Polymer powder for the manufacture of high definition and low roughness parts

Abstract

The invention mainly relates to a thermoplastic polymer powder composition suitable for additive manufacturing by selective melting, in which the polymer powder has a particle size characterized by: a volume average diameter Dv < 55 µm, and a span less than 1.20, and such that a ratio d is between 0.40 and 0.55, the ratio d being of the following formula: in which dp is the apparent density of the powder measured according to the ISO 787-11:1981 standard; and dm is the density of the material measured on the powder after melting according to the ISO 1183-1 standard.

Description

Title of the invention: Polymer powder for the manufacture of high-definition, low-roughness parts Technical field

[0001] The present patent application relates to a thermoplastic polymer powder for the additive manufacturing of high definition and low roughness parts. Prior art

[0002] 3D printing by selective fusion of thermoplastic polymer powders (SLS, MJF, HSS, etc.) makes it possible to construct parts with complex geometry. However, the definition of the parts thus printed and their surface roughness are not yet completely satisfactory.

[0003] It is known to improve the surface condition of parts manufactured by selective melting by physical and / or chemical treatment. However, these treatments substantially increase the production time and therefore the manufacturing cost of the parts.

[0004] Certain methods have also been described in which the polymer powder to be used in 3D printing is treated. Thus, European patent EP1742986 B1 teaches that a polyamide powder having an enthalpy of fusion and a melting temperature far from the crystallization temperature makes it possible to improve the definition of parts constructed by selective melting.

[0005] Patent EP 1 413 595 B1 describes a process for increasing at least one of the following two parameters of a polyamide: (i) its melting temperature and (ii) its enthalpy of fusion AHf in which this polyamide in the solid state is brought into contact with water or water vapor at a temperature close to its crystallization temperature Te for a time sufficient to effect this increase, then the water (or water vapor) is separated from the polyamide and the polyamide is dried.

[0006] Furthermore, patents EP 2 115 043 B1 and EP 2 627 687 B1 teach that the heat treatment of PAEK powders makes it possible to improve the definition of the parts constructed.

[0007] However, these methods are specific to certain polymers and do not always provide complete satisfaction. Summary of the invention

[0008] The invention therefore aims to propose a polymer powder making it possible to improve the definition and surface appearance of parts produced by selective melting.

[0009] Indeed, the present invention is based on the observation that a powder of suitable morphology and having an appropriate particle size makes it possible to improve part definition and reduces surface roughness of items produced by selective melting 3D printing methods.

[0010] More specifically, it has been found that a powder with a narrow particle size distribution with few fine particles makes it possible to optimize the fusion of the target grains, in that it reduces the risk of fusion of neighboring grains, and therefore improves the definition of the parts constructed. Furthermore, the low concentration of large particles limits the texturing of the surface and therefore the loss of definition and surface roughness which could result from it.

[0011] Finally, it has been found that the use of a powder whose apparent density is such that the ratio with that of the material is between 0.40 and 0.55 makes it possible to optimize the definition of the parts. The apparent density of the powder varies in particular according to the morphology of the powder but also according to its crystallinity. Such a powder also makes it possible to avoid construction defects on parts, in particular round or inclined parts, while maintaining good productivity.

[0012] Also, according to a first aspect, the invention relates to a thermoplastic polymer powder composition suitable for additive manufacturing by selective fusion, in which the polymer powder has - a granulometry characterized by: • a volume average diameter Dv <55 pm, and • a span less than 1.2, and - such that a ratio d is between 0.40 and 0.55, the ratio d being of the following formula:

[0013] [Math.l]

[0014] in which

[0015] dp is the apparent density of the powder measured according to ISO 787-11:1981; and

[0016] dm is the density of the material measured on the powder after fusion according to the ISO standard 1183-1.

[0017] According to one embodiment, the thermoplastic polymer comprises or consists of a thermoplastic polymer selected from the group consisting of polyesters, polyvinyl chloride, polyacetal, polyolefins such as polypropylene and polyethylene, polystyrene, polycarbonate, poly-(N-methylmethacrylate, PMMI), polymethylmethacrylate (PMMA), ionomers, polyamides, thermoplastic elastomers such as polyetherblock amides, PAEK, and mixtures thereof, and in particular it comprises or consists of PA 11, PA 12, polyamide semi-aromatic such as PA 11 / 10T, a PEBA or a PAEK such as PEKK, PEEK, PEEK-PEDEK and PEEK-PEmEK.

[0018] According to one embodiment, the composition further comprises a flow agent.

[0019] Advantageously, the polymer powder has a span of less than 1.00, and preferably less than 0.90.

[0020] Preferably, the polymer powder has a ratio d of between 0.45 and 0.55, and in particular of between 0.47 and 0.51.

[0021] Advantageously, the polymer powder also has an inherent viscosity of 0.65 to 1.50, preferably of 0.85 to 1.40, and more preferably of 1.00 to 1.30.

[0022] According to a second aspect, the invention relates to a method for manufacturing the composition of the powder described, comprising the steps of: i. Prepolymerization of the monomer(s) of the thermoplastic polymer and subsequent granulation; ii. Grinding into a powder; iii. Optional subsequent sieving of the prepolymer powder obtained; and iv. Subjecting the obtained prepolymer powder to solid-phase polycondensation to obtain a polymer powder.

