Use of polyamide powder and its use in powder aggregation methods by sintering

Abstract

The present invention relates to a polyamide powder for use in a process for agglomerating powders by sintering, comprising at least one chain limiter.

Description

Technical Field

[0001] The present invention is intended to be used in a method for aggregating powders by melting, and relates to polymers, particularly polyamide powders, that can be recycled several times.

Background Art

[0002] The polyamide powder aggregation technique is used to produce three-dimensional objects by adding or melting powders layer by layer to aggregate the powders. This technique is particularly used in various fields such as the automotive, marine, aviation, aerospace, medical, textile, clothing and decoration fields, housings for electronic devices, telephone communication, home automation, computing and lighting, fashion, sports and industrial tool fields, etc. to manufacture prototypes and molds.

[0003] Aggregation of powders by melting (or "sintering") is brought about by radiation such as, for example, a laser beam (also known as laser sintering), infrared rays, ultraviolet rays, LED-type radiation, or any source of electromagnetic radiation that enables melting of powder layers layer by layer to produce three-dimensional objects.

[0004] In laser sintering, a thin layer of polyamide powder is deposited on a horizontal plate maintained in a chamber heated to a temperature between the crystallization temperature Tc and melting temperature Tm of the polyamide powder. The laser allows the powder particles at various points within the layer, which slowly crystallize after passing through the laser, to fuse according to the geometric shape corresponding to the object, for example, by using a computer that memorizes the shape of a 3D object and reproduces this shape in the form of a 2D slice. Subsequently, the horizontal plate is lowered by a value corresponding to the thickness of the powder layer (e.g., between 0.05 and 2 mm, generally around 0.1 mm), and then a new powder layer is deposited. The laser allows the powder particles in this new layer, which slowly crystallizes according to the geometric shape corresponding to the object, to fuse according to the geometric shape corresponding to the object. This procedure is repeated until the entire object is manufactured. An object bordered with powder is obtained in the chamber. The parts that did not aggregate remain in a powder state in this way.

[0005] In laser sintering, at least 50% of the powder is not targeted by the laser. Therefore, it is advantageous to be able to reuse this powder between subsequent fabrications (or the next "operation"), i.e., to recycle it. For this reason, the polyamide powder should retain its initial properties such as particle size, pourability, color, and viscosity as much as possible.

[0006] During sintering, the bordered powder, i.e., the powder not exposed to radiation, remains above its crystallization temperature (Tc) for several hours, which can lead to an increase in the molecular weight of the polyamide and, consequently, an increase in viscosity. Subsequently, during continuous operation, fusion between powder particles becomes increasingly difficult. Thus, with certain polyamide powders, it is necessary to change the parameters of the sintering apparatus, particularly dramatically increasing the radiation output, during each recycling of the powder during continuous operation. Furthermore, a very significant decrease in the mechanical properties of the resulting parts is observed as operation progresses.

[0007] To limit the increase in molecular weight of polyamide powders, a metal soap (0.5%) was added to the polyamide powder (US2004106691). However, when these powders come into contact with certain solvents, objects made from them tend to leach metal salt derivatives, limiting their use to specific applications.

[0008] Furthermore, before recycling the processed powder for subsequent operations, the powder used during operation was subjected to high-temperature steam treatment (US20090291308). However, this method requires steam treatment and drying of the powder between two consecutive operations and near the sintering apparatus, which necessitates numerous intermediate steps between operations and is not economically viable.

[0009] Therefore, there is a need to provide a powder that is easy to use, can be recycled several times without the need to modify the operating conditions of the sintering apparatus, and allows for the production of objects with reproducible mechanical properties. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent Application Publication No. 2004 / 106691 [Patent Document 2] U.S. Patent Application Publication No. 2009 / 0291308 [Overview of the Initiative]

[0011] The present invention stems from the unexpected demonstration by the inventors that by adding at least one chain limiting agent, in solid or liquid form, particularly a monoacid, dicarboxylic acid, monoamine, or diamine, to polyamide powder, it is possible to control, particularly reduce, stabilize, or remove the increase in viscosity and melting temperature of unaggregated polyamide powder that occurs during a continuous cycle or operation of a melt-induced agglomeration method. This makes it possible to reuse or recycle the unaggregated powder and to obtain an object with reproducible properties during the continuous operation process.

[0012] Therefore, the present invention relates to a polyamide powder intended for use in a method of powder aggregation by melting, comprising at least one chain limiting agent.

[0013] Furthermore, the present invention relates to the use of the above-mentioned polyamide powder for manufacturing an object by agglomeration of the powder by melting.

[0014] Furthermore, the present invention relates to a method for producing an object by agglomerating the above-mentioned polyamide powder by melting.

[0015] Furthermore, the present invention relates to an object manufactured using at least one of the above-mentioned polyamide powders.

[0016] Furthermore, the present invention relates to the above method for recovering polyamide powder that has not been aggregated.

[0017] Furthermore, the present invention relates to the use of unaggregated polyamide powder recovered according to the above method for the production of an object by agglomeration of powder by melting.

[0018] Furthermore, the present invention relates to the use of at least one chain limiting agent for controlling the increase in viscosity or melting temperature of polyamide powder intended for use in methods of manufacturing objects by powder aggregation due to melting.

