers (b1b), with 1,3-dioxepanes being highly preferred as first comonomers (b1b).

[0130] Likewise suitable are polyoxymethylene (POM) polymers obtained by reacting a formaldehyde source with a first comonomer (b1b) and a second comonomer (b1c), the addition of which in particular allows the preparation of polyoxymethylene (POM) terpolymers.

[0131] The second comonomer (b1c) is preferably selected from the group consisting of compounds of formula (III) and compounds of formula (IV),

[0132] [ka]

[0133] (wherein Z represents a chemical bond, a (—O—) group, and a (—OR 6 -O-) groups, where R 6 is selected from the group consisting of unsubstituted C1-C8-alkylene and C3-C8-cycloalkylene).

[0134] In the context of the present invention, the definition C1-C8-alkylene means C1-C8-alkanediyl. C1-C8-Alkylene is a hydrocarbon having two free valences and a number of carbon atoms from 1 to 8. C1-C8-Alkylene according to the present invention can be branched or unbranched.

[0135] In the context of the present invention, the definition C3-C8-cycloalkylene means C3-C8-cycloalkanediyl. C3-C8-cycloalkylene is a cyclic hydrocarbon having two free valences and a number of carbon atoms from 3 to 8. Hydrocarbons having two free valences, cyclic and linear components, and a number of carbon atoms from 3 to 8 also fall under this definition.

[0136] Preferred examples of the second comonomer (b1c) include ethylene diglycidyl, diglycidyl ethers, and diethers prepared from a glycidyl compound and formaldehyde, dioxane, or trioxane in a 2:1 molar ratio, and similarly, diethers prepared from 2 moles of a glycidyl compound and 1 mole of an aliphatic diol having 2 to 8 carbon atoms, such as the diglycidyl ethers of ethylene glycol, 1,4-butanediol, 1,3-butanediol, 1,3-cyclobutanediol, 1,2-propanediol, and 1,4-cyclohexanediol.

[0137] In a preferred embodiment, component (b1) is a polyoxymethylene (POM) copolymer prepared by polymerization of at least 50 mol % of a formaldehyde source, 0.01 to 20 mol % of at least one first comonomer (b1b), and 0 to 20 mol % of at least one second comonomer (b1c).

[0138] In a particularly preferred embodiment, component (b1) is a polyoxymethylene (POM) copolymer prepared by polymerization of 80 to 99.98 mol %, preferably 88 to 99 mol %, of a formaldehyde source, 0.1 to 10 mol %, preferably 0.5 to 6 mol % of at least one first comonomer (b1b), and 0.1 to 10 mol %, preferably 0.5 to 6 mol % of at least one second comonomer (b1c).

[0139] In a further preferred embodiment, component (b1) is a polyoxymethylene (POM) copolymer prepared by polymerization of at least 50 mol % of a formaldehyde source, 0.01 to 20 mol % of at least one first comonomer (b1b) of general formula (II), and 0 to 20 mol % of at least one second comonomer (b1c) selected from the group consisting of compounds of formula (III) and compounds of formula (IV).

[0140] Another subject of the invention is therefore a process in which component (b1) is a polyoxymethylene (POM) copolymer prepared by polymerization of - at least 50 mol % of a formaldehyde source, - 0.01 to 20 mol % of at least one first comonomer (b1b) of general formula (II)

[0141] [ka]

[0142] (In the formula, R 1 ~R 4are each independently selected from the group consisting of H, C1-C4-alkyl, and halogen-substituted C1-C4-alkyl; R 5 is a chemical bond, (-CR 5a R 5b -) group, and (-CR 5a R 5b O-) groups, where R 5a and R 5b are each independently selected from the group consisting of H and unsubstituted or at least monosubstituted C1-C4-alkyl, the substituents are selected from the group consisting of F, Cl, Br, OH and C1-C4-alkyl; n is 0, 1, 2, or 3); and - 0 to 20 mol % of at least one second comonomer (b1c) selected from the group consisting of compounds of formula (III) and compounds of formula (IV)

[0143] [ka]

[0144] (wherein Z represents a chemical bond, a (—O—) group, and a (—OR 6 -O-) groups, where R 6 is selected from the group consisting of unsubstituted C1-C8-alkylene and C3-C8-cycloalkylene).

[0145] In a preferred embodiment of the present invention, at least a portion of the OH end groups of the polyoxymethylene (POM) are capped. Methods for capping OH end groups are known to those skilled in the art. For example, the OH end groups can be capped by etherification or esterification.

[0146] Preferred polyoxymethylene (POM) copolymers have a melting point of at least 150° C. and a weight average molecular weight M in the range of 5000 g / mol to 300000 g / mol, preferably 6000 g / mol to 150000 g / mol, particularly preferably 7000 g / mol to 100000 g / mol. W It has.

[0147] Particularly preferred are polydispersities (M W / M n ) is a polyoxymethylene (POM) copolymer.

[0148] Mass average molecular weight (M W ) and number average molecular weight (M n Measurement of ) is commonly performed by gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC).

[0149] Methods for preparing polyoxymethylene (POM) are known to those skilled in the art.

[0150] Component (b2) / Polyolefin (PO) Furthermore, the binder (B) may contain a component (b2).