[0023] According to a third aspect, the invention aims at the use of the composition described or obtained according to the above process for the manufacture of articles by additive manufacturing by means of selective melting, in particular chosen from SLS, MJF and HSS.

[0024] According to a fourth aspect finally, the invention relates to an article capable of being obtained by additive manufacturing by means of selective melting of the composition described or obtained according to the method described. Brief description of the drawings

[0025] The invention will be better understood with regard to the following description and the figures, which show:

[0026] [Fig.l] a 3D printing device by SLS type sintering (English acronym for “selective laser sintering”);

[0027] [Fig.2] the evolution of the thickness e of the powder deposited after fusion by irradiation as a function of the number of layers n of 100 pm each in a laser sintering construction, calculated for powders having a d ratio of 0.3 (•), 0.5 (■) and 0.7 (♦). Description of the embodiments Definition of terms#

[0028] The term "thermoplastic polymer" is understood to mean a polymer having the property of softening when heated sufficiently, and which, upon cooling, becomes hard again. The polymer has a molar mass as measured by CES (size exclusion chromatography) greater than 5000 g / mol.

[0029] The term "volume mean diameter" or "Dv" also means the volume mean diameter of a powdery material, as measured according to ISO 13319-1:2021, for example on a Coulter Counter-Multisizer 3 particle counter (Beckmann Coulter). Different diameters are distinguished. More specifically, Dv50 designates the volume median diameter, and Dv10 and Dv90 designate respectively the diameters below which 10 or 90% by volume of the particles are located.

[0030] The term "span" is understood to mean a ratio describing the width of the particle size distribution of a powder, of the following formula:

[0031] [Math.2] - D^IO

[0032] in which: - DvlO designates the diameter below which 10% by volume of the polymer powder particles are found; - Dv50 denotes the diameter below which 50% by volume of the polymer powder particles are found (by definition Dv50 is also the median diameter by volume), and - Dv90 designates the diameter below which 90% by volume of the polymer powder particles are found,

[0033] these diameters being measured as indicated above.

[0034] Finally, the term "3D printing by sintering" refers to processes in which a layer of polymer powder is irradiated by electromagnetic radiation (e.g., laser beam, infrared radiation, UV radiation), so as to selectively melt the powder particles impacted by the radiation. The molten particles coalesce and solidify to lead to the formation of a solid mass. This process can produce 3D articles by repeatedly irradiating a succession of freshly applied powder layers.

[0035] The term "surface roughness" is understood to mean the arithmetic mean deviation Ra of the surface profile of a sample according to ISO4287:1997, for example using a PERTHOMETER S8P device. In the case of 3D printing, the build orientation can have an impact on the roughness, and it can therefore be It is useful to distinguish between the bottom and the top of an item, the bottom corresponding to the first layer of construction and the top to the last layer of construction.

[0036] The term "viscosity" is understood to mean the inherent viscosity as measured in an Ubbelohde type viscometer according to ISO 307:2019, except when using m-cresol as the solvent and a temperature of 20°C. The dimension of the inherent viscosity is the inverse of a concentration and is equal to the natural logarithm of the relative viscosity, all divided by the concentration of polymer dissolved in the solvent.

[0037] The nomenclature used to designate polyamides follows the ISO 1874-1 standard. In particular, in the PA X notation, X represents the number of carbon atoms of the polyamide units resulting from the condensation of an amino acid or lactam. In the PA XY notation designating a polyamide resulting from the condensation of a diamine with a dicarboxylic acid or an acid derivative having difunctional, X represents the number of carbon atoms of the diamine and Y represents the number of carbon atoms of the dicarboxylic acid or the acid derivative. The notation PA X / Y, PA X / Y / Z, etc. refers to copolyamides in which X, Y, Z, etc. represent homopolyamide units as described above.

[0038] In the broad sense, the present invention provides a thermoplastic polymer powder composition suitable for additive manufacturing by selective fusion, in which the polymer powder has a particle size characterized by an average diameter Dv <55 pm, a specific particle size distribution, characterized by a span less than 1.2, and finally a ratio d between the density of the powder and that of the material of between 0.40 and 0.55.

[0039] The use of powders having a low d ratio most often compromises the properties of the constructed articles, particularly in terms of mechanical strength. Furthermore, such a powder is difficult to transform due to the powdery behavior of the particles. Finally, a bed of such a powder is not able to support the weight of the article being constructed. The article then collapses during printing, and cannot be completed. The use of powders having a high d ratio makes it possible to achieve better mechanical properties. However, such powders comprise large particles, and the constructed articles then often have high roughness. Also, it has been found that a d ratio as defined above constitutes a good compromise between the two requirements of roughness and mechanical properties.

[0040] It has also been found that a powder with such a ratio d makes it possible to more quickly absorb the thickness differences of the powder layer at the start of construction, linked to the contraction of the powder at the sintered areas. These thickness differences can create stresses in the part and also affect its quality to the extent where the laser power may not be sufficient to melt the polymer to ensure perfect coalescence. Such defects can lead to porosity which may deteriorate the mechanical properties.

