Method for producing inorganic filtration supports by entanglement and resulting membranes

Abstract

The invention relates to a method for manufacturing a porous monolithic inorganic support (1) using a 3D printer comprising at least one extrusion head (6) mounted movably in space, which method consists in driving the extrusion head according to a numerical trajectory such that the deposited material partially overlaps at least one edge of a previously deposited material deposit by an overlapping material portion shown in its thickness, the overlapping material portion having a thickness strictly smaller than the nominal height (e), in the case of overlapping paths, and such that there is no space between the rounded edge of the deposited material deposit and the rounded edge of the previously deposited material deposit, and such that the deposited material crosses at least one previously deposited material deposit by an overlapping material portion shown in its thickness, the overlapping material portion having a thickness strictly smaller than the nominal height (e), in the case of crossing paths, and completely overlaps said previously deposited material deposit.

Description

[Technical field]

[0001] The present invention relates to a method for the manufacture of a porous monolithic inorganic support which can be used in particular to obtain filtration membranes, and especially tangential filtration membranes. More precisely, the porous support is made by a technique involving the addition of material. [Background technology]

[0002] Filtration membranes constitute a selective barrier, which, under the action of a transport force, can pass or block some components of the liquid medium to be treated. The passage or blocking of each component depends on their size relative to the pore size of the membrane, so that the membrane behaves like a filter. Depending on the pore size, such techniques are called "microfiltration", "ultrafiltration" or "nanofiltration".

[0003] The membrane consists of a porous support on which one or more isolating layers are deposited. Conventionally, the support is first shaped by extrusion. The support is then sintered to obtain the required robustness while retaining the open, interconnected porous structure. In this method, straight channels must be formed, inside which the isolating layers are then deposited and sintered. The membrane thus obtained therefore undergoes at least two sintering operations. The organic binders added during the preparation of the paste before extrusion are completely burned off during the sintering of the support.

[0004] In FR 3,006,606, the applicant describes the preparation of a filtration membrane, the porous support of which is prepared by additive techniques, by repeatedly depositing successive powder beds and then locally compacting them according to a predetermined pattern. This technique allows the preparation of filtration membranes that have mechanical resistance and are suitable for use in tangential filtration. However, this technique has the disadvantage that the powder needs to be adjusted so that it can flow perfectly when the powder bed is deposited. This technique also requires the removal of unconsolidated powder, which can be reused, which can prove to be difficult, time-consuming and expensive, especially when the unconsolidated powder is present in the non-linear flow paths of the porous support.

[0005] With WO2020 / 109715 and WO2020 / 109716, the applicant also proposes novel processes for the preparation of porous supports which do not have the disadvantages of the prior art and which, in particular, can be quickly and easily carried out and which allow obtaining porous supports which are easy to change in shape, in particular in the shape of non-linear channels, and which have mechanical resistance. The porous supports obtained are homogeneous, mechanically resistant and have a porosity suitable for use in filtration, i.e. a porosity between 10% and 60%, open and interconnected, with an average pore size in the range of 0.5 μm to 50 μm.

[0006] For this purpose, the method uses a 3D printer that includes an extrusion head that is movably mounted in the space above a fixed horizontal plate. The inorganic composition emerges from the extrusion head in the form of a ribbon or bead of material, which makes it possible to build a manipulable three-dimensional green structure from a 3D digital model to form a monolithic porous inorganic support. The manipulable three-dimensional green structure is then subjected to a sintering process.

[0007] As described in these patent applications, a manipulable three-dimensional green structure is obtained by superposing layers, each corresponding to a set of parallel or non-parallel continuous or discontinuous beads extruded at the same elevation according to a 3D digital model. Different layers can be stacked along the longitudinal axis in different ways.

[0008] In the state of the art, a method for producing a 3D object by modeling is also known from WO 2020 / 109716 by depositing molten filaments with overlapping paths. Similarly, US 2017 / 165917 describes a method for producing a 3D object by modeling, in particular by intersecting two beads of material using two controlled material deposition nozzles.

[0009] Applicants therefore envisioned creating each layer by vertically stacking a deposit of adjacent material beads c, as shown in Figure 1 A. Applicants found that after a sintering operation (Figure 1 B), such a structure would contain material voids v, whose pore size would be larger and would reduce the mechanical strength of the porous support.

[0010] The applicant also envisaged making each layer by depositing staggered material beads c, as shown in Figure 1C. This solution does nothing with regard to the elimination of the residual voids v between the material beads. After the sintering operation (Figure 1D), the structure still has internal material voids v. This solution also results in gaps in every other layer, which causes the material deposit of the upper layer to collapse, resulting in poor lateral quality. Summary of the Invention [Means for solving the problem]

[0011] The object of the present invention is precisely to remedy the shortcomings of the state of the art by proposing a new method for producing porous monolithic inorganic supports, designed to avoid the occurrence of material voids liable to reduce the mechanical strength of the porous support.

[0012] Another object of the invention is to propose a method for manufacturing a three-dimensional structure, designed to allow control of its dimensions, and in particular of the profile of its walls.

[0013] Another object of the invention is to propose a method for manufacturing a three-dimensional structure comprising at least one flow channel for circulating the fluid medium to be treated, the flow channel having walls suitable for depositing a separation layer.

[0014] Another object of the invention is to propose a method for manufacturing a three-dimensional structure comprising at least one flow channel for circulating the fluid medium to be treated, the flow channel having walls with an uninterrupted series of rounded reliefs that cause variations in the passage cross section of the flow channel while avoiding the appearance of excessive load losses.

[0015] To achieve these goals, the present invention provides a method for producing at least one porous monolithic inorganic support having at least one flow path for circulating a fluid to be treated, and having a porosity of 10% to 60% and an average pore size in the range of 0.5 μm to 50 μm, by using a 3D printer including at least one extrusion head movably mounted in the space above a fixed horizontal plate, moving continuously at a nominal height along a predetermined numerical trajectory to superimpose each material deposit having a nominal width and a defined thickness between the lower surface and the upper surface, the 3D printer comprising: a bead having rounded edges so as to form a rounded peripheral relief on the wall of at least one of the circulation channels, which is responsible for the generation of turbulence; A composition for constructing walls of a three-dimensional green structure operable from a predetermined numerical trajectory onto said horizontal plate to form a monolithic porous inorganic support. and wherein the method comprises: For walls with a width greater than the nominal width of the material deposit, decomposition of the numerical trajectories into overlapping and intersecting paths only; providing a composition to an extrusion head of a 3D printer; * in the case of overlapping paths, such that within the operable three-dimensional green structure, the deposited material partially overlaps at least one edge of a previously deposited material deposit with an overlapping material portion indicated in its thickness and having a thickness strictly smaller than the nominal height, such that there is no space between the rounded edge of the deposited material deposit and the rounded edge of the previously deposited material deposit; * in the case of a crossing path, within the operable three-dimensional green structure, the material to be deposited crosses at least one previously deposited material deposit by an overlapping material portion shown in its thickness and having a thickness strictly smaller than the nominal height, so that there is no space between the rounded edge of the material deposit to be deposited and the rounded edge of the previously deposited material deposit, and completely overlaps said previously deposited material deposit; Driving the extrusion head according to the numerical trajectory; The present invention relates to a method comprising the steps of:

[0016] According to an embodiment of an advantageous feature, the extrusion head is mounted movably along a predetermined numerical trajectory in order to perform a series of rotations each corresponding to a path traveled to find the same position in a horizontal plane having an altitude corresponding to the nominal height.

