Polymer binder and polymer binder formulation based on ceramic particles for the production of ceramic parts by a 3D printing process, manufacturing process of the formulation and method for obtaining a ceramic object

Description

[0001] The present invention relates to the field of manufacturing parts in technical ceramics, i.e. in non-metallic mineral materials.

[0002] In particular, the object of the present invention falls within the field of manufacturing ceramic parts by three-dimensional (3D) printing, by extrusion, also known as "CIM-like" for "Ceramic Injection Moulding like", or "Material Extrusion" according to the definition of the ASTM ISO 17296-2 standard.

[0003] More particularly, the present invention relates to a new formulation or composition comprising, in particular, as a ceramic material, zirconia, or zirconium dioxide ZrO2, preferably stabilized with yttrium oxide (also called yttria-stabilized zirconia or YSZ), and a polymeric binder consisting of at least partially bio-based polymers, namely polyethylene glycol, or PEG, on the one hand, and poly(butylene succinate-co-adipate), or PBSA, or PBS (poly(butylene succinate)), on the other hand.

[0004] This formulation is used more specifically in the form of granules that can be subsequently extruded for the manufacture of various ceramic parts by three-dimensional (3D) printing.

[0005] The final ceramic parts, manufactured from the formulation of the invention, by 3D printing can in particular have applications in various fields such as the medical or health industry, or even in the chemical industry.

[0006] Thus, for example, it is conceivable, by means of the formulation according to the present invention, to manufacture parts such as filters for applications in chemistry, bone substitutes or scaffold structures in the medical field.

[0007] However, the applications mentioned above should in no way be considered as being exhaustive.

[0008] In the state of the art, we already know of compositions for three-dimensional printing of ceramic parts, as well as manufacturing processes for such parts.

[0009] Thus, traditionally, 3D printing of ceramic parts is carried out using granules composed of a plastic-ceramic polymer mixture, constituting the raw material, or "feedstock", and whose composition is adapted to 3D printing.

[0010] This is done using a machine, consisting of a 3D printer, equipped with a means of extruding granules, for additive manufacturing of a solid object, layer by layer, based on a digital model.

[0011] After the extrusion stage, and in order to obtain a fully ceramic part, a debinding stage is carried out. The objective of this stage is the complete removal of the plastic polymer binder, thus facilitating the subsequent densification stage. The part obtained after debinding is brittle and porous, with no dimensional change due to the loss of the binder.

[0012] Finally, high-temperature solid-phase sintering is carried out to densify and consolidate the ceramic part.

[0013] The debinding stage can be carried out in different ways, and is particularly delicate as it can cause damage to the structure of the part finally obtained.

[0014] In particular, incomplete or poorly controlled removal of the polymer binder is likely to result in defects such as cracks, or chemical contamination of the final part by the presence of carbon residues from the binder that have not been properly removed.

[0015] Effective and optimal debinding should prevent deformation, crumbling, swelling, or even breakage of the final ceramic part obtained by 3D printing.

[0016] Thus, the main debinding techniques that can be implemented in the manufacture of ceramic parts are: thermal debinding, by applying a controlled temperature; chemical, or catalytic, debinding, by bringing the part, depending on its printing, into contact with a solvent.

[0017] The main drawback of implementing thermal unbinding is that it is particularly long and energy-intensive.

[0018] As for chemical debinding, it also requires contact between the part and the solvent for a relatively long time, and it is generally not sufficient for satisfactory and complete removal of the polymer binder.

[0019] Therefore, chemical unbinding must almost always be followed by thermal unbinding, the major drawback of which has been mentioned above.

[0020] Furthermore, the implementation of chemical unbinding is harmful to the environment and the safety of people, due to the use of chemical solvents which may, for example, produce toxic fumes.

[0021] This is notably the case of the US application published under number US 2018 / 162048, in which compositions and processes with powder / binder systems are described, in which a primary binder is associated with a secondary binder, said primary binder comprising a high molecular weight polymer that can be chemically decomposed by exposure to a solvent, while the secondary binder is insoluble in that solvent.

[0022] The solvent in question may consist of an aliphatic hydrocarbon, ethyl acetate, acetone, methyl ethyl ketone, trans-dichloroethylene, benzene, or toluene. It may also include water, 1,4-dioxane, dimethylformamide, or cyclohexanone.

[0023] The compositions currently known and used as polymer binders in the manufacture of ceramic parts by 3D printing thus have the disadvantage of requiring several successive debinding steps.

[0024] It should also be noted that some formulations, containing a ceramic base and a plastic polymer binder, are particularly difficult to print, the mixture being either very viscous or, on the contrary, extremely fluid.

