Polyamide powders for 3D printing

Abstract

The present invention relates to a long-chain polyamide powder composition for manufacturing articles by 3D printing, particularly by sintering, which improves the material's processability during printing. The invention also relates to a method for preparing this powder composition, its use in a sintering manufacturing process, and articles manufactured from said powder composition.

Description

Title of the invention: Polyamide powders for 3D printing Scope of the invention

[0001] The present invention relates to a composition of long chain polyamide powders for the manufacture of articles by 3D printing, in particular by sintering, making it possible to improve the processability of the material during printing.

[0002] The invention also relates to a process for preparing this powder composition and its use in a manufacturing process by sintering, and articles manufactured from said powder composition. Technical background

[0003] Additive manufacturing using thermoplastic polymer powder bed (SLS, MJF, HSS...) makes it possible to build parts with complex geometries, including in series. It allows for the simultaneous production of a large number of parts, with excellent resolution and very good mechanical properties, giving it an advantage over other additive manufacturing processes such as fused filament fabrication.

[0004] However, few thermoplastic polymer materials are commercially available because very specific temperature behavior is required for the material to be processable on polymer powder bed additive manufacturing machines. Indeed, if the build temperature is too low, "curling" phenomena occur, i.e., a deformation of the built part under the effect of internal stresses, appearing particularly when the polymer layers crystallize too quickly. The appearance of "curling" most often compromises all the parts built in the chamber. Furthermore, problems with the cohesion of the powder bath, necessary for supporting the part being built, can be observed, as well as fusion defects that affect the mechanical properties of the printed part.

[0005] The processability of the material, that is to say its ability to be transformed into a final part in additive manufacturing machines, can be defined by the width of the working window. This working window corresponds to the temperature range over which the material can be transformed into a final part while avoiding the "curling" problem described above.

[0006] It is described in EP3542430 that a mixture of two resin powders, more specifically, two polybutylene terephthalate (PBT) powders for the fabrication of solid freeform parts, made it possible to produce a printed part with a good compromise between dimensional accuracy and strength. The two resin powders are of the same chemical nature.

[0007] Long-chain polyamide powders are particularly interesting for the aforementioned additive manufacturing technology. Examples include commercial polyamide 12-based powders such as Orgasol® from Arkema, Durafom® from 3D-Systems, Vestosint® from Evonik, or PA2200® from EOS.

[0008] We can also mention commercial powders based on polyamide 11 such as Rilsan® from Arkema.

[0009] However, the working windows of the aforementioned polyamides can be relatively narrow, generally from two to four degrees, which complicates the printing process. Therefore, there is a continuing need to improve the temperature behavior of long-chain polyamides, particularly long-chain aliphatic polyamides, to make them more easily processed, specifically by widening the working window to obtain sintered objects with satisfactory mechanical properties.

[0010] There is also a desire to extend the operating window towards lower temperatures, as the evolution of polymer powders (such as degradation and discoloration) is less pronounced at lower temperatures within the printing machine. This reduced evolution will lead to easier reuse of the powder in subsequent printing. Summary of the invention

[0011] The present invention aims to provide a solution to the problems mentioned above. To this end, the present invention proposes adding a specific quantity of a particular polyamide powder to a polyamide powder of a different chemical composition, thereby widening the working window of the latter, more advantageously by reducing the sintering temperature and consequently reducing or even eliminating the curling phenomenon. It also improves the recyclability of the powders by decreasing the thermal stresses (which can be caused by higher temperatures) experienced by the powders and thus their negative effects (e.g., degradation, yellowing, viscosity changes). The composition of the powders of the present invention can improve the elongation at break of printed parts along the Z-axis.

[0012] Thus, according to a first aspect, the invention relates to a composition of polyamide powders, suitable for use in 3D printing by sintering, comprising:

[0013] (i) a polyamide Al powder having a C / N ratio greater than or equal to 8, of preference greater than or equal to 9, advantageously greater than or equal to 10,

[0014] (ii) more than 10% by mass, preferably 15 to 50% by mass, more preferably 30 to 50% by mass, relative to the total mass of the composition, of a polyamide A2 powder,

[0015] polyamide A2 being distinct from polyamide Al by their chemical nature,

[0016] the Al and A2 polyamides having in absolute value at least a difference in C / N ratio equal to Iratio C / N(A1) - ratio C / N (A2)l < 3,

[0017] the polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the carbonyl of the amide) denoted Cl,

[0018] polyamide A2 comprising at least 45 mol%, preferably at least 50 mol%, preferably at least 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2,

[0019] with at least one of the ICI-C2I < 3 equations satisfied,

[0020] (iii) 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers relative to the total mass of the composition.

[0021] According to one embodiment, the polyamide A2 powder has a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10.

[0022] According to one embodiment, polyamide Al and / or polyamide A2 are aliphatic polyamides.

[0023] The composition of polyamide powders may comprise from 11 to 50% by mass, preferably 15 to 50%, 20 to 50%, 30 to 50%, 15 to 45%, 15 to 40%, 15 to 30%, 20 to 50%, 20 to 40%, 25 to 35%, 30 to 50% or even 30 to 40% by mass of polyamide powder A2, relative to the total mass of the composition.

[0024] The Dv50 of the powder composition is typically from 20 to 100 pm, preferably from 30 to 80 pm, even more preferably from 40 to 60 pm.