[0041] Finally, it was found that the surface roughness Ra of an article constructed by 3D construction, if it is directly linked to the granulometric characteristics of the powder used, in particular to the average diameter Dv, also depends on the span, the thickness ep of the construction layer, and the ratio d between the density of the powder and that of the material. For several polyamides, a correlation was found in the following form:

[0042] [Math.3] , R ■■ sp • e faiïÿsus's 4 8 a 0.381 ■ & t 4- Z. ¢4 3

[0043] The effect of the ratio d on roughness is particularly unexpected.

[0044] Overall, the thermoplastic polymer powder compositions according to the invention make it possible to obtain parts having low roughness, and also make it possible to avoid construction defects on parts, particularly round or inclined parts, while maintaining good productivity.

[0045] A. Thermoplastic polymer powder composition

[0046] The thermoplastic polymer powder composition provided according to the invention comprises a polymer powder which has: - a granulometry characterized by: • a volume average diameter Dv <55 pm, and • a span less than 1.20, and - such that a ratio d is between 0.40 and 0.55, the ratio d being of the following formula:

[0047] [Math.4] , dp d = t-dtn

[0048] in which

[0049] dp is the apparent density of the powder measured according to ISO 787-11:1981; and

[0050] dm is the density of the material measured on the powder after fusion by vertical thrust in water (21°C) according to ISO 1183-1.

[0051] According to the invention, the thermoplastic polymer powder has a specific particle size.

[0052] Indeed, the thermoplastic polymer powder of the invention has a volume average diameter Dv of less than 55 μm. According to certain embodiments, the powder of thermoplastic polymer has a volume average diameter Dv of between 30 and 55 pm, in particular between 35 and 50 pm and most particularly between 40 and 45 pm.

[0053] Besides the average diameter alone, the particle size distribution of the thermoplastic polymer powder can also have a significant impact on the performance in 3D printing by sintering.

[0054] Thus, according to the invention, the thermoplastic polymer powder has a span, as defined above, less than 1.2, and in particular less than 1, and very particularly less than 0.9. According to one embodiment, the span of the thermoplastic polymer powder is between 0.20 and 1.20, or between 0.30 and 1.10, or between 0.35 and 1.00, or between 0.40 and 0.90.

[0055] According to one embodiment, the volume diameter Dv10 of the powder is preferably greater than 15 μm. According to certain embodiments, the thermoplastic polymer powder has a volume diameter Dv10 of between 15 and 50 μm, or between 25 and 45 μm or between 30 and 40 μm.

[0056] According to one embodiment, the volume diameter Dv50 of the powder is preferably between 30 and 60 μm. According to certain embodiments, the thermoplastic polymer powder has a volume diameter Dv50 between 35 and 55 μm, or between 40 and 50 μm.

[0057] According to one embodiment, the thermoplastic polymer powder has a volume diameter Dv90 of less than 120 pm, in particular less than 100 pm, and very particularly less than 90 pm. According to certain embodiments, the thermoplastic polymer powder has a volume diameter Dv90 of between 40 and 120 pm, or between 45 and 100 pm, or between 50 and 80 pm.

[0058] The thermoplastic polymer powder in the composition according to the invention is further characterized by a specific ratio d, which is between 0.40 and 0.55. The ratio d has the following formula:

[0059] [Math.5] dp d = —-dm

[0060] As explained above, the ratio d as specified expresses the compromise proposed according to the invention between the search for a maximum density of the powder and therefore a high ratio d on the one hand, and the fact that such powders generate articles with high roughness and require a greater number of layers to absorb the difference in thickness resulting from the difference in density at the start of construction (8 to 10 layers or almost 1 mm on the constructed article, see [Fig. 2]). Thus, it has been found that a ratio d of between 0.40 and 0.55 makes it possible to best reconcile the interest of having a dense powder with a view to good mechanical properties of the articles. printed and that of having a powder that is not too dense in order to limit constraints and defects at the start of construction.

[0061] The apparent density dp of the thermoplastic polymer powder depends, in addition to its particle size, in particular on the shape of the particles, their porosity and their crystalline structure. The thermoplastic polymer powder preferably has an apparent density dp of 0.200 to 0.600, preferably of 0.300 to 0.550, and extremely preferably of 0.400 to 0.500.

[0062] The density dm of the thermoplastic polymer depends on the polymer considered and is generally between 0.850 and 1.850, preferably between 0.900 and 1.450, and extremely preferably between 0.950 and 1.150.

[0063] The thermoplastic polymers that can be used in the context of the present invention may in particular be chosen from polyesters, polyvinyl chloride, polyacetal, polyolefins such as polypropylene and polyethylene, polystyrene, polycarbonate, poly-(N-methylmethacrylimide, PMMI), polymethylmethacrylate (PMMA), ionomers, polyamides, thermoplastic elastomers such as polyetherblock amides (PEBA), PAEK, and their copolymers and blends.