[0025] Thus, for example, in the prior art, from US patent document 10376956, we know of an extrudable mixture containing a metal or a ceramic powder, with a thermoplastic binder, the latter consisting of polylactic acid (PLA).

[0026] We also know, from the publication in the name of Checot-Moinard D., et al., (Powder injection moulding PIM of feedstock based on hydrosoluble binder and submicronic powder to manufacture parts having micro-details, Powder technology, 25 March 2011, Vol.208, pages 472-479), of a polymeric binder based on PEG 4000 and PP.

[0027] However, the application of these binders requires several debinding steps, namely debinding with water at 50°C for 24 hours, and thermal debinding. During water debinding, the water becomes contaminated with polymer residues and cannot be discharged without further treatment, as the COD (Chemical Oxygen Demand) is too high.

[0028] From the publication entitled MIM of nitrogen-Strengthened austetinic stainless steel using biopolymer-based binder, WorldPM 2016 - MIM Iron and Steel, 2016, XP040686799, we also know of a powder injection molding process, in which the binder for steel powders contains 45% by weight of PHBV, 45% by weight of PEG 4000 and 10% by weight of stearic acid.

[0029] Here again, water debinding is carried out, before thermal debinding.

[0030] European patent EP 0 413 231 describes a process for manufacturing an inorganic sintered part, by forming a mixture of a sinterable inorganic powder, in particular ceramic, and polyoxymethylene (POM) as a binder, by injection molding or extrusion, into a green body, removal of the binder and sintering.

[0031] In this process, POM is eliminated by treating the green body in an atmosphere containing a gaseous acid, such as nitric acid, or gaseous boron trifluoride.

[0032] European patent EP 2 686 286 also describes a process for manufacturing a molded metallic or ceramic body from a thermoplastic material containing: A) 40 to 65% by volume of at least one inorganic frittable powder A, B) 35 to 60% by volume of a mixture of: B1) 50 to 95% by weight of one or more polyoxymethylene (POM) homo- or copolymers; B2) 5 to 50% by weight of a polymer (selected from polyolefins, aliphatic polyurethanes, non-crosslinked aliphatic polyepoxides, polyethers, aliphatic polyamides and polyacrylates) dissolved homogeneously or dispersed in B1), and C) 0 to 5% by volume of a dispersion aid.

[0033] In this process, for binder removal, the molded part is treated with a solvent that extracts the binder component B2) from the molded part and in which the binder component B1) is insoluble, then the solvent is removed by drying the molded part.

[0034] Finally, the molded part is treated in an atmosphere containing an acid, in particular nitric acid, which removes the B1 binding component from the molded body.

[0035] However, the implementation of these processes requires a special enclosure to debind these products, with highly dangerous fuming nitric acid, and ovens that produce formaldehyde as a reaction product.

[0036] US patent application US 2021 / 163364 also describes a method for manufacturing a ceramic by 3D printing, in which granules containing zirconia and organic binders are printed and sintered.

[0037] The first binder used in this process is POM, already mentioned above, with the disadvantages that the use of this binder implies, while a second binder can be chosen from thermosetting polymer materials, such as phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, organic silicone resin and polyurethane, and / or thermoplastic polymer materials.

[0038] The present invention is intended to remedy, at least in part, the drawbacks of prior art formulations.

[0039] In an inventive approach, the development of a new polymeric binder and a new composition comprising a ceramic powder and said polymeric binder was conceived for 3D printing of ceramic parts, particularly zirconia-based parts, preferably yttria-based parts, the polymeric binder and the composition based on it allowing both optimal printing quality of a ceramic and polymer composite element, while simplifying the subsequent debinding step to obtain a final part made exclusively of ceramic.

[0040] To this end, the invention relates to a polymeric binder for three-dimensional extrusion printing of a composite element based on a ceramic compound and said polymeric binder, the latter being composed of: PEG (polyethylene glycol) 4000 g / mol in a proportion of between 25 and 50% (w / w); PEG (polyethylene glycol) 10000 g / mol in a proportion of between 0 and 25% (w / w); a bio-based structural polymer selected from PBSA (poly(butylene succinate co-adipate) and PBS (poly(butylene succinate)), said structural polymer being in a proportion of between 30 and 50% (w / w).

[0041] Preferably, the polymeric binder consists of PEG (polyethylene glycol) 4,000 g / mol in a proportion of between 25 and 30% (w / w), PEG (polyethylene glycol) 10,000 g / mol in a proportion of between 20 and 25% (w / w) and a bio-based structural polymer chosen from PBSA and PBS in a proportion of 50% (w / w).

