Composition of thermoplastic polymer powders for 3D printing

Abstract

The present invention relates to a composition of thermoplastic polymer powders for manufacturing articles by 3D printing, in particular by sintering, comprising a mixture of powders of thermoplastic polymers, one of which is present in a small amount, making it possible to obtain printed parts having an improved mechanical property. The invention also relates to a process for preparing the powder composition, to the use of the composition in a laser sintering manufacturing process, and to the articles produced from said powder composition.

Description

[0001] DESCRIPTION

[0002] Title: Composition of thermoplastic polymer powders for 3D printing

[0003] Field of invention

[0004] The present invention relates to a composition of thermoplastic polymer powders for the manufacture of articles by 3D printing, in particular by sintering, comprising a mixture of thermoplastic polymer powders, one of which is present in a small quantity, making it possible to obtain printed parts having an improved mechanical property.

[0005] The invention also relates to a process for preparing this powder composition as well as its use in a laser sintering manufacturing process, and to the articles manufactured from said powder composition.

[0006] Technical background

[0007] Additive manufacturing on thermoplastic polymer powder beds (SLS, M JF, HSS, etc.) allows the construction of parts with complex geometry, including in series production. It allows the production of a large number of parts simultaneously, with excellent resolution and very good mechanical properties, which gives them an advantage over other additive manufacturing processes such as fused deposition.

[0008] Polyamide powders are particularly interesting for the aforementioned additive manufacturing technology. Examples include commercial powders based on polyamide 12 such as Orgasol® from Arkema, Durafom® from 3D-Systems, Vestosint® from Evonik, or PA2200® from EOS.

[0009] We can also cite commercial powders based on polyamide 11 such as Rilsan® from Arkema.

[0010] Other types of thermoplastic polymers are also available on the market, for example polyetherketoneketone powders such as Kepstan® from Arkema.

[0011] Parts printed from these powders have interesting mechanical properties. However, there is a continuous need to improve their mechanical properties, particularly fracture properties such as elongation at break, in order to meet the search for performance with increasingly high requirements over time. It is also known that fracture properties are, in general, lower following an additive manufacturing process compared to more traditional processes, such as injection; which reinforces the need to improve fracture properties for additive manufacturing processes.

[0012] Summary of the invention

[0013] Thus, the aim of the present invention is to propose a composition of thermoplastic polymer powders containing at least two distinct and particularly chosen thermoplastic polymer powders, one powder of which is present in the composition in a small quantity (called "auxiliary powder"), making it possible to obtain sintered objects with better mechanical properties, in particular in terms of elongation at break.

[0014] For the purposes of the present invention, the two powders of distinct thermoplastic polymers may be powders of the same thermoplastic polymer or two different thermoplastic polymers. The powders of thermoplastic polymers differ in at least one of their properties. These properties may be their appearance, for example their particle size, or their thermal properties (for example, the degree of crystallinity, the nature of the crystalline phases, the melting temperature, the enthalpy of fusion, etc.) or their rheological properties.

[0015] According to a first aspect, the invention relates to a composition of thermoplastic polymer powders comprising:

[0016] (i) a thermoplastic polymer powder A;

[0017] (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a thermoplastic polymer powder B, powder B having a melting point (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume melt index (MVR) ratio of powder B to volume melt index (MVR) of powder A greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to standard ISO 1133. According to another aspect, the subject of the invention is a composition of thermoplastic polymer powders comprising, relative to the total mass of the composition:

[0018] (i) 59.5 to 99.5% by mass of a thermoplastic polymer powder A as defined above;

[0019] (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, of a thermoplastic polymer powder B as defined above;

[0020] (iii) 0 to 40% by mass, preferably 0.05 to 40% by mass of one or more additives and / or one or more fillers.

[0021] The composition of thermoplastic polymer powders comprises 0.1 to 3% by mass, preferably 0.1 to 2%, 0.1 to 1.8%, 0.1 to 1.5%, 0.5 to 2%, 0.5 to 1.8%, 0.5 to 1.5%, 0.7 to 1.5%, 0.9 to 1.5%, 1 to 1.5% or 0.9 to 1.4% by mass of powder B, relative to the total mass of the composition.

[0022] According to one embodiment, the melting temperature (Tf) of powder B is at least 1°C lower than that of powder A, preferably at least 3°C ​​lower than that of powder A, or at least 10°C lower than that of powder A.