[0025] The Dv50 of the Al polyamide powder is typically from 20 to 100 pm, preferably from 30 to 80 pm, even more preferably from 40 to 60 pm.

[0026] The Dv50 of the polyamide A2 powder is typically from 20 to 100 pm, preferably from 30 to 80 pm, even more preferably from 40 to 60 pm.

[0027] According to one embodiment, the Dv50 values ​​of the Al and A2 powders have an absolute difference of 30%. In other words, the Dv50 of the Al powder is 70% to 130% of the Dv50 of the polyamide A2 powder.

[0028] Preferably, the difference is less than or equal to 10%.

[0029] According to one embodiment, the SPAN of the polyamide A2 powder is less than that of the AL polyamide powder

[0030] According to one embodiment, the DvlO of the polyamide A2 powder is greater than the DvlO of the polyamide AL powder

[0031] According to one embodiment, the morphologies of the Al and A2 polyamide powders are different. For example, the A2 powder particles may have a spheroidal or substantially spheroidal shape, while the Al polyamide powder particles have an irregular shape, which can be obtained by grinding. Or again, the A2 polyamide powder particles may have a spheroidal or potato-like shape, which can be obtained by a dissolution-precipitation process, while the Al polyamide powder particles have an irregular shape, which can be obtained by grinding.

[0032] According to one embodiment, the polyamide powder composition comprises, relative to the total mass of the composition, i. 50 to 85%, preferably 55 to 70%, by mass of the Al polyamide powder as defined above, ii. 15 to 50%, preferably 20 to 50%, even more preferably 30 to 50% by mass of the polyamide A2 powder as defined above, iii. 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers.

[0033] It has been observed in the context of the present invention that adding a specific quantity of a second polyamide powder of a different chemical nature to a polyamide powder makes it possible to broaden its operating window towards lower temperatures. This avoids the "curling" phenomenon and results in better adhesion between the layers, which ultimately improves the Z-axis stability of the sintered objects.

[0034] For the purposes of the present invention, "improving the working window" means an expansion of the working window, including in particular an expansion of the working window towards lower temperatures.

[0035] The present invention also relates to a 3D printing method, preferably, a sintering method caused by electromagnetic radiation, using the powder composition as defined above.

[0036] Preferably, the electromagnetic radiation is chosen from one or more laser beams, infrared radiation or UV radiation.

[0037] The present invention also relates to an article obtained by the 3D printing process as defined above.

[0038] Preferably, the article obtained using the powder composition as defined above may exhibit a tensile modulus greater than 1200 MPa, preferably 1400 MPa, an elongation at break greater than 8%, preferably greater than 9%, and / or a tensile strength greater than 35 MPa, preferably greater than 40 MPa.

[0039] The article may be chosen from prototypes, models and parts, particularly in the automotive, nautical, aeronautical, aerospace, medical (prostheses, hearing systems, cellular tissues...), textile, clothing, fashion, decoration, design, enclosures for electronics, telephony, computing, lighting, sports, industrial tools.

[0040] According to yet another aspect, the invention relates to the use of more than 10% by mass, preferably from 15 to 50% by mass, more preferably 30 to 50% by mass, of a polyamide A2 powder, relative to the total mass of the composition, in a composition comprising a polyamide Al powder having a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10,

[0041] Polyamide A2 being distinct from polyamide Al by their chemical nature,

[0042] the Al and A2 polyamides having in absolute value at least a difference in C / N ratio equal to Iratio C / N(A1) - ratio C / N (A2)l < 3,

[0043] the polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the carbonyl of the amide) denoted Cl,

[0044] polyamide A2 comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2,

[0045] with at least one of the ICI-C2I < 3 equations satisfied,

[0046] in a 3D printing process, preferably by sintering, to improve the working window.

[0047] For example, 11 to 50% by mass can be used, preferably 15 to 50%, 20 to 50%, 30 to 50%, 15 to 45%, 15 to 40%, 15 to 30%, 20 to 50%, 20 to 40%, 25 to 35%, 30 to 50% or even 30 to 40% by mass of powder A2, relative to the total mass of the composition.

[0048] The invention is now described in detail and in a non-limiting manner in the following description. Brief description of the figures

[0049] [Fig. 1] represents the half-crystallization time curve as a function of the different temperatures to which Powder 0 was subjected for measurement. The temperature (in °C) is shown on the x-axis and the half-crystallization time (in min) is shown on the y-axis.

[0050] The half-crystallization times were measured for Powder 1, 2 and 3 subjected to 174°C and the values ​​were shown on [Fig.1]. Description of the invention Definition

[0051] In the present description of the invention, including in the examples below.

[0052] The term "powder" is meant to designate a solid material in finely divided form, generally in the form of very small particles, generally on the order of a few hundred micrometers or less.

[0053] The SPAN parameter defines the particle size distribution of the powder particles and is calculated in a known manner by the following formula: SPAN = (Dv90 - Dv10) / Dv50, where: - Dv90 denotes the particle size at the 90th percentile, by volume, of the cumulative particle size distribution (in other words, it is the diameter corresponding to the cumulative function of particle diameters, weighted by volume, equaling 90%). - DvlO denotes the particle size at the 10th percentile, by volume, of the cumulative particle size distribution (in other words, it is the diameter corresponding to the cumulative function of particle diameters, weighted by volume, equaling 10%), and - Dv50 is the median diameter in volume of the particles and corresponds to the particle size at the 50th percentile (in volume) of the cumulative distribution of particle sizes.