[0042] According to a preferred embodiment, said binder consists of: PEG 4,000 g / mol in a proportion equal to 25% (w / w); PEG 10,000 g / mol in a proportion equal to 25% (w / w); a bio-based structural polymer selected from PBSA and PBS in a proportion equal to 50% (w / w).

[0043] Preferably, the structural polymer in question is PBSA.

[0044] The present invention also relates to a composite formulation for the three-dimensional printing of a composite element by extrusion, the formulation comprising: Powder of a ceramic compound selected from zirconia (ZrO2), yttria zirconia (YSZ), aluminium oxide (Al2O3), hydroxyapatite (HAPCa5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion of between 74 and 85% (w / w); Said polymeric binder consisting of PEG 4000, PEG 10000 and a bio-based structural polymer selected from PBSA and PBS, in a proportion of between 14 and 25% (w / w); Stearic acid powder in a proportion of between 0.2 and 1% (w / w).

[0045] Advantageously, the composite formulation consists of: Zirconia powder (ZrO2) or yttria zirconia (YSZ) in a proportion of approximately 80% (w / w); Polymeric binder, consisting of 25% PEG 4000, 25% PEG 10000 and 50% PBSA or PBS, in a proportion of approximately 19.6% (w / w); Stearic acid powder in a proportion of approximately 0.4% (w / w).

[0046] The invention further relates to a method for preparing such a composite formulation, and for obtaining composite granules from this formulation, said method comprising, at least, the following steps taken in order: Dissolving stearic acid in a volume V1 of diethyl ether under stirring to obtain a dissolved stearic acid solution of a volume V1'; Adding ceramic powder and a volume V2 of diethyl ether to said stearic acid solution, under stirring, so that the total volume of liquid, equal to V1'+V2, is greater than the volume of powder; Evaporating the ether at room temperature under a fume hood to obtain ceramic powder particles coated with stearic acid; Mixing the coated ceramic powder particles and the polymeric binder, by dry method in a mixer and then together by melting at a temperature of approximately, or equal to, 110 °C, in a twin-screw extruder, and obtaining the composite formulation; Extruding filaments from said composite formulation and grinding said filaments to obtain composite granules.

[0047] The present invention also relates to composite granules obtained from the composite formulation and obtainable according to the process described above, said granules comprising: Powder of a ceramic compound selected from zirconia (ZrO2), yttria zirconia (YSZ), aluminum oxide (Al2O3), hydroxyapatite (HAPCa5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion of between 74 and 85% (w / w); The polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion of between 14 and 25% (w / w); Stearic acid powder in a proportion of between 0.2 and 1% (w / w).

[0048] Preferably, composite granules have the following composition: Zirconia powder (ZrO2) or yttria zirconia (YSZ) in a proportion of approximately 80% (w / w); Binderpolymeric, consisting of 25% PEG 4000, 25% PEG 10000 and 50% PBSA or PBS, in a proportion of approximately 19.6% (w / w); Stearic acid powder in a proportion of approximately 0.4% (w / w).

[0049] The invention also relates to a method for manufacturing a ceramic part from composite granules, said method comprising the following steps: Three-dimensional printing of a composite part from composite granules; Application of thermal debinding to the composite part obtained in the previous step, the thermal debinding being carried out in temperature steps according to the following program: ∘ From an initial temperature of 25 °C, increase the temperature to which the composite part is subjected up to a first temperature step of 140 °C at a heating rate of 2 °C / min; ∘ From this first temperature step, increase the temperature up to a second temperature step of 170 °C at a heating rate of 0.1 °C / min; ∘ From this second temperature step, increase the temperature up to a third temperature step of 200 °C at a heating rate of 1 °C / min; ∘ From this third temperature stage, increase the temperature up to a final temperature of 380 °C at a heating rate of 0.4 °C / min;Sintering at a temperature between 1450 and 1500 °C for consolidation and obtaining the final ceramic part.

[0050] Finally, the present invention relates to a ceramic part manufactured by three-dimensional printing from composite granules.

[0051] Other objects and advantages of the present invention will become apparent during the following description relating to embodiments which are given only as indicative and non-limiting examples.

[0052] Understanding this description and the significance of the invention will be facilitated by referring to the attached drawings, in which: [ Fig.1] represents three photographs of three thermally debonded parts, the part in the left-hand photograph in the figure having been obtained by 3D printing from yttria-based zirconia granules and a particular example of a polymeric binder composition according to the invention, while the photographs on the left illustrate two parts, also obtained by 3D printing with different polymeric binders. Fig. 2 ] represents yttria-stabilized zirconia ceramic parts after the sintering step is completed, at different fill levels, between 10 and 100%, after implementation of the manufacturing process of the invention, and in particular the process-specific thermal debinding program, and from composite granules manufactured using an example embodiment of the formulation of the invention. FIG.3] corresponds to a graph illustrating the different temperature stages implemented in the thermal debinding cycle of the manufacturing process for a ceramic part of the invention. FIG.4 ] corresponds to a tomography of a ceramic part after debinding, obtained after implementation of the manufacturing process of the invention, and from composite granules manufactured using an example of an embodiment of the formulation of the invention.

