Method for manufacturing graphitized shaped parts by 3D printing

Abstract

The invention relates to a method for manufacturing a graphitized shaped part from conventional filaments made of plastic by 3D printing. The invention aims to provide a simplified method for manufacturing a graphitized 3D shaped part or another three-dimensional structure made of thermoplastic material by 3D printing. This is achieved by melting the filaments made of meltable and solidifiable plastic and applying the filaments layer by layer by means of a 3D printer until the desired structure has been manufactured, stabilizing the 3D structure (1) printed from the material of the filaments by temperature treatment to chemically or crystallographically change the plastic, wherein a pre-stabilization at about 180°C is carried out over a longer period of time, followed by a stabilization step at about 250°C until the printed 3D structure (1) is dimensionally stable enough as a stabilized structure (8), and carbonizing or graphitizing the 3D structure to manufacture a graphitized structure (9).

Description

[0001] This invention relates to a method for manufacturing graphitized shaped parts using filaments composed of fusible plastics via 3D printing.

[0002] WO 2018 / 196965 A1 describes a method for manufacturing ceramic objects by 3D printing.

[0003] To this end, carbon- or graphite-containing precursor materials are mixed with inorganic components, and carbide-based ceramic objects are manufactured through heat treatment and 3D printing. The inorganic components are metals, such as silicon, titanium, tungsten, or metal oxides.

[0004] The precursor materials also include carbon black or graphite powder, as well as polymers such as polyacrylonitrile.

[0005] Using a 3D printer, the precursor material prepared in this way is printed layer by layer to form the desired object through 3D printing technology (i.e., fused deposition modeling technology).

[0006] After the object has been printed, it is stabilized in air at a temperature between approximately 160°C and approximately 250°C, and then subjected to a carbonization process at a temperature between 1000°C and 1500°C.

[0007] In addition, WO 01 / 98207 A1 describes formable mixtures and their uses.

[0008] Formable raw materials include powdered silicon, carbon precursors including water-soluble, crosslinkable and thermosetting synthetic resins, powdered silicon fillers, and water-soluble thermoplastic adhesives.

[0009] Methods for manufacturing honeycomb structures include mixing materials to prepare a formable material mixture, and then shaping a green body, preferably by extrusion, drying and curing the green body.

[0010] The green body is then heated in a nitrogen atmosphere to a temperature sufficient to carbonize the resin and sintered at a temperature sufficient to transform the green body into porous silicon carbide, preferably above 1400°C.

[0011] One object of the present invention is to provide a method for manufacturing graphitized shaped parts (e.g., in a honeycomb structure or any other three-dimensional structure) from thermoplastic materials by 3D printing, which is significantly simplified compared to the prior art and serves as a carrier for catalysts, filters, etc., or some other component.

[0012] This objective of the present invention is achieved by the following means:

[0013] A 3D structure is printed by melting and solidifying filaments made of plastic using a 3D printer, and then applying the filaments layer by layer until the desired structure is formed.

[0014] The printed 3D structure, composed of filamentary material, is stabilized by temperature treatment to chemically or crystallographically alter the plastic. This is achieved through the following:

[0015] The 3D structure is pre-stabilized at 150°C to approximately 180°C for a specified time, and then...

[0016] A stabilization step was performed at approximately 250°C ± 20°C until the dimensions of the 3D structure were sufficiently stable.

[0017] Surprisingly, it has been discovered that 3D artifacts, such as honeycomb structures and shapes, can be created by printing plastic filaments without any other mixtures using a 3D printer. These 3D artifacts can then be directly transformed into graphitized molded parts through a high-temperature treatment that follows a two-step stabilization process, while retaining the printed structure.

[0018] In a first embodiment of the invention, the meltable filament is composed of a thermoplastic, such as ABS (acrylonitrile-butadiene-styrene copolymer), PVA / BVOH (polyvinyl alcohol), or BVOH (butene glycol-vinyl alcohol copolymer).

[0019] In another embodiment of the invention, in each case, the printed 3D structure is heated to the pre-stabilization temperature and the stabilization temperature at a heating rate of 0.2 °C / min to 1 °C / min.