[0064] Among the polyamides, mention may be made in particular of aliphatic polyamides such as PA 6, PA 6.6, PA 11 and PA 12 and their copolymers, and semi-aromatic polyamides such as PA 11 / 10T for example.

[0065] Among the PAEK polymers, mention may be made in particular of polyetherketoneketone (PEKK), polyetheretherketone (PEEK) and their copolymers such as polyetheretherketone-polyetherdiphenyletherketone (PEEK-PEDEK) and polyetheretherketone-polyethermetaetherketone (PEEK-PEmEK).

[0066] According to one embodiment, the polymer comprises or consists of a polyamide, in particular PA 11, PA 12, a PEBA, or a semi-aromatic polyamide such as PA 11 / 10T or a PAEK such as PEKK, as well as their mixtures or copolymers.

[0067] The thermoplastic polymer powder generally comprises at least 50% by weight of thermoplastic polymer relative to the total weight of powder.

[0068] According to certain embodiments, the powder comprises at least 50%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 92.5%, or at least 95%, or at least 97.5%, or at least 98%, or at least 98.5%, or at least 99%, or at least 99.5% by weight of thermoplastic polymer relative to the total weight of the thermoplastic polymer powder of the invention.

[0069] According to some embodiments, the thermoplastic polymer powder may comprise a single thermoplastic polymer, for example only a polyester, a polyolefin, a polyamide, a polyester, a PEBA or a PAEK. According to certain embodiments, the powder according to the invention comprises several polymers that differ in at least one of their properties. These properties may include, in particular, molar mass, crystallinity, but also thermal properties or even particle size.

[0070] According to certain embodiments, the thermoplastic polymer powder has a viscosity of 0.65 to 1.50, preferably 0.85 to 1.40, and more preferably 1.00 to 1.30. These viscosity ranges are particularly advantageous and make it possible to obtain a good compromise for having both good coalescence properties during sintering (sufficiently low viscosity) and good mechanical properties of the sintered object (sufficiently high viscosity).

[0071] The thermoplastic polymer powder may comprise, in addition to the thermoplastic polymer(s), one or more usual additives and fillers.

[0072] The additives generally represent less than 5% by weight relative to the total weight of the composition. Preferably, the additives represent less than 1% by weight of the total weight of powder. Among the additives, mention may be made of flow agents, stabilizing agents (light, in particular UV, and heat), optical brighteners, dyes, pigments, energy-absorbing additives (including UV absorbers).

[0073] 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 weight relative to the total weight of the composition. In other embodiments, the pulverulent composition does not comprise a flow agent.

[0074] The thermoplastic polymer powder may also comprise one or more fillers. The fillers generally represent less than 50% by weight, and preferably less than 40% by weight relative to the total weight of the final powder. Among the fillers, there are reinforcing fillers, 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 even glass in another form, for example in the form of flakes or beads, hollow or not.

[0075] B. Process for manufacturing thermoplastic polymer powder

[0076] The thermoplastic polymer powder can in particular be obtained by grinding thermoplastic polymer in the form of extruded granules or flakes, according to conventional techniques.

[0077] The 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.

[0078] When the powder comprises several polymers and / or certain additives and / or certain reinforcing fillers, some or all of them may be incorporated by melt mixing, for example by extrusion (compounding) and granulation followed by a grinding of the granules. Alternatively, it is also possible to add other polymers and / or certain additives and / or certain reinforcing fillers by dry blending. Preferably, the flow agent is added by dry blending.

[0079] According to one embodiment, and in particular for polyamides, the method of manufacturing the powder composition comprises the steps of: i. Prepolymerization of the monomer(s) of the thermoplastic polymer and subsequent granulation; ii. Grinding into a powder; iii. Possible subsequent sieving of the prepolymer powder obtained; iv. Subjecting the obtained prepolymer powder to solid-phase polycondensation to obtain a polymer powder.

[0080] The additives and / or reinforcing fillers can then be added to the prepolymer, by melt mixing (compounding) or dry mixing, between steps (i) and (ii), or subsequently, by dry mixing. C. Use of the powder

[0081] The polymer powder composition as described above is useful in particular for use in a 3D printing process by sintering. Preferably, the composition of the invention is used in 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.

[0082] 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.

[0083] 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 often, heating to the build temperature is carried out 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 restores 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 . A new layer of powder is spread, heated, and then sintered in the same way. The procedure is repeated until the object is manufactured.

[0084] The layer of powder deposited on a horizontal plate may have, before sintering, for example a thickness of 20 to 200 μm, and preferably 50 to 150 μm. 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 μm, and preferably 30 to 100 μm.

[0085] For the MJF and HSS process, the entire layer of the build 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, a black ink. It is selectively applied to the selected region of the build material. The fusing agent is capable of penetrating the layer of the build material and transmits the absorbed energy to the neighboring build material, thereby causing the latter to melt or be sintered. By melting, bonding, and subsequent hardening of each layer of the build material, the object is formed.

[0086] 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 better definition.

[0087] Advantageously, the use of the polymer powder composition of the invention in these processes does not require any particular modification. As mentioned above, it does, however, make it possible to obtain parts having lower roughness and better definition.