[0053] According to a first aspect, the present invention relates to a polymeric binder intended for use in 3D printing techniques for ceramic parts by extrusion.

[0054] More particularly, the polymeric binder according to the invention is intended to be mixed with at least one ceramic compound, in particular, but not limited to, zirconia, i.e. zirconium oxide ZrO2, or yttria zirconia, in order to obtain a composition, referred to in the following description as the composite formulation, which will then be used to obtain composite granules.

[0055] Therefore, according to a second aspect of the invention, it also relates to a composite formulation for three-dimensional printing of a composite element by extrusion, this formulation comprising at least one ceramic compound and said polymeric binder.

[0056] Also, according to a third aspect of the invention, it relates to a process for preparing a composite formulation and obtaining composite granules from this formulation.

[0057] A fourth aspect of the invention then relates to composite granules obtained from the composite formulation and capable of being obtained according to the preparation process.

[0058] From the composite granules obtained using said formulation, a composite element consisting of the polymeric binder of the invention and the ceramic will be manufactured initially by implementing 3D printing by extrusion.

[0059] Following the implementation, on this composite element, of a thermal debinding step, followed by a sintering step, a part made exclusively of ceramic can finally be obtained.

[0060] Thus, a fifth aspect of the present invention relates to a method for manufacturing such a ceramic part from composite granules, in which only thermal unbinding is implemented, more particularly thermal unbinding where the temperature is increased gradually in stages, and without the need to carry out chemical unbinding.

[0061] Finally, a sixth aspect of the invention relates to a ceramic part manufactured by three-dimensional printing from these composite granules.

[0062] With regard to the polymeric binder according to the invention, intended to be used in a three-dimensional printing process by extrusion of a composite element based on a ceramic compound and said polymeric binder, the latter is essentially composed, in mass percentage (w / w) considering the total mass of binder, of: PEG (polyethylene glycol) 4000 g / mol in a proportion of between 25 and 50% (w / w), preferably between 25 and 30% by mass; PEG (polyethylene glycol) 10000 g / mol in a proportion of between 0 and 25% (w / w), preferably between 20 and 25% by mass; a structural polymer selected from PBSA (poly(butylene succinate co-adipate) and PBS (poly(butylene succinate)), said structural polymer being in a proportion of between 30 and 50% (w / w), preferably between 45 and 50% by mass.

[0063] The sum of the constituents of the polymeric binder (PEG 4000, PEG 10000 and structural polymer) is 100% by mass.

[0064] Preferably, the polymers used in mixtures to obtain the polymeric binder of the invention, namely PEG 4000, PEG 10000 and, preferably, PBSA or PBS, consist of polymers that are at least partially bio-based.

[0065] Advantageously, in the polymeric binder of the invention, PBSA constitutes the structural polymer. It is, particularly advantageously, at least partially bio-based and exhibits no toxicity.

[0066] The melting point of PBSA is 90°C.

[0067] The presence of this constituent in the polymeric binder of the invention, when mixed with zirconia powder, in particular yttria-treated zirconia powder, for example, to obtain a composite formulation, makes it possible for this formulation to be printable, by 3D printing techniques, at a relatively low temperature, namely between 100 and 110 °C, in comparison with the formulations traditionally used which require higher temperatures, more specifically around 170 °C.

[0068] Consequently, the presence of PBSA in such proportions in the polymeric binder of the invention allows for energy savings during the 3D printing stage, and the implementation of the latter is also facilitated.

[0069] In another example of the realization of the polymeric binder, which is equally advantageous, the structural polymer is PBS.

[0070] This one has a melting temperature of around 112 to 116 °C, so that it also allows extrusion and printing to be carried out at relatively low temperatures, with, therefore, the same advantages as those conferred by PBSA.

[0071] The second constituent polymer of said polymeric binder, PEG, has the advantage of being ecological and non-toxic in use.

[0072] The presence of this polymer allows for fluidity of the composite formulation, obtained by mixing the polymeric binder and a ceramic powder, depending on its molar mass.

[0073] Thus, PEG makes it easier to 3D print, by lowering the viscosity of the feedstock, namely the granules obtained from the composite formulation containing the polymeric binder.

