Photocrosslinkable ceramic slip and method for the volumetric additive manufacturing of a ceramic component

Abstract

The invention relates to a photocrosslinkable ceramic slip having a filler content of ceramic particles of at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.%, in a photocrosslinkable organic matrix for a volumetric additive manufacturing process, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; 99.9% of the ceramic particles of the slip have a diameter which is ≤ 1 / 10 of the suitable wavelength; 99.0% of the ceramic particles of the slip have a diameter which is ≤ 1 / 20 of the suitable wavelength; and the diameter is measured by means of dynamic light scattering (DLS). The invention further relates to a method for the volumetric additive manufacturing of a ceramic component.

Description

Description Photocrosslinkable ceramic slurry and process for volumetric additive manufacturing of a ceramic component TECHNICAL FIELD

[0001] The present disclosure relates to a photocrosslinkable ceramic slurry and a method for volumetric additive manufacturing of a ceramic component. TECHNICAL BACKGROUND

[0002] With the help of volumetric additive manufacturing, such as xolography, three-dimensional structures can be created by volumetric crosslinking of a photocrosslinkable polymer. Crosslinking of the polymer in volume can be achieved, for example, by introducing light with two different wavelengths into the polymer. In this way, components with a volume of several tens of mm can be produced. 3 be built.

[0003] Ceramic components can be manufactured using layer-by-layer additive manufacturing, such as stereolithography. For this purpose, mixtures of fine ceramic particles and a photocrosslinkable resin are typically applied layer by layer and crosslinked to create a ceramic green body with a predetermined three-dimensional structure. The green body can be further processed into a ceramic component. For example, US 2018 / 0 148 378 A1 describes an additive manufacturing process for producing ceramic objects using a slurry containing nano-sized particles. The slurry is translucent but not transparent, but is applied layer by layer and then exposed to light, so the transparency requirements can be lower. Furthermore, it is known to produce ceramic thin-film foils with a 2D contour.

[0004] For volumetric additive manufacturing, a transparency of several tens of mm optical path length of the material to be cross-linked is usually required. Currently, this transparency is essentially only available with polymer materials, so that Volumetric additive manufacturing is currently essentially limited to polymeric materials.

[0005] Joseph T. Toombs et al.: "Volumetric additive manufacturing of silica glass with microscale computed axial lithography" describes the volumetric additive manufacturing of silica glass using computed axial lithography at the microscale. Publication WO 2021 / 023452 A1 describes a method and apparatus for the volumetric additive manufacturing of "cell-loaded resins," whereby a problem resulting from the scattering of a 10 pm particle is to be solved by adjusting the refractive index.

[0006] The object of the present invention is to make ceramic materials accessible to volumetric additive manufacturing. BRIEF DESCRIPTION OF THE INVENTION

[0007] This object is achieved by a photocrosslinkable ceramic slip according to claim 1, as well as by a method for volumetric additive manufacturing according to claim 8. Further embodiments, configurations, and advantages emerge from the dependent claims and the following description.

[0008] According to one aspect of the present disclosure, a photocrosslinkable ceramic slip having a filling level of ceramic particles of at least 50 wt. %, in particular at least 60 wt. %, preferably at least 70 wt. % in a photocrosslinkable organic matrix for volumetric additive manufacturing is provided, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS). The ceramic slip thus has a sufficiently high transparency and can thus be used to produce ceramic components via volumetric additive manufacturing.

[0009] According to a further aspect of the present disclosure, a method for volumetric additive manufacturing is provided, comprising providing a photocrosslinkable ceramic slurry having a filling level of ceramic particles of at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.% in a photocrosslinkable organic matrix for volumetric additive manufacturing, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS). The method further comprises light-induced crosslinking of the organic matrix at the suitable wavelength to form a ceramic green body, wherein the light-induced crosslinking takes place such that the ceramic green body has a predetermined three-dimensional contour.Furthermore, the method may comprise a thermal treatment of the green body, comprising expelling the organic matrix of the photocrosslinkable ceramic slip and sintering the ceramic particles to form a ceramic component.