[0020] Finally, in one embodiment of the invention, depending on the size of the 3D structure, after reaching and maintaining a specified constant temperature, the printed 3D structure is pre-stabilized and stabilized for several hours to several days. Preferably, the pre-stabilization temperature is 180°C to accelerate the process.

[0021] For stabilization, it is important to adapt the highest possible temperature to the selected filament material in each case, at which melting or severe deformation does not occur, thereby accelerating stabilization overall.

[0022] Furthermore, it is advantageous to stabilize the printed 3D structure with support devices during pre-stabilization and stabilization to prevent deformation, especially in the case of large parts.

[0023] Supports for 3D structures that can be advantageously used for printing are temperature-stable materials, such as metals or graphite, although shaped parts manufactured by this method can also be used as supports.

[0024] Alternatively, the printed 3D structure can be embedded in a temperature-stable powder, such as graphite powder or fine-grained salt, to serve as a support.

[0025] In one embodiment of the invention, the stabilized 3D structure is carbonized at a high temperature and finally graphitized, which is achieved at a temperature >1800°C, preferably >2000°C.

[0026] It should be understood that graphitization must be carried out under reduced pressure or in an inert gas (such as argon, krypton, xenon, or nitrogen) to prevent carbon combustion.

[0027] During graphitization, a cleaning process can be initiated to remove foreign elements (such as metals) by supplying halogen gases (such as chlorine) to the furnace atmosphere.

[0028] In another embodiment of the invention, after the three-dimensional structure has been graphitized, it is coated with pyrolytic carbon to seal the three-dimensional structure and to enable the three-dimensional structure to be used as a catalyst support, thereby making the catalyst more stable, or to enable the three-dimensional structure to be used as a support in the form of a framework, for example, so that the framework (e.g., a honeycomb structure) can be used as a catalyst support through appropriate coating of the three-dimensional structure.

[0029] In addition, graphitized structures can be coated with silicon carbide, silicon nitrite, or tantalum carbide, or graphitized structures can be converted into silicon carbide or tantalum carbide.

[0030] Graphitized 3D structures impregnated with bitumen or resin can also be used to achieve pressing.

[0031] In a particular embodiment of the invention, a support member or support structure or bracket is first printed and stabilized on a suitable substrate in a first step, and then the support member is used as a carrier, pillar or support for the printed 3D structure in a second step.

[0032] This allows the printed 3D structure supported by the support member or support structure to be easily separated from, lifted, or removed from it. After printing the support member or support structure, a release agent is applied to at least the area of ​​the support member or support structure that will come into contact with the 3D structure during subsequent printing.

[0033] Alternatively, the support components or support structures can be printed simultaneously with the 3D structure.

[0034] For example, a crucible or pot, along with a support structure in a honeycomb pattern on the exterior and / or interior of the crucible or pot, can be printed, resulting in a significantly more stable structure. Finally, the support structure can be mechanically removed after graphitization. This can be done by scraping the crucible or pot.

[0035] The invention will now be illustrated in more detail with reference to working embodiments. The accompanying drawings show:

[0036] Figure 1 A schematic diagram of a 3D printer;

[0037] Figure 2 (a) in the text: The three-dimensional structure that appears as a honeycomb structure after printing;

[0038] Figure 2 (b) in the text: the stabilized three-dimensional structure;

[0039] Figure 2 (c) in the figure: the three-dimensional structure after graphitization;

[0040] Figure 3 Examples of three-dimensional structures manufactured by the method according to the invention, for example, in the form of carriers, containers, and structural components (cubes) for catalysts or filters;

[0041] Figure 4 Typical thermal profiles used for pre-stabilization and stabilization;

[0042] Figure 5 Another embodiment of a 3D structure in the form of a frog;

[0043] Figure 6a After printing and stabilization, a crucible or pot with a finely structured honeycomb-like internal support structure; and

[0044] Figure 6b : Crucible or pot in which the support structure has been mechanically removed after graphitization.

[0045] To fabricate shaped parts from molten and solidifiable plastics using filaments made of heat-fusible plastics, such as honeycomb structures (see...). Figure 2 ) or any other three-dimensional structure 1, conventional 3D printers ( Figure 1 ) is the most suitable. The filament used can be a commercially available filament.