[0023] According to one embodiment, the difference between the melting temperatures of powders B and A is less than or equal to 30°C.

[0024] According to one embodiment, the Tf of powder B is equal to the Tf of powder A and the MVR ratio of powder B to MVR of powder A is greater than 3, preferably greater than 5, more preferably greater than 10, even more preferably greater than 20, the MVR being measured according to the ISO 1133 standard.

[0025] According to one embodiment, powder B has a melting temperature lower than the Tf of powder A and an MVR ratio of the powder to MVR of powder A greater than 3, preferably greater than 5, more preferably greater than 10, even more preferably greater than 20, the MVR being measured according to standard ISO 1133.

[0026] The thermoplastic polymer powders that can be used in the context of the present invention may in particular be chosen from polyolefins such as polypropylene and polyethylene (olefin base waxes would not fall outside the scope of the present invention), polycarbonate, polymethylmethacrylate (PMMA), polyamides and thermoplastic elastomers such as polyether block amides (PEBA), polyesters and polyether blocks (COPE), thermoplastic polyurethanes (TPU) and their mixtures, PAEK such as PEKK and PEEK-based copolymer, preferably polyamides and polyether block amides, even more preferably polyamides.

[0027] Thermoplastic polymers are typically semi-crystalline thermoplastic polymers.

[0028] According to one embodiment, the thermoplastic polymer powders used in the context of the present invention are to be chosen from polyolefins such as polypropylene and polyethylene (olefinic base waxes would not depart from the scope of the present invention), polyamides and thermoplastic elastomers such as polyether block amides (PEBA), polyesters and polyether blocks (COPE), thermoplastic polyurethanes (TPU) and their mixtures, PAEK such as PEKK and PEEK-based copolymer, preferably polyamides and polyether block amides, even more preferably polyamides.

[0029] Thus, according to a particular aspect of the invention, the present invention aims to propose a composition of polyamide powders containing at least two distinct and particularly chosen polyamide powders, one powder of which is present in the composition in a small quantity (called "auxiliary powder"), making it possible to obtain sintered objects with better mechanical properties, in particular in terms of elongation at break.

[0030] Preferably, powder A and / or powder B is a polyamide powder, preferably, powder A and powder B are polyamide powders.

[0031] According to one embodiment, powder A is a polyamide 12 or polyamide 11 powder.

[0032] According to one embodiment, powder B is a polyamide 12 or polyamide 11 powder.

[0033] According to one embodiment, when powder A is a polyamide 11 powder, powder B is a polyamide 11 powder or a polyamide 12 powder.

[0034] According to one embodiment, when powder A is a polyamide 12 powder, powder B is a polyamide 12 powder.

[0035] According to one embodiment, powder A has a melting temperature (Tm) less than or equal to 250°C, preferably less than or equal to 210°C. According to one embodiment, powder B has a melting temperature (Tm) less than or equal to 210°C, preferably between 80 and 210°C, preferably between 100 and 200°C.

[0036] The melt flow rate (MVR) of powder B can typically be greater than 50 cm 3 / 10min, preferably greater than 100 cm 3 / 10min, even more preferably greater than 200 cm 3 / 10 min.

[0037] According to one embodiment, powder A has a Dv50 of 20 to 100 pm, preferably of 30 to 80 pm, even more preferably of 40 to 60 pm.

[0038] According to one embodiment, powder B has a Dv50 of 1 to 60 pm, preferably of 3 to 50 pm, even more preferably of 4 to 20 pm.

[0039] The Dv50 of powder B can be higher, lower or equal to the Dv50 of powder A.

[0040] Preferably, the Dv50 of powder B is lower than the Dv50 of powder A. According to one embodiment, the Dv50 of powder B is 5 to 80% of the Dv50 of powder A, preferably 10 to 60% of the Dv50 of powder A.

[0041] It has been observed in the context of the present invention that the addition of a small quantity of a particular auxiliary powder to a thermoplastic polymer powder, in particular to a polyamide powder, suitable for 3D printing by sintering, surprisingly makes it possible to obtain sintered objects with better mechanical properties, in particular in terms of improved elongation at break.

[0042] The present invention also relates to a 3D printing method, preferably an electromagnetic radiation-induced sintering method, using the powder as defined above, or a powder comprising a portion of said non-agglomerated powder and recovered after one or more builds within the same or a different printing process.