[0054] Dv50, Dv90 and DvlO can be measured by laser diffraction particle size analysis according to ISO 13320:2009, for example on an Insitec® type Malvern diffractometer.

[0055] The "melting temperature (Tf)" refers to the temperature at which a compound that is at least partially crystalline changes to a viscous liquid state as measured according to standard NF EN ISO 11357-3:2018. In the present invention, the value was determined during the heating step at a rate of 20 °C / min during the first heating.

[0056] Unless otherwise indicated, this refers more specifically to the peak melting temperature.

[0057] In the present description, it is specified that when reference is made to intervals, expressions of the type "between... and..." or "from... to..." include the bounds of the interval.

[0058] Unless otherwise stated, the percentages expressed are mass percentages. Unless otherwise stated, the parameters referred to are measured at atmospheric pressure and ambient temperature (23°C). Composition of polymer powders

[0059] The nomenclature used to define polyamides is described in ISO 1874-1:2011 "Plastics - Polyamide (PA) materials for molding and extrusion - Part 1: Designation", particularly on page 3 (tables 1 and 2) and is well known to the person skilled in the art.

[0060] The word "polyamide" covers both homopolyamides and copolyamides.

[0061] Polyamides can be obtained by a polycondensation reaction of monomers, which can be amino acids or lactams, denoted Z, or chains of diacids and diamines, denoted XY, where X designates a diamine and Y designates a diacid. Thus, an amide function is indeed formed by the reaction of an amine function with an acid function.

[0062] Polyamides can also be obtained by anionic polymerization of monomers, for example, lactams, denoted Z.

[0063] By unit, for the purposes of the present invention, means a Z or XY link resulting from the polymerization of monomers.

[0064] By motif, in the context of the present invention, we mean the sequence Z or the sequence X or the sequence Y. In other words, the unit Z consists of a motif Z and the unit XY consists of a motif X and a motif Y.

[0065] The Al polyamide present in the composition according to the invention is obtained from at least one motif selected from an alpha,omega-aminocarboxylic acid in C8 to C18, a lactam in C8 to C12 and a unit (diamine in Ca).(diacid in Cb), with a representing the number of carbon atoms of the diamine and b representing the number of carbons of the diacid, a and b being between 4 and 36.

[0066] Polyamides can be obtained from at least one lactam selected from pyrrolidinone, 2-piperidinone, enantholactam, caprylolactam, pelargolactam, decanolactam, undecanolactam, and lauryllactam.

[0067] The polyamides present in the composition according to the invention can also be obtained from at least one amino acid selected from 9-aminononanoic acid, 10-aminodecanoic acid (denoted 10), 11-aminoundecanoic acid (denoted 11), 12-aminododecanoic acid (denoted 12).

[0068] Polyamides can be obtained by polycondensation of at least one motif corresponding to the formula (diamine in Ca ). (diacid in Cb ), with a representing the number of carbon atoms of the diamine and b representing the number of carbons of the diacid, a and b being between 4 and 36.

[0069] The motif (diamine in Ca) is typically aliphatic. The diamine can be chosen from butanediamine (a=4), pentanediamine (a=5), hexanediamine (a=6), heptanediamine (a=7), octanediamine (a=8), nonanediamine (a=9), decanediamine (a=10), undecanediamine (a=11), dodecanediamine (a=12), tridecanediamine (a=13), tetradecanediamine (a=14), hexadecanediamine (a=16), octadecanediamine (a=18), methylpentamethylenediamine.

[0070] Advantageously, said at least one diamine Ca in C6 to Cl2, is in particular selected from 1,5-pentanediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine.

[0071] Advantageously, the Ca diamine used is in C12 C10, in particular chosen from 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine.

[0072] The diacid motif in Cb is typically aliphatic. It can be chosen from succinic acid (b=4), pentanedioic acid (b=5), adipic acid (b=6), heptanedioic acid (b=7), octanedioic acid (b=8), azelaic acid (b=9), sebacic acid (b=10), undecanedioic acid (b=11), dodecanedioic acid (b=12), brassylic acid (b=13), tetradecanedioic acid (b=14), hexadecanedioic acid (b=16), octadecanedioic acid (b=18) and diacids obtained from fatty acids.

[0073] Advantageously, said diacid motif in Cb is selected from adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, octadecanedioic acid. Polyamides Al and A2

[0074] Advantageously, the polyamide Al and / or the polyamide A2 present(s) in the composition according to the invention is / are aliphatic.

[0075] Advantageously, the polyamide Al and / or the polyamide A2 present(s) in the composition according to the invention is / are chosen from PA 11, PA 12, PA 513, PA 516, PA 610, PA 612, PA 613, PA 614, PA 618, PA 1010, PA 1012, PA 1014, PA 1018, PA 129, PA 1212, PA 6 / 12, PA 1010 / 12, PA 1010 / 11, PA 69 / 12, PA 4 / 12, PA 12 / 8 and PA 11 / 12.

[0076] More particularly, polyamide Al and / or polyamide A2 is / are chosen from PA 11, PA 12, PA 612, PA 613, PA 1010, PA 1012, PA 1212, even more preferably chosen from PA 11 and PA 12.