[0046] The 3D printer essentially consists of a base plate 2 with threaded supports 3, which are spaced apart from each other and vertically oriented, and movable in the Y direction (i.e., forward and backward). Between the threaded supports 3, a horizontal screw 4 is suspended from the threaded supports 3 by means of a threaded sleeve 5 to move vertically in the Z direction. Finally, the screw 4 carries the actual 3D print head 6, which is movable in the X direction (lateral direction). This 3D print head 6 is used to print the 3D structure 1 by fused deposition modeling of filaments 7 supplied to the heated print head 6. Precise X, Y, and Z positioning is typically ensured by properly controlled stepper motors.

[0047] Using a relatively simple 3D printer and a corresponding programmable control system, any 3D structure can be realized. Examples of such 3D structures are described below. Figure 2 , Figure 3 and Figure 5 As shown in the image.

[0048] However, if the 3D structure 1 prepared in this way is graphitized after printing, there is a specific problem that the heat-fusible plastic used to print the 3D structure 1 will remelt or at least deform at the high temperatures above 2000°C required for graphitization. This means that the desired final product consisting solely of graphite structures cannot be manufactured in this way.

[0049] This invention begins here by first using a 3D printer to print a three-dimensional structure 1 by melting and layering filaments 7 made of suitable plastic through a 3D printer until the desired 3D structure, such as a honeycomb structure, skeleton, or scaffold, is formed. Figure 2 (a) of the text. Particularly suitable plastic materials for filaments are ABS (acrylonitrile-butadiene-styrene copolymer), PVA (polyvinyl alcohol), or BVOH (butene glycol-vinyl alcohol copolymer).

[0050] TPU (thermoplastic polyurethane) is also suitable, but TPU has a higher temperature-dependent deformation, similar to ABS.

[0051] Subsequently, the printed 3D structure 1 is stabilized by altering the chemical or crystallographic structure of the plastic and by treating it at a specific temperature.

[0052] This is achieved by performing pre-stabilization at approximately 150°C to 180°C for a relatively long period until the printed 3D structure 1 is dimensionally stable, followed by a stabilization step at approximately 250°C ± 20°C until the 3D structure is sufficiently dimensionally stable to allow it to be transported or handled in some other manner without damage. Preferably, the pre-stabilization temperature is approximately 180°C because stabilization is accelerated at this temperature without initiating melting.

[0053] Figure 4 The corresponding temperature profiles for the entire stabilization process are shown, in which the 3D structure is heated to the pre-stabilization temperature and the stabilization temperature at a heating rate of 0.2 to 1 °C / min, preferably 0.5 °C / min, in each case.

[0054] The actual pre-stabilization and stabilization of the printed 3D structure 1 were achieved by maintaining a constant temperature for several hours to several days over a long period, depending on the size of the 3D structure. The result of this heat treatment process is a stabilized 3D structure 8, such as... Figure 2 As shown in the example.

[0055] Furthermore, it is advantageous if the 3D structure 1 is stabilized by supports at least at the critical point during pre-stabilization and stabilization to prevent deformation. This risk of deformation is particularly evident in relatively larger printed 3D structures 1.

[0056] Advantageously, the supports that can be used for the 3D structure are scaffolds made of temperature-stable materials (e.g., metals or graphite) that support the printed 3D structure 1 at multiple suitable locations (e.g., on the exterior, bottom, or interior). The supports used can also be scaffolds prepared by this method.

[0057] In the first step, a support or support structure or bracket may be printed on a suitable substrate, for example by the method described, and then in the second step, the support may be used as a carrier, pillar or support for the 3D structure to be printed.

[0058] Supports or support structures may also be printed at a higher or lower density than 3D Structure 1; at a minimum, supports or support structures should have sufficient mechanical strength, such as a honeycomb structure or a similar structural form.

[0059] In addition, it must be ensured that the material used for printing the support does not join or bond with the material used for printing the 3D structure so that the 3D structure can be easily removed from the support or support structure after stabilization; or, it must be ensured that the support or support structure has a sufficiently low density, such as a honeycomb structure, so that the support or support structure can be mechanically and easily removed from the 3D structure without damaging the 3D structure.