[0074] According to a highly preferred embodiment, the polymeric binder of the invention consists of: PEG (polyethylene glycol) 4000 g / mol in a proportion equal to 25% (w / w); PEG (polyethylene glycol) 4000 g / mol in a proportion equal to 25% (w / w); PBSA (poly(butylene succinate co-adipate) or PBS (poly(butylene succinate)) in a proportion equal to 50% (w / w).

[0075] Such a polymeric binder formulation allows for easier printing and the achievement of thermal debinding only, for the manufacture of composite parts, as will be illustrated in the detailed example in the rest of the description, in connection with the figures.

[0076] As regards the second aspect of the invention, namely the composite formulation for three-dimensional printing of a composite element by extrusion, this comprises, at least, a ceramic compound, a polymeric binder and stearic acid, in the following proportions, expressed by mass relative to the total mass of the formulation (m / m): between 74 and 85% of a powder of a ceramic compound chosen from zirconia (ZrO2), yttria zirconia (YSZ), aluminum oxide Al2O3, hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP); between 14 and 25% of polymeric binder as defined previously in the description; between 0.2 and 1% of stearic acid powder.

[0077] The sum of the constituents of the composite formulation (ceramic compound, polymeric binder and stearic acid) is 100% by mass.

[0078] Preferably, said composite formulation consists of: zirconia powder (ZrO 2 ) or yttria zirconia powder (YSZ) in a proportion equal to 80% (w / w); polymeric binder, consisting of PEG 4000, PEG 10000 and PBSA or PBS, in a proportion equal to 19.6% (w / w); stearic acid powder in a proportion equal to 0.4% (w / w).

[0079] The polymeric binder used in this formulation is preferably made up of 25% PEG 4000, 25% PEG 10,000 and 50% PBSA or PBS.

[0080] Zirconia is preferentially yttria zirconia.

[0081] From this composite formulation, according to a third aspect of the invention, it is possible to manufacture composite granules, or feedstock, by implementing a process for preparing the composite formulation and obtaining composite granules from this formulation, said process comprising at least the following steps: Dissolving the acid, initially in powder form, in a volume V1 of diethyl ether under magnetic stirring until the stearic acid dissolves and a stearic acid solution of volume V1' is obtained; Adding ceramic powder and a volume V2 of diethyl ether to said dilute stearic acid solution, under vigorous stirring, so that the total volume of liquid, equal to V1' (dissolved stearic acid solution) + V2 (additional volume of diethyl ether), is greater than the volume of powder; thus, all the ceramic powder particles are coated with stearic acid, which will subsequently allow optimal dispersion of the ceramic filler in the polymer matrix; Evaporating the ether at room temperature (between 20 and 25 °C) under a fume hood to obtain stearic acid-coated ceramic powder particles;This evaporation step can typically be carried out for a period of approximately 24 hours. The ceramic powder particles coated with stearic acid and the polymer binder are mixed in the appropriate proportions, first dry in a mixer, then melted together at a temperature of approximately 110°C in a twin-screw extruder, resulting in the composite formulation. This step allows the ceramic filler, already coated with stearic acid, to be mixed with the polymer binder, ultimately obtaining a perfectly homogeneous mixture. Filaments are then extruded from this composite formulation and ground into composite granules.

[0082] Thus, in a preferred example of this process, to obtain a mass equal to 1 kg of raw material (granules), 4 g of stearic acid (0.4% by mass) is used, preferably diluted in a volume V1 of the order of 150 mL of diethyl ether, 800 g of yttria-treated zirconia powder ZrO2 (80% by mass), 98 g of PBSA or PBS (9.8% by mass), 49 g of PEG 4000 (4.9% by mass) and 49 g of PEG 10000 (4.9% by mass).

[0083] According to a fourth aspect of the invention, it therefore also relates to composite granules obtained by means of the composite formulation which has been defined previously in the description, said granules being moreover likely to be obtained according to the aforementioned process.

[0084] In particular, such composite granules contain the following constituents in their composition, in the proportions indicated: of a ceramic compound powder selected from zirconia (ZrO 2 ), yttria zirconia (YSZ), aluminium oxide Al 2 O 3 , hydroxyapatite HAP, tricalcium phosphate TCP, in a proportion of between 74 and 85% (w / w); of a polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion of between 14 and 25% (w / w); of stearic acid powder in a proportion of between 0.2 and 1% (w / w).

[0085] Here again, advantageously, taking into account the preferred embodiment of the invention, the composite granules consist of: yttria-stabilized zirconia (YSZ) powder in a proportion of 80% (w / w); polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion of 19.6% (w / w); preferably, the composition of the polymeric binder used to manufacture the granules, and therefore forming part of the granules, is: 25% PEG 4000, 25% PEG 10000 and 50% PBSA or PBS. Stearic acid powder in a proportion of 0.4% (w / w).

