Polyamide composition suitable for 3D printing by powder sintering

Abstract

The present invention relates to a powder composition suitable for 3D printing by sintering, comprising: (a) at least one linear aliphatic polyamide, (b) from 0 to 3500 ppm by weight of phosphoric acid, (c) from 500 to 2000 ppm by weight of at least one compound selected from hypophosphorous acid, its salts and mixtures thereof, and (d) at least one chain limiter. The invention also relates to a process for preparing this preparation, and also to a process for manufacturing an article by 3D printing comprising sintering this powder composition using electromagnetic radiation, preferably by laser or by applying infrared radiation to the powder previously selectively coated with one or more inks, and to the resulting article.

Description

[0001] Polyamide composition suitable for 3D printing by powder sintering

[0002] FIELD OF INVENTION

[0003] The present invention relates to a powder composition suitable for 3D printing by sintering, comprising: (a) at least one linear aliphatic polyamide, (b) 0 to 3,500 ppm by weight of phosphoric acid, (c) 500 to 2,000 ppm by weight of at least one compound selected from hypophosphorous acid, its salts, and mixtures thereof, and (d) at least one chain-limiting agent. The invention also relates to a method for preparing this powder composition, as well as a method for manufacturing an article by 3D printing, comprising sintering this powder composition using electromagnetic radiation, preferably by laser, and the article thus obtained.

[0004] TECHNICAL BACKGROUND

[0005] Electromagnetic radiation polyamide powder agglomeration technology is a 3D printing process that has been used for several years to manufacture three-dimensional objects such as prototypes and models, which find applications in fields as varied as clothing, medical devices (prostheses in particular), architecture, or aeronautics, for example.

[0006] According to this process, a thin layer of polyamide powder (referred to as the "building 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 within the powder layer according to a geometry corresponding to the desired object, for example, using a computer that stores the object's shape 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 around 0.1 mm), and 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 unbound powder, which can represent approximately 85% of the total powder used. This unbound powder is then reused to manufacture a new object, generally after sieving and mixing with a fraction of unprocessed powder.

[0007] It is recommended that the powder used in this process have the largest possible temperature difference (Tf-Te, corresponding to the working window) to avoid deformation (or "curling") during manufacturing. Furthermore, the highest possible enthalpy of fusion (AHf) is required to obtain good geometric definition of the manufactured parts. Indeed, if this enthalpy is too low, the energy supplied by the laser is sufficient to sinter the powder particles near the walls being built by thermal conduction, and thus the geometric accuracy of the part is no longer satisfactory.

[0008] In this context, the Applicant proposed polyamides subjected to a water treatment designed to increase their melting point and enthalpy of fusion without negatively affecting their crystallization temperature (EP1413595). These polyamides are therefore well suited to 3D printing by powder sintering.

[0009] However, it became apparent that the mechanical properties of the object degraded with each build cycle. For example, in document EP 2530121, a decrease in the object's elongation at break was observed, along with an increase in the inherent viscosity of the recycled polyamide powder in solution, leading to insufficient coalescence and thus an increase in the object's porosity. These phenomena are attributed to an increase in the molar mass of the recycled polyamide powder with each build cycle.

[0010] US2004 / 0102539 suggests a solution for improving the recyclability of polyamides, consisting of adding chain restrictors in the form of carboxylic acids during polyamide polymerization. However, the resulting parts exhibit insufficient elongation at break, according to US2006 / 071359. WO2021 / 069851 also describes a polyamide powder for 3D printing, the recyclability of which is improved through the use of a chain restrictor and possibly a thioether as an antioxidant.

[0011] Another solution proposed by the Applicant involves incorporating at least 4,000 ppm of phosphoric acids into the polyamide powder, particularly during the polyamide synthesis (EP25301 1). Phosphoric acid is especially suitable for this purpose and can optionally be combined with hypophosphorous acid. While this solution does address the aforementioned problems, it has been observed that the elongation at break of the manufactured parts along the Z-axis (vertical axis) is not always satisfactory. Therefore, the need remains for a polyamide powder, specifically polyamide 11 or polyamide 12, that can be used and recycled in a 3D printing process using powder sintering to obtain objects with good mechanical properties, and in particular, high elongation at break along the Z-axis.It would also be desirable for this objective to be achieved even if the recycled polyamide powder is not mixed with virgin polyamide powder or only with a small amount of this powder.

[0012] SUMMARY OF THE INVENTION

[0013] The invention thus relates to a powder composition suitable for 3D printing by sintering, comprising:

[0014] (a) at least one linear aliphatic polyamide,

[0015] (b) from 0 to 3,500 ppm by weight of phosphoric acid,

[0016] (c) from 500 to 2,000 ppm by weight of at least one compound selected from hypophosphorous acid, its salts and mixtures thereof,

[0017] (d) at least one chain-limiting agent selected from: linear, cyclic or branched mono- or dicarboxylic acids comprising from 2 to 30 carbon atoms, their anhydrides or esters; linear, cyclic or branched mono- or diamines comprising from 2 to 30 carbon atoms; and mixtures thereof.

[0018] It also relates to a process for preparing this powder composition, comprising the following steps:

[0019] (1) the synthesis of a polyamide,

[0020] (2) optionally, the mixing of polyamide with one or more additives, in an extruder,

[0021] (3) grinding or dissolving-precipitating the polyamide from step (1) or the mixture from step (2) to obtain a polyamide powder,

[0022] (4) optionally, the addition of one or more additives, characterized in that constituents b), c) and d) are independently introduced during and / or between steps (1), (2) and / or (4).