[0017] According to an embodiment of another advantageous feature, the extrusion head is driven to rise at least once over at least one revolution to an intermediate height which is a fraction of the nominal height.

[0018] According to another feature of the invention, the extrusion head is positioned at different points on the path over at least one revolution and is driven such that at each point it rises by a height increment, the sum of which corresponds to the nominal height.

[0019] Advantageously, the extrusion head is driven to rise through a series of rotations, following a trajectory with uninterrupted material deposition from start to finish of the construction of the manipulable three-dimensional green structure, to build the manipulable three-dimensional green structure according to the 3D digital model.

[0020] According to an advantageous feature, the extrusion head is driven such that during each revolution it is offset in the horizontal plane so that the deposited material partially overlaps the edge of the previously deposited deposit of material.

[0021] In the case of a crossing pass, the extrusion head is driven to reduce the amount of material deposited to create overlapping material portions having a thickness strictly less than the nominal height.

[0022] For paths with the same overlap, the extrusion head is driven to keep the flow rate of deposited material constant.

[0023] In the case of overlapping passes, the extrusion head is driven to adjust its position in a plane to define an overlapping degree of material on a previously deposited material deposit.

[0024] In the case of overlapping passes, the flow rate of the extrusion head is adjusted according to the degree of overlap of the overlapping material portion on the previously deposited material deposit.

[0025] Typically, an extrusion head is mounted for movement along a predetermined numerical trajectory to superimpose each material deposit in layers, each of which rises a nominal height.

[0026] According to another feature of the invention, an extrusion head is actuated to provide in the operable three-dimensional green structure at least one flow path for circulating a fluid medium to be treated, said flow path having walls with a series of rounded reliefs which cause variations in the passage cross section of said flow path, said rounded reliefs being formed by material portions located on opposite sides of the overlapping material portions.

[0027] According to an advantageous feature, the extrusion parameters are adjusted and the extrusion head is configured such that the material portion located opposite the overlapping material portion has rounded edges.

[0028] Conventionally, the manipulable three-dimensional green structure is placed in a heat treatment furnace to carry out the sintering operation.

[0029] Another object of the present invention is to provide a method for the preparation of tangential filtration membranes, comprising the steps of producing a porous monolithic inorganic support provided with at least one flow channel for circulating the fluid medium to be treated, followed by the formation of at least one separating layer on the walls of the flow channels after sintering said support.

[0030] Another object of the present invention is to provide a porous monolithic inorganic support manufactured according to the method according to the invention, having an outer surface with a series of rounded peripheral reliefs and circulation channels, the walls of which have rounded peripheral reliefs responsible for the generation of turbulence.

[0031] Another object of the present invention is to provide a tangential filtration membrane comprising a porous monolithic inorganic support with at least one flow channel for circulating the fluid medium to be treated, the walls of said flow channel having a rounded peripheral relief being coated with at least one separating layer. [Brief description of the drawings]

[0032] [Figure 1-1] FIG. 1A is a cross-sectional view of a wall made by vertically stacking deposits of beads of material, showing voids.

[0033] [Figure 1-2] FIG. 1B is a diagram of the wall shown in FIG. 1A, illustrating the persistence of voids.

[0034] [Figure 1-3] FIG. 1C is a cross-section of a wall made by vertically staggering stacks of material beads, showing voids.

[0035] [Figure 1-4] FIG. 1D is a view of the wall shown in FIG. 1C after a sintering operation, illustrating the persistence of voids.

[0036] [Figure 2-1] FIG. 2A is a schematic diagram of a 3D printer that allows the implementation of the present invention.

[0037] [Figure 2-2] FIG. 2B is a perspective view of one embodiment of a manipulable three-dimensional green structure.

[0038] [Figure 3-1] FIG. 3 is a schematic top view showing material deposition in a conventional mode to produce a tubular wall of width equal to the nominal width of the material deposit.

[0039] [Figure 3-2] FIG. 3A is a cross-sectional view taken substantially along line AA of FIG. 3 and shows successive material deposition in a conventional mode to create a tubular wall.

[0040] [Figure 4-1] FIG. 4 is a schematic top view showing material deposition in a vase mode to create a tubular wall of width equal to the nominal width of the material deposit.

[0041] [Figure 4-2] FIG. 4A is a cross-sectional view taken substantially along line AA of FIG. 4, illustrating successive material deposition in a vase mode to create a tubular wall.

[0042] [Figure 5-1] FIG. 5 is a schematic top view illustrating the principle according to the invention of material deposition in a path with overlap of extrusion heads.

[0043] [Figure 5-2] FIG. 5A is a cross-sectional view taken substantially along line AA of FIG. 5, illustrating the overlap of material deposits in paths with overlapping extrusion heads.

[0044] [Figure 6-1] FIG. 6 is a schematic top view showing material deposition in a path with an intersection of the extrusion head.

[0045] [Figure 6-2]FIG. 6A is a cross-sectional view taken substantially along line AA of FIG. 6, illustrating the inventive overlap of material deposits in paths with intersections of extrusion heads.

[0046] [Figure 6-3] FIG. 6B is a cross-sectional view taken substantially along line BB of FIG. 6, illustrating the inventive overlap of material deposits in paths with intersections of extrusion heads.

[0047] [Figure 7-1] FIG. 7 is a schematic top view showing the principle steps of material deposition in sequential vase mode to create a tubular wall with a width larger than the nominal width of the material deposit.

[0048] [Figure 7-2] FIG. 7A is a cross-sectional view taken substantially along line AA of FIG. 7 and illustrates the principle steps of sequential vase mode material deposition to create a tubular wall of width greater than the nominal width of the material deposit.

[0049] [Figure 7-3] FIG. 7B is a schematic top view showing the course of material deposition in a sequential vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0050] [Figure 8-1] FIG. 8 is a schematic top view showing another principle step of material deposition in sequential vase mode to create a tubular wall having a width larger than the nominal width of the material deposit.

[0051] [Figure 8-2] FIG. 8A is a cross-sectional view taken substantially along line AA of FIG. 8 and illustrates another principle step of sequential vase mode material deposition to create a tubular wall of width greater than the nominal width of the material deposit.

[0052] [Figure 8-3]FIG. 8B is a schematic top view showing the course of material deposition in a sequential vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0053] [Figure 8-4] FIG. 8C illustrates another principle process of material deposition in sequential vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0054] [Figure 9-1] FIG. 9 is a schematic top view showing the principle steps of material deposition in continuous vase mode to create a tubular wall with a width larger than the nominal width of the material deposit.

[0055] [Figure 9-2] FIG. 9A is a cross-sectional view taken substantially along line AA of FIG. 9, illustrating the principle steps of material deposition in a continuous vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0056] [Figure 9-3] FIG. 9B is a schematic top view showing the course of material deposition in a continuous vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0057] [Figure 10-1] FIG. 10 is a schematic top view showing another principle process of material deposition in a continuous vase mode to create a tubular wall of width larger than the nominal width of the material deposit.