[0151] Preferably, the binder (B) contains 2 to 35% by weight, more preferably 3 to 20% by weight, most preferably 4 to 15% by weight of the component (b2).

[0152] Preferably, component (b2) is at least one polyolefin (PO). In the present invention, "at least one polyolefin (PO)" means exactly one polyolefin (PO) and a mixture of two or more polyolefins (PO).

[0153] Polyolefins (PO) are known per se and commercially available. They are usually prepared by polymerization of C2-C8 alkene monomers, preferably C2-C4 alkene monomers.

[0154] In the context of the present invention, C2-C8-alkene means an unsubstituted or at least monosubstituted hydrocarbon having 2 to 8 carbon atoms and at least one carbon-carbon double bond (C-C double bond). "At least one carbon-carbon double bond" means exactly one carbon-carbon double bond, as well as two or more carbon-carbon double bonds.

[0155] In other words, C2-C8-alkene means that a hydrocarbon having 2 to 8 carbon atoms is unsaturated. The hydrocarbon may be branched or unbranched. Examples of C2-C8-alkene having one C-C double bond include ethene, propene, 1-butene, 2-butene, 2-methyl-propene (=isobutylene), 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-hexene, 3-hexene, and 4-methyl-1-pentene. Examples of C2-C8-alkene having two or more C-C double bonds include allene, 1,3-butadiene, 1,4-pentadiene, 1,3-pentadiene, and 2-methyl-1,3-butadiene (=isoprene).

[0156] When the C2-C8 alkene has one C-C double bond, the polyolefin (PO) prepared from these monomers is linear. When the C2-C8 alkene has two or more double bonds, the polyolefin (PO) prepared from these monomers can be crosslinked. Linear polyolefins (PO) are preferred.

[0157] It is also possible to use polyolefin (PO) copolymers, which are prepared by using different C2-C8-alkene monomers during the preparation of the polyolefin (PO).

[0158] Preferably, the polyolefin (PO) is selected from the group consisting of polymethylpentene, poly-1-butene, polyisobutylene, polyethylene and polypropylene, particularly preferred are polyethylene and polypropylene and their copolymers known to those skilled in the art and commercially available.

[0159] Polyolefins (PO) can be prepared by any polymerization process known to those skilled in the art, preferably by free radical polymerization, such as emulsion polymerization, bead polymerization, solution polymerization, or bulk polymerization. Initiators that can be used are free radical initiators, such as peroxide compounds and azo compounds, depending on the type of monomer and polymerization, and the amount of initiator is generally in the range of 0.001 to 0.5% by weight based on the monomer.

[0160] Component (b3) / Further Polymer (FP) The binder (B) may comprise a further polymer (FP) as component (b3).

[0161] For the purposes of the present invention, the terms "component (b3)" and "further polymer (FP)" are synonymous and are used interchangeably throughout the present invention.

[0162] Preferably, the binder (B) contains 2 to 40% by mass, more preferably 5 to 30% by mass, most preferably 10 to 26% by mass of component (b3) based on the total mass of the binder (B).

[0163] Component (b3) according to the present invention is at least one further polymer (FP). "At least one further polymer (FP)" in the context of the present invention means exactly one further polymer (FP) and mixtures of two or more further polymers (FP).

[0164] As already mentioned above, the at least one further polymer (FP) is different from component (b1) polyoxymethylene (POM) and component (b2) polyolefin (PO).

[0165] According to the present invention, the at least one further polymer (FP) is preferably selected from the group consisting of polyethers, polyurethanes, polyepoxides, polyamides, vinyl aromatic polymers, poly(vinyl esters), poly(vinyl ethers), poly(alkyl(meth)acrylates) and copolymers thereof.

[0166] Preferably, the at least one further polymer (FP) of component (b3) is selected from the group consisting of poly(C2-C6-alkylene oxides), aliphatic polyurethanes, aliphatic uncrosslinked epoxides, aliphatic polyamides, vinyl aromatic polymers, poly(vinyl esters) of aliphatic C1-C8-carboxylic acids, poly(vinyl ethers) of C1-C8-alkyl vinyl ethers, C 1~8 -alkyl poly(alkyl(meth)acrylates) and copolymers thereof.

[0167] The preferred at least one further polymer (FP) is described in more detail below.

[0168] The polyether comprises repeating units of formula (V)

[0169] [ka]

[0170] (In the formula, R 11 ~R 14 are each independently selected from the group consisting of H, C1-C4-alkyl, and halogen-substituted C1-C4-alkyl; R 15 is a chemical bond, (-CR 15a R 15b -) group, and (-CR 15a R 1515b O-) groups, where R 15a and R 15b are each independently selected from the group consisting of H and unsubstituted or at least monosubstituted C1-C4-alkyl, the substituents are selected from the group consisting of F, Cl, Br, OH and C1-C4-alkyl; where n is 0, 1, 2 or 3).

[0171] If n is 0, R 15 is the chemical bond between adjacent carbon and oxygen atoms. 15 (-CR 15a R 15b -) group, (-CR 15a R 15b The oxygen atom (O) of the (O-) group is bonded to another carbon atom (C) of formula (V), not to the oxygen atom (O) of formula (V). In other words, formula (V) does not include peroxide compounds. The same applies to formula (VI).