[0010] According to a further aspect, the use of a photocrosslinkable ceramic slip having a filling degree of ceramic particles of at least 50 wt. %, in particular at least 60 wt. %, preferably at least 70 wt. % in a photocrosslinkable organic matrix is provided, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter of < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter of < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS); for volumetric additive manufacturing for producing a ceramic green body or a ceramic component.

[0011] The details of one or more aspects of the disclosure are set forth in the accompanying figures and the following description. Other features, objects, and advantages of the principles described in this disclosure will be apparent from the description and drawings, as well as from the claims. BRIEF DESCRIPTION OF THE CHARACTERS

[0012] The invention is explained in more detail below with reference to embodiments, without these being intended to limit the scope of protection defined by the claims.

[0013] The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. The elements of the drawings are relative to one another and are not necessarily to scale. Like reference characters indicate similar parts.

[0014] Fig. 1 shows a schematic particle size distribution of a ceramic slip suitable for volumetric additive manufacturing. DETAILED DESCRIPTION

[0015] The principles described in this disclosure relate to the expansion of volumetric additive manufacturing to include a further class of materials, namely ceramic materials. According to the invention, light scattering within the material is reduced to a level that permits volumetric additive manufacturing. In particular, this enables crosslinking of the material even after several tens of mm of optical path length, in particular after more than 100 mm. In this way, ceramic green bodies can be formed volumetrically. These can then be further processed into ceramic components.

[0016] Typically, the ceramic particles of the photocrosslinkable slip are spherical or nearly spherical and not fractured, since such small particles are not produced by grinding, but rather by chemical reaction, e.g., in a hydrothermal synthesis. The particle size (also referred to as diameter) of suitable particles of a suitable slip is typically less than or equal to 1 / 10 of the smallest exposure wavelength used for crosslinking. However, the particle size is subject to variation.

[0017] According to the invention, the particle size distribution of the ceramic material of the slurry is selected such that the diameter of 99.9% of the ceramic particles reaches a maximum of 1 / 10 of the wavelength used for crosslinking, and that the diameter of 99.0% of the ceramic particles reaches a maximum of 1 / 20 of the wavelength used for crosslinking. This means that, with typical 400 nm radiation for light-based crosslinking, 99.9% of the particles have a maximum diameter of 40 nm, and 99.0% of the particles have a maximum diameter of 20 nm.

[0018] In this description, particle size is a value measured using dynamic light scattering (DLS). For example, Malvern Panalytical Ltd offers instruments for DLS measurement (e.g., Zetasizer®).

[0019] This disclosure describes a photocrosslinkable ceramic slip based on a photocrosslinkable organic matrix. The slip has a ceramic particle content of at least 50 wt. %, meaning that at least 50% of the total mass of the ceramic slip is formed from the ceramic particles. In particular, the ceramic slip can have a ceramic particle content of at least 60 wt. %, preferably at least 70 wt. The photocrosslinkable organic matrix is adapted for light-induced crosslinking at a suitable wavelength.

[0020] The matrix can preferably be a photocrosslinkable resin, which can comprise a crosslinkable monomer and / or a polymer crosslinkable therewith or with itself, a photoinitiator, and, if necessary, additives for controlling the rheological properties of the slurry and the reactivity of the monomer and polymer during their crosslinking triggered by the photoinitiator. The crosslinkable monomer and the crosslinkable polymer can each have reactive groups. Crosslinking can involve a reaction of the reactive groups with each other. Thus, the photocrosslinkable resin can comprise photocrosslinkable mono- or polymers having one or more terminal double bonds, such as acrylated polyethylene glycol (PEG-DA), 1,6-hexanediol diacrylate (HDDA), urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), 4-acryloylmorpholine (ACMO), etc. Solvents, dispersants, plasticizers, inhibitors and / or sintering reagents may also be added.

[0021] In the present case of the light-induced crosslinkable ceramic slip, the photocrosslinkable organic matrix is filled with ceramic particles. The ceramic particles can ultimately form the ceramic green body. The described mixture of the organic matrix, comprising dispersed ceramic particles and, if present, all other components, is referred to here as a photocrosslinkable ceramic slip. Naturally, the matrix is configured such that, at the wavelength and radiation intensity used, polymerization of the organic components of the ceramic slip is initiated, thereby forming the green body. The matrix is therefore adapted for light-induced cross-linking of a suitable wavelength.