[0077] PA11 has the advantage of being manufactured from plant-based raw materials. Plant materials can be cultivated in large quantities, according to demand, across most of the globe and are bio-based. A bio-based raw material is a natural resource, animal or plant-based, whose stock can be replenished over a short period on a human timescale. In particular, this stock must be able to renew itself as quickly as it is consumed.

[0078] The basic raw material of PA11 is castor oil, extracted from the castor bean plant (the common castor bean), from the castor seeds. PA11 is obtained by polycondensation of 11-aminoundecanoic acid. Difference in ratios

[0079] By "C / N ratio", for the purposes of the present invention, we mean the average number of carbon atoms per nitrogen atom per unit.

[0080] In the case of a PA Z type homopolyamide, where Z designates a motif obtained from an amino acid or a lactam, the number of carbon atoms per nitrogen atom is the number of carbon atoms in the motif. For example, PA 11 obtained by polycondensation of 11-aminoundecanoic acid has a C / N ratio of 11.

[0081] In the case of a PA XY type homopolyamide, where X designates a motif obtained from a diamine and Y designates a motif obtained from a diacid, the number of carbon atoms per nitrogen atom is the average of the number of carbon atoms present in the XY unit. For example, PA 1012, obtained by polycondensation of decanediamine, a diamine in C10, and dodecanedioic acid, a diacid in C12, has a C / N ratio of 11, resulting from the following calculation (10+12) / 2 = 11.

[0082] For copolyamides, for example with the structure XaYa / XbYb, the number of carbon atoms per nitrogen atom is calculated according to the same principle. The calculation is performed in molar proportion of the different amide units, that is to say, the XaYa and XbYb units. Thus, the 11 / 1010 copolyamide, comprising 90 molar percent of 11 and 10 molar percent of 1010, has a molar ratio of 10.9: 90%x11+10%x[(10+10) / 2] = 10.9.

[0083] Polyamide Al has a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10.

[0084] Preferably, the polyamide A2 has a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10.

[0085] Polyamides Al and A2 have in absolute value a difference in C / N ratio equal to Iratio C / N(A1) - ratio C / N (A2)l < 3, preferably Iratio C / N(A1) - ratio C / N (A2)l < 2, preferably Iratio C / N(A1) - ratio C / N (A2)l < 1.

[0086] In other words, the Al and A2 polyamides have similar chain lengths.

[0087] Surprisingly, the mixture of two powders as defined above made it possible to widen the working window towards the low temperature, thus avoiding, or at least reducing, the curling phenomenon. Difference in pattern length

[0088] The Al polyamide comprises at least 45% molar, preferably at least 50% molar, preferably 70%, or 80% or 90%, or advantageously 100% molar of a motif comprising a number of carbon atoms between the amide functions (including the carbonyl of the amide) denoted Cl.

[0089] If the Al polyamide is formed of only one type of unit, as in the case of homopolyamides of lactams or amino acids, then the Al polyamide has only one Cl number.

[0090] As an example, PA11 has a Cl number equal to 11.

[0091] As an example, PA 12 has a Cl number equal to 12.

[0092] If the Al polyamide is formed of two types of unit, as in the case of homopolyamides formed of XY units (diamine.diacid) or of copolyamides, then the Al polyamide has several Cl numbers.

[0093] By way of example, PA610 has a Cl number equal to 6 and a Cl number equal to 10; PA11 / 610 has a Cl number equal to 11, a Cl number equal to 6, a Cl number equal to 10. In other words, if the polyamide PA Al has n units, then n Cl will be taken into consideration to evaluate the ICI-C2I < 3 condition, n being an integer between 1 and 6.

[0094] Polyamide A2 comprises at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2.

[0095] The explanations given for the number Cl also apply to the number C2. In other words, if the polyamide PA A2 has m units, then m C2 will be taken into consideration to evaluate the condition IC1-C2I < 3, m being an integer between 1 and 6.

[0096] Polyamides Al and A2 are chosen so as to respect the following absolute value difference IC1-C2I < 3, preferably Cl-C2I < 2, preferably IC1-C2I < 1.

[0097] If the Al and A2 polyamides contain several Cl and several C2, then at least one condition ICln-C2ml < 3 must be met. Preferably, all the conditions ICln-C2ml < 3 must be met.

[0098] For example, in a composition comprising, among other things, 70% PAU and 30% PA12, the following conditions must be verified:

[0099] Polyamide Al is PAU: ratio C / N(A1) = 11; Cl = 11.

[0100] Polyamide A2 is PA12: ratio C / N(A2) = 12; C2 = 12.

[0101] Regarding the condition Iratio C / N(A1) - ratio C / N(A2)I < 3:

[0102] Ratio C / N(A1) - ratio C / N(A2)I = 111- 121 = 1, the condition is met;

[0103] Regarding the condition IC1-C2I < 3:

[0104] IC11-C2I = Il 1-121 = 1, the condition is also met.

[0105] For example, in a composition comprising, among other things, 70% PA1012 and 30% PA12, the following conditions must be verified:

[0106] Polyamide Al is PAIO. 12 (50 / 50 molar): ratio C / N(A1) = 11; Cli = 10, Cl2 = 12.

[0107] Polyamide A2 is PA12: ratio C / N(A2) = 12; C2 = 12.

[0108] Regarding the condition Iratio C / N(A1) - ratio C / N(A2)I < 3:

[0109] Ratio C / N(A1) - ratio C / N(A2)I = 111- 121 = 1, the condition is met.