[0058] [Figure 10-2] FIG. 10A is a cross-sectional view taken substantially along line AA of FIG. 10 and illustrates another principle process of material deposition in a continuous vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0059] [Figure 10-3] FIG. 10B is a schematic top view showing the course of material deposition in a continuous vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0060] [Figure 10-4] FIG. 10C illustrates another principle process of material deposition in a continuous vase mode to create a tubular wall of width greater than the nominal width of the material deposit.

[0061] [Figure 11] FIG. 11 is a schematic diagram showing examples of extrusion head courses for a method called "sequential vase mode" and a method called "sequential vase mode."

[0062] [Figure 12-1] FIG. 12A is a top view showing another example of a wall separating two adjacent channels and having a width greater than twice the nominal width of the material deposit.

[0063] [Figure 12-2] FIG. 12B is a cross-sectional view taken substantially along line BB of FIG. 12A.

[0064] [Figure 13-1] FIG. 13A is a cross-sectional view showing, in the case of a path having an intersection, material deposition performed according to a prior art method before traversing the intersection.

[0065] [Figure 13-2] FIG. 13B is a cross-sectional view showing, for a path having an intersection, material deposition performed according to a prior art method when passing through the intersection.

[0066] [Figure 13-3] FIG. 13C is a cross-sectional view illustrating, for a path having an intersection, material deposition performed according to a prior art method after traversing the intersection.

[0067] [Figure 13-4] FIG. 13D is a cross-sectional view showing a material deposition performed according to a prior art method in the case of a path having an intersection, superimposed on a previously performed material deposition.

[0068] [Figure 13-5] FIG. 13E is a cross-sectional view showing material deposition performed according to a prior art method for a path having an intersection, superimposed on a previously performed material deposition, showing the formation of voids at the intersections of the material deposition.

[0069] [Figure 14] FIG. 14 is a cross-sectional view of an example embodiment of the present invention having a material deposit fabricated by layer-by-layer stacking in accordance with the principles of the present invention.

[0070] [Figure 15] FIG. 15 is an oblique cross-sectional image of a porous monolithic inorganic support having eight filtration channels and showing the absence of voids.

[0071] [Figure 16] FIG. 16 is a cross-sectional image of a tangential filtration membrane comprising an eight channel porous monolithic inorganic support whose channel walls having rounded peripheral relief are coated with a separating layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072] The object of the present invention relates to the manufacture of a porous monolithic inorganic support 1 (FIG. 2B) intended to constitute an element for the tangential flow separation of a liquid medium to be treated into a filtrate (or permeate) and a retentate (commonly known as a tangential filtration membrane).

[0073] In many applications, such porous supports have a tubular shape and at least one flow path or passage for circulating the fluid to be filtered, the flow path or passage comprising at least one separation layer. The circulation flow path has an inlet and an outlet. Typically, the inlet of the circulation flow path is located at one end of the porous support, which serves as an inlet zone for the fluid medium to be treated, and the outlet of the circulation flow path is located at the other end of the porous support, which serves as an outlet zone for the retentate. The inlet and outlet zones are connected by a continuous peripheral zone in which the permeate is collected.

[0074] In other applications, the porous support may be in the form of a block, for example of parallelepiped shape, in which at least one circulation channel or path for the fluid to be filtered, comprising at least one separating layer, is arranged. The permeate is collected at the periphery of the block or by a collection circuit arranged in the block. In the illustrated example, the porous support has a tubular shape, but it is clear that the object of the invention is applicable to porous supports of any shape.

[0075] When the porosity (average pore size) of the sintered support is suitable for the fluid medium to be treated (filtration threshold), the sintered support can be used directly for filtration and is called an autogenous or homogeneous membrane.

[0076] If the porosity of the sintered support is not suitable for the fluid medium to be treated (the size of the pores is too large compared to the required filtration threshold), the walls of the circulation channels are continuously covered by at least one separation layer that allows the fluid medium to be treated to be filtered. This at least one separation layer is porous and has an average pore size smaller than that of the support. The separation layer can be deposited directly on the porous support (in the case of a single-layer separation layer) or on an intermediate layer with a smaller average pore size, which itself can be deposited directly on the porous support (in the case of a multi-layer separation layer). A part of the fluid medium to be filtered thus passes through the separation layer and the porous support, so that a part of this treated fluid, called permeate, flows through the outer peripheral surface of the porous support. The separation layer defines the surface of the filtration membrane that is intended to come into contact with the fluid to be treated and with which the fluid to be treated comes into contact as it circulates.

[0077] The pores of the monolithic inorganic support 1 are open, i.e. they form a network of interconnected pores in three dimensions, which allows the fluid filtered by the separating layer to pass through the porous support and be collected at the periphery, thus the permeate is collected at the peripheral surface of the porous support.

[0078] The porous monolith inorganic support 1 has an average pore size in the range of 0.5 μm to 50 μm. The porosity of the porous monolith inorganic support 1 is 10 to 60%, and preferably 20 to 50%.

[0079] The average pore size means the d50 value of the volume distribution, where 50% of the total pore volume corresponds to the volume of pores with a pore size smaller than this d50. The volume distribution is a curve (analytical function) that represents the frequency of the pore volume as a function of the pore size. The d50 corresponds to the median value that halves the area under the frequency curve obtained by mercury porosimetry. In particular, the technique described in ISO standard 15901-1:2005 can be used for the measurement technique by mercury porosimetry.

[0080] The porosity of the support corresponds to the total volume of interconnected voids (pores) present in the material, and is a physical quantity between 0 and 1 or 0% and 100%. The flow rate and retention of the porous body are defined. For the material to be used in filtration, the total interconnected open porosity must be at least 10% to allow sufficient filtrate flow rate through the support, and at most 60% to ensure suitable mechanical strength of the porous support.

[0081] The porosity of a porous body can be measured by weighing the material before and after an extended residence time in liquid (water or other solvent) and determining the volume of the liquid contained in the porous body. Since the density of the material and the liquid used are known, the mass difference converted to volume directly represents the pore volume and thus the total open porosity of the porous body.

[0082] Other techniques can be used to accurately measure the total open porosity of a porous body, including: Mercury intrusion porosimetry (ISO standard 15901-1 mentioned above): Mercury is injected to fill the pores accessible at the pressure used, the volume of injected mercury corresponds to the pore volume. Small angle X-ray scattering: This technique uses neutrons or X-rays, but provides physical quantities averaged over the entire sample. The measurement consists of analyzing the angular distribution of the intensity scattered by the sample. -Analysis of 2D images obtained by microscopy. -Analysis of 3D images obtained by X-ray tomography.

[0083] Moreover, the porous monolithic inorganic support 1 has a mechanical strength suitable for use in tangential filtration. More precisely, the porous monolithic inorganic support 1 withstands an internal pressure of at least 10 bar without bursting, preferably at least 30 bar without bursting, advantageously at least 50 bar without bursting. According to the invention, the burst pressure corresponds to the pressure at which a support whose pores have been previously blocked (with a heat-fusible material such as paraffin) bursts under the effect of an excessive internal pressure with respect to the pressure outside the support, this excess pressure being that applied in the flow passage with water, the pressure outside the support being atmospheric pressure.