[0023] The invention further relates to a method of manufacturing an article by 3D printing comprising sintering the aforementioned powder composition using electromagnetic radiation, preferably by laser or by applying infrared radiation to the powder previously selectively coated with one or more inks, as well as to an article obtained by this method.

[0024] Finally, the invention also relates to the use of the aforementioned powder composition in a 3D printing process by powder sintering.

[0025] It has been observed that adding a limited amount of phosphoric acid combined with a chain-limiting agent to polyamide powder makes it possible to obtain, by 3D printing, parts with satisfactory mechanical properties across an industrial production, avoiding the production of parts with, in particular, low elongation at break along the Z-axis.

[0026] FIGURES

[0027] Figure 1 represents the model used to prepare an article according to the invention and a comparative article by 3D printing.

[0028] DETAILED DESCRIPTION

[0029] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the description that follows.

[0030] It is specified that the expressions "between... and..." and "from... to..." used in this description should be understood as including each of the mentioned limits.

[0031] Furthermore, unless otherwise stated, all percentages and proportions are mass percentages and proportions.

[0032] Polyamide

[0033] The composition according to the invention comprises an aliphatic and linear polyamide.

[0034] The term "polyamide" refers to a polymer comprising the polymerization product of one or more monomers selected from: amino acid or aminocarboxylic acid monomers, preferably alpha- and omega-aminocarboxylic acids; lactam monomers; diamine-diacid monomers resulting from the reaction between an aliphatic diamine and a dicarboxylic acid; and mixtures thereof, with monomers having a different number of carbon atoms in the case of mixtures between an amino acid monomer and a lactam monomer. The term "monomer" in this description of polyamides should be understood as "repeating unit." Indeed, when a repeating unit of polyamide (PA) consists of the association of a diacid with a diamine, it is considered to be the association of a diamine and a diacid, that is, the diamine-diacid pair. diacid (in equimolar quantity), which corresponds to the monomer.

[0035] Polyamide can be a homopolyamide and / or a copolyamide.

[0036] When a polyamide is a homopolyamide, it comprises the polymerization product of a single monomer. When a polyamide is a copolyamide, it comprises the polymerization product of at least two different monomers. Examples of copolyamides formed from the different types of monomers described above include copolyamides resulting from the condensation of at least two alpha, omega-aminocarboxylic acids, or two lactams, or a lactam and an alpha, omega-aminocarboxylic acid. Other examples include copolyamides resulting from the condensation of at least one alpha, omega-aminocarboxylic acid (or a lactam), at least one diamine, and at least one dicarboxylic acid.We can also mention copolyamides resulting from the condensation of an aliphatic diamine with an aliphatic dicarboxylic acid and at least one other monomer chosen from aliphatic diamines different from the previous one and aliphatic diacids different from the previous one.

[0037] The nomenclature used to define polyamides is described in ISO 1874-1:2011 and is well known to those skilled in the art. Thus, PA Z denotes the polycondensation product of a lactam or an amino acid with Z carbon atoms; PA XY denotes the polycondensation product of a diamine with X carbon atoms and a diacid with Y carbon atoms. Furthermore, the notations PA X / Y, PA X / Y / Z, etc., refer to copolyamides in which X, Y, Z, etc., represent homopolyamide units as described above.

[0038] Monomers of amino acids (PA Z)

[0039] Examples of alpha, omega-amino acids include those with 4 to 18 carbon atoms, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic, N-heptyl-11-aminoundecanoic and 12-aminododecanoic acids.

[0040] Monomers of lactams (PA Z)

[0041] Examples of lactams include those with 3 to 18 carbon atoms on the main ring and which can be substituted. Examples include p,p-dimethylpropiolactam, α,α-dimethylpropiolactam, amylolactam, caprolactam (also called lactam 6), capryllactam (also called lactam 8), oenantholactam, and lauryllactam (also called lactam 12).

[0042] Monomers of “diamine. diacid” (PA XY)

[0043] Examples of dicarboxylic acids include acids with 4 to 36 carbon atoms and preferably 4 to 18 carbon atoms, such as adipic acid, sebacic acid, azelaic acid, suberic acid, butanedioic acid, 1,4-cyclohexane dicarboxylic acid, dimerized fatty acids, dodecanedioic acid, and tetradecanedioic acid, preferably adipic acid, sebacic acid, azelaic acid, suberic acid, butanedioic acid, dimerized fatty acids, dodecanedioic acid, tetradecanedioic acid and mixtures thereof.

[0044] Fatty acid dimers, or dimerized fatty acids, are the products of the dimerization reaction of fatty acids, generally containing 18 carbon atoms, often a mixture of oleic and / or linoleic acids, which are preferably hydrogenated. This mixture preferably comprises 0 to 15% by weight of C18 monoacids, 60 to 99% by weight of C36 diacids, and 0.2 to 35% by weight of C54 or higher triacids or polyacids.

[0045] Examples of diamines include aliphatic diamines with 2 to 36 atoms, preferably 4 to 18 atoms, such as hexamethylenediamine, piperazine, aminoethylenepiperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophorone diamine (IPD), methyl pentamethylenediamine (MPMD), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), methaxylyenediamine, and bis-p-aminocyclohexylmethane, preferably hexamethylenediamine, tetramethylenediamine, octamethylenediamine, decamethylene diamine, dodecamethylene diamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, and mixtures thereof.

