Polymeric binder and formulation based on ceramic powder and polymeric binder for the manufacture of ceramic parts by a 3D printing process, process for obtaining such a formulation and process for obtaining a ceramic part from such a formulation

Abstract

A polymeric binder and a formulation based on ceramic powder and a polymeric binder for manufacturing ceramic parts by a 3D printing process, and a method for obtaining such a formulation, and a method for obtaining a ceramic part from such a formulation. The invention relates in particular to a polymeric binder for three-dimensional extrusion printing of a composite element based on a ceramic compound and said polymeric binder. The latter consists of: - PEG 4000 in a proportion of between 25 and 50% (w / w); - PEG 10000 in a proportion of between 0 and 25% (w / w); - a bio-based structural polymer selected from PBSA, PBS, PHA, and PHB, said structural polymer being in a proportion of between 30 and 50% (w / w). Figure for the abstract: Fig. 1

Description

Title of the invention: Polymeric binder and formulation based on ceramic powder and polymeric binder for the manufacture of ceramic parts by a 3D printing process, method for obtaining such a formulation and method for obtaining a ceramic part from such a formulation

[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 called "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 for Yttria-Stabilized Zirconia), 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 which 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 limiting.

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

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

[0010] This is carried out by means of a machine, consisting of a 3D printer, equipped with a means of extruding granules, for an additive manufacturing of a solid object, layer by layer, on the basis of a digital model.

[0011] After the extrusion step, and in order to obtain a part made entirely of ceramic, a debinding step is carried out, the objective of which is the complete removal of the plastic polymer binder, in order to facilitate the subsequent densification step. The part obtained after debinding is brittle and porous without dimensional change due to the loss of the binder.

[0012] Finally, high-temperature solid-phase sintering is carried out, for densification and consolidation of the ceramic part.

[0013] The debinding step can be carried out in different ways, and is particularly delicate because 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 in chemical contamination of the final part by the presence of carbon residues from the binder which 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:

[0017] - a thermal unbinding, by the application of a controlled temperature;

[0018] - a chemical or catalytic debinding by contacting the part, according to its printing, using a solvent.

[0019] The implementation of thermal unbinding has the main disadvantage of being particularly long and energy-intensive.

[0020] As regards 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.

[0021] Consequently, chemical unbinding must, almost systematically, be followed by thermal unbinding, the major drawback of which has been mentioned above.

[0022] In addition, the implementation of chemical unbinding is harmful to the environment and the safety of persons, due to the use of chemical solvents which may, for example, produce toxic fumes.

[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 certain formulations, comprising 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, an extrudable mixture containing a metal or a ceramic powder, with a thermoplastic binder, the latter consisting of polylactic acid (PLA).

[0026] A polymeric binder based on PEG 4000 and PP is also known 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).

[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 debinding with water, the water becomes contaminated with polymer residues and cannot be discharged without further treatment, as the COD (Chemical Oxygen Demand) is too high.

[0028] 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) serving as a binder, by injection molding or extrusion, into a green body, removal of the binder and sintering.

[0029] In this process, the POM is eliminated by treating the green body in an atmosphere containing a gaseous acid, such as nitric acid, or gaseous boron trifluoride.

[0030] A process for manufacturing a molded metallic or ceramic body from a thermoplastic material, containing: is also known from European patent EP 2 686 286.

[0031] A) 40 to 65% by volume of at least one inorganic frittable powder A,

[0032] B) 35 to 60% by volume of a mixture of:

[0033] B1) 50 to 95% by weight of one or more homo- or copolymers of polyoxymethylene (POM);

[0034] B2) 5 to 50% by weight of a polymer (chosen from polyolefins, polyurethanes) aliphatics, non-crosslinked aliphatic polyepoxides, polyethers, aliphatic polyamides and polyacrylates) dissolved homogeneously or dispersed in Bl), and

[0035] C) 0 to 5% by volume of a dispersion adjuvant.