[0088] The polymer powder composition according to the invention can be recycled and reused in several successive constructions. In this case, it can be reused alone or in a mixture with other recycled or non-recycled powders.

[0089] As an example, the use of the thermoplastic polymer powder composition described in a method for constructing a three-dimensional object layer by layer by sintering caused by electromagnetic radiation in a device 1, such as that shown diagrammatically in [Fig.l], is described below.

[0090] The electromagnetic radiation may be, for example, infrared radiation, ultraviolet radiation, or preferably laser radiation. In particular, in a device 1 such as that shown diagrammatically in [Fig.l], the electromagnetic radiation may comprise a combination of infrared radiation 100 and laser radiation 200.

[0091] The sintering process is a layer-by-layer manufacturing process for building a three-dimensional object 80.

[0092] The device 1 comprises a sintering enclosure 10 in which are arranged a feed tank 40 containing the thermoplastic polymer powder and a movable horizontal plate 30. The horizontal plate 30 may also act as a support for the three-dimensional object 80 under construction. However, objects made from the thermoplastic polymer powder generally do not require additional support and can generally be self-supported by the unsintered powder of previous layers.

[0093] According to the method, thermoplastic polymer powder is taken from the feed tray 40 and deposited on the horizontal plate 30, forming a thin layer 50 of powder constituting the three-dimensional object 80 under construction. The layer of powder 50 is heated using infrared radiation 100 to reach a substantially uniform temperature equal to the predetermined minimum construction temperature Te.

[0094] The energy required to sinter the thermoplastic polymer powder particles at different points of the powder layer 50 is then provided by a laser beam 200 from the laser 20 moving in the (xy) plane, according to a geometry corresponding to that of the object. The molten powder re-solidifies forming a sintered portion 55 while the remainder of the layer 50 remains in the form of unsintered powder 56. A single pass of a single laser beam 200 is generally sufficient to ensure sintering of the powder. However, in certain embodiments, several passes at the same location and / or several electromagnetic radiations reaching the same location may also be envisaged to ensure sintering of the powder.

[0095] Then, the horizontal plate 30 is lowered along the axis (z) by a distance corresponding to the thickness of a layer of powder, and a new layer is deposited. The laser 20 provides the energy necessary to sinter the powder particles according to a geometry corresponding to this new slice of the object and so on. The procedure is repeated until the object 80 has been manufactured.

[0096] The temperature in the sintering chamber 10 of the layers lower than the layer being built may be lower than the build temperature. This temperature, however, generally remains above, or even well above, the glass transition temperature of the powder. It is particularly advantageous for the temperature of the bottom of the chamber to be maintained at a temperature Tb, called the “tank bottom temperature”, such that Tb is lower than Te by less than 40°C, preferably by less than 25°C and even more preferably by less than 10°C.

[0097] Once the object 80 is finished, it is removed from the horizontal plate 30 and the unsintered powder 56 can be sieved before being returned, at least in part, to the feed bin 40 to serve as recycled powder. D. Part capable of being manufactured

[0098] The use of a composition according to the invention thus makes it possible to manufacture good quality three-dimensional articles, having a very satisfactory surface appearance, in particular low roughness and precise and well-defined dimensions and contours.

[0099] The thermoplastic polymer powder composition allows the manufacture by 3D printing by sintering of parts which have properties, in particular mechanical properties, at least similar to the parts obtained if not superior compared to conventional thermoplastic polymer powders.

[0100] The invention will be explained in more detail in the following examples. Example 1

[0101] A polyamide 11 powder composition was prepared according to the following method.

[0102] First, a polyamide 11 prepolymer was synthesized from 1.2 kg of amino-11-undecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid (50% strength, expressed as % by weight in the aqueous solution) and 9.8 g of phosphoric acid (75% strength, expressed as % by weight in the aqueous solution). The mixture was heated to a temperature of 190 °C in 2 h under stirring as soon as the temperature reached 160 °C or the pressure exceeded 8.5 bar. During the synthesis, the water initially loaded with amino-11-undecanoic acid was removed by evaporation at constant pressure (P = 10 bar). After withdrawing a quantity of 430 g of water, the prepolymer was extracted from the reactor under pressure through a die. It was then cooled using two steel rollers with circulation of cold water to be solidified, cooled and crushed into flakes.

[0103] The prepolymer thus obtained was mixed in a suitable container with 3.3 g of carbon black. This mixture was introduced into a twin-screw extruder to be melted and intimately mixed and then extruded. The mixture was then cooled using two steel rollers with cold water circulation to be solidified and cooled and then crushed into flakes.

[0104] The flake-form recovered additive prepolymer is then ground in a hammer mill equipped with an internal selector until a powder having a volume median diameter Dv50 of 64 µm is obtained. The powder thus obtained is then subjected to solid-phase polycondensation in a dryer at 140 - 155 °C under vacuum in order to increase the inherent viscosity of the polyamide to 1.15.

[0105] The obtained pigmented polyamide 11 powder was then sieved using a FINEX 22 type ultrasonic plugging nutating sieve, using a 80 µm square mesh.