[0019] Furthermore, the present invention relates to the use of at least one chain limiting agent to improve the recyclability of polyamide powder intended for use in a powder agglomeration method by melting. [Modes for carrying out the invention]

[0020] <Definition> In this description, the D50 of the powder, also referred to as the "volume median diameter", corresponds to the value of the particle size that divides the accurately analyzed population of particles into two equal parts. The D50 is measured in accordance with ISO standard 9276-Part 1~6: "Representation of results of particle size analysis" or ISO standard 13319.

[0021] The intrinsic viscosity of the solution (especially the intrinsic viscosity of an object obtained by a method of aggregating polyamide powder or powder by melting) is preferably measured according to a method including the following steps. - A step of sampling a sample of 0.07 to 0.10 grams, preferably at most 0.15 grams. - A step of adding an m-cresol solvent by weighing to obtain a concentration of 0.5% by weight based on the total weight of the solution. A step of dissolving on a hot plate stirrer adjusted to 100 °C ± 5 °C until the sample is completely dissolved. A step of cooling the solution to room temperature, preferably for at least 30 minutes. - A step of measuring the flow-down time T0 of the pure solvent and the flow-down time T of the solution using a micro-Ubbelohde viscometer in a bath controlled by a thermostat adjusted to 20 °C ± 0.05 °C. A step of calculating the viscosity according to the formula 1 / C×Ln(T / T0) (where C represents the concentration and Ln represents the natural logarithm). For each sample, the average of three measurements is taken from three different solutions.

[0022] The melting temperature according to the present invention is preferably measured by differential scanning calorimetry (DSC) in accordance with ISO standard 11357-6, particularly using a DSC Q2000 apparatus (TA Instruments) with equilibration at -20 °C (temperature change rate: increase by 20 °C / min to 240 °C, decrease by 20 °C / min to -20 °C, increase by 20 °C / min to 240 °C).

[0023] For the purposes of the present invention, the term "reproducible mechanical properties" means mechanical properties, in particular tensile modulus, elongation at break and tensile strength. And these remain above at least 90% of those values measured for objects of the same shape formed by 3D printing from unused powder, respectively.

[0024] Unless otherwise specified, the percentages stated are percentages by weight.

[0025] Unless otherwise specified, the parameters referred to are measured at atmospheric pressure and room temperature (about 23 °C).

[0026] NF standard EN standard ISO standard 1874-1:2011 defines the nomenclature of polyamides. The term "monomer" in the present description of polyamide-based powders should be taken to mean "repeating unit". In special cases, the repeating unit of polyamide consists of a combination of a diacid and a diamine. It is a combination of an equimolar amount of diamine and diacid, i.e., a "diamine-diacid" or "XY" pair, which is considered to correspond to the monomer. This is explained by the fact that individually, the diacid or diamine is merely a structural unit and is insufficient to form a polymer on its own.

[0027] <Chain Limiting Agent> Preferably, the chain limiting agent according to the present invention is selected from the group consisting of dicarboxylic acids, monocarboxylic acids, diamines and monoamines, each of which can be linear or cyclic.

[0028] Preferably, the chain limiting agent has a melting temperature below 180 °C.

[0029] The chain-restricted monocarboxylic acid according to the present invention preferably has 2 to 20 carbon atoms. Examples of chain-restricted monocarboxylic acids include acetic acid, propionic acid, benzoic acid and stearic acid, lauric acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, hexadecanoic acid, octodecanoic acid and tetradecanoic acid.

[0030] The chain-restricted dicarboxylic acid according to the present invention preferably has 2 to 20 carbon atoms, more preferably 6 to 10 carbon atoms. Examples of chain-restricted dicarboxylic acids according to the present invention include sebacic acid, adipic acid, azelaic acid, suberic acid, dodecanedicarboxylic acid, butanedioic acid, and ortho-phthalic acid.

[0031] Preferably, the chain-restricted monoamine according to the present invention is a primary amine having 2 to 18 carbon atoms. Examples of chain-restricted monoamines according to the present invention include 1-aminopentane, 1-aminohexane, 1-aminoheptane, 1-aminooctane, 1-aminononane, 1-aminodecane, 1-aminoundecane, 1-aminododecane, benzylamine, and oleylamine.

[0032] Preferably, the chain-restricted diamine according to the present invention has 4 to 20 carbon atoms. Examples of chain-restricted diamines according to the present invention include isomers of bis(4-aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), and 2,2-bis(3-methyl-4-aminocyclohexyl)propane (BMACP), as well as para-aminodicyclohexylmethane (PACM), isophorone diamine (IPDA), 2,6-bis(aminomethyl)norbornane (BAMN), and piperazine.

[0033] Preferably, the chain limiting agent according to the present invention corresponds to 0.01% to 10% by weight, preferably 0.01% to 5% by weight, preferably 0.01% to 4% by weight, preferably 0.01% to 3% by weight, preferably 0.01% to 2% by weight, and preferably 0.01% to 1% by weight, based on the total weight of the polyamide powder corresponding to 100%. More preferably, the chain limiting agent according to the present invention corresponds to 0.01% to 0.5% by weight, 0.01% to 0.4% by weight, 0.01% to 0.3% by weight, and 0.01% to 0.2% by weight, based on the total weight of the polyamide powder corresponding to 100%.

[0034] The chain limiting agent is preferably in powder form.

[0035] The chain limiting agent according to the present invention is preferably added to a medium containing an already formed polyamide and is not incorporated into the polyamide composition.

[0036] Preferably, the chain limiter is incorporated into the polyamide powder by any suitable method known to those skilled in the art, such as dry blending, liquid mixing, aqueous dispersion, compounding, or diffusion mixing.