[0043] Preferably, the electromagnetic radiation is chosen from one or more laser beams, infrared radiation or UV radiation.

[0044] The present invention also relates to an article obtained by the 3D printing process as defined above.

[0045] The article can be chosen from prototypes, models and parts, particularly in the automotive, nautical, aeronautical, aerospace, medical (prosthetics, hearing systems, cellular tissues, etc.) fields, textiles, clothing, fashion, decoration, design, cases for electronics, telephony, IT, lighting, sport, industrial tools.

[0046] According to yet another aspect, the invention relates to the use of 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a thermoplastic polymer powder B, in a composition containing a thermoplastic polymer powder A, in a 3D printing process, preferably by sintering, the powder B having a melting temperature (Tf) less than or equal to, preferably less than, the Tf of the powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume flow index (MVR) ratio of powder B to volume flow index (MVR) of powder A being greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to standard ISO 1133, to improve the elongation at break.

[0047] The thermoplastic polymer powders are preferably polyamide powders.

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

[0049] Description of the invention

[0050] Definition

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

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

[0053] The Dv50 also called herein "volume median diameter" corresponds to the value of the particle size which divides the population of particles examined exactly in two, as measured by laser diffraction according to the ISO 13320: 2009 standard, for example on a Malvern diffractometer of the Insitec® type. The term "melting temperature (Tf)" is understood to mean the temperature at which an at least partially crystalline compound passes into the viscous liquid state as measured according to the NF EN ISO 11357-3:2018 standard. In the present invention, the value was determined during the heating step at a rate of 20 °C / min during the first heating.

[0054] Unless otherwise stated, this refers more specifically to the peak melting temperature as defined below.

[0055] More specifically, the following terms are understood to mean in relation to melting temperature:

[0056] • a “peak” means the portion of the differential scanning calorimetry (DSC) thermogram that deviates from the specimen baseline to reach a maximum or minimum and then returns to the specimen baseline. Such a peak may indicate a first-order transition;

[0057] • a “baseline” means the part of the recorded thermogram without any transition, in particular here without any first-order transition of the melting type. At a transition zone, a virtual baseline can be determined: it is an imaginary line drawn through the transition zone, assuming that the heat due to the transition is zero. The virtual baseline can be drawn by interpolating the baseline of the specimen by means of a straight line;

[0058] • a “melting peak temperature” means the temperature at which the distance is greatest between the thermogram and the virtual baseline during a peak.

[0059] The melt flow rate (MVR) is measured by a Zwick MFlow measuring device, manufactured by Zwick according to ISO 1133.

[0060] Elongation at break is measured according to ISO 527-1:2019.

[0061] In this description, it is specified that when reference is made to intervals, expressions of the type "between... and..." or "from... to..." include the limits of the interval. 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).

[0062] Composition of thermoplastic polymer powders

[0063] Thermoplastic polymer powders A and B

[0064] Thermoplastic polymer powders A and B may be commercial powders available on the market.

[0065] Examples include commercial powders based on polyamide 12 such as Orgasol® from Arkema, Durafom® from 3D-Systems, Vestosint® from Evonik, or PA2200® from EOS.

[0066] We can also cite commercial powders based on polyamide 11 such as Rilsan® Invent from Arkema.

[0067] Commercial powders based on PEKK such as Arkema's Kepstan® can also be mentioned.

[0068] Thermoplastic polymer powders A and B can be obtained by any suitable method known to those skilled in the art.

[0069] Preferably, powder A and / or powder B is a polyamide powder.

[0070] Preferably, powders A and B are polyamide powders, even more preferably, chosen from polyamide 11 and polyamide 12 powders.

[0071] The polyamides within the scope of the present invention may be homopolyamides or copolyamides.

[0072] For the purposes of the invention, homopolyamide means the polymerization products of aminocarboxylic acid, lactam or diacid monomers with diamines.

[0073] By copolyamide in the sense of the invention, is meant a copolymer resulting from the polymerization of at least two different monomers, called "co-monomers", that is to say at least one monomer and at least one co-monomer (monomer different from the first monomer), being chosen from aminocarboxylic acids, lactams, diamine diacid couples. The copolyamide may comprise a so-called majority monomer, that is to say representing at least 80% by mass of the total mass of the mixture of monomers, and at least one so-called minority co-monomer, representing at most 20% by mass of the total mass of the total mixture of monomer(s) and co-monomer(s).

