Method for manufacturing parts by centrifugation-assisted micro-molding

Abstract

The invention relates to a method for preparing a part by centrifugation-assisted micro-molding comprising, in particular, the preparation of a rigid polymer mold, the preparation of a suspension comprising, in particular, a ceramic or metal powder, and a heat treatment.

Description

[0001] Centrifuge-assisted micromolding manufacturing process for parts

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention belongs to the field of ceramic or metallic materials. More particularly, the present invention relates to a method for manufacturing a part by centrifugally assisted micromolding.

[0004] STATE OF THE ART

[0005] Complex ceramic or metallic micro-components are components that are generally microscopic in size and possess a complex three-dimensional shape or architecture. These can be made from technical ceramic materials such as alumina oxide, silicon carbide, or zirconium oxide, or from metallic materials such as precious metals (gold, platinum, palladium, etc.), non-ferrous metals (aluminum, titanium, copper, etc.), or precision alloys (iron-nickel, iron-nickel-cobalt, etc.). Such micro-components find applications in various technical fields, including microelectronics, telecommunications and aerospace, optics and photonics, medical imaging, and watchmaking.These micro-parts can have complex shapes including fine geometric features such as grooves, holes, very small channels, precise contours or other miniature structures, requiring tight dimensional tolerances and / or sophisticated surface finishes.

[0006] To manufacture such complex ceramic or metallic micro-parts, it is known to use methods such as direct micromachining, laser engraving, or 3D lithography (two-photon polymerization). However, these methods have significant limitations.

[0007] Direct micromachining can generate internal stresses or cracks, particularly in very high-resolution micro-parts, which are detrimental to the properties of the final part. The three-dimensional geometry of patterns created by direct micromachining is also limited by the size of the available tools (diameter and length). Finally, although micromachining is compatible with a wide variety of materials (e.g., ceramics or metals), these materials can cause varying degrees of wear on the cutting tools, resulting in high maintenance costs for production equipment.

[0008] 3D lithography makes it possible to generate objects with submicron precision, but its use remains to date essentially limited to polymer materials.

[0009] Finally, laser engraving, like direct micromachining and 3D lithography, remains extremely expensive to implement due to the equipment required for its operation (high-power laser, CNC machining center, cutting tools, photosensitive resins), as well as the associated safety and control requirements. These methods are also time-consuming, both in optimizing process parameters for a given material (machining strategy, laser power, beam scanning speed in laser engraving, resin selection and light exposure parameters in 3D lithography) and in their execution.

[0010] As an alternative to direct micromachining, laser engraving, or 3D lithography, document CN104369254A describes a method for manufacturing 3D ceramic microcomponents by centrifugally assisted micromolding. The disclosed process includes preparing a flexible polydimethylsiloxane (PDMS) mold; preparing a ceramic mixture with a high solids content (greater than 50% by volume) and low viscosity; adding this ceramic mixture to the flexible PDMS mold; centrifuging to enable micromolding; drying; and demolding the part before sintering. However, using a flexible PDMS mold has significant drawbacks; for example, the demolding operation can lead to deformation or breakage of the microcomponents due to the mechanical stresses it generates.

[0011] Document US2001 / 0038803A1 discloses the manufacture of microscopic, or even submicroscopic, metallic components using a composition comprising metallic nanoparticles and a rigid mold structured by LIGA lithography, the X-ray sensitive material of which may be either PMMA or one of its copolymers (e.g. poly(methyl methacrylate-co-butyl methacrylate), a poly(lactide) such as poly(lactide-co-glycolide), polymethacrylamide, polyoxymethylene, polyalkenesulfone or poly(glycidyl methacrylate-ethyl co-acrylate)), or an epoxy resin (SU8-25). The process disclosed in this document includes the preparation of a structured mold, the application of a composition comprising metallic nanoparticles and optionally a binder (at a level of 1 to 50% (mass) of the composition, preferably 5 to 30% mass) in the structured mold and its pressing.The process of filling the mold and then pressing the composition into the mold cavities is repeated at least three times, which can lead to mold deformation and / or non-homogeneous filling. The organic mold is then removed by pyrolysis (thermal debinding), demolding (mechanical operation), or dissolution in a suitable solvent (chemical debinding).

[0012] Thus, there is a considerable need to develop new, easy-to-implement processes to produce complex-shaped micro-parts with very tight dimensional tolerances, and which do not generate internal stresses or cracks on the micro-parts.

[0013] DESCRIPTION OF THE INVENTION

[0014] In the context described above, the present invention aims to overcome, in whole or in part, the drawbacks of the prior art mentioned above. The inventors have developed a method for preparing a ceramic or metallic part by centrifugally assisted micromolding in a rigid sacrificial mold. The method according to the invention advantageously allows the production of complex-shaped parts with very tight dimensional tolerances, without generating internal stresses or cracks in the produced parts, unlike alternative methods such as conventional machining or microcasting in flexible molds. This makes it possible to obtain ceramic or metallic microparts with geometric details on the order of a few microns. Also advantageously, the method according to the invention is easy to implement, quick to execute, and inexpensive, unlike laser engraving processes, for example.

[0015] Thus, the invention relates to a method for preparing a part by centrifugally assisted micromolding comprising:

[0016] 1) a step of preparing a rigid polymer mold comprising a cavity having a pattern,

[0017] 2) a step of preparing a suspension comprising: - between 1% and 50% (volume of powder / volume of solution) of a powder of a mineral filler, the powder comprising particles having a size between 1 nm and 10 pm, the mineral filler comprising: i) a ceramic powder, ii) a metallic powder, iii) a powder of a metal-ceramic composite, iv) a mixture of these; between 0.1 and 5% by mass of dispersant, between 0.1 and 20% by mass of binder, between 0.1 and 20% by mass of plasticizer, and a solvent,

[0018] 3) a step of filling the cavity of said rigid mold with said suspension,

[0019] 4) a centrifugation step of said rigid mold comprising said suspension, thereby filling the pattern in the cavity of said mold entirely with a granular compact from the suspension,

[0020] 5) a drying step of the granular compact in said rigid mold,

[0021] 6) a demolding step whereby the said granular compact is recovered, and the said rigid mold is possibly disposed of,

[0022] 7) a debinding step of the granular compact by which said binder is removed and a raw piece is thus recovered having a raw density equal to or greater than 60%,

[0023] 8) a sintering step of said raw piece.