[0084] As can be seen more precisely in Figure 2A, the porous monolithic inorganic support 1 according to the invention is produced by sintering a manipulable three-dimensional green structure 2. Said structure 2 is built up by superposing, in a general sense, a material deposit 3 of composition 4 according to a 3D digital model M. In particular, the material deposit is produced using a three-dimensional printer comprising a horizontal plate 5, which may be removable, above which at least one extrusion head 6 is placed.

[0085] The term "three-dimensional green structure" 2 is understood to mean a three-dimensional structure obtained by superimposing deposits of composition 4 and which has not yet undergone sintering. The shape and dimensions of this green structure are determined level by level by a 3D digital model M, as will be explained in detail in the remainder of this specification. The 3D digital model M is determined by computer design software to build the three-dimensional green structure 2.

[0086] This three-dimensional green structure 2 is described as "manipulable" since it does not deform under its own weight and can even be tilted, thanks to the accelerated consolidation that gives it a stable mechanical stiffness over time, as explained below, and therefore can be moved without deformation or damage and removed from the horizontal plate 5, in particular for the subsequent heat treatment operations necessary to obtain the monolithic porous support according to the invention.

[0087] The extrusion head 6 of the three-dimensional printer is supported by a movement mechanism (not shown), such as a robot, capable of moving along at least three axes (x, y and z). The extrusion head 6 can thus be moved in the horizontal plane (x and y axes) and in the vertical direction (z axis) thanks to a movement mechanism driven by any kind of computer R known per se. This computer R controls the movement of the movement system, and thus of the extrusion head 6, along a predetermined trajectory according to a 3D digital model M from which a three-dimensional green structure 2 is produced, from which a porous monolithic inorganic support 1 can be obtained after a heat treatment operation.

[0088] The extrusion head 6 has an inlet (not shown) for the composition 4. As shown, the extrusion head 6 also has an extrusion nozzle with a calibrated flow orifice 8 through which the composition 4 emerges. The extrusion head 6, and thus the extrusion nozzle with the flow orifice 8 integral with the extrusion head 6, are movable according to said 3D digital model M. According to the method of the invention, the composition 4 is introduced into the extrusion head 6 of the machine via an inlet to feed into the flow orifice 8. A mechanical action can be applied to introduce the composition 4 into the head 6 via this inlet.

[0089] In the context of the present invention, "mechanical action" is understood to mean the application of pressure by any known technical means, such as, for example, a piston, a pump or an extrusion screw. This step will not be described in detail here, since it can be carried out in a conventional manner by a person skilled in the art. The material leaves the flow orifice 8 by a certain pressure higher than atmospheric pressure. This results in a vertical force being exerted on the material during extrusion from top to bottom, which tends to crush the material between the extrusion nozzle and the hardened material below.

[0090] The flow orifice 8 is positioned opposite and adjacent to the horizontal plate 5. The flow orifice 8 is movable vertically (i.e. along the z-axis) and horizontally (i.e. along the x-axis and y-axis) relative to the fixed horizontal plate 5. The vertical and / or horizontal movement of the flow orifice 8 relative to the fixed horizontal plate 5 allows for the extrusion of a bead of material through the flow orifice 8 and then construction according to a digital 3D model M of a manipulable three-dimensional green structure 2 resting on the horizontal plate 5.

[0091] According to the embodiment shown, the extrusion head 6 comprises a flow orifice 8 of circular cross section. When the flow orifice 8 is of circular cross section, its diameter advantageously ranges from 0.1 mm to 10 mm, preferably from 0.1 mm to 1 mm and preferentially from 0.2 mm to 0.8 mm.

[0092] It should be noted that for a given extrusion speed E (for example determined by the rotation speed of the extrusion screw), a given movement speed F of the extrusion head 6 and a nominal movement height e of the extrusion head 6 correspond to a material deposit 3 having a nominal width L such that L=f(E,F,e). The material deposit 3 has a cross section with a nominal height e defined between a substantially flat upper surface 3s and a substantially flat lower surface 3i connected to each other on both sides by two edges 3b of rounded shape (FIGS. 3 and 3A). The nominal width L of the material deposit 3 can therefore be adjusted or changed depending on the movement speed F of the extrusion head 6 and / or the extrusion speed.

[0093] The extrusion head 6 is supplied with a composition 4, for example in the form of a paste as described in PCT / FR2019 / 052807, or in the form of filaments or granules as described in PCT / FR2019 / 052808. Advantageously, the composition 4 is an inorganic composition, typically of ceramic and / or metallic nature.

[0094] Ceramic compositions consist of a powdered solid inorganic phase and a matrix.

[0095] The powdered solid inorganic phase of the ceramic composition comprises one or more solid inorganic materials in the form of particles each having an average diameter of from 0.1 μm to 150 μm.

[0096] The concept of mean size is related to that of particle distribution. In fact, powder particles are rarely monosized or monodisperse, so powders are mostly characterized by a particle size distribution. The mean size is therefore the average value of the particle size distribution. The distribution can be expressed in different ways, for example as a frequency or cumulative distribution. Some measurement techniques give the distribution directly on a number basis (microscopy) or on a mass basis (sieving). The mean size is a representative value.

[0097] The most commonly used measures of central tendency are the mode, median and mean. The mode is the most frequent diameter in a distribution and corresponds to the maximum of the frequency curve. The median represents the value above which the total frequency of values ​​below is the same (i.e. the number of particles or total volume is the same around the median). The mean must be calculated to determine the point where the moments of the distribution are equal. In a normal distribution, the mode, mean and median are coincident, but in non-normal distributions they are different.

[0098] The average particle size of the inorganic powder can be measured in particular by the following method. For particles in the range of 3 mm to approximately 0.1 μm, laser light diffraction Sedimentation / Centrifugation For particles in the range of 0.5 μm to 2 nm, dynamic light scattering (DLS) -Analysis of images obtained by microscopy Small angle X-ray diffraction

[0099] The particle size of the powdered solid inorganic phase is understood to mean the size of the particles constituting the powdered solid inorganic phase. The particle size is characterized by the concept of average diameter mentioned above.

[0100] In most cases, the ceramic composition comprises oxides and / or nitrides and / or carbides, either alone or as a mixture, as powdered ceramic materials. Examples of oxides that may be suitable in the context of the present invention include in particular metal oxides, especially titanium oxide, zirconium oxide, aluminum oxide and magnesium oxide, with titanium oxide being preferred. Examples of carbides include in particular metal carbides, especially silicon carbide. Examples of nitrides that can be used include in particular titanium nitride, aluminum nitride and boron nitride. According to a preferred embodiment, the ceramic composition comprises at least one metal oxide, preferably titanium oxide, as powdered inorganic material.

[0101] In the context of the present invention, the ceramic composition has a suitable rheology in terms of plasticity when extruded through the extrusion head 6 .

[0102] According to a first embodiment, the matrix of the ceramic composition comprises one or more solvents. The solvents may be aqueous or organic. Examples include water, ethanol or acetone.

[0103] Furthermore, the matrix of the ceramic composition contains one or more organic additives, which are advantageously soluble in the solvent of the matrix. Organic additives suitable for the purposes of the invention can be selected, by way of non-limiting example, from: Binders, for example the polymer cellulose ethers such as hydroxyethyl cellulose, the polysaccharide gum arabic, or polyethylene glycol (PEG). Lubricants and plasticizers, such as glycerol or stearic acid. · Thickening and gelling agents such as xanthan gum or agar, which is a galactose polymer.