[0172] Typical polyethers and their preparation are known to those skilled in the art.

[0173] Preferred polyethers according to the present invention are, for example, poly(alkylene glycols), also known as poly(alkylene oxides).

[0174] Polyalkylene oxides and their preparation are known to those skilled in the art. Polyalkylene oxides are usually synthesized by the interaction of water, a dihydric or polyhydric alcohol, and a cyclic ether of general formula (VI), i.e., an alkylene oxide. The reaction is catalyzed by an acidic or basic catalyst. This reaction is the so-called ring-opening polymerization of the cyclic ether of general formula (VI):

[0175] [ka]

[0176] (In the formula, R 11 ~R 15 has the meaning defined above for general formula (V).

[0177] A preferred poly(alkylene oxide) according to the present invention is derived from a monomer of general formula (VI) having 2 to 6 carbon atoms in the ring. In other words, the poly(alkylene oxide) is preferably a poly(C2-C6-alkylene oxide). Particularly preferred is a poly(alkylene oxide) derived from a monomer selected from the group consisting of 1,3-dioxolane, 1,3-dioxepane, and tetrahydrofuran (IUPAC name: oxolane). In other words, the poly(alkylene oxide) is particularly preferably selected from the group consisting of poly-1,3-dioxolane, poly-1,3-dioxepane, and polytetrahydrofuran.

[0178] In one embodiment, the poly(alkylene oxide) can include OH end groups. In another embodiment, at least a portion of the OH end groups of the poly(alkylene oxide) can be capped. Methods for capping OH end groups are known to those skilled in the art. For example, the OH end groups can be capped by etherification or esterification.

[0179] The mass average molecular weight of the poly(alkylene oxide) is preferably in the range of 1,000 to 150,000 g / mol, particularly preferably in the range of 1,500 to 120,000 g / mol, and more preferably in the range of 2,000 to 100,000 g / mol.

[0180] Polyurethanes are polymers containing carbamate units. Polyurethanes and their preparation are known to those skilled in the art.

[0181] In the present invention, aliphatic polyurethanes are preferred. These can be prepared, for example, by polyaddition of an aliphatic polyisocyanate with an aliphatic polyhydroxy compound. Among polyisocyanates, diisocyanates of general formula (VII) are preferred:

[0182] [ka]

[0183] (In the formula, R 7 is a substituted or unsubstituted C1-C 20 -Alkylene or C4-C 20 -cycloalkylene, where the substituents are selected from the group consisting of F, Cl, Br and C1-C6-alkyl.

[0184] Preferably, R 7 is substituted or unsubstituted C2 to C 12 -Alkylene or C6-C 15 -cycloalkylene.

[0185] In the context of the present invention, C1 to C 20 -Alkylene is defined as C1-C 20 -alkanediyl. C1~C 20 -Alkylene is a hydrocarbon having two free valences and a number of carbon atoms from 1 to 20. 20 The alkylene may be branched or unbranched.

[0186] In the context of the present invention, C4 to C 20 -Cycloalkylene is defined as C4-C 20 -Cycloalkanediyl. 20 -Cycloalkylene is a cyclic hydrocarbon having two free valences and 4 to 20 carbon atoms. Hydrocarbons having two free valences, cyclic and linear components, and 4 to 20 carbon atoms fall under this definition as well.

[0187] Preferred diisocyanates are selected from the group consisting of hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 1,2-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane and isophorone diisocyanate (IUPAC name: 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane).

[0188] Diisocyanates can also be used in the form of oligomers, for example dimers or trimers. Instead of polyisocyanates, it is also possible to use conventional blocked polyisocyanates which are obtained from the above-mentioned isocyanates, for example by addition reaction with phenols or caprolactam.

[0189] Suitable polyhydroxy compounds for the preparation of aliphatic polyurethanes are, for example, polyesters, polyethers, polyesteramides or polyacetals or mixtures thereof.

[0190] Suitable chain extenders for the preparation of polyurethanes are low molecular weight polyols, especially diols and polyamines, especially diamines, or water.

[0191] The polyurethanes are preferably thermoplastic and therefore essentially uncrosslinked, i.e., can be repeatedly melted without noticeable signs of decomposition. Their reduced specific viscosity, measured in dimethylformamide at 30°C, is as a rule between 0.5 and 3 dL / g, preferably between 1 and 2 dL / g.

[0192] A polyepoxide contains at least two epoxide groups, also known as glycidyl or oxirane groups. "At least two epoxide groups" means exactly two epoxide groups, as well as three or more epoxide groups.

[0193] Polyepoxides and their preparation are known to those skilled in the art. For example, polyepoxides can be prepared by reacting epichlorohydrin (IUPAC name: chloromethyloxirane) with diols, polyols, or dicarboxylic acids. Polyepoxides prepared in this manner are polyethers with epoxide end groups.

[0194] Another possibility for preparing polyepoxides is the reaction of glycidyl (meth)acrylate (IUPAC name: oxiran-2-ylmethyl-2-methylprop-2-enoate) with polyolefins or polyacrylates, resulting in polyolefins or polyacrylates with epoxy end groups.