[0074] The term "monomer" in the following description should be taken to mean "repeating unit". The case where a repeating unit is made up of the association of a diacid with a diamine is special. It is considered that it is the association of a diamine and a diacid, that is to say the diamine.diacid pair (in equimolar quantity), which corresponds to the monomer. This is explained by the fact that individually, the diacid or the diamine is only a structural unit, which is not sufficient on its own to form a polymer.

[0075] Examples of amino acid or aminocarboxylic acid monomers include those having 4 to 18 carbon atoms, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic, n-heptyl-11-aminoundecanoic and 12-aminododecanoic acids.

[0076] Examples of lactam monomers include those having 3 to 18 carbon atoms on the main ring and which may be substituted. Examples include p,p-dimethylpropriolactam, a,a-dimethylpropriolactam, amylolactam, caprolactam also known as lactam 6, capryllactam also known as lactam 8, oenantholactam, 2-pyrrolidone and lauryllactam also known as lactam 12.

[0077] Examples of dicarboxylic acids include acids having between 4 and 18 carbon atoms. Examples include adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid.

[0078] Examples of diamines include aliphatic diamines having 4 to 18 atoms, which may be aryl and / or saturated cyclic. Examples include hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, 5-dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophoronediamine (IPD), methyl pentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, and trimethylhexamethylenediamine.

[0079] According to one embodiment, powder A is a polyamide powder, which may be a homopolyamide or a copolyamide.

[0080] According to one embodiment, powder B is a polyamide powder, which may be a homopolyamide or a copolyamide.

[0081] According to one embodiment, powder A and / or powder B is chosen from PA 6, PA 11, PA 12, PA 66, PA 610, PA 613, PA 611, PA 612, PA 614, PA 618, PA 1010, PA 1012, PA 1014 or PA 1018.

[0082] According to one embodiment, powder A and / or powder B is chosen from PA 6 / 12, PA 6 / 66, PA 1010 / 12, 1010 / 11, PA 6 / 12 / 66, PA 6 / 69 / 11 / 12, PA 6 / 66 / 11 / 12, PA 69 / 12, PA 4 / 6, PA 4 / 12, PA 6 / 11, PA 12 / 8, PA11 / 4, PA 11 / 12, PA 8 / 6, PA 8 / 4, PA 12 / 8, PA 12 / 11.

[0083] Preferably, powder A and / or powder B is a homopolyamide 11 or 12 powder.

[0084] Preferably, powder A and / or powder B is a copolyamide 11 or 12 powder. According to one embodiment, powder A is a copolyamide 11 powder containing an amino-11-undecanoic monomer, preferably containing a majority amino-11-undecanoic monomer. Advantageously, the minority comonomer comprises amino-12-dodecanoic, lactam 12, caprolactam and / or capryllactam.

[0085] According to one embodiment, powder A is a copolyamide 12 powder containing a monomer of amino-12-dodecanoic acid or a monomer of lactam 12, preferably containing a majority monomer of amino-12-dodecanoic acid or a monomer of lactam 12. Advantageously, the minority comonomer comprises amino-11-undecanoic acid, caprolactam and / or capryllactam.

[0086] According to one embodiment, the minority co-monomer represents from 0.1 to 20% by mass, preferably from 0.5 to 15%, from 1% to 10%, from 1 to 7%, from 1 to 5% by mass of the total mass of the monomer(s) and comonomer(s). Additives

[0087] The additives generally represent less than 5% by mass relative to the total mass of the composition. Preferably, the additives represent less than 3%, preferably less than 2% of the total mass of the composition.

[0088] Additives include flow agents, stabilizers (light, especially UV, and heat), optical brighteners, dyes, pigments, energy-absorbing additives (including UV absorbers), a wax (e.g., polyethylene and polypropylene wax, polytetrafluoroethylene wax, ketone wax, acid wax, partially esterified acid wax, acid anhydride wax, ester wax, aldehyde wax, amide wax, derivatives thereof, and mixtures thereof) and / or surfactants.

