Process for recycling thermoplastic elastomer powder for 3D printing

Abstract

This patent application relates to a 3D printing process by powder sintering, comprising a shearing step of the unsintered powder to enable its recycling. It also relates to the use of a mixer equipped with an agitator comprising at least one blade rotating at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature below 50°C, to improve the recyclability of a powder composition comprising at least one thermoplastic elastomer in a 3D printing process by sintering.

Description

Title of the invention: Process for recycling thermoplastic elastomer powder for 3D printing. Technical field

[0001] This patent application relates to a 3D printing process by powder sintering, comprising a shearing step of the unsintered powder to enable its recycling. It also relates to the use of a mixer equipped with an agitator comprising at least one blade rotating at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, to improve the recyclability of a powder composition comprising at least one thermoplastic elastomer in a 3D printing process by sintering. Previous technique

[0002] Electromagnetic radiation polymer powder sintering technology is a 3D printing process that has been used for several years to manufacture a wide variety of objects.

[0003] According to this process, a thin layer of polymer powder (referred to as "construction material") is deposited onto a horizontal plate held in a chamber heated to a temperature between the crystallization temperature Te and the melting temperature Tf of polyamide. A laser or other radiation source agglomerates the powder particles at various points in the powder layer according to a geometry corresponding to the desired object, for example, using a computer that has the shape of the object stored in memory and renders it as slices. The horizontal plate is then lowered by a value corresponding to the thickness of a powder layer (for example, between 0.05 and 2 mm and generally on the order of 0.1 mm), and then a new layer of powder is deposited. The powder particles are again agglomerated according to a geometry corresponding to this new slice of the object. The procedure is repeated until the entire object has been manufactured.This process yields a block of powder containing the 3D object. The unbound parts remain in powder form. The entire block is then slowly cooled, and the object solidifies as soon as its temperature drops below the crystallization temperature (Te). After complete cooling, the object is separated from the unsintered powder, which can represent approximately 85% to 90% of the total powder used. This unsintered powder is then generally reused to manufacture a new object.

[0004] Among the polymers that can be used in this process, thermoplastic elastomers are particularly interesting since they combine mechanical properties Thermoplastic elastomers (TPEs) offer excellent resistance to thermal and UV aging, as well as low density, enabling the production of lightweight and flexible articles. They are used, in particular, to manufacture sports equipment, such as soles or sole components, gloves, golf rackets or balls, and personal protective equipment for sports (vests, helmet and shell liners, etc.). Such applications require a material with a specific set of physical properties, including good rebound, low tensile set, and the ability to withstand repeated impacts and return to its original shape. Document WO 2022 / 153017 discloses a thermoplastic elastomer powder for 3D printing.

[0005] However, some thermoplastic elastomers, and in particular polyether / polyamide block polymers (PEBA), have a wide melting temperature range and therefore a poorly defined working window, leading to powder agglomeration during each build cycle and a decrease in the packed density of the recycled powder. As a result, the powder forming the support structure of the parts being built tends to slump, which affects the dimensional accuracy of the parts (printing defects), or even causes the object to be destroyed by the scraper. In the case of other polymers, this problem is generally not observed; it is therefore possible to directly mix virgin powder with the powder obtained after a build cycle, possibly after sieving the latter.In the case of thermoplastic elastomers, this drop in powder density necessitates mixing the powder obtained after the first build cycle (possibly sieved), and then after each subsequent cycle, with a significant fraction of virgin powder, in order to achieve a powder density sufficient to build parts with acceptable geometry. This results in an unacceptable material loss.

[0006] There is therefore a major interest in finding a solution to limit the decrease in density of a thermoplastic elastomer powder after use, in order to promote its recycling and thus reduce the cost per part.

[0007] Document CN 109517376 suggests, in order to increase the density of a polyamide powder from a 3D printing process, mixing it with new polymer powder in a high-speed mixer according to two temperature steps, respectively at 70-80°C and then at 30-40°C, before subjecting the mixture to a sieving step and then recycling the powder thus obtained.

[0008] For its part, US patent 2021 / 0129383 proposes subjecting a thermoplastic polymer powder, in particular a polyamide, to thermomechanical treatment in a mixer, at a speed of at least 100 rpm and at a temperature of at least 30°C, so as to increase the uncompacted density of the powder of at least 10%, before using it in a 3D printing process. There are no plans to treat the unsintered powder recovered after one or more build cycles, nor to apply this process to thermoplastic elastomers with the aforementioned problems.

[0009] There therefore remains a need for a simple and effective process to improve the recyclability of a thermoplastic elastomer powder after a 3D printing cycle, i.e. to optimize its reuse rate without negatively affecting the mechanical properties of the object produced.

[0010] The present invention makes it possible to meet this need. Summary of the invention

[0011] The invention thus relates to a 3D printing process by powder sintering, comprising the steps of: a. provide a powder composition comprising at least one thermoplastic elastomer and having a packed density Di, b. to carry out several successive cycles consisting of preparing a bed of said powder and then selectively sintering a portion of said powder using an electromagnetic energy source, until one or more objects are constructed, c. Recover the unsintered powder, d. subject the powder from step (c) to a shearing step in a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, and e. Recover the powder from step (d).

[0012] The invention also relates to the use of a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 revolutions per minute and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, to improve the recyclability of a powder composition comprising at least one thermoplastic elastomer in a 3D printing process by sintering.