[0046] As "diamines. diacids", we can cite more particularly those resulting from the condensation of 1,6-hexamethylenediamine with a dicarboxylic acid having from 6 to 36 carbon atoms and those resulting from the condensation of 1,10-decamethylenediamine with a dicarboxylic acid having from 6 to 36 carbon atoms.

[0047] Examples of "diamine-diacid" type monomers include monomers: 66, 610, 611, 612, 613, 614, 618, and those resulting from the condensation of decanediamine with a C6 to C36 diacid, including monomers: 1010, 1012, 1014, 1018. Advantageously, the polyamide of the powder comprises or is made up of one (or more) homopolyamide(s).

[0048] In a preferred embodiment, the polyamide is a semi-crystalline polyamide. "Semi-crystalline polyamide" means a polyamide that exhibits:

[0049] - a crystallization temperature (Te) determined according to ISO 11357-3:2013, during the cooling step at a rate of 20°K / min in DSC (differential scanning calorimetry) below 180°C, preferably below 160°C; and

[0050] - and an enthalpy of fusion (AHf) determined according to ISO 11357-3:2013 during the heating step at a speed of 20 K / min in DSC, which is greater than 5 J / g, preferably greater than 10 J / g, for example greater than 20 J / g and is generally less than 200 J / g, preferably less than 150 J / g.

[0051] Furthermore, polyamide can advantageously have an inherent viscosity ranging from 0.2 to 1.5 (g / 100 g) 1 , preferably from 0.9 to 1.5 (g / 100 g) 1 , more preferably from 1.0 to 1.5 (g / 100 g) 1The inherent viscosity is measured using an Ubbelhode tube. The measurement is performed at 20°C on a 75 mg sample at a concentration of 0.5% (w / w) in m-cresol. The inherent viscosity is expressed in (g / 100 g). 1 and is calculated according to the following formula: Inherent viscosity = ln(t s / t0) x 1 / C with C = m / px 100, in which t s t0 is the flow time of the solution, t0 is the flow time of the solvent, m is the mass of the sample whose viscosity is determined, and p is the mass of the solvent. This measurement corresponds to ISO 307:2019, except that the measurement temperature is 20°C instead of 25°C.

[0052] The polyamide implemented according to the invention advantageously has a polydispersity index of less than 3.5, preferably less than 3 and for example between 2.4 and 2.5.

[0053] Advantageously, the polyamide used in the invention is selected from PA 11, PA 12, PA 6, PA 6Yi, PA 10, PA 10Y2, PA 10Y3 / Z, or combinations thereof. In the list above, Yi is selected from 10, 12, 13, 14, or 18; Y2 is selected from 10, 12, 13, or 14; Y3 is selected from 10, 12, or 13; and Z is selected from 11, 12, or 14. Preferably, the polyamide comprises or is made up of PA 11 or PA 12, preferably PA 11. PA 11 is obtained by polycondensation of amino-II-undecanoic acid, which has the advantage of being manufactured from raw materials of vegetable origin, namely castor oil, extracted from castor seeds. The polyamide advantageously represents 60 to 99% by weight, preferably 97 to 99% by weight, relative to the total weight of the powder composition.

[0054] chain limiting agent

[0055] The powder composition according to the invention further comprises at least one chain-limiting agent selected from: linear, cyclic or branched mono- or dicarboxylic acids comprising from 2 to 30 carbon atoms (preferably from 2 to 20 carbon atoms), their anhydrides or esters; linear, cyclic or branched mono- or diamines comprising from 2 to 30 carbon atoms (preferably from 2 to 18 carbon atoms); and mixtures thereof.

[0056] Preferably, the chain limiting agent has a melting point below 180°C or even 150°C.

[0057] Examples of monocarboxylic acids include acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic (or lauric) acid, tetradecanoic (or myristic) acid, hexadecanoic acid, octadecanoic (or stearic) acid, benzoic acid, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid and mixtures thereof, preferably stearic acid.

[0058] Examples of dicarboxylic acids include succinic acid, glutaric acid, sebacic acid, adipic acid, azelaic acid, suberic acid, dodecanedioic acid, brassylic acid, terephthalic acid, isophthalic acid and orthophthalic acid, preferably sebacic acid.

[0059] Monoamines can include primary amines with 2 to 18 carbon atoms. Examples of monoamines include 1-aminopentane, 1-aminohexane, 1-aminoheptane, 1-aminooctane, 1-aminononane, 1-aminodecane, 1-aminoundecane, 1-aminododecane, benzylamine, oleylamine, and mixtures thereof.

[0060] The diamine can be, in particular, a primary diamine comprising 4 to 20 carbon atoms. Examples of diamines include isomers of bis(aminomethyl)cyclohexane, such as 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), isomers of bis-(4-aminocyclohexyl)methane (BACM), bis-(3-methyl-4-aminocyclohexyl)methane (BMACM), 2-2-bis-(3-methyl-4-aminocyclohexyl)-propane (BMACP), and para-amino-di-cyclohexyl-methane (PACM), isophoronediamine (IPDA), 2,6-bis-(aminomethyl)-norbornane (BAMN), piperazine, and mixtures thereof.