[0086] Such composite granules can then be used for three-dimensional printing of a ceramic part, using a 3D printer adapted to use such granules, such as, for example, but not limited to, the "Freeformer ®<" printer (registered trademark) from "Arburg ®<" (registered trademark) or the granule extruder offered by Mahor.

[0087] The invention is, therefore, according to a fifth aspect, also related to a method of manufacturing a ceramic part from the composite granules defined above.

[0088] The manufacturing process for a ceramic part from composite granules involves the following steps, taken in order: Three-dimensional printing of a composite part by extrusion from the aforementioned composite granules; Application of thermal debinding to the composite part obtained in the previous step, the thermal debinding being carried out in temperature steps according to the following program: ∘ From an initial temperature of 25 °C, increase the temperature to which the composite part is subjected up to a first temperature step of 140 °C at a heating rate of 2 °C / min; ∘ From this first temperature step, increase the temperature up to a second temperature step of 170 °C at a heating rate of 0.1 °C / min; ∘ From this second temperature step, increase the temperature up to a third temperature step of 200 °C at a heating rate of 1 °C / min;∘ From this third temperature stage, increase the temperature to a final temperature of 380 °C at a heating rate of 0.4 °C / min; Sintering at a temperature between 1450 and 1500 °C for 2 hours for consolidation and obtaining the final ceramic piece.

[0089] A unique feature of this ceramic part manufacturing process is that only thermal debinding is required. In other words, thanks to the formulation of the polymeric binder used in the composite granules, chemical debinding is unnecessary.

[0090] The debinding step implemented here, with the recommended temperature parameters and heating speeds, allows for the removal of the polymeric binder by decomposition, by heating the composite part to the binder degradation temperature.

[0091] Finally, the sintering stage, carried out in a furnace, consolidates the ceramic particles, particularly zirconia ZrO2 or yttria zirconia.

[0092] The presence, in the polymer matrix, in addition to the bio-based structural polymer, of a second polymer, namely PEG, which is more fluid than the said structural polymer, makes it possible to facilitate three-dimensional printing by lowering the viscosity of the composite granules.

[0093] The formulation, due to the polymers it contains in the proportions that have been defined, has an optimized viscosity, greater than 9 Pa.s (for a shear rate of 10 5< s -1< through the printer nozzle), which allows it to be printable without being degraded during its extrusion and printing.

[0094] The thermal debinding step is also facilitated, in particular, by the presence of small chains from low molecular weight PEG 4000.

[0095] In addition, extrusion and three-dimensional printing are carried out at temperatures of around 100 to 110 °C, lower than what is traditionally used (between 170 and 200 °C), thanks to the presence of these polymers, in particular PBSA or PBS, thus making it easier to implement the formulation, limit energy consumption and, consequently, reduce costs.

[0096] The invention also relates to a ceramic part manufactured by three-dimensional printing from the composite granules as defined above in their composition.

[0097] The invention will now be illustrated through an example of the realization of thermally unbound parts, obtained from a formulation having the composition as defined in the present invention, or from formulations having different compositions. Example: Manufacturing ceramic parts from different formulations including polymers

[0098] The composite formulation according to the present invention which has been tested contains 80% by mass of yttria-stabilized zirconia, 0.4% by mass of stearic acid, 9.8% by mass of PBSA, 4.9% by mass of PEG 4000 and 4.9% by mass of PEG 10,000.

[0099] In comparison, a second composite formulation was tested. It is similar to that of the invention, except that it contains only PBSA, namely: 80% by mass of yttria-treated zirconia, 0.4% stearic acid, and 19.6% PBSA.

[0100] Also, a third composite formulation was tested: this one contains, as a polymeric binder, only PEG, namely: 80% by mass of yttria zirconia, 0.4% of stearic acid, 9.8% of PEG 4000 and 9.8% of PEG 10,000.

[0101] The production of composite granules is carried out as follows, to obtain a mass of 1 kg of granules:

[0102] The first step is done using a solvent to coat all the yttria zirconia particles with stearic acid and promote good dispersion of the filler in the polymer matrix.

[0103] Indeed, stearic acid was dissolved in diethyl ether (150 mL of ether for 4 g of stearic acid) under magnetic stirring for a few minutes until a completely transparent solution was obtained.

[0104] Next, yttria-treated zirconia was added to the solution with a little more ether to coat all the zirconia particles while maintaining magnetic stirring.

[0105] Finally, the mixture remains under the fume hood at room temperature for 24 hours in order to evaporate all the ether and obtain zirconia particles coated with stearic acid.

[0106] The volume of ether used is slightly greater than the volume of zirconia. It is necessary for the zirconia particles to be completely coated in the ether for the coating to be done in a liquid state.