[0022] Furthermore, in the present context, a ceramic green body is understood to be the matrix formed as a three-dimensional structure filled with ceramic particles after photocrosslinking. This is a manageable structure with the highest possible fill level (typically at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.%) of ceramic particles. Finally, a ceramic component is understood to be the purely ceramic three-dimensional structure obtained from the ceramic green body after debinding and sintering, which no longer contains any organic components.

[0023] According to the invention, 99.9% of the ceramic particles of the slurry have a diameter < 1 / 10 of the appropriate wavelength, and 99% of the ceramic particles in the slurry have a diameter of < 1 / 20 of the appropriate wavelength. It has been shown that even a small proportion of ceramic particles with a diameter > 1 / 10 increases light scattering to a level that prevents targeted local crosslinking in the volume.

[0024] Typically, the ceramic slurry does not contain any non-ceramic particles. If additional particles are added to the slurry, 99.9% of the total particles in the slurry can have a diameter n 1 / 10 of the appropriate wavelength, and 99.0% of the total particles in the slurry can have a diameter < 1 / 20 of the appropriate wavelength.

[0025] The ceramic slip of the present disclosure typically has a transmittance of 50% to 95% at a path length of 10 mm and substantially perpendicular incidence at the transition from a flat surface to the slip at the wavelength suitable for light-induced crosslinking of the ceramic slip. Conceivable with regard to a perpendicular incidence at the transition from a flat surface to the slip is, for example, a cuvette made of quartz glass and filled with slip and having a rectangular base. Preferably, the ceramic slip can have a transmittance of approximately 90% at a path length of 10 mm and substantially perpendicular incidence at the transition from a flat surface to the slip at the wavelength suitable for light-induced crosslinking of the ceramic slip. The transmittance describes the proportion of an incident radiation flux or The luminous flux that completely penetrates the ceramic slurry over the specified path length. The transmittance is measured in the beam direction. Scattered light is usually not taken into account.

[0026] According to some embodiments, the wavelength suitable for light-induced crosslinking of the ceramic slip can be in a wavelength range from 100 nm to 850 nm, preferably in the range 350-550 nm, more preferably in the range 350-405 nm. When using a two-stage photocrosslinking, the wavelength suitable for light-induced crosslinking of the ceramic slip can be in a combination of these wavelength ranges.

[0027] In some embodiments, 99.9% of the ceramic particles may have a diameter of less than 40 nm. Such embodiments may enable longer optical path lengths.

[0028] According to some embodiments, 99.5% of the ceramic particles may have a diameter of less than 30 nm. Such embodiments may enable longer optical path lengths.

[0029] In some embodiments, 99.0% of the ceramic particles may have a diameter of less than 20 nm. Such embodiments may enable longer optical path lengths.

[0030] According to one embodiment, a material of the ceramic particles is selected from materials for high-performance ceramics such as silicon nitride - Si3N4, zirconium oxide - ZrO2, aluminum oxide - Al2O3, spinels - MgAI2O4, silicon carbide - SiC, etc. The chemical formulas given correspond to an idealized chemical composition of the designated materials.

[0031] According to one embodiment, the photocrosslinkable ceramic slurry comprises a suspension of particles comprising metal oxide, metal nitride, metal carbide, and / or spinel particles. In such embodiments, 99.9% of the total particles present in the slurry can have a diameter of <1 / 10 of the suitable wavelength, and 99.0% of the total particles present in the slurry can have a diameter of <1 / 20 of the suitable wavelength.

[0032] According to another aspect of the present disclosure, a method for volumetric additive manufacturing is provided. The method comprises providing the photocrosslinkable ceramic slurry according to the present disclosure.

[0033] The method further comprises light-induced crosslinking of the organic matrix at the appropriate wavelength to form a ceramic green body, wherein the light-induced crosslinking occurs such that the ceramic green body has a predetermined three-dimensional contour. For this purpose, for example, the electromagnetic radiation which causes the photocrosslinking of the ceramic slurry, or at least the crosslinking of its organic matrix, can be directed onto a volume such that the structure obtained by crosslinking has a desired 3D geometry. The electromagnetic radiation can comprise two different wavelengths, such as approximately 400 nm and approximately 700 nm. The ceramic structure is thus defined exclusively during crosslinking.This can be achieved, for example, by means of targeted beam guidance, such as continuous or raster-guided laser light, or with the help of photomasks and floodlight and / or laser light. Xolography can be used, for example.