[0061] According to the invention, it is preferred that the chain limiting agent be chosen from: linear, cyclic or branched mono- or dicarboxylic acids comprising 4 to 20 carbon atoms, preferably 6 to 12 carbon atoms, their anhydrides, their esters and their mixtures, preferably linear Cs-Cu dicarboxylic acids, more preferably sebacic acid.

[0062] In one embodiment of the invention, the chain-limiting agent is partially integrated into the polyamide structure. In this case, the powder composition according to the invention comprises the reaction product of the polyamide with the chain-limiting agent.

[0063] In another embodiment, the chain-limiting agent is not part of the polyamide structure.

[0064] According to one embodiment, the chain limiting agent is present in the powder composition, or used in its preparation, at a rate of 0.01 to 10%, preferably 0.01 to 5%, preferably 0.01 to 4%, preferably 0.01 to 3%, preferably 0.01 to 2%, preferably 0.01 to 1% by weight, relative to the total weight of the powder composition.

[0065] More preferably, the chain limiting agent is present in the powder composition, or used in its preparation, at a rate of 0.01 to 0.5%, 0.01 to 0.4%, 0.1 to 0.4%, or even 0.1 to 0.3% by weight, relative to the total weight of the powder composition.

[0066] Phosphoric and hypophosphorous acids (or their salts)

[0067] The powder composition according to the invention contains an amount of phosphoric acid (b) of between 0 and 3,500 ppm by weight. Preferably, the phosphoric acid represents from 500 to 3,500 ppm, preferably from 2,000 to 3,500 ppm, and more preferably from 3,000 to 3,500 ppm by weight, relative to the total weight of the powder composition.

[0068] It also contains from 500 to 2,000 ppm by weight of at least one compound selected from hypophosphorous acid, its salts, and mixtures thereof. A preferred salt of hypophosphorous acid is sodium hypophosphite. Preferably, component c) represents from 700 to 1,200 ppm by weight, relative to the total weight of the powder composition.

[0069] The determination of phosphoric acid and hypophosphorous acid or its salts can notably be carried out by phosphorus NMR ( 31P) after dilution of 400 mg of the powder composition in a solvent such as hexafluoropropan-2-ol (HFIP) and / or deuterated dichloromethane (CD2Cl2), preferably in a mixture of H Fl P / CD2Cl23 / 1 v / v, for example using a BRÜKER Avance 400 NEO instrument (400 MHz, 23°C).

[0070] Additives

[0071] The composition according to the invention advantageously comprises at least one additive selected from antioxidants, metal oxides and / or hydroxides, fillers, flow agents, pigments, flame retardants (or flame retardants), anti-UV agents, anti-abrasion agents, light stabilizers, shock modifiers, antistatic agents, polymers and mixtures thereof.

[0072] The antioxidant can be chosen from: phenolic antioxidants, phosphorus antioxidants, thioethers and their mixtures.

[0073] Examples of phenolic antioxidants include:

[0074] - 3,3'-Bis(3,5-di-tert-butyl-4-hydroxyphenyl)-N,N'-hexamethylenedipropionamide, marketed notably under the name Palmarole® AO.OH.98 by Palmarole,

[0075] - (4,4'-Butylidenebis(2-t-butyl-5-methylphenol) marketed notably under the name Lowinox® 44B25 by Addivant,

[0076] - Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) marketed notably under the name Irganox® 1010 by BASF,

[0077] - N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) marketed notably under the name Irganox® 1098 by BASF, 3,3',3',5,5',5'-hexa-tert-butyl-α,α',α'-(mesitylene-2,4,6-triyl)tri-p-cresol marketed notably under the name Irganox® 1330 by BASF, ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-μ-tolyl)propionate) marketed notably under the name Irganox® 245 by BASF, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione marketed notably under the name Irganox® 3114 by BASF,

[0078] - N'N'-(2-ethyl-2'-ethoxyphenyl)oxanilide, marketed notably under the name Tinuvin® 312 by BASF,

[0079] - 4,4',4"-trimethyl-l,3,5-benzenetriyl) tris-(methylene)] tris 2,6-bis(l,l-dimethylethyl)phenol marketed notably under the name Alvinox® 1330 by 3V or Hostanox® 245 FF or Hostanox® 245 Pwd by Clariant, - pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) marketed notably under the names Evernox® 10 or Evernox® 10GF by Everspring Chemical Company Limited,

[0080] - octadecyl-3-(3,5-di-tert-4-hydroxyphenyl)-propionate, marketed notably under the names Evernox® 76 or Evernox® 76GF by Everspring Chemical Company Limited,

[0081] - tetrakis [methylene-3(3',5'-di-tert-butyl-4-hydroxyphenyl) propionate] methane, marketed notably under the name BNX® 1010 by Mayzo,

[0082] - thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] marketed notably under the name BNX® 1035 by Mayzo,

[0083] - tetrakis [methylene-3 (3',5'-di-tert-butyl-4-hydroxyphenyl)propionate] methane,

[0084] - octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate marketed notably under the name BNX® 2086 by Mayzo, and l,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-l,3,5-triazine-2,4,6(lH,3H,5H) trione marketed notably under the name BNX® 3114 by Mayzo.