[0013] The Applicant has demonstrated that the use of the particular shearing step makes it possible to bring the density of the thermoplastic elastomer powder back after each build cycle to a level close to that of the virgin powder and therefore to mix it with a smaller quantity of virgin powder for the next cycle, to obtain a 3D object with good mechanical properties. Description of implementation methods

[0014] The process according to the invention uses a powder comprising at least one thermoplastic elastomer.

[0015] The term “thermoplastic elastomer” or “TPE” refers to polymers that combine the elastic properties of elastomers with a thermoplastic character, that is to say, they melt and harden reversibly under the action of heat.

[0016] These thermoplastic elastomers may, in particular, be mechanical blends of polymers, that is to say, a "polymer-polymer" blend, most often a thermoplastic polymer and an elastomer. Alternatively, they may be thermoplastic elastomer copolymers. The term "thermoplastic elastomer copolymer" refers to a polymer comprising flexible and rigid segments, for example in the form of a block copolymer, in which the rigid segments, generally semi-crystalline or having a high glass transition temperature, melt or soften as the temperature increases. Above the melting temperature or the glass transition temperature of the rigid segment regions, the material can be processed using conventional techniques.

[0017] Below the melting temperature of the rigid segment domains, the thermoplastic elastomer exhibits elastic properties close to those of cross-linked elastomers. The flexible blocks preferably have a glass transition temperature

[0018] (Tg) less than or equal to 0°C, as determined by differential scanning calorimetry (DSC) according to ISO 11357-2.

[0019] The flexible blocks and the rigid blocks are covalently linked in the elastomers by functions in particular chosen from among the amide, ester, methane, and urea functions.

[0020] According to embodiments, the ratio between the flexible blocks and the rigid blocks is chosen so that the tensile modulus according to ISO 527 is between 5 and 800 MPa, preferably between 10 and 300 MPa, and more preferably between 20 and 150 MPa.

[0021] According to embodiments, the TPE copolymer has a Shore D hardness between 10D and 70D, in particular between 25D and 45D.

[0022] According to some embodiments, the TPE is chosen from: - Polyamide elastomers, such as amide block polyethers (PEBA), - Thermoplastic polyurethanes (TPU), which are isocyanate and ether or ester block copolymers, - polyester elastomers, in particular polyester-polyether block copolymers (COPE), and - styrenic block copolymers (TPS), in particular polystyrene and polybutadiene block copolymers (SBS), polystyrene and polyisoprene block copolymers (SIS), or polystyrene and poly(ethylene / butylene) block copolymers (SEBS).

[0023] According to embodiments, a mixture of TPE copolymers is used, in particular a mixture of PEBA, TPU and / or thermoplastic polyester, preferably a mixture of polymers of the same family, for example of two PEBA.

[0024] According to another embodiment, the thermoplastic elastomer is a mixture of a flexible polymer phase dispersed in a continuous rigid polymer phase. Examples of such mixtures include EPDM dispersed in a polyolefin (TPO) or a thermoplastic vulcanizate (TPV), a butadiene and acrylonitrile copolymer (NBR), vulcanized or not, dispersed in a polypropylene (PP / NBR), a chlorinated polyethylene dispersed in a polyolefin (PO / CPE-VD), an EVA dispersed in vinylidene chloride (EVA / VC), or a butadiene and acrylonitrile copolymer (NBR), vulcanized or not, dispersed in a polyvinyl chloride (PVC / NBR).

[0025] The thermoplastic elastomer may, in particular, have an enthalpy of fusion between 10 and 80 J / g. In particular, it may be from 25 to 60 J / g; or from 35 to 55 J / g.

[0026] Thermoplastic elastomers are commercially available, for example products under the names CAWITON®, THERMOLAST K®, THERMOLAST M®, Sofprene®, Dryflex® and Laprene® (TPS), Desmopan® or Elastollan® (TPU), Santoprene®, Termoton®, Solprene®, THERMOLAST V®, Vegaprene®, or Forprene® (TPV), and For-Tec E® or Ninjaflex® (TPO).

[0027] According to a particularly interesting embodiment, the thermoplastic elastomer is a "PEBA" copolymer. These copolymers are notably marketed by Arkema France under the name Pebax®, by Evonik® under the name Vestamid®, by EMS under the name Grilamid®, and by Sanyo under the name Pelestat®.

[0028] PEBAs can result from the condensation of reactive-end polyamide (PA) blocks with reactive-end polyether (PE) blocks, such as:

[0029] 1) polyamide blocks with diamine chain ends with polyoxyalkylene blocks dicarboxylic chain ends;

[0030] 2) polyamide blocks with dicarboxylic chain ends with blocks diamine-ended polyoxyalkylene;

[0031] 3) polyamide blocks with dicarboxylic chain ends containing polyetherdiols, the products obtained being, in this particular case, polyetheresteramides.

[0032] Polyamide blocks with dicarboxylic chain ends are obtained, for example, from the condensation of polyamide precursors in the presence of a chain-limiting dicarboxylic acid. Polyamide blocks with diamine chain ends are obtained by example of the condensation of polyamide precursors in the presence of a diamine as a chain limiter.

[0033] Three types of polyamide blocks can be used advantageously.