[0107] As for the second step, it takes place in a mixer by dry process and then by melt process using a twin-screw extruder at a temperature T equal to 110 °C. This step serves to mix the already coated charge and the binder (PEG 4000, PEG 10000 and PBSA in the context of the composition of the invention, PBSA alone in the case of the first comparative example and, in the case of the second comparative example, PEG 4000 and PEG 10000) and finally obtain a perfectly homogeneous mixture.

[0108] The filaments obtained after extrusion are ground to obtain granules.

[0109] These granules were then printed using a suitable 3D printer, namely the "Freeformer ®<" (registered trademark) printer from "Arburg ®<" (registered trademark) to obtain, initially, composite parts.

[0110] In order to obtain parts made entirely of ceramic, the printed composite parts underwent a thermal debinding step to remove the polymer binder by decomposition by heating to the binder degradation temperature, before a sintering step in a furnace to consolidate the yttria zirconia particles.

[0111] The results obtained using the three tested polymeric binder compositions are illustrated in the figure 1 attached drawings.

[0112] There figure 2 , meanwhile, illustrates final ceramic pieces, after sintering, obtained using the polymeric binder formulation according to the invention, at different filling rates (10%, 30%, 50%, 60%, 80%, 85%, 90%, 95%, and 100%).

[0113] There figure 3illustrates the step-by-step thermal unbinding program that was developed and optimized by the NETZSCH Kinetics Neo software from three TGA (Thermogravimetric Analysis) curves of the pellets at four different heating speeds.

[0114] This thermal unbinding program is also detailed in the table below: Levels Heating speed 25-140°C 2°C / min 140-170°C 0.1°C / min 170-200°C 1°C / min 200-380°C 0.4°C / min

[0115] To return now to the photographs of the thermally debonded ceramic pieces reproduced on the figure 1 : Part 1 was obtained from the polymeric binder formulation of the invention (50% PBSA + 25% PEG 4000 and 25% PEG 10,000); this part was easy to print, and the thermal debinding step proceeded correctly; the figure 4This is a tomography of the part after debinding, showing its satisfactory intrinsic quality. Part 2 was obtained with a polymer binder formulation containing only PBSA; it was very difficult to print, as the binder was very viscous, and thermal debinding was also extremely difficult. The photograph clearly illustrates that the quality of the final part is not optimal. Part 3 was obtained with a polymer binder formulation containing half PEG 4000 and half PEG 10000; printing was difficult due to the mixture being too fluid. However, the thermal debinding step proceeded correctly.

[0116] There figure 2 illustrates that the present formulation of polymeric binder makes it possible to obtain ceramic parts of satisfactory quality, regardless of the filling rate of said parts that one seeks to obtain.

[0117] These results demonstrate that the addition of PEG with PBSA in the polymer binder is particularly important for the success in obtaining good quality ceramic parts and for the implementation of the preparation steps of these parts, as well as the choice of the molar mass of PEG.

[0118] Indeed, the long chains from PEG 10,000 will ensure the good processability of the printing shaping step because the greater the molar mass of the PEG chains, the greater the activation energy and therefore the sensitivity of the polymer to temperature becomes low.

[0119] As for the small polymer chains from PEG 4000, these will facilitate the debinding step.

[0120] Therefore, to meet the requirements of the process, a 50:50 ratio between PEG 4000 and PEG 10000, mixed with PBSA, is particularly optimal to allow co-extrusion of PEG and PBSA, and also to facilitate thermal debinding, due to the degradation rate of these polymers.

[0121] That being said, an increase in the proportion of PEG 4000 compared to that of PEG 10,000 is also conceivable, in the proportions which are claimed, always mixed with PBSA as a structural polymer, in the proportions indicated.

[0122] It should be noted here that the tested polymeric binder formulation made it possible to achieve thermal debinding of printed parts only (without chemical debinding) in a time of only 14 hours, allowing a saving of time, therefore of productivity, and a saving of energy, compared with the solutions currently implemented which require a longer debinding time, namely typically a duration of 24h.

Claims

1. Polymeric binder for three-dimensional printing by extrusion of a composite element based on a ceramic compound and said polymeric binder, characterized in that said binder consists of: - PEG (polyethylene glycol) 4,000 g / mol in a proportion of between 25 and 50% (w / w); - PEG (polyethylene glycol) 10,000 g / mol in a proportion of between 0 and 25% (w / w); - a biosourced structural polymer chosen from PBSA (poly(butylene succinate co-adipate) and PBS (poly(butylene succinate)), said structural polymer being in a proportion of between 30 and 50% (w / w).