[0034] The resulting 3D geometry of the ceramic structure can, for example, exhibit a complex geometry. For example, the structure can have corners, straight, convex, and / or concave curved sections, such as edges (outer edges) and recesses, overhangs, and / or similar features. Likewise, it can exhibit regularly or irregularly shaped openings, holes, and / or recesses distributed throughout its dimensions.

[0035] The method may further comprise thermally treating the green body, comprising expelling the organic matrix of the photocrosslinkable ceramic slip and sintering the ceramic particles to form a ceramic component.

[0036] The thermal treatment of the green body causes the organic matrix to be expelled and the ceramic particles of the structure to sinter, ultimately forming the ceramic component. The expulsion process, also known as debinding, typically occurs at a temperature between 200 and 600°C, while sintering, depending on the material composition of the respective ceramic material, typically takes place between 800 and 1500°C with heating rates between 1 and 30°C / min to form the ceramic component.

[0037] According to a typical embodiment, the density of the sintered ceramic structure, i.e., the ceramic component, is more than 50% of the theoretical density of the ceramic, preferably 70-100% of the theoretical density, more preferably more than 90% of the theoretical density of the present ceramic. Advantageously, the resulting ceramic components are completely pore-free.

[0038] In particular, reference is made below to embodiments of the disclosure, some examples of which are illustrated in the figures. Each example is provided to illustrate the disclosure, not to limit the disclosure. For example, features illustrated or described as part of embodiments may be used with other embodiments to yield further embodiments.

[0039] Fig. 1 schematically shows a particle size distribution 100 of a ceramic slurry containing ceramic particles suitable for volumetric additive manufacturing. The particle size distribution 100 was measured via dynamic light scattering (DLS).

[0040] The ceramic slurry can, for example, have a ceramic particle content of approximately 70 wt.% in a photocrosslinkable organic matrix. The slurry is configured to crosslink at a wavelength of approximately 400 nm.

[0041] The abscissa represents the logarithmic particle size in nm (110). The ordinate represents the particle size distribution according to the number of particles in % (120).

[0042] As shown in Fig. 1, at least 99.9% of the ceramic particles have a diameter of < 40 nm, i.e., 1 / 10 of the wavelength suitable for crosslinking the slurry (400 nm wavelength in this example). Furthermore, at least 99.0% of the ceramic particles have a diameter of < 20 nm, i.e., 1 / 20 of the wavelength suitable for crosslinking the slurry.

[0043] This enables cross-linking of the material even after several 10 mm of optical path length, so that the ceramic slurry can be used for the production of ceramic components with several 10 mm extension in all directions via volumetric additive manufacturing, in particular via xolography.

[0044] Further useful examples of the present disclosure are described in the following embodiments: -io-

[0045] Embodiment 1: Photocrosslinkable ceramic slip with a filling degree of ceramic particles of at least 50 wt. %, in particular at least 60 wt. %, preferably at least 70 wt. % in a photocrosslinkable organic matrix for volumetric additive manufacturing, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS).

[0046] Embodiment 2: Photocrosslinkable ceramic slip according to embodiment 1, wherein the wavelength suitable for light-induced crosslinking of the ceramic slip is in a wavelength range from 100 nm to 850 nm, preferably in the range 350-550 nm, more preferably in the range 350-405 nm.

[0047] Embodiment 3: Photocrosslinkable ceramic slip according to one of the embodiments 1 to 2, wherein 99.9% of the ceramic particles have a diameter of less than 40 nm.

[0048] Embodiment 4: Photocrosslinkable ceramic slip according to one of embodiments 1 to 3, wherein 99.5% of the ceramic particles have a diameter of less than 30 nm.

[0049] Embodiment 5: Photocrosslinkable ceramic slip according to one of the embodiments 1 to 4, wherein 99.0% of the ceramic particles have a diameter of less than 20 nm.

[0050] Embodiment 6: Photocrosslinkable ceramic slip according to one of embodiments 1 to 5, wherein the matrix is a photocrosslinkable resin.