[0110] Regarding the condition IC1-C2I < 3: [YES] IC11-C2I = 110-121 = 2 and IC12-C2I = 112-121 = 0, the condition is also respected.

[0112] For example, in a composition comprising, among other things, 80% PAU and 20% PA610, the following conditions must be verified:

[0113] Polyamide Al is PA 11: ratio C / N(A1) = 11; Cl = 11 and

[0114] Polyamide A2 is PA610: ratio C / N(A2) = 8; C2i = 6 and C22 = 10.

[0115] Regarding the condition Iratio C / N(A1) - ratio C / N(A2)I < 3:

[0116] Ratio C / N(A1) - ratio C / N(A2)I = Il 1 - 81 = 3, the condition is met.

[0117] Regarding the condition IC1-C2I < 3:

[0118] IC1-C21I = 111-61 = 5 and IC1-C2J = Il 1-101 = 1, the condition is also met.

[0119] According to another example, in a composition comprising, among other things, 80% PAU and 8% PA6 / 812 (80 / 20 molar), the following conditions must be verified:

[0120] Polyamide Al is PAU: ratio C / N(A1) = 11; Cl = 11 and

[0121] Polyamide A2 is PA6 / 812: C / N ratio (A2) = (0.8*6 + 0.2*10) = 6.8; C2i = 6, C22 = 8, C23 = 12.

[0122] Regarding the condition Iratio C / N(A1) - ratio C / N(A2)I < 3:

[0123] Ratio C / N(A1) - ratio C / N(A2)I = Il 1-6.81 = 4.2, the condition is not met.

[0124] Regarding the condition IC1-C2I < 3:

[0125] Motif 6 is present in a content of at least 50% molar. Therefore, this motif is to be taken into consideration, not motifs 8 and 12.

[0126] IC1-C21I = Il 1-61 = 5, the condition is not met.

[0127] This composition is therefore outside the definition of the invention.

[0128] Preferably, Cl and C2 are greater than or equal to 8, preferably greater than or equal to 9.

[0129] The composition constituting the structure according to the invention preferably comprises:

[0130] PA11 as PA Al and PA12 as PA A2,

[0131] PA11 as PA Al and PA1012 as PA A2,

[0132] PA 12 as PA Al and PA 1012 as PA A2,

[0133] the PA12 as PA Al and the PA612 as PA A2,

[0134] the PA 12 as PA Al and the PA613 as PA A2

[0135] the PA613 as PA Al and the PA12 as PA A2

[0136] the PA612 as PA Al and the PA12 as PA A2,

[0137] the PA513 as PA Al and the PA516 as PA A2,

[0138] the PA516 as PA Al and the PA513 as PA A2,

[0139] the PA 1012 as PA Al and the PA 12 as PA A2,

[0140] the PA 1012 as PA Al and the PA11 as PA A2,

[0141] the PA1010 as PA Al and the PA12 as PA A2,

[0142] The PA 1010 as PA Al and the PA11 as PA A2. Polyamide powders

[0143] Polyamide Al powder and polyamide A2 powder can be obtained by any suitable type of process, for example by anionic polymerization, by dissolution-precipitation process, or by grinding, for example, granulation grinding.

[0144] Preferably, the Al polyamide powder has a melting temperature (Tf) between 150 and 230°C, preferably between 160 and 220°C, even more preferably between 170 and 210°C.

[0145] Preferably, the polyamide A2 powder has a melting temperature (Tf) between 150 and 230°C, preferably between 160 and 220°C, even more preferably between 170 and 210°C. Additives

[0146] The additives may represent less than 5% by mass of the total mass of the composition. Preferably, the additives represent less than 3%, preferably less than 2% by mass of the total mass of the composition.

[0147] Among the additives, we may mention flow agents, stabilizing agents (light, in particular UV, and heat), optical brighteners, colorants, pigments, energy-absorbing additives (including UV absorbers), a wax (for example, polyethylene and polypropylene wax, polytetrafluoroethylene wax, ketones, acid, partially esterified acid, acid anhydride, ester, aldehydes, amides, their derivatives and mixtures thereof) and / or surfactants.

[0148] Examples of flow agents include hydrophilic or hydrophobic silica. Advantageously, the flow agent represents 0.01 to 0.4% by mass relative to the total mass of the composition. In other embodiments, the powder composition does not include a flow agent.

[0149] The pigment can be, for example for HSS or MJF technology, a pigment having an absorbance of light at a wavelength of 1000 nm, as measured according to ASTM E1790, of less than 40%. Charges

[0150] The composition of polymer powders may also include one or more fillers. The fillers generally represent less than 40% by mass, In particular, less than 30% by mass, and preferably less than 25% by mass, relative to the total mass of the final powder composition. Among the fillers, examples include reinforcing fillers, notably mineral fillers such as carbon black, talc, nanotubes (carbon or non-carbon), and fibers, particularly glass or carbon fibers, ground or unground, or glass in another form, for example, as flakes or beads, hollow or solid. Other fillers providing an additional property may be used without departing from the scope of the invention, for example, flame retardants, fillers providing electrical or thermal conductivity.