[0024] Advantageously, the rigid polymer mold prepared in a process according to the invention may not deform during the centrifugal filling step.

[0025] Advantageously, the rigid polymer mold prepared in a process according to the invention may not react with the organic components of the suspension, in particular the binder, dispersant, plasticizer, or solvent. Advantageously, the rigid polymer mold prepared in a process according to the invention can be easily removed, for example, during a demolding step. In a particular embodiment, such a rigid mold may be pyrolyzable and thus be removed during a demolding step by heat treatment. In an alternative embodiment, such a rigid mold may be dissolvable and thus be removed during a demolding step by chemical treatment.The rigid mold prepared in a process according to the invention can be made of acrylic polymers, polycarbonates, polyethylenes, polypropylene, wax, paraffin or polysaccharides (celluloses and their derivatives) or a mixture thereof, preferably polymethyl methacrylate (PMMA).

[0026] The rigid polymer mold may include a cavity containing a specific pattern, this pattern imparting a particular geometry to the part produced in said mold. Advantageously, the pattern of the cavity of the rigid mold according to the invention may have a significant depth-to-width ratio. For the purposes of this invention, a "significant depth-to-width ratio" means a ratio equal to or greater than 2, for example, a ratio greater than 3. In one particular embodiment, the pattern of the cavity of the rigid polymer mold is obtained by LIGA lithography or by direct machining.

[0027] The process according to the invention can advantageously be implemented with a wide variety of ceramic or metallic powders (mineral fillers). A mineral filler usable in a process according to the invention can take the form of a ceramic and / or metallic powder whose particles have a size between 1 nm and 10 pm.

[0028] According to a particular embodiment, the mineral charge usable in a process according to the invention comprises a ceramic powder, preferably a ceramic powder comprising nitrides, borides, carbides, or mixtures thereof, even more preferably Al2O3, ZrÛ2, TiC>2, MgO, YSZ, SrTiOs, BaTiOs, CeC>2, SiC>2, NiO, LasOs, HfC>2, SiC, SislXL, MgAl2O4, AIN, B4C, WC, BN or mixtures thereof.

[0029] According to an alternative embodiment, the mineral feed usable in a process according to the invention comprises a metal powder, preferably a metal powder comprising copper, nickel, iron, platinum, palladium, niobium, molybdenum, titanium, gold, tungsten, aluminum, or an alloy of these metals. Preferably, the mineral feed usable in a process according to the invention is a metal powder comprising copper, nickel, iron, or an alloy of these metals.

[0030] According to another embodiment, the mineral filler usable in a process according to the invention comprises a powder of a metal-ceramic composite. Preferably, a powder of a metal-ceramic composite comprising at least one ceramic element selected from Al₂O₃, ZrC₂, TiC₂, MgO, Y₂Z, SrTiO₂, BaTiO₂, CeO₂, SiO₂, NiO, LasO₂, HfO₂, SiC, SisN₄, MgAhO₄, A₂N, B₄C, WC, or BN; and at least one metallic element selected from copper, nickel, iron, platinum, palladium, niobium, molybdenum, titanium, gold, tungsten, or aluminum. By way of example, a metal-ceramic composite may be Al / SiC or Al / WC.

[0031] According to another embodiment, the mineral filler usable in a process according to the invention comprises a mixture of a ceramic powder, a metallic powder or a powder of a metal-ceramic composite.

[0032] In one embodiment, the dispersant in a suspension prepared in a process according to the invention comprises a surfactant, a polyelectrolyte, a complexing agent, or mixtures thereof. In another embodiment, the binder in a suspension prepared in a process according to the invention comprises polyvinyl alcohol, polyethylene glycol, cellulose or its derivatives, acrylic latex, a polysaccharide gel, or mixtures thereof.

[0033] According to one embodiment, the plasticizer in a suspension prepared in a process according to the invention comprises glycerol, stearic acid, polyethylene glycol or mixtures thereof.

[0034] According to one embodiment, the suspension prepared in a process according to the invention comprises an aqueous solvent, preferably water, or an organic solvent, preferably ethanol, methyl ethyl ketone (MEK) or a mixture thereof.

[0035] According to a particular embodiment, the step of preparing a suspension in a process according to the invention comprises successively:

[0036] - 2a) the mixing of the mineral filler and the dispersant in the solvent, thereby obtaining a first mixture,

[0037] - 2b) the addition of the binder and plasticizer to said first mixture.

[0038] Such a two-step preparation advantageously allows the mineral filler to be dispersed while avoiding a competition of adsorption between the dispersant and other components (e.g., binder or plasticizer) on the surface of the mineral filler particles, thus improving the dispersion of the mineral filler.

[0039] According to a particular embodiment, the process according to the invention also includes a step of homogenizing the suspension, preferably an ultrasonic homogenization step. Such a step advantageously breaks down any agglomerates and ensures uniform dispersion of the particles in the suspension.

[0040] Advantageously, the centrifugation step in a process according to the invention ensures homogeneous filling of the rigid mold cavity and complete filling of the patterns present within the cavity, thus guaranteeing the repeatability and reproducibility of the part manufacturing process. In a particular embodiment, the centrifugation step in a process according to the invention is carried out at a centrifugal force of 50 g to 50,000 g for a duration of 1 min to 60 min (where g corresponds to the centrifugal acceleration, 1 g being equal to 9.81 m / s²). -2 ).