[0104] The mass content of the powdered inorganic material in the ceramic composition can be in the range of 50-90% by weight, preferably 80-85% by weight, relative to the total weight of the ceramic composition.

[0105] The total mass content of the matrix in the ceramic composition can range from 10 to 50% by weight, preferably from 15 to 20% by weight, relative to the total weight of the composition.

[0106] The ceramic composition is not a powder, but a paste. The rheology of the ceramic composition can be adjusted by the particle size of the powdered solid inorganic phase and / or the nature and / or respective proportions of the organic additives, if present. Indeed, the rheology of the ceramic composition can be modified, for example, by using a matrix that contains one or more organic additives that are soluble in one or more solvents contained in the matrix.

[0107] According to a second embodiment, the ceramic composition comprises a matrix of one or more heat-fusible polymers, the matrix being essentially organic and solid at room temperature.

[0108] "Heat-fusible polymer" means a polymer that softens under the influence of heat.

[0109] Examples of heat-fusible polymers that may be suitable in the context of the present invention include polymers or polymer families such as polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyethylene, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyolefins, thermoplastic elastomers (TPE), polyolefin-based elastomers (TPE-O) and polycarbonates, which may be functionalized and may be used alone or in mixtures in the matrix.

[0110] The mass content of the powdered inorganic material in the ceramic composition can be in the range of 40 to 95% by weight, preferably 70 to 90% by weight, relative to the total weight of the ceramic composition.

[0111] In the context of the present invention, the ceramic composition, preferably in the form of granules, is preheated upstream so that the heat-fusible polymer softens and can pressurize the ceramic composition upstream of the flow orifice 8. Typically, the extrusion head 6 is heated to soften the heat-fusible polymer before the ceramic composition can be extruded. The temperature of the extrusion head 6 and the flow orifice 8 can be adjusted depending on the heat-fusible polymer present in the ceramic composition.

[0112] It is also possible within the scope of the present invention to adjust the rheology of the ceramic composition by the temperature of the ceramic composition at the extrusion head and / or the particle size of the powdered solid inorganic phase and / or the nature of the heat-fusible polymer and / or their proportions.

[0113] According to the invention, the method of the invention aims at decomposing the numerical trajectory into each path so that no space occurs inside the three-dimensional manipulable green structure between the rounded edge of the current material deposit and the rounded edge of the previously deposited material deposit. As illustrated in Figures 1A and 1C, the deposition of adjacently made material beads according to the state of the art is likely to result in the formation of material voids that remain after sintering and reduce the mechanical strength of the porous monolithic inorganic support.

[0114] The method according to the invention aims at determining whether a manipulable three-dimensional green structure has a wall with a width equal to or greater than the nominal width L of the material deposit. Indeed, in the case of a wall with a width equal to the nominal width L of the material deposit, this wall is built using material deposits that are simply overlapped without the occurrence of material voids. It should be noted that in the case of this type of wall, as can be seen with reference to Figure 6 and Figures 13A-13E, the overlapping deposition of material beads does not result in material voids, except in the case where the trajectory includes paths with intersections.

[0115] As shown in FIG. 6, in the figure-8 structure, a path with an intersection appears. The intersection appears when the looping trajectory returns to point I with coordinates Xi, Yi where a material deposit (n-1) has already been deposited. The passage of material deposit (n-1) is performed by contacting the ongoing material deposit (n) with the previously performed material deposit (FIG. 13A). It then stops extruding material while sliding at the same height (FIG. 13B) and resumes extruding after the downstream edge of the n-1 material deposit (FIG. 13C). The n+1 material deposit overlaps the n-1 material deposit and the passage of this new material deposit is performed as described above (FIGS. 13D and 13E). As can be clearly seen, the juxtaposition or joining of two material deposits during the complete passage of the previously deposited material deposit creates a void.

[0116] 3 and 3A show a first variant embodiment, known as the conventional mode, for producing a wall 10 with a width equal to the nominal width L of the material deposit. By way of example, this wall 10 forms part of a three-dimensional green structure operable as a support of circular cross section with a single central channel 11. The trajectory of the extrusion head 6 is divided into circular paths of average diameter D, each of length πD, and with each revolution the extrusion head rises along the vertical axis by an increment e. The extrusion head 6 performs a first rotation t, placed at an elevation e relative to the level of the plate 5, so as to extrude a certain amount of material to produce a material deposit of a certain thickness e. By way of example, the arrow F here indicates the counterclockwise movement direction of the extrusion head 6. Once the first rotation t has been performed, the extrusion head 6 is raised by a value equal to the thickness e of the material deposit to perform a second rotation, extruding a certain amount of material to deposit the material continuously. The material deposit 3 is thus produced until the desired height is obtained.

[0117] Figures 4 and 4A show a second variant embodiment, called vase mode, for producing a wall 10 in the case of a manipulable three-dimensional green structure such as a support of circular cross section with a single central channel 11. The trajectory of the extrusion head 6 is resolved into circular paths of average diameter D, each of length πD, and at the end of each revolution the extrusion head rises along the vertical axis by a series of increments whose sum makes it possible to obtain at each revolution a material deposit of thickness e.

[0118] During the first rotation t, the extrusion head extrudes material in increasing amounts proportional to its position at the average tilt e / πD. Once the first rotation t has been performed, the extrusion head 6 performs a second rotation according to the same average tilt e / πD, extruding a constant amount of material to continuously deposit the material according to an elevation corresponding to the thickness e. The material deposit 3 is thus created until the desired height is obtained.

[0119] If the manipulable three-dimensional green structure has a wall with a width greater than the nominal width L of the material deposit, the material deposit must be produced according to the invention, since it is no longer possible to construct this wall using only overlapping material deposits. According to the invention, the method provides for an entanglement of the material deposits as a result of the alternating stacking by overlapping and / or crossing of said material deposits 3, in order to avoid material spaces or voids between the material deposits. Entanglement in the sense of the invention is understood to mean an entanglement of the material deposits by overlapping and / or crossing, independent of the quantum mechanical definition.

[0120] Thus, in the case of a wall 10 having a width greater than the nominal width L of the material deposit 3, the method according to the invention aims at decomposing the numerical trajectory of the extrusion head 6 into only overlapping and / or intersecting paths. It must be understood that the extrusion head 6 (more precisely its carriage) follows a trajectory, completely defined by a series of points, point by point, from the beginning to the end of the manufacturing process of the manipulable three-dimensional green structure 2. Each of these points is spatially predefined by its Cartesian coordinates Xi, Yi, Zi. Xi and Yi precisely define the position of the center of the circular orifice 8 of the extrusion nozzle. Thus, the extrusion head 6 moves from point A (Xa, Ya, Za) to point B (Xn, Yn, Zn) according to the vector AB, then from point B to point C, ..., ..., and so on, by following a series of command lines, called G-code commands, of the intermediate software between the 3D digital model and the printer. It should be noted that in addition to determining the trajectory at each point determined by the Cartesian coordinates Xi, Yi, Zi, for each of these points, all the parameters are defined, namely in particular the extrusion flow rate E and the movement speed F of the extrusion head 6.