[0060] It is also possible that, after printing the support or support structure, a release agent is applied to at least the area of ​​the support or support structure that can come into contact with the 3D structure when it is subsequently printed.

[0061] Furthermore, it is possible to simultaneously print supports or support structures (e.g., in the form of a fine honeycomb structure) and 3D structures. The fine honeycomb structure has the advantage of particularly high stability, but after graphitization, the honeycomb structure can be easily mechanically removed without damaging the 3D structure.

[0062] In another alternative, the printed 3D structure 1 can be embedded in a temperature-stable powder (such as graphite powder or fine salt) as a support.

[0063] The downside here is that the powder has relatively poor thermal conductivity, which requires a long stabilization period to rebalance.

[0064] After stabilization is completed, the stabilized 3D structure 8 can be stabilized with high dimensional stability in a suitable furnace at high temperature with air removal. Figure 2(b) Graphitization, which can be achieved at temperatures >1800°C, preferably >2000°C. In this process, the carbonization of a stabilized 3D structure is achieved first, i.e., the plastic is transformed into a carbon-containing structure or an amorphous carbon structure, which is eventually transformed into graphite.

[0065] It should be understood that the graphitization of the stabilized 3D structure 8 must be carried out in a furnace suitable for this purpose under reduced pressure or in an inert gas (e.g., argon, krypton, xenon, or nitrogen) to avoid oxidative damage. The result is a graphitized 3D structure 9 ( Figure 2 (c) in the middle.

[0066] During graphitization, a cleaning process to remove foreign elements (e.g., metals) from the graphitized 3D structure 9 can be initiated simultaneously by supplying additional halogen gas (e.g., chlorine) to the furnace atmosphere.

[0067] Figure 2 Example 9 of a graphitized 3D structure 9 in the form of a honeycomb structure is shown in (c). The honeycomb structure has relatively high mechanical stability and contains particularly little material, although other 3D structures can of course be prepared as needed using the method according to the invention; see [reference]. Figure 3 or Figure 5 The example shown is a frog prepared by the method according to the present invention.

[0068] After graphitization, the graphitized 3D structure 9 can be coated with pyrolytic carbon to seal the structure, making it more stable, or it can be used as a carrier in the form of a skeleton.

[0069] Alternatively, silicon carbide (SiC), silicon nitride, or tantalum carbide coating can be used, or the graphitized 3D structure can be converted to silicon carbide or tantalum carbide by exposing the 3D structure in the furnace to a gas of the material (e.g., SiO or Ta2O5).

[0070] In addition, graphitized three-dimensional structures impregnated with bitumen or resin can be used to achieve compaction, for example, for filtration purposes.

[0071] Since coating and impregnation are performed at high temperatures, at least pre-stabilization is necessary for 3D structures.

[0072] Figure 3 Some application examples of 3D structures prepared by the method according to the invention are shown, for example in the form of supports (top), containers (middle), and structural components (e.g., cubes (bottom)) for catalysts or filters.

[0073] To use the graphitized 3D structure 9 as a catalyst support, the only requirement is to coat the graphitized 3D structure with the material required for the catalyst's function using a suitable coating apparatus. Known coating methods suitable for this purpose include CVD (chemical vapor deposition), PVD (physical vapor deposition), PECVD (plasma-enhanced chemical vapor deposition), etc.

[0074] Alternatively, the graphitized 3D structure can be wet-coated using a sol-gel method to enable its use as a catalyst.

[0075] Figure 6a An embodiment of a 3D structure 1 in the form of a crucible or pot 10 and an internal support structure 11 in the form of a honeycomb structure within the crucible or pot are shown, which has been printed simultaneously with the crucible or pot. Figure 6a It should be understood that 3D structures can also have different shapes.

[0076] The delicate support structure 11 can be easily and mechanically removed after graphitization. This can be done by scraping the crucible or pot 10.

[0077] Figure 6b A crucible or pot 10 is shown, in which the support structure 11 has been removed after graphitization. The traces 12 of the removed support are visible on the inner bottom of the crucible or pot 10.