[0041] The drying step in a process according to the invention can be carried out by applying a load to the sample, for example, a load of 2 newtons. According to a particular embodiment, the drying step in a process according to the invention comprises a first drying 5a) at room temperature for a period of 1 to 48 hours, preferably 12 hours; then a second drying 5b) at a temperature between 40°C and 100°C, preferably 50°C, even more preferably for a period of 1 to 72 hours, preferably 24 hours. A drying step in a process according to the invention can be carried out until the mold containing the part no longer loses mass.

[0042] The demolding step in a process according to the invention advantageously allows recovery of said granular compact and possibly elimination of the rigid mold, and may include heat treatment, chemical treatment, or mechanical removal.

[0043] The debinding step in a process according to the invention makes it possible to remove the binder from the granular compact and to obtain a raw part, which may advantageously have a raw density equal to or greater than 60%.

[0044] In one particular embodiment, the demolding step includes a heat treatment during which the granular compact is recovered, and the rigid mold is removed by pyrolysis. In such an embodiment, the demolding and debinding steps can be carried out simultaneously during the same heat treatment, advantageously allowing both the rigid mold to be removed by pyrolysis and the binder (debinding) present in the granular compact to be removed. This yields a raw part, advantageously having a raw density equal to or greater than 60%.

[0045] In an alternative embodiment, the demolding step includes a chemical treatment in which the rigid mold is removed, for example by dissolution. In this case, the debinding step takes place after the demolding step.

[0046] According to another alternative embodiment, the demolding step includes the mechanical removal of the mold. In this case, the unbinding step also takes place after the demolding step.

[0047] The debinding step (or the demolding and debinding steps in the case where these are carried out simultaneously during the same heat treatment), can be carried out at a temperature between 500°C and 700°C, preferably between 550°C and 650°C, even more preferably at a temperature of 600°C, for a period of 1 hour.

[0048] The present invention also relates to a part that can be obtained by the process according to the invention.

[0049] BRIEF DESCRIPTION OF THE FIGURES

[0050] Figure 1A is an optical electron microscopy image of a part prepared according to Example 1, in top view. Figure 1B is a 3D optical electron microscopy reconstruction of a part prepared according to Example 1.

[0051] Figure 2A is an optical electron microscopy image of the LIGA lithography-structured mold used in Example 2.

[0052] Figure 2B is a scanning electron microscopy image of a part prepared according to example 2 in the LIGA lithography-structured mold shown in figure 2A.

[0053] Figure 3A is an optical electron microscopy image of a part prepared according to example 3, in top view.

[0054] Figure 3B is a 3D optical electron microscopy reconstruction of a part prepared according to example 3.

[0055] Figure 4 is a 3D optical electron microscopy reconstruction of a part prepared according to example 4.

[0056] DETAILED DESCRIPTION OF THE INVENTION

[0057] Definitions:

[0058] For the purposes of this invention, a "part" or "micro-part" is any manufactured object that can be obtained by the centrifugally assisted micromolding process according to the invention. Such a part may be made of ceramic, metallic, or a combination thereof. The composition of such a part will depend on the mineral filler used to formulate the suspension used in the process according to the invention. A part according to the invention may be microscopic in size. A part according to the invention may have a wide variety of shapes depending on the mold design used in the process according to the invention, its shape being chosen according to the intended applications.Advantageously, the process according to the invention makes it possible to obtain parts with complex shapes, for example, parts with patterns where the depth-to-width ratio is equal to or greater than 3, and / or parts with geometric details on the order of micrometers, for example, crenellated structures or periodic arrays of microcylinders. Also advantageously, the process according to the invention makes it possible to obtain parts with tight dimensional tolerances.

[0059] A part obtainable by a process according to the invention can find application in a wide variety of fields. For example, a part according to the invention is suitable for various industrial applications, for example in the medical, telecommunications, aerospace, defense, watchmaking, photonics, or any other field requiring high-precision micro-parts sectors.

[0060] Dimensional tolerance refers to an acceptable range of variation on a given dimension of a part or a feature of a part. Dimensional tolerance thus defines the limits within which the dimension of the part or a feature of the part may deviate from its nominal (or theoretical) value, while still meeting the part's quality or functionality specifications. A narrow dimensional tolerance implies that the part's manufacturing process exhibits high reproducibility. A narrow dimensional tolerance, as defined in the invention, is a dimensional tolerance less than or equal to 20 µm, preferably less than or equal to 15 µm, and even more preferably less than or equal to 10 µm, 5 µm, 3 µm, 2 µm, or 1 µm.

[0061] For the purposes of this invention, "micromolding" or "centrifuge-assisted micromolding" refers to a method for manufacturing micro-parts from a suspension of ceramic or metallic particles in a liquid medium, which is introduced into a rigid mold. The mold filled with the suspension is then subjected to a centrifugal force to ensure homogeneous filling of the mold.

[0062] For the purposes of this invention, the terms "mold," "rigid mold," or "sacrificial rigid mold" refer to a mold designed to be removed, or even destroyed or eliminated, during the demolding of the part, for example, by heat treatment (pyrolysis). Such a mold can be made from rigid polymers. Advantageously, such a rigid mold maintains its shape and dimensions during the steps of filling its cavity, centrifugation, and drying, thus limiting the mechanical stresses exerted on the part. Preferably, a rigid mold usable in a process according to the invention may have a Young's modulus greater than or equal to 0.1 GPa, preferably greater than or equal to 0.5 GPa, and even more preferably greater than or equal to 3 GPa.