[0195] Preferably, aliphatic uncrosslinked polyepoxides are used, with copolymers of epichlorohydrin and 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A) being particularly preferred.

[0196] Component (b3) (at least one further polymer (FP)) may also comprise a polyamide. Aliphatic polyamides are preferred.

[0197] Suitable polyamides generally have an intrinsic viscosity of 150 to 350 mL / g, preferably 180 to 275 mL / g, measured here from a 0.5% by weight solution of the polyamide in 96% by weight sulfuric acid at 25°C according to ISO 307.

[0198] Preferred polyamides are semi-crystalline or amorphous polyamides.

[0199] Examples of suitable polyamides as component (b3) are those derived from lactams having 7 to 13 ring members. Other suitable polyamides are those obtained by reacting dicarboxylic acids with diamines.

[0200] Examples of polyamides derived from lactams include polyamides derived from polycaprolactam, polycaprylolactam, and / or polylaurolactam.

[0201] When using polyamides obtainable from dicarboxylic acids and diamines, the dicarboxylic acids that can be used are alkanedicarboxylic acids having 6 to 14 carbon atoms, preferably 6 to 10 carbon atoms. Aromatic dicarboxylic acids are also suitable.

[0202] Examples which may be mentioned here as dicarboxylic acids are adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and also terephthalic acid and / or isophthalic acid.

[0203] Examples of suitable diamines include alkanediamines having 4 to 14 carbon atoms, especially alkanediamines having 6 to 8 carbon atoms, and also aromatic diamines such as m-xylylenediamine, di(4-aminophenyl)methane, di(4-aminocyclohexyl)methane, 2,2-di(4-aminophenyl)propane, 2,2-di(4-aminocyclohexyl)propane, and 1,5-diamino-2-methylpentane.

[0204] Other suitable polyamides are those obtainable by copolymerization of two or more of the above and below mentioned monomers, as well as mixtures of several polyamides in any desired mixing ratio.

[0205] Preferred polyamides are polyhexamethylene adipamide, polyhexamethylene sebacamide, polycaprolactam, and also nylon 6 / 6,6, in particular having a proportion of caprolactam units of 75 to 95% by weight.

[0206] Particularly preferred are mixtures of nylon-6 with other polyamides, in particular nylon-6 / 6,6 (PA 6 / 66), and especially mixtures of 80 to 50% by weight of PA 6 and 20 to 50% by weight of PA 6 / 66, where the PA 6 / 66 contains 75 to 95% by weight of caprolactam units, based on the total weight of the PA 6 / 66 in the mixture.

[0207] The following non-exclusive list includes the polyamides described above and other suitable polyamides and monomers that may also be included: AB polymer: PA 4 Pyrrolidone PA 6 ε-caprolactam PA 7 Ethanol Lactam PA 8 Caprylolactam PA 9 9-aminopelargonic acid PA 11 11-aminoundecanoic acid PA 12 Laurolactam AA / BB polymer: PA 46 Tetramethylenediamine, Adipic Acid PA 66 Hexamethylenediamine, Adipic Acid PA 69 Hexamethylenediamine, Azelaic Acid PA 610 Hexamethylenediamine, Sebacic Acid PA 612 Hexamethylenediamine, Decanedicarboxylic acid PA 613 Hexamethylenediamine, Undecanedicarboxylic Acid PA 1212 1,12-Dodecanediamine, Decanedicarboxylic acid PA 1313 1,13-Diaminotridecane, undecanedicarboxylic acid PA 6T Hexamethylenediamine, Terephthalic Acid PA MXD6 m-xylylenediamine, adipic acid PA 6I Hexamethylenediamine, Isophthalic Acid PA 6-3-T Trimethylhexamethylenediamine, Terephthalic Acid PA 6 / 6T (see PA 6 and PA 6T) PA 6 / 66 (see PA 6 and PA 66) PA 6 / 12 (see PA 6 and PA 12) PA 66 / 6 / 610 (see PA 66, PA 6 and PA 610) PA 6I / 6T (see PA 6I and PA 6T) PA PACM 6 Diaminodicyclohexylmethane, Adipic Acid PA PACM 12 Diaminodicyclohexylmethane, Laurolactam PA 6I / 6T / PACMT PA 6I / 6T+Diaminodicyclohexylmethane PA 12 / MACMI Laurolactam, Dimethyldiaminodicyclohexylmethane, Isophthalic Acid PA 12 / MACMT Laurolactam, Dimethyldiaminodicyclohexylmethane, Terephthalic Acid PA PDA-T Phenylenediamine, Terephthalic Acid.

[0208] Preferred polyamides are PA 6, PA 66, and PA PACM 6.

[0209] Vinyl aromatic polymers are polyolefins having unsubstituted or at least monosubstituted styrene as a monomer unit. Suitable substituents are, for example, C1-C6 alkyl, F, Cl, Br, and OH. Preferred vinyl aromatic polymers are selected from the group consisting of polystyrene, poly-α-methylstyrene, and copolymers thereof having up to 30% by weight of a comonomer selected from the group consisting of acrylic acid esters, acrylonitrile, and methacrylonitrile.