[0078] List of reference numerals

[0079] 1. Printed 3D structure

[0080] 2 substrate

[0081] 3. Threaded support components

[0082] 4 screws

[0083] 5. Threaded sleeve

[0084] 6. Printhead

[0085] 7. Fine filaments

[0086] 8. Stabilized 3D Structure

[0087] 9. Graphitized 3D Structure

[0088] 10. Crucible or pot

[0089] 11 Supporting Structure

[0090] 12. Traces of the removed support components

Claims

1. A method for manufacturing graphitized shaped parts by 3D printing filaments made of plastic, wherein the filaments are composed of a thermoplastic without any other mixtures, by: A filament (7) made of fusible and curable plastic is melted and applied layer by layer using a 3D printer until the desired structure is produced. The 3D structure printed from the filament (7) is stabilized by temperature treatment to chemically or crystallographically alter the plastic, which is achieved by the following: Pre-stabilization was performed at 150°C to 180°C for a relatively long period until the printed 3D structure was dimensionally stable, and then... A stabilization step was performed at 250℃±20℃ until the printed 3D structure was sufficiently stable in size. The stabilized 3D structure was graphitized at temperatures >1800℃ with or without a supporting structure (11). Its features are, The molten filaments (7) used are ABS plastic (acrylonitrile-butadiene-styrene copolymer), PVA (polyvinyl alcohol), BVOH (butene glycol-vinyl alcohol copolymer) or TPU (thermoplastic polyurethane).

2. The method according to claim 1, characterized in that, Graphitize the stabilized 3D structure with or without a support structure (11) at temperatures >2000℃.

3. The method according to claim 1 or 2, characterized in that, In each case, the printed 3D structure is heated to the pre-stabilization temperature and the stabilization temperature at a heating rate of 0.2 °C / min to 1.0 °C / min.

4. The method according to claim 1 or 2, characterized in that, The printed 3D structure is stabilized by a support device during pre-stabilization and stabilization to prevent deformation.

5. The method according to claim 4, characterized in that, The support structure used for the printed 3D structure is made of a temperature-stable material.

6. The method according to claim 5, characterized in that, The temperature-stable material is selected from metals or graphite.

7. The method according to claim 4, characterized in that, The printed 3D structure is embedded in temperature-stable powder.

8. The method according to claim 7, characterized in that, The temperature-stable powder is selected from graphite powder or fine-grained salt.

9. The method according to claim 1 or 2, characterized in that, Graphitization is achieved under reduced pressure or in an inert gas atmosphere.

10. The method according to claim 9, characterized in that, The inert gas is selected from argon, krypton, or xenon.

11. The method according to claim 1 or 2, characterized in that, During the graphitization of the stabilized 3D structure, halogen gas is supplied to the furnace atmosphere.

12. The method according to claim 11, characterized in that, The halogen gas is chlorine.

13. The method according to claim 1 or 2, characterized in that, A graphitized 3D structure is coated with pyrolytic carbon.

14. The method according to claim 1 or 2, characterized in that, Graphitized 3D structures are coated with silicon carbide, silicon nitrite, or tantalum carbide.

15. The method according to claim 1 or 2, characterized in that, The graphitized 3D structure is transformed into silicon carbide or tantalum carbide.

16. The method according to claim 1 or 2, characterized in that, 3D structures using graphitized materials impregnated with bitumen or resin.

17. The method according to claim 1 or 2, characterized in that, In the first step, a support structure (11) is first printed on a suitable substrate and the support structure (11) is stabilized, and then in the second step, the support structure (11) is used as a carrier, pillar or support for the 3D structure to be printed.

18. The method according to claim 17, characterized in that, The supporting structure (11) is a bracket.

19. The method according to claim 17, characterized in that, After printing the support structure (11), a release agent is applied to at least the area of ​​the support structure (11) that will be in contact with the printed 3D structure when the 3D structure is subsequently printed with the support structure (11).

20. The method according to claim 1 or 2, characterized in that, Simultaneously print the support structure (11) and the 3D structure.

21. The method according to claim 1 or 2, characterized in that, Simultaneously, a pot (10) as a printed 3D structure and a support structure (11) on the outside and / or inside of the pot (10) are printed, and the support structure (11) is mechanically removed after the printed 3D structure has been graphitized.

22. The method according to claim 21, characterized in that, The pot (10) is a crucible.

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