[0063] Method according to the invention:

[0064] A first object of the invention relates to a method for preparing a part by centrifugally assisted micromolding comprising:

[0065] 1) a step of preparing a rigid polymer mold comprising a cavity having a pattern,

[0066] 2) a step of preparing a suspension comprising: - between 1% and 50% (volume of powder / volume of solution) of a powder of a mineral filler, the powder comprising particles having a size between 1 nm and 10 pm, the mineral filler comprising: i) a ceramic powder, il) a metallic powder, ill) a powder of a metal-ceramic composite, or iv) a mixture of these; between 0.1 and 5% by mass of dispersant, between 0.1 and 20% by mass of binder, between 0.1 and 20% by mass of plasticizer, and a solvent,

[0067] 3) a step of filling the cavity of said rigid mold with said suspension,

[0068] 4) a centrifugation step of said rigid mold comprising said suspension, thereby filling the pattern in the cavity of said mold entirely with a granular compact from the suspension,

[0069] 5) a drying step of the granular compact in said rigid mold,

[0070] 6) a demolding step whereby the said granular compact is recovered, and the said rigid mold is possibly disposed of,

[0071] 7) a debinding step of the granular compact by which said binder is removed and a raw piece is thus recovered having a raw density equal to or greater than

[0072] 60%

[0073] 8) a sintering step of said raw piece.

[0074] Rigid mold:

[0075] A rigid mold usable in a process according to the invention may have a Young's modulus greater than or equal to 0.1 GPa, preferably greater than or equal to 0.5 GPa, and even more preferably greater than or equal to 3 GPa. The Young's modulus of a rigid mold may, for example, be determined by tensile mechanical testing according to DIN EN ISO 527-2, or by flexural mechanical testing according to DIN EN ISO 178. Alternatively, the Young's modulus of a rigid mold may be determined by contact ultrasonic testing according to NF EN 14186.

[0076] A rigid mold usable in a process according to the invention may comprise, be essentially made of, or be made of polymers derived from acrylic acid or its derivatives, for example polymethyl methacrylate (PMMA), or epoxy polymers, for example SU-8. Such polymers can advantageously be easily structured on a micrometer scale, for example by LIGA lithography, to form the patterns of the mold, and are easily machinable.

[0077] A rigid mold usable in a process according to the invention may comprise, be essentially made of, or be made of polyetheretherketone (PEEK), polyetherimide (PEI), polyimide (PI), polyamide-imide (PAI), or polycarbonate (PC). Such polymers advantageously exhibit good mechanical strength and can be easily and precisely machined to produce a mold with complex patterns.

[0078] A rigid mold usable in a process according to the invention may comprise, be essentially composed of, or be composed of polymers (for example, polyetheretherketone or polyetherimide) reinforced with glass or carbon fibers. For example, such a composite rigid mold may comprise from 5% to 70% glass or carbon fibers, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70% glass or carbon fibers, preferably from 15% to 50% glass or carbon fibers. Such composite materials advantageously combine the benefits of polymers while improving certain of their properties (such as dimensional stability or mold rigidity).

[0079] Finally, a rigid mold usable in a process according to the invention may comprise, be essentially made of, or be made of waxes (for example, synthetic waxes such as polyetherimides (POM)), paraffins, celluloses or polystyrene.

[0080] A rigid mold usable in a process according to the invention may include patterns for giving the part a particular geometry. Such patterns may exhibit significant complexity with high resolution. These patterns may have various structures, for example, crenellated structures, or at least a periodic array of micro-cylinders, preferably embedded in the mold within a cavity at least 1 mm deep. This cavity depth advantageously ensures that a sufficiently large amount of material remains above the patterns of the mold after the centrifugation step, in order to protect the patterns during mold handling, for example, when removing it from the centrifuge tube, and to prevent any deformation of the micro-part during the heat treatment step.The patterns of a rigid mold usable in a process according to the invention will advantageously be imprinted on the prepared part. The use of a rigid mold in a process according to the invention advantageously prevents any deformation of said mold, particularly during the filling and centrifugation steps, so as to produce parts with high resolution (for example, geometric details on the order of micrometers), and tight dimensional tolerances (for example, less than or equal to 3 µm). The patterns of a rigid mold usable in a process according to the invention may advantageously have a depth-to-width ratio greater than or equal to 2, preferably greater than or equal to 3, and even more preferably greater than or equal to 5.For example, the patterns of a rigid mold usable in a process according to the invention may have a depth / width ratio of approximately 3, approximately 4, approximately 5, approximately 6, or approximately 7.

[0081] The use of a rigid mold, for example a sacrificial rigid mold, advantageously allows the preparation of parts with such depth / width ratios without imposing mechanical stresses on the granular compact during demolding, which could generate cracks detrimental to the integrity of the part.

[0082] It is understood that the patterns of a rigid mold usable in a process according to the invention may also have a depth / width ratio of less than 3, for example about 1, about 1.5, about 2 or about 2.5.

[0083] The patterns of a rigid mold usable in a process according to the invention can be created by LIGA lithography or by direct machining. For example, a rigid mold usable in a process according to the invention can be prepared by plastic injection molding or hot stamping with micrometer or even sub-micrometer precision. This method of preparation by plastic injection molding is particularly well-suited to thermoplastic polymers, such as cycloolefin (co)polymers (COP / COC), polymethyl methacrylate (PMMA), polycarbonate (PC), polypropylene (PP), polystyrene (PS), or polyethylene terephthalate (PET). A rigid mold usable in a process according to the invention can also be prepared by laser ablation, 3D printing, thermoforming, or plastic sheet metal fabrication.

[0084] Preparing the suspension:

[0085] The suspension prepared in the process according to the invention advantageously comprises a powder of a mineral filler comprising a ceramic powder, a metallic powder, a powder of a metal-ceramic composite, or a mixture thereof.

[0086] The powder of a mineral filler used to prepare a suspension in a process according to the invention may comprise particles with a size between 1 nm and 10 pm, preferably between 0.1 pm and 10 pm, and even more preferably between 0.5 pm and 2 pm. The particle size of the mineral filler powder may, for example, be measured by laser diffraction.

[0087] The term "ceramic powder" refers to a powder comprising a non-metallic inorganic material, such as oxides, nitrides, carbides, or borides. For example, a ceramic powder may include Al2O3, ZrC>2, TiC>2, MgO, YSZ, SrTiO3, BaTiO3, CeO2, SiO2, NiO, La2O3, HfO2, SiC, Si3N4, MgAl2O4, AIN, B4C, WC, BN, or mixtures thereof.