[0051] Embodiment 7: Method for the volumetric additive manufacturing of a ceramic component, comprising: providing a photocrosslinkable ceramic slip, in particular according to one of claims 1 to 6, with a filling level of ceramic particles of at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.% in a photocrosslinkable organic matrix for volumetric additive manufacturing, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the Slip has a diameter of < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter of < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS); light-induced crosslinking of the organic matrix at the suitable wavelength to form a ceramic green body, wherein the light-induced crosslinking takes place such that the ceramic green body has a predetermined three-dimensional contour; thermal treatment of the green body, comprising expelling the organic matrix of the photocrosslinkable ceramic slip and sintering the ceramic particles to form the ceramic component.

[0052] Embodiment 8: Use of a photocrosslinkable ceramic slip with a filling level of ceramic particles of at least 50 wt. %, in particular at least 60 wt. %, preferably at least 70 wt. % in a photocrosslinkable organic matrix, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS); for volumetric additive manufacturing for producing a ceramic component.

[0053] In the foregoing description, a photocrosslinkable ceramic slurry and a method for volumetric additive manufacturing of a ceramic component have been presented with reference to specific examples. It should be appreciated that various aspects and embodiments disclosed herein may be combined in combinations other than the specific combinations illustrated in the figures. It is understood that various modifications may be made to the recited embodiments without departing from the scope of the disclosure and the following claims.

Claims

Claims 1. Photocrosslinkable ceramic slip with a filling degree of ceramic particles of at least 50 wt. %, in particular at least 60 wt. %, preferably at least 70 wt. % in a photocrosslinkable organic matrix for volumetric additive manufacturing, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slip have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS).

2. Photocrosslinkable ceramic slip according to claim 1, wherein the wavelength suitable for light-induced crosslinking of the ceramic slip is in a wavelength range from 100 nm to 850 nm, preferably in the range 350-550 nm, more preferably in the range 350-405 nm.

3. Photocrosslinkable ceramic slurry according to one of the preceding claims, wherein 99.9% of the ceramic particles have a diameter of less than 40 nm.

4. Photocrosslinkable ceramic slurry according to one of the preceding claims, wherein 99.5% of the ceramic particles have a diameter of less than 30 nm.

5. Photocrosslinkable ceramic slurry according to one of the preceding claims, wherein 99.0% of the ceramic particles have a diameter of less than 20 nm.

6. Photocrosslinkable ceramic slurry according to one of the preceding claims, wherein the matrix is a photocrosslinkable resin.

7. Photocrosslinkable ceramic slip according to one of the preceding claims, wherein the organic matrix is light-induced crosslinked at the appropriate wavelength, so that a ceramic green body is formed with a predetermined three-dimensional contour.

8. A method for volumetric additive manufacturing, comprising: Provision of a photocrosslinkable ceramic slip, in particular according to one of claims 1 to 6, with a filling level of ceramic particles of at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.% in a photocrosslinkable organic matrix for volumetric additive manufacturing, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a Diameter < 1 / 10 of the appropriate wavelength; and wherein 99.0% of the ceramic particles of the slurry have a Have a diameter < 1 / 20 of the appropriate wavelength; the diameter is measured by Dynamic Light Scattering (DLS); Light-induced crosslinking of the organic matrix at the appropriate wavelength to form a ceramic green body, wherein the light-induced crosslinking is carried out such that the ceramic green body has a predetermined three-dimensional contour.

9. The method according to claim 8, further comprising thermally treating the green body, comprising expelling the organic matrix of the photocrosslinkable ceramic slip and sintering the ceramic particles to form a ceramic component.

10. Use of a photocrosslinkable ceramic slip having a ceramic particle content of at least 50 wt.%, in particular at least 60 wt.%, preferably at least 70 wt.% in a photocrosslinkable organic matrix, wherein the matrix is adapted for light-induced crosslinking at a suitable wavelength; wherein 99.9% of the ceramic particles of the slip have a diameter of < 1 / 10 of the suitable wavelength; and wherein 99.0% of the ceramic particles of the slurry have a diameter < 1 / 20 of the suitable wavelength; wherein the diameter is measured by means of dynamic light scattering (DLS); for volumetric additive manufacturing to produce a ceramic component or a ceramic green body.

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