[0036] In this process, for the removal of the binder, the molded part is treated with a solvent which extracts the binder component B2) from the molded part and in which the binder component Bl) is insoluble, then the solvent is removed by drying the molded part.

[0037] Finally, the molded part is treated in an atmosphere containing an acid, in particular nitric acid, which removes the binding component B1 from the molded body.

[0038] However, the implementation of these processes requires a special enclosure to debind these products, with highly dangerous fuming nitric acid, and ovens which produce formaldehyde as a reaction product.

[0039] The present invention is intended to remedy, at least in part, the drawbacks of prior art formulations.

[0040] In an inventive approach, the development of a new polymeric binder, and a new composition comprising a ceramic powder and said polymeric binder, has been conceived for 3D printing of ceramic parts, in particular zirconia-based, preferably yttria-based zirconia, the polymeric binder and the composition based thereon allowing, at the same time, optimal printing quality of a ceramic and polymer composite element, while simplifying the subsequent debinding step to obtain a final part exclusively in ceramic.

[0041] To this end, the invention relates to a polymeric binder for three-dimensional printing by extrusion of a composite element based on a ceramic compound and said polymeric binder, the latter being composed of:

[0042] - PEG (polyethylene glycol) 4000 g / mol in a proportion between 25 and 50 % (m / m);

[0043] - PEG (polyethylene glycol) 10000 g / mol in a proportion between 0 and 25 % (m / m);

[0044] - a bio-based structural polymer selected from PBSA (poly(butylene succinate) co-adipate), PBS (poly(butylene succinate)), PHA (Polyhydroxyalkanoates) and PHB (Poly-[3-hydroxybutyrate], said structural polymer being in a proportion between 30 and 50% (w / w).

[0045] According to a preferred embodiment, said binder consists of:

[0046] - PEG 4000 g / mol in a proportion equal to 25% (w / w);

[0047] - PEG 10,000 g / mol in a proportion equal to 25% (w / w);

[0048] - a bio-based structural polymer selected from PBSA and PBS in a proportion equal to 50% (m / m).

[0049] Most preferably, said structural polymer is PBSA.

[0050] 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 chosen from zirconia (ZrO2), yttria zirconia (YSZ), aluminium oxide (Al2O3), hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion between 74 and 85% (w / w); - Said polymeric binder consisting of PEG 4000, PEG 10000 and a bio-based structural polymer chosen from PBSA, PBS, PHA and PHB, in a proportion between 14 and 25% (w / w); - Stearic acid powder in a proportion between 0.2 and 1% (w / w).

[0051] 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 approximately equal to or equal to 19.6% (w / w); - Stearic acid powder in a proportion of approximately equal to or equal to 0.4% (w / w).

[0052] 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 VI of diethyl ether under stirring to obtain a solution of dissolved stearic acid of a volume VI'; - Addition, to the said stearic acid solution, of ceramic powder and a volume V2 of diethyl ether, under agitation, so that the total volume of liquid, equal to Vl'+V2, is greater than the volume of powder; - Evaporation of ether at room temperature under a fume hood to obtain ceramic powder particles coated with stearic acid; - Mixing of coated ceramic powder particles and polymeric binder, by dry method in a mixer then together by melting at a temperature of, or equal to, 110 °C, in a twin-screw extruder, and obtaining the composite formulation; - Extrusion of filaments from said composite formulation and grinding of said filaments to obtain composite granules.

[0053] 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 chosen from zirconia (ZrO2), yttria zirconia (YSZ), aluminium oxide (Al2O3), hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP) in a proportion between 74 and 85% (w / w); - The polymeric binder consisting of PEG 4000, PEG 10000 and PB SA or PBS in a proportion between 14 and 25% (w / w); - Stearic acid powder in a proportion between 0.2 and 1 % (m / m).