[0089] Among the flow agents, mention may be made, for example, of a hydrophilic or hydrophobic silica. Advantageously, the flow agent represents from 0.01 to 0.4% by mass relative to the total mass of the composition. In other embodiments, the powdery composition does not comprise a flow agent.

[0090] The pigment may be, for example for HSS or MJ F technology, a pigment having an absorbance of light with a wavelength of 1000 nm, as measured according to ASTM E1790, of less than 40%.

[0091] Charges

[0092] The thermoplastic polymer powder composition may also comprise 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, reinforcing fillers may be mentioned, in particular mineral fillers such as carbon black, talc, nanotubes, carbon or not, and fibers, in particular glass or carbon fibers, ground or not, or glass in another form, for example in the form of flakes or beads, hollow or not. Other fillers providing an additional property may be used without departing from the scope of the invention, for example flame-retardant fillers, fillers providing electrical or thermal conductivity. Method for preparing the powder composition

[0093] According to one aspect, the invention relates to a method for manufacturing the powder composition as described above, by mixing: i. a thermoplastic polymer powder A; ii. 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a polyamide powder B, powder B having a melting point (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume melt index (MVR) ratio of powder B to volume melt index (MVR) of powder A being greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to standard ISO 1133; iii. possibly one or more additives and / or one or more fillers.

[0094] Mixing can typically be achieved by dry mixing.

[0095] According to one embodiment, the method for manufacturing the powder composition as described above is carried out by mixing:

[0096] (i) 59.5 to 99.5% by mass of a thermoplastic polymer powder A;

[0097] (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a thermoplastic polymer powder B, powder B having a melting point (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume melt index (MVR) ratio of powder B to volume melt index (MVR) of powder A being greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to standard ISO 1133;

[0098] 0 to 40% by mass, preferably 0.05 to 40% by mass of one or more additives and / or one or more fillers, relative to the total mass of the composition. The thermoplastic polymer powders A and B can be manufactured according to the usual processes.

[0099] Typically, the powder A and / or B contained in the composition can be obtained by grinding thermoplastic polymers in the form of extruded granules or flakes, according to conventional techniques.

[0100] Grinding can be room temperature grinding.

[0101] 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.

[0102] 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.

[0103] The powder A and / or B contained in the composition can obviously be obtained by any other process other than the grinding process known to those skilled in the art.

[0104] Depending on a certain method of preparation, the thermoplastic polymer powder may be subjected to different treatments, in particular thermal or hydraulic treatments. Reference may be made in particular to patent application EP 1413595 A1.

[0105] When the powder contains, in addition to the polymer powders, one or more additives and / or one or more fillers, preferably reinforcing and / or flame-retardant fillers, these additives and / or fillers may be incorporated by melt mixing, for example by extrusion (compounding) and granulation followed by grinding of the granules.

[0106] Preferably, additives and / or fillers are added by dry blending.

[0107] According to one embodiment, the step of introducing the additives and / or fillers can be carried out during the synthesis of powder A and / or B.

[0108] For example, it is possible to mix polymer A or polymer B by means of co-precipitation of the polymer from a solution in the presence of certain additives and / or fillers (dissolution / precipitation). The conditions can be easily adapted by those skilled in the art. Reference may be made, for example, to document EP 0863174 B1. It is also possible to use several of these methods, depending on the additives, for their introduction into the polymer powder.

[0109] Additives and / or fillers may be used in any form suitable for the preparation method.

[0110] According to one embodiment, one or more additives / fillers are used in powder form. The shape and size of the particles forming the powder is not particularly limited, except by the application of 3D printing by sintering. The particles most often have a spherical shape. However, their use in other forms such as rod-shaped or lamellar forms is not excluded.

[0111] When the additives / fillers are added to the polymer in dry-blend, they advantageously have a volume median diameter Dv50 substantially equal to or less than that of the powder with which it will be mixed.

[0112] 3D printing process by sintering

[0113] The process which is the subject of the invention may in particular be a selective laser sintering (SLS) process, a sintering process of the MJF (Multi Jet Fusion) type or a sintering process of the HSS (High Speed ​​Sintering) type.

[0114] The SLS process is widely known. In this context, reference may be made in particular to documents US 6,136,948 and WO 96 / 06881.

