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 polyamide, (b) 0 to 3,500 ppm by weight of phosphoric acid, (c) 500 to 2,000 ppm 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 or by applying infrared radiation to the powder, which has been previously selectively coated with one or more inks, and the article thus obtained.

Description

Title of the invention: Polyamide composition suitable for 3D printing by powder sintering. FIELD OF THE INVENTION

[0001] The present invention relates to a powder composition suitable for 3D printing by sintering, comprising: (a) at least one polyamide, (b) 0 to 3,500 ppm by weight of phosphoric acid, (c) 500 to 2,000 ppm 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. TECHNICAL BACKGROUND

[0002] The technology of agglomerating polyamide powders under electromagnetic radiation constitutes a 3D printing process 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.

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

[0004] It is recommended that the powder used in this process have the largest possible Tf - Te difference (corresponding to the working window) to avoid deformation (or "curling") phenomena 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.

[0005] 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.

[0006] However, it appeared 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, as well as 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.

[0007] US patent 2004 / 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 US patent 2006 / 071359.

[0008] Another solution proposed by the Applicant consists of incorporating at least 4,000 ppm of phosphoric acids into the polyamide powder, particularly during the synthesis of the polyamide (EP2530121). Phosphoric acid is particularly suitable for this purpose and can optionally be combined with hypophosphorous acid. While this solution does indeed 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.

[0009] There therefore remains a need for a polyamide powder, in particular polyamide 11 or polyamide 12, that can be used and recycled in a 3D printing process by 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 powder recycled polyamide would not be mixed with virgin polyamide powder or only with a small amount of this powder. Summary of the invention

[0010] The invention thus relates to a powder composition suitable for 3D printing by sintering, comprising:

[0011] (a) at least one polyamide,

[0012] (b) from 0 to 3,500 ppm by weight of phosphoric acid,

[0013] (c) from 500 to 2,000 ppm of at least one compound selected from the acid hypophosphorous, its salts and their mixtures,

[0014] (d) at least one chain-limiting agent selected from: mono- or linear, cyclic or branched dicarboxylics comprising from 2 to 30 carbon atoms, their anhydrides or their esters; linear, cyclic or branched mono- or diamines comprising from 2 to 30 carbon atoms; and their mixtures.

[0015] It also relates to a process for preparing this powder composition, comprising the following steps: 1. the synthesis of a polyamide, 2. Optionally, the mixing of polyamide with one or more additives in an extruder,

[0016] (3) grinding or dissolving-precipitating the polyamide from step (1) or the mixture from step (2) to obtain a polyamide powder,

[0017] (4) possibly, the addition of one or more additives,

[0018] characterized in that constituents b), c) and d) are independently introduced during and / or between steps (1), (2), and / or (4).

[0019] 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.

[0020] Finally, the invention also relates to the use of the aforementioned powder composition in a 3D printing process by powder sintering.

[0021] 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 over the course of an industrial production, avoiding the production of parts having, in particular, a low elongation at break along the Z axis. FIGURES

[0022] Fig. 1 represents the model used to prepare an article according to the invention and a comparative article by 3D printing. DETAILED DESCRIPTION

[0023] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the following description.

[0024] It is specified that the expressions "between... and..." and "from... to..." used in this description should be understood as including each of the limits mentioned.

[0025] In addition, unless otherwise indicated, all percentages and proportions are mass percentages and proportions.

[0026] Polyamide

[0027] By "polyamide" is meant a polymer comprising the polymerization product of one or more monomers selected from: - amino acid or aminocarboxylic acid monomers, and preferably alpha, omega-aminocarboxylic acids; - lactam-type monomers; - the "diamine.diacid" type monomers resulting from the reaction between a an aliphatic diamine and a dicarboxylic acid; and - their mixtures, with monomers having a different number of carbons in the case of mixtures between an amino acid type monomer and a lactam type monomer.

[0028] The term "monomer" in the present description of polyamides should be taken to mean "repeating unit". Indeed, in the case where a repeating unit of the polyamide (PA) is made up of the association of a diacid with a diamine, it is considered that the association of a diamine and a diacid, that is to say the diamine-diacid pair (in equimolar quantity), corresponds to the monomer.

[0029] The polyamide can be a homopolyamide and / or a copolyamide.