[0088] By "metallic powder" is meant a powder comprising a metal (such as an alkali, an alkaline earth, a transition metal or a post-weak metal), for example Cu, Ni, Fe, Au, Pt, Ag, Mo, Nb, Pd, W, Al, Ti, or an alloy of these metals.

[0089] The suspension prepared in the process according to the invention may also include a mineral filler comprising a powder of a metal-ceramic composite. Such a metal-ceramic composite powder may comprise at least one ceramic element selected from Al₂O₃, ZrO₃, TiO₃, MgO, YSZ, SrTiO₃, BaTiO₃, CeO₂, SiO₃, NiO, La₂O₃, HfO₂, SiC, Si₃N₄, MgAhO₄, AIN, B₄C, WC, BN; and at least one metallic element selected from Cu, Ni, Fe, Au, Pt, Ag, Mo, Nb, Pd, W, Al, Ti. By way of example, a metal-ceramic composite may be Al / SiC or Al / WC.

[0090] The suspension prepared in the process according to the invention may also include a mixture of a ceramic powder, a metal powder or a powder of a metal-ceramic composite.

[0091] Advantageously, the suspension prepared in the process may comprise between 1% and 50% (powder volume / solution volume) of a ceramic and / or metallic powder, preferably between 1% and 45%, and even more preferably between 5% and 30%. Such a volume proportion of the ceramic and / or metallic powder (solid phase) in the suspension is also called the "solid loading rate".

[0092] The suspension prepared in the process according to the invention may advantageously include a dispersant. By "dispersant," we mean an agent that improves the homogeneity of the mineral charge distribution in the suspension. The dispersant advantageously allows for obtaining a stable and homogeneous suspension. A dispersant usable for preparing a suspension in the process according to the invention may include a surfactant, a polyelectrolyte, or a complexing agent. By way of example, a dispersant usable for preparing a suspension in the process according to the invention may include citric acid, poly(acrylic acid) (PAA), polyacrylates or their derivatives (for example, a solution of sodium poly(acrylate)), lignosulfonate or its derivatives, polyvinylpyrrolidone (PVP).

[0093] According to a particular embodiment, the suspension prepared in the process according to the invention comprises between 0.1% and 10% of dispersant, preferably between 0.1% and 5%, even more preferably between 0.1% and 2% (as a mass percentage relative to the mass of dry mineral filler).

[0094] The suspension prepared in the process according to the invention may advantageously include a binder. By "binder" is meant an agent that improves the cohesion of the mineral charge in the suspension, and thus its stability. By way of example, a binder that can be used to prepare a suspension in the process according to the invention may include cellulose and its derivatives, polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyethylene glycol (PEG), preferably high molecular weight polyethylene glycol (greater than 1000 Da), for example PEG 6000, acrylic latex, or polysaccharides, for example in gel form.

[0095] According to a particular embodiment, the suspension prepared in the process according to the invention comprises between 0.1% and 20% of binder, preferably between 0.1% and 10%, even more preferably between 0.1% and 5% (mass percentage relative to the mass of dry mineral filler).

[0096] The suspension prepared in the process according to the invention advantageously comprises a plasticizer. "Plasticizer" means an agent that improves the flexibility and plasticity of the mineral filler in the suspension. The plasticizer advantageously reduces the viscosity of the suspension while facilitating the shaping and consolidation of the mineral filler within the suspension. For example, a plasticizer that can be used to prepare a suspension in the process according to the invention may comprise glycerol, stearic acid, or polyethylene glycol (PEG), preferably low molecular weight polyethylene glycol (less than 1000 Da), for example, PEG 300.

[0097] When polyethylene glycol is used as a plasticizer or binder in the suspension, the suspension may include at least one other plasticizer or binder besides polyethylene glycol. Alternatively, the suspension prepared in the process according to the invention may include high molecular weight polyethylene glycol, for example PEG 6000, as a binder, and low molecular weight polyethylene glycol, for example PEG 300, as a plasticizer. In one particular embodiment, the suspension prepared in the process according to the invention comprises between 0.1% and 20% plasticizer, preferably between 0.1% and 10%, and even more preferably between 0.1% and 5% (mass percentage relative to the mass of dry mineral filler).

[0098] The suspension prepared in the process according to the invention can be prepared in an aqueous solvent or in an organic solvent.

[0099] The term "aqueous solvent" refers to a solution in which water acts as the primary solvent. Preferably, the aqueous solvent is demineralized water (obtained through permutation or distillation), meaning water free of mineral salts, contaminants, and other impurities. The aqueous solvent can also be tap water or reverse osmosis water, meaning water that has been filtered by a reverse osmosis process using a semi-permeable membrane to remove unwanted ions and molecules.

[0100] An "organic solvent" is defined as a solution in which an organic substance acts as the principal solvent. Preferably, the organic solvent is a hydrocarbon, an alcohol, a ketone, an ether, an ester, an amine, or a mixture thereof. Particularly preferred, the organic solvent is ethanol, methyl ethyl ketone (MEK), or a mixture thereof.

[0101] The suspension preparation step in the process according to the invention can be carried out in two successive sub-steps, namely:

[0102] A step of mixing the mineral filler and the dispersant in the solvent, thereby obtaining a first mixture,

[0103] A step of adding the binder and plasticizer to said first mixture.

[0104] Such a two-step preparation is particularly advantageous, as it improves the dispersion of the mineral filler in the solvent, avoiding a competition of adsorption between the dispersant and the other components (namely binder and / or plasticizer) on the surface of the mineral filler particles.

[0105] The mixing of the various components in the suspension preparation step can be carried out under agitation, for example using balls in a three-dimensional dynamic mixer. After preparation, the suspension can be kept under agitation, for example on a roller agitator, until its use in the next step of the process according to the invention, namely mold filling.