[0151] Process for preparing the powder composition

[0152] According to one aspect, the invention relates to a method for manufacturing the composition of powders as described above, by mixing:

[0153] (i) a polyamide Al powder having a C / N ratio greater than or equal to 8, of preferably greater than or equal to 9, advantageously greater than or equal to 10,

[0154] (ii) more than 10% by mass, preferably 15 to 50% by mass, more preferably 30 to 50% by mass, relative to the total mass of the composition, of a polyamide A2 powder,

[0155] polyamide A2 being distinct from polyamide Al by their chemical nature,

[0156] polyamides Al and A2 having in absolute value at least one difference in C / N ratio equal to Iratio C / N(A1) - ratio C / N (A2)l < 3,

[0157] polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted Cl,

[0158] polyamide A2 comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2,

[0159] with at least one of the ICI-C2I < 3 equations satisfied,

[0160] (iii) 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers relative to the total mass of the composition.

[0161] The mixing can typically be carried out by dry mixing.

[0162] The composition of polyamide powders may comprise from 11 to 50% by mass, preferably 15 to 50%, 20 to 50%, 30 to 50%, 15 to 45%, 15 to 40%, 15 to 30%, 20 to 50%, 20 to 40%, 25 to 35%, 30 to 50% or even 30 to 40% by mass of polyamide powder A2, relative to the total mass of the composition.

[0163] According to one embodiment, the process for manufacturing the powder composition as described above is carried out by mixing: i. 50 to 85%, preferably 55 to 70%, by mass of the Al polyamide powder as defined above, ii. 15 to 50%, preferably 20 to 50%, even more preferably 30 to 50% by mass of the polyamide A2 powder as defined above, iii. 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers,

[0164] relative to the total mass of the composition.

[0165] Polyamide Al and A2 polymer powders can be manufactured using conventional processes.

[0166] Typically, the polyamide Al powder and / or the polyamide A2 powder contained in the composition can / can be obtained by grinding polymers in the form of extruded granules or flakes, according to conventional techniques.

[0167] The grinding can be ambient temperature grinding.

[0168] The grinding can be cryogenic grinding. In this process, the material to be ground is cooled, for example by means of liquid nitrogen, liquid carbon dioxide or liquid helium, to make the material easier to grind.

[0169] Grinding can be carried out on equipment known for this purpose, for example by means of a counter-rotating pin mill, a hammer mill or in a whirl mill.

[0170] Polyamide powders can also be manufactured by other known processes in this field, for example the preparation of a polyamide 12 powder by precipitating anionic polymerization as described for example in EP 1 814 931 B1 or FR 06.56024 B1 or by dissolution precipitation process as described in US patent 4334056.

[0171] The powders can be sieved or subjected to a selection step to obtain the desired particle size profile.

[0172] According to a certain preparation method, the Al and / or A2 polyamide powder may, where appropriate, be subjected to different treatments, in particular thermal or hydraulic treatments. Reference may be made, in particular, to patent application EP 1413595 AL

[0173] When the powder composition includes, in addition to polyamide powders, one or more additives and / or one or more fillers, preferably reinforcing or flame-retardant fillers, these additives and / or fillers can be incorporated by mixing in the molten state, for example by extrusion (compounding) and granulation followed by grinding of the granules.

[0174] Preferably, the additives and / or fillers are added to the powder by dry blend.

[0175] According to one embodiment, the step of introducing the additives and / or fillers can be carried out during the synthesis of the Al and / or A2 polyamide powder.

[0176] For example, it is possible to mix polyamide Al or polyamide A2 by means of coprecipitation of the polymer with a solution in the presence of certain additives and / or fillers (dissolution / precipitation). The conditions can be adapted by those skilled in the art. Reference may be made, for example, to document EP 0863174 Bl.

[0177] It is also possible to use several of these processes, depending on the additives, for their introduction into the polymer powder.

[0178] Additives and / or fillers may be used in any form suitable according to the preparation method.

[0179] According to one embodiment, one or more additives / fillers are used in powder form. The shape and size of the particles forming the powder are not particularly limited, except by the application of 3D printing by sintering. The particles are most often spherical. However, their use in other forms, such as rods or lamellars, is not excluded.

[0180] When additives / fillers are added to the polymer in dry-blend, they advantageously have a median volume diameter Dv50 substantially equal to or less than that of the powder with which it will be mixed. 3D printing process by sintering

[0181] The process of the invention may in particular be a selective laser sintering (SLS) process, an MJF (Multi Jet Fusion) type sintering process or an HSS (High Speed ​​Sintering) type sintering process.

[0182] The SLS process is widely known. In this context, reference can be made in particular to documents US 6,136,948 and WO 96 / 06881.

[0183] In this type of process, a thin layer of powder is deposited 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 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.Electromagnetic radiation, for example in the form of a laser, then provides the energy needed 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 that has the shape of an object stored in memory and reproduces it as slices. Next, the horizontal plate is lowered by a height corresponding to the thickness of a powder layer, and a... A new layer of powder is spread, heated, and then sintered in the same way. The procedure is repeated until the object has been made.

[0184] The layer of powder deposited on a horizontal plate may, before sintering, have 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 may have, for example, a thickness of 10 to 150 µm, and preferably 30 to 120 µm.

[0185] In 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 selectively applied to the chosen region of the building material. The melting agent penetrates the layer of the building material and transfers the absorbed energy to the adjacent building material, causing it to melt or sinter. Through the melting, bonding, and subsequent hardening of each layer of the building material, the object is formed.

[0186] 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.

[0187] Advantageously, the use of the polyamide powder composition described below in these processes does not require any particular modification. On the other hand, it makes it possible to obtain parts with a good surface finish, in particular lower roughness and better definition.