[0030] When the polyamide is a homopolyamide, it comprises the polymerization product of a single monomer. When the 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. Finally, examples include copolyamides resulting from the condensation of an aliphatic diamine. with an aliphatic dicarboxylic acid and at least one other monomer chosen from among the aliphatic diamines different from the previous one and the aliphatic diacids different from the previous one.

[0031] 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 designates the polycondensation product of a lactam or an amino acid with Z carbon atoms; PA XY designates 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.

[0032] Amino acid type monomers (PA Z):

[0033] 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.

[0034] Lactam-type monomers (PA Z):

[0035] Examples of lactams include those with 3 to 18 carbon atoms on the main ring and which can be substituted. Examples include [3,[3-dimethylpropriolactam, α,α-dimethylpropriolactam, amylolactam, caprolactam (also called lactam 6), capryllactam (also called lactam 8), oenantholactam, and lauryllactam (also called lactam 12).

[0036] Monomers of the "diamine-diacid" type (PA XY):

[0037] Examples of dicarboxylic acids include acids having from 4 to 36 carbon atoms and preferably from 4 to 18 carbon atoms, such as adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexane dicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulfoisophthalic 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.

[0038] Fatty acid dimers, or dimerized fatty acids, are understood to be the product 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.

[0039] By way of example of a diamine, one can cite aliphatic diamines having from 2 to 36 atoms, preferably from 4 to 18 atoms, such as hexamethylenediamine, piperazine, aminoethylenepiperazine, tetramethylenediamine, roctamethylene diamine, decamethylene diamine, dodecamethylene diamine, 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, tetramethylene diamine, octamethylene diamine, decamethylene diamine, dodecamethylene diamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, and mixtures thereof.

[0040] As "diamines.diacids", one 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.

[0041] 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.

[0042] Advantageously, the polyamide of the powder comprises or is made up of one (or more) homopolyamide(s).

[0043] According to one embodiment, the polyamide is aliphatic and linear.

[0044] According to a preferred embodiment, the polyamide is a semi-polyamide Crystalline. "Semi-crystalline polyamide" refers to a polyamide that exhibits:

[0045] - a crystallization temperature (Te) determined according to ISO standard 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

[0046] - and an enthalpy of fusion (AHf) determined according to ISO 11357-3: 2013 during the heating stage 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.

[0047] Preferably, the polyamide according to the invention is a semi-crystalline aliphatic and linear polyamide.

[0048] Furthermore, the polyamide may 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)1. The inherent viscosity is measured using an Ubbelhode tube. The measurement is carried out 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:

[0049] Inherent viscosity = ln(ts / t0) x 1 / C

[0050] with C = m / px 100, where ts 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.

[0051] Advantageously, the polyamide used in the invention is selected from PA 11, PA 12, PA 6, PA 6Yb, PA 10, PA 10Y2, PA 10Y3 / Z, or combinations thereof. In the list above, Y1 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 chosen 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-11-undecanoic acid, which has the advantage of being manufactured from raw materials of vegetable origin, namely castor oil, extracted from castor seeds.

[0052] Polyamide advantageously represents from 60 to 99% by weight, preferably from 97 to 99% by weight, relative to the total weight of the powder composition.

[0053] Phosphoric and hypophosphorous acids (or their salts)

[0054] 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.

[0055] It further contains from 500 to 2,000 ppm 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, relative to the total weight of the powder composition.

[0056] The determination of phosphoric acid and hypophosphorous acid or its salts can in particular be carried out by phosphorus (31P) NMR after dilution of 400 mg of the powder composition in a solvent such as hexafluoropropan-2-ol (HFIP) and / or deuterated dichloromethane (CD2C12), preferably in a 3 / 1 v / v HFIP / CD2C12 mixture, for example using a BRÜKER Avance 400 NEO instrument (400 MHz, 23°C).

[0057] Chain limiter

[0058] The powder composition according to the invention further comprises at least one chain-limiting agent selected from: linear mono- or dicarboxylic acids, cyclic or branched compounds 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.

[0059] Preferably, the chain limiter has a melting temperature below 180°C or even 150°C.

[0060] 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.

[0061] 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.

[0062] Monoamine can be, in particular, a primary amine having from 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.

[0063] The diamine can in particular be 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.

[0064] 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 dicarboxylic acids in C6-Ci2, more preferably sebacic acid.