[0085] Phosphorus antioxidants can be aromatic or aliphatic and are selected from a range of sources, including phosphonates and organophosphonates; phosphites and organophosphites, particularly trialkyl- and trialkylaryl-phosphites, notably trinonyl-, tri(nonylphenyl)-, and tri[(2,4-di-tert-butyl-5-methyl)phenyl] phosphites, or cyclic diphosphites derived from pentaerythritol, including distearylpentaerythritol diphosphite; and mixtures thereof. Examples of phosphorus antioxidants include Hostanox® P-EPQ®, marketed by Clariant, and Irgafos® 168, marketed by BASF.

[0086] If the antioxidant contains a thioether, it can be chosen from among the following: dilauryl thiodipropionate (DLTDP), ditridecyl thiodipropionate (DTDTDP), distearyl thiodipropionate (DSTDP), dimyristyl thiodipropionate (DMTDP), pentaerythritol tetrakis (3-dodecylthiopropionate or 3-laurylthiopropionate), 3,3'-thiodipropionate, alkyl (C12-14) thiopropionate, dilauryl 3,3'-thiodipropionate, ditridecyl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, dioctadecyl 3,3'-thiodipropionate, and lauryl stearyl. 3,3-thiodipropionate, tetrakis[methylene 3-(dodecylthio)propionate] methane, thiobis(2-tert-butyl-5-methyl-4,l-phenylene)bis(3-(dodecylthio)propionate), 2,2'-thiodiethylene bis(3-aminobutenoate), 4,6-bis(octylthiomethyl)-o-cresol, 2,2'-thiodiethylene bis 3-(3,5-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-thiobis(4-methyl 6-tert-butyl-phenol), 2,2'-thiobis(6-tert-butyl-p-cresol), 4,4'-thiobis (6-tert-butyl-3-methylphenol), 4,4'-thiobis (4-methyl 6-tert-butyl phenol), bis(4,6-tert-butyl-l-yl-2-) sulfide, tridecyl-3,5-di-tert-butyl-4-hydroxybenzyl thioacetate, l,4-bis(octylthiomethyl)-6-phenol, 2,4-bis (dodecylthiomethyl)-6-methylphenol, distearyl disulfide, bis (methyl-4-3-n-alkyl (C12 / C14) thiopropionyloxy 5-tert-butylphenyl) sulfide and mixtures thereof.

[0087] Preferably, the thioether is selected from the group consisting of dilauryl thiodipropionate (DLTDP), ditridecyl thiodipropionate (DTDTDP), distearyl thiodipropionate (DSTDP), dimyristyl thiodipropionate (DMTDP), pentaerythritol tetrakis (3-dodecylthiopropionate or 3-laurylthiopropionate), and mixtures thereof.

[0088] According to one embodiment, thioether is DLTDP.

[0089] According to another embodiment, thioether is DSTDP.

[0090] Preferably, the thioether is pentaerythritol tetrakis (3-dodecylthio propionate). This compound is notably marketed by companies such as Songnox and Adeka under the trade name ADK STAB AO-412S.

[0091] Preferably, the thioether has a melting point less than or equal to 180°C, preferably less than or equal to 160°C, preferably less than or equal to 140°C, even more preferably less than or equal to 130°C or 100°C. can be chosen from among the oxides of poor metals (preferably aluminium, gallium, indium, zinc, and / or tin, more preferably zinc and / or aluminium).

[0092] Metal hydroxides include, in particular, hydroxides of alkaline earth metals (preferably magnesium, calcium, strontium and / or barium) or of post-earth metals (preferably aluminum, gallium, indium, zinc, and / or tin, more preferably zinc and / or aluminum), including hydrotalcites of formula M a 2+ MB 3+ (OH)2a+2b"(X' )b / i, yH2O in which M a 2+ represents divalent metal ions, Mb 3+ represents trivalent metal ions and X 1 ' represents an anion, typically a carbonate or a nitrate.

[0093] For example, a hydrotalcite usable in the powder of the invention can be a compound of formula MgsAkCOatOHjis-Atl-hO).

[0094] The powder of the invention generally comprises from 0.05 to 2%, preferably 0.1 to 1% by weight of metal oxide and / or hydroxide, relative to the total weight of the powder composition.

[0095] They can notably be chosen from those described in Kirk-Othmer's Encyclopedia of Chemical Technology and in Ullmann's Encyclopedia of Industrial Chemistry.

[0096] The pigments may be of natural origin or not. These pigments may be in powder or paste form. They may be coated or uncoated. The pigments may be chosen from mineral pigments, organic pigments, and mixtures thereof. Examples of mineral pigments useful in the present invention include ochres such as red ochre (clay, in particular kaolinite, and iron hydroxide, in particular hematite), brown ochre (clay, in particular kaolinite, and limonite), and yellow ochre (clay, in particular kaolinite, and goethite); titanium dioxide, optionally surface-treated; zirconium or cerium oxides; iron oxides (black, yellow, or red) or chromium oxides; manganese violet, ultramarine blue, chromium hydrate, and ferric blue; and mixtures thereof.

[0097] The organic pigment may be chosen from among the compounds nitroso, nitro, azo, xanthene, pyrene, quinoline, quinoline, anthraquinone, triphenylmethane, fluorane, phthalocyanine, metal complex type, isoindolinone, isoindoline, quinacridone, perinone, perylene, diketopyrrolopyrrole, indigo, thioindigo, dioxazine, triphenylmethane or quinophthalone.