[0106] Centrifugal micromolding: Before filling the rigid mold cavity, a suspension homogenization step can optionally be implemented. This step advantageously breaks up any agglomerates of mineral filler and ensures a uniform dispersion of the mineral filler particles within the suspension. This homogenization step can be carried out, for example, using a sonotrode or any other homogenization technique well known to those skilled in the art.

[0107] Before filling, the rigid mold prepared in the process according to the invention can be placed in a container suitable for withstanding a centrifugation step. This container may then include a support for receiving and holding the rigid mold. Preferably, such a container suitable for withstanding a centrifugation step may be a centrifuge tube. One or more rigid molds may be placed in the same container suitable for withstanding a centrifugation step, depending on their respective sizes.

[0108] The rigid mold filling step can be implemented by filling the rigid mold cavity with the suspension prepared in the process according to the invention.

[0109] A centrifugation step of the rigid mold containing the suspension follows the filling step. This step advantageously ensures homogeneous filling of the rigid mold cavity, particularly when the mold pattern is complex and microscopic. This homogeneous filling guarantees the repeatability and reproducibility of the part preparation process.

[0110] According to a particular embodiment, the centrifugation step in a process according to the invention can be carried out at a centrifugal force of 50 g to 50,000 g. Preferably, the centrifugation step in a process according to the invention can be carried out at a centrifugal force greater than or equal to 120 g. Even more preferably, the centrifugation step in a process according to the invention can be carried out at a centrifugal force greater than or equal to 400 g. This centrifugation step can advantageously be carried out for a sufficient duration to allow the filling of the patterns present in the mold cavity. The centrifugation time can therefore depend on the applied centrifugal force, as well as on the size and complexity of the mold patterns. By way of example, the centrifugation step can last from 1 min to 60 min.

[0111] Following the centrifugation step, the rigid mold is completely filled with a granular compact. "Granular compact" refers to an agglomerate of the mineral filler from the suspension after the centrifugation step, forming a dense and coherent mass. The formation of such a granular compact by centrifugation allows for the production, after the drying and debinding steps, of a raw part with improved density.

[0112] At the end of the centrifugation step, the supernatant, that is to say the part of the suspension which is not included in the mold, can be removed to allow the recovery of the filled mold.

[0113] Drying

[0114] The rigid mold containing the granular compact can be recovered after the centrifugation step. The granular compact can then undergo a drying step directly in the rigid mold. This drying step can be carried out at ambient temperature, i.e., between 18°C ​​and 25°C, preferably at 20°C. Alternatively, it can be carried out at a temperature between 40°C and 60°C, preferably at 50°C, for example, in an oven.

[0115] The drying step can be implemented under pressure, for example by applying a force of 2N to the granular compact.

[0116] The drying step may comprise several sub-steps of drying at different temperatures. In one particular embodiment, the drying step comprises a first drying 5a) at a temperature between 18°C ​​and 25°C, preferably 20°C, for a duration of 1 to 48 h, preferably 12 h; followed by a second drying 5b) at a temperature between 40°C and 100°C, preferably 50°C, for example, for a duration of 1 to 72 h, preferably 24 h. The duration of the drying step (or the plurality of sub-steps) may depend on the size and shape of the granular compact to be dried. Advantageously, such a drying step (or the plurality of sub-steps) may be carried out until the mold containing the granular compact no longer loses mass.

[0117] Demolding - Debinding

[0118] Following the drying stage, the rigid mold containing the dried granular compact is removed, and possibly disposed of, during a demolding stage. Such a demolding stage may include heat treatment (the mold is removed by pyrolysis), chemical treatment (the mold is removed by dissolution in a solvent), or mechanical removal (the dried granular compact is manually removed from the rigid mold). The demolding stage may also include a combination of the aforementioned treatments, for example, a combination of heat treatment and mechanical removal, a combination of heat treatment and chemical treatment, a combination of mechanical removal and chemical treatment, or a combination of heat treatment, chemical treatment, and mechanical removal.

[0119] A debinding step is performed after the demolding step, whereby the binder is removed from the dried granular compact, yielding a raw part with a density preferably greater than or equal to 40%. This debinding step can be carried out by heat treatment or chemical treatment.

[0120] The terms "raw part," "green part," or "green part" refer to a part formed in a rigid mold during the process according to the invention, from ceramic or metallic materials, in an intermediate form, after undergoing a drying and debinding step, but before undergoing a sintering step. Such a green part can be characterized by a "green density," which refers to the density of the compacted material, in g / cm³. -3before the sintering stage. The raw density can also be expressed relatively, as a percentage, representing the ratio between the measured raw density and the theoretical density of the material. The raw density reflects the mass of the compacted material per unit volume and is an indicator of the initial compaction and cohesion of the particles.

[0121] In one particular embodiment, the demolding step includes a heat treatment. In this embodiment, the demolding and debinding steps can be carried out simultaneously during the same heat treatment, which allows both the rigid mold to be removed by pyrolysis and the binder to be removed (debinding) from the granular compact.

[0122] Such a heat treatment (carried out during the debinding stage and possibly during demolding when the latter is carried out simultaneously with debinding by the same heat treatment) can advantageously be carried out at a temperature high enough to allow the removal of the binder from the granular compact, and the removal of the rigid mold by pyrolysis where appropriate, but at a temperature lower than the sintering temperature of the part.

[0123] According to a particular embodiment, such heat treatment is carried out at a temperature between 500°C and 700°C, preferably between 550°C and 650°C, and even more preferably at a temperature of 600°C.

[0124] Such heat treatment can be carried out under ambient air.

[0125] Alternatively, such heat treatment can be carried out under a neutral atmosphere, for example under nitrogen or argon. Heat treatment performed under a neutral atmosphere advantageously allows for control of the pyrolysis of the binders and limits any deformations or defects in the part that may appear after the sintering step.