[0210] Vinyl aromatic polymers are commercially available and known to those skilled in the art, and their preparation is also known to those skilled in the art.

[0211] Preferably, the vinyl aromatic polymer is prepared by free radical polymerization, such as emulsion polymerization, bead polymerization, solution polymerization or bulk polymerization. Possible initiators can be free radical initiators such as peroxy compounds and azo compounds, depending on the monomer and type of polymerization, and the amount of initiator is generally in the range of 0.001 to 0.5% by weight, based on the monomer.

[0212] Poly(vinyl esters) and their preparation are known to those skilled in the art. Poly(vinyl esters) are preferably prepared by polymerization of vinyl esters. In a preferred embodiment of the present invention, the vinyl esters are vinyl esters of aliphatic C1-C6 carboxylic acids. Preferred monomers are vinyl acetate and vinyl propionate. These monomers form poly(vinyl acetate) and poly(vinyl propionate) polymers.

[0213] Poly(vinyl ether) is prepared by polymerization of vinyl ether monomers. Poly(vinyl ether) and its preparation are known to those skilled in the art. In a preferred embodiment, the vinyl ether is an aliphatic C1-C8 alkyl ether vinyl ether. Preferred monomers are methyl vinyl ether and ethyl vinyl ether, which form poly(methyl vinyl ether) and poly(ethyl vinyl ether) during polymerization.

[0214] Preferably, the poly(vinyl ether) is prepared by free radical polymerization, such as emulsion polymerization, bead polymerization, solution polymerization, suspension polymerization, or bulk polymerization. Possible initiators can be free radical initiators such as peroxy compounds and azo compounds, depending on the monomer and type of polymerization, and the amount of initiator is generally in the range of 0.001 to 0.5% by weight based on the monomer.

[0215] The poly(alkyl(meth)acrylate) of the present invention includes poly(alkyl acrylate), poly(alkyl methacrylate), and copolymers thereof. The poly(alkyl(meth)acrylate) comprises units derived from a monomer of formula (VIII):

[0216] [ka]

[0217] where R 8 is selected from the group consisting of H and C1-C8 alkyl; R 9 is a radical of formula (IX),

[0218] [ka]

[0219] (In the formula, R 10 is C1~C 14 alkyl).

[0220] Preferably, R8 is selected from the group consisting of H and C1-C4-alkyl, particularly preferably R 8 is H or methyl. Preferably, R 10 is C1-C8-alkyl, and particularly preferably R 10 is methyl or ethyl.

[0221] R in formula (VIII) 8 is H and R 9 is a radical of formula (IX), and R 10 When is methyl, the monomer of formula (VIII) is methyl acrylate.

[0222] R in formula (VIII) 8 is H and R 9 is a radical of formula (IX), and R 10 When is ethyl, the monomer of formula (VIII) is ethyl acrylate.

[0223] R in formula (VIII) 8 is methyl and R 9 is a radical of formula (IX), the monomer of formula (VI) is a methacrylic acid ester.

[0224] The poly(alkyl(meth)acrylate) preferably contains 40 to 100 mass% of methacrylic acid ester as a monomer, particularly preferably 70 to 100 mass% of methacrylic acid ester, and more preferably 80 to 100 mass% of methacrylic acid ester, based on the total amount of the poly(alkyl(meth)acrylate).

[0225] In another preferred embodiment, the poly(alkyl(meth)acrylate) contains, as a monomer, 20 to 100% by mass of methyl acrylate, ethyl acrylate, or a mixture thereof, preferably 40 to 100% by mass of methyl acrylate, ethyl acrylate, or a mixture thereof, particularly preferably 50 to 100% by mass of methyl acrylate, ethyl acrylate, or a mixture thereof, each based on the total amount of the poly(alkyl(meth)acrylate).

[0226] Such polymers of the monomer of formula (VIII) and further monomers can be prepared by conventional, preferably free-radical, polymerization, such as emulsion polymerization, bead polymerization, solution polymerization, or bulk polymerization (see Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Vol. 1, pp. 330-342, Vol. 18, pp. 720-755, J. Wiley; H. Rauch-Puntigam, Th. Voelker, Acryl- und Methacrylverbindungen). Depending on the type of monomer and polymerization, possible initiators are free-radical initiators such as peroxy compounds and azo compounds. The amount of initiator is generally in the range of 0.001 to 0.5% by weight, based on the monomers.

[0227] Suitable initiators for emulsion polymerization are, for example, peroxodisulfates, and suitable redox systems for bulk polymerization are peroxides, such as dibenzoyl peroxide or dilauroyl peroxide, as well as azo compounds, such as azobisisobutyrodinitrile, as well as for solution or bead polymerization. The molecular weight can be controlled using conventional regulators, in particular mercaptans, such as dodecyl mercaptan.

[0228] Preferably, the polymerization is carried out at elevated temperatures, for example above 50°C. W) is generally in the range of 2000 to 5,000,000 g / mol, preferably 20,000 to 3,000,000 g / mol (determined by light scattering; see HoubenWeyl, Methoden der Org. Chemie, 4th edition, Volume 14 / 1, Georg Thieme-Verlag Stuttgart 1961).