[0034] According to a first type, the polyamide blocks are obtained by the condensation of a dicarboxylic acid with an aliphatic, cycloaliphatic, or aromatic diamine. The dicarboxylic acid may have 4 to 36, and preferably 6 to 18, carbon atoms. It is preferably an aliphatic dicarboxylic acid, in particular a linear one, or an aromatic one. Examples include butanedioic, adipic, azelaic, suberic, sebacic, dodecanedicarboxylic, octadecanedicarboxylic, terephthalic, and isophthalic acids, as well as dimerized fatty acids. These dimerized fatty acids preferably have a dimer content of at least 98%; preferably, they are hydrogenated; This includes, for example, products marketed under the brand name "PRIPOL®" by the company CRODA, or under the brand name EMPOL® by the company BASF, or under the brand name Radiacid® by the company OLEON, and polyoxyalkylenes α,co-diacids.The diamine can contain, in particular, 2 to 20, preferably 6 to 14 carbon atoms. Examples include tetramethylene diamine, hexamethylene diamine, 1,10-decamethylene diamine, dodecamethylene diamine, and trimethylhexamethylene diamine. The polyamide blocks PA 412, PA 414, PA 418, PA 54, PA 59, PA 510, PA 512, PA 513, PA 514, PA 516, PA 518, PA 536, PA 64, PA 69, PA 610, PA 612, PA 613, PA 616, PA 618, PA are preferred. 636, PA 912, PA 104, PA 109, PA 1010, PA 1012, PA 1013, PA 1014, PA 1016, PA 1018, PA 1036, PA 10T, PA 124, PA 129, PA 1210, PA 1212, PA 1213, PA 1214, PA 1216, PA 1218, PA 1236, PA 12T, and their mixtures. PA 610, PA 1010, PA 1012 blocks, as well as their mixtures, are particularly preferred.

[0035] According to a second type, the polyamide blocks result from the condensation of one or more α,co-aminocarboxylic acids and / or one or more lactams. Examples of α,co-aminocarboxylic acids include aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic, and 12-aminododecanoic acids. Examples of lactams include those having 6 to 12 carbon atoms, and in particular caprolactam, oenantholactam, and lauryllactam. The PA 11, PA 12, and PA 6 polyamide blocks are particularly preferred.

[0036] According to a third type, the polyamide blocks are copolyamides. These blocks can be obtained, for example, by condensation of one or more α,co-aminocarboxylic acids or lactams and at least one diamine with at least one dicarboxylic acid.

[0037] According to one embodiment, the polyamide blocks result from the condensation of at least two α,co-aminocarboxylic acids or at least two lactams having from 6 to 12 carbon atoms or of one lactam and one α,co-aminocarboxylic acid having a number of different carbon atoms. α,co-aminocarboxylic acids, lactams, diamines, and diacids can be selected, in particular, from those listed above for polyamide blocks of the first and second types. PA 66 / 6 and PA 66 / 610 / 11 / 12 are particularly preferred.

[0038] Advantageously, the PEBA comprises polyamide blocks chosen from PA 6, PA 11, PA 12, PA 412, PA 414, PA 418, PA 54, PA 59, PA 510, PA 512, PA 513, PA 514, PA 516, PA 518, PA 536, PA 64, PA 69, PA 610, PA 612, PA 613, PA 614, PA 616, PA 618, PA 636, PA 912, PA 104, PA 109, PA 1010, PA 1012, PA 1013, PA 1014, PA 1016, PA 1018, PA 1036, PA 10T, PA 124, PA 129, PA 1210, PA 1212, PA 1213, PA 1214, PA 1216, PA 1218, PA 1236, PA 12T, PA 66 / 6, PA 66 / 610 / 11 / 12, in particular among PA 6, PA 11, PA 12, PA 610, PA 1010, PA 1012, as well as their mixtures and copolymers.

[0039] These polyamide blocks can be prepared by polycondensation of the monomers in the presence of a suitable chain limiter. Such chain limiters are, for example, dicarboxylic acids, particularly those comprising 4 to 10 carbon atoms, and diamines. Optionally, the dicarboxylic acid or diamine used as the monomer can be used as the chain limiter, introduced in excess. In the case of polycondensation of α,β-aminocarboxylic acids or lactams, a chain limiter can be added to the monomers.

[0040] The PEBA polyether blocks essentially comprise or are made up of alkylene oxide motifs.

[0041] Polyether blocks can be derived from alkylene glycols such as PEG (polyethylene glycol), PPG (propylene glycol), PO3G (polytrimethylene glycol), or PTMG (polytetramethylene glycol). They can also be derived from copolyethers comprising different alkylene oxides distributed in the chain in a regular manner, particularly by blocks, or statistically. Polyether blocks can also be obtained by oxyethylation of bisphenols, such as bisphenol A. These products are described, in particular, in document EP 613919 AL

[0042] Polyether blocks can also be ethoxylated amines, such as products of formula:

[0043] [Chem.l] H—-(OCHaCH^^ —N—4CH3CH3O)n—H (CHÀS. CH.

[0044] in which m and n are integers between 1 and 20 and x is an integer between 8 and 18. These products are, for example, commercially available under the NORAMOX® brand of the company ARKEMA and under the GENAMIN® brand of the company CLARIANT.

[0045] Polyether blocks may also comprise or be composed of polyoxyalkylene blocks with NH2 chain ends. Such blocks can be obtained by cyanoacetylation of polyetherdiols. Such polyethers are sold by the HUNTSMAN company under the name Jeffamine® or Elastamine® (for example, Jeffamine® D400, D2000, ED 2003, XTJ 542).

[0046] A two-step method for preparing PEBA having ester bonds between PA and PE blocks is described in document FR 2846332 A1. A method for preparing PEBA having amide bonds between PA and PE blocks is described in document EP 1482011 A1. Polyether blocks can also be mixed with polyamide precursors and a diacid chain limiter to prepare PEBA by a one-step process.