[0065] According to one embodiment, the chain limiter represents from 0.01 to 10%, preferably from 0.01 to 5%, preferably from 0.01 to 4%, preferably from 0.01 to 3%, of preferably 0.01 to 2%, preferably 0.01 to 1% by weight, relative to the total weight of the powder composition.

[0066] More preferably, the chain limiter represents 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.

[0067] Additives

[0068] 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.

[0069] The antioxidant can be chosen from: phenolic antioxidants, phosphorus antioxidants, thioethers and mixtures thereof.

[0070] Examples of phenolic antioxidants are:

[0071] - the 3,3'-Bis(3,5-di-tert-butyl-4-hydroxyphenyl)-N,N'-hexamethylenedipropionamide marketed notably under the name Palmarole® AO.OH.98 by Palmarole,

[0072] - the (4,4'-Butylidenebis(2-t-butyl-5-methylphenol) marketed in particular under the name Lowinox® 44B25 by Addivant,

[0073] - Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) marketed notably under the name Irganox® 1010 by BASF,

[0074] - N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) marketed notably under the name Irganox® 1098 by BASF,

[0075] - the 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,

[0076] - ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate) marketed notably under the name Irganox® 245 by BASF,

[0077] - 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 in particular under the name Tinuvin® 312 by BASF,

[0079] - 4,4',4"-trimethyl-1,3,5-benzenetriyl) tris-(methylene)] tris 2,6-bis(1,1- dimethylethylphenol marketed notably under the name Alvinox® 1330 by 3V or Hostanox® 245 FF or Hostanox® 245 Pwd by Clariant,

[0080] - pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) marketed notably under the names Evemox® 10 or Evernox® 10GF by Everspring Chemical Company Limited,

[0081] - octadecyl-3-(3,5-di-tert-4-hydroxyphenyl)-propionate marketed in particular under the names Evernox® 76 or Evemox® 76GF by Everspring Chemical Company Limited,

[0082] - tetrakis [methylene-3(3',5'-di-tert-butyl-4-hydroxyphenyl) propionate] methane marketed notably under the name BNX® 1010 by Mayzo,

[0083] - thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] marketed notably under the name BNX® 1035 by Mayzo,

[0084] - tetrakis [methylene-3 (3',5'-di-tert-butyl-4-hydroxyphenyl)propionate] methane,

[0085] - octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate commercially notably under the name BNX® 2086 by Mayzo, and

[0086] - 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 BNX® 3114 by Mayzo.

[0087] Phosphorus antioxidants may be aromatic or aliphatic and may be selected, in particular, from phosphonates and organophosphonates; phosphites and organophosphites, especially 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 are Hostanox® P-EPQ®, marketed by Clariant, and Irgafos® 168, marketed by BASF.

[0088] In the case where the antioxidant comprises a thioether, this may be chosen from 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, 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.

[0089] 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-dodecylthio propionate or 3-laurylthiopropionate), and mixtures thereof.

[0090] According to one embodiment, the thioether is the DLTDP.

[0091] According to another embodiment, the thioether is the DSTDP.

[0092] Preferably, the thioether is pentaerythritol tetrakis (3-dodecylthio propionate). Such a compound is notably marketed by the companies Songnox, or Adeka under the trade name ADK ST AB AO-412S.

[0093] 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.

[0094] The metal oxide can be chosen from among the oxides of poor metals (preferably aluminium, gallium, indium, zinc, and / or tin, more preferably zinc and / or aluminium).

[0095] Metal hydroxides include in particular hydroxides of alkaline earth metals (preferably magnesium, calcium, strontium and / or barium) or of poor metals (preferably aluminium, gallium, indium, zinc, and / or tin, more preferably zinc and / or aluminium), including hydrotalcites of formula Ma2+ Mb3+(OH)2a+2b IX )b / i, yH2O in which Ma2+ represents divalent metal ions, Mb3+ represents trivalent metal ions and X1 represents an anion, typically a carbonate or a nitrate.

[0096] For example, a hydrotalcite usable in the powder of the invention can be a compound of formula Mg6Al2CO3(OH)i6-4(H2O).

[0097] 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.

[0098] The pigments may in particular be chosen from those described in Kirk-Othmer's Encyclopedia of Chemical Technology and in Ullmann's Encyclopedia of Industrial Chemistry.

[0099] 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 selected from mineral pigments, organic pigments, and mixtures thereof.