[0229] Those skilled in the art know that the monomers described above for the preparation of components (b1), (b2) and (b3) may change their structure during the polymerization reaction. As a result, the building blocks of the polymer are not the same as the monomers from which they are derived. However, those skilled in the art know which monomers correspond to which building blocks of the polymer.

[0230] Under the conditions of compounding or processing by injection molding or melt filament production, substantially no transacetalization occurs between the polyoxymethylene (POM) of component (b1) and the at least one further polymer (FP) of component (b3), i.e. substantially no exchange of comonomer units occurs.

[0231] Three-dimensional green body The at least one three-dimensional green body (GB) can be prepared by any method known to those skilled in the art, for example, an additive manufacturing process such as a fused filament fabrication process or injection molding. Preferably, the at least one three-dimensional green body (GB) is prepared by a fused filament fabrication process.

[0232] Fused filament fabrication processes for producing at least one three-dimensional green body (GB) are well known in the art and are described in detail in the above cited documents. Fused filament fabrication processes are also referred to as 3D printing processes. The filaments can include continuous filaments, rods, pellets, and / or powders.

[0233] Preferably, the fused filament manufacturing process comprises the following steps: i) supplying a mixture (M) to a nozzle, the mixture (M) comprising an inorganic powder (IP) and a binder (B), the binder (B) comprising at least one polyoxymethylene (POM); ii) Mixture (M) at temperature (T M ) and iii) depositing the mixture (M) in a build chamber using layer-based additive techniques to form at least one three-dimensional green body (GB); Includes:

[0234] The above-mentioned embodiments and preferences regarding at least one three-dimensional green body (GB) comprising an inorganic powder (IP) and a binder (B), wherein the binder (B) comprises at least one polyoxymethylene (POM), apply equally to the mixture (M).

[0235] The mixture (M) can be prepared by any method known to those skilled in the art. Preferably, the mixture (M) is produced by melting the binder (B) and mixing it with the inorganic powder (IP) and, if necessary, at least one dispersant. For example, the binder (B) can be melted in a twin-screw extruder, preferably at a temperature of 150 to 220°C, in particular 170 to 200°C. The inorganic powder (IP) is then metered in the required amount into the molten stream of the binder (B) at the same temperature range. The inorganic powder (IP) advantageously contains at least one dispersant on its surface. However, the mixture (M) of the present invention can also be produced by melting the binder (B) and, optionally, at least one dispersant in the presence of the inorganic powder (IP) at a temperature of 150 to 220°C, preferably 170 to 200°C.

[0236] A particularly preferred device for metering the inorganic powder (IP) is arranged in a heatable metal cylinder and comprises as an essential element a transport screw which transports the inorganic powder (IP) into the melt of the binder (B). The above-described process has the advantage over mixing the components at room temperature and then extruding at elevated temperature that degradation of the polyoxymethylene (POM) used as binder as a result of the high shear forces that occur in this variant is largely avoided.

[0237] Step b) In step b) an acid is provided.

[0238] Suitable acids are, for example, inorganic acids that are gaseous at room temperature or can be vaporized below the temperature of step c). Examples include hydrogen halides and nitric acid. Hydrogen halides include hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen iodide. Suitable organic acids are those with a boiling point of less than 130°C at atmospheric pressure, such as formic acid, acetic acid, trifluoroacetic acid, and mixtures thereof. Acids with a boiling point greater than 130°C, such as methanesulfonic acid, can also be used when administered as a mixture with a low-boiling acid and / or water. Preferred acids are, for example, nitric acid, a 10% by weight solution of oxalic acid in water, or a 50% by volume mixture of methanesulfonic acid in water.

[0239] Additionally, BF3 and its adducts with inorganic ethers can be used as acids.

[0240] When using a carrier gas, the carrier gas is generally passed through an acid and pre-charged with acid. The carrier gas thus charged with acid is then heated to the temperature at which step c) is carried out. This temperature is preferably higher than the charging temperature to avoid condensation of the acid.

[0241] Preferably, the temperature at which step c) is carried out is at least 1° C., particularly preferably at least 5° C., most preferably at least 10° C. higher than the loading temperature.

[0242] Preferably, the acid is mixed into the carrier gas by a metering device and the mixed gas is heated to a temperature at which the acid can no longer condense, preferably at least 1°C, particularly preferably at least 5°C, most preferably at least 10°C above the sublimation and / or vaporization temperature of the acid and / or carrier gas.

[0243] Generally, the carrier gas is any gas that is inert under the reaction conditions of the debinding process. The preferred carrier gas according to the present invention is nitrogen.

[0244] In a particularly preferred embodiment, in step b), 0.01 to 5.0 wt. % of anhydrous oxalic acid is provided, more preferably 0.05 to 2.5 wt. % and most preferably 0.1 to 1.5 wt. % of anhydrous oxalic acid, based on the total mass of the at least one three-dimensional green body (GB).

[0245] The purity of the anhydrous oxalic acid is preferably 95% or more, more preferably 98% or more.