2. Polymeric binder for three-dimensional printing according to claim 1, characterized in that it consists of: - PEG (polyethylene glycol) 4,000 g / mol in a proportion of between 25 and 30% (w / w); - PEG (polyethylene glycol) 10,000 g / mol in a proportion of between 20 and 25% (w / w); - a biosourced structural polymer chosen from PBSA and PBS in a proportion equal to 50% (w / w).

3. Polymeric binder for three-dimensional printing according to claim 1 or claim 2, characterized in that it consists of: - PEG (polyethylene glycol) 4,000 g / mol in a proportion equal to 25% (w / w); - PEG (polyethylene glycol) 10,000 g / mol in a proportion equal to 25% (w / w); - a biosourced structural polymer chosen from PBSA and PBS in a proportion equal to 50% (w / w).

4. Polymeric binder for three-dimensional printing according to any of claims 1 to 3, characterized in that said structural polymer is PBSA.

5. Composite formulation, for three-dimensional printing of a composite element by extrusion, characterized in that it comprises at least one ceramic compound, stearic acid and a polymeric binder according to any of claims 1 to 4, said formulation comprising: - powder of a ceramic compound chosen from zirconia (ZrO2), yttriated zirconia (YSZ), aluminum oxide (Al2O3), hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion of between 74 and 85% (w / w); - said polymeric binder consisting of PEG 4000, PEG 10000 and a biosourced structural polymer chosen from PBSA and PBS, in a proportion of between 14 and 25% (w / w); - stearic acid powder in a proportion of between 0.2 and 1% (w / w).

6. Composite formulation, for three-dimensional printing of a composite element by extrusion, according to claim 5, characterized in that it consists of: - zirconia (ZrO2) or yttriated zirconia (YSZ) powder in a proportion approximately equal to or equal to 80% (w / w); - polymeric binder, consisting of 25% PEG 4000, 25% PEG 10000 and 50% PBSA or PBS, in a proportion approximately equal to or equal to 19.6% (w / w); - stearic acid powder in a proportion approximately equal to or equal to 0.4% (w / w).

7. Method for preparing a composite formulation according to either of claims 5 or 6, and for obtaining composite granules from this formulation, said method being characterized in that it comprises, at least, the following steps: - dissolving stearic acid in a volume V1 of diethyl ether with stirring to obtain a solution of dissolved stearic acid of a volume V1'; - adding ceramic powder and a volume V2 of diethyl ether to said stearic acid solution, with stirring, so that the total volume of liquid, equal to V1'+V2, is greater than the volume of powder; - evaporating ether at room temperature in a fume hood to obtain stearic acid-coated ceramic powder particles; - mixing coated ceramic powder particles and polymeric binder together dry in a mixer and then melted together in a twin-screw extruder at a temperature of the order of, or equal to, 110°C, and obtaining the composite formulation; - extruding filaments from said composite formulation and grinding said filaments to obtain composite granules.

8. Composite granules based on the composite formulation according to claim 5 or claim 6, obtainable according to the method of the preceding claim and comprising: - powder of a ceramic compound chosen from zirconia (ZrO2), yttriated zirconia (YSZ), aluminum oxide (Al2O3), hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion of between 74 and 85% (w / w); - the polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion of between 14 and 25% (w / w); - stearic acid powder in a proportion of between 0.2 and 1% (w / w).

9. Composite granules according to claim 8, characterized in that they have the following composition: - zirconia (ZrO2) or yttriated zirconia (YSZ) powder in a proportion approximately equal to or equal to 80% (w / w); - polymeric binder, consisting of 25% PEG 4000, 25% PEG 10000 and 50% PBSA or PBS, in a proportion approximately equal to or equal to 19.6% (w / w); - stearic acid powder in a proportion approximately equal to or equal to 0.4% (w / w).

10. Method for producing a ceramic part from composite granules according to claim 8 or claim 9, characterized in that it comprises the following steps: - three-dimensional printing of a composite part from composite granules according to claim 8 or claim 9; - applying thermal debinding to the composite part obtained in the previous step, the thermal debinding being carried out in temperature stages according to the following program: ∘ from an initial temperature of 25°C, increasing the temperature to which said composite part is subjected up to a first temperature stage of 140°C at a heating rate of 2°C / min; ∘ from this first temperature stage, increasing the temperature up to a second temperature stage of 170°C at a heating rate of 0.1°C / min; o from this second temperature stage, increasing the temperature up to a third temperature stage of 200°C at a heating rate of 1°C / min; ∘ from this third temperature stage, increasing the temperature up to a final temperature of 380°C at a heating rate of 0.4°C / min; - sintering at a temperature of between 1450 and 1500°C to consolidate and obtain the final ceramic part.