[0037] According to one embodiment, the chain limiter is preferably in powder form and is dry-blended with polyamide powder.

[0038] Surprisingly, the reaction between the chain limiting agent and the ends of the polyamide chains that occurs during the 3D printing process effectively limits the increase in the intrinsic viscosity of the powder and does not disrupt the 3D printing conditions.

[0039] In this way, the present invention proposes a powder containing a chain limiting agent that is very easy to use.

[0040] According to one embodiment, a chain limiter, preferably in powder form, is mixed with a powder of a polyamide prepolymer having an intrinsic viscosity of 0.80 or less. This mixture then undergoes a solid-phase polycondensation process to obtain a polyamide powder having a desired viscosity.

[0041] The solid-phase polycondensation process is carried out at a temperature above the glass transition temperature of the polyamide but below its melting temperature. Solid-phase polycondensation is typically performed in a dryer.

[0042] This embodiment makes it possible to provide a ready-to-use powder for use in a 3D printing method, which has several advantages, including the following: - This eliminates the need for grinding, which often requires complex conditions, in polyamide powders with high intrinsic viscosity. - This avoids the use of solvents during preparation.

[0043] If the prepolymer undergoes one or more intermediate steps before the polycondensation step, such as a water treatment step and / or an acid treatment step, it is preferable to add a chain limiter after the intermediate step.

[0044] Thus, the added chain limiting agent either reacts with the chain ends of the polyamide prepolymer during the polycondensation process, or reacts with functional groups available for reaction on the polyamide chain during 3D printing.

[0045] Therefore, the loss of the chain limiting agent used is avoided. In particular, when a chain limiting agent is added during polymerization in the presence of a monomer, some of the limiting agent molecules are incorporated into the polyamide chain and thus lose their ability to limit the elongation of the polyamide chain.

[0046] According to one embodiment, the chain limiting agent is mixed with a polyamide prepolymer powder that has undergone a water treatment and / or acid treatment step in advance.

[0047] For this embodiment, the chain limiter preferably has a melting temperature that is above the glass transition temperature of the polyamide and below the melting temperature of the polyamide.

[0048] Advantageously, the chain limiting agent according to the present invention is used in a melt-induced agglomeration method, but it enables the control, in particular, reduction, stabilization, or removal of the viscosity and / or melting temperature of the non-aggregated polyamide powder, and enables the reuse of the powder in the powder agglomeration method. Therefore, particularly advantageously, the chain limiting agent according to the present invention enables the recycling or reuse of the non-aggregated polyamide powder, and enables the acquisition of an object with reproducible properties in the course of continuous operation (cycle).

[0049] <Polyamide> The polyamide according to the present invention may be a homopolyamide, a copolyamide, or a mixture thereof. The polyamide according to the present invention may also be a mixture of a polyamide and at least one other polymer, where the polyamide forms the matrix and the other polymer forms the dispersed phase.

[0050] Preferably, the polyamide according to the present invention is the following condensation product. - One or more amino acids, - One or more lactams, - A salt or mixture of one or more diamines and diacids.

[0051] Examples of amino acids include α,ω-amino acids, such as aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid, n-heptyl-11-aminoundecanoic acid, and 12-aminododecanoic acid.

[0052] The lactam monomer according to the present invention preferably contains between 3 and 12 carbon atoms on the main ring, and may be substituted. Examples of lactams according to the present invention include β,β-dimethylpropiolactam, α,α-dimethylpropiolactam, amyloractam, caprolactam, capryllactam, enantractam, 2-pyrrolidone, and lauryllactam.

[0053] Preferably, the diamine included in the composition of the polyamide according to the present invention is an aliphatic diamine, aryl diamine, and / or saturated cyclic diamine having 6 to 12 carbon atoms. Examples of diamines according to the present invention include hexamethylenediamine, decanediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, polyoldiamine, isophoronediamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), meta-xylylenediamine, bis(p-aminocyclohexyl)methane, and trimethylenediamine.

[0054] Preferably, the dicarboxylic acid contained in the composition of the polyamide according to the present invention has between 4 and 18 carbon atoms. Examples of dicarboxylic acids include adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanediic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, sodium or lithium salts of sulfisoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have at least 98% dimer content and are preferably hydrogenated), and dodecanediic acid HOOC-(CH2). 10 -COOH is one example.

[0055] Preferably, the copolyamide according to the present invention is obtained from the condensation of at least two different monomers, for example, at least two different α,ω-aminocarboxylic acids, or two different lactams, or a lactam and an α,ω-aminocarboxylic acid having a different number of carbon atoms. Alternatively, a copolyamide obtained from the condensation of at least one α,ω-aminocarboxylic acid (or one lactam), at least one diamine, and at least one dicarboxylic acid can be mentioned. Furthermore, a copolyamide obtained from the condensation of an aliphatic diamine, an aliphatic dicarboxylic acid, and at least one other monomer selected from aliphatic diamines other than those mentioned above and aliphatic diacids other than those mentioned above can be mentioned.

[0056] Preferably, the polyamide powder according to the present invention comprises at least one polyamide or copolyamide containing at least one monomer selected from the group consisting of 46, 4T, 54, 59, 510, 512, 513, 514, 516, 518, 536, 6, 64, 69, 610, 612, 613, 614, 616, 618, 636, 6T, 9, 104, 109, 1010, 1011, 1012, 1013, 1014, 1016, 1018, 1036, 10T, 11, 12, 124, 129, 1210, 1212, 1213, 1214, 1216, 1218, 1236, 12T, MXD6, MXD10, MXD12, MXD14, and mixtures thereof.