[0246] Thus, the anhydrous oxalic acid preferably contains at most 5% by weight, more preferably at most 2% by weight, most preferably at most 1% by weight, and particularly preferably 0% by weight, of water, based on the total weight of the anhydrous oxalic acid.

[0247] Process c) In step c), at least one three-dimensional green body (GB) is treated with acid in a tube furnace to obtain at least one three-dimensional Brownian body (BB).

[0248] By carrying out step c), a portion of the binder (B) is preferably removed. Preferably, in step c), the binder (B) is removed to an extent of at least 90% by mass, more preferably at least 95% by mass, based on the total mass of the binder (B) contained in the at least one three-dimensional green body (GB) provided in step a). This can be confirmed, for example, by the height of the mass reduction.

[0249] After removal of the binder (B) in step c), the resulting three-dimensional object is called a "three-dimensional Brownian body." The three-dimensional Brownian body contains the inorganic powder (IP) and the portion of the binder (B) that was not removed during debinding. Those skilled in the art know that a three-dimensional Brownian body containing a ceramic material as the inorganic powder (IP) is also called a three-dimensional white body. However, for the purposes of the present invention, the terms "three-dimensional Brownian body" and "three-dimensional white body" are used synonymously and are interchangeable.

[0250] In a preferred embodiment, the at least one three-dimensional Brownian body (BB) formed in step c) comprises 90-100 vol. % of the inorganic powder (IP) and 0-10 vol. % of the binder (B), preferably 95-100 vol. % of the inorganic powder (IP) and 0-5 vol. % of the binder (B), based on the total volume of the at least one three-dimensional Brownian body (BB).

[0251] It is known to those skilled in the art that at the temperatures during step c), the inorganic powder (IP) contained in the at least one three-dimensional green body (GB) can undergo chemical and / or physical reactions, in particular the particles of the inorganic powder (IP) can fuse and the inorganic powder can undergo a solid-state phase transformation.

[0252] The same applies to binder (B). During step c), the composition of binder (B) can change.

[0253] Consequently, in one embodiment of the present invention, the inorganic powder (IP) and / or binder (B) contained in at least one three-dimensional green body (GB) is different from the inorganic powder (IP) and / or binder (B) contained in the three-dimensional Brownian body (BB) obtained in step c) of the method.

[0254] The debinding process before the sintering process is important to extract part of the binder matrix. There are various methods for debinding, such as thermal, solvent dissolution, and chemical. One type of chemical debinding process is the so-called catalytic debinding process, where the binder polymer is decomposed by the use of gaseous acids.

[0255] In a particularly preferred embodiment, in step c) at least one three-dimensional green body (GB) is treated with anhydrous oxalic acid at a temperature (T1) of <140° C. in the presence of an inert gas.

[0256] In this case, preferably in step c) the at least one three-dimensional green body (GB) is treated with anhydrous oxalic acid at a temperature (T1) between 110 and 135°C, more preferably at a temperature (T1) between 110 and 130°C.

[0257] The inert gas can be any gas that is substantially free of oxygen and water, and is preferably selected from the group consisting of hydrogen, nitrogen, and the noble gases, and more preferably selected from nitrogen and argon.

[0258] Step c) is carried out in a tube furnace according to the invention.

[0259] In a preferred embodiment, anhydrous oxalic acid and at least one three-dimensional green body (GB) are placed in a tubular furnace of the present invention, which is preferably heated to a temperature (T1) of <140°C, which is lower than the sublimation temperature of anhydrous oxalic acid, more preferably a temperature (T1) of 110-135°C, and most preferably a temperature (T1) of 110-130°C.

[0260] Step d) Optionally, an additional step d) may be carried out.

[0261] Preferably, step c) is followed by step d), in which at least one three-dimensional Brownian body (BB) is sintered to form at least one three-dimensional sintered body (SB). Method step d) is also called sintering. For the purposes of the present invention, the terms "method step d)" and "sintering" are synonymous and are used interchangeably throughout the present invention.

[0262] The three-dimensional object after sintering is a three-dimensional sintered body (SB). The three-dimensional sintered body (SB) contains the inorganic powder (IP) and is substantially free of the binder (B).

[0263] According to the present invention, "substantially free of binder (B)" means that the three-dimensional sintered body (SB) contains less than 5% by volume, preferably less than 2% by volume, particularly preferably less than 0.5% by volume, and most preferably less than 0.01% by volume of binder (B), based on the total volume of the three-dimensional sintered body (SB).

[0264] Those skilled in the art know that inorganic powders (IP) are sintered together during the sintering process to obtain a sintered inorganic powder. Furthermore, during the sintering process, the inorganic powders (IP) may undergo chemical and / or physical reactions. As a result, the inorganic powders (IP) contained in the three-dimensional Brownian body (BB) are usually different from the sintered inorganic powders contained in the three-dimensional sintered body (SB).

[0265] In one embodiment of the present invention, after process step c) and before process step d), the three-dimensional Brownian body (BB) obtained in process step c) is heated preferably at a temperature of 250 to 700°C, particularly preferably at 250 to 600°C, for preferably 0.1 to 12 hours, particularly preferably 0.3 to 6 hours, in order to completely remove residual binder (B).