[0106] The powder composition obtained was then characterized in terms of particle size and density as indicated below. The results are collated in Tables 1 and 2 below. Characterization of powders Granulometry

[0107] The particle size of the powders was characterized by measuring the particle size distribution on a Coulter Counter-Multisizer 3 device (Beckmann Coulter) in accordance with ISO 13319-1:2021. From this, the mean diameter and the diameter corresponding to the 1st, 5th and 9th deciles of the distribution were determined, then the span was calculated according to the following formula:

[0108] [Math.6] Report of

[0109] The apparent density of the powder dp was measured in accordance with ISO 787-11:1981 using a 250 mL precision glass cylinder graduated in 2 mL increments and having an ungraduated upper portion of at least 50 mL. The powder is slowly introduced into the cylinder inclined at 45°, a volume of powder between 220 and 250 mL. This volume of powder is then weighed to calculate the apparent density and then divided by the density of water to deduce its density.

[0110] The density of the material dm was measured after melting the powder under a heating press (T > Tf + 40°C and pressure of 2 tons). The density of the film obtained, i.e. that of the material, is measured by vertical thrust in water (21°C) according to ISO 1183-1 using a Sartorius AC 210P hydrostatic balance with YDK 01 density kit.

[0111] The ratio d between the apparent density dp of the powder and the density of the material dm measured on the powder after fusion was calculated according to the following formula:

[0112] [Math.7] dp d = -— arm

[0113] [Tables 1] Properties of thermoplastic polymer powders Example Dvio[pm] Dv50[pm] Dv90[pm] Average diameter [pm] Span dp 1 21.1 50.8 74.5 44.6 1.05 0.500 2 19.5 47.3 74.4 48.2 1.16 0.495 3 30.4 51.2 75.0 49.1 0.87 0.475 4 28.9 46.6 66.8 42.1 0.81 0.465 Cl 27.7 73.9 124.6 78.6 1.31 0.450 C2 45.6 91.0 124.6 94.4 1.01 0.460 C3 20.0 48.7 82.9 51.3 1.29 0.490 C4 42.5 60.2 83.6 59.3 0.68 0.455 C5 58.9 81.5 119.0 84.7 0.74 0.505

[0114] [T ables 2] Properties of printed articles Example Roughness Roughness after polishing wise dm Ratio d top[pm] bottom[pm] top[pm] bottom[pm] 1 9.7 4.9 NDND 1.040 0.481 2 5.6 5.5 NDND 1.025 0.483 3 8.9 7.1 NDND 0.980 0.475 4 5.4 5.3 NDND 0.990 0.465 Cl 13.8 13.5 5.1 4.9 1.030 0.437 C2 13.5 13.2 NDND 1.030 0.447 C3 10.6 7.2 NDND 1.025 0.478 C4 8.7 12.5 NDND 0.995 0.455 C5 15.1 14.6 NDND 0.970 0.567

[0115] The polymer powder obtained was then used to manufacture by 3D printing by sintering, more specifically by SLS, a 1BA XY specimen (1BA specimen according to the ISO 527-1BA standard, called “XY” because it is printed in the horizontal plane of the printer) by laser sintering on a P100 machine (marketed by the company EOS) by setting the thickness of the powder layer to 100 μm and using the following set of parameters:

[0116] [Tables3] Exposure chamber temperature 185°C Removal chamber temperature 158°C Layer thickness 0.1 mm Contour Power 16 W Speed ​​1,400 mm / s Hatching Power 24 W Speed ​​3,000 mm / s Beam displacement 0.25 mm Energy per layer 0.32 J / mm3

[0117] The specimens are visually evaluated for print definition. The results are summarized in Table 2 above.

[0118] The test pieces are further characterized by their upper and lower surface roughness by means of the arithmetic mean deviation Ra of the surface profile of a sample according to ISO4287:1997, using a PERTHOMETER S8P device (the result corresponds to the average of three values ​​taken over three different base lengths).

[0119] The test pieces are then mechanically polished using a sander equipped with a 320 grit emery cloth, then the surface roughness measurement of these test pieces is repeated under the same conditions as those described above. The results are collated in Table 2 below. Example 2

[0120] The PA11 powder prepared in example C2 is sieved using a nutating sieve with ultrasonic unclogging RUSSEL type FINEX 22, using a square mesh of 80 μm.

[0121] The granulometric characteristics of the polyamide 11 powder obtained were determined as indicated in Example 1. The results are collated in Table 1 above. Furthermore, the density of the material was measured as explained in Example 1 (see Table 2 above).

[0122] The powder obtained is used to manufacture test pieces as indicated in Example 1. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above. Example 3

[0123] First, a polyamide 12 prepolymer was synthesized from 1 kg of lauryllactam in the presence of 0.1 kg of water. The mixture was heated to a temperature of 260°C in 4 hours with stirring as soon as the temperature reached 160°C or the pressure exceeded 8.5 bars. During the synthesis, the water initially loaded with the lauryllactam was removed by evaporation at constant pressure (P=20 bars). After withdrawing a quantity of water of 30 g, the prepolymer is extracted from the reactor under pressure through a die. It was then cooled using two steel rollers with circulating cold water to be solidified, cooled and crushed into flakes.