[0047] While PEBAs generally comprise a polyamide block and a polyether block, they can also comprise two, three, four or more different blocks chosen from those described above.

[0048] Particularly preferred PEBAs are copolymers comprising blocks of: PA 11 and PEG; PA 11 and PTMG; PA 11 and PPG; PA 12 and PEG; PA 12 and PTMG; PA 12 and PPG; PA 1010 and PEG; PA 1010 and PTMG; PA 1010 and PPG; PA 610 and PTMG; PA 610 and PEG; PA 610 and PPG; PA 6 and PEG; PA 6 and PTMG; and PA 6 and PPG.

[0049] The number-average molar mass of the polyamide blocks in PEBA is preferably 100 to 20000 g / mol, in particular 200 to 10000 g / mol, and especially 200 to 2000 g / mol. It can be, in particular, from 100 to 200 g / mol, or 200 to 500 g / mol, or 500 to 1000 g / mol, or 1000 to 1500 g / mol, or 1500 to 2000 g / mol, or 2000 to 2500 g / mol, or 2500 to 3000 g / mol, or 3000 to 3500 g / mol, or 3500 to 4000 g / mol, or 4000 to 5000 g / mol, or 5000 to 6000 g / mol, or 6000 to 7000 g / mol, or 7000 to 8000 g / mol, or 8000 to 9000 g / mol, or 9000 to 10000 g / mol, or 10000 to 11000 g / mol, or 11000 to 12000 g / mol, or 12000 to 13000 g / mol, or 13000 to 14000 g / mol, or 14000 to 15000 g / mol, or 15000 to 16000 g / mol, or 16000 to 17000 g / mol, or 17000 to 18000 g / mol, or 18000 to 19000 g / mol, or 19000 to 20000 g / mol.

[0050] The number-average molar mass of the polyether blocks in the PEBA is preferably 100 to 6000 g / mol, more preferably 200 to 3000 g / mol, and even more preferably 800 to 2500 g / mol. It may, in particular, be 100 to 200 g / mol, or 200 to 500 g / mol, or 500 to 800 g / mol, or 800 to 1000 g / mol, or 1000 to 1500 g / mol, or 1500 to 2000 g / mol, or 2000 to 2500 g / mol, or 2500 to 3000 g / mol, or 3000 to 3500 g / mol, or 3500 to 4000 g / mol, or 4000 to 4500 g / mol, or 4500 to 5000 g / mol, or 5000 to 5500 g / mol, or 5500 to 6000 g / mol.

[0051] The mass ratio of the polyamide blocks to the polyether blocks of the PEBA can in particular range from 0.1 to 20. This mass ratio can be calculated by dividing the number-average molar mass of the polyamide blocks by the number-average molar mass of the polyether blocks.

[0052] Thus, the mass ratio of the polyamide blocks to the polyether blocks of the PEBA can be from 0.1 to 0.2; or from 0.2 to 0.3; or from 0.3 to 0.4; or from 0.4 to 0.5; or from 0.5 to 1; or from 1 to 2; or from 2 to 3; or from 3 to 4; or from 4 to 5; or from 5 to 7; or from 7 to 10; or from 10 to 13; or from 13 to 16; or from 16 to 19; or from 19 to 20. A mass ratio of 0.5 to 2.5 and more specifically of 0.6 to 2 is particularly preferred.

[0053] According to another embodiment, the thermoplastic elastomer is a copolyetherester (COPE).

[0054] The COPEs comprise at least one polyether (PE) block, and at least one polyester PES (homopolyester or copolyester) block.

[0055] The COPEs comprise flexible PE blocks derived from polyetherdiols and rigid polyester blocks resulting from the reaction of at least one dicarboxylic acid with at least one short diol. The PES blocks and the PE blocks are linked by ester bonds resulting from the reaction of the acidic functions of the dicarboxylic acid with the OH functions of the polyetherdiol.

[0056] The chaining of polyethers and diacids forms the flexible blocks while the chaining of the short diol with the diacids forms the rigid blocks of the copolyetherester.

[0057] Advantageously, diacids are aromatic dicarboxylic acids having from 8 to 14 carbon atoms. Up to 50 mole percent of the aromatic dicarboxylic acid can be replaced by at least one other aromatic dicarboxylic acid having from 8 to 14 carbon atoms, and / or up to 20 mole percent can be replaced by an aliphatic dicarboxylic acid having from 2 to 14 carbon atoms. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, bibenzoic acid, naphthalene dicarboxylic acid, 4,4'-diphenylenedicarboxylic acid, 1,4-tetramethylene bis(p-oxybenzoic acid), ethylene bis(p-oxybenzoic acid), and 1,3-trimethylene bis(p-oxybenzoic acid).

[0058] The short diol may be in particular an aliphatic glycol of formula HO(CH2)nOH in which n is an integer from 2 to 10, in particular ethylene glycol, 1,3-trimethylene glycol, 1,4-tetramethylene glycol, 1,6-hexamethylene glycol, 1,3-propylene glycol, 1,8-octamethylene glycol and 1,10-decamethylene glycol, or neopentyl glycol.

[0059] Preferred PES motifs are obtained from the reaction of an aromatic dicarboxylic acid, in particular terephthalic acid, with a glycol, in particular ethanediol or 1,4-butanediol. Such copolyetheresters are described in patents EP 402883 Al and EP 405227 Al.

[0060] The PE motifs can be derived from polyetherdiols as defined above, for example polyethylene glycol (PEG), polypropylene glycol (PPG), polytrimethylene glycol (PO3G) or polytetramethylene glycol (PTMG).