[0098] In particular, organic pigments can be chosen from carmine, carbon black, aniline black, azo yellow, quinacridone, phthalocyanine blue, the blue pigments coded in the Color Index under references Cl 42090, 69800, 69825, 74100, 74160, the yellow pigments coded in the Color Index under references Cl 11680, 11710, 19140, 20040, 21100, 21108, 47000, 47005, the green pigments coded in the Color Index under references Cl 61565, 61570, 74260, the orange pigments coded in the Color Index under references Cl 11725, 71105, the red pigments coded in the Color Index under the references Cl 12085, 12120, 12370, 12420, 12490, 14700, 15525, 15580, 15620, 15630, 15800, 15850, 15865, 15880, 26100, 45380, 45410, 58000, 73360, 73915, 75470.

[0099] The materials may include, in particular: 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, atta pulgite, carbon nanotubes, glass powder, glass fibers and carbon fibers, solid or hollow glass beads possibly coated with silane, and mixtures thereof.

[0100] According to one embodiment, the powder composition according to the invention is free of fillers.

[0101] By way of example, the flow agent may be selected from silicas, including fumed silica (possibly hydrophobically treated), 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.

[0102] Furthermore, the composition according to the invention may comprise at least one polymer in addition to polyamide, which may in particular be selected from: poly(phenylene oxide), poly(phenylene sulfide), polyolefins, polyesters, polycarbonates, thermoplastic elastomers, and mixtures thereof. In one embodiment, the powder composition according to the invention is free of any polymer other than polyamide.

[0103] Preparation process

[0104] The composition according to the invention can be prepared by dry mixing its various constituents in one step (the constituents being all added to the mixture simultaneously) or in several steps (a premixing of some constituents being carried out first before the addition of other constituents).

[0105] In a preferred embodiment, the process for preparing the powder composition according to the invention comprises the following steps:

[0106] (1) the synthesis of a linear aliphatic polyamide,

[0107] (2) optionally, the mixing of polyamide with one or more additives, in an extruder,

[0108] (3) grinding or dissolving-precipitating the polyamide from step (1) or the mixture from step (2) to obtain a polyamide powder,

[0109] (4) optionally, the addition of one or more additives, characterized in that constituents b), c) and d) are independently introduced during and / or between steps (1), (2) and / or (4).

[0110] The synthesis of polyamide can be any process for obtaining a polyamide known to those skilled in the art. It is preferably carried out by polycondensation. Constituents (b), (c) and / or (d) may optionally be introduced during step (1).

[0111] In one embodiment particularly well-suited to polyamide 12, component (d) is introduced in step (1). In another embodiment of the invention, which is particularly well-suited to polyamide 11, the polyamide prepared in step (1) may be in the form of a prepolymer, i.e., a polyamide having an inherent viscosity between 0.20 and 0.90 (g / 100g). 1 , preferably between 0.30 and 0.60 (g / lOOg) 1 measured as described previously. In this case, a polycondensation step is then carried out subsequently, preferably before step (4). The polycondensation step can be carried out dry and hot (for example, in a dryer or oven). In one embodiment, components c) and / or d) are introduced during the polycondensation step.

[0112] In a preferred embodiment of the invention, the chain-limiting agent d) is made to react with the polyamide during its synthesis (generally by polycondensation) or during the synthesis of a prepolymer of this polyamide or during a polycondensation step of this prepolymer.

[0113] The polyamide from step (1) may be in the form of granules or flakes, which may optionally be ground before the implementation of step (2), or the compounding step. This grinding step may be carried out at ambient temperature or using cryogenic grinding; it may be performed in a counter-rotating pin mill, a hammer mill, or a vortex mill, for example.

[0114] Optional compounding step (2) allows the polyamide to be mixed with one or more additives, including the chain-limiting agent. At the end of this step, a mixture is obtained, which may again be in the form of flakes or granules, and which is then generally subjected to a grinding step in step (3). In another embodiment of the invention, particularly adapted to polyamide 12, the polyamide may be subjected in step (3) to a dissolution-precipitation process as described in US 4,334,056.

[0115] In one embodiment, one or more additives may be added in step (3), preferably by dry mixing.

[0116] In all cases, a polyamide powder is obtained which, in a preferred embodiment of the invention, can be subjected to a hydrothermal treatment step as described in document EP1413595, preferably after step (3) and before step (4). This step increases the melting point and enthalpy of fusion of the polyamides and thus widens their build window in a 3D printing process by powder sintering. It comprises contacting the polyamide powder with an aqueous solution (in particular water) or steam, at a temperature close to the crystallization temperature of the polyamide (i.e., differing by less than 20°C, preferably less than 10°C, or even less than 5°C, from its crystallization temperature). This step can be carried out for a period of 2 to 100 hours, preferably 2 to 30 hours, at a temperature of 140 to 170°C, for example.The weight ratio of polyamide powder to solution generally ranges from 5 to 75%, preferably from 15 to 50%. The mixture is then cooled to a temperature of 20 to 50°C, preferably 20 to 30°C, before separating the polyamide and proceeding with drying.

[0117] In one embodiment, components b) and / or c) are introduced during the hydrothermal treatment step.

[0118] As previously stated, components b), c), and d) are independently introduced during and / or between steps (1), (2), and / or (4), where applicable during the hydrothermal treatment step and / or the polycondensation step. The choice of the step for introducing these components depends, in particular, on their physical form (solid or liquid) under the temperature conditions of each step, in order to obtain a homogeneous mixture. Thus, liquid components at room temperature can, in particular, be added during the optional hydrothermal treatment step. Solid additives at room temperature can be mixed with the polyamide by compounding during step (2) or introduced in step (4).