[0057] Preferably, the polyamide according to the present invention is selected from the group consisting of PA6, PA66, PA1010, PA11, PA12, PA1011, PA610, PA612, PA613, and mixtures thereof.

[0058] Examples of copolyamides include a copolymer of caprolactam and laurylactam (PA6 / 12), a copolymer of caprolactam, adipic acid and hexamethylenediamine (PA6 / 66), a copolymer of caprolactam, laurylactam, adipic acid and hexamethylenediamine (PA6 / 12 / 66), and a copolymer of caprolactam, laurylactam, 11-aminoundecanoic acid, azelaic acid and hexamethylenediamine. Examples include copolymers (PA6 / 69 / 11 / 12), copolymers of caprolactam, laurylactam, 11-aminoundecanoic acid, adipic acid, and hexamethylenediamine (PA6 / 66 / 11 / 12), copolymers of laurylactam, azelaic acid, and hexamethylenediamine (PA69 / 12), and copolymers of 11-aminoundecanoic acid, terephthalic acid, and decamethylenediamine (PA11 / 10T).

[0059] With respect to a mixture of polyamide and at least one other polymer, it takes the form of a mixture with a polyamide matrix, where the other polymer forms a dispersed phase. Examples of these other polymers according to the present invention include polyolefins, polyesters, polycarbonates, PPO (an abbreviation for polyphenylene oxide), PPS (an abbreviation for polyphenylene sulfide), and elastomers such as ether-amide block copolymers (PEBA), thermoplastic polyurethanes (TPU), and elastomeric polyphenylene ethers (PPE).

[0060] It is also possible to use blends of polyamides. These include, for example, blends of aliphatic polyamides and semi-aromatic polyamides, and blends of aliphatic polyamides and alicyclic polyamides.

[0061] For example, a composition based on a semicrystalline polyamide (A), an amorphous polyamide (B), a flexible polyamide (C), and a compatibilizer (D) contains the following by weight, totaling 100%: • Amorphous polyamide (B) 5%~40% essentially resulting from the following condensations, - At least one diamine selected from alicyclic diamines and aliphatic diamines, and at least one diacid selected from alicyclic diacids and aliphatic diacids, wherein at least one of these diamine units or diacid units is alicyclic. - Or, alicyclic α,ω-aminocarboxylic acid, - Or, any combination of these two options, - and optionally, at least one monomer selected from α,ω-aminocarboxylic acid or any corresponding lactam, aliphatic diacid, and aliphatic diamine. • Flexible polyamide (C) 0-40% selected from copolymers and copolyamides containing polyamide blocks and polyether blocks. • Compatibilizer (D) 0-20% for semi-crystalline polyamides (A) and (B), • Flexible modifier (M) 0-40%, However, provided that (C)+(D)+(M) is between 0% and 50%, • Residual semi-crystalline polyamide (A) up to 100%.

[0062] Furthermore, the composition is based on a semicrystalline polyamide (A), optionally an amorphous polyamide (B), a flexible polyamide (C), and a compatibilizer (D), and contains the following by weight, with the total being 100%. Optionally, 5% to 40% amorphous polyamide (B) essentially resulting from the condensation of at least one arbitrary alicyclic diamine, at least one aromatic diacid, and optionally at least one monomer selected from α,ω-aminocarboxylic acids, aliphatic diacids, and aliphatic diamines. • Flexible polyamide (C) 0-40% selected from copolymers and copolyamides containing polyamide blocks and polyether blocks. • Semicrystalline polyamide (A) and optionally a compatibilizer (D) for (B) 0-20%, (C)+(D) is between 2% and 50%. However, (B) + (C) + (D) must be 30% or more. • Residual semi-crystalline polyamide (A) up to 100%.

[0063] Substituting a portion of the polyamide with a copolymer containing a polyamide block and a polyether block, that is, using a mixture containing at least one of the preceding polyamides and at least one copolymer containing a polyamide block and a polyether block, would not constitute a departure from the scope of the present invention.

[0064] Copolymers comprising polyamide blocks and polyether blocks are obtained, for example, from the copolymerization of a polyamide block having the following reactive ends and a polyether block having the following reactive ends. 1) A polyamide block having a diamine chain terminus, and a polyoxyalkylene block having a dicarboxyl chain terminus. 2) A polyamide block having a dicarboxyl chain terminus, and a polyoxyalkylene block having a diamine chain terminus obtained by cyanoethylation and hydrogenation of an α,ω-dihydroxylated aliphatic polyoxyalkylene block known as a polyetherdiol. 3) A polyamide block having dicarboxyl chain ends and a polyetherdiol are combined, and the resulting product, in this particular case, is a polyetheresteramide.

[0065] Polyamide blocks having dicarboxyl chain ends are obtained, for example, from the condensation of α,ω-aminocarboxylic acids, lactams, or dicarboxylic acids and diamines in the presence of chain-restricting dicarboxylic acids.

[0066] The polyether can be, for example, polytetramethylene glycol (PTMG), also known as polytetrahydrofuran (PTHF).

[0067] The number-average molar mass of the polyamide block is between 300 and 5000 g / mol, preferably between 600 and 1500 g / mol. The molar mass of the polyether block is between 100 and 6000, preferably between 200 and 3000 g / mol.

[0068] Polymers having polyamide blocks and polyether blocks can also contain randomly distributed units. These polymers can be prepared by the simultaneous reaction of a polyether with a polyamide block precursor.