[0115] In this type of process, a thin layer of powder is deposited on a horizontal plate held in an enclosure heated to a temperature called the build temperature. Most commonly, heating to the build temperature is achieved by means of IR radiation lamps, for example halogen lamps, which generally have an emission maximum 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 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 that stores the shape of an object and reproduces it in the form of slices. Then, the horizontal plate is lowered by a height corresponding to the thickness of a powder layer, and a new layer of powder is spread, heated and then sintered in the same way. The procedure is repeated until the object has been manufactured.

[0116] The layer of powder deposited on a horizontal plate may have, before sintering, for example a thickness of 20 to 200 pm, and preferably 50 to 150 pm. After sintering, the thickness of the layer of agglomerated material is a little lower, and may have, for example, a thickness of 10 to 150 pm, and preferably 30 to 120 pm.

[0117] For the MJ F and HSS process, the entire layer of the building material is exposed to radiation, but only a portion covered with a fusing agent is melted to become a layer of a 3D part. The fusing agent is a compound capable of absorbing radiation and converting it into thermal energy, for example, black ink. It is selectively applied to the selected region of the building material. The fusing agent is able to penetrate the layer of the building material and transmits the absorbed energy to the neighboring building material, thus causing it to melt or sinter. By melting, bonding, and subsequent hardening of each layer of the building material, the object is formed.

[0118] In the particular case of MJ F, a detailing agent is additionally added to the edges of the area to be melted to allow the pieces to have better definition.

[0119] Advantageously, the use of the polyamide powder composition described below in these processes does not require any particular modification. However, it makes it possible to obtain parts with a good surface appearance, in particular lower roughness and better definition.

[0120] Advantageously, the process allows the polyamide powder composition to be used in several successive constructions. In this case, it can be reused alone or mixed with other powders, recycled or not.

[0121] The invention will be further explained in a non-limiting manner using the following Examples.

[0122] Examples

[0123] 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.

[0124] Granulometry

[0125] The powders were characterized in terms of particle size using a Malvern Insitec laser diffractometer with RT Sizer software, according to ISO 13320:2009. Laser light is shone on the particles moving in the air.

[0126] The measurement is carried out on 30 g of powder.

[0127] Measurement of melting temperature (Tf)

[0128] The melting temperature of the powders was measured by DSC on a TA Instruments Q2000 calorimeter, in accordance with the NF EN ISO 11357-3:2018 standard. The value was determined during the heating step at a rate of 20°C / min during the first heating.

[0129] MVR measurement

[0130] MVR is measured by a Zwick MFlow device, manufactured by Zwick, at 235°C under a load of 2.16 kg according to ISO 1133.

[0131] Measurement of elongation at break

[0132] Elongation at break is measured according to ISO 527-1:2019.

[0133] Powder compositions

[0134] Powders B-1, B-2, B-4, A-1 and A-2 are polyamide powders marketed by Arkema. Their trade names are shown in Table 1.

[0135] B-3 powder was obtained from a polyamide 11 powder marketed by ARKEMA under the name Rilsan® Invent Natural. The Rilsan® Invent Natural powder was ground in a mini hammer mill with an internal selector until a powder with a Dv50 of 10 μm was obtained.

[0136] The properties of the powders used in the examples are shown in the table below.

[0137] Table 1]

[0138] 1% by mass of Powder B was added to Powder A in a dry-blend in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The compositions of the powders tested are shown in the table below.

[0139] Table 2]

[0140] Measurement of elongation at break

[0141] Powder compositions A-1, A-2, 1 to 4 and were used to manufacture 1 B XY specimens by 3D printing by laser sintering (1 B specimen according to ISO 527-1:2019, called “XY” because it is printed in the plane of the printer, i.e. horizontally) on a P1000 machine (marketed by Prodways) by setting the thickness of the powder layer to 100 pm. The printing parameters used are as follows:

[0142] Laser power: 24W

[0143] Laser speed: 3000mm / s

[0144] Distance between two laser passes: 0.25mm

[0145] The results obtained are gathered in the two tables below (average of 10 specimens tested). Table 3]

[0146] It was observed, at different construction temperatures, that Powder 1 of the invention exhibits an improved elongation at break, compared to the powder without the auxiliary powder (Powder A-1).

[0147] On the other hand, advantageously, it was possible to transform Powder 1 at a lower temperature (at 170°C), compared to Powder A-1. Thus, the addition of 1% of Powder B-1, made it possible to widen the working window, and even more advantageously towards low temperatures, which brings a benefit on a lesser evolution of the powder, which will favor its reuse in another printing test.