[0054] Preferably, the composite granules have the following composition: - 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 approximately equal to or equal to 19.6% (w / w); - Stearic acid powder in a proportion of approximately equal to or equal to 0.4% (w / w).

[0055] 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 plateau of 140 °C at a heating rate of 2 °C / min; • From this first temperature stage, increase the temperature up to a second temperature stage of 170 °C at a heating rate of 0.1 °C / min; • From this second temperature stage, increase the temperature up to a third temperature stage 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 piece.

[0056] Finally, the present invention relates to a ceramic part manufactured by three-dimensional printing from composite granules.

[0057] Other objects and advantages of the present invention will become apparent during the following description relating to embodiments which are given only by way of indicative and non-limiting examples.

[0058] Understanding this description and the significance of the invention will be facilitated by referring to the drawings attached hereto, in which:

[0059] [Fig.1] represents three photographs of three thermally unbound parts, the part in the left 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 left photographs illustrate two parts, also obtained by 3D printing with different polymeric binders.

[0060] [Fig.2] represents yttria zirconia ceramic parts once the sintering step is completed, at different filling rates, between 10 and 100% filling, after implementation of the manufacturing process of the invention, and in particular of the thermal debinding program specific to the process, and from composite granules manufactured using an example of an embodiment of the formulation of the invention.

[0061] [Fig.3] corresponds to a graph illustrating the different temperature stages implemented in the thermal debinding cycle of the manufacturing process of a ceramic part of the invention.

[0062] [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.

[0063] 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.

[0064] 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, in other words zirconium oxide ZrO2, or yttria zirconia, in order to obtain a composition, referred to in the rest of this description as a composite formulation, which will then be used to obtain composite granules.

[0065] Consequently, 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.

[0066] 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.

[0067] 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.

[0068] 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, in the first instance, by implementing 3D printing by extrusion.

[0069] 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.

[0070] Thus, a fifth aspect of the present invention relates to a method of 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.

[0071] Finally, a sixth aspect of the invention relates to a ceramic part manufactured by three-dimensional printing from these composite granules.

[0072] 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 (m / m) considering the total mass of binder, of:

[0073] - PEG (polyethylene glycol) 4000 g / mol in a proportion between 25 and 50 % (m / m), preferably between 25 and 30% by mass;

[0074] - PEG (polyethylene glycol) 10000 g / mol in a proportion between 0 and 25 % (m / m), preferably between 20 and 25% by mass;

[0075] - a structural polymer selected from PBSA (poly(butylene succinate co- adipate), PBS (poly(butylene succinate)), PHA (Polyhydroxyalkanoates) and PHB (Poly-[3-hydroxybutyrate], said structural polymer being in a proportion between 30 and 50% (w / w), preferably between 45 and 50% by mass.

[0076] The sum of the constituents of the polymeric binder (PEG 4000, PEG 10000 and structural polymer) is 100% by mass.

[0077] Most 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.

[0078] Advantageously, in said polymeric binder of the invention, PBSA constitutes the structural polymer. It is, particularly advantageously, at least partially bio-based and exhibits no toxicity.

[0079] The melting temperature of PBSA is 90 °C.

[0080] 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.

[0081] Consequently, the presence of PBSA in such proportions in the polymeric binder of the invention allows for energy savings during the 3D printing step, and the implementation of the latter is also facilitated.

[0082] In another example of an embodiment of the polymeric binder, which is equally advantageous, the structural polymer is PBS.

[0083] This 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.

[0084] The second constituent polymer of said polymeric binder, PEG, has the advantage of being environmentally friendly and non-toxic in use.

[0085] The presence of this polymer allows fluidity of the composite formulation, obtained by mixing the polymeric binder and a ceramic powder, depending on its molar mass.

[0086] Thus, PEG makes it possible to facilitate 3D printing, by lowering the viscosity of the feedstock, namely the granules obtained from the composite formulation containing the polymeric binder.