[0069] For example, polyetherdiols, lactams (or α,ω-amino acids), and chain-limiting diacides can be reacted in the presence of small amounts of water. This results in polymers that not only have polyether and polyamide blocks of essentially a wide variety of lengths, but also a variety of reactants that react randomly, with these reactants randomly distributed along the polymer chain.

[0070] Polyetherdiol blocks are used in their unmodified form and are either copolymerized with carboxyl-terminated polyamide blocks, or converted to polyetherdiamines and aminated for condensation with carboxyl-terminated polyamide blocks. They can also be blended with polyamide precursors and chain limiters to produce polymers containing polyamide and polyether blocks with randomly distributed units.

[0071] The weight ratio of the copolymer containing polyamide blocks and polyether blocks to the amount of polyamide is favorably between 1 / 99 and 15 / 85.

[0072] <Powder> Preferably, the polyamide powder particles according to the present invention have a volume median diameter (D50) between 5 and 200 μm, more preferably between 10 and 150 μm.

[0073] Preferably, the polyamide powder according to the present invention has a difference of more than 3°C between the crystallization temperature (Tc) and the first heating and melting temperature (Tm1) (Tc-Tm1).

[0074] This difference advantageously allows for the avoidance of deformation phenomena and the acquisition of good shape definition in the manufactured parts. Furthermore, this difference increases the window for handling polyamide powder, making its use in firing methods much easier.

[0075] Preferably, the intrinsic viscosity of the polyamide powder solution according to the present invention, and in particular their intrinsic viscosity before use in the powder aggregation method according to the present invention, is less than 1.90, preferably less than 1.70, preferably less than 1.60, and preferably less than 1.50.

[0076] Preferably, the intrinsic viscosity of the polyamide powder solution according to the present invention, and in particular the viscosity after the first operation in the powder agglomeration method according to the present invention, is greater than 1.

[0077] Preferably, the polyamide powder according to the present invention increases in viscosity when melted to reach a sufficient molecular weight and, preferably, to ensure a viscosity of the part solution greater than 1.50, so that the part (3D article) has acceptable mechanical properties. More preferably, the viscosity of the part is greater than 1.60, preferably greater than 1.70, preferably greater than 1.80, preferably greater than 1.90, and preferably greater than 2.

[0078] Preferably, the powder according to the present invention can be recycled at least 3 times, preferably at least 5 times, and more preferably at least 10 times.

[0079] <Other compounds> The polyamide according to the present invention may contain organic or inorganic fillers, pigments, antioxidants (particularly in combination with thioether antioxidants), UV stabilizers, plasticizers, dyes, and pourability agents, whether or not as a blend with at least one other polymer.

[0080] The polymer powder according to the present invention may contain a thioether antioxidant. Advantageously, the addition of such an antioxidant to the polymer powder according to the present invention makes it possible to stabilize the color of the powder, particularly its whiteness when it is white, by limiting its yellowing, especially during recycling of the powder according to the present invention.

[0081] The thioether antioxidants according to the present invention are preferably dilauryl thiodipropionate (DLTDP), ditridecyl thiodipropionate (DTDTDP), distearyl thiodipropionate (DSTDP), dimyristyl thiodipropionate (DMTDP), pentaerythrityltetrakis(3-dodecyl thiopropionate or 3-lauryl thiopropionate), 3,3'-thiodipropionate, (C12-14) alkyl thiopropionate, and dilauryl 3,3'-thiodipropionate. Odipropionate, ditridecyl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, dioctadecyl 3,3'-thiodipropionate, laurylstearyl 3,3-thiodipropionate, tetrakis[methylene 3-(dodecylthio)propionate]methane, thiobis(2-tert-butyl-5-methyl-4,1-phenylene)bis(3-(dodecylthio)propionate), 2,2'-thiodiethylene Nbis(3-aminobutenoate), 4,6-bis(octylthiomethyl)-o-cresol, 2,2'-thiodiethylenebis-3-(3,5-tert-butyl-4-hydroxyphenyl)propionate, 2,2'-thiobis(4-methyl-6-tert-butylphenol), 2,2'-thiobis(6-tert-butyl-p-cresol), 4,4'-thiobis(6-tert-butyl-3-methylphenol), 4,4'-thiobis(4-methyl-6-tert-butylphenol) Selected from the group consisting of ), bis(4,6-tert-butyl-l-yl-2-) sulfide, tridecyl-3,5-di-tert-butyl-4-hydroxybenzylthioacetate, 1,4-bis(octylthiomethyl)-6-phenol, 2,4-bis(dodecylthiomethyl)-6-methylphenol, distearyl disulfide, bis(methyl-4-3-n-(C12 / C14)alkylthiopropionyloxy5-tert-butylphenyl) sulfide, and mixtures thereof.More preferably, the thioether antioxidant according to the present invention is selected from the group consisting of dilauryl thiodipropionate (DLTDP), ditridecyl thiodipropionate (DTDTDP), distearyl thiodipropionate (DSTDP), dimyristyl thiodipropionate (DMTDP), pentaerythrityltetrakis (3-dodecylthiopropionate or 3-lauryl thiopropionate), and mixtures thereof. More preferably, the thioether antioxidant according to the present invention is DLTDP or pentaerythrityltetrakis (3-dodecylthiopropionate).

[0082] Such antioxidants are specifically marketed by Songnox or Adeka.