[0188] Advantageously, the process allows the composition of polyamide powders to be implemented in several successive constructions. In this case, it can be reused alone or in a mixture with other powders, whether recycled or not. Examples

[0189] The examples below illustrate the present invention without limiting its scope. In the examples, unless otherwise indicated, all percentages and parts are expressed by mass. Particle size

[0190] The powders were characterized in terms of particle size using an Insitec type laser diffractometer from Malvem with RT Sizer type software, according to ISO 13320: 2009.

[0191] The light from a laser is directed at particles that are moving in the air.

[0192] The measurement is carried out on 30 g of powder. Measurement of the melting temperature (Tf)

[0193] The melting temperature of the powders was measured by DSC on a TA Instruments Q2000 calorimeter, in accordance with standard NF EN ISO 11357-3:2018. The value was determined during the heating step at a rate of 20 °C / min during the first heating. Powder compositions

[0194] Al powder is a polyamide 11 powder marketed by the company ARKEMA under the name Rilsan® Invent Natural.

[0195] The A2 powder is a polyamide 12 powder marketed by the company ARKEMA under the name ORGASOL® Invent Smooth.

[0196] The properties of the powders used in the examples are shown in Table 1 below.

[0197] [Tables] Powder Powder Dv50 (pm) SPAN Dvl0( pm) Tf (°C) Powder Al Polyamide 11 Rilsan® Invent Natural 47 1.33 19 202°C Powder A2 Polyamide 12 ORGASOL® Invent Sm ooth 42 0.43 33 181°C

[0198] 10%, 30% and 50% by mass of Powder A2 were added to Powder Al in dry blending in a Henschel mixer at a rotational speed of 900 rpm for 100 seconds.

[0199] The compositions of the tested powders are shown in Table 2 below.

[0200] [Tables2] Powder Composition: Powder A1, Powder A2, Powder 0 (comparative example) 100%, 0%; Powder 1 (comparative example) 90%, 10%; Powder 2 70%, 30%; Powder 3 50%, 50% Measurement of the half-crystallization time

[0201] The temperature gain measurement for the working window was carried out by measuring the half-crystallization time according to the protocol below.

[0202] The apparatus used is a TA Instruments Q2000. The capsules containing the sample to be analyzed or the reference are TA Instruments Tzero aluminum crucibles. An empty reference capsule and a A capsule containing 5 to 10 mg of the sample to be analyzed. During the analysis, a flow of nitrogen is sent into the device to prevent thermo-oxidation of the polymer.

[0203] The thermal profile of the analysis is as follows: - Equilibration at 0°C for 5 minutes - Temperature rise up to 250°C at 60°C / min - Isothermal at 250°C for 5 minutes - Cooling to the desired measurement temperature at 60°C / min - Isothermal at the measurement temperature for 4 hours.

[0204] The crystallization rate at time t is calculated using Equation 1, where W corresponds to the heat flux exchanged at time t, t0 is the initial measurement time corresponding to the beginning of the isotherm, and tfc is the final measurement time corresponding to the end of the isotherm. The half-crystallization time corresponds to the time at which the crystallization rate is equal to 50%.

[0205] [Math.l] f 14^(0 dt Xc(0 = — ^(t) dt - r3 -

[0206] Equation 1: Crystallization rate Xc Curling

[0207] Powder compositions 0 to 3 were used to manufacture IB XY test specimens (IB specimen according to ISO 527-1:2019, called "XY" because it is printed in the printer plane, i.e., horizontally) by laser sintering 3D printing on a P1000 machine (marketed by Prodways) with the powder layer thickness set to 100 µm. The printing parameters used were as follows:

[0208] Laser power: 24W

[0209] Laser speed: 3000mm / s

[0210] Distance between two laser passes: 0.25mm

[0211] The powder bed in the machine was observed visually.

[0212] Curling corresponds to the raising of the corners and edges of the bed of powder being sintered. Results

[0213] The results in curling observation and in working window widening gain have been summarized in Table 3 below.

[0214] [Tables3] Powder Composition Curling at 174°C Working Window Enlargement Gain Powder 0 (comparative example) Yes / Powder 1 (comparative example) Yes / Powder 2 No 0.6°C Powder 3 No 1.4°C

[0215] It has been observed that prints made with Powder 2 and Powder 3 do not have a curling phenomenon, whereas curling has been observed for prints made with Powder 0 and Powder 1. These deformations of the molten layers lead to dimensioning defects in the final parts.

[0216] Powder mixtures 2 and 3 therefore made it possible to produce satisfactory sintered parts at T=174°C, which was impossible with powder 0 and powder 1.

[0217] It can also be seen in [Fig. 1] that the half-crystallization times at 174°C of Powders 2 and 3 are 17.1 and 21.8 minutes, respectively. These half-crystallization times correspond to those of Powder 0 at 174.6°C and 177.4°C, respectively. This means that the crystallization rates of Powders 2 and 3 at 174°C are equal to those of Powder 0 at 174.6°C and 177.4°C. Powders 2 and 3 can therefore be processed at 174°C in the same way as Powder 0 at 174.6°C and 177.4°C. Powders 2 and 3 therefore exhibit a gain in their transformation temperatures compared to Powder 0 of 0.6°C and 1.4°C, respectively, towards lower temperatures. This equates to a widening of the working window towards lower temperatures of 0.6°C and 1.4°C.