[0087] According to a highly preferred embodiment, the polymeric binder of the invention consists of:

[0088] - PEG (polyethylene glycol) 4000 g / mol in a proportion equal to 25% (w / w);

[0089] - PEG (polyethylene glycol) 4000 g / mol in a proportion equal to 25% (w / w);

[0090] - PBSA (poly(butylene succinate co-adipate) or PBS (poly(butylene succinate)) in a proportion equal to 50% (m / m).

[0091] 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.

[0092] Now, with regard to 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):

[0093] - between 74 and 85% of a powder of a ceramic compound selected from zirconia (ZrO2), yttria zirconia (YSZ), aluminium oxide A12O3, hydroxyapatite (HAP Ca5(PO4)3(OH)), tricalcium phosphate (TCP);

[0094] - between 14 and 25% polymeric binder as defined previously in the description ;

[0095] - between 0.2 and 1% stearic acid powder.

[0096] The sum of the constituents of the composite formulation (ceramic compound, polymeric binder and stearic acid) is 100% by mass.

[0097] Preferably, said composite formulation consists of:

[0098] - zirconia powder (ZrO2) or yttria-treated zirconia powder (YSZ) in a proportion equal to 80% (m / m);

[0099] - polymeric binder, consisting of PEG 4000, PEG 10000 and PBSA or PBS, in a proportion equal to 19.6% (m / m);

[0100] - stearic acid powder in a proportion equal to 0.4% (w / w).

[0101] The polymeric binder used in this formulation is preferably made up of 25% PEG 4000, 25% PEG 10,000 and 50% PBSA or PBS.

[0102] The zirconia is preferably yttria zirconia.

[0103] From this composite formulation, according to a third aspect of the invention, it is conceivable 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:

[0104] - Dissolving the acid, initially in powder form, in a volume V1 diethyl ether under magnetic stirring until the stearic acid dissolves and a stearic acid solution of volume VI' is obtained;

[0105] - Addition, to said dilute stearic acid solution, of ceramic powder and of a volume V2 of diethyl ether, under vigorous stirring, so that the total volume of liquid, equal to VI' (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 charge in the polymer matrix;

[0106] - Evaporation of ether at room temperature (between 20 and 25 °C) under a fume hood for to obtain ceramic powder particles coated with stearic acid; this evaporation step can typically be carried out for a period of approximately 24 hours.

[0107] - Mixture of stearic acid-coated ceramic powder particles and binder polymeric, in the appropriate proportions, by dry method in a mixer and then together by melting at a temperature of, or equal to, 110 °C, in a twin-screw extruder, and obtaining the composite formulation; this step allows mixing of the ceramic filler, already coated with stearic acid, with the polymeric binder, in order to finally obtain a perfectly homogeneous mixture;

[0108] - Extrusion of filaments from said composite formulation and grinding of said filaments filaments for obtaining composite granules.

[0109] Thus, in a preferred embodiment 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 VI of the order of 150 mL of diethyl ether, 800 g of yttria-treated zirconia powder (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 10,000 (4.9% by mass).

[0110] 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.

[0111] In particular, such composite granules have the following constituents in their composition, in the proportions indicated:

[0112] - powder of a ceramic compound selected from zirconia (ZrO2), zirconia yttria (YSZ), aluminium oxide A12O3, hydroxyapatite HAP, tricalcium phosphate TCP, in a proportion between 74 and 85% (w / w);

[0113] - a polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion between 14 and 25% (m / m);

[0114] - stearic acid powder in a proportion of between 0.2 and 1% (w / m).

[0115] Here again, advantageously, taking into account the preferred embodiment of the invention, the composite granules consist of:

[0116] - yttria zirconia powder (YSZ) in a proportion equal to 80% (w / w);

[0117] - polymeric binder consisting of PEG 4000, PEG 10000 and PBSA or PBS in a proportion equal to 19.6% (w / w); preferably, the composition of the polymeric binder enabling the manufacture of the granules, and therefore entering into the composition of the latter, is: 25% of PEG 4000, 25% of PEG 10,000 and 50% of PBSA or PBS.