[0124] The prepolymer recovered in the form of flakes is then ground in a hammer mill equipped with an internal selector while using a second dynamic selector at the outlet in order to eliminate the finest particles until a powder having a volume median diameter Dv50 of 82 pm is obtained. The powder thus obtained is then subjected to solid-phase polycondensation in a dryer at 140-155°C under vacuum in order to increase the inherent viscosity of the polyamide up to 1.10.

[0125] The powder thus obtained is sieved using a nutating sieve with ultrasonic unclogging RUSSEL type FINEX 22, using a square mesh of 80 μm.

[0126] The granulometric characteristics of the polyamide 12 powder obtained were determined as indicated in Example 1. The results are collated in Table 1 above. Furthermore, the density of the material was measured as explained in Example 1 (see Table 2 above).

[0127] The powder obtained is used to manufacture test pieces as indicated in Example 1, using the following set of parameters:

[0128] [Tables4] Exposure chamber temperature 172°C Removal chamber temperature 140°C Layer thickness 0.1 mm Contour Power 16 W Speed ​​1,500 mm / s Hatching Power 18 W Speed ​​3,000 mm / s Beam displacement 0.20 mm Energy per layer 0.3 J / mm3

[0129] These test pieces are then characterized by their surface roughness on the top and bottom. The results are collected in Table 2 above. Example Cl

[0130] A polyamide 11 powder composition was prepared according to the following method.

[0131] First, a low viscosity polyamide 11, called in the following "prepolymer", from 1.2 kg of amino-11-undecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid (50% strength) and 9.8 g of phosphoric acid (75% strength). The mixture is heated to a temperature of 190°C in 2 hours with stirring as soon as the temperature reaches 160 °C or the pressure exceeds 8.5 bars. During the synthesis, the water initially loaded with amino-ll-undecanoic acid is removed by evaporation at constant pressure (P = 10 bars). After withdrawing a quantity of water of 430 g, the prepolymer is extracted from the reactor under pressure through a die. It is then cooled using two steel rollers with circulation of cold water to be solidified, cooled and crushed into flakes.

[0132] The prepolymer recovered in the form of flakes is then ground in a hammer mill equipped with an internal selector until a powder having a volume median diameter Dv50 of 74 pm is obtained. The powder thus obtained is then subjected to solid-phase polycondensation in a dryer at 140-155°C under vacuum in order to increase the viscosity of the polyamide up to 1.18.

[0133] The powder obtained is used to manufacture test pieces as indicated in Example 1. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above. Example C2

[0134] The PA11 prepolymer recovered in the form of flakes from Example C1 is ground with the same grinding parameters as C1 while using a second dynamic selector at the outlet in order to eliminate the finest particles until a powder having a volume median diameter Dv50 of 91 pm is obtained. The powder thus obtained is then subjected to solid-phase polycondensation in a dryer at 140-155°C under vacuum in order to increase the viscosity of the polyamide up to 1.16. A PAU powder having the particle size characteristics indicated in Table 1 above is obtained.

[0135] The powder obtained is used to manufacture test pieces as indicated in Example 1. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above. Example C3

[0136] The PA11 powder prepared according to example C1 is sieved using a nutating sieve with ultrasonic unclogging RUSSEL type FINEX 22, using a square mesh of 80 μm. A PA11 powder is obtained having the granulometric characteristics indicated in table 1 above.

[0137] The powder obtained is used to manufacture test pieces as indicated in Example 1. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above. Example C4

[0138] Granules of polyamide 12 (Rilsamid® AECNO TL marketed by Arkema) are extruded using a die making it possible to obtain fibers with a diameter of 60 μm. which are cooled so that they can be micro-granulated over a length of 70 μm. The polyamide powder thus obtained has an inherent viscosity of 1.09.

[0139] The granulometric characteristics of the polyamide 12 powder obtained were determined as indicated in Example 1. The results are collated in Table 1 above. Furthermore, the density of the material was measured as explained in Example 1 (see Table 2 above).

[0140] The powder obtained is used to manufacture test pieces as indicated in Example 3. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above. Example C5

[0141] A polyamide 12.12 powder was obtained according to example 1 of patent CN104356643B. First, dodecanedioic acid is solubilized in ethanol at 60°C, a solution of dodecanediamine in ethanol is gradually introduced while monitoring the pH. When pH = 7, the solution then contains a stoichiometric nylon 12.12 salt which precipitates. This salt is recovered after filtration and drying to be placed in an autoclave to polymerize at a temperature of 250°C to obtain PA12.12 with an inherent viscosity of 1.15, which is then extracted from the reactor through a die and cooled to be granulated. These granules are then dissolved in ethanol at a temperature of 140°C and a pressure of 8 bar and then precipitated directly in powder form by cooling. This powder is recovered after spinning and drying. The polyamide powder thus obtained has an inherent viscosity of 1.12.

[0142] The particle size characteristics of the obtained polyamide 12.12 powder were determined as indicated in Example 1. The results are collated in Table 1 above. Furthermore, the density of the material was measured as explained in Example 1 (see Table 2 above).