[0061] The number-average molar mass of the polyester blocks is preferably 100 to 20,000 g / mol, in particular 200 to 10,000 g / mol, or better, 200 to 2,000 g / mol. That of the polyether blocks is as described above for PEBA.

[0062] The mass ratio of the polyester blocks to the polyether blocks of the COPE can in particular range from 0.1 to 20. The mass ratio can in particular be from 0.1 to 0.2; or from 0.2 to 0.3; or from 0.3 to 0.4; or from 0.4 to 0.5; or from 0.5 to 1; or from 1 to 2; or from 2 to 3; or from 3 to 4; or from 4 to 5; or from 5 to 7; or from 7 to 10; or from 10 to 13; or from 13 to 16; or from 16 to 19; or from 19 to 20.

[0063] According to yet another embodiment, the thermoplastic elastomer is a TPU, i.e. a copolymer of polyurethane (PU) and polyether (PE) blocks, also called polyetherurethane, or a copolymer of polyurethane (PU) and polyester (PES) blocks, also called polyesterurethane.

[0064] The TPUs of the first type mentioned above result from the condensation of polyetherdiols with polyurethanes. The rigid PU blocks and the flexible PE blocks are linked by bonds resulting from the reaction of the isocyanate groups of the polyurethane with the -OH groups of the polyetherdiol.

[0065] The PU blocks can be obtained from the reaction of at least one diisocyanate, which may be selected from aromatic diisocyanates (e.g., MDI, TDI) and / or aliphatic diisocyanates (e.g., HDI or hexamethylenediisocyanate), with at least one short diol or a short diamine. The short diol may be selected from the glycols mentioned previously in the description of the copolyetheresters, in particular polyethylene glycol (PEG), poly(1,2-propylene glycol) (PPG), poly(1,3-propylene glycol) (PO3G), or polytetramethylene glycol (PTMG).

[0066] The TPUs of the second type mentioned above result from the condensation of flexible polyesters with polyisocyanates. The rigid PU blocks and the flexible PES blocks are linked by bonds resulting from the reaction of the isocyanate groups of the polyurethane with the terminal groups of the polyester.

[0067] The PU blocks can be as described above for the TPUs of the first type. The flexible PES blocks can be obtained from the reaction of an aliphatic dicarboxylic acid having 4 to 12 carbon atoms, in particular adipic acid, with a glycol such as ethanediol or 1,4-butanediol. Such copolyetheresters are described in patents EP 402883 Al and EP 405227 Al.

[0068] The number-average molar mass of the PU blocks in TPUs is preferably 100 to 20,000 g / mol, in particular 200 to 10,000 g / mol, and especially 200 to 2,000 g / mol. That of the polyether blocks is as described above for PEBA.

[0069] The mass ratio of the polyurethane blocks to the polyether blocks of the TPU can in particular range from 0.1 to 20. In particular, it can be from 0.1 to 0.2; or from 0.2 to 0.3; or from 0.3 to 0.4; or from 0.4 to 0.5; or from 0.5 to 1; or from 1 to 2; or from 2 to 3; or from 3 to 4; or from 4 to 5; or from 5 to 7; or from 7 to 10; or from 10 to 13; or from 13 to 16; or from 16 to 19; or from 19 to 20.

[0070] The elastomer present in the powder used according to the invention preferably has a melting temperature (Tf) ranging from 100 to 300°C, and preferably from 120 to 200°C. This Tf corresponds to that measured during the first heating. Furthermore, the thermoplastic elastomer preferably has a crystallization temperature (Te) ranging from 40 to 250°C, and preferably from 45 to 200°C, for example, from 45 to 150°C. Typically, the Tf and Te are determined directly from the polymer powder. When dealing with a polymer blend, the Tf used is the lowest Tf in the polymer blend, and the Te used is the highest Te in the polymer blend.

[0071] Finally, the difference between the Te and the Tf of the thermoplastic elastomer is preferably greater than or equal to 20°C, preferably greater than or equal to 30°C, preferably even greater than or equal to 40°C, or 50°C, or 60°C, or 70°C, or 80°C.

[0072] The powder may comprise one or more thermoplastic elastomers as described above. According to one embodiment, it may also comprise up to 50% by weight of one or more additional thermoplastic polymers.

[0073] Preferably, the powder used according to the invention comprises 30 to 99%, preferably 40 to 95%, in particular 50 to 90% and especially 70 to 85% by weight of thermoplastic elastomer.

[0074] In addition to the thermoplastic elastomer, the powder according to the invention generally comprises at least one additive selected from antioxidants, flow agents, flame retardants (or flame retardants), anti-UV agents, anti-abrasion agents, light stabilizers, shock modifiers, antistatic agents, pigments, polymers and mixtures thereof.

[0075] The antioxidant may be selected from: phenolic antioxidants, phosphorus antioxidants (such as hypophosphorous acid, phosphonates, phosphites or hypophosphites, such as trialkyl- and trialkylaryl-phosphites, in particular trinonyl-, tri(nonylphenyl)- and tri[(2,4-di-tert-butyl-5-methyl)phenyl] phosphites or cyclic diphosphites derived from pentaerythritol, including distearylpentaerythritol diphosphite), thioethers (such as dilauryl thiodipropionate, distearyl thiodipropionate and pentaerythritol tetrakis (3-dodecylthio propionate or 3-laurylthiopropionate) and mixtures thereof.