[0118] - stearic acid powder in a proportion equal to 0.4% (w / w).

[0119] 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.

[0120] 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.

[0121] The process for manufacturing a ceramic part from composite granules comprises 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 plateau of 140 °C at a heating rate of 2 °C / min; • From this first temperature stage, increase the temperature up to a second temperature stage of 170 °C at a heating rate of 0.1 °C / min; • From this second temperature stage, increase the temperature up to a third temperature stage 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 2 hours for consolidation and obtaining the final ceramic piece.

[0122] According to a particular feature of this ceramic part manufacturing process, only thermal debinding is required. In other words, thanks to the formulation of the polymeric binder used in the composition of the composite granules, chemical debinding is not necessary.

[0123] The debinding step implemented here, with the recommended temperature parameters and heating speeds, allows the polymeric binder to be removed by decomposition, by heating the composite part to the binder degradation temperature.

[0124] Finally, the sintering step, carried out in a furnace, consolidates the ceramic particles, in particular zirconia ZrO2 or yttria zirconia.

[0125] The presence, in the polymeric matrix, in addition to the bio-based structural polymer, of a second polymer, namely PEG, which is more fluid than said structural polymer, makes it possible to facilitate three-dimensional printing by lowering the viscosity of the composite granules.

[0126] The formulation has, in fact, due to the polymers it contains in the proportions that have been defined, an optimized viscosity, greater than 9 Pa.s (for a shear rate of 105 s 1 through the printer nozzle), which allows it to be printable without being degraded during its extrusion and printing.

[0127] The thermal debinding step is also facilitated, in particular, by the presence of small chains from low molecular weight PEG 4000.

[0128] 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, to limit energy consumption and, consequently, to reduce costs.

[0129] The invention also relates to a ceramic part manufactured by three-dimensional printing from the composite granules as defined above in their composition.

[0130] 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.

[0131] Example: Manufacture of ceramic parts from different formulations comprising polymers

[0132] The composite formulation according to the present invention which has been tested contains 80% by mass of yttria-treated 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.

[0133] 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% of stearic acid, and 19.6% of PBSA.

[0134] Also, a third composite formulation was tested: this one contains, as a polymeric binder, only PEG, namely: 80% by mass of yttria-treated zirconia, 0.4% of stearic acid, 9.8% of PEG 4000 and 9.8% of PEG 10,000.

[0135] The production of the composite granules is carried out as follows, to obtain a mass of 1 kg of granules:

[0136] The first step is carried out by solvent in order to coat all the yttria zirconia particles with stearic acid and promote good dispersion of the filler in the polymer matrix.

[0137] 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 totally transparent solution was obtained.

[0138] Next, yttria-treated zirconia was added to the solution with a little more ether to coat all the zirconia particles while maintaining magnetic stirring.

[0139] 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.

[0140] The volume of ether used is slightly greater than the volume of zirconia. It is necessary that the zirconia particles be completely coated in the ether for the coating to be done in the liquid state.

[0141] As for the second step, it is carried out 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.

[0142] The filaments obtained after extrusion are ground to obtain granules.

[0143] These granules were then printed using a suitable 3D printer, at to know the "Freeformer®" printer (registered trademark) from "Arburg®" (registered trademark) to obtain, initially, composite parts.

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[0151]

[0152]

[0153] 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. The results obtained using the three tested polymeric binder compositions are illustrated in [Fig.1] of the attached drawings. Figure 2 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%). Figure 3 illustrates 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. This thermal unbinding program is also detailed in the table below: Heating Speed ​​Ranges 25-14°C 2x / min 140-17°C arc / min 170-20°C 1T / min 200-38°C Returning now to the photographs of the thermally debonded ceramic pieces shown in [Fig. 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 went well; [Fig. 4] is a tomography of this part after debinding, showing its satisfactory intrinsic quality. Part 2 was produced using a polymer binder formulation containing only PBSA; it was very difficult to print, as the binder was highly viscous, and thermal debinding was also extremely challenging. The photograph clearly illustrates that the quality of the final part is not optimal. - Part 3 was produced using a polymeric 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.