[0266] The temperature, duration and atmosphere during step d) of the method depend on the inorganic powder (IP) contained in the mixture (M). The temperature program, duration and atmosphere of the sintering process are generally adapted to the needs of the inorganic powder (IP) contained in the mixture (M). Suitable conditions for step d) of the method are known to those skilled in the art.

[0267] Generally, step d) of the process is carried out under an atmosphere of a gas inert to the inorganic powder (IP) and the binder (B). Typical inert gases are, for example, nitrogen and / or argon.

[0268] Depending on the inorganic powder (IP) contained in the mixture (M), it is also possible to carry out step d) of the process in air, under vacuum or under a hydrogen atmosphere.

[0269] The temperature (T2) in step d) of the method is, for example, generally in the range of 750 to 1600°C, preferably 800 to 1500°C, particularly preferably 850 to 1450°C.

[0270] Step d) is carried out in a tube furnace of the present invention, where the tube furnace is preferably the same as the tube furnace in which step c) is carried out.

Claims

1. 1. A method of using a tube furnace in a sintering and / or debinding process, said tube furnace comprising a tube (T) comprising an oxide ceramic matrix composite (OCMC).

2. 2. The method of claim 1, wherein the tube (T) comprises an inner tube (IT) and an outer layer (OL), the outer layer (OL) is attached to the inner tube (IT), the inner tube (IT) comprises a non-porous monolithic oxide ceramic, and the outer layer (OL) comprises the oxide ceramic matrix composite (OCMC).

3. 3. The method of claim 1 or 2, wherein the tube (T) comprises two ends, the tube (T) being closed at both ends, open at both ends, or one closed end and the other open end.

4. The method according to claim 2 or 3, wherein the inner diameter of the inner tube (IT) is in the range of 50 mm to 500 mm.

5. Use according to any one of claims 1 to 4, wherein the tube (T) is heated over a length of between 100 mm and 1000 mm, preferably between 300 mm and 600 mm.

6. Use according to any one of claims 1 to 5, wherein the tube (T) is heated to a temperature in the range of 1250°C to 1500°C.

7. The oxide ceramic matrix composite (OCMC) a matrix (M) containing ceramic oxide particles (P), and - Fiber (F) Including, 7. The method of claim 1, wherein the fibers (F) are embedded between the ceramic oxide particles (P) of the matrix (M) in the form of wires, sheets, or a three-dimensional woven structure.

8. 8. The method according to claim 7, wherein the ceramic oxide particles (P) are particles comprising an oxide of at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, Pd, Cu, Ag, Au, Cd, In, TI, Pb, P, As, Sb, Bi, S, Se and Te, or a mixture of these oxides.

9. The fibers (F) are ceramic fibers (F), preferably non-oxidized and / or oxidized ceramic fibers (F), more preferably oxidized ceramic fibers (F), and the oxidized ceramic fibers (F) are preferably selected from the group consisting of Be, Mg, Ca, Sr, Ba, rare earths, Th, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, B, Al, Ga, Si, Ge, Sn, Li, Na, K, Rb, Cs, Re, Ru, Os, Ir, Pt, Rh, 9. The use according to claim 7 or 8, wherein the oxidized ceramic fibers (F) comprise an oxide of at least one element selected from the group consisting of Pd, Cu, Ag, Au, Cd, In, Ti, Pb, P, As, Sb, Bi, S, Se and Te, or a mixture of these oxides, more preferably wherein the oxidized ceramic fibers (F) comprise a compound selected from the group consisting of alumina, mullite, a mixture of alumina and mullite, zirconia toughened alumina (ZTA) and zirconia toughened mullite (ZTM).

10. Use according to any one of claims 7 to 9, wherein the fibres (F) have a diameter in the range of 5 to 15 μm, preferably in the range of 10 to 12 μm.

11. 11. Use according to any one of claims 1 to 10, wherein the tubular furnace is provided with heating elements on the outside of the tube (T).

12. The non-porous monolithic oxide ceramic is at least 97% by weight of aluminum oxide (Al ２ O ３ 12. The method of claim 11, comprising at least one compound selected from the group consisting of ammonium nitrate, ...

13. The pipe (T) is subjected to at least the following steps i) and ii) i) providing said inner tube (IT) comprising said non-porous monolithic oxide ceramic; and ii) attaching said outer layer (OL) to said inner tube (IT), preferably by lamination techniques; 13. The use of any one of claims 2 to 12, wherein the compound is prepared by a process comprising:

14. A tube furnace for use in a sintering and / or debinding process, the tube furnace comprising a tube (T) containing an oxide ceramic matrix composite (OCMC).

15. 15. Use of the tube furnace according to claim 14 in the treatment process of at least one three-dimensional green body (GB), said treatment process comprising at least the following steps: a) providing at least one three-dimensional green body (GB), wherein the at least one three-dimensional green body (GB) comprises an inorganic powder (IP) and a binder (B); b) providing an acid; c) treating said at least one three-dimensional green body (GB) with said acid in said tube furnace to obtain at least one three-dimensional Brown body (BB); and, optionally d) sintering said at least one three-dimensional Brownian body (BB) obtained in step c) in said tubular furnace to obtain at least one three-dimensional sintered body (SB). Including, how to use.

Images