[0076] The fillers may in particular be chosen from: calcium carbonate, magnesium carbonate, dolomite, calcite, barium sulfate, calcium sulfate, dolomite, alumina hydrate, wollastonite, montmorillonite, zeolites, perlite, nano-clays, calcium silicates, magnesium silicates, such as talc, mica, kaolin, attapulgite, carbon nanotubes, glass powder, glass fibers and carbon fibers, solid or hollow glass beads possibly coated with silane, and mixtures thereof.

[0077] According to one embodiment, the powder composition according to the invention is free of fillers.

[0078] By way of example, the flow agent may be selected from silicas, including fumed silica, possibly hydrophobically treated, such as the product marketed under the name Cab-o-Sil® TS610 by Cabot Corporation, precipitated silica, hydrated silica, vitreous silica, vitreous phosphates, vitreous borates, alumina, such as amorphous alumina, and mixtures thereof. Fumed silica is preferred for use in the present invention. Alternatively or in addition, the flow agent may comprise at least one wax, selected, for example, from polyethylene, polypropylene, polytetrafluoroethylene, ketone, acid, partially esterified acid, acid anhydride, ester, aldehyde, amide, derivatives, and mixtures thereof.The wax may include, in particular, a product marketed under the name Crayvallac® WN1135, WN 1495 or WN1265 by ARKEMA or a product marketed under the name Ceridust® 9615A or 8020 marketed by CLARIANT.

[0079] The thermoplastic elastomers useful in the present invention are commercially available, in particular in the form of granules, flakes or powder. If necessary, they can be transformed into powder by means of known processes, in particular by grinding.

[0080] Preferably, the grinding is cryogenic grinding. In this process, the material to be ground is cooled below the glass transition temperature of the thermoplastic elastomer, for example, by means of liquid nitrogen, liquid carbon dioxide, or liquid helium. The grinding can be carried out, for example, in a counter-rotating pin mill, a hammer mill, or a vortex mill.

[0081] Any additives may be added to the thermoplastic elastomer before grinding, particularly in an extruder (by compounding). Alternatively or in addition, one or more additives may be added after grinding, by for example by dry mixing. Furthermore, it is possible to mix the thermoplastic elastomer and any additives by dissolution / precipitation.

[0082] The powder thus obtained can then be sieved (in particular using a vibrating sieve possibly combined with ultrasound) or subjected to a selection step to obtain the desired particle size profile.

[0083] Before use, the polymer powder can then, if necessary, be subjected to thermal or hydraulic treatments, in order to make it better suited to 3D printing by sintering.

[0084] The powder described above is implemented according to the invention in a 3D printing process by powder sintering.

[0085] This process includes the steps of:

[0086] (a) provide a powder composition comprising at least one elastomer thermoplastic and having a compact density Di,

[0087] (b) perform several successive cycles consisting of preparing a bed of said powder then to selectively sinter a portion of said powder using an electromagnetic energy source, until one or more objects are constructed,

[0088] (c) recover the unsintered powder,

[0089] (d) subject the powder from step (c) to a shearing step in a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 revolutions per minute and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, and

[0090] (e) recover the powder from step (d).

[0091] In one embodiment, the following steps are implemented at the end of the process:

[0092] (f) mix the powder from step (e) with an amount of powder of density Di,

[0093] (g) perform several successive cycles consisting of preparing a bed of said mixture of powders and then selectively sintering a portion of said powder mixture using an electromagnetic energy source, until one or more objects are constructed,

[0094] (h) optionally, repeat steps (c) to (g) until the quantity is obtained of desired objects.

[0095] The electromagnetic energy source can be any energy source capable of producing infrared or UV radiation. Preferably, it should be a laser. The 3D printing process according to the invention can be a selective laser sintering (SLS) process, a high-speed sintering (HFS) process, or a multijet fusion (MJF) process.

[0096] In the SLS process, step (b) comprises the deposition of a thin layer of powder onto a horizontal plate held in a chamber heated to a temperature called the build temperature. Most often, heating to the build temperature is achieved using IR radiating lamps, for example halogen lamps, which generally have a maximum emission at a wavelength between 750 nm and 1250 nm.

[0097] Electromagnetic radiation, for example in the form of a laser, then provides the energy necessary to sinter the powder particles at different points in the powder layer according to a geometry corresponding to an object, for example using a computer which has the shape of an object in its memory and reproduces it in the form of slices.

[0098] Next, the horizontal plate is lowered to a height corresponding to the thickness of a layer of powder, and a new layer of powder is spread, heated, and then sintered in the same way. The procedure is repeated until one or more objects have been produced.

[0099] In the case of the MJF and HSS processes, the entire layer of the building material is exposed to radiation, but only a portion coated with a melting agent is melted to become a layer of a 3D part. The melting agent is a compound capable of absorbing radiation and converting it into thermal energy, for example, black ink. It is applied selectively to the selected region of the building material. The melting agent is able to penetrate the layer of the building material and transfers the absorbed energy to the adjacent building material, causing it to melt or be sintered. Through the melting, bonding, and subsequent hardening of each layer of the building material, the object(s) are formed.

[0100] In the particular case of MJF, a detailing agent is further added to the edges of the area to be melted to allow the parts to have a better definition.

[0101] Once the desired 3D article (consisting of one or more objects) has been formed, it is separated from the bed of agglomerated but not sintered powder and the latter is recovered in step (c).

[0102] The process according to the invention is characterized by the fact that the powder from step (c) is subjected to a shearing step (d).