[0154] Fig. 2 illustrates that the present polymeric binder formulation makes it possible to obtain ceramic parts of satisfactory quality, regardless of the filling rate of said parts that one seeks to obtain.

[0155] These results demonstrate that the addition of PEG with PBSA in the polymeric 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.

[0156] 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.

[0157] As regards the small polymer chains from PEG 4000, these will facilitate the debinding step.

[0158] 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.

[0159] That being said, an increase in the proportion of PEG 4000 relative to that of PEG 10,000 is also conceivable, in the proportions claimed, always mixed with PBSA as a structural polymer, in the proportions indicated.

[0160] It should be noted here that the tested polymeric binder formulation made it possible to achieve thermal debinding of the 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

Demands

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 is made up 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).

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 equal to 25% (w / w); - PEG (polyethylene glycol) 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).

3. Polymeric binder for three-dimensional printing according to claim 1 or claim 2 characterized in that said structural polymer is PBSA.

4. A 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 one of claims 1 to 3, said formulation comprising: - Powder of a ceramic compound selected from zirconia (ZrO2), yttria-stabilized zirconia (YSZ), aluminum oxide (Al2O3), hydroxyapatite (HAP Ca5(PO4)3(OH)), and 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

5.

6. PBSA and PBS, in a proportion between 14 and 25% (m / m); - Stearic acid powder in a proportion between 0.2 and 1% (w / w). Composite formulation for three-dimensional printing of a composite element by extrusion, according to claim 4, characterized in that it 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 approximately equal to or equal to 19.6% (w / w); - Stearic acid powder in a proportion of approximately equal to or equal to 0.4% (w / w). A process for preparing a composite formulation according to any one of claims 4 or 5, and for obtaining composite granules from this formulation, said process being characterized in that it comprises, at least, the following steps: - Dissolving stearic acid in a volume VI of diethyl ether under stirring to obtain a solution of dissolved stearic acid of a volume VI'; - Addition, to the said stearic acid solution, of ceramic powder and a volume V2 of diethyl ether, under agitation, so that the total volume of liquid, equal to Vl'+V2, is greater than the volume of powder; - Evaporation of ether at room temperature under a fume hood to obtain ceramic powder particles coated with stearic acid; - Mixing of coated ceramic powder particles and polymeric binder, by dry method in a mixer then together by melting at a temperature of, or equal to, 110 °C, in a twin-screw extruder, and obtaining the composite formulation; - Extrusion of filaments from said composite formulation and grinding of said filaments to obtain composite granules.

7. Composite granules based on the composite formulation according to claim 4 or claim 5, which can be obtained according to the process of the preceding claim and comprising: - Powder of a ceramic compound selected from zirconia (ZrO2), yttria 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).

8. Composite granules according to claim 7 characterized in that they have the following composition: - Zirconia (ZrO2) or yttria zirconia (YSZ) powder 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).

9. A method for manufacturing a ceramic part from composite granules according to claim 7 or claim 8, characterized in that it comprises the following steps: - Three-dimensional printing of a composite part from composite granules according to claim 7 or claim 8; - Application of thermal debinding to the composite part obtained in the preceding step, the thermal debinding being carried out in temperature steps according to the following program: • Starting from an initial temperature of 25 °C, increasing the temperature to which said composite part is subjected until a first temperature plateau of 140 °C at a heating rate of 2 °C / min; • From this first temperature stage, increase the temperature up to a second temperature stage of 170 °C at a heating rate of 0.1 °C / min; • From this second temperature stage, increase the temperature up to a third temperature stage 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 piece.