[0119] It is preferred that components (b) and (c) be introduced during the synthesis of the polyamide, or added in the optional hydrothermal treatment step. In practice, the addition of component (b) and / or (c) to the polyamide can be carried out by impregnating the polyamide in an aqueous dispersion of that component.

[0120] Preferably, the median volume diameter Dv50 of the particles in the composition according to the invention ranges from 10 to 300 pm, more preferably from 30 to 150 pm, and even more preferably from 40 to 80 pm. Dv50 corresponds to the particle size at 50 ème Percentile (by volume) of the cumulative particle size distribution. It can be determined by laser granulometry according to ISO 13320.

[0121] Uses

[0122] The composition according to the invention can be used in a 3D printing process by powder sintering. More particularly, the invention relates to a method for manufacturing an article by 3D printing comprising sintering a powder composition according to the invention using electromagnetic radiation, preferably by laser or by applying infrared radiation to the powder previously selectively coated with one or more inks.

[0123] Such a process typically includes the following steps:

[0124] (a) provide a powder composition comprising at least one polyamide,

[0125] (b) prepare a bed of said powder,

[0126] (c) selectively agglomerate a portion of powder using an electromagnetic energy source,

[0127] (d) repeat steps (b) and (c) until an object is obtained, and

[0128] (e) separate the object from the unagglomerated powder.

[0129] 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.

[0130] In the SLS process, step (b) consists of depositing 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 infrared lamps, for example, halogen lamps, which typically have maximum emission at a wavelength between 750 nm and 1250 nm. The build temperature refers to the temperature to which the powder bed of a constituent layer of a three-dimensional article under construction is heated during the layer-by-layer sintering process of the powder.

[0131] Electromagnetic radiation, for example in the form of a laser, then provides in step (c) 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.

[0132] Next, the horizontal plate is lowered to a height corresponding to the thickness of a powder layer, and a new layer of powder is spread, heated, and then sintered in the same way. The procedure is repeated until the object has been manufactured. The powder layer deposited on a horizontal plate can have, before sintering, a thickness of, for example, 20 to 200 µm, and preferably 50 to 150 µm. After sintering, the thickness of the agglomerated material layer is somewhat less, and can range, for example, from 10 to 150 µm, and preferably from 30 to 100 µm.

[0133] In the MJF and HSS processes, the entire layer of the build material is exposed to radiation, but only a portion coated with a fusing agent is melted to form a layer of a 3D part. The fusing agent is a compound capable of absorbing radiation and converting it into thermal energy, such as black ink. It is selectively applied to the chosen area of ​​the build material. The fusing agent penetrates the layer of the build material and transfers the absorbed energy to the adjacent layer, causing it to melt or sinter. Through the melting, bonding, and subsequent hardening of each layer of the build material, the object is formed.

[0134] In the specific case of MJF, a detailing agent is also added to the edges of the area to be melted to allow the parts to have better definition.

[0135] In one embodiment of the invention, the non-agglomerated powder from step (e) can be recycled in step (a), optionally mixed with a fraction of virgin (non-recycled) powder, for example in a recycled powder / virgin powder weight ratio of 70 / 30 to 90 / 10, preferably 80 / 20 to 85 / 15.

[0136] The present invention also relates to an article obtained according to the above process. This article can be chosen from prototypes and models, used in particular in the automotive, nautical, aeronautical, aerospace, medical (prostheses, hearing systems, cellular tissues...), textile, clothing, fashion, decoration, design, and electronics, telephony, home automation, computer or lighting sectors.

[0137] The parts manufactured by powder sintering according to the invention advantageously exhibit an elongation at break along the Z axis which is greater than 15%, even after several recyclings (at least 4 recyclings) of the powder, as determined according to ISO527-1 (unfilled powder) or ISO527-2 (filled powder).

[0138] The invention will be better understood in light of the following non-limiting examples. EXAMPLES

[0139] Preparation of polyamide powders for 3D printing

[0140] Preparation of a powder according to the invention

[0141] We synthesized a polyamide 11 designated here as "prepolymer", from amino-11-undecanoic acid in the presence of water and phosphoric acid (5,300 ppm).

[0142] This prepolymer was then ground (Dvso = 52 µm) and subsequently subjected to hydrothermal treatment according to the process described in EP 1413595A. During this hydrothermal treatment, hypophosphorous acid (1,700 ppm) was added. The resulting powder, after dewatering, contained 3,500 ppm of H3PO4 and 1,000 ppm of H3PO2. It was then subjected to solid-phase polycondensation in the presence of antioxidants (0.9%) and sebacic acid (0.20%). Zinc oxide (0.25%) and silica (0.13%) were then added to the powder by dry mixing in a Henschel® IAM 6L mixer at 900 rpm for 100 seconds at room temperature.

[0143] The powder thus obtained is hereinafter referred to as "Powder IA".

[0144] Preparation of comparative powders

[0145] A low viscosity polyamide 11, referred to here as "prepolymer", was synthesized from amino-11-undecanoic acid in the presence of water and phosphoric acid (5,300 ppm).