[0103] This shearing step consists of mixing the thermoplastic elastomer powder in a powder mixer equipped with an agitator comprising at least one blade. In a preferred embodiment, the agitator comprises at least two blades, advantageously three blades, arranged along the axis of a rotating shaft. More preferably, the agitator comprises two blades substantially perpendicular to the shaft and positioned relative to each other at an angle of 90° in the plane horizontal. One of these blades may have tips inclined at least 30° relative to the plane of the other blade.

[0104] It is also preferred that the mixer include a fixed blade or a deflector, extending in a plane substantially parallel to the rotating shaft.

[0105] The agitator is rotated at a speed of at least 100 rpm, preferably at least 500 rpm, more preferably at least 1,000 rpm, better still at least 1,500 rpm, and generally less than 2,000 rpm, for example, at most 1,800 rpm. This applies a shear force of 10 to 70 m / s², and preferably 10 to 50 m / s², more preferably 15 to 40 m / s², at the blade tip. Furthermore, the shearing is carried out at a temperature below 50°C. Preferably, the mixer is operated at an initial temperature below 30°C, more preferably between 15 and 25°C, for a duration of, for example, 5 to 30 minutes, preferably 7 to 15 minutes. We prefer to perform thermal regulation of the mixer during all or part of the mixing stage, by cooling the mixer so that the temperature during mixing remains below 50°C, or even below 30°C.

[0106] The mixer can in particular be chosen from those marketed by companies such as Henschel, Diosna, Eirich, Lôdige or Kahl.

[0107] The resulting powder has a packed density Df that varies by less than 10% after each build cycle, compared to the packed density Di of the powder initially used. The packed density can be measured as described in the following examples.

[0108] In one embodiment, the powder recovered after the shearing step is then mixed in step (f) with a fraction of powder of density Di, preferably a fraction of virgin powder, for example in a weight ratio of unsintered powder to powder of density Di of 65 / 35 to 90 / 10, preferably 80 / 20 to 85 / 15, until a new 3D article is obtained. "Virgin powder" means powder of the same thermoplastic elastomer that has not been introduced into a 3D printer. The process according to the invention allows, in some embodiments, limiting the proportion of virgin powder mixed with the powder from step (d).

[0109] The powder mixture is then subjected to a new building cycle, i.e., to a step (g) similar to step (b) described previously. Steps (c) to (g) can optionally be repeated until the desired quantity of 3D objects is obtained.

[0110] The present invention also relates to the use of a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, to improve the recyclability of a powder composition comprising at least one thermoplastic elastomer in a 3D printing process by sintering.

[0111] The 3D object obtained according to the above process is preferably chosen from shoe components such as soles, sports equipment parts such as ski pole parts, racket or golf club handles, goalkeeper gloves, treadmills, aquatic equipment such as diving booties, mask and snorkel parts, eyeglass frame parts (sleeve, temples, nose pads), ski mask frames, vibration isolation parts in electronics and on machines, external battery cases, automotive parts (seals, tips), toys, watch straps, machine buttons, sealing gaskets, or conveyor belt components.

[0112] The invention will be better understood in light of the following non-limiting examples. Examples

[0113] EXAMPLE 1: Evolution of the packed density of powders for 3D printing

[0114] A powder for 3D printing by sintering was prepared by mixing: a Thermoplastic elastomer in powder form having a Dv50 of 82 pm, comprising a polyamide (PA11) / polyether block copolymer with a crystallization temperature of 61°C, a melting temperature of 127°C, and a Shore D hardness of 35; 3% flow agents and 0.7% antioxidants. Its packed density was measured in accordance with ISO 3953:2011 after 2500 compactions.

[0115] This powder was then used in the 3D printing by SLS of 1BA XY test specimens (1BA test specimen according to ISO 527-1BA, called "XY" because printed in the horizontal plane of the printer), using a Promaker® P1000 printer supplied by PRODWAYS, with a powder thickness of 100 µm, a manufacturing temperature of 109°C and a laser with a power of 15.75W, an engraving speed of 2,500 mm / s and an engraving depth of 0.18 mm.

[0116] The unsintered powder from this process was recovered and is hereinafter referred to as "Waste Powder 1," and the packed density of a fraction of this powder was measured again. It was observed that the packed density of the powder had decreased by 15%, from a value of 0.562 g / cm³ to a value of 0.478 g / cm³.

[0117] Additional tests were carried out by varying the nature of the thermoplastic elastomer. The characteristics of the elastomers tested and the results obtained (variation in packed density after construction) are summarized in Table 1 below.

[0118] [Tables 1] PEBA Polyamide Base Hardness (Shore D) Crystallization Temperature Melting Temperature Construction Temperature Variation in Packed Density (%) PAU 35 61°C 127°C 109°C -15% PAU 55 129°C 171°C 150°C -17.4% PA12 45 94°C 147°C 110°C -21.7%

[0119] Thus, in all the tests carried out, the packed density of the powder drops by more than 10% after a single build cycle.

[0120] In addition, a 3D printing test was carried out starting from a mixture of these used powders in a weight ratio of Used Powder / Virgin Powder of 80 / 20 then sieved at 160 pm: the 3D object could not be printed because the movements of the printer's scraper (or "recoater" in English) damaged the object. EXAMPLE 2: Powder Processing

[0121] The Used Powder 1 of Example 1 was introduced into a Henschel mixer equipped with a paddle agitator rotated at a speed of 1,800 rpm (blade tip speed: 19 m / s) for 10 minutes at an initial temperature of 23°C.