[0126] The rate of temperature increase during such a heat treatment can advantageously be modulated according to the geometry of the part and the debinding atmosphere. The temperature increase in the heat treatment step can, for example, be carried out at a rate between 0.5 and 5 °C / min, preferably at a rate of approximately 0.5 °C / min or approximately 1 °C / min.

[0127] Such heat treatment can advantageously be carried out for a sufficient duration to allow for the complete removal of the mold by pyrolysis, as well as the complete removal of the binder from the granular compact. According to a particular embodiment, the heat treatment step can be carried out for a duration of 1 hour once the chosen heat treatment temperature is reached.

[0128] Sintering

[0129] Following the debinding stage, the raw part undergoes a sintering stage, resulting in the final part. This sintering stage advantageously allows the ceramic or metallic particles to partially or completely fuse, thus reducing the part's porosity and increasing its strength and density. The sintering stage can be carried out at a temperature dependent on the initial mineral filler used, for example, between 60% and 80% of the mineral filler's melting point. The conditions of this sintering stage can be adapted according to the nature of the mineral filler (ceramic and / or metallic powder) used, its size, its reactivity, and any impurities it may contain.

[0130] For example, such a sintering step can be carried out at a temperature between 1100°C and 2200°C for ceramic materials, or at a temperature between 600°C and 1400°C for metallic materials. A person skilled in the art will be able to choose a temperature and duration for the sintering step that are appropriate for the material being sintered.

[0131] The sintering step can advantageously be carried out immediately following the heat treatment step. In this embodiment, the temperature ramp, starting from the debinding (and demolding, if applicable) heat treatment temperature, can, for example, be achieved at a rate of 5 °C / min. Alternatively, the raw part can undergo an optional cooling step before the sintering step.

[0132] Part that can be obtained by the process according to the invention:

[0133] The invention also relates to a part that can be obtained by a process according to the invention. Such a part may be ceramic, metallic, or metal-ceramic. Preferably, such a part has a tight dimensional tolerance.

[0134] The embodiments exemplified below are given only as illustrations and do not in any way constitute a limitation of the present invention.

[0135] Example 1: Preparation of a micro-part in TiO2 from a PMMA mold structured by LIGA lithography.

[0136] A micro-part made of TiC₂ is manufactured by a process according to the invention. A rigid PMMA mold is fabricated and structured by LIGA lithography. This rigid mold includes patterns for preparing parts comprising micro-notches with a width of 130 µm and a height of 80 µm. A suspension in aqueous medium (distilled water) is prepared from rutile (TiC₂) powder, in an amount of 15% (volume of rutile powder relative to the total volume of the suspension). The rutile powder used to prepare the suspension has an average diameter of 2 µm. A dispersant, a binder, and a plasticizer are then added to the suspension. 0.50 mL of a poly(acrylate) solution (Vanderbilt Minerals) at 1.11 g / mL is then added to the suspension as a dispersant; 487 mg of polyvinyl alcohol (Sigma-Aldrich) are added as a binder; and 262 mg of poly(ethylene glycol) (Sigma-Aldrich) are added as a plasticizer.After homogenization of the suspension, it is poured into the rigid PMMA mold previously fixed in a centrifuge tube. The micro-molding of the parts is then carried out by applying a centrifugal acceleration of 1572 g (corresponding to 3500 rpm) for 8 min.

[0137] After drying at 50 °C for 12 hours, the mold undergoes pyrolysis and the granular compact is debound under air at 600 °C for one hour, with a temperature ramp rate of 0.5 °C / min. Finally, a sintering step at 1300 °C for one hour, with a ramp rate of 5 °C / min, consolidates the micro-part, shown in Figures 1A and 1B. Figure 1A shows a top view of the part obtained by digital optical microscopy. Figure 1B shows its 3D reconstruction by digital optical microscopy. The prepared micro-part has a relative density of 95%, calculated using Archimedes' principle.

[0138] 3D optical profilometer measurements were performed to characterize the verticality of the walls (side walls of the micro-part's slots). These measurements showed that the offset in the (XY) plane between the top and bottom of a wall of the part is less than 1 pm (corresponding to a slope angle of less than 1°). The surface roughness of the pattern's top edge was measured at 3 pm. This value corresponds to the roughness of what was previously the mold bottom produced by LIGA lithography, meaning that the process allows for the production of parts with a tight dimensional tolerance of less than 3 pm.

[0139] 2: Preparation of a rough micro-part in TiO2 from a mold structured by LIGA lithography.

[0140] A rigid PMMA mold is prepared. A pattern is structured on the mold using LIGA lithography. The pattern on the rigid mold thus exhibits a particular surface roughness resulting from the LIGA lithography technique. A scanning electron microscopy image of the structured mold is shown in Figure 2A. A rutile (TiU2) suspension prepared according to Example 1 is used. The rigid mold is fixed in a centrifuge tube and filled with this suspension. The micromolding of the part is then performed by centrifugation at 3500 rpm for 8 minutes.

[0141] The part is dried for 24 hours at room temperature, then for 2 hours at 50 °C. After drying, the mold containing the dried granular compact is immersed for 60 minutes in an acetone solution. After the mold dissolves, the part is removed from the acetone solution. The part, containing structured patterns, is then debound under air at 600 °C for one hour, with a temperature ramp rate of 5 °C / min, and then sintered at 1300 °C for one hour.

[0142] After sintering, the resulting pattern on the part was observed using both digital optical microscopy and scanning electron microscopy. A scanning electron microscopy image of the sintered part is shown in Figure 2B. It appears that the top of the pattern perfectly reproduces the roughness inherent to the LIGA lithography structure observed at the bottom of the rigid mold (shown in Figure 2A). Measurements were taken on the obtained micrographs. These measurements revealed that the structured part exhibits alternating thin and thick bars, 135 ± 3 pm high and spaced 83 ± 3 pm apart, with widths of 51 ± 1 pm and 92 ± 2 pm, respectively. The centrifugal-assisted micromolding process thus makes it possible to produce parts with a tight dimensional tolerance of 3 pm or less, which corresponds to the resolution of the LIGA-structured mold.