[0100] Among the mineral pigments useful in the present invention, one can cite ochres such as red ochre (clay, in particular kaolinite, and iron hydroxide, in particular hematite), brown ochre (clay, in particular kaolinite, and limonite), 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; manganese violet, ultramarine blue, chromium hydrate and ferric blue; and mixtures thereof.

[0101] The organic pigment may in particular be selected from 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.

[0102] In particular, the organic pigments may be selected 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 reference CI 11725, 71105, the red pigments coded in the Color Index under the references CI 12085, 12120, 12370, 12420, 12490, 14700, 15525, 15580, 15620, 15630, 15800, 15850, 15865, 15880, 26100, 45380, 45410, 58000, 73360, 73915, 75470.

[0103] The fillers may in particular be chosen from: calcium carbonate, magnesium carbonate, dolomite, calcite, barium sulfate, calcium sulfate, dolomite, alumina hydrate, wollastonite, montmorillonite, zeolites, perlite, nano-clays, calcium silicates, magnesium silicates, such as talc, mica, kaolin, attapulgite, carbon nanotubes, glass powder, glass fibers and carbon fibers, solid or hollow glass beads possibly coated with silane, and mixtures thereof.

[0104] According to one embodiment, the powder composition according to the invention is free of fillers.

[0105] By way of example, the flow agent may be selected from silicas, including fumed silica, possibly hydrophobically treated, such as the product marketed under the name Cab-o-Sil® TS610 by Cabot Corporation, precipitated silica, hydrated silica, vitreous silica, vitreous phosphates, vitreous borates, alumina, such as amorphous alumina, and mixtures thereof. Fumed silica is preferred for use in the present invention. Alternatively or in addition, the flow agent may comprise at least one wax, selected, for example, from polyethylene, polypropylene, polytetrafluoroethylene, ketone, acid, partially esterified acid, acid anhydride, ester, aldehyde, amide, derivatives thereof, and mixtures thereof. The wax may include 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.

[0106] 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. According to one embodiment, the powder composition according to the invention is free of any polymer other than polyamide.

[0107] Preparation process

[0108] 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).

[0109] In a preferred embodiment, the process for preparing the powder composition according to the invention comprises the following steps: 1. The synthesis of a polyamide, 2. Optionally, the mixing of polyamide with one or more additives in an extruder,

[0110] (3) grinding or dissolving-precipitating the polyamide from step (1) or the mixture from step (2) to obtain a polyamide powder,

[0111] (4) possibly, the addition of one or more additives,

[0112] characterized in that constituents b), c) and d) are independently introduced during and / or between steps (1), (2) and / or (4).

[0113] The synthesis of the polyamide can be any process for obtaining a polyamide known to those skilled in the art. Constituents (b), (c) and / or (d) may optionally be introduced during step (1).

[0114] In one 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 of between 0.20 and 0.90 (g / 100g), preferably between 0.30 and 0.60 (g / 100g), measured as described above. In this case, a polycondensation step is then carried out subsequently, preferably before step (4). The polycondensation step may 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.

[0115] The polyamide from step (1) may be in the form of granules or flakes which may optionally be ground before implementation of step (2) or compounding step. This grinding step can be carried out at ambient temperature or using cryogenic grinding; it can be carried out in a counter-rotating pin mill, a hammer mill or a vortex mill, for example.

[0116] The 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.

[0117] In one embodiment, one or more additives may be added in step (3), preferably by dry mixing.

[0118] 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.

[0119] In one embodiment, components b) and / or c) are introduced during the hydrothermal treatment step.

[0120] As previously stated, constituents 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 during the polycondensation step. The choice of the step for introducing these constituents 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 constituents at room temperature may, in particular, be added during the optional hydrothermal treatment step. Solid additives at room temperature can be mixed with the polyamide by compounding in step (2) or introduced in step (4).

[0121] It is preferred that components (b) and (c) be introduced during the synthesis of the polyamide, or be 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.

[0122] 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 the 50th percentile (by volume) of the cumulative particle size distribution. It can be determined by laser granulometry according to ISO 13320.

[0123] Uses

[0124] 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.

[0125] Such a process classically comprises the steps of: a. provide a powder composition comprising at least one polyamide, b. prepare a bed of said powder, c. selectively agglomerate a portion of powder using an electromagnetic energy source, d. repeat steps (b) and (c) until an object is obtained, and e. separate the object from the unagglomerated powder.

[0126] 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.