[0218] Whereas in cases where Powder 1 contains 10% of Polyamide A2 Powder, no increase in half-crystallization time and no improvement in working window were observed.

[0219] Thus, the addition of 30% or 50% of the polyamide A2 powder to the polyamide Al powder increased the crystallization time of the powder mixture, which made it possible to print parts at a lower temperature while avoiding curling, which also provides a benefit of less powder evolution, thus promoting its reuse in another printing test.

Claims

Demands

1. A polyamide powder composition suitable for use in 3D printing by sintering, comprising: (i) a polyamide Al powder having a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10, (ii) more than 10% by mass, preferably 15 to 50% by mass, more preferably 30 to 50% by mass, relative to the total mass of the composition, of a polyamide A2 powder, the polyamide A2 being distinct from the polyamide Al by their chemical nature, the polyamides Al and A2 having in absolute value at least a C / N ratio difference equal to 1 / C / N(A1) - 1 / C / N(A2) < 3, the polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted Cl, polyamide A2 comprising at least 45 mol%,preferably at least 50 mol%, preferably at least 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2, with at least one of the IC 1-C2I < 3 equations satisfied, (iii) 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers relative to the total mass of the composition.

2. Composition according to claim 1, wherein the composition has a Dv50 of 20 to 100 pm, preferably of 30 to 80 pm, even more preferably of 40 to 60 pm.

3. Composition according to claim 1 or 2, wherein polyamide A2 has a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10.

4. Composition according to any one of the preceding claims comprising, relative to the total mass of the composition: i. 50 to 85%, preferably 55 to 70%, by mass of Al polyamide powder, ii. 15 to 50%, preferably 20 to 50%, even more preferably 30 to 50% by mass of polyamide A2 powder, iii. 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers.

5. Composition according to any one of the preceding claims, wherein the following condition is met: Iratio C / N(A1) - ratio C / N (A2)l < 2, preferably Iratio C / N(A1) - ratio C / N (A2)l < 1.

6. Composition according to any one of the preceding claims, wherein the following condition is met IC1-C2I < 2, preferably IC1-C2I < 1.

7. Composition according to any one of the preceding claims, wherein polyamide Al and / or A2 are aliphatic polyamides.

8. Composition according to any one of the preceding claims, wherein the polyamide Al and / or the polyamide A2 is / are selected from PA 11, PA 12, PA 513, PA 516, PA 610, PA 612, PA 613, PA 614, PA 618, PA 1010, PA 1012, PA 1014, PA 1018, PA 129, PA 1212, PA 6 / 12, PA 1010 / 12, PA 1010 / 11, PA 69 / 12, PA 4 / 12, PA 12 / 8 and PA 11 / 12, preferably selected from PA 11, PA 12, PA 612, PA 613, PA 1010, PA 1012, PA 1212, even more preferably chosen from PA 11 and PA 12.

9. Composition according to any one of the preceding claims, wherein the melting temperature (Tf) of the Al polyamide powder and / or the A2 polyamide powder is / are between 150 and 230°C, preferably between 160 and 220°C, even more preferably between 170 and 210°C.

10. A process for manufacturing the powder composition, by mixing: (i) a polyamide Al powder having a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10, (ii) more than 10% by mass, preferably 15 to 50% by mass, more preferably 30 to 50% by mass, relative to the total mass of the composition, of a polyamide A2 powder, polyamide A2 being distinct from polyamide Al by their chemical nature, Polyamides Al and A2 having, in absolute value, at least one C / N ratio difference equal to Iratio C / N(A1) - ratio C / N(A2)l < 3, polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted Cl, polyamide A2 comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2, with at least one of the equations IC 1-C2I < 3 satisfied, (iii) 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers relative to the total mass of the composition.

11. The process according to claim 10, being carried out by mixing: i. 50 to 85%, preferably 55 to 70%, by mass of polyamide Al powder, ii. 15 to 50%, preferably 20 to 50%, even more preferably 30 to 50% by mass of polyamide A2 powder, iii. 0 to 40%, preferably 0.05 to 40% by mass of additives and / or fillers, relative to the total mass of the composition.

12. Method according to claim 10 or 11, the mixing being carried out by dry mixing.

13. A 3D printing method, preferably an electromagnetic radiation-induced sintering method, using at least in part a powder composition according to any one of claims 1 to 9.

14. Manufactured article obtained by the 3D printing process of claim 13.

15. Use of more than 10% by mass, preferably 15 to 50% by mass, more preferably 30 to 50% by mass, of a polyamide A2 powder, relative to the total mass of the composition, in a composition comprising a polyamide Al powder having a C / N ratio greater than or equal to 8, preferably greater than or equal to 9, advantageously greater than or equal to 10, Polyamide A2 is distinct from polyamide Al due to their chemical nature. polyamides Al and A2 having in absolute value at least a difference in C / N ratio equal to Iratio C / N(A1) - ratio C / N (A2)l < 3, polyamide Al comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the carbonyl of the amide) denoted Cl, polyamide A2 comprising at least 45 mol%, preferably at least 50 mol%, preferably 70%, or 80% or 90%, or advantageously 100 mol% of a motif comprising a number of carbons between the amide functions (including the amide carbonyl) denoted C2, with at least one of the equations IC 1-C2I < 3 respected, in a 3D printing process, preferably by sintering, to improve the working window.