[0121] It should be understood that the numerical trajectory of the extrusion head 6 is decomposed into overlapping and / or intersecting paths. The overlapping paths correspond to the portions of the trajectory where the material deposit 3(nth) partially overlaps with at least one edge 3b of the previously deposited material deposit 3(n-1th) so that there is no space between the rounded edge of the ongoing material deposit and the rounded edge of the previously deposited material deposit, as shown in Figures 5 and 5A, inside the manipulable three-dimensional green structure. As can be seen more specifically in Figure 5A, the deposited material (nth) partially overlaps with at least one edge 3b of the previously deposited material deposit (n-1th) by an overlapping material portion 3c shown within its thickness, i.e. between the upper surface 3s and the lower surface 3i of its ongoing deposit. Moreover, this overlapping material portion 3c has a thickness strictly smaller than the nominal height e.

[0122] According to one feature of the method according to the invention, in the case of paths with overlap, the extrusion head 6 is driven to adjust the extrusion speed depending on the degree of overlap of the overlapping material portion on the previously deposited material deposit.

[0123] The crossing path corresponds to a portion of a trajectory where a depositing material deposit (n-th) crosses and completely overlaps at least one previously deposited material deposit (n-1-th) so that there is no space between the rounded edge of the ongoing material deposit and the rounded edge of the previously deposited material deposit, inside the manipulable three-dimensional green structure, as shown in Figures 6A and 6B. In the crossing path, the depositing material (n-th) completely overlaps the previously deposited material deposit (n-1-th) by the overlapping material portion 3c, i.e., it extends from at least one edge 3b of the previously deposited material deposit to the other edge. This crossing between these two material deposits can occur at any conceivable angle between the directions of these two material deposits. The overlapping material portion 3c is considered to be within the thickness of the ongoing material deposit, i.e., between the top and bottom surfaces of said ongoing deposit. Moreover, this overlapping material portion 3c has a thickness strictly smaller than the nominal height e.

[0124] The foregoing results in an alternating stack of material deposits 3. Such an alternating stack exists if there is at least one overlapping and / or intersecting path in a revolution. Each subsequent revolution, which necessarily "covers" the previous overlap and / or intersection, results in an intertwining of material deposits 3. Thus, the intertwining of material deposits is the result of multiple revolutions, each with at least one path with overlap and / or one path with intersection.

[0125] According to one feature of the method according to the invention, in the case of paths with intersections, the extrusion head 6 is driven to reduce the amount of material deposited in order to create overlapping material portions having a thickness strictly less than the nominal height e. Thus, as is clearly evident in Figures 6A and 6B, each material deposit has a nominal height e, except when it is at right angles to or passes through an already created material deposit.

[0126] Thus, in the example shown in Figures 6A and 6B, the first material deposit n is made with a thickness smaller than the nominal height e, for example equal to e / 2. For the material deposit n that crosses the previously made material deposit n-1, this material deposit n is made with the nominal thickness e, except when it overlaps the previous material deposit n-1. When the extrusion head covers the material deposit, the extrusion speed is reduced so that the overlapping part 3d of the deposit has a thickness smaller than the nominal thickness e, in the example shown equal to e / 2. In this way, the crossing path obtained according to the principles of the invention does not have material voids, unlike the prior art, as shown in Figures 13C-13E.

[0127] According to a preferred embodiment of the invention, the extrusion head 6 is mounted movably along a predetermined numerical trajectory T in order to perform a series of rotations t each corresponding to a path traveled to find the same position in the horizontal plane having an altitude corresponding to a nominal height e. In other words, the numerical trajectory of the extrusion head 6 is decomposed into rotations, taking into account that in each rotation the extrusion head rises by a nominal height e. Naturally, the number of rotations t is selected in order to obtain the desired height of the manipulable three-dimensional green structure 2.

[0128] In each of these rotations t, the course of the extrusion head 6 is one or more overlapping paths and / or one or more intersecting paths. For each of these rotations, the extrusion head 6 follows a course formed by a series of points with coordinates Xi, Yi, Zi, as explained above, and may rise along the vertical axis at one or more of these points.

[0129] According to a first embodiment example, which is more precisely described with reference to Figures 7 to 7B and 8 to 8C, the method provides for driving the extrusion head 6 so that, in at least one revolution, the extrusion head rises at least once from an intermediate height which is a fraction of the nominal height e.

[0130] According to a second embodiment example, which will be described more precisely with reference to Figures 9 to 9B and 10 to 10C, the method provides for driving the extrusion head 6 in at least one revolution such that the extrusion head is positioned at different points on the path and at each point rises by a height increment, the sum of which height increments corresponds to the nominal height e.

[0131] In the following description, with respect to Figures 7-7B and 8-8C, a first example embodiment of a method called "sequential vase mode" is described, which consists in building a part of a path at the same altitude a (for example a=e / 2) and then increasing the altitude by a value a to complete a rotation and overlapping a part of the overlapping material of value a with the previous deposit. According to this method, the nominal height e is an integer multiple of a.

[0132] Figure 7B shows the first half of the path travelled by the extrusion head corresponding to the circle of diameter D1. As shown in Figures 7 and 7A, a first material bead 3 is deposited on the horizontal plate 5 at an altitude equal to e / 2, which continues over the entire course of the circle of diameter D1. In the sense of the present invention, this course covering a circumference of 360° corresponds to half a revolution. When this half revolution is covered with the same altitude e / 2, the extrusion head 6, and thus the centre of the flow orifice 8, moves radially towards the centre of the circle by a distance equal to d=(D2-D1) / 2, rising by an equal increment e / 2 according to the circle of diameter D2 (Figures 8A, 8B). This results in the material deposit partially overlapping the inner edge 3b of the previously deposited material deposit, by an overlapping material portion 3c, which is shown in its thickness. It should be noted that the overlapping material portion 3c has a thickness strictly smaller than the nominal height e. Thus, the extrusion head 6 has moved a rotation t in the sense of the invention, which corresponds to a path in which a circle of diameter D1 is followed by a circle of diameter D2 (FIG. 8B).

[0133] In the position shown in FIG. 8A, the extrusion head 6 (and therefore the center of the flow orifice 8) is offset radially outward from the circle D2 by a distance equal to d and rises again by an increment e / 2 so as to overlap the previous material deposit along the circle D1. This results in the material deposit partially overlapping the outer edge 3b of the previously deposited material deposit by an overlapping material portion 3d shown in its thickness. The overlapping material portion 3d has a thickness strictly smaller than the nominal height e. The extrusion head 6 is offset radially inward from the circle D1 by a distance equal to d and rises again by an increment e / 2 so as to overlap the previous material deposit along the circle D2. This results in the material deposit partially overlapping the inner edge 3b of the previously deposited material deposit by an overlapping material portion 3c shown in its thickness. The extrusion head 6 has thus traveled a second rotation t in the sense of the invention, which corresponds to a path in which a circle of diameter D1 is followed by a circle of diameter D2 (FIG. 8C).

[0134] In this way, the extrusion head 6 is driven through a number of revolutions that allows the construction of the manipulable three-dimensional green structure 2 according to the desired height. It should be noted that in the example shown, each course through the first and second revolution is identical. Of course, it is also conceivable that each course of the different revolutions is different from each other. Likewise, the nominal height e of each revolution, which is identical in the example shown, may be different in the different revolutions.