[0083] Preferably, the at least one thioether antioxidant corresponds to at least 0.1% by weight, preferably 0.1% to 5% by weight, preferably 0.1% to 4% by weight, preferably 0.1% to 3% by weight, preferably 0.1% to 2% by weight, and preferably 0.1% to 1% by weight, based on the total weight of the powder equivalent to 100%.

[0084] According to the present invention, the thioether antioxidant described above is incorporated into the powder by any suitable method known to those skilled in the art, for example, by adding the thioether during the synthesis of the polyamide, particularly at the beginning or end of the synthesis; by blending by formulation, particularly by blending by formulation in any step of a powder manufacturing method starting from the polyamide; in particular by dissolution-precipitation of the polyamide in a solvent containing the thioether (e.g., dispersed or dissolved in the solvent); or by dry blending with the polyamide powder according to the present invention.

[0085] According to one embodiment, the chain limiting agent is mixed with polyamide powder and at least one thioether antioxidant by dry blending.

[0086] According to one embodiment, a thioether is added to a polyamide prepolymer powder having an intrinsic viscosity of 0.80 or less, along with a chain limiting agent, and this is subjected to a solid-phase polycondensation process to obtain a polyamide powder having a desired viscosity.

[0087] According to one embodiment, the chain limiter is mixed with a polyamide prepolymer powder and at least one thioether antioxidant after a water treatment step and / or an acid treatment step.

[0088] The thioether according to the present invention is preferably in powder form.

[0089] Preferably, the thioether-based antioxidant has a melting point of less than 140°C, preferably less than 100°C, preferably less than 90°C, and preferably less than 70°C.

[0090] Examples of antioxidants other than thioether antioxidants used in the present invention include phenolic antioxidants intended to counteract the thermal oxidation of polyamides, such as 3,3'-bis(3,5-di-tert-butyl-4-hydroxyphenyl)-N,N'-hexamethylenedipropionamide, sold by Palmorole under the name Palmorole AO.OH.98; (4,4'-butylidenebis(2-t-butyl-5-methylphenol), sold by Addivant under the name Lowinox 44B25; and pentaerythrityltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, sold by BASF under the name Irganox(R) 1010. N,N'-hexane-1,6-diyrbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) sold under the name 1098, and especially 3,3',3',5,5' sold by BASF under the name Irganox(R) 1330. ,5'-Hexa-tert-butyl-α,α',α'-(mesitylene-2,4,6-triyl)tri-p-cresol, especially ethylenebis(oxyethylene)bis(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate) sold by BASF as Irganox(R) 245, especially 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione sold by BASF as Irganox(R) 3114, especially N',N'-(2-ethyl-2'-ethoxyphenyl)oxyanilide sold by BASF as Tinuvin(R) 312, especially Alvinox(R) 1330 from 3V, and Hostanox 245 from Clariant. FF, sold under the name Hostanox 245 Pwd, 4,4',4”-trimethyl-1,3,5-benzenetriyl)tris(methylene)tris[2,6-bis(1,1-dimethylethyl]phenol, especially pentaerythrityltetrakis(3-(3,5-di-tert-4-hydroxyphenyl)propionate sold by Everspring Chemical Company Limited under the names Evernox 10 and Evernox 10GF, especially octadecyl 3-(3,5-di-tert-hydroxyphenyl)propionate sold by Everspring Chemical Company Limited under the names Evernox 76 and Evernox 76GF, especially tetrakis[methylene-3-(3',5'-di-tert-butyl-4-hydroxyphenyl]propionate]methane sold by Mayzo under the name BNX(R) 1010, especially BNX(R) Thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], sold under the name 1035, tetrakis[methylene-3-(3',5'-di-tert-butyl-4-hydroxyphenyl]propionate]methane, and especially octadecyl 3-(3, sold by Mayzo under the name BNX(R) 2086Examples include 5-di-tert-butyl-4-hydroxyphenyl)propionate, particularly 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)trione, which is sold by Mayzo under the name BNX(R) 3114.

[0091] <Method of coagulation by melting> As understood herein, the method of powder aggregation by melting is considered synonymous with sintering.

[0092] The powder agglomeration method by melting according to the present invention is preferably a method for manufacturing an object or article, particularly a three-dimensional (3D) object or article.

[0093] Melting is preferably achieved using the input of radiation or electromagnetic energy. The radiation can be selected from any radiation known to those skilled in the art. Examples of radiation include laser beams, infrared rays, ultraviolet rays, and LED radiation. Particularly preferably, melting is achieved by laser radiation, referring to the “laser sintering” method. Even more preferably, the method of powder aggregation by melting according to the present invention is a method known as “selective laser sintering” or “high-speed sintering” (HSS) or “multi-jet fusion” (MJF).

[0094] Preferably, the method for agglomerating powder by melting according to the present invention is a layer-by-layer method or an additive manufacturing method.

[0095] As an example, the method for agglomerating powder by melting according to the present invention includes the following steps. a. A step of depositing a thin layer (layer 1) of polyamide powder according to the present invention onto a horizontal plate maintained in a chamber heated to a temperature between the crystallization temperature (Tc) and melting temperature (Tm) of the powder, b. A process in which, by radiation, particularly laser radiation, the aggregation of powder particles by melting is possible at various locations within the powder layer (layer 1) according to the geometric shape corresponding to the article to be manufactured. c. A step in which the horizontal plate is lowered by a value corresponding to the thickness of the first powder layer, and then a new powder layer (layer 2) is deposited. d. A process in which, by radiation, particularly laser radiation, the particle aggregation of the powder layer (layer 2) is made possible by melting the powder layer according to the geometric shape corresponding to this new slice of the article to be manufactured. e. A process that repeats the previous steps to form a cycle until an item is created. f. A process in which an article bordered with powder is obtained inside a chamber. g. The process of separating the article from the powder after it has been completely cooled.