[0146] This prepolymer was then ground and subsequently subjected to hydrothermal treatment according to the process described in EP 1413595A. During this hydrothermal treatment, phosphoric acid (6,000 ppm) and hypophosphorous acid (1,700 ppm) were added. The resulting powder, after dewatering, contained 4,300 ppm of H3PO4 and 1,000 ppm of H3PO2. It was then subjected to solid-phase polycondensation in the presence of antioxidants (0.9%) and sebacic acid (0.2%). Zinc oxide (0.25%) and silica (0.13%) were then added to the powder by dry mixing in a Henschel® IAM 6L mixer at 900 rpm for 100 seconds at room temperature.

[0147] The powder thus obtained is hereinafter referred to as "IB Powder".

[0148] A similar powder has been prepared without the use of sebacic acid and is hereinafter referred to as "IC Powder".

[0149] These comparative powders are representative of the prior art (WO2023 / 118763). Example 2: Mechanical properties

[0150] Powders IA, IB, and IC prepared in Example 1 were used to print a series of ISO 527-1A geometry specimens arranged in two blocks (Figure 1). These specimens were built along the Z-axis (vertical axis) in a multi-jet fusion 3D printer (MJF5200® commercially available and configured by HP). The conditions used were the same for all prints. The model was prepared using Materialise Magies® 22.0 software.

[0151] During build-up, the powder temperature at the surface of the build vat was set at 159°C, as measured by an infrared thermal sensor, and maintained at this value by the heating lamps. The machine parameters were those recommended by the manufacturer for PA 11 (HP 3D HR PAU).

[0152] The construction time for the two test specimen blocks was approximately 10 hours and 30 minutes, and they were allowed to cool at room temperature for 48 hours. The specimens (150 pieces) in the lower block were constructed first. Their average elongation at break was measured on an INSTRON 5966 machine according to ISO 527-2.

[0153] The unagglomerated powders were then separated from the test specimens and mixed with virgin polyamide 11 powder in a weight ratio of 80 / 20 (unagglomerated powder to virgin powder). This powder mixture was used in a new test specimen construction cycle. The mean elongation at break along the Z-axis of the 150 specimens produced in this second construction cycle was then measured.

[0154] The following results were obtained:

[0155] [Table 1]

[0156] This test demonstrates that reducing the amount of H3PO allows the object made from Powder IA to achieve a Z-axis elongation at break that is significantly greater than that obtained with Powders IB and IC after each build cycle. Furthermore, comparing the results obtained for Powders IB and IC shows that simply adding the chain-limiting agent (sebatic acid) to Powder IC to obtain Powder IB has little effect on the desired properties.

Claims

Demands 1. Powder composition suitable for 3D printing by sintering, comprising: (a) at least one linear aliphatic polyamide, (b) from 0 to 3,500 ppm by weight of phosphoric acid, (c) from 500 to 2,000 ppm by weight of at least one compound selected from hypophosphorous acid, its salts and mixtures thereof, and (d) at least one chain-limiting agent selected from: linear, cyclic or branched mono- or dicarboxylic acids comprising from 2 to 30 carbon atoms, their anhydrides or esters; linear, cyclic or branched mono- or diamines comprising from 2 to 30 carbon atoms; and mixtures thereof.

2. Composition according to claim 1, characterized in that said at least one polyamide is selected from: PA 11, PA 12, PA 6, PA 6.Y1, PA 10, PA 1O.Y2, PA 1O.Y3 / Z or combinations thereof, where Yi is selected from 10, 12, 13, 14 or 18, Y2 is selected from 10, 12, 13 or 14, Y3 is selected from 10, 12 or 13, and Z is selected from 11, 12 or 14, more preferably the polyamide comprises or is made up of polyamide 11 or 12, better, polyamide 11.

3. Composition according to claim 1 or 2, characterized in that phosphoric acid represents from 500 to 3,500 ppm, preferably from 2,000 to 3,500 ppm and more preferably from 3,000 to 3,500 ppm by weight, relative to the weight of the powder composition.

4. Composition according to any one of the preceding claims, characterized in that the chain-limiting agent is selected from: linear, cyclic or branched mono- or dicarboxylic acids comprising from 4 to 20 carbon atoms, preferably from 6 to 12 carbon atoms, their anhydrides, their esters and mixtures thereof, preferably linear C6-Ci2 dicarboxylic acids, more preferably sebacic acid.

5. Composition according to any one of the preceding claims, characterized in that constituent c) represents from 700 to 1,200 ppm by weight, relative to the total weight of the powder composition.

6. Composition according to any one of the preceding claims, characterized in that it further contains at least one compound selected from metal oxides, metal hydroxides and mixtures thereof.

7. A process for preparing a powder composition according to any one of claims 1 to 6, comprising the following steps: (1) the synthesis of a linear aliphatic polyamide, (2) optionally, the mixing of polyamide with one or more additives, in an extruder, (3) grinding or dissolving-precipitating the polyamide from step (1) or the mixture from step (2) to obtain a polyamide powder, (4) optionally, the addition of one or more additives, characterized in that constituents b), c) and d) are independently introduced during and / or between steps (1), (2) and / or (4).

8. Method of manufacturing an article by 3D printing comprising sintering a powder composition according to any one of claims 1 to 6 using electromagnetic radiation, preferably by laser or by application of infrared radiation to the powder previously selectively coated with one or more inks.

9. Article obtained by the process according to claim 8.

10. Use of a powder composition according to any one of claims 1 to 6 in a 3D printing process by powder sintering.

Images