[0143] The obtained powder is used to manufacture test specimens as indicated in Example 3. These test specimens are then characterized by their surface roughness on the top and on the bottom. The results are collated in Table 2 above. Example 4

[0144] The PA 12.12 powder prepared according to Example C5 (Example 1 of Patent CN104356643B) is sieved using a FINEX 22 type RUSSEL ultrasonic plugging gyratory sieve, using a 80 µm square mesh and then subjected to deflashing.

[0145] The granulometric characteristics of the polyamide 12.12 powder obtained were determined as indicated in example 1. The results are collated in the Table 1 above. Furthermore, the density of the material was measured as explained in Example 1 (see Table 2 above).

[0146] The powder obtained is used to manufacture test pieces as indicated in Example 3. These test pieces are then characterized by their surface roughness on the top and bottom. The results are collated in Table 2 above.

[0147] All the results show that a powder having the granulometry as claimed makes it possible to very significantly improve the roughness of the parts obtained by 3D printing from it. In this context, not only the average diameter but also the span which illustrates the width of the granulometric distribution counts. Thus, the roughness obtained with the powder of examples 1 to 3 is notably lower than that obtained with the powder of example C3, having a similar average diameter Dv10, Dv50 and Dv90, but a higher span.

[0148] The study also reveals a favorable effect of the value of the average diameter, since a high roughness is observed for the parts obtained from the powders of examples C2 and C5 while these powders have a very low span value.

[0149] Furthermore, the examples highlight that the roughness is correlated with the parameters studied according to the following equation:

[0150] [Math. 8] d ■ and? • (above) + (below? = 0-381 • Dt' -r

[0151] the best understanding being obtained for powder compositions according to the invention. List of cited documents

[0152] EP1742986B1

[0153] EPI 413 595 B1

[0154] EP2 115043B1

[0155] EP2 627 687B1

[0156] US 6,136,948

[0157] WO 96 / 06881

[0158] CN104356643B

Claims

Claims

1. A thermoplastic polymer powder composition suitable for additive manufacturing by selective melting, wherein the polymer powder has - a particle size distribution characterized by: • a volume average diameter Dv <55 pm, as measured according to ISO 13319-1:2021, for example on a Coulter Counter-Multisizer 3 particle counter (Beckmann Coulter), and • a span of less than 1.20, the volume average diameters used to calculate the span also being measured according to ISO 13319-1:2021, for example on a Coulter Counter-Multisizer 3 particle counter (Beckmann Coulter), and - such that a ratio d is between 0.40 and 0.55, the ratio d being of the following formula: [Math.9], dp d = v-dm in which dp is the apparent density of the powder measured according to ISO 787-11:1981; and dm is the density of the material measured on the powder after fusion according to ISO 1183-1.

2. The composition of claim 1, wherein the thermoplastic polymer comprises or consists of a thermoplastic polymer selected from the group consisting of polyesters, polyvinyl chloride, polyacetal, polyolefins such as polypropylene and polyethylene, polystyrene, polycarbonate, poly-(N-methylmethacrylate, PMMI), polymethylmethacrylate (PMMA), ionomers, polyamides, thermoplastic elastomers such as polyetherblock amides, PAEK, and mixtures thereof.

3. A composition according to claim 2, wherein the thermoplastic polymer comprises or consists of PA 11, PA 12, semi-aromatic polyamide such as PA 11 / 10T, a PEBA or a PAEK such as PEKK, PEEK, PEEK-PEDEK and PEEK-PEmEK.

4. Composition according to one of claims 1 to 3, further comprising a flow agent.

5. Composition according to one of claims 1 to 4, in which the polymer powder has a span of less than 1.

00.

6. A composition according to claim 5, wherein the polymer powder has a span of less than 0.

90.

7. Composition according to one of claims 1 to 6, in which the polymer powder has a ratio d of between 0.45 and 0.

55.

8. Composition according to claim 7, in which the polymer powder has a ratio d of between 0.47 and 0.

51.

9. Composition according to one of claims 1 to 8, in which the polymer powder has an inherent viscosity of 0.65 to 1.50, preferably of 0.85 to 1.40, and more preferably of 1.00 to 1.30, as measured in an Ubbelohde type viscometer according to ISO 307:2019 standard, except using m-cresol as solvent and a temperature of 20°C.

10. A method of manufacturing the powder composition according to one of claims 1 to 9, comprising the steps of: (i) Prepolymerization of the monomer(s) of the thermoplastic polymer and subsequent granulation; (ii) Grinding into a powder; (iii) Optional subsequent sieving of the obtained prepolymer powder; and (iv) Subjecting the obtained prepolymer powder to solid-phase polycondensation to obtain a polymer powder.

11. Use of the composition according to one of claims 1 to 9 or obtained with the method according to claim 10 for the manufacture of articles by additive manufacturing by means of selective melting.

12. Use according to claim 11, wherein the additive manufacturing is chosen from selective laser sintering (SLS), Multi Jet Fusion (MJF) sintering and High Speed Sintering (HSS) sintering.

13. Article capable of being obtained by additive manufacturing by means of selective melting of the composition according to one of claims 1 to 9 or capable of being manufactured with the method according to claim 10.

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