[0096] Particularly preferred is the method of powder aggregation by melting according to the present invention, which is a 3D printing method.

[0097] The powder agglomeration method by melting according to the present invention can be carried out using appropriate equipment, particularly in a 3D printer. Examples of such equipment include sintering equipment from EOS, 3D Systems, Aspect, Trump Precision Machinery, Hewlett Packard, Sinterit, Sintratec, Sharebot, FormLabs, Sonda Sys, Farsoon, Prodways, Ricoh, Wematter3D, VoxelJet, or other Xaar-sold equipment. In particular, the EOSINT P396 and Formiga P100 equipment from EOS GmbH can be cited.

[0098] The powder reused or recycled according to the present invention is powder that has not agglomerated or melted during the various powder melting cycles necessary for the manufacture or shaping of an article. As understood herein, the various cycles constitute a “work.” In other words, the “work” corresponds to shaping.

[0099] Preferably, in each set of molding cycles or "operations," the recycled powder content is at least 50% by weight, preferably at least 60% by weight, and more preferably at least 70% by weight, relative to the total weight of powder used in the machine in each operation. Preferably, starting with an initial operation using 100% unused, i.e., non-recycled powder, each subsequent operation reuses or recycles at least 50% by weight, preferably at least 60% by weight, and more preferably at least 70% by weight, of the powder from the preceding operation that did not agglomerate, relative to the total weight of powder used in the machine in each operation.

[0100] <object> The object or article according to the present invention is preferably a three-dimensional (3D) object or article, particularly a 3D printed object.

[0101] Preferably, the object is selected from prototypes, component templates ("rapid prototyping"), and finished parts in small-batch production series ("rapid manufacturing") for the fields of automotive, marine, aviation, aerospace, medical (prosthetics, hearing systems, etc.), textiles, clothing, fashion and decoration, electronic equipment housings, telecommunications, home automation, computing, lighting, sports, and industrial tools.

[0102] Preferably, the object according to the present invention has the following characteristics even after several recyclings of the powder, for an object manufactured in X / Y, i.e., mainly in two horizontal dimensions or "flat" in an apparatus for powder agglomeration by melting: - Elastic modulus exceeding 1500 MPa, - Elongation at fracture exceeding 40%, - Tensile strength exceeding 40 MPa, preferably 45 MPa. The above mechanical properties (modulus of elasticity, elongation at fracture, and tensile strength) are preferably all measured in accordance with ISO standard 527-1B:2012.

[0103] The present invention can be further described in a non-limiting manner by the following embodiments. [Examples]

[0104] [Example 1] The inventors of the present invention studied the aging of the powder according to the present invention by reproducing the conditions to which the powder for 3D printing is exposed during several printing operations.

[0105] [A. Materials and Methods] 1. Materials Used 1.1. Polyamide Powder According to the Present Invention The 3D printing powder tested was obtained by pulverizing a polymer resulting from the polycondensation of 11-aminoundecanoic acid catalyzed by phosphoric acid (H3PO4) (Powder 1) or phosphorous acid (H3PO2) (Powder 2), and was 1000 parts by weight of PA11 powder mixed with 2 to 5 parts by weight of a phenolic antioxidant (Irganox 245 (BASF)), 3 to 8 parts by weight of a thioether antioxidant (ADK Stab AO412S (Adeka)), and 1 to 3 parts by weight of a fluidizing agent (Cab-O-Sil TS 610 (CABOT)). Three samples containing 2 parts by weight, 4 parts by weight, and 6 parts by weight of sebacic acid (DC10) were formulated. Sebacic acid, an antioxidant, and a fluidizing agent were added to the PA11 prepolymer, and then the mixture was subjected to a solid-phase polycondensation step to obtain the powder of Example 1.1.

[0106] 1.2. Comparative Example The comparative example consisted of 1000 parts by weight of PA11 powder obtained by pulverizing a polymer resulting from the polycondensation of 11-aminoundecanoic acid catalyzed by phosphoric acid (H3PO4) (Powder 1) or phosphorous acid (H3PO2) (Powder 2), and mixed with 3 parts by weight of a phenolic antioxidant (Irganox 245 (BASF)), 5 parts by weight of a thioether antioxidant (ADK Stab AO412S (Adeka)), and 2 parts by weight of a fluidizing agent (Cab-O-Sil TS 610 (CABOT)). An antioxidant and a fluidizing agent were added to the PA11 prepolymer, and then the mixture was subjected to a solid-phase polycondensation step to obtain the powder of Example 1.2.

[0107] 2. Aging The test consists of exposing the polyamide powder to a temperature 10 to 50 °C lower than the melting temperature Tm of pure polyamide. The polyamide powder (comparative example and polyamide powder according to the present invention) is placed in a glass bottle sealed with a perforated aluminum cap. The bottle is placed in an oven (ITEM FGE 140) adjusted to 180 °C and aged in air. This test simulates the exposure conditions under which the powder is exposed in a 3D device during one or several runs depending on the exposure time. The exposure time is from 0 to 90 hours.

[0108] 3. Intrinsic viscosity of polyamide powder The intrinsic viscosity is measured in a 0.5 wt% meta-cresol solution at 20 °C according to the viscosity measurement method described in detail above.