[0148] An improvement in elongation at break was observed for Powder 2, Powder 3, Powder 4 and Powder 5, compared to Powder A-2, which does not contain auxiliary powder.

Claims

Claims 1. Composition of thermoplastic polymer powders comprising: (i) a thermoplastic polymer powder A; (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a thermoplastic polymer powder B, powder B having a melting point (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume melt index (MVR) ratio of powder B to volume melt index (MVR) of powder A greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to standard ISO 1133.

2. Composition according to claim 1 comprising, relative to the total mass of the composition: (i) 59.5 to 99.5% by mass of the thermoplastic polymer powder A; (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, of the thermoplastic polymer powder B; (iii) 0 to 40% by mass, preferably 0.05 to 40% by mass of one or more additives and / or one or more fillers.

3. Composition according to claim 1 or 2, in which the thermoplastic polymer powders A and B are chosen from polyolefins such as polypropylene and polyethylene (olefin base waxes would not fall outside the scope of the present invention), polycarbonate, polymethylmethacrylate (PMMA), polyamides and thermoplastic elastomers such as polyether block amides (PEBA), polyesters and polyether blocks (COPE), thermoplastic polyurethanes (TPU) and their mixtures, preferably polyamides and polyether block amides, even more preferably polyamides.

4. Composition according to one of the preceding claims, in which powder A and / or powder B is a polyamide powder, preferably, powders A and B are polyamide powders, even more preferably, chosen from polyamide 11 and polyamide 12 powders.

5. Composition according to one of the preceding claims, in which powder A and / or powder B is a homopolyamide 11 or 12 powder or a copolyamide 11 or 12 powder.

6. Composition according to one of the preceding claims, in which powder A has a melting temperature (Tf) less than or equal to 250°C, preferably less than or equal to 210°C and / or powder B has a melting temperature (Tf) less than or equal to 210°C, preferably between 80 and 210°C, preferably between 100 and 200°C.

7. Composition according to one of the preceding claims, in which the MVR of powder B is greater than 50 cm 3 / 10min, preferably greater than 100 cm 3 / 10min, even more preferably greater than 200 cm 3 / 10 min.

8. Composition according to one of the preceding claims, in which powder A has a Dv50 of 20 to 100 pm, preferably 30 to 80 pm, even more preferably 40 to 60 pm, and / or powder B has a Dv50 of 1 to 60 pm, preferably 3 to 50 pm, even more preferably 4 to 20 pm.

9. Composition according to one of the preceding claims, in which the Dv50 of powder B is lower than the Dv50 of powder A, preferably, the Dv50 of powder B is 5 to 80% of the Dv50 of powder A, preferably 10 to 60% of the Dv50 of powder A.

10. A method of manufacturing the powder composition, by mixing: i. a thermoplastic polymer powder A; ii. 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a polyamide powder B, powder B having a melting point (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume melt index (MVR) ratio of powder B to volume melt index (MVR) of powder A greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to the ISO 1133 standard, iii. possibly one or more additives and / or one or more fillers.

11. Method according to claim 10, being carried out by mixing: (i) 59.5 to 99.5% by mass of the thermoplastic polymer powder A; (ii) 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of the thermoplastic polymer powder B; (iii) 0 to 40% by mass, preferably 0.05 to 40% by mass of one or more additives and / or one or more 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. 3D printing method, preferably a sintering method caused by electromagnetic radiation, using at least in part a powder composition according to one of claims 1 to 9.

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

15. Use of 0.1 to 3% by mass, preferably 0.5 to 2% by mass, more preferably 0.7 to 1.5% by mass, relative to the total mass of the composition, of a thermoplastic polymer powder B, preferably a polyamide powder, in a composition containing a thermoplastic polymer powder A, preferably a polyamide powder, in a 3D printing process, preferably by sintering, powder B having a melting temperature (Tf) less than or equal to, preferably less than, the Tf of powder A, the Tf being measured according to standard NF EN ISO 11357-3:2018; and / or a volume flow index (MVR) ratio of powder B to volume flow index (MVR) of powder A greater than 3, preferably greater than 5, even more preferably greater than 10, the MVR being measured according to the ISO 1133 standard; to improve elongation at break.

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