[0122] It was then mixed with a fraction of virgin powder, in a waste powder / virgin powder ratio of 80 / 20, and then recycled in the same 3D printing process. The waste powder from the second build cycle (referred to as Waste Powder 2) was then subjected to a shearing step in the same mixer as Waste Powder 1 and for different durations.

[0123] The change in packed density was measured after each cycle and after each shear treatment. The results are summarized in Table 2 below.

[0124] [Tables2] Packed Density (g / cm³) Variation (%) Virgin Powder 0.562 — Used Powder 1 0.478 14.9% Used Powder 1 after shearing (10 min) 0.538 4.3% Used Powder 2 0.469 16.5% Used Powder 2 after shearing: 10 min 30 min 60 min 0.540 0.524 0.514 3.9% 6.8% 8.5%

[0125] A comparative test was carried out using, instead of the mixer described above, a concrete mixer equipped with a single blade rotating at a speed of 20 to 30 rpm: after 5 hours of processing, followed by sieving the powder at 160 µm, the compacted density of the Used Powder 1 was only 0.312 g / cm³, representing a variation of 44.4%. Furthermore, a 3D printing test was performed using a mixture of this used powder in a weight ratio of Used Powder / Virgin Powder of 80 / 20, then sieved at 160 µm: the 3D object could not be printed because the movements of the printer's recoater damaged the object.

[0126] Another test was carried out by sieving the Used Powder 1 to 160 pm before mixing it with virgin powder in a weight ratio of Used Powder 1 / virgin powder of 80 / 20: the 3D object could not be printed because the movements of the printer's scraper (or "recoater" in English) damaged the object.

[0127] The same observation was made after 4 hours of treatment in a concrete mixer.

[0128] Thus, only high shear allows the spent powder to regain a The packed density is close to that of virgin powder, thus allowing it to be recycled. Increasing the shear time has no positive effect on the packed density of the powder.

Claims

Demands

1. A 3D printing process by powder sintering, comprising the steps of: (a) providing a powder composition comprising at least one thermoplastic elastomer and having a packed density Di, (b) carrying out several successive cycles of preparing a bed of said powder and then selectively sintering a portion of said powder by means of an electromagnetic energy source, until the construction of one or more objects, (c) recovering the unsintered powder, (d) subjecting the powder from step (c) to a shearing step in a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, and (e) recovering the powder from step (d).

2. A process according to claim 1, characterized in that the following steps are carried out at the end of the process: (f) mixing the powder from step (e) with a quantity of powder of density Di, (g) carrying out several successive cycles consisting of preparing a bed of said powder mixture and then selectively sintering a portion of said powder mixture by means of an electromagnetic energy source, until the construction of one or more objects, (h) optionally, repeating steps (c) to (g) until the desired quantity of objects is obtained.

3. The method according to claim 2, characterized in that the thermoplastic elastomer is selected from the group consisting of: block copolymers SBS, SIS, SEBS, TPU, COPE and PEBA and mixtures thereof, preferably a mixture of PEBA; EPDM dispersed in a polyolefin (TPO) or thermoplastic vulcanizate (TPV), butadiene and acrylonitrile copolymer (NBR), vulcanized or not, dispersed in a polypropylene (PP / NBR), chlorinated polyethylene dispersed in a polyolefin (PO / CPE-VD), EVA dispersed in vinylidene chloride (EVA / VC), or butadiene and acrylonitrile copolymer (NBR), vulcanized or not, dispersed in a polyvinyl chloride (PVC / NBR).

4. A process according to claim 3, characterized in that the thermoplastic elastomer comprises or is made up of a PEBA, preferably selected from the following copolymers comprising blocks of: PA 11 and PEG; PA 11 and PTMG; PA 11 and PPG; PA 12 and PEG; PA 12 and PTMG; PA 12 and PPG; PA 1010 and PEG; PA 1010 and PTMG; PA 1010 and PPG; PA 610 and PTMG; PA 610 and PEG; PA 610 and PPG; PA 6 and PEG; PA 6 and PTMG; and PA 6 and PPG.

5. A method according to any one of claims 2 to 4, characterized in that, in step (f), the unsintered powder is mixed with an amount of density powder Di in a weight ratio of the unsintered powder to the density powder Di of between 65 / 35 and 90 / 10, preferably of 80 / 20 and 85 / 15.

6. A method according to any one of claims 1 to 5, characterized in that, in step (d), the blade is rotated at a speed of at least 500 rpm, preferably at least 1,000 rpm, more preferably at least 1,500 rpm and generally less than 2,000 rpm, for example at most 1,800 rpm.

7. A method according to any one of claims 1 to 6, characterized in that, in step (d), the blade is rotated at a blade tip speed of 10 to 70 m / s, and preferably of 10 to 50 m / s, more preferably of 15 to 40 m / s.

8. A method according to any one of claims 1 to 7, characterized in that, in step (d), the shearing is carried out at an initial temperature between 15 and 25°C.

9. A method according to any one of claims 1 to 8, characterized in that, in step (d), the shearing is carried out for a period of 5 to 30 minutes, preferably 7 to 15 minutes.

10. A method according to any one of claims 1 to 9, characterized in that the 3D printing sintering method is selected from the selective laser sintering (SLS) method, the multi-jet fusion (MJF) method and the high-speed sintering (HSS) method.

11. Use of a mixer equipped with an agitator comprising at least one blade rotated at a speed of at least 100 rpm and / or at a blade tip speed of at least 10 m / s, at a temperature of less than 50°C, to improve recyclability of a powder composition comprising at least one thermoplastic elastomer in a 3D printing process by sintering.