[0109] 4. Melting temperature of polyamide powder The melting temperature of the powder is measured by differential scanning calorimetry (DSC) according to ISO 11357-6 on a DSC Q2000 device (TA Instruments), using equilibration at -20 °C (temperature change rate of 20 °C / min increase to 240 °C, 20 °C / min decrease to -20 °C, 20 °C / min increase to finish at 240 °C).

[0110] <B. Results> Table 1 below includes the viscosity measurement values of polyamide powders (comparative example and polyamide powders according to the present invention) having an initial viscosity of 1.35.

[0111]

Table 1

[0112] Table 2 below shows the viscosity measurement values of the polyamide powders according to the present invention having an initial viscosity of 1.10.

[0113]

Table 2

[0114] Table 3 below includes measured values of the melting temperature of the polyamide powder according to the present invention having an initial viscosity of 1.10.

[0115]

Table 3

[0116] <C. Conclusion> The presence of sebacic acid, which is a chain-limiting dicarboxylic acid, makes it possible to control the increase in viscosity and melting temperature of the polyamide powder that occurs during aging, which represents continuous 3D printing operation (cycles).

[0117] [Example 2][[ID=1%]] Samples were prepared according to the protocol described in Example 1 (see 1.1).

[0118] An aging test was carried out according to the protocol described in Example 1 (see 1.2), except that the test was carried out at 180 °C under vacuum.

[0119]

Table 4

[0120] It was observed that the presence of sebacic acid makes it possible to reduce the increase in viscosity of the polyamide powder that occurs during aging under vacuum, which represents continuous 3D printing operation (cycles).

[0121] [Example 3] The 3D printing powder tested consisted of 1000 parts by weight of PA11 powder dry-blended with 2 to 5 parts by weight of a phenolic antioxidant (Irganox 245 (BASF)), 3 to 8 parts by weight of a thioether antioxidant (ADK Stab AO412S (Adeka)), and 1 to 3 parts by weight of a fluidizing agent (Cab-O-Sil TS 610 (CABOT)). Three samples containing 2 parts by weight, 4 parts by weight, and 6 parts by weight of sebacic acid (DC10), and 6 parts by weight of dodecanedioic acid (DC12) were formulated.

[0122] <-W0000462->The aging test was performed at 180°C under vacuum according to the protocol described in Example 1 (see 1.1).

[0123] [Table 5]

[0124] It was observed that the presence of sebacic acid or dodecanedioic acid can reduce the increase in viscosity of polyamide powder that occurs during aging under vacuum, which is typical of continuous 3D printing operations (cycles).

Claims

1. A polyamide powder intended for use in a method of powder aggregation by melting, comprising at least one chain limiting agent, wherein the chain limiting agent comprises sebacic acid, and the chain limiting agent is mixed with the polyamide powder and, if necessary, at least one thioether antioxidant by dry blending.

2. The powder according to claim 1, wherein the chain limiting agent is in an amount of 0.01% to 10% by weight relative to the total weight of the polyamide powder, which is 100%.

3. The powder according to claim 1 or 2, wherein the polyamide comprises at least one monomer selected from the group consisting of 46, 4T, 54, 59, 510, 512, 513, 514, 516, 518, 536, 6, 64, 69, 610, 612, 613, 614, 616, 618, 636, 6T, 9, 104, 109, 1010, 1011, 1012, 1013, 1014, 1016, 1018, 1036, 10T, 11, 12, 124, 129, 1210, 1212, 1213, 1214, 1216, 1218, 1236, 12T, MXD6, MXD10, MXD12, MXD14, and mixtures thereof.

4. The powder according to claim 1 or 2, wherein the polyamide is selected from the group consisting of PA6, PA66, PA1010, PA11, PA12, PA1011, PA610, PA612, PA613, and mixtures thereof.

5. The powder according to any one of claims 1 to 4, further comprising at least one thioether antioxidant.

6. The powder according to claim 5, wherein the at least one thioether antioxidant is selected from the group consisting of dilauryl thiodipropionate (DLTDP), ditridecyl thiodipropionate (DTDTDP), distearyl thiodipropionate (DSTDP), dimyristyl thiodipropionate (DMTDP), pentaerythrityltetrakis (3-dodecyl thiopropionate or 3-lauryl thiopropionate), and mixtures thereof.

7. The powder according to claim 5 or 6, wherein the at least one thioether antioxidant is present in an amount equivalent to 0.1% to 5% by weight of the total weight of the powder, which is equivalent to 100%.

8. A method for producing an object, comprising agglomerating a polyamide powder according to any one of claims 1 to 7 by melting.

9. An object manufactured using at least one polyamide powder as described in any one of claims 1 to 7.

10. The method according to claim 8, wherein the polyamide powder that did not aggregate is recovered.

11. Use of unaggregated polyamide powder recovered by the method of claim 10 for the production of an object by agglomeration of the powder by melting.

12. The use of at least one chain limiter for controlling the increase in viscosity or melting temperature of a polyamide powder intended for use in a powder aggregation method by melting, wherein the chain limiter contains sebaciic acid, and the chain limiter is mixed by dry blending with the polyamide powder and, if necessary, at least one thioether antioxidant.

13. The use of at least one chain restrictor for improving the recyclability of polyamide powder intended for use in a powder agglomeration method by melting, wherein the chain restrictor contains sebaciic acid, and the chain restrictor is mixed by dry blending with the polyamide powder and, if necessary, at least one thioether antioxidant.

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