[0135] The following description, with respect to Figures 9-9B and 10-10C, describes a second example embodiment of a method called "continuous vase mode" in which the extrusion head 6 extrudes material in increasing amounts proportional to its position.

[0136] Figure 9B shows the first half of the path travelled by the extrusion head corresponding to the circle of diameter D1. As shown in Figures 9 and 9A, the first material bead rises continuously and progressively along the entire course of the circle of diameter D1 and is deposited on the horizontal plate 5, reaching a height equal to e / 2 at the end of the course of the circle D1. It should be noted that, in the sense of the present invention, this course corresponds to half a turn, and that in a quarter of a turn, the thickness of the material deposit is equal to e / 4. When this half turn is completed and the height e / 2 is reached, the extrusion head 6 is displaced radially towards the centre of the circle by a distance equal to D=(D2-D1) / 2 and rises progressively and continuously according to the circle of diameter D1, reaching the height e at the end of the path travelled along this diameter D1 (Figures 10, 10A, 10B). This results in the material deposit partially overlapping the inner edge 3b of the previously deposited material deposit, by an overlapping material portion 3d, indicated in its thickness. It should be noted that the overlapping material portion has a thickness strictly less than the nominal height e. Thus, the extrusion head 6 has moved a rotation t in the sense of the invention, which corresponds to a path in which a circle of diameter D1 is followed by a circle of diameter D2.

[0137] In the position shown in FIG. 10A, the extrusion head 6 is offset radially outward from the circle D2 by a distance equal to d and gradually rises by an increment e / 2 so as to overlap the previous material deposit along the circle D1. This results in the material deposit partially overlapping the outer edge 3b of the previously deposited material deposit by an overlapping material portion 3d shown in its thickness. The overlapping material portion has a thickness strictly smaller than the nominal height e. The extrusion head 6 is offset radially inward from the circle D1 by a distance equal to d and gradually rises again by an increment e / 2 so as to overlap the previous material deposit along the circle D2. This results in the material deposit partially overlapping the inner edge of the previously deposited material deposit by an overlapping material portion shown in its thickness. The extrusion head has thus traveled a second rotation t in the sense of the invention, which corresponds to a path in which a circle of diameter D1 is followed by a circle of diameter D2 (FIG. 10C).

[0138] In this way, the extrusion head 6 is driven through a number of revolutions that allows the construction of a manipulable three-dimensional green structure according to the desired height. It should be noted that in the illustrated example, each course through the first and second revolutions is identical. Of course, it is also conceivable that each course of the different revolutions is different from each other. Likewise, the nominal height of each revolution, which is identical in the illustrated example, may be different in the different revolutions.

[0139] By way of example, Figure 11 shows by curve A the course of the extrusion head 6 in the process called "sequential vase mode" described with reference to Figures 7-7B and 8-8C. This path proceeds, for example, in two stages of increment e / 2 from point to point. According to this example, over at least one revolution t, the extrusion head 6 is driven to rise at least once to an intermediate height that is a fraction of the nominal height.

[0140] Curve B describes the course of the extrusion head 6 in a process called "successive vase mode" shown in Figures 9-9B and 10-10C. In the example shown, each path (one revolution t) proceeds along 15 points (X, Y coordinates), i.e. with 15 increments or steps of height dZ proportional to the distance between two successive points, i.e. with 15 increments of equal height dZ=e / 15. Thus, the method aims to drive the extrusion head 6 so that, over at least one revolution, it is located at each of the different points of the path and at each point rises by a height increment, the sum of which height increments corresponds to the nominal height e. It should be noted that Figure 11 shows a continuous and gradual rise curve C corresponding to the gradual rise of the extrusion head along the Z axis.

[0141] From what has been described so far, through a series of rotations, the extrusion head 6 is driven to rise so that the material deposit 3 follows an uninterrupted trajectory from the beginning to the end of the construction of the manipulable three-dimensional green structure 2, building the manipulable three-dimensional green structure according to the 3D digital model.

[0142] Also, during each revolution t, the extrusion head 6 is driven to be offset in the horizontal plane X,Y so that the deposited material partially overlaps the edge of the previously deposited material deposit. Advantageously, in case of overlapping passes, the extrusion head 6 is driven to adjust its position in the horizontal plane X,Y so as to define the degree of overlap of the overlapping material portion 3d on the previously deposited material deposit. As mentioned above, the offset d in the horizontal plane X,Y between each successive course makes it possible to select the degree of overlap between the material deposits.

[0143] It should be noted that in the example embodiment illustrating the principles of the invention, the wall constructed has a width that can be constructed from two partially overlapping material deposits. Naturally, the principles of the invention can be implemented to construct walls with widths that require a larger number of material deposits, as shown in Figs. 12A and 12B with three deposits as an example. According to this example embodiment, the wall constructed separates two adjacent flow paths and has a width with three overlapping deposits. The construction of this wall is obtained in vase mode by following the path a1+b1+c1+d1+e1+f1+g1, then a2+b2+c2+d2+e2+f2+g2, then a3+b3+···, etc. The flow rate of the extrusion head 6 dropped to zero when the extrusion head 6, having completed fi, merges with ei until it merges with ai+1 at the branch (following gi). The thickness of the material deposit from the first revolution is proportional to the path traveled, and the thickness of the material deposit from the second revolution is equal to the nominal thickness.

[0144] It should be noted that according to a feature of an embodiment of the present invention, in the case of paths with overlaps, the extrusion head 6 is driven to keep the flow rate of the deposited material constant, while in the case of paths with intersections, the flow rate of the extrusion head 6 is reduced.

[0145] Thus, the method according to the invention allows to build a manipulable three-dimensional green structure 2 without material voids, regardless of the shape or dimensions of the walls. Figure 15 shows an example of a manipulable three-dimensional green structure 2 with no material voids in the walls produced after sintering. The above example illustrates a variation of the first advantageous embodiment, known as the conventional mode or vase mode, in which the extrusion head follows an uninterrupted trajectory of the material deposit 3 throughout the construction of the manipulable three-dimensional green structure 2.

[0146] 14 shows a variant of the second embodiment in which the extrusion head 6 is mounted movably along a predetermined numerical trajectory T in order to superimpose layer-like material deposits, each of which rises by a nominal height e. Layer-like material deposits are described in particular in WO2020 / 109715 and WO2020 / 109716. The method consists in forming first layers 31 and 32 by horizontal movement of a flow orifice 8 above a horizontal plate 5 according to a 3D digital model M predetermined by computer design software.

[0147] The extrusion head 6 moves horizontally, thus parallel to the horizontal plate 5, along a predetermined path according to the 3D digital model M to form a first layer. After depositing the first layer, the extrusion head 6 moves so that the depositing beads form a second layer 33 according to the 3D digital model M. For this purpose, the extrusion head 6 moves vertically (i.e. along the Z axis) and horizontally (i.e. along the X and / or Y axes) to the desired position. The extrusion of the inorganic composition 4 through the extrusion head 6 can be continuous or discontinuous. Thus, the second layer is deposited on the first layer by superimposing a material deposit on the previously deposited layer according to the 3D digital model M.