[0127] 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 IR radiation lamps, for example halogen lamps, which generally have a maximum emission at a wavelength between 750 nm and 1250 nm. The build temperature refers to the temperature at 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.

[0128] 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 in memory the shape of an object and reproduces the latter in the form of slices.

[0129] Next, the horizontal plate is lowered to a height corresponding to the thickness of a layer of powder, and a new layer of powder is spread, heated, and then sintered in the same way. The procedure is repeated until the object has been manufactured.

[0130] The layer of powder deposited on a horizontal plate can have, before sintering, for example, a thickness of 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.

[0131] In the case of the MJF and HSS processes, the entire layer of the building material is exposed to radiation, but only a portion coated with a melting agent is melted to become a layer of a 3D part. The melting agent is a compound capable of absorbing radiation and converting it into thermal energy, for example, black ink. It is applied selectively to the selected region of the building material. The melting agent is able to penetrate the layer of the building material and transfers the absorbed energy to the adjacent building material, causing it to melt or be sintered. Through the melting, bonding, and subsequent hardening of each layer of the building material, the object is formed.

[0132] In the particular case of MJF, a detailing agent is further added to the edges of the area to be melted to allow the parts to have a better definition.

[0133] 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.

[0134] The present invention further 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 fields.

[0135] 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).

[0136] The invention will be better understood in light of the following non-limiting examples. EXAMPLES

[0137] Example 1: Preparation of polyamide powders for 3D printing

[0138] Example IA - Preparation of a powder according to the invention

[0139] A low viscosity polyamide 11, referred to herein as "prepolymer", was synthesized from amino-11-undecanoic acid in the presence of water and phosphoric acid (5,300 ppm).

[0140] This prepolymer was then ground (Dv50 = 52 pm) 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 powder obtained 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.

[0141] The powder thus obtained is hereinafter referred to as "Powder IA".

[0142] Example IB - Preparation of comparative powders

[0143] A low viscosity polyamide 11, referred to herein as "prepolymer", was synthesized from amino-11-undecanoic acid in the presence of water and phosphoric acid (5,300 ppm).

[0144] 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 (0.00 ppm) and hypophosphorous acid (1.700 ppm) were added. The powder obtained 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.

[0145] The powder thus obtained is hereinafter referred to as "Powder IB".

[0146] A similar powder has been prepared without the use of sebacic acid and is hereinafter referred to as "IC Powder".

[0147] These comparative powders are representative of the prior art (WO2023 / 118763). Example 2: Mechanical Properties

[0148] The IA, IB, and IC powders prepared in Example 1 were used to print a series of ISO 527-1A geometry test specimens, arranged in two blocks ([Fig. 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 the Magies® 22.0 Materialized software.

[0149] During construction, the powder temperature at the surface of the build tray was set at 159°C, as measured by means of 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).

[0150] The construction time for the two test block blocks was approximately 10.5 hours, and they were allowed to cool at room temperature for 48 hours. The test 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.

[0151] 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 test specimens from this second construction cycle was then measured.

[0152] The following results were obtained:

[0153] [Tables 1] Powder IA (invention) Powder IB (comparative) Powder IC (comparative) Elongation 1st cycle 32% 23% 26% (%) 2nd cycle 29% 23% 19%

[0154] This test demonstrates that reducing the amount of H3PO4 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, a comparison of the results obtained for Powders IB and IC shows that simply adding the chain limiter (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 polyamide, (b) 0 to 3,500 ppm by weight of phosphoric acid, (c) 500 to 2,000 ppm 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 2 to 30 carbon atoms, their anhydrides or esters; linear, cyclic or branched mono- or diamines comprising 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.Yb, PA 10, PA 10.Y2, PA 10.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, relative to the total weight of the powder composition.

6. A composition according to any one of the preceding claims, characterized in that it further contains at least one compound chosen from among metallic oxides, metallic hydroxides and their mixtures.

7. A method for preparing a powder composition according to any one of claims 1 to 6, comprising the following steps: (1. the synthesis of a polyamide, (2. optionally, the mixing of the polyamide with one or more additives, in an extruder, (3) the grinding or dissolution-precipitation of the polyamide from step (1) or of 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. A method for 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 applying infrared radiation to the powder previously selectively coated with one or more inks.

9.

10. Article obtained by the process according to claim 8. Use of a powder composition according to any one of claims 1 to 6 in a 3D printing process by powder sintering.

Images