PROCESS FOR PRODUCING MOULDED ARTICLES FROM CARBON OR GRAPHITE BY 3D PRINTING

Abstract

A process for 3D printing articles made of carbon or graphite includes producing a flowable polymeric mixture from a UV permeable and polymerizable polymer or cellulose and a UV crosslinkable resin, admixing the polymeric mixture with sugar and/or cellulose until the mixture has a consistency such that it can be filled into a 3D printer and processed thereby, homogenizing the mixture at room temperature or elevated temperature, filling a 3D printer with the mixture, layerwise printing a shaped article with simultaneous exposure to UV radiation for layerwise crosslinking of the UV crosslinkable resin, cleaning the shaped article, introducing the UV precured shaped article into a furnace and stabilizing the UV precured shaped article in air at a predetermined stabilizing temperature until all volatile constituents have outgassed from the prefabricated shaped article and subsequently high temperature treating the shaped article for carbonization or graphitization in a furnace under protective gas.

Claims

1.-12. (canceled)

13. A process for producing shaped articles made of carbon or graphite by 3D printing, comprising: producing a flowable polymeric mixture from a UV permeable and polymerizable polyacrylonitrile dissolved in a solvent selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP), or cellulose and a UV crosslinkable resin selected from the group consisting of DLP photopolymer resin and SLA resin, wherein the polymeric mixture is admixed with sugar and/or cellulose until the polymeric mixture may be filled into a 3D printer and processed thereby; homogenizing the polymeric mixture at an elevated temperature up to 60? C.; filling a 3D printer with the polymeric mixture; layerwise printing a shaped article with the 3D printer with simultaneous exposure to UV radiation for layerwise crosslinking of the UV crosslinkable resin, thereby forming a UV precured shaped article; cleaning the UV precured shaped article of liquid residues and foreign particles; introducing the UV precured shaped article into a furnace and stabilizing the UV precured shaped article in air at a predetermined stabilizing temperature of 200? C. to 450? C. until all volatile constituents have outgassed, thereby forming a prefabricated shaped article; and subsequently high temperature treating the prefabricated shaped article for carbonization or graphitization in a furnace under protective gas.

14. The process as claimed in claim 13, wherein the flowable polymeric mixture of a UV permeable and polymerizable polymer or cellulose is admixed with a further solvent.

15. The process as claimed in claim 13, wherein the stabilizing of the UV precured shaped article is carried out by uniform heating of the precured shaped article in the furnace up to a predetermined stabilizing temperature and subsequent short duration heat treatment at constant temperature.

16. The process as claimed in claim 15, wherein the stabilizing of the prefabricated shaped article is undertaken over a duration of two or more hours at a temperature of 250? C.

17. The process as claimed in claim 13, wherein after stabilizing, the prefabricated shaped article is carbonized in the furnace under protective gas or under vacuum at a temperature around 1000? C.

18. The process as claimed in claim 13, wherein the prefabricated shaped article is graphitized in the furnace under a protective gas or under vacuum at a temperature from 2000? C.

19. The process as claimed in claim 13, wherein a full graphitization of the prefabricated shaped article is performed under a protective gas or under vacuum at a temperature of >2500? C.

20. The process as claimed in claim 17, wherein the carbonization or graphitization of the prefabricated shaped article is undertaken at a pressure of 700 mbar under argon as protective gas with a heating ramp of 1? C./min.

21. The process as claimed in claim 13, wherein the polymeric mixture is admixed with a metal or silicon oxide so that after prefabricating of the prefabricated shaped article with the 3D printer and subsequent stabilization thereof a high temperature treatment at >1000? C. may be undertaken to form metal or silicon carbides.

Description

DETAILED DESCRIPTION

[0038] The invention will now be more particularly elucidated with reference to a working example.

[0039] For production of shaped articles made of graphite with a 3D printer it is necessary to initially produce a polymeric mixture of a stabilizable polymer and a UV crosslinkable resin, wherein the polymeric mixture is admixed with sugar and/or cellulose until the polymeric mixture has a consistency amenable to processing with a 3D printer.

[0040] The flowable polymeric mixture of a UV permeable and polymerizable polymer or cellulose may also have a solvent, such as DMSO, admixed with it.

[0041] The stabilizable polymer employed is polyacrylonitrile (PAN) which may have been dissolved in a solvent.

[0042] Instead of polyacrylonitrile (PAN) it is in principle also possible to employ other polymerizable and thus stabilizable polymers or cellulose. However this is provided that the employed polymers or the cellulose are permeable to UV radiation.

[0043] It is also possible in principle to dissolve the polyacrylonitrile (PAN) in a solvent or to completely replace it with cellulose.

[0044] Contemplated solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP), wherein DMSO is preferred on account of its lower health hazard.

[0045] The UV crosslinkable resin may be a DLP photopolymer resin or an SLA resin or else any other suitable UV transparent resin.

[0046] The polymeric mixture may additionally also be admixed with metal oxides, such as silicon oxide, wherein care must be taken to ensure that the mixture does not become nontransparent for UV radiation as would be the case upon admixture of pitch for example.

[0047] Subsequently, a shaped article is produced by layerwise printing of the polymeric mixture with a 3D printer with simultaneous exposure to UV radiation for layerwise crosslinking of the UV sensitive resin.

[0048] For layerwise crosslinking of the UV sensitive resin the radiation of a projector whose UV filter has been removed is sufficient.

[0049] The thus produced precured shaped article is immediately thereafter stabilized in a furnace at a temperature of 200? C. to not more than 450? C., preferably at a temperature of 250? C., in air to outgas volatile constituents from the precured shaped article.

[0050] It is only by using the UV sensitive resin that is crosslinked/cured by exposure to UV radiation that it is possible to print a shaped article which during the printing operation achieves a sufficient stability to allow handling thereof for the further production steps.

[0051] The stabilizing of the UV cured shaped article is carried out by uniform heating of the shaped article in the furnace up to the stabilizing temperature and subsequent short duration heat treatment at constant temperature until all volatile constituents of the mixture have outgassed.

[0052] The stabilizing is preferably carried out over a duration of two or more hours according to the size of the shaped article.

[0053] For the subsequent graphitization the furnace is further heated to a temperature necessary for complete graphitization. After stabilizing, the prefabricated shaped article is carbonized in the furnace under protective gas or under vacuum at a temperature of about 1000? C.

[0054] Alternatively, the prefabricated shaped article may be graphitized in the furnace under a protective gas or under vacuum at a temperature from 2000? C., wherein a full graphitization may be achieved at a temperature of >2500? C.

[0055] The graphitization of the shaped article is preferably carried out at a pressure of 700 mbar under argon as protective gas or under vacuum with a heating ramp of 1? C./min, wherein other noble gases such as neon, krypton, xenon may also be employed in principle.