[0143] Example 3: Preparation of a micro-part in TiO2 whose pattern has a variable height, from a rigid polymer mold structured by direct micromachining.

[0144] A rigid PMMA mold is prepared and structured by micromachining. A rutile suspension (TiC>2) prepared according to example 1 is used, and a part is formed in the rigid mold structured by micromachining according to the protocol presented in example 2.

[0145] The sintered part, shown in Figures 3A and 3B, features a pattern composed of cylinders with diameters of 550 and 715 µm and heights of 150 and 400 µm, reproducing the pattern of the mold structured by direct micromachining. Figure 3A shows a top view of the part obtained by digital optical microscopy. Figure 3B shows its 3D reconstruction by digital optical microscopy. (This refers to a copper micropart.)

[0146] A rigid PMMA mold is prepared and structured by micromachining.

[0147] A metallic suspension in aqueous medium (distilled water) is prepared from copper powder, in an amount of 8% (volume of copper powder relative to the total volume of the suspension), using a solution of poly(acrylate), polyvinyl alcohol and poly(ethylene glycol) respectively as dispersant, binder and plasticizer respectively in the same mass proportions as those described in Example 1.

[0148] The micromachining-structured mold is fixed in a centrifuge tube and filled with the prepared metal suspension. Micromolding is performed by centrifugal force with a centrifugal acceleration of 1572 g (corresponding to 3500 rpm) for 8 minutes. The mold is then dried in an oven at 50 °C for 24 hours. After chemical demolding and debinding, followed by sintering, a micropart is obtained. This micropart, shown in Figure 4, has a periodic array of bars with a width of 200 µm and a height of 600 µm, corresponding to a aspect ratio (height / width ratio) of 3, and reproducing the pattern of the directly micromachining-structured mold.

Claims

DEMANDS 1. A process for preparing a part by centrifugally assisted micromolding comprising: 1) a step of preparing a rigid polymer mold comprising a cavity with a pattern, 2) a step of preparing a suspension comprising: - between 1% and 50% (volume of powder / volume of solution) of a powder of a mineral filler, said powder comprising particles having a size between 1 nm and 10 pm, said mineral filler comprising: i) a ceramic powder, ii) a metallic powder, iii) a powder of a metal-ceramic composite, or iv) a mixture of these; between 0.1 and 5% by mass of a dispersant, between 0.1 and 20% by mass of a binder, between 0.1 and 20% by mass of a plasticizer, and a solvent, 3) a step of filling the cavity of said rigid mold with said suspension, 4) a centrifugation step of said rigid mold comprising said suspension, thereby filling the pattern in the cavity of said mold entirely with a granular compact from the suspension, 5) a drying step of the granular compact in said rigid mold, 6) a demolding step whereby the said granular compact is recovered, and the said rigid mold is possibly disposed of, 7) a debinding step of the granular compact by which said binder is removed and a raw piece is thus recovered having a raw density equal to or greater than 60%, 8) a sintering step of said raw piece.

2. A process according to claim 1, wherein said powder comprises: i) a ceramic powder comprising oxides, nitrides, borides or carbides, or mixtures thereof, more preferably Al2O3, ZrO3, TiC2, MgO, YSZ, SrTiO3, BaTiO3, CeO2, SiO2, NiO, La2O3, HfO2, SiC, Si3N4, MgAl2O4, AIN, B4C, WC, BN or mixtures thereof; or (ii) a metallic powder comprising copper, nickel, iron, platinum, molybdenum, aluminium, gold, titanium, niobium, palladium, tungsten, silver or their alloys; or (iii) a powder of a metal-ceramic composite comprising at least one ceramic element selected from Al2O3, ZrCl2, I1O2, MgO, YZ, SrTiO3, BaTiO3, CeO2, SiO2, NiO, La2O3, HfO2, SiC, Si3N4, MgAl2O4, AIN, B4C, WC, or BN; and at least one metallic element selected from copper, nickel, iron, platinum, molybdenum, aluminium, gold, titanium, niobium, palladium, tungsten, or silver; or (iv) a mixture of these.

3. A method according to claim 1, wherein said powder of a mineral filler is a metallic powder comprising copper, nickel, iron or their alloys.

4. A method according to any one of the preceding claims, wherein the rigid polymer mold is made of acrylic polymers, polycarbonates, polysaccharides, wax, paraffin, polyethylenes, polypropylene, or a mixture thereof, preferably polymethyl methacrylate (PMMA).

5. A method according to any one of the preceding claims, wherein the pattern of the cavity of the rigid polymer mold is obtained by LIGA lithography or by direct machining.

6. A method according to any one of the preceding claims, wherein: - the dispersant comprises a surfactant, a polyelectrolyte, a complexing agent or mixtures thereof, - the binder comprises polyvinyl alcohol, polyethylene glycol, cellulose and its derivatives, acrylic latex, a polysaccharide gel or mixtures thereof, - The plasticizer comprises glycerol, stearic acid, polyethylene glycol, or mixtures thereof. - the solvent is an aqueous solvent, preferably water; or an organic solvent, preferably ethanol, methyl ethyl ketone (MEK) or a mixture thereof.

7. A process according to any one of the preceding claims, wherein step 2) of preparing a suspension comprises successively: 2a) mixing the mineral filler and the dispersant in the solvent, thereby obtaining a first mixture, 2b) adding the binder and the plasticizer to said first mixture.

8. A method according to any one of the preceding claims, said method further comprising a step of homogenizing the suspension, preferably a homogenization step by ultrasound.

9. A method according to any one of the preceding claims, wherein step 4) of centrifugation is carried out at a centrifugal force of 50 g to 50,000 g, for a period of 1 min to 60 min.

10. A method according to any one of the preceding claims, wherein the debinding step 7) is carried out at a temperature between 500°C and 700°C, preferably between 550°C and 650°C, even more preferably at a temperature of 600°C, for a period of 1 h.

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