[0148] Naturally, the material deposition is carried out to ensure (partial or complete) overlap as described above to avoid voids between the material deposits. Thus, in the example shown in Figure 14, the second layer material deposit 33 can partially overlap from its two opposing edges with the adjacent edges of the two previously deposited material deposits 31 and 32 to avoid voids.

[0149] The method according to the invention allows the construction of a manipulable three-dimensional green structure 2 intended to form a monolithic porous inorganic support 1 with mechanical strength properties suitable for use in tangential filtration. Advantageously, the extrusion head 6 is driven to provide at least one channel 11 for circulating the fluid medium to be treated in the manipulable three-dimensional green structure 2. The walls of this channel 11 are formed by the rounded edges 3b of the material deposits located opposite the overlapping material portions. As shown, the extrusion head 6 is configured such that the material deposits have rounded edges 3b. The channels 11 therefore have walls with rounded reliefs, each relief extending over the entire circumference of the channel and defined by the rounded edges 3b of the material deposits. These rounded peripheral reliefs extend superimposed over the length of the channel, as shown in figures 15 and 16. At the scale of the thickness e of the material deposit, these rounded peripheral reliefs contribute in this channel in tangential filtration to the generation of turbulence at their level along the entire length of the channel. Figure 16 shows that these rounded peripheral reliefs are present even when the inner wall of the channel 11 is covered with a separation layer having a profile that appears as a white line in Figure 16. In this way, the separation layer matches the rounded peripheral relief and its rounded profile persists and participates in the generation of turbulence in the channel 11. It should be noted that the porous monolithic inorganic support 1 manufactured according to the method according to the invention has an outer surface that also has a series of rounded peripheral reliefs St superimposed and extending along the support, as shown in Figures 2B, 15 and 16.

Claims

1. A method for producing at least one porous monolithic inorganic support (1) having at least one flow path for circulating a fluid to be treated and having a porosity of 10% to 60% and an average pore size in the range of 0.5 μm to 50 μm, by using a 3D printer (I) including at least one extrusion head (6) movably mounted in the space above a fixed horizontal plate (5) and moving it continuously at a nominal height (e) along a predetermined numerical trajectory (T) to superimpose each material deposit having a nominal width and a defined thickness between the lower surface and the upper surface, the 3D printer comprising: a bead having rounded edges so as to form a rounded peripheral relief on the wall of at least one of the circulation channels, which is responsible for the generation of turbulence; A composition (4) that builds the walls of a three-dimensional green structure (2) that can be manipulated from a predetermined numerical trajectory (T) onto said horizontal plate (5) to form a monolithic porous inorganic support (1). and wherein the method comprises: For walls with a width greater than the nominal width (L) of the material deposit, decomposing the numerical trajectory into overlapping and intersecting paths only; Supplying a composition (4) to an extrusion head (6) of a 3D printer (I); In the case of overlapping paths, the deposited material partially overlaps at least one edge of a previously deposited material deposit with an overlapping material portion shown in its thickness and having a thickness strictly less than the nominal height (e) so that there is no space between the rounded edge of the deposited material deposit and the rounded edge of the previously deposited material deposit inside the operable three-dimensional green structure; In case of cross paths, within the operable three-dimensional green structure, the deposited material crosses and completely overlaps at least one previously deposited material deposit with an overlapping material portion shown in its thickness, the overlapping material portion having a thickness strictly smaller than the nominal height (e), such that there is no space between the rounded edge of the deposited material deposit and the rounded edge of the previously deposited material deposit; Driving the extrusion head according to the numerical trajectory; A method comprising:

2. The extrusion head (6) has a nominal height (e Ｎ 2. The method according to claim 1, wherein the object is movably mounted along a predetermined numerical trajectory (T) to perform a series of rotations each corresponding to a path traveled to find the same position in the horizontal plane having an altitude corresponding to the predetermined numerical trajectory (T).

3. 3. The method of claim 2, wherein the extrusion head is driven to rise at least once over at least one revolution to an intermediate height that is a fraction of the nominal height.

4. 3. The method of claim 2, wherein the extrusion head is driven to be positioned at different points in the path over at least one revolution and to rise at each point by a height increment, the sum of which height increments corresponds to the nominal height.

5. The method according to any one of claims 2 to 4, wherein the extrusion head is driven to rise by a series of rotations such that the material deposit (3) follows an uninterrupted trajectory throughout the construction of the manipulable three-dimensional green structure (2) and to build the manipulable three-dimensional green structure (2) according to the 3D digital model (M).

6. 6. The method according to claim 2, wherein the extrusion head is driven such that during each revolution the deposited material is offset in the horizontal plane so as to partially overlap the edge of the previously deposited material deposit.

7. In the case of cross paths, the extrusion head is at a nominal height (e Ｎ 7. The method of claim 1, wherein the step of depositing the first and second layers is driven to reduce the amount of material deposited to create an overlapping material portion having a thickness strictly smaller than the thickness of the first and second layers.

8. The method according to any one of claims 1 to 7, wherein for paths with the same overlap, the extrusion head is driven to keep the flow rate of deposited material constant.

9. A method according to any one of claims 1 to 8, wherein in the case of overlapping passes the extrusion head is driven to adjust its position in a plane to define an overlapping degree of the overlapping material portion on a previously deposited material deposit.

10. A method according to any one of claims 1 to 9, wherein in the case of overlapping passes, the flow rate of the extrusion head is adjusted depending on the degree of overlap of the overlapping material portions on the previously deposited material deposit.

11. 2. The method according to claim 1, wherein the extrusion head (6) is mounted movably along a predetermined numerical trajectory (T) for superimposing each material deposit in layers, each of which rises by a nominal height (e).

12. 12. The method according to any one of claims 1 to 11, in which an extrusion head is driven to provide in the manipulable three-dimensional green structure (2) at least one flow channel for circulating the fluid medium to be treated, said flow channel having walls with a series of rounded reliefs which cause variations in the passage cross section of said flow channel, said rounded reliefs being formed by material portions located on opposite sides of overlapping material portions.

13. A method according to any one of the preceding claims, wherein the extrusion head is configured such that the material portion opposite the overlapping material portion has rounded edges.

14. The method according to any one of the preceding claims, wherein the manipulable three-dimensional green structure (2) is placed in a heat treatment furnace to carry out a sintering operation.

15. A method for the preparation of a tangential filtration membrane, comprising the steps of producing a porous monolithic inorganic support (1) according to any one of claims 1 to 14, provided with at least one flow channel (11) for circulating the fluid medium to be treated, followed by the formation of at least one separating layer on the walls of the flow channel (11) after sintering said support.

16. A porous monolithic inorganic support (1) manufactured according to any one of claims 1 to 14, having a porosity of 10% to 60% and an average pore size in the range of 0.5 μm to 50 μm, an outer surface having a series of rounded peripheral reliefs (st) and at least one flow channel for circulating a fluid to be treated, the walls of said flow channels having a rounded peripheral relief responsible for the generation of turbulence.

17. A tangential filtration membrane comprising a porous monolithic inorganic support (1) according to claim 16, comprising at least one flow channel (11) for circulating the fluid medium to be treated, the walls of said flow channel having a rounded peripheral relief being